Final Version
Micro-Arcsecond X-ray Imaging Mission Pathfinder (MAXIM-PF)
Eric Stoneking Paul Mason
May 17, 2002
ACS
MAXIM-PF, May 13-17, 2002Goddard Space Flight Center
Attitude ControlPage 2
Final Version
ACS Drivers
Very tight attitude and translation control requirements 1 arcsec is limit of existing state of the art Subarcsec attitude, sub-millimeter translation control to be achieved
through technology under development “Super star tracker” Very stable gyros Micro-thrusters Swarm sensors
Formation Flying Requires inter-spacecraft sensors and communication Requires distributed control laws , fault detection, safing algorithms
MAXIM-PF, May 13-17, 2002Goddard Space Flight Center
Attitude ControlPage 3
Final Version
Technologies
Key Hardware Technologies Sensors
“Super Star Tracker” Quad cell laser beacon tracker Very low-drift gyros ( < 1 uas/day)
Swarm Sensor Low bias Accelerometer
Micro-Newton Thrusters
Formation Flying Algorithms Formation acquisition and maintenance
Micro-thrust Control Disturbance estimation and rejection Parameter estimation and adaptation
CG migration/fuel usage Bias/drift estimation
MAXIM-PF, May 13-17, 2002Goddard Space Flight Center
Attitude ControlPage 4
Final Version
ACSControl Modes
Coarse Formation Acquisition Omni RF ranging with small programmed maneuvers to solve “Lost in Space” Maneuver to assigned positions in formation (within meters)
Fine Formation Acquisition Acquire laser beacons in star trackers For Phase 2, freeflyers acquire swarm sensors Maneuver Detector to acquire science target
Science Hold attitude and relative position
Maneuver Execute commanded attitude/translation maneuver while maintaining formation Translation requirements relaxed from Science mode One day in Phase 1, ~ 1 week in Phase 2, dependent on thrust level
Safehold Point solar arrays to Sun Collision avoidance
MAXIM-PF, May 13-17, 2002Goddard Space Flight Center
Attitude ControlPage 5
Final Version
“Super Star Tracker” (Laser beacon tracker + low-drift gyros) needed for detector control(Instrument)
Thruster impulse bit < 20 N-sec (Propulsion) Omni RF used for coarse formation acquisition (Comm) Lowest structure mode should be > 10 Hz, to minimize
interaction with attitude control loop (Mechanical)
ACS Requirements Imposed On Other Sub-Systems
MAXIM-PF, May 13-17, 2002Goddard Space Flight Center
Attitude ControlPage 6
Final Version
ACS Concerns and Comments
Technologies, while not “miracles”, still carry significant development risk
Concerns Contamination due to thruster firing Lost in Space problem Misalignment of Star Trackers, gyros, optics
Due to tolerances of the Phase 1 S/C connections If impulsive thrusters are used, drive frequencies must be chosen to stay from
structural resonant frequencies Tight control and knowledge requirements
Requires higher control bandwidths Ensure quiet motion in formation mode
Advanced estimation and control techniques are needed Trade bandwidth against estimator complexity
Control authority levels should overlap During retargeting coarse control is utilized
Settling times Maintaining the formation control during retargeting will help to provide a quiet
structure
MAXIM-PF, May 13-17, 2002Goddard Space Flight Center
Attitude ControlPage 7
Final Version
Future Studies
Expansion to full MAXIM mission architecture Several freeflyers will have the capability to lead a subgroup ACE and C&DH should be developed to handle an increase in
the number of S/C Tighter safehold and collision avoidance constraints
Direct inter-FF ranging? Higher Formation and individual S/C Bandwidth Increase the number of reference fiducials on Hub
MAXIM-PF, May 13-17, 2002Goddard Space Flight Center
Attitude ControlPage 8
Final Version
Backup Slides
Sensor Configurations Components Trade Studies
MAXIM-PF, May 13-17, 2002Goddard Space Flight Center
Attitude ControlPage 9
Final Version
Hub/Detector Sensor Configuration
Super Star Trackercenters on Laser Beacon
Normal Star Trackerplaces Laser Beaconagainst fixed stars
Laser Beacon illuminatesDetector S/C
Laser Detector measures rangeby time-of-flight of reflectedlaser beam
Reflector Cube reflectslaser beam back to Hubfor ranging
