Navfilter Architecture (IMU, TDS) Velocity Analysis Ground Estimates Attitude Initialization TDS Performance Conclusions/Open Items
EDL Challenge EDL Challenge Land a 950Kg Rover over terrain with:  < 30 degree slopes, and
 < 1.2 meter rocks
Response 6Axis PoweredDescent + SkyCrane  Parachute terminal velocity
 Vertical = 65 to 100 m/sec
 Horizontal = 0 to 40 m/sec
 PoweredDescent Start Altitude
 Rover touchdown velocity
 Vertical = 0.75 m/sec, +/ 0.1m/sec (3sigma)
 Horizontal = 0 m/sec, +/ 0.5 m/sec (3sigma)
 Descent Stage touchdown velocity
 Vertical = 0.75 m/sec, +/ 0.1 m/sec (3sigma)
 Horizontal = 0 m/sec, +/ 0.1 m/sec (3sigma)
Requirements Provide state information to all modules throughout EDL  200 Hz (DIMU sample rate) integration of Attitude, Position, and Velocity
 DIMU internal Coning and Sculling compensation (Internal DIMU sampling rate is 1600Hz)
 J2 Gravity Model
Attitude Initialization from Cruise ACS Position and Velocity state Initialization from Ground Navigation in EdlParms (Epoch at E9minutes)
TDS Description  Kaband (35.75 GHz) center frequency
 Pulse doppler radar design, LOS Velocity and LOS Slant Range
 6 beams: 3 beams canted 20° off nadir, 2 beams canted 50° off nadir,1 nadir beam
TDS data is used to correct errors in Inertially propagated Velocity, Acceleration and Altitude Velocity Filter is 6 state Least Squares Filter  3 Axis Velocity Error
 3 Axis Acceleration Error (attitude, misalignment, etc)
 Recursive (but finite) data editing
Altitude Filter  Estimates ground over MSF frame
 Mean of ground altitudes in measurement buffer
Flight Reported Values Velocity Correction when Navfilter converged  [ .5884 .4567 .1942 ] m/s (MSF Frame, EastNorthUp)
 Velocity correction .77 m/s
Altitude Correction when Navfilter converged  [ .02203 .003505 .76501 Z ] m/s ( MSF Frame, EastNorthUp)
Position of Descent Stage Reported at Touchdown  [ 1597.74 246.3 7.677 ] meters ( MSF Frame, EastNorthUp )
Knowledge Error at Touchdown Based on MRO photos  Using OD179 770 meters ( Flight , 5 day old at time of EDL)
 Using OD230 162 meters ( After landing rerun standalone Navfilter using od230 state)

The first thing we noticed was the acceleration term in the velocity solution for Z axis The first thing we noticed was the acceleration term in the velocity solution for Z axis
ReRun the Navfilter without any TDS data after 935 seconds past T0 (~450 m above terrain)  This was done to remove any potential sandy radar effects on TDS measurements close to the ground
 This matched the touchdown velocity from the RIMU (Rover IMU) very well
Analysis  Using best estimate of reconstructed trajectory to determine the best estimate of gravity using both RIMU and DIMU data
 Obtain the best estimate from gravity at touchdown location from the Navigators using MGM2011 knowledge

 The TDS produced no ambiguities during all of EDL
 The Navfilter Data Editing was never invoked
 TDS passed 1 measurement of the Heat shield and the Navfilter rejected it in the prefilter

Performance  Attitude Init. 30 millidegrees
 Position Knowledge error 162 meters
 Velocity at touchdown [.1694 .0482 .6312 ] m/s
 Velocity Knowledge error [ .19 .045 .134 ] m/s (almost 5σ)
Open Items
Do'stlaringiz bilan baham: 