Final Version Micro-Arcsecond X-ray Imaging Mission Pathfinder (MAXIM-PF) Eric Stoneking Paul Mason May 17, 2002 ACS.

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



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



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



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



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



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



Final Version

Backup Slides

Sensor Configurations Components Trade Studies



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



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



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



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


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



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


Star Tracker sees hub laser beaconStar tracker sees hub laser beacon

Swarm Sensor

GyroGyro



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



Final Version

ACS Components Detector






Gyro Litton SI RU 1 1000 5.44 22 40 22



EVD 1 300 6 11 26 11


f or I &T


I &T 300 N/ A N/ A N/ A N/ A

Subtotal = 2656 29.3 55 88 35



Final Version

ACS Components Free Flyer




Swarm Sensor MSTAR 1 TBD 10 15 15 15



Gyro Litton SI RU 1 1000 5.44 22 40 22



EVD 1 300 6 11 26 11


f or I &T


I &T 300 N/ A N/ A N/ A N/ A

Subtotal = 2656 39.3 70 103 50



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



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



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



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)



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



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



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

Final Version Micro-Arcsecond X-ray Imaging Mission Pathfinder (MAXIM-PF) Eric Stoneking Paul Mason May 17, 2002 ACS.

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