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Combined Platform for Boost Guidance and Attitude

1. straight lines in the plane In this case the 3 axis problem is divided into 3 1 axis problem This simplifies the solution and implementation 6 2 Control Law for ACS There are some differences between the control for small and large maneuvers The largest different is that the error has to be sufficiently small for small maneuvers so that only local optimum switching criteria have to be studied and not global optimum switching criteria as in large control Due to this the control law for small maneuvers can be divided into three separate control laws one for each axis The control law for large maneuvers has to have one control law for the whole system except the roll axis which is possible to control separately Therefore are the control functions for the large and small control are studied separately 6 3 Control Law for Small Maneuvers The control law that is chosen for this case is a one axis loss function This control law will result in a switching criteria for the thrusters that are lines in the phase plane This plane has the angular velocity and the attitude error as axis The lines are derived from the solution to an optimization problem The solution is obtained by minimizing the Hamilton function H These computations are similar to those in 6 These calculations are similar for all axes min H L Vp Vow 6 1 6 2 Where y is the attitude error w the angular velocity and V and V are loss functions The fol
2. i j2 k2 ij ji k jk kj i ki ik j This gives that the inverse of q is defined as 69 70 Quaternion Definition A 3 x q qo iq1 jq2 kqa A 7 The norm or length of the quaternion is defined as Definition A 4 lal vVar VT a V t Br ara A 8 The transformation matrix A that is based on the quaternion is described by 0 G 93 200193 dog2 209243 goa qo 41 92 T 9B 71493 T 40g2 4243 q0q1 A q 200193 go G ap G 43 2 q192 093 4 9 2 q293 q091 2 q192 4043 4 qi q 43 For a more detailed description of quaternion see 16 Appendix B Coordinate Systems In this chapter the different coordinate systems that are used in the report are described B 1 Payload Fixt Coordinate System This coordinate system is a body fix coordinate system where origin is the mass center of the payload and the x axis goes through the nose of the sounding rocket The other axis are chosen so that when the rocket is in the launch pad the y axis points towards the rail B 2 Thruster Plane Coordinate System This system is similar to the Payload fixt system The difference is that this system is rotated 45 in the y z plane of the payload fix coordinate system B 3 Launch Pad Coordinate System This is the chosen initial frame for the sounding rocket Origin is placed at the bottom of the launch pad and the x axis is a normal to the su
3. QUATERNION SELECT MN TRANSLOW i PACKET Lt Figure C 1 The file structure of the MATLAB implementation of DS19 where the lines indicates the interchanges between the files C 3 Output The outputs to the function are the data listed in table C 2 C 4 Program Execution 75 Table C 2 Outputs to the function Name Description Unit XS qvec us This variable is a matrix where each row contains the state values for the system for specific time There is one row for each 0 01 s of the simulation This variable contains the starting state of the simulation The variable is the same as a row in the variable x This is a vector containing all the times for which x is sampled This variable is a matrix containing the reference attitude for all times t in quaternions This variable is a matrix containing the control commands to the thrusters for each time in t The columns represent roll pitch and yaw in that order gt gt H rad s rad s rad s 2 sel EL El rad s rad s rad s HE C 4 Program Execution The program is executed by typing the command main tend plotflag in MATLAB This can be done when MATLAB have access to all files in the program packet The output is then saved in the file ACSsimulation mat in the current directory 76 User Manual Index Accelerometers 8 ACS Table of 10 ACS control law 34 ACS functions
4. 1999 06 29 INERTIAL SCIENCE Inc DMARS user s manual INERTIAL SCIENCE Inc Newbury Park CA US 1995 12 MathWorks Inc MATLAB Using MATLAB version 6 MathWorks Inc Natick MA US 2000 67 68 Bibliography 13 L Ljunge Integrated DS19 ACS RCS functions in the NSROC program Technical Report DS19 NOT 5004 SE Saab Ericsson Space AB Link ping Sweden 1998 03 23 14 L Ljunge DS19 guidance and control system specification Technical Report P DS19 SPC 5001 SE Saab Ericsson Space AB Link ping Sweden 1998 12 01 15 W Staberg ACS power budget Technical Report POIVRE TNT 5030 SAAB Saab Ericsson Space AB Link ping Sweden 1991 10 22 16 James R Wertz editor Spacecraft Attitude Determination and Control D Reidel Publishing Company Dordrecht Holland 1985 Appendix A Quaternion Quaternions are a way to describe a transformation from one coordinate system to another The quaternions are based on the Euler angles for description of the transformation The parameters are defined as follows Definition A 1 do cos gt A 1 q esin 7 A 2 q esin El A 3 q3 e3sin gt A 4 As seen these equation are not independent but they have to satisfy the constraint do 4 a a 1 A 5 These parameters can be seen as the components of a quaternion defined as Definition A 2 q qo 1q1 jq2 kas A 6 where i j and k are the hyper imaginary numbers satisfying the conditions
5. 00 46 7 4 11 Ready for Launch Flag Computation 46 7 4 12 BGS Control 0 0 0 0 rss os ss orsa 46 TATI ACS Control 22 4 44 ae Seb wa ea we A 46 7 4 14 ACS Large Control sse rroa oo o e 46 7 4 15 ACS Small Contral e 46 7 4 16 ACS Fine Control 0 0 00000002 eee 47 7 4 17 ACS Pressure Transit Low 47 7 4 18 ACS Pressure Transit High o 47 7 4 19 ACS Valve Control 2 a a 47 7 4 20 ACS Control Selection 0 0 000000 4s 47 7 5 Software Module Hierarchy o 47 8 Preliminary Software Design 51 8 1 Compiler 2 4 4 6 24 S YAO ee ee ee ee ee 51 8 2 Program Functions ee saasaa 4 en 51 8 2 1 Attitude Reference ACS 0000084 57 8 2 2 Ready toLaunch 2 2000 58 8 2 3 20 Hz Routine 2 2 0 0 ee ee 58 8 2 4 100 Hz Routine 0 0 00 2 eee ee 58 8 2 5 Choice of Control Mode 00 58 8 3 Implementation e e 59 9 Verification and Simulation 61 9 1 Rocket Dynamics 0000000000000 61 9 2 Result From Simulation 63 10 Conclusion and Further Work 65 10 1 Conclusions s seso s saana s e Ea a a e o Mr a SE NER RV AR 65 10 2 Further Work s s 2 s 2 444222 ani yea aa dd ee RER ww 66 Bibliography 67 A Quaternion 69 Appendix 69 Contents B Coordinate Systems B 1 Payload Fixt Coordinate System B 2 Thruster Plane
6. boost phase experi ment phase and reentry phase During the boost phase the rocket is accelerates using the motors and the boost guidance system BGS controls the sounding rocket The sounding rocket is boosted up to an altitude of approximative 100 700 km by the motor that can consist of one or more stages In the end of this phase the motors is separated and the yo yo mechanism reduces the roll rate of the payload An attitude control system ACS is used during the experiment phase to stabilize and control the payload in order to give the right conditions for performing the scientific experiments In the reentry phase the payload reenters the atmosphere 1 2 Introduction Table 1 1 Subsystems in a sounding rocket Subsystem Function Motors Generates the thrust for the sounding rocket It can consist of one or more stages Payload Experiments control recovery and service systems Boost Guidance System Controls the rocket during the boost phase The purpose of the system is to maintain constant attitude and or control the trajectory This is done in order to control the impact point for the rocket See section 1 2 Attitude Control System Controls the payload attitude during the experiment phase See section 1 3 and deploys a parachute to soften the impact 1 2 Boost Guidance System The BGS controls the rocket during the boost phase The purpose of the control is to reduce the impact point disper
7. control Table 5 17 Changes in the TM during ACS control New Data Old Data For the 100 Hz data The command word to the CGS valves Reference attitude in pitch The regulated pressure for the CGS Reference attitude in yaw For the 20 Hz data Information on which control that is active Empty Reference quaternion 1 Command signal pitch canards Reference quaternion 2 Command signal yaw canards Reference quaternion 3 Return signal from pitch servo Reference quaternion 4 Return signal from yaw servo For the 4 Hz data The bottle pressure for the CGS Temperature DS19 structure The regulated pressure for the CGS Temperature DS19 gyro The starting time for the ACS control Empty The lowest starting altitude for the ACS Empty control 30 Design of DS19 5 5 Software Expansion for DS19 The changes that are needed in the S W for the combined system is addition of new control strategies for the ACS control Mainly how the CGS will be controlled based on the present attitude and rate This results in a control routine that has to be computed during the ballistic phase of the flight This control routine is never done at the same time as the control routine for the boost guidance Therefore is the CPU power in the present system enough for both applications The only other thing that needs to be computed during the time the strategies are computed is the TM signal This is al
8. e Jz is the moment of inertia for rocket two e R is the length of the level for rocket one e Ro is the length of the level for rocket two The results from these calculations are shown in table 5 5 where the terms e are shown for each axis for the rockets Where M is the moment needed for RACS 24 Design of DS19 Table 5 5 Scaling factors for gas consumption Small 12 Large 4 1 M2 In Roll In Pitch and Yaw 1 54 2 0 Table 5 6 Amount of gas needed for the standard rockets Small 17 in Large 22 in Maneuver description Impulse Ns Acquisition maneuver 891 6 1617 8 Maneuvers during flight 408 770 180 transverse reentry maneuver 339 594 Spin up before reentry 80 184 Duty cycle pulsing 90 162 Dumping 20 20 Total impulse 1828 6 3347 8 Table 5 4 are used as a base for the making of table 5 6 which shows the gas consumption for a nominal flight with the standard rockets As shown in table 5 6 the amount of gas needed for the rockets are very shifting between the rockets Therefore the best design is to have the CGS in a separate module 5 3 3 Power Budget This budget is done in order to investigate if the battery in DS19 has enough power to support the complete DS19 system Power Consumption The parts that consume energy in the system are the DMARS which is the internal measurement unit IMU in DS19 power distributing unit PDU attitude sensors the
9. and a CGS system This ACS shall hold a payload that spins with 0 5 2 0 rps and within an alignment of 1 2 The system shall also be able to control the spin rate This is a system that is not normally used in the larger sounding rockets therefore there will be no focus on it in this report To expand the functionality of DS19 to this system only minor changes are needed So if this type of ACS were to come into use a new system could quickly be designed 18 DS19 Heritage Chapter 5 Design of DS19 The integration between the two systems can be done in many ways In this chapter the components of the systems are analyzed and a preliminary design for DS19 is derived 5 1 Mechanical Design In this section the mechanical design alternatives of DS19 are described The design alternatives can be seen in figure 5 1 5 1 1 Single Module System This solution is based on one module containing all the parts of the system The benefit with this is the reductions of joints between modules in the sounding rocket This will increase the strength of the system There are some drawbacks with this solution The first is the large amount of changes that has to be made to the DS19 module Another is that the system has to be redesigned between flights due to the changes in the requirements 5 1 2 Combined Sensor and CGS Module The structural changes from the single module design to this design is that the sensors and CGS is moved
10. calculated every time the function is called When changing to a new mode the function sets the data needed in that mode LARGE CONTROL MODE 1 wy Ee T lt Oinsmall 2 transtime done m gt 0 an and gt Moutsmall condition 2 p lt Pinsmall or P gt Poutsmall or reentrymaneuver SMALL CONTROL MODE TRANSFER FUNCTION HIGH transtime done and NOT condition 2 comp lt G a 5 and gt Moutfine Ps lt P2 and P gt P3 and and P gt Poutfine stabile true 4 readyflag 1 TRANSFER FUNCTION LOW FINE CONTROL MODE Figure 8 1 A state diagram over the select function 54 Preliminary Software Design Valve Control The input to this function is the commands that is calculated in the control rou tines The function then maps these commands to the command word that is returned In the command word every bit represent a thruster Large Control This function needs the following input e The attitude error e The angular body rates e The reentry flag e The previous output from the function e The remaining time for the acquisition maneuver e The angular acceleration for the axes e The total error in the transverse plane e The quaternions for a transformation from the body frame to a equatorial polar frame The data that has to be stored between the calls is the loss time for the function The out