Hub S/C Detector S/C
Super gyroshold inertialattitude
Coarse Ranging by omni RF comm link
MAXIM-PF, May 13-17, 2002Goddard Space Flight Center
Attitude ControlPage 10
Final Version
Hub/Freeflyer Sensor Configuration
Small LaserBeacon Normal Star Tracker
places Hub beacon againstfixed stars
Swarm Sensor measures range by bouncingRF, laser off Hub
Reflector Cube
Hub S/CFreeflyer S/C
Coarse Ranging by omni RF comm link
MAXIM-PF, May 13-17, 2002Goddard Space Flight Center
Attitude ControlPage 11
Final Version
Attitude/Translation Requirements and Sensors: Optics Hub
Optics HubAxis Control Reqt Knowledge Reqt Control Reqt Knowledge ReqtRoll TBD arcmin 1 arcsec TBD arcmin 1 arcsecPitch 1 arcsec 1 arcsec 1 arcsec 1 arcsecYaw 1 arcsec 1 arcsec 1 arcsec 1 arcsecX Trans 5 m TBD cm 5 m TBD cmY Trans TBD cm 30 um 10 um 10 umZ Trans TBD cm 30 um 10 um 10 um
Optics HubAxisRollPitchYawX TransY TransZ Trans Accel, 1E-9 m/s^2
Position SensorStar Tracker (X-Y)Star Tracker (X-Y)Star Tracker (X-Z)
Time-of-flight laser ranging to detectorNoneNone
GyroGyroAccel
Accel, 1E-9 m/s^2
Phase 1 Phase 2
Rate SensorGyro
MAXIM-PF, May 13-17, 2002Goddard Space Flight Center
Attitude ControlPage 12
Final Version
Attitude/Translation Requirements and Sensors: Detector
DetectorAxis Control Reqt Knowledge Reqt Control Reqt Knowledge ReqtRoll 0.5 arcmin 1 arcsec 0.5 arcmin 1 arcsecPitch 0.5 arcmin 1 arcsec 0.5 arcmin 1 arcsecYaw 0.5 arcmin 1 arcsec 0.5 arcmin 1 arcsecX Trans 5 m TBD cm 5 m TBD cmY Trans 5 cm 15 um 5 cm 15 umZ Trans 5 cm 15 um 5 cm 15 um
DetectorAxisRollPitchYawX TransY TransZ Trans Accel, 1E-9 m/s^2
Position SensorStar Tracker (X-Y)Star Tracker (X-Y)Star Tracker (X-Z)
Time-of-flight laser ranging from hubLaser beacon tracker, Gyro ( <1 uas/day)Laser beacon tracker, Gyro ( <1 uas/day)
GyroGyroAccel
Accel, 1E-9 m/s^2
Phase 1 Phase 2
Rate SensorGyro
MAXIM-PF, May 13-17, 2002Goddard Space Flight Center
Attitude ControlPage 13
Final Version
Attitude/Translation Requirements and Sensors: Freeflyer
FreeflyerAxis Control Reqt Knowledge Reqt Control Reqt Knowledge ReqtRoll N/A N/A 1 arcsec 1 arcsecPitch N/A N/A 1 arcsec 1 arcsecYaw N/A N/A 1 arcsec 1 arcsecX Trans N/A N/A 0.5 mm [1] 0.5 mm [1]Y Trans N/A N/A 10 um 10 umLOS to hub N/A N/A 10 um 10 um
[1] 2 arcsec @ 100 m
FreeflyerAxisRollPitchYawX TransY TransLOS to hub
Accel, 1E-9 m/s^2Accel, 1E-9 m/s^2
Phase 1 Phase 2
Rate SensorGyro
Accel, 1E-9 m/s^2
Position SensorStar Tracker (X-Y)Star Tracker (X-Y)Star Tracker (X-Z)
Star Tracker sees hub laser beaconStar tracker sees hub laser beacon
Swarm Sensor
GyroGyro
MAXIM-PF, May 13-17, 2002Goddard Space Flight Center
Attitude ControlPage 14
Final Version
ACS Components Optical Hub
Cost Mass Orbit Avg Peak Saf ehold
Components Model Quantity ($K) (Kg) (W) (W) (W)
Coarse Sun Sensor Adcole 11866 8 56 0.04 0 0 0
Laser Beacons f or Freefl yers 6 60 6 6 6 0
Laser Beacon f or Detector 1 TBS TBS TBS TBS TBS
Accelerometer Onera 1 TBD 6 2 2 2
Star Tracker Ball CT-602 2 1300 11.8 18 18 0
Gyro Litton SI RU 1 1000 5.44 22 40 22
ACE (Like SDO & GPM)
I ndependent processor, includes
EVD 1 300 6 11 26 11
Dynamic Simulator Dynamic Simulator 50 N/ A N/ A N/ A N/ AGround Support equipment
f or I &T
Ground Support equipment f or
I &T 300 N/ A N/ A N/ A N/ A
Subtotal = 2716 35.3 59 92 35
MAXIM-PF, May 13-17, 2002Goddard Space Flight Center
Attitude ControlPage 15
Final Version
ACS Components Detector
Cost Mass Orbit Avg Peak Saf ehold
Components Model Quantity ($K) (Kg) (W) (W) (W)
Coarse Sun Sensor Adcole 11866 8 56 0.04 0 0 0
Accelerometer Onera 1 TBD 6 2 2 2
Star Tracker Ball CT-602 2 1300 11.8 20 20 0
Gyro Litton SI RU 1 1000 5.44 22 40 22
ACE (Like SDO & GPM)
I ndependent processor, includes
EVD 1 300 6 11 26 11
Dynamic Simulator Dynamic Simulator 50 N/ A N/ A N/ A N/ AGround Support equipment
f or I &T
Ground Support equipment f or
I &T 300 N/ A N/ A N/ A N/ A
Subtotal = 2656 29.3 55 88 35
MAXIM-PF, May 13-17, 2002Goddard Space Flight Center
Attitude ControlPage 16
Final Version
ACS Components Free Flyer
Cost Mass Orbit Avg Peak Saf ehold
Components Model Quantity ($K) (Kg) (W) (W) (W)
Coarse Sun Sensor Adcole 11866 8 56 0.04 0 0 0
Swarm Sensor MSTAR 1 TBD 10 15 15 15
