slides

RESULTS OF PRISMA / FFIORD EXTENDED MISSION AND
APPLICABILITY TO FUTURE MISSIONS
M. Delpech1, J.C.Berges1, F.Malbet2, T. Karlsson3
1
CNES, 2 IPAG, 3 OHB-Sweden
ISFFMT 2013 / Munich / Germany/ May 29-31, 2013
Content
■ Context & Motivation
■ PRISMA overview
■ Experiments description
Š Vision based RDV
Š Metrology transition &
Vision based based proximity control
Š µ-NEAT pathfinder
■ Applicability to ADR scenario
■ Conclusion
SFFMT 2013 / Munich / Germany / May 29-31, 2013
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Context and motivation
■ PRISMA nominal mission enabled numerous contributions in formation flying and
autonomous rendezvous (validation of sensors, algorithms, operations)
Š Formation flying
• GPS navigation and all GPS based tasks (DLR, OHB-S)
• RF navigation and all RF based tasks (CNES with the FFIORD experiment)
Š Autonomous RDV
• Vision based RDV with a non cooperative object (OHB-S)
• Proximity operations in a cooperative context (OHB-S)
Î All experiment objectives were fulfilled
■ PRISMA extended mission started in August 2011 with opportunities of new experiments
(including new software)
■ CNES responded positively to demonstrate capabilities required in future missions
Š Vision based RDV (RDV)
Š Metrology transition (FF, RDV)
Š Re-pointing manoeuvers (FF, RDV)
Î push the PRISMA system to its limits
SFFMT 2013 / Munich / Germany / May 29-31, 2013
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PRISMA overview
GPS
antenna
Mango S/C
Relative sensing
• FFRF (CNES): range + LOS (1 cm / 1°)
• 2 smart vision sensors (DTU) with IP functionalities
• VBS FR: target direction + camera attitude at long range
DVS
VBS FR
• VBS CR: pos + attitude in cooperative mode (LEDs)
• GPS (DLR): relative navigation 10 cm OB accuracy
VBS CR
FFRF
antennas
Position reference measurement: POD from GPS (DLR)
Æ accuracy < 1 cm (3D)
Propulsion:
6 x 1N hydrazine thrusters (MIB = 0.7 mm/s)
GPS
antenna
Tango S/C
SFFMT 2013 / Munich / Germany / May 29-31, 2013
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Vision based RDV (1)
Experiment plan
Experiment #1
Experiment #2
Experiment #3
Objective
• Acquire flight expertise in Angles-only Navigation Æ RDV with non cooperative objects (ex: ADR),
possible back-up for FF mission
Description
• Navigation: EKF (6 states vector) with Yamanaka Ankersen relative dynamic model + target orbit propagator
• Guidance: waypoint oriented strategy (manœuvre dates defined on the ground)
Plan
• 4 rehearsals
• 3 m/s total budget
Desired trajectory 10 km -> 0.1 km
• Navigation uncertainty: 10-12% range - 100 m / 10 cm/s
on RN position/ rate coordinates
• Fuel constraint:
Î Long duration RDV with no crosstrack manœuvres
Î Conservative filter tuning to reduce dispersions
SFFMT 2013 / Munich / Germany / May 29-31, 2013
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Vision based RDV (2)
Flight results
Experiment
Duration
(hours)
Range
accuracy
(%)
Expected
Delta V
(cm/s)
Real
Delta V
(cm/s)
RdV 4 km to 100 m (OL)
16.2
1.8%
N/A
N/A
RdV 4 km to 100 m (CL)
16.2
2%
54.0
42.6
RdV 10 km to 100 m (CL)
18.5
3%
98.5
86.8
RdV 10 km to 50 m (CL)
19.5
5.5%
74.0
73.6
• All rendezvous were achieved successfully
• VBS behaviour was satisfactory at long and medium range
(target detection and tracking)
• Fuel usage remained within allocated budget
• Range uncertainty reduction is not significant above 2 km
• Limited range accuracy at short range due to the target
direction uncertainty
SFFMT 2013 / Munich / Germany / May 29-31, 2013
Experiment #1
Experiment #2
Experiment #3
Range
profile
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Vision based RDV (3)
Flight results
Experiment #1
Experiment #2
Experiment #3
Relative range error and uncertainty
RDV #4 (10 km -> 50 m)
Run in replay mode
with different tuning
LVLH frame
initial attitude
error
Initial attitude
error of the LOF
Short range
degradation
Target
pictured
at 10 km
SFFMT 2013 / Munich / Germany / May 29-31, 2013
Target
pictured
at 3 km
Target size:
50 pixels
at 50 m
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Vision based RDV (4)