11. changes in the software design also has to be done for the new functions Bibliography 10 11 Saab Ericsson Space AB DS19 electrical diagram Diagram L Eklind ACS performance report Technical Report POIVRE TRP 5005 SAAB Saab Ericsson Space AB Link ping Sweden 1991 10 30 L Hall Specification for the DS19 RACS module Technical Report DS19 SPC 5008 SAAB Saab Ericsson Space AB Link ping Sweden 1999 02 01 A Helmersson Cold gas system design for poivre ACS Technical Report POIVRE TNT 5013 SAAB Saab Ericsson Space AB Link ping Sweden 1990 10 01 A Helmersson Attitude control design analysis Technical Report POIVRE TRP 5019 SAAB Saab Ericsson Space AB Link ping Sweden 1992 06 01 J Hjertstr m Control law design Technical Report RCS TNT 5026 SAAB Saab Ericsson Space AB Link ping Sweden 1991 03 15 J Hjertstr m ACS cold gas budget Technical Report POIVRE TNT 5049 SAAB Saab Ericsson Space AB Link ping Sweden 1991 11 04 J Hjertstr m ACS control law specification Technical Report POIVRE SPC 5014 SAAB Saab Ericsson Space AB Link ping Sweden 1992 06 01 J Hjertstr m Flight software architectural design document ADD Techni cal Report DS19 NOT 5000 SE Saab Ericsson Space AB Link ping Sweden 1999 02 12 J Hjertstr m and L Ljunge DS19 main interface control document Techni cal Report DS19 ICD 5001 SE Saab Ericsson Space AB Link ping Sweden
12. control to stop the control pulsing during sensitive measuring phases The second design gives the best interfaces but also the largest changes in the DS19 module This design is the best one if further changes has to be done in the system The third solution is time demanding and difficult to implement and it does not solve any problem better then any of the other designs The PDU has to be rebuild for all solutions This because an interface towards the CGS is needed and there are no space for this interface in the present design see 10 5 4 2 Implemented Design The design that is chosen for implementation is the design that is based on reas sociation of the pins It is chosen based on that it is easy to implement and that there exist signals that currently are unused that can be removed The choice of design results in that the sun pointing ACS RCS and real time can not be done Therefore is these control systems excluded from the rest of the report The changes in the interfaces needed to be done for this design are described in the following sections 5 43 DMARS PDU The changes that has to be done in this interface for the chosen design is reassoci ation of pins according to table 5 12 and table 5 13 Table 5 12 Pin reassociation in 44 pins DMARS to PDU interface pin New signal Old function 22 CGS bottle pressure IMS temperature 23 CGS regulated pressure Deck temperature 33 Opening command solenoid valve 1 Emp
13. easy to draw the conclusion that a simulation of only the attitude is enough The equations for the attitude dynamic is then derived from 16 Ly 0 T5s XG T7 T La 1 T5 0 X7 Te Ta 3 2 Te T7 0 T5 T3 La 17 z 15 0 La 9 1 Tx Nx w It Ty Ny Tz Nz where the T elements are the description of the coupling between the rates and quaternions and the state and N elements are the combined torque from the control torque and the torques from the disturbances The disturbance is made of two parts in each axis One constant part and one part that consist of impulses The constant part are 0 02 Nm in the roll axis and 0 1 Nm totally in the transverse axes The impulse part consists of impulses that occurs simultaneously in both the roll and transverse axes The magnitude of the impulse in roll is 0 2 Nms and 2 Nms totally in the transverse axes This according to 2 These equation is implemented in MATLAB They are solved with the ode23s differential solver in MATLAB This solver uses the Rosenbrock method to solve differential equations according to 12 This type of solver is used on stiff differen tial equations that is that the solver uses a fix step length to solve the equation The simulation of the the system runs the attitude control algorithms every 0 01 s whit the input from the latest simulation and the control torques from the CGS in the body frame as an output Between each call the attitude for the syst
14. flow and the thick lines represent functional flow the 4 Hz data information that is not time crucial is sent The data in the 20 Hz and 100 Hz data is changed depending on if the ACS control or the BGS control is used This can be determined from the variable ACSflag 7 4 Guidance and Control Calculations 45 7 4 4 Time Computation In this function the time since lift off is calculated 7 4 5 EGSE Decoding In this function the commands sent from the Electric ground support equipment EGSE is decoded These are commands for both the control system and the IMS 7 4 6 20 Hz Control Routine This routine uses a modulo 5 computation of the time to divide the computation into five parts This function calls the functions depending on which part that is executed The functions that are called are e Impact point calculations e Parameter scheduler e ACS flag setting e BGS reference attitude e ACS reference attitude The last two functions are never called simultaneous The ACSflag determines which one of them that will be called 7 4 7 ACS Flag Setting This function takes the time since lift off the altitude and a control command from the EGSE as input The output is a boolean variable that denotes true or false The output is false if the BGS control is to be used and true if the ACS control is to be used 7 4 8 BGS Reference Attitude This function is called by the 20 Hz routine with IMS data as input The function th
15. for the command computation After this is done the chosen control function is called The return from the control function is a control signal for the thrusters The command signal takes the following values e 0 means all thrusters off e 1 means that the thrusters in the positive direction is on e 1 means that the thrusters in the negative direction is on e 2 means that all thrusters in the axis are on This value is only valid for the transverse axes These signals is then sent to the valve control that computes the command word for the valves which is used as an output from the function Control Selection This function handles the selection of control mode in the ACS control The input to the function is e The attitude error e The angular body rates e The previous commands to the valves e The reentry flag e A ready flag set by the transit low function e The remaining time for the acquisition maneuver e The command to the latching valve e The current position in the phase plane e The updated angular rate 8 2 Program Functions 53 The previous control mode has to be saved between the calls to the function and also the a stabilization flag for the payload This flag is also used by the attitude reference function for the ACS The output from this function is a command word that indicates which control mode that has been chosen The function has a state diagram according to figure 8 2 The switches is
16. from the DS19 module to a separate module This design has the benefit of a more intact DS19 module The drawbacks is that it has to be redesigned between missions and that the extra sensors not can be positioned freely 5 1 3 Modularized Design This design has an intact DS19 module and has two extra modules One for the CGS and one for the extra sensors 19 20 Design of DS19 The two separate modules for sensors and CGS is chosen because in most flights the sensor module is not needed and can then be easily excluded The structure also gives extra freedom for the position of the sensors The construction of the CGS can also easily be made by an external manufacturer Extra Sensors Extra Sensors CGS Module Extra EA Sensors ccs ccs Toe weal gr ces esol DS19 DS19 DS19 Modulerized Combined CGS and Single module system Sensors system Figure 5 1 The design alternatives 5 2 Cold Gas System The CGS for the payload is chosen to have the schematic design according to figure 5 2 The regulators and latching valve is used to control the gas pressure by the solenoid valves The roll thrusters are activated in pairs to reduce the effect on the transverse axes The configuration makes it possible to use two pressure levels This is necessary because then large errors can be quickly corrected and the minimum error that can be corrected is still suffi
17. function takes the pressure from low to high 7 4 19 ACS Valve Control This function takes the commands from the control functions as inputs and com putes the digital command signals that is sent to the valves 7 4 20 ACS Control Selection This function uses the the previous control mode the pressure level and the attitude error as inputs From this data the function chooses which control mode that is going to be used 7 5 Software Module Hierarchy This section contains a short description of the S W hierarchy The top level hierarchy is shown in figure 7 3 The applications developed by the IMS manufacturer is marked IMS in the figure The hierarchy for the G amp C application is shown in figure 7 4 48 Architectural Software Design INTERRUPT IMS SER H amp C APPLICATION HEADER FILE IMS APPLICATION IMS Figure 7 3 The top level design for the system 7 5 Software Module Hierarchy 49 amp C APPLICATION DECODE EGSE 100Hz ROUTIN OMPILE TM ROHz ROUTIN ET IMS MODE OMPILE OMPILE TM4 M100 OMPILE SEND EGSE M20 SEND TM ACSFLAG IMPACT ATTITUDE SCHEDULER IPOINT REFERENCCE ATT REF ATT REF BGS ACS IME READY TO DISCRETE ATTITUDE DAC LAUNCH OUTPUT ONTROL OUTPUT AD ATTITUDE ATTITUDE ONVERTER IROUTIN ALVE ELECTION ONTROL MALL LARGE PRESURE INE PRESURE ONTROL ONTROL RANSIT HIGH ONTROL RANSIT LOW Figure 7 4 The hierarchy for the G amp C application 50 Architectural Software D
18. s and the mean value for the maneuver are 19 4 s These values are derived from a Monte Carlo simulation of the system These simulations has been done with the disturbance set to zero 64 Verification and Simulation 120 T T 100 fF 60 gt 40 207 Figure 9 2 A histogram over the acquisition time for the payload As seen above are the requirement on the system from section 3 3 fulfilled The system also seems to function as expected and can therefore be used for implemen tation in C and Assembler for further testing Chapter 10 Conclusion and Further Work 10 1 Conclusions This report handles the preliminary design for the DS19 control system which include both attitude control and boost control functions The control laws for the system are derived from the RACS and DS19 systems A pointing attitude control function is added to the DS19 system to derive DS19 This function is chosen because of the limited amount of free interfaces between the PDU and IMU and also that flight proved code from RACS can be used for the development of the system The computer and memory capacity in DS19 is sufficient to support the DS19 with pointing attitude control Hardware wise DS19 is designed to consist of separate CGS and DS19 modules according to chapter 5 this is done to minimize the changes in the DS19 module An advantage with this is that only small small changes will occur if the system is extended with ex
19. system that includes both attitude control and boost control functionality for sounding rockets This is done to reduce the weight and volume for the control system A sounding rocket is a small rocket compared to a satellite launcher It is used to launch payloads into suborbital trajectories The payload consists of scientific experiments for example micro gravity experiments and astronomic observations The boost guidance system controls the sounding rocket during the launch phase This is done to minimize the impact dispersion The attitude control system con trols the payload during the experiment phase The system that is developed in this report is based on the DS19 boost guidance system from Saab Ericsson Space AB The new system is designed by extending DS19 with software and hardware The new system is therefore named DS19 Hardware wise a study of the mechanical and electrical interfaces and also of the system budgets for gas mass and power for the system are done to determine the feasibility for the combined system Further a preliminary design of the control software is done The design has been implemented as pseudo code in MATLAB for testing and simulations A simulation model for the sounding rocket and its surroundings during the experiment phase has also been designed and implemented in MATLAB The tests and simulations that have been performed show that the code is suitable for implementation in the real system Keywords sou
