Using Onboard Telemetry for MAVEN Orbit Determination...MAVEN Background •Mars orbiter studying...
Transcript of Using Onboard Telemetry for MAVEN Orbit Determination...MAVEN Background •Mars orbiter studying...
AAS/AIAA Space Flight Mechanics Meeting, 14.Jan.2014 1
Using Onboard Telemetry for
MAVEN Orbit Determination
Drew Ryan Jones
Try Lam, Nick Trawny, Cliff LeeJet Propulsion Laboratory, California Institute of Technology
2AAS/AIAA Space Flight Mechanics Meeting, Jan-14-2014
MAVEN Background
• Mars orbiter studying the upper atmosphere and
exploring the climate history
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• Science Orbit:
– 4.5 hour period
– 75 degree inclination
– Range of periapsis latitudes
– Periapsis altitude ~140-170
km (<120 km Deep-Dips)
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• MAVEN Navigation requirements:
– Target a density corridor (0.05-0.15 kg/km3)
– Predict periapsis passage to 20 seconds
• Navigation challenges:
– Limited Doppler tracking (only 1-in-5 orbits)
– Between aerobraking and prior Mars science orbits
– Frequently changing attitude (incl. drag passes)
– Momentum desaturations after every periapsis (+11 min)
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Modeling
• Mars-GRAM 2005 (MG05) - baseline atmosphere,
only estimate scale factor
– Quality density reconstruction better prediction
– But Mars atmosphere does not play nice!
• Lat/Lon dependence, unexpected trends, ect
• Scale factor variance up to 100% (orbit-2-orbit)
• Estimated Parameters (baseline):
– Epoch state
– Solar radiation pressure scale factor
– MG05 scale factor as stochastic (batch update each orbit)
– Desats as impulsive burns
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6AAS/AIAA Space Flight Mechanics Meeting, Jan-14-2014
Motivation / Goals
• Supplement sparse radiometric data with telemetry
derived measurements
– Improve density reconstruct/predict performance
– Combine observables into single batch estimation
• Generally valuable capability
– Enable cheaper (less tracking) and autonomous missions
– Applications to non-grav estimation:
• Aerobraking
• Thruster and SRP calibrations
• Finite burn reconstruction
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7AAS/AIAA Space Flight Mechanics Meeting, Jan-14-2014
IMU Observable Formulation
• Accelerometer (IMU):
– IMU frame body frame via gyros (onboard)
• CFD model of tabulated drag/moment coefficients
– Interpolant is relative velocity direction on unit sphere
Typically just compute bias (and IMU clock offset) apriori, and don’t
estimate further
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8AAS/AIAA Space Flight Mechanics Meeting, Jan-14-2014
Results: MAVEN cruise (TCM-1)
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• Largest maneuver
until MOI
• 6-second IMU
clock offset
observed
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Results: MAVEN cruise (TCM-1)
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Fitting offset IMU data with
Doppler data does not work
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Results: MAVEN Science
• Single drag pass fit (F2 and IMU)
– Bias of around 5 μm/s2
– Peak IMU acceleration: 100 μm/s2
– Centroid shifted by ~30 seconds
IMU observed net ΔV:
8.6 mm/s
Scaled MG05 net ΔV:
10.8 mm/s
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Typical MAVEN
reconstruction batch
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Conclusions
• Demonstrated uses:
– Reconstructed density information for 4/5 orbits where
radiometric data is absent
– Atmospheric functional data (beyond net ΔV)
• Larger ΔV during first deep-dip will be a real test
• Absence of telemetry during desats unfortunate
– If available, would it help? Noise still prohibitive?
• Further work
– Reduce data noise in IMU measurements (smoothing)
– Use alternate atmosphere model (more parameters)
– Utilize/test torque observable
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BACKUP
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Torque Observable Formulation
• CFD model of tabulated drag/moment coefficients
– Interpolant is relative velocity direction on unit sphere
• Torque from reaction wheel speeds
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16AAS/AIAA Space Flight Mechanics Meeting, Jan-14-2014
Results: MAVEN science
• Drag pass in IMU observable (unsmoothed)
– Bias of around 5 μm/s2
– Peak IMU acceleration: 100 μm/s2
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17AAS/AIAA Space Flight Mechanics Meeting, Jan-14-2014
Results: MAVEN Science
• Single drag pass fit (F2 and IMU), unsmoothed
– Bias of around 5 μm/s2
– Peak IMU acceleration: 100 μm/s2
– Centroid shifted by ~45 seconds
IMU observed net ΔV:
9.1 mm/s
Scaled MG05 net ΔV:
10.8 mm/s
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IMU accelerations, orbit 307
IMU accelerations, orbit 314
MAVEN reconstruction batch
• IMU data suggests less ΔV
• IMU centroid always later (but
as little as 5 sec)
IMU observed
net ΔV: 4.1
mm/s
Scaled MG05
net ΔV: 6.0
mm/s
IMU observed
net ΔV: 3.4
mm/s
Scaled MG05
net ΔV: 4.6
mm/s
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MRO: Mars-GRAM Scale Variation