Short range performance
100 m
Experiment #1
Experiment #2
Experiment #3
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50 m
Direction bias causes transversal error variations up
to 1 m in the 50-100m range domain
Î Station keeping was not demonstrated
Î Accuracy good enough to place the chaser in relative
orbit-keeping near the target
Regions of
interest
Lessons learned
• angles-only navigation efficiency demonstrated - even in
presence of periodic data loss i.e. eclipses (replay mode)
• robust image processing techniques are needed
at short range to improve safety/performance
target size -> 50 pixels at 50 m
SFFMT 2013 / Munich / Germany / May 29-31, 2013
Experiment #1
Experiment #2
Experiment #3
Proximity operations with
metrology transition (1)
Objective
FFRF Navigation
Š Exercise metrology transitions to emulate some phases of
future FF missions
RF (coarse sensor) ÅÆ optical (fine sensor)
Š Attempt to achieve fine position control
VBS Navigation
Parking
orbit
A
Mango
B
Tango
Description
Š Single navigation filter with metrology handover (no
data fusion) - EKF
Š Gain update with smoothing phase to deal with bias
and noise variations
Š Position control is kept identical in both regimes
(LQR)
Š Possibility to use an alternate navigation function in
the loop (OHB-S) for comparison purposes
Limitation
Š Control period = 200 s with 0.7 mm/s MIB
Æ high control sensitivity to relative position rate errors
SFFMT 2013 / Munich / Germany / May 29-31, 2013
transition
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Experiment #1
Experiment #2
Experiment #3
Proximity operations with
metrology transition (2)
FFRF
VBS
FFRF
Experiment
4 transition experiments were
performed with a satisfactory
functional behaviour
VBS
FFRF
Navigation error (cm)
POD as ref
Control error (cm)
VBS nav as ref
Control error (cm)
POD as ref
PROX @ 20 m
(OHB nav)
Bias [0.8 2.4 3.1]
Std [5.6 1.4 1.2
Bias [2.8 0.1 0.1]
Std [14 4.4 5.3]
Bias [4.1 2.4 2.9]
Std [14 4.5 5.2]
PROX @ 15 m
(CNES nav)
Bias [2.0 12 6.4]
Std [1.9 3.8 2.0]
Bias [0.2 1.1 1.6]
Std [2.2 5.3 2.9]
Bias [2.2 11 8.2]
Std [2.5 6.0 3.3]
control accuracy is not improved w.r.t. FFRF navigation
SFFMT 2013 / Munich / Germany / May 29-31, 2013
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Experiment #1
Experiment #2
Experiment #3
Proximity operations with
metrology transition (3)
Target satellite at 15 m distance
VBS measurement error (POD reference)
Bias variation
Noise
increase
RF antenna
Solar panel
LED detection process frequently perturbed Æ VBS measurements suffer from temporary noise
increase (distance) and bias variations that affect control performance
Î Positioning stability could not reach the level obtained with FFRF measurements even through
ground replay tests
Î High performance is achievable but requires cleaner optical conditions (robustness of the
optical target detection to be improved)
SFFMT 2013 / Munich / Germany / May 29-31, 2013
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Experiment #1
Experiment #2
Experiment #3
µ-NEAT Pathfinder (1)
Context: Missions proposed to ESA: NEAT (M-class) / µ-NEAT (S-class)
Î detection and characterization of exo-planets
in the Habitable Zone
• L2 Lagrange point mission
• 2 FF spacecraft (Telescope and Detector)
• Spacecraft distance: 40 m / 12 m
• Up to 20 reorientation manoeuvres per day
• Telescope pointing accuracy: 3 arcsec
• Detector positioning accuracy: 2 mm / 1 cm
• 200 targets visited 50 times
Objective:
perform a sequence of re-pointing manœuvres / observation
phases to be achieved in a typical day of µ-NEAT mission
Z
Configuration
Constraints
Tango
12 m
Mango
Mango
S/C
Direction
cones within
which Mango
must be
located to
avoid antenna
switches
0.8 m
Sun
SFFMT 2013 / Munich / Germany / May 29-31, 2013
x
Earth
y
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Experiment #1
Experiment #2
Experiment #3
µ-NEAT Pathfinder (2)
Guidance & Control
Trajectory: sequence of linear segments for re-pointing
manœuvres and fixed positions for the observations phases