20. time control from the ground control The accuracy for the sun pointing ACS should be according to table 4 2 Table 4 2 Performance for the sun pointing ACS Accuracy 3 0 arcsec Drift rate 2 arcsec min Resolution of the real time control 1 2 arcsec This system can be seen as an extension of the pointing ACS with additional sensors The CGS for this ACS should be rater similar to the one in the pointing ACS 4 2 4 Fine Pointing ACS This system shall function as the pointing ACS but with much better accuracy compared with the systems above This system shall have an accuracy according to table 4 3 4 2 Attitude Control Functionality 17 Table 4 3 Performance for the fine pointing ACS Accuracy 2 5 arcmin Drift rate 10 arcsec min Resolution of the real time control 1 2 arcsec These requirements could be met by adding a star sensor The star sensor has the advantages that the attitude in all three directions can be calculated from one measurement The ground control shall also be able to control the system with real time commands from the ground This system can be designed from the pointing ACS in almost the same way as the sun pointing ACS The difference between these systems is the sensors and some parts in the S W 4 2 5 ACS for Spinning Payloads This system is an ACS thats only works for spinning payloads The components that are needed are a 3 axis magnetometer
21. to control the payload These actuators normally consist of a gas system of some kind See section 2 3 this way with the same amount of gas compared to a CGS The drawback for the system is that the system itself has a higher weight and volume Due to the small amount of thrust needed for a sounding rocket the weight increase for the HGS is greater then the decrease in weight for the gas Therefore is the CGS most commonly used The gas used in the CGS is nitrogen in most applications There are also alterna tives to this gas Argon is also a commonly used gas Argon and Nitrogen generates approximately the the same thrust for the same amount of gas The drawback with Argon is that is has a lower outlet temperature then Nitrogen therefore larger noz zles and valves has to be used according to 4 Therefore is Nitrogen used in this application A CGS can be built in it is own self contained module as long as it has an interface to the main module for receiving and sending control signals 2 4 Sensors In this part various sensors that can be used by the ACS will be described 2 4 1 Sun Sensors The sun sensor is the most commonly used sensor type It is used in almost every satellite and also in a number of sounding rockets For satellites this is because of the fact that almost all satellites rely on the sun as a power source In sounding rocket applications this type of sensor is used to determine the attitude and also the dir
22. used to control the direction of the motor thrust See section 1 2 1 DS19 e K GUIDANCE NAVIGATION amp CONTROL SYSTEM Figure 1 1 The DS19 module 1 3 Attitude Control System The ACS is used to control the sounding rocket during the experiment phase The main purpose for the control the payload during the experiments and reentry The control during the experiments are done of several purposes they are for example minimize disturbances to achieve micro gravity or control the pointing sequence to perform observations This is done with rate and or attitude control for the system The ACS usually uses a gas system as an actuator A detailed description of the ACS can be found in chapter 2 Introduction Figure 1 2 The GCS module Chapter 2 Attitude Control System In this chapter a more detailed description of the ACS will be presented including a description of the parts in it 2 1 Missions The purpose of an ACS is to control the payload during the ballistic phase The control that is necessary is determined by the type of experiment that is conducted There is some basic kinds of missions listed in table 2 1 The share of each type of missions compared to the total amount of sounding rocket missions flown by NASA is also listed The figures are derived from 13 Table 2 1 Basic mission control Mission type Sensor Accuracy Zero gravity Rate gyro 0 2 s 10 Solar Gyroplatform and sun sens
23. used in both systems for example IMS and battery There is two benefits that can occur when the weight is lowered for the sounding rocket either can the weight of the payload be increased which gives room for more experiments or the maximum apogee is increased which results in a increase of the time for the experiment phase of the flight 5 3 2 Gas Budget In this section the gas consumption for DS19 is discussed To estimate the amount of gas needed in the CGS system data from typical sound ing rockets are used see table 5 1 This table shows the moment of inertia and other physical properties two sounding rockets Table 5 1 Rocket Properties for Sounding Rockets Small Large Moment of Inertia Roll kg m2 10 23 Moment of Inertia Pitch Yaw kg m 1000 2700 Lever Roll m 0 22 0 22 Lever Pitch Yaw m 1 3 2 The gas consumption for the RACS sounding rocket can be found in 7 this consumption is listed in table 5 3 and the physical properties for the rocket is listed in table 5 2 Table 5 2 Physical Properties for RACS Moment of Inertia Roll kg m 10 Moment of Inertia Pitch Yaw kg m 500 Lever Roll m 0 22 Lever Pitch Yaw m 1 000 The acquisition maneuver consists of several phases One roll rate reduction from 90 s to 0 s and one transverse rate reduction from 25 7 s to 0 s and also one 180 transverse reorientation maneuver The RACS ACS is a system that
24. 5 ACS missions List of 5 Architectural design 41 Components in the Attitude control system Table of 7 Components in the Boost Guidance system Table of 3 Detailed design 51 Development tree of the system figure of 13 DS19 module figure of 2 Fine pointing ACS performance 17 Functions and data flow for the B amp C figure of 42 GCS module figure of 2 GPS 8 Guidance and control S W Purpose of 41 Gyros 8 Interface Design 27 Interfaces 25 Interfaces new Table of 26 77 Magnetic ACS 17 Magnetometers 8 Mechanical design 19 PDU to CGS signals Table of 26 PDU to DMARS signals Table of 26 PDU to Sensors signals Table of 26 Power consumption for the system Table of 25 RACS 14 RACS gas consumption Table of 23 RACS nominal gas consumption Table of 23 RACS performance 14 RACS rocket properties Table of 22 Rate Control 15 Rate Gyro types Table of 9 S W changes 30 Simulation Software states 61 Software architecture schematic descrip tion figure of 42 Sounding rocket Model of 61 SPINRAC 13 Standard ACS 16 Standard rockets Table of 22 78 Index Standard rockets gas consumption Table of 24 Star ACS 16 Star sensors 8 Subsystems in the sounding rocket Table of 2 Sun ACS 16 Sun pointing ACS performance 16 Sun sensors 7 System design Description of 31 hy Pa LINK PING UNIVERSITY st ELECTRONIC PRESS Ka P svensk
25. 5 1 Existing Software oso esse rss a 30 5 5 2 New Functionality o 30 5 5 3 Design Considerations o e 31 5 6 Conclusions sas dre 644 ds oa A oes 31 6 Control Law 33 6 1 Control Concepts ara kee eee ee KERR Se 33 6 2 Control Law for ACS 0 000200002 eee 34 6 3 Control Law for Small Maneuvers omer esse rosor 34 6 3 1 Fine Control sa padae sva sag ee eR SEEN eS 37 6 4 Control Law for Large Maneuvers o ooa 37 6 4 1 Roll Control sss 24 66 eee ee eee a 38 6 4 2 Transverse Control ooo esse reses sosse 38 6 5 Control Law for RCS aoaaa aaa 0 020020 ve 39 7 Architectural Software Design 41 7 1 System Design q geid sa a i a bd E 8 hh ee 41 T2 IMbertac es Ves ee a oe a aa A Gag e 2 42 Go Initialization 4 43 65 a 44 as A RN e o 42 7 4 Guidance and Control Calculations 42 7 4 1 Parameter Scheduler o o 42 7 4 2 Impact Point Calculations o o vv 42 7 4 3 Telemetry Compilation o vor 43 Contents ix 7 4 4 Time Computation e ss ss oss vor 45 7 4 5 EGSE Decoding 000048 45 7 4 6 20 Hz Control Routine ooo ses oss ss ss sosse or 45 TAT ACS Flag Setting 4 446 24 2 RNA RR RAR He ee eG 45 7 4 8 BGS Reference Attitude 2 2000 4 45 7 4 9 ACS Reference Attitude 0 000 4 45 7 4 10 100 Hz Control Routine
26. AC e All other S W to H W communication The design only handles the first two parts listed above The third part is handled by the IMS S W The interfaces between the different S W applications are handled by a header file This file shall be included in both IMS and G amp C application files The interchange of data is partly done through partly pointer references in the program and by global data All signals to or from the H W that not is handled by the G amp C application is routed through the S W of the IMS A schematic description of the system is seen in figure 7 1 7 3 Initialization The initialization is handled by a function that is called by the IMS at startup for the system The function sets all variables and parameters that has to be predefined The function is divided into subfunctions for the different subsystems of the S W 7 4 Guidance and Control Calculations This section contains a short description of the functions in the G amp C application A description of functions and data flow for the G amp C application can be seen in figure 7 2 7 4 1 Parameter Scheduler This function selects predefined parameters from tables using the time since lift off velocity attitude and position parameters The function then interpolates a value from the table which is returned to the program The values that can be stored in the table is for instance parameters for the BGS control 7 4 2 Impact Point Calculations This fun
27. Combined Platform for Boost Guidance and Attitude Control for Sounding Rockets Examensarbete utf rt i Reglerteknik vid Tekniska H gskolan i Link ping av Per Abrahmsson Reg nr LiTH ISY EX 3479 2004 Link ping 2003 Combined Platform for Boost Guidance and Attitude Control for Sounding Rockets Examensarbete utf rt i Reglerteknik vid Tekniska H gskolan i Link ping av Per Abrahmsson Reg nr LiTH ISY EX 3479 2004 Supervisors Albert Thuswaldner David Lindgren Examiner Anders Helmersson Link ping 26th February 2004 of by Avdelning Institution Datum ES LJ k Division Department Date 3 ely 2004 02 25 Nos s Institutionen for systemteknik LINKOPINGS UNIVERSITET 581 83 LINK PING Sprak Rapporttyp ISBN Language Report category Svenska Swedish Licentiatavhandling X Engelska English X Examensarbete ISRN ENED Y EX 3479 2004 C uppsats Serietitel och serienummer ISSN D uppsats Title of series numbering Ovrig rapport URL f r elektronisk version http www ep liu se exjobb isy 2004 3479 Titel Kombinerad Plattform f r Ban och Attiydstyrning av Sondraketer Title Combined Platform for Boost Guidance and Attitude Control for Sounding Rockets F rfattare Per Abrahamsson Author Sammanfattning Abstract This report handles the preliminary design of a control system that includes both attitude control and boost control functionality for sounding rockets This is done to reduce the weight a
28. Coordinate System B 3 Launch Pad Coordinate System C User Manual C 1 File Structure o 6 2 Tnp t 44 44 ra a DAR AE 03 Output 444 6 owe ee ee SD fr KR ds C 4 Program Execution o Index Chapter 1 Introduction A sounding rocket is controlled by two separate control system for attitude control and boost guidance These system does not interchange any information even though they use similar subsystems This result in an increased weight and volume for the control system Therefore is it desirable to merge these system into one system The purpose of the report is to examine the possibility to merge the impact and attitude control functions for a sounding rocket to one system Both hardware H W and software S W have to be analyzed to determine the possibility to design a merged system A preliminary design for a merged system is also done The software for the design is given in detail 1 1 Sounding Rockets A sounding rocket is a small rocket compared to a satellite launcher that boosts up over the atmosphere to conduct experiments and then returns to the earth This is a cost effective way to do space related science experiments The sounding rocket flies in a suborbital trajectory up to an altitude of 200 700 km and then down again The sounding rocket consists of several subsystems that are listed in table 1 1 A typical sounding rocket mission is divided into three parts
29. FF 6 15 36 Control Law A combination of these gives alti ta die 2w This gives the following change in the attitude for the system Ag pAt 2wA At t t gt a 2 2 Kee wr a The criteria to switch on the system is then set to This results in a switch off criteria that is 2 p2 p1 Ap ZUHA This gives the switching criteria a P lt pe2 U x3 4a p gt y 0 p2 lt p lt y 6 16 6 17 6 18 6 19 6 20 6 21 6 22 To reduce the duty pulsing that can occur for small errors a dead band is introduced in the equation The dead band is symmetrical around zero and it is wide A reducing factor p is also introduced p is a reduction factor that is introduced to avoid overshoots This is done because of the large negative effect an overshot has 6 4 Control Law for Large Maneuvers 37 on the system This results in the modified switching criteria w gt 0 p gt o U a a p lt p p lt U 4 a gt E 0 Pp ps E a p gt w 243 0 lt p lt U 2 i sau es ap w lt 0 p lt d U a a p lt p gt o U lt a p gt 924 6 0 348 pes e a sp lt w lt y lt 6 U ia 6 23 do paa 22465 One more variable that is introduced in the switch criteria is a hysteresis function that make the system hold a specific output during a time interval This is done to make sure that the thrusters does not go on and off ever
