Relative Navigation between Two Spacecrafts Using X-ray Pulsars

Amir A. Emadzadeh
Advisor: Jason L. Speyer

Friday, July 10, 2009 at 10:00am-12:00pm
Engr IV Room 57-124

Abstract:
Autonomous formation flying of multiple spacecrafts is an important technology for deep space applications. One of the main requirements of a formation flight is accurate knowledge of the relative position between the vehicles. In order to reduce the dependence of navigation systems to ground-based operations and achieve more autonomy, the utilization of celestial-based navigation systems is desirable. Due to their special characteristics, X-ray pulsars are potential candidates for use in navigation systems. Pulsars are rapidly rotating, highly magnetized neutron stars which produce a uniquely identifiable signature that is periodic and predictable. The main advantage of spacecraft navigation using X-ray pulsars is that small sized detectors may be employed. This provides savings in power and mass for the spacecraft.

In this talk, I first introduce the relative position estimation problem between two spacecrafts utilizing signals emitted from X-ray pulsars. The pulse delay estimation problem is formulated for pulsar signals and the Cramér-Rao Lower Bound (CRLB) for any unbiased estimator of the time delay is presented. Then, depending on employing photon counts or photon time of arrivals (TOAs), two different time-delay-estimation strategies are introduced and their performance is mathematically analyzed. It is assumed that the spacecraft velocity data, which is necessary to determine the Doppler shifts, is available through a navigation system, which is integrated from the inertial measurement unit (IMU) data. The time delay estimates are used as measurements, and based on models of spacecraft and IMU dynamics, a Kalman filter is employed to obtain a three-dimensional relative position estimate. Numerical simulations are performed to verify the theoretical results.

Biography:
Amir Emadzadeh is a Ph.D. candidate in Electrical Engineering Department at the University of California, Los Angeles. He earned his M.Sc. at Sharif University of Technology, Tehran, Iran, in 2003, and his B.Sc. at Isfahan University of Technology, Isfahan, Iran, in 2005, both in Electrical Engineering. His research interests are estimation theory, control theory and signal processing.