Observation
phase n°k
x
Guidance module:
1 - Generation of desired position and velocity input @ 1 Hz in
specified frame (inertial)
2 - Conversion in LVLH frame to feed the control algorithm:
- observation phase: circular trajectory at orbital rate
- re-pointing manœuvre: portion of helix
Control module:
- LQR algorithm with a LTI relative dynamic model (CW-Hill)
u = −[ K p K v ] X + [ M p M v ]. X d + G
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K: regulator gain
M: gain to follow a profile
G: feedforward gain
M matrix is tuned for each type of input profile to achieve the
best possible performance (reference tracking control)
• Control cycle: 100 s
• dV budget: 16 cm/s / orbit (observation phase)
SFFMT 2013 / Munich / Germany / May 29-31, 2013
Re-pointing
manoeuvre
U1
d2
d1
LVLH
frame
y
U2
R1
z
R2
Observation
phase n°k+1
µ-NEAT Pathfinder (3)
Experiment scenario
Experiment #1
Experiment #2
Experiment #3
2 sessions (each duration = 3 consecutive orbits or 5 hours)
Æ Session 1: RF navigation with 9 targets Æ 2000 s per target (600 s re-pointing + 1400 s observation)
Æ Session 2: GPS navigation with 4 targets including the Moon for illustration, purposes
Sequence designed to maximize star
tracker availability
Man Id
Manœuvre
magnitude (°)
Translation
magnitude (m)
1
26.8377
5.41
2
21.7218
4.44
3
28.5856
5.74
4
18.7034
3.84
5
24.7205
5.02
6
21.7623
4.45
7
16.1635
3.34
8
21.2071
4.34
9
23.8714
4.85
SFFMT 2013 / Munich / Germany / May 29-31, 2013
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µ-NEAT Pathfinder (4)
Flight results
1st session: RF navigation (best control performance)
SFFMT 2013 / Munich / Germany / May 29-31, 2013
Experiment #1
Experiment #2
Experiment #3
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µ-NEAT Pathfinder (5)
Illustration with DVS images
Experiment #1
Experiment #2
Experiment #3
Expertise is applicable to the field of Active Debris Removal (guidance & control aspects and
system constraints)
SFFMT 2013 / Munich / Germany / May 29-31, 2013
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Applicability to others missions (1)
Context
Æ CNES system studies on active debris removal (Orbital Transfer Vehicle) – vehicle architecture,
capture concept
Æ Analysis of critical phases in simulation (sensing strategy, system constraints)
Activities
Æ Simulator design relying on PRISMA heritage
•Re-use of existing functionalities
•Collected metrology data to improve sensor fidelity
Illustrative scenario
• RDV from 6-7 km followed by inspection phase at 15 m
• Camera down to ~100 m
• Low resolution LIDAR for proximity operations
LIDAR picture of Tango S/C
SFFMT 2013 / Munich / Germany / May 29-31, 2013
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Applicability to others missions (2)
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Simulation results
Angles only navigation
• Range observability improvement
• Performance robustness in
presence of eclipses
transition
Forced trajectories @ short range
• 50 s control rate
• Control accuracy in 4-5 cm (1 σ)
during revolutions
SFFMT 2013 / Munich / Germany / May 29-31, 2013
Conclusion
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■ PRISMA extended mission allowed to show the capabilities / flexibility of the overall
system and increase the CNES technical return
Š second vision based autonomous RDV experiment (first by OHB-S)
Î angles-only navigation is a valid technique to RDV with a non cooperative object
Š transition between RF and optical metrology stages
Î evaluate issues in terms of navigation / control performance
Š first demonstration of LEO formation flying with inertial pointing
Î illustrate the margin of improvement achievable on higher orbits
■ The applicability of this technical return was illustrated in the field of Active Debris
Removal (sensor flight data, GNC functions) to speed-up the evaluation of approach
candidate scenarii
■ Perspectives: Next studies like NEAT will benefit from the same experience (phase 0
to be started soon in CNES)
SFFMT 2013 / Munich / Germany / May 29-31, 2013