30. SPINRAC 45544445 de ss be bad dd s a ATI RAGS ssis de eb heh one ee eee aci ada 4 2 Attitude Control Functionality sosse secs 4 2 1 Rate Control System 2 0 0 0 ss so 4 2 2 Pointing ACS a oc aadi aa na aa a e 4 2 3 Sun Pointing ACS a soc 64 sh ch har e ee vil 11 11 11 11 viii Contents 4 2 4 Fine Pointing ACS e e o 16 4 2 5 ACS for Spinning Payloads o 17 5 Design of DS19 19 5 1 Mechanical Design e e 19 5 1 1 Single Module System 19 5 1 2 Combined Sensor and CGS Module 19 5 1 3 Modularized Design 19 5 2 Cold Gas System aoaaa 20 5 2 1 Thruster Configuration oem ere rr sr rss rr ses 20 5 3 Budgets sa s saaara ee Gane db ttt daaa NR RR aa dads 22 5 3 1 Mass Budget lt vad s a eS ae ee a a a aS 22 5 3 2 Gas Budget va 24 4 on oe wee ba ee Sa oie 6 oak ee 22 5 3 3 Power Budget 2 0 0 2 00 00000000004 24 5 4 Electrical Interfaces 2 0 20 2 0 00002 eee eee 25 5 4 1 Design Options os s eaa coc e 0 0 ho dea eee eee 26 5 4 2 Implemented Design o 27 5 43 DMARS PDU e 27 DAA PDU SeEnsorsS 24 daa Se ee ele Sa a e 28 SAD PDU Valv siccsa2a 28 8 bebe bb dane dbo ea og 28 5 4 6 Changes in the TM format 29 5 5 Software Expansion for DS19 200 30 5
31. U PDU CGS PDU Extra Sensors The extra data that need to be sent between the DMARS and the PDU is listed in table 5 9 In the same way the new signals for PDU to CGS and PDU to Extra Sensors is listed in tables 5 10 and 5 11 Table 5 9 New signals between PDU and DMARS Control signals for the CGS Data from the CGS Control signals for the sensors Data from the sensors Table 5 10 New signals between PDU and CGS Control signals for the solenoid valves Control signals for the latching valve Measured pressures from the CGS Power supply and ground connection to the CGS Table 5 11 New signals between PDU and Attitude Sensors Control signals to the sensor Data from the sensor Power supply and ground connection to the sensor 5 4 1 Design Options There are several designs for the electric interfaces between DMARS and PDU Three alternative designs are Reassociation Remove signals from the present interface to create room for new important signals Rebuilding Rebuild all the interfaces to fit in all signals 5 4 Electrical Interfaces 27 Sharing Share the existing pins between the signals The first design is easy to implement and results in minor changes to the DS19 module The drawback with this design is that it does not free enough space for the sun pointing ACS the real time control and the RCS this due to that a interface towards the payload is needed during this
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33. al S W is needed The changes in the H W is limited to an addition of a small CGS 4 2 2 Pointing ACS The pointing ACS is a control system with relatively low accuracy and stability requirements These requirements is possible to meet with no extra sensors beside the IMS in the DS19 This makes the function easy to incorporate in DS19 The system shall be able to point with an total accuracy of 0 7 3 o in all three axis The incorporation with the DS19 is done in a similar way as with the RCS The difference is that this system also controls the attitude for the rocket This results in a more complex control strategy with the effect that more CPU power is needed But as the application is computed in a period where there are much CPU power unused this should not cause a problem There is also a difference in the CGS The CGS for this application has to be larger than the one for the RCS This is a result of that the sounding rocket has to perform more and larger maneuvers to control the attitude 4 2 3 Sun Pointing ACS The sun pointing ACS is similar to the pointing ACS The difference is that it should be more precise especially when pointing at the sun This can be done with the help of sun sensors They are used to determine the attitude towards the sun The point of having several sensors is that the direction can be more accurately determined The ACS should be able to follow a predetermined pointing sequence or be controlled via a real
34. c Field Missions The missions that are flown to conduct experiments on the earths magnetic field usually use an ACS that uses magnetometers as sensors These are described in section 2 4 4 Non Controlled Missions There are some missions that do not need any kind of control during the ballistic phase and no ACS is used at all 2 2 ACS Hardware The components in the ACS are listed in table 2 2 2 3 Actuators An ACS normally uses a pressurized gas system as an actuator The force acting on the body is then generated when the gas is let out of nozzles The most commonly used system is the Cold Gas System CGS The CGS consists of a pressure vessel containing the gas regulators nozzles and valves to control the outlet of the gas This system is based on a cold gas that generates the thrust There is also an other system Hot Gas System HGS In this system the gas is heated before it is used The HGS consists of the same parts as the CGS and also a device to heat the gas before it is let out the nozzles More thrust can be generated 2 4 Sensors 7 Table 2 2 ACS Hardware Components Function Sensors The system can have several sensors mounted on it These sensors are used to determine the attitude of the payload during the flight See section 2 4 Computer The computer is used for calculating the control strategies for the ACS Actuators The actuators is the part of the system that produces the force that is used
35. can perform a large amount of maneuvers Most of the reorientation maneuvers is not necessary in other ACS The gas that is used by RACS for a nominal ACS mission is according to table 5 4 5 3 Budgets 23 Table 5 3 Amount of Gas needed for RACS Maneuver description Impulse Ns Gas Mass kg Acquisition maneuver 614 0 97 5 x 30 0 off thruster axis 515 0 82 2 x 40 45 off thruster axis 187 0 30 10 x 45 roll 290 0 46 180 transverse reentry maneuver 220 0 35 Spin up before reentry 80 0 13 Duty cycle pulsing 60 0 1 Dumping 15 0 02 Total impulse 1981 3 15 Table 5 4 Amount of Gas needed for RACS in nominal flight Maneuver description Impulse Ns Gas Mass kg Acquisition maneuver 614 0 97 Maneuvers during flight 300 0 5 180 transverse reentry maneuver 220 0 35 Spin up before reentry 80 0 13 Duty cycle pulsing 60 0 1 Dumping 15 0 02 Total impulse 1289 2 07 From this information the amount of gas that the typical sounding rockets use are derived by looking on how the moment of inertia and the levels i e the distances between the center of mass and the nozzle have changed The impulse amount needed for a maneuver that uses an impulse of Mo for another rocket becomes Ra LR M Mz 5 1 Where the values represent the following e M is the moment needed for rocket one e Mo is the moment needed for rocket two e I is the moment of inertia for rocket one
36. ce Computation The second is a function that takes the time as input and returns the reference and reentry flag as output The attitude reference is given in quaternions the quaternions are described in appendix A The function is the same for all ACS that has a requirement on the reference attitude 5 6 Conclusions 31 The function matches the time to the index in a table If there is a new attitude there will be a transition phase that uses linear interpolation between the present and new attitude This function is not the same as the reference computation for the BGS because the ACS needs a fix reference in all three axis The BGS uses a reference that is calculated from a formula that only returns a reference in pitch and yaw 5 5 3 Design Considerations The changes that has to be done in the other functions is that in all communication functions ACS commands has to be added A changing command between BGS and ACS also has to be added to determine which of the attitude control laws and reference computation that is to be used This criteria is used in the top level control A study of the feasibility of the combination of the code has also been done From this study the results are that there is enough computation power and memory capacity in DS19 to handle both a BGS and a pointing ACS 5 6 Conclusions The design that is chosen for the system is specified in this section The design that is chosen is a modularized design for th
37. ciently small The minimum error that can be corrected depends on the gas pressure minimum active time for the solenoid valves and the size of the nozzles 5 2 1 Thruster Configuration The position of the thrusters are chosen according to figure 5 3 The thruster position is chosen in straight angles to be able to control all possible transverse axes This is the best choice if the direction of the thrusters not can be changed during the flight The position of the roll thrusters that are the thrusters that is position in pairs by the x axis are chosen to reduce the effect on the transverse axes from them The roll thrusters are only operated in pairs to get a clean roll maneuver These thruster is not necessary placed in the same plane as the transverse thrusters 5 2 Cold Gas System 21 PRESSURE VESSEL REGULATOR 1 LATCHING SOLENOID VALVES NOZZLES Figure 5 3 The thruster configuration This configuration for the thrusters are valid for systems that controls the attitude Another thruster design has to be chosen if the system only is to control the body rate This because of that some thrusters is not needed in that design 22 Design of DS19 5 3 Budgets This section contains the mass gas and power budget for DS19 5 3 1 Mass Budget The changes in the weight is some loss in the weight due to the synergism effect that occur when the systems is merged such as the removal of similar components
38. ction takes IMS data as input and calculates the apogee altitude time to impact impact point and the corrections of the attitude reference This information is then returned to the main function 7 4 Guidance and Control Calculations 43 amp C NITIALIZATION TM BUFFER INTERRUPT EGSE CMD SPORADIC INTERRUPT MS APPLICATION OMMUNICATION ILIFT OFF DETECTION Figure 7 1 Schematic description of the S W architecture The thiner arrows represent data flows and the thicker arrows represent the calling of different ap plications 7 4 3 Telemetry Compilation This function creates a TM format from given inputs This format is then sent to the IMS application to be routed to the ground control The TM format contains 100Hz 20Hz and 4Hz data In the 100 Hz data is for example the quaternions from the IMS sent In the 20 Hz data is for example the results from the impact point calculations sent Finally in 44 Architectural Software Design DIRECT OUT DAC DIGITAL OUT HEADER FILE EGSE COMMAND DECODE VALIDATE XECUTE EGSE COMMAND SERVO COMMAND DECOUPLING ALCULATE THE ATTITUDE ONTROL AND COMMANDS O THE ACTUATORS OMPILE TM OMPILE AND SEND M AND EGSE DATA PREFORM THE 20Hz UIDANCE FUNCTIONS ATTITUDE REF POHz ROUTIN M DATA TOTM ACSFLAG M DATA TO EGSE Figure 7 2 Function and data flow for the B amp C application The thin lines represent data
39. d both of these use Bang Bang control The first one is a minimization of a loss function The other one is the use of fuzzy control The first strategy gives more calculations for the flight computer but has the advantages that already flight proved code can be used for the implementation therefore that strategy is chosen There are two sorts of Bang Bang control with loss functions that can be imple mented The first one is the Bang Bang control for 3 dimensional control where the com plete control is computed from one algorithm This algorithm uses the attitude error in all axes and also the angular velocity in all axes This results in an algo rithm that is very precise A drawback with this is that it is very complex to do and results in difficult calculations and optimization problems The other alternative is to handle each axis separately and then combine them into one control algorithm This is somewhat less optimized for the whole problem But the computations is much easier and faster There is some loss in the solution due to that the problem only is optimized for the different axes and not the whole problem For the ACS a combination of these methods is used The control is constructed that way to optimize the control for the cases in the flight For the RCS the Bang Bang control is also chosen but the switching lines is only depending on the body rate of the rocket Therefore the switching criteria will be 33 34 Control Law
40. d to download to print out single copies for your own use and to use it unchanged for any non commercial research and educational purpose Sub sequent transfers of copyright cannot revoke this permission All other uses of the document are conditional on the consent of the copyright owner The pub lisher has taken technical and administrative measures to assure authenticity security and accessibility According to intellectual property law the author has the right to be men tioned when his her work is accessed as described above and to be protected against infringement For additional information about the Link ping University Electronic Press and its procedures for publication and for assurance of document integrity please refer to its WWW home page http www ep liu se O Per Abrahamsson