Accelerometer Onera 1 TBD 6 2 2 2
Star Tracker Ball CT-602 2 1300 11.8 20 20 0
Gyro Litton SI RU 1 1000 5.44 22 40 22
ACE (Like SDO & GPM)
I ndependent processor, includes
EVD 1 300 6 11 26 11
Dynamic Simulator Dynamic Simulator 50 N/ A N/ A N/ A N/ AGround Support equipment
f or I &T
Ground Support equipment f or
I &T 300 N/ A N/ A N/ A N/ A
Subtotal = 2656 39.3 70 103 50
MAXIM-PF, May 13-17, 2002Goddard Space Flight Center
Attitude ControlPage 17
Final Version
ROM ACS Labor Cost
Note: 1) Estimated cost derived from MAP cost in $K
GNC / Systems Engineering $1,529
ACS Design & Analysis Labor $4,032
ACS Hardware Labor $4,762
ACE Hardware Labor $961
Hybrid Dynamic Simulator (HDS) $2,111
Integration and Testing $1,948
TOTAL $15,343
Dynamic Simulator Hardware Labor $300
GRAND TOTAL $15,643
MAXIM-PF, May 13-17, 2002Goddard Space Flight Center
Attitude ControlPage 18
Final Version
Phase 1 Command structure
ACE/C&DH in charge of the unit sensor/actuators
Receive measurements from freeflyer attitude sensors
Sends thruster commands to freeflyer
Thrust commands
Attitude and Position Information
ThrustAttitude and position
Attitude and position
Thrust
MAXIM-PF, May 13-17, 2002Goddard Space Flight Center
Attitude ControlPage 19
Final Version
Formation
Configuration: Expandable
Increase the number of free flyers with several acting as local leaders Redundancy
For the full version local leaders can take the place of the hub or detector
Communication issues Reduces communicate traffic Improves local and global autonomy
MAXIM-PF, May 13-17, 2002Goddard Space Flight Center
Attitude ControlPage 20
Final Version
Formation Configuration
Detector: Communicates with ground and Hub Has more fuel and thrust authority for retargeting Additional safehold communication/ranging capabilities can be utilized
to provide position of self and hub (full mission)
Optical Hub: Provides command for formation structure and retargeting Safehold beacon used to keep free flyers near In safehold sends detector updates on current estimated location of FF
and self (full mission).
Freeflyers: In Safehold, execute collision avoidance and stay close to Hub Freeflyers can lead a subgroup as numbers of S/C grows (full mission) Can replace some of the functionality of the Hub (full mission)
MAXIM-PF, May 13-17, 2002Goddard Space Flight Center
Attitude ControlPage 21
Final Version
High Accuracy Formation Control Technologies
External and Internal Disturbance estimation Estimate fuel usage and CG migration Sensor bias and drift Uncertainty bounds Localized disturbance levels Other system parameters
Control Utilize estimated states compensation scheme Adaptive/Robust schemes can account for variations in parameters
(Mass Properties, CP-CG offset, local variations in solar pressure)
Phase 2 may employ distributed control schemes to decentralize control Reduces risk by S/C-level redundancy May reduce computational load on Hub
MAXIM-PF, May 13-17, 2002Goddard Space Flight Center
Attitude ControlPage 22
Final Version
Trades performed
Reaction Wheels vs. Thrusters for Attitude Control Reaction wheels would be jitter sources Continuous micro-thrust needed for translation control Recommendation: Use thrusters for attitude as well as translation
control
Do Freeflyers talk to each other? Inter-FF comm would simplify “Lost in Space” solution
Direct measurement of FF-FF ranges Inter-FF comm complicates RF comm system
More channels required Recommendation: No FF-FF comm
Avoids complicating RF comm system “Lost in Space” may be solved with Hub-FF ranging, with small programmed
maneuvers
MAXIM-PF, May 13-17, 2002Goddard Space Flight Center
Attitude ControlPage 23
Final Version
Sensor/Actuator Resolution
Minimum Impulse Bit = 20 N-sec achievable by PPTs or FEEPs Assumes 100-sec limit cycle on 10 m translation control, and 100-kg
S/C PPTs provide 10 N-sec or less FEEPs provide 1 N thrust resolution
Accelerometer Resolution Required ~= 1.0x10-9 m/s^2 Acceleration “bit” is thruster resolution divided by S/C mass FEEP thruster resolution = 1.0E-6 N, S/C mass < 1000 kg Onera (GRACE) accelerometer resolution = 3.0x10-9 m/s^2
Right order of magnitude
Top Related