Systems Engineering Seminar
Gyroless: The Tale of How to Operate a Spacecraft with a Gyro Without One
Julie Halverson, Ph.D.
Lead Systems Engineer in Space Science Mission Operations (SSMO)
Tuesday, June 11, 2019
Building 3 Auditorium
The Lunar Reconnaissance Orbiter (LRO) was launched in 2009 and, with its seven science instruments, has made numerous contributions to our understanding of the moon. LRO is in an elliptical, polar lunar orbit and nominally maintains a nadir orientation. There are frequent slews off nadir to observe various science targets. The LRO attitude control system has two star trackers and a gyro for attitude estimation in an extended Kalman filter, and four reaction wheels used in a proportional-integral-derivative controller. LRO is equipped with thrusters for orbit adjustments and momentum management. In early 2018, the gyro was powered off following a fairly rapid decline in the laser intensity on the X-axis. Without the gyro, the Kalman filter was disabled. Attitude was provided by a single star tracker and a coarse rate estimate was computed by a back differencing of the star tracker quaternions. All slews were disabled. A novel gyro rate replacement was developed, tested, and uploaded to the spacecraft in December 2018. The approach uses a complementary filter, combining the star tracker derived rates and the integrated control torque. The Kalman filter was re-enabled, using the new rate estimate, resulting in an immediate improvement in control system performance. In January 2019, LRO completed the first gyroless science slew to view the Chang'e 4 landing site and has since successfully completed numerous science slews. The gyro rate replacement effort was a collaboration between the Space Science Mission Operations Systems Engineering team, Code 591, Code 584, Code 582, and the LRO Mission Operations Team.
Dr. Julie Halverson is the lead systems engineer in Space Science Mission Operations at NASA Goddard Space Flight Center, which manages 21 astrophysics, heliophysics, and planetary missions. Julie began her career at Goddard working in ground attitude estimation and then moved into guidance, navigation, and control. She served on the faculty of the US Naval Academy and worked as a GSFC proposal manager, then joined SSMO in 2015. She has a BS in aerospace engineering, an MS in applied physics, and a PhD in aerospace engineering, and is an Associate Fellow of the AIAA.
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