41. e 16 Operating solenoid valve 4 4 Out bottle pressure measure 17 Operating solenoid valve 4 5 5V regulated pressure measure 18 Operating solenoid valve 5 6 5V regulated pressure measure 19 Operating solenoid valve 5 7 Out regulated pressure measure 20 Operating solenoid valve 6 8 Out regulated pressure measure 21 Operating solenoid valve 6 9 Empty 22 Operating latching valve 10 Operating solenoid valve 1 23 Operating latching valve 11 Operating solenoid valve 1 24 Empty 12 Operating solenoid valve 2 25 Empty 13 Operating solenoid valve 2 5 4 Electrical Interfaces 29 5 4 6 Changes in the TM format The change that has to be done in the TM format are that other data has to be sent to ground control depending on which control function that is active The changes that has to be done are the following e Ifthe BGS control is active changes in the TM format according to table 5 16 has to be done e If the ACS control is active changes in the TM format according to table 5 17 has to be done Table 5 16 Changes in the TM during BGS control New Data Old Data For the 100 Hz data No changes For the 20 Hz data Information on which control that is active Empty For the 4 Hz data The bottle pressure for the CGS Temperature DS19 structure The regulated pressure for the CGS Temperature DS19 gyro The starting time for the ACS control Empty The lowest starting altitude for the ACS Empty
42. e structure of the system this is done to get a flexible system that has a minimum of changes in the DS19 module The budgets that is done indicates that the power supply from DS19 is enough to support the complete system Therefore is there no need to include extra batteries in DS19 The budget for the gas is done in order to know how large the CGS has to be for a specific sounding rocket The chosen design for for the electrical interfaces in the system is based on re association of pins to make room for the new data The reassociation is done according to section 5 4 2 The changes in the TM format also has to be done for this application This design does only free enough space for the pointing ACS If any other attitude control application is done a redesign for the IMS and spe cially the interfaces is recommended The changes in the TM format also has to be redesigned The software design is therefore done for a DS19 with a pointing ACS The computer and memory capacity in DS19 is enough for this system 32 Design of DS19 Chapter 6 Control Law In this chapter the control law concept that is used for the ACS and RCS is dis cussed 6 1 Control Concepts Several concepts can be considered for use in both the ACS and RCS control The report will focus on Bang Bang control for the control system This is because the thrusters only has two states open or closed There are two forms of control strategies that can be implemente
43. ection to the sun in the case where the sun is the object that will be studied This according to the sensor chapter in 16 A drawback for the sensor is that the attitude only can be determined in two axis There exist a variety of sun sensors on the market They have somewhat different functionality 8 Attitude Control System 2 4 2 Star Sensors Star sensors use the stars to determine the attitude A star sensor consists of a star detector and a star map To determine the attitude the sensor takes a picture of the stars Then it tries to match the three to five brightest stars against an on board star map to determine in which direction it is facing After this the attitude of the sounding rocket can be calculated This sensor determines the absolute attitude in all three axes unlike the previous A drawback with this sensor is that it often has a longer response time than the other sensors The sensor is also heavier and has a higher power consumption than the other sensors This is also a more expensive sensor then the other 2 4 3 Rate Gyros Gyros are used to determine the rate of the spacecraft The principle of attitude determination with gyros is integration of the angular rates measured by the gyros and a known starting position A benefit with gyros is the high sampling rate that can be achieved There are several types of gyros on the market some of these are listed in table 2 3 The most commonly used gyros in space applicatio
44. ed for in the system to handle the data from the extra sensors Therefore a new design has to be done if these functions are to be added to the system 10 2 Further Work The work that is left to make a completely functional DS19 are Implement TM changes The changes in the TM format has to be implemented Detailed design Extend the preliminary design in this document to a detailed design and implement it in C and Assembler Flight table editing Implement a simplified way to change the flight table which is changed in the initialization file for the system This is a poor solution because this is a variable for the flight and the other inputs in the file are constant for the system Split up the initialization Split up the initialization in separate files for the initialization for the system and for the model and the simulation Implementation The implementation of the code in C and Assembler Testing of the system Further testing in the sounding rocket simulation pro gram made by SE and hardware in the loop tests for the system to assure that it functions according to the requirements Changes in the H W The changes that is needed in the H W has to be de signed and implemented in the DS19 module Further development Further development of the system into fine or sun point ing systems with extra sensors This results in that a new or changed IMU has to be developed to make room for the new interfaces that is needed Some
45. em IMU Inertial Measurement Unit NASA National Aeronautics and Space Administration PID Proportional integration and derivation controller PDU Power Distributing Unit RACS Rate and Attitude Control System an ACS built by Saab Ericsson Space AB RCS Rate Control System SE Saab Ericsson Space AB SPINRAC SPINning Rocket Attitude Control a BGS built by Saab Ericsson Space AB S W Software TM Telemetry TVC Thrust Vector Control Contents 1 Introduction 1 1 Sounding Rockets oo 0 ses 0 0 00 0 000000000 1 2 Boost Guidance System e 12 11 Actuators a do ba e RR is a A rdr de Ge GE ee 1 3 Attitude Control System 2 o ee ee 2 Attitude Control System 2 1 Missions decre hb a Be ee De ewe ee ee ew 2 2 ACS Hardware soo ss sc hhh dr 233 Actuators s m dar en an a A eR eee So a Ar RR eR DA SCNSORS eek s GM RGA dr Aw Ee EO A AA AA a a NR 2 4 1 Sun Sensors gt cce ra addat da es 24 2 Otar Sensis 2 ala a a e 24 3 Rate Gyros us 3 5 5 4 ce ewe dd v rvare ee ee ee 2 4 4 Magnetometer 0 0 0 0 oss er 2 4 5 Accelerometers 2 0 ee rss ss ss orsa 2 4 66 GPS Receive 2 5 Existing Attitude Control Systems 0 3 Problem Formulation 3 1 Purpose of the Report 2000000004 32 DSI Fe cece eae anteaddeceebuea a cet 3 3 Requirements on the DS194 4 4 DS19 Heritage 4 1 Present Control Systems a a ALL Dolors a A eeu 4 1 2
46. em is simulated The input to the simulation is the control torques and the torques from 9 2 Result From Simulation 63 the disturbances Both of them is assumed to be constant for each interval This way is chosen for the simulation to make shore that the control function only is called at 100Hz and to get a sufficiently good description of the system 9 2 Result From Simulation The result from the simulation of the system is shown in this section The system is simulated for a nominal where there are no misalignments The phase planes for a nominal case for the system looks as figure 9 1 The combined maximum error during the stable phase are less then 0 2 This is a result that is better then the requirements in section 3 3 This can be a result of that the disturbance is implemented with a effect that is to small ox 10 Phase plane in roll 2 10 Phase plane in pitch 4 15 2 2 1 0 y 5 amp 05 3 3 2al 2 lt lt 0 0 5 3 1 1 1 5 2 2 5 3 3 5 4 4 5 5 5 5 Angle x10 Angle x10 x10 Phase plane in Yaw Total error in angle 6 0 7 0 6 Pik 0 5 T o E 5 0 4 Z 2 T gt 9 0 3 lt 0 0 2 01 A 0 0 2 0 500 1000 1500 Angle x107 Sample Figure 9 1 The phase planes for the system after a simulation The acquisition time for the system has also been investigated for the system a histogram for the time is shown in figure 9 2 The maximum time for a acquisition are 28 3
47. en calculates the reference attitude from the in data and the scheduled parame ters The reference attitude is then returned from the function 7 4 9 ACS Reference Attitude This function is called at 20 Hz The input data to the function is the flight plan The reference attitude remaining time for the acquisition for the maneuver and the reentry flag that indicates when the reentry maneuver is to be initialized are the output from the function 46 Architectural Software Design 7 4 10 100 Hz Control Routine This function is a top level routine that calls the following functions e 20 Hz control routine e BGS control e ACS control The two control functions are never called in the same 100 Hz routine The ACSflag determines which one of the functions that is going to be called The function also determines when the rocket is ready for launch and when the canards is to be decoupled The digital output and the output on the digital to analog converter DAC is also handled Through the digital output is the commands for the valves and the signals ready to launch and canards decoupling sent The signals that uses the DAC is the commands for the servos that control the canards 7 4 11 Ready for Launch Flag Computation This function computes the ready to launch signal The signal is computed from the status of the sounding rocket 7 4 12 BGS Control This function uses data from the IMS and the reference attitude as input the con
48. escribed The results from the simulation is also discussed 9 1 Rocket Dynamics To be able to test the control system for the sounding rocket a model of the rocket dynamics has to be derived To determine the model a coordinate frame for the model has to be chosen Several frames can be used but the chosen frame is a frame fix in the launch pad for a more detailed description see B 3 The model has the following states Three states describing the position of the sounding rocket in the coordinate frame x x position y y position z Zz position Three states representing the velocity for the sounding rocket V Velocity in x direction V Velocity in y direction Vz Velocity in z direction 61 62 Verification and Simulation Four states representing the transfer function described in quaternions from the inertial frame to the body frame For more information see A qo q q2 q3 Three states representing the angular velocity of the spacecraft expressed in the initial frame We Angular x velocity wy Angular y velocity w Angular z velocity This model describes both the movement and attitude change of the sounding rocket A difficulty with this system is that the step length when solving the equations are varying between the equations A simulation of the attitude requires a small step size and a simulation of the movement requires a larger step size The fact that the two parts are independent of each other makes it
49. esign Chapter 8 Preliminary Software Design This chapter deals with the detailed design for the the program The structure of the subprograms for the application is described 8 1 Compiler The compiler that is used for compiling the program is a Cross Code C C compiler The code has to be compiled for a Motorola processor to get the best real time results for the functions 8 2 Program Functions In this section the functions for the ACS specific tasks for DS19 is described in detail Main Function for the Attitude Control The input to the function is e The attitude in quaternions from the IMS e The reference attitude in quaternions e A reentry flag e The remaining time for the acquisition maneuver The function needs to have the following stored data between calls e The command for the latching valve e The attitude in quaternions from the previous call ol 52 Preliminary Software Design e The previous output from the function e Ready flag for the transit low function e The updated angular rate e The current position in the phase plane The output from the function is the command word to the valves in the CGS The function first uses the data to calculate the angular body rates and to transform the attitude to a polar frame in the thruster plane The attitude error is then calculated with this information The select function is then called to determine which control function that is going to be used
