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Correlated Errors in Earth Pointing MissionsTwo different Earth-pointing missions dealing with attitude control and dynamics changes illustrate concerns with correlated error sources and coupled effects that can occur. On the OrbView-2 (OV-2) spacecraft, the assumption of a nearly-inertially-fixed momentum axis was called into question when a residual dipole bias apparently changed magnitude. The possibility that alignment adjustments and/or sensor calibration errors may compensate for actual motions of the spacecraft is discussed, and uncertainties in the dynamics are considered. Particular consideration is given to basic orbit frequency and twice orbit frequency effects and their high correlation over the short science observation data span. On the Tropical Rainfall Measuring Mission (TRMM) spacecraft, the switch to a contingency Kalman filter control mode created changes in the pointing error patterns. Results from independent checks on the TRMM attitude using science instrument data are reported, and bias shifts and error correlations are discussed. Various orbit frequency effects are common with the flight geometry for Earth pointing instruments. In both dual-spin momentum stabilized spacecraft (like OV-2) and three axis stabilized spacecraft with gyros (like TRMM under Kalman filter control), changes in the initial attitude state propagate into orbit frequency variations in attitude and some sensor measurements. At the same time, orbit frequency measurement effects can arise from dynamics assumptions, environment variations, attitude sensor calibrations, or ephemeris errors. Also, constant environment torques for dual spin spacecraft have similar effects to gyro biases on three axis stabilized spacecraft, effectively shifting the one-revolution-per-orbit (1-RPO) body rotation axis. Highly correlated effects can create a risk for estimation errors particularly when a mission switches an operating mode or changes its normal flight environment. Some error effects will not be obvious from attitude sensor measurement residuals, so some independent checks using imaging sensors are essential and derived science instrument attitude measurements can prove quite valuable in assessing the attitude accuracy.
Document ID
20050245089
Acquisition Source
Goddard Space Flight Center
Document Type
Conference Paper
Authors
Steve Bilanow (Science Applications International Corporation (United States) McLean, Virginia, United States)
Frederick S Patt (Science Applications International Corporation (United States) McLean, Virginia, United States)
Date Acquired
September 7, 2013
Publication Date
October 18, 2005
Publication Information
Publication: 2005 Flight Mechanics Symposium
Publisher: National Aeronautics and Space Administration
Subject Category
Spacecraft Instrumentation And Astrionics
Meeting Information
Meeting: Flight Mechanics Symposium
Location: Greenbelt, MD
Country: US
Start Date: October 18, 2005
End Date: October 20, 2005
Sponsors: National Aeronautics and Space Administration
Distribution Limits
Public
Copyright
Public Use Permitted.

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