50. ex e A counter that indicates the sequential stable time for the payload First the function checks if there is a new maneuver After that the output variables for the function is set Then the stable time counter is updated and if the stable time is the same as the stable time in the flight plan the new maneuver flag is set 58 Preliminary Software Design 8 2 2 Ready to Launch The changes in this function is the following The bottle pressure and the regulated pressure in the CGS has to be above a certain value to give the ready to launch signal The implementation is done similar to the pressure checks for the BGS servo system 8 2 3 20 Hz Routine The changes for this module are the following e For time after lift off modulo 5 0 The function that sets the ACSFLAG is called e For time after lift off modulo 5 3 The BGS attitude reference function is called if ACSFLAG is false If the ACSFLAG is true the ACS attitude reference function is called The ACSFLAG is an input from the 100 Hz routine and also an output from this function 8 2 4 100 Hz Routine The changes that are needed in this function are the following The ACSFLAG has to be sent to the 20 Hz routine The function attcnt is called when ACSFLAG is false and the function attcntacs when it is true All the digital outputs is saved in parameters that is added together before the sending of the command 8 2 5 Choice of Control Mode This function needs t
51. g ACS designed by SE seen in figure 4 2 RACS is constructed of a self contained module that uses a CGS as an actuator The performance of RACS can be seen in table 4 1 Table 4 1 Performance for RACS Accuracy 0 7 Drift rate 0 07 s 4 2 Attitude Control Functionality 15 Figure 4 2 The RACS module 4 2 Attitude Control Functionality In this section some functionalities for DS19 and which additional components that is needed for them is described 4 2 1 Rate Control System A free falling sounding rocket with low angular body rates provides a near zero gravity environment The Rate Control System RCS is used to control the body rate of the sounding rocket to provide this environment To achieve zero gravity environment two conditions must be fulfilled 1 No acceleration of the body 2 No angular body rates Condition one is met because the payload is in free fall above the atmosphere The second condition is fulfilled with a working RCS A working RCS will hold the rate of the payload less than 0 2 s in all three axes Control pulses from the RCS should be avoided during the measurmentphase 16 DS19 Heritage This results in an environment of 1074 107 g To get as much time as possible in zero gravity environment the RCS shall minimize the rate as quick as possible The RCS only controls the rates which makes it easy to integrate with the DS19 system since only addition
52. he following input e Time after lift off e Altitude e A test flag that can set the ACSFLAG The output from the function is the variable ACSFLAG that indicates which control routine that has to be chosen The ACSFLAG is set true if Time after lift off is higher then a predefined value the altitude is high enough and that decoupling of the canards is done or that the test flag is true If non of these holds the output is set to false 8 3 Implementation 59 8 3 Implementation First a development environment for the code has to be chosen The environments that are used for these type of developments is C Fortran and MATLAB The benefit with MATLAB is that it has a short development time and the drawback is that it has a long execution time for the simulation C has a benefit of short execution time but has a long development time Fortran has approximately the same properties as C Due to the nature of the system and that the duration for the simulation is short the MATLAB environment is chosen for the development The control system has been implemented according to this chapter Rocket spe cific constants are chosen to be the same as for the RACS sounding rocket The constants has been retrieved from 8 The final flight code shall be developed in C and Assembler 60 Preliminary Software Design Chapter 9 Verification and Simulation In this chapter the simulation of the control law and a model for the system is d
53. ilar logic as the switching between the attitude control functions 40 Control Law Chapter 7 Architectural Software Design The S W for the system is divided in two subsystems e The S W for the IMS e The S W for the Guidance and control G amp C application The S W for subsystem one is designed and written by the developer of the IMS This design is therefore not considered in the rest of the report Instead the archi tectural design of the G amp C application will be discussed The architectural design for the top level of DS19 is mainly the same as for the DS19 Therefore much of the architectural design is derived from 9 7 1 System Design The main functions of the G amp C application are listed in table 7 1 The design is focused on the functions and changes that are generated from the adding of the ACS functionality to the system The final program shall be written in C to be compatible with the existing code Table 7 1 Purpose of the G amp C application S W Impact point calculations Parameter scheduling Telemetry compilation Command calculations for Canards Thruster valves Attitude control calculations for BGS application ACS application 41 42 Architectural Software Design 7 2 Interfaces The interfaces can be divided into three parts e All S W interfaces between IMS and G amp C e The signals from the G amp C application to the digital output and to the digital to analog converter D
54. ion will be according to table 5 7 Table 5 7 Power consumption Activity Consumption Ah Pressure sensors 0 25 DMARS 0 5 PDU 0 1 CGS 0 2 Servo system 0 1 Attitude sensors 0 4 total 1 55 Conclusions From table 5 7 the worst case power consumption is 1 55 Ah and according to 1 the power that can be generated from the battery in the DS19 is 2 2 Ah This gives a resulting over capacity of 42 For the ACS were no extra sensors is used the power consumption is as low as 1 15 Ah which result in a over capacity of 91 The power consumption is calculated with a run time of 30min which is longer then any run time for the system This gives the result that the battery power is sufficient to support the complete system If this had not been the case the battery system would have been extended with either a new sort of batteries in the DS19 module or extra batteries in the DS19 or CGS module 5 4 Electrical Interfaces The merging of the system results in several new interfaces that has to be added in the DS19 module These interfaces emerge because new signals are needed in the system These signals result in the new or changes interfaces listed in table 5 8 26 Design of DS19 There is also some extra data that has to be sent by the telemetry from the DS19 to the ground This will only cause some minor changes in the telemerty TM format Table 5 8 New or changed interfaces From To DMARS PD
55. lowing relation holds for the derivate paw 6 3 w au 6 4 Where a is the angular acceleration produced by the thrusters and u is the control signal u has the following properties u 0 1 1 L is a function of A and u A is a design parameter that represents the trade off between gas consumption and maneuver time L 1 Alul 6 5 A gt 0 6 3 Control Law for Small Maneuvers 35 The function that is going to be minimized then gets the form min H 1 Aju Vw Vau 6 6 This results in three cases for the minimization 1 Vow u 0 min H 4 1 A Vpw V sa u 1 6 7 1 Vpw Vsa u 1 These equations gives the following result 1 A gt V a u 4 1 A lt V a 6 8 0 JAS lt V a lt A The equations for motion from Hamilton is OH Vv OH z gt WwW dp e av OH OH on Qo av EN OH dL eh o H L Vo Vu Ot dt aes Kg In combination with the results from above and these equations the following result is derived OH Oy p OH on Vo gt Vo Vo C gt V Ct D 6 10 The steady state solution for the Hamilton function is min H 0 6 11 This result must also be valid for u 0 therefore must C The switching lines can be derived from equation 6 8 Va ON A V a OFF These criterias can be rewritten with the values from above Where t and ta is on and off times for the control A a D ON 6 14 a D O
56. m and how these are derived 3 1 Purpose of the Report The systems flown in present missions consist of two separate control systems for attitude and trajectory control These systems have no exchange of information between them Both of them use their own computer actuators and sensor plat form The purpose of this report is to study the feasibility of merging the two systems into a single system 3 2 DS19 The system called DS19 that is designed is a combined ACS and BGS that uses a DS19 module as the main structure The DS19 module should be used with as few changes as possible 3 3 Requirements on the DS19 The requirements on the system are that the boost control should remain the same as for DS19 The requirements for DS19 can be found in 14 The total pointing accuracy for DS19 where no extra sensors are used should be better than 0 7 3 0 This requirement is derived from 3 The first acquisition maneuver the maneuver to a new reference frame should have a duration that is less then 35 s 11 12 Problem Formulation The components in DS19 shall follow the requirements on similar components in DS19 If no mayor changes are done to the DS19 module these requirements will automatically fulfilled New components in DS19 shall follow the requirements in 3 Chapter 4 DS19 Heritage This chapter discuss the use of present systems to design DS19 In the design of DS19 knowhow and technical solution
57. nd volume for the control system A sounding rocket is a small rocket compared to a satellite launcher It is used to launch payloads into suborbital trajectories The payload consists of scientific experiments for example micro gravity experiments and astronomic observations The boost guidance system controls the sounding rocket during the launch phase This is done to minimize the impact dispersion The attitude control system controls the payload during the experiment phase The system that is developed in this report is based on the DS19 boost guidance system from Saab Ericsson Space AB The new system is designed by extending DS19 with software and hardware The new system is therefore named DS19 Hardware wise a study of the mechanical and electrical interfaces and also of the system budgets for gas mass and power for the system are done to determine the feasibility for the combined system Further a preliminary design of the control software is done The design has been implemented as pseudo code in MATLAB for testing and simulations A simulation model for the sounding rocket and its surroundings during the experiment phase has also been designed and implemented in MATLAB The tests and simulations that have been performed show that the code is suitable for implementation in the real system Nyckelord Keyword sounding rocket attitude control stabilization boost guidance Abstract This report handles the preliminary design of a control
58. nding rocket attitude control stabilization boost guidance ii Acknowledgment I would like to thank the following people for their help during the writing of this report Albert Thuswaldner my supervisor at Saab Ericsson Space AB for all the help with the work report and presentation and also for putting up with all my questions I would also like to thank Anders Helmersson my examiner for the help with the design of the system and also for all the help with 4 TpXduring the writing Further I would like to thank David Lindgren my supervisor at ISY for the help with the report I would also like to thank Jan Olof Hjertstr m and Lars Ljunge plus the rest of the staff at Saab Ericsson Space AB for all the support and help during my work there I would also like to thank Anneli N sstr m my girlfriend for her mental support and for the help with the grammar in the report iii lv Notation Abbreviations ACS Attitude Control System BGS Boost Guidance System CGS Cold Gas System CPU Central Processor Unit DAC Digital to Analog Converter DMARS Digital Minature Attitude Reference System DS19 A BGS built by Saab Ericsson Space AB DTG Dynamically Tuned Gyro EGSE Electrical Ground Support Equipment FOG Fiber Optical Gyro GCS Guidance and Control System a BGS built by Saab Ericsson Space AB GPS Global Positioning System G amp C Guidance and Control HGS Hot Gas System H W Hardware IMS Inertial Measurement Syst
59. ne This is not true because the thrusters is mounted with a straight angle between them This approach is however valid because the real problem is solved by L where L is the idealized loss function and is the factor go LVA o 1 A This is done because the thrust is in fix directions and not in arbitrary directions as the loss function is calculated for this according to 5 The control strategy is based on several locally optimal trajectories The the most optimal is chosen from loss functions for the system The local trajectories are based on the trajectories from RACS ACS described in 5 These trajectories describe solution of how the payload can go from the present state to the wanted state A loss function is calculated for each trajectory and then the smallest of them is chosen as base for the control The choice between the trajectories are done for every call to the large control The trajectories are L This loss function represent a trajectory that is made of one turn towards the reference attitude a coast phase and a deceleration phase L This loss function represent a trajectory that consists of a deceleration to a complete halt followed by a attitude maneuver in one axis L3 This loss function represent a trajectory that consists of a coast phase followed by a deceleration and finally a maneuver in one axis L4 This loss function has a trajectory made of a coast phase followed by a combined turn and decelerati
60. ns today are the FOG and DTG gyros Silicon gyros are a relatively new kind of gyros Because of this they have not had enough time to prove their efficiency 2 4 4 Magnetometer Magnetometers use the earth magnetic field to determine the attitude This type of sensor have many advantages They are small light have no moving parts and they are tolerant to external conditions However there exist a disadvantage which is that the magnetic field is not completely known and the models that exist for prediction of the field have errors according to 16 Despite of this the sensors are commonly used especially for experiments concerning the magnetic field 2 4 5 Accelerometers The only difference between commonly used accelerometers and the ones used in spacecrafts is that the later has a smaller bias This is because the spacecraft needs extremely accurate information about the acceleration to be able to determine the position The accelerometer uses a mass that is attached to springs to determine the acceleration This is done by measuring the displacement of the mass 2 4 6 GPS Receiver The GPS receiver is used for low altitude spacecrafts to get information about their position This system is mostly used as an extra sensor for tracking of the rocket The GPS receiver provides information about the position and velocity for the spacecraft This information is normally not used by the ACS or BGS But it is common that the information is sen
61. ody rates e The angular acceleration for the payload 8 2 Program Functions 57 The outputs from the function are e Commands for the thrusters e The command to the latching valve e A ready flag A time parameter has to be saved between the calls for the function The function conducts a series of tasks that results in that the regulated pressure is lowered in a way that does not result in any increase in the body rates This function is divided into several parts First there is a coast phase for the control After that a loss function is calculated and from this the command to the thrusters is calculated and also the active time for the thrusters is calculated After this the output for the thrusters is set to the calculated value for that time Then the latching valve is closed and a new loss function is calculated to determine which thrusters that is to be used during the pressure dumping Then the the commands to the thrusters are sent Finally the ready flag is set to true Pressure Transit High This function needs no input The output from the function is an open command to the latching valve 8 2 1 Attitude Reference ACS This function does not need any input The outputs from this function are e The attitude in quaternions e The reentry flag e The remaining time for the acquisition maneuver The saved data in this function are e A flag that indicates a new maneuver e A counter that indicates the flight plan ind
62. on This function is valid for small equatorial rates Ls This function has a trajectory made of an acceleration towards the reference attitude This function is valid for small equatorial rates 6 5 Control Law for RCS 39 La and Ls is needed because the others has discontinuities for small equatorial rates The drawback with them is that they are only valid for a restricted domain The loss functions are only valid for specific intervals If the state of the sounding rocket is outside the valid interval the loss function is set to infinity At least one function is always valid 6 5 Control Law for RCS The Control law used in the RCS is the same as the one used for rate reduction in the ACS This control is also based on Bang Bang control and uses a Hamilton function similar to the Hamilton function in the attitude control The loss function for the rate control has the following form Crw CT L M2 4 SL 2 w2 y A lug 8 Where a is the angular acceleration and C is a weight constant for each axis The loss function inserted in the Hamiltonian then results in a control law with the following form a w lt f a C A L u 4 a u gt fla C A L 0 f 0 C A L lt w lt fla C A L Where f a C A L is a function determined by the minimization of the Hamilton function This is the principle for both large and small angular rates The difference between them is the constants The switching between them is based on a sim
63. one and the other counters is set to zero 56 Preliminary Software Design Fine Control The inputs needed in this function are e The attitude error e The angular body rates e The previous valve command e The angular acceleration The output from the function is e Commands for the thrusters The data that has to be saved between the calls are e The time for how long the control has been consecutively in fine mode The switching lines in the phase plane The present point in the phase plane The sequential operating time for the thrusters The filtered angular rate e The reference attitude The function first calculates the stability of the system This is done by checking the angular velocity and attitude error compared to constants The attitude control is then computed in a similar way as for the small control The stabilization flag is used to select between two control routines in this part of the function The control function that is used when the rocket is unstable is a simplified version of the control law The control used for the stabilized case is the complete control function After this the sequential operating time for the thrusters is updated in a similar way as to the update in the small control The function then returns the control command to the valves Pressure Transit Low The inputs needed in this function are e The present command to the latching valve e The attitude error e The angular b
64. or 1 arcsec 10 Coarse pointing Gyro platform 0 7 30 Fine pointing Gyro platform and star sensor 60 arcsec 20 Magnetic field Magnetometers 2 0 5 Non controlled No sensor 25 Zero Gravity Missions Experiments that require a zero gravity environment is normally only controlled in rate The ACS used in this type of missions normally uses a gyro platform or magnetometers to measure the rate Descriptions of these sensors can be seen in section 2 4 3 and section 2 4 4 6 Attitude Control System Solar Observation Missions The sun is a target that often is studied during sounding rocket missions Solar observation missions have requirements on the attitude and rate of the payload for the conduction of the experiments These ACS uses sun sensors to determine the direction towards the sun Sun sensors is described in section 2 4 1 Coarse Pointing Missions This control is similar to the solar observation control The differences are the sensors used and the requirements on rate and attitude The sensors used in these missions are for instance gyros or magnetometers A description of these can be found in sections 2 4 3 and 2 4 4 Fine Pointing Missions The fine pointing control are similar to coarse pointing control but with higher re quirements on accuracy for the attitude and rate To achieve this a sensor platform supported by a star sensor is used The star sensor is described in section 2 4 2 Magneti
65. or the prediction of the angular increment and body rate increment The old values for these variables also has to be saved for use in the next call The output from the function is the control signals for the thrusters This function computes the control for each axis separately The function first predict the angle increment and body rate for the axis This is done in the following way e If the positive on counter is greater than zero the rate is increased with a constant times the angular acceleration and the angle increment is changed with the body rate e If the negative on counter is greater than zero the computations is as above but with a change in the sign e If the off counter is greater than a given constant the values is changed with a body specific parameter e If the off counter is lower than the constant the old values is used for the parameters The control law from section 6 3 is then applied The result is used as output from the function The sequential operating time for the thrusters is then updated This is done in the following way for each axis 1 If the thrusters is used in the positive direction of the axis the positive on counter is increased by one and the other counters is set to zero 2 If the thrusters is used in the negative direction of the axis the negative on counter is increased by one and the other counters is set to zero 3 If no thrusters is used in the axis the off counter is increased by
66. pressure sensors the CGS and the servo system for the canards e The DMARS has a consumption of 1 A in the nominal case according to 11 and a flight does nor last for more than 30 min The power consumption of the DMARS is according to these numbers 0 5 Ah e The PDU in the RACS system has a power consumption of 0 055 Ah accord ing to 15 The PDU in the DS19 has a similar structure as this one A restrictive number on the power consumption is then 0 1 Ah e To get a restrictive power consumption for the extra sensors several sensors are studied The highest power consumption for the sensors where found to be 0 4 Ah 5 4 Electrical Interfaces 25 e The power consumption of all three pressure sensors is set to 0 25 Ah This number is derived from the fact that one old pressure sensor from the RACS consumes 0 055 Ah according to 15 e To empty the CGS completely in the RACS 0 113 Ah is needed according to 4 The CGS for this application is up to 1 7 times as large as the RACS system Therefore a consumption of 0 2 Ah is a restrictive number on the consumption e The power consumption that is needed for the canard servos is also derived from the RACS CGS power consumption This because of that the servo system works in a similar way as the CGS The servo system is naturally much smaller and therefore easier to empty A restrictive number for the power consumption for the servo system are 0 1 Ah The results of the power consumpt
67. put from the function is the control signal to the valves First the function checks the reentry flag If the flag is true the reentry maneuver is initialized If the flag is false the control function is executed The reentry maneuver consists of roll rate and transverse rate control The reentry maneuver first controls the transverse rates and attitude errors If these are suf ficiently small the function activates the roll thrusters to increase the spin of the rocket If the transverse rates are to large the function activates the thrusters to reduce these The control function consist of two parts roll control and transverse control The roll control is first initialized to reduce the roll rate for this the RCS control is used whit a hysteresis function added to it After that the roll control waits until the transverse error is sufficiently small before the roll error is corrected The control law from section 6 4 is used for this The command signal for each axis is then sent as an output Small Control This function needs the following input e The attitude error e The angular body rates 8 2 Program Functions 55 The previous valve command The angular acceleration The switching lines in the phase plane e The present point in the phase plane e The remaining time for the acquisition maneuver The sequential operating time for the thrusters has to be saved between the calls to the function This information is used f
68. ready done in the present system so the difference should not be significant 5 5 1 Existing Software The code that is used as a ground for the DS19 S W is the flight S W from the DS19 module This S W is flight proved and many of the functions that are used in it can be used in the ACS S W without any modification or very small modifications The largest changes that are needed to be done are the functions that are used for the attitude control computation This includes an attitude reference computation and the function that computes the control law 5 5 2 New Functionality There are two completely new functions that have to be implemented in the DS19 for the ACS control ACS Control Function The first one is a function that computes the control law for the ACS This function uses a completely different strategy compared to the DS19 control algorithm This is due to the use of other actuators and also the fact that the ACS controls the rocket in all three axis and the DS19 only controls it in two axis For the ACS that uses extra sensors this function needs to consider the sensor information as well as the gyro information This function uses information from the IMS and the reference attitude as input for the ACS that does not use extra sensors From this information the control signals to the valves is computed This signal is then the output from the function The function uses the control laws described in chapter 6 ACS Referen
69. rface of the earth The z axis points towards the true north pole and the y axis is placed so that a right handed orthogonal Cartesian system is formed This system is chosen as a inertial system based on the previous use of this system in sounding rocket applications 71 72 Coordinate Systems Appendix C User Manual This Chapter is a description of the S W that is produced for the attitude control and simulation C 1 File Structure The file structure of the program are shown in figure C 1 C 2 Input The inputs to the function are the data listed in table C 1 Table C 1 Inputs to the function Name Description tend plotflag tabell This input variable is set in the function call and represent the execution length of the simulation This is a variable that controls the call to the plotfil in the main function If it is set to one the function is called for all other values the is not called This is the flight plane for the system It is set in the initfile for the system The variable is a matrix where each row represent different maneuver The first column is the time for the acquisition for the maneuver the second column the time for which the attitude has to be stable and the last columns are the attitude in quaternions 73 74 User Manual INITFILE PLOTFIL CONTROLF EQ2 DISTURBANCE ATTCNTACS REFATT UPPDATECOUNT TRANSF LARGE VERO ATECDUNE
70. s from other SE control systems is used mostly from DS19 and RACS but also from SPINRAC these system are described in section 4 1 The heritage tree for DS19 can be seen in figure 4 1 In section 4 2 the basic types of attitude control is described the changes that are needed in DS19 to achieve this functionality is also described 4 1 Present Control Systems These sections describe the systems that DS19 is based on 4 1 1 DS19 The DS19 system is a digital BGS DS19 uses a gyro platform named DMARS as a measurement instrument The information from the gyro platform is computed and a control signal is sent to the canards This system can only function within the atmosphere because of the use of aerodynamic forces by the canards 4 1 2 SPINRAC SPINning Rocket Attitude Control system SPINRAC is a boost guidance system that is used to minimize the impact dispersion by controlling the attitude of the sounding rocket before the third stage of a large sounding rocket is ignited This is done with the use of an IMS controlled CGS system A CGS is used instead of canards because the control is done above the atmosphere 13 14 DS19 Heritage SPINRACS DS19 SPINRACS MAGNETOMETER F DS19 ACS SPINNING PAYLOAD DS19 POINTING STAR SENSOR SUN SENSOR DS19 DS19 FINE POINTING SUN POINTING Figure 4 1 Heritage tree with the DS19 module as base 4 1 3 RACS Rate and attitude control system RACS is a pointin
71. sion for the rocket The dispersion is minimized to keep the impact point within the borders of the missile range This is done by controlling the trajectory and transverse attitude for the rocket The boost guidance is done during the duration of the motor burn There is mainly two means of controlling the rocket during the boost phase Either with canards or with thrust vector control These methods are described in the following sections The hardware for the BGS is listed in table 1 2 1 2 1 Actuators Aerodynamic control in the form of fins so called canards are used to control the sounding rocket during the boost phase A typical system that uses this strategy is the Saab Ericsson Space AB SE DS19 seen in figure 1 1 TVC controls the sounding rocket by altering the thrust vector of the motor This results in a change of the movement for the rocket A system that uses this type of control is the SE Guidance and Control System GCS seen in figure 1 2 1 3 Attitude Control System 3 Table 1 2 BGS Hardware Components Function IMS The Inertial Measurement System IMS is the sensor platform the system It usually contains gyros and accelerometers Computer The computer is used for calculating the control strategies Actuator The set of actuators are the part of the system that provides the control forces on the body This can be done with a servo system with canards or with a thrust vector control TVC that is
72. t down to the ground control with the other 2 4 Sensors 9 Table 2 3 Rate Gyros Type Description Mechanical gyro This is the standard type of gyros that consist of a spinning disk that is mounted so that it can rotate around one axis The rate in the different axis is measured by the deviation angel from the ground position that the gyro gets This type of gyro is heavy and large They are not as accurate as other gyros Standard laser These gyros consist of a platform where several mirrors gyro are mounted The rate is measured by the interference that occurs when the platform is spinning These gyros is fairly large and heavy The accuracy is better then for the mechanical gyro FOG The Fiber Optical Gyro FOG is a laser gyro that instead of mirrors uses fiber optics This makes the gyro both lighter and smaller then the standard laser gyro These gyros is both accurate and small which makes them usable in space applications DTG The Dynamically Tuned gyro DTG consist of a spinning disk that spins at a tuned frequency that makes it dynamically decoupled from the sounding rocket The bending of the disk is then measured and compensated for with a coil This design makes the gyro efficient light and small This gyro has a very god accuracy Wine glass gyro These type of gyros vibrates and then the position of the nodes is measured to determine the rate This gyro is extremely accurate but also sensitive to en
73. tra attitude control functions that uses extra sensors The design also gives extra freedom for the position of the sensors The design also simplifies the construction of the CGS if it is built by an external manufacturer The electrical interfaces and TM format is changed according to the design in chapter 5 These interfaces has to be redesigned if another attitude control function is added to the DS19 system The attitude control S W for DS19 is derived from the control laws in chapter 6 These control laws and a S W function that is used to chose between the them are implemented in MATLAB with a model of the sounding rocket from chapter 9 The model is used to perform simulations of the control system The pointing error for the system is totally less then 0 2 3 0 in all axis which fulfills the requirements of a total error less the 0 7 3 0 in all axis The result from the simulations can also be seen in chapter 9 As seen above and in chapter 9 the system fulfills the requirements on the DS19 system found in section 3 3 The system should there 65 66 Conclusion and Further Work fore be functional when it is implemented in C together with the boost guidance S W from DS19 and some of the changes listed in the next section If other attitude control functions such as fine pointing or sun pointing have to be added to the DS19 the IMU interfaces has to be redesigned to make room for the extra signals needed Extra S W is also need
74. trol signal to the servos is then computed with a PID control algorithm 7 4 13 ACS Control This function uses IMS data and reference attitude as input The output is com puted with a control function that uses several control algorithms The control algorithm is chosen based on the attitude and rate error The output from this function is control signals to the CGS valves 7 4 14 ACS Large Control This function is used by the ACS attitude control if the attitude error are large The function is divided into two different parts a reorientation maneuvers part and a reentry maneuver part 7 4 15 ACS Small Control This function is used for small errors and when the regulated pressure level is high It uses the present error and old outputs as input and the output is control signals for the valves in the CGS 7 5 Software Module Hierarchy 47 7 4 16 ACS Fine Control This function is used for small errors and low regulated pressure This function is similar to the ACS small control This function only uses other constants than the ACS small control 7 4 17 ACS Pressure Transit Low This function is used as a transit function between the small and fine control The purpose of the function is to reduce the pressure in the system from high to low without any appearance of unwanted body rates 7 4 18 ACS Pressure Transit High This function works in a similar way as the transit function for low pressure The difference is that this
75. ty 34 Opening command solenoid valve 2 Empty 35 Opening command solenoid valve 3 Empty 36 Opening command solenoid valve 4 Empty 37 Opening command solenoid valve 5 Empty 38 Opening command solenoid valve 6 Empty 39 Opening command latching valve Empty 28 Design of DS19 Table 5 13 Pin reassociation in 26 pins DMARS to PDU interface pin New signal Old function 22 TX extra sensor RS232 interface TX GPS RS232 interface 23 RX extra sensor RS232 interface RX GPS RS232 interface 5 4 4 PDU Sensors The interface between the PDU and the arm safe plug has free pins that can be used for communication with the attitude sensors The changes that has to be done in this interface are the ones described in table 5 14 Table 5 14 Pin reassociation in 25 pins PDU to arm safe plug interface pin New signal Old function 6 Power feeding Empty 7 Power feeding Empty 12 TX extra sensor Empty 13 RX extra sensor Empty 22 Power ground Empty 23 Power ground Empty 5 4 5 PDU Valves The communication between the PDU and the valves could be done through a new interface with pin association according to table 5 15 Table 5 15 Pin association in 25 pins PDU to VALVES interface pin New signal pin New signal 1 5V bottle pressure measure 14 Operating solenoid valve 3 2 5V bottle pressure measure 15 Operating solenoid valve 3 3 Out bottle pressure measur
76. vironmental constrains Silicon gyros These gyros are small and lightweight They also have a fairly good accuracy attitude and position information The GPS receivers are normally used in pairs to introduce redundancy in the system 10 Attitude Control System 2 5 Existing Attitude Control Systems A list of the ACS used by NASA is displayed in table 2 4 Table 2 4 Existing ACS Type System Accuracy Sensors Manufacturer Course Rate Control lt 0 2 s 3 axis rate Space Vector Attitude sensor Control Magnetic ACS lt 2 0 Tree axis Space Vector magnetometer single axis rate gyro Inertial ACS lt 2 0 MIDAS Space Vector platform Fine MARK VI lt 3 02 Inertial gyro Aerojet Attitude MARI Control platform MARK VI lt 120 arcsec Inertial gyro Aerojet Stellar Update Star Tracker MARK VI lt 60 arcsec Inertial gyro Aerojet Stellar Pointer Star Tracker MARK VI D lt 60 arcsec Inertial gyro Aerojet Stellar Update Star Tracker SPARCS VI lt 1 arcsec Course Fine NSROC in Pitch amp Yaw sun sensors lt 5 in Roll SPARCS VII lt 1 arcmin Course Fine NSROC in Pitch amp Yaw sun sensors lt 5 Magnetometer in Roll or rate gyro Chapter 3 Problem Formulation This section contains an overview of how the control systems work today and the purpose of the report There will also be a description of the requirements on the new syste
77. y interval when the system is close to the switching criteria in the phase plane 6 3 1 Fine Control The fine control is done in the same way as the small control The difference is that other numbers is used for the criteria and that a lower pressure is used which makes it possible to correct small errors 6 4 Control Law for Large Maneuvers The large maneuver control law is based on the control law for the RACS control that can be found in 5 This control law is based on the same Hamilton function as for the small maneuvers The control of the sounding rocket is divided in two parts transverse and roll control This can be done because of that the coupling between the roll axis and the transverse axes is sufficiently small This simplifies the development of the control system The control that is derived for the control is based on 6 22 Where the transverse maneuver is the main contributor to the time and fuel consumption 38 Control Law 6 4 1 Roll Control The roll control is divided into two separate procedures Rate reduction This procedure reduces the roll rate before the the attitude control starts Attitude control In this procedures the roll attitude is controlled The control algorithm that is used are similar to the attitude control for small maneu vers 6 23 6 4 2 Transverse Control The transverse control will be designed as if the thrusters can be used in an ar bitrary direction in the transverse pla

Combined Platform for Boost Guidance and Attitude

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