Showing papers by "Penina Axelrad published in 2013"
TL;DR: In this article, an approach is presented for estimating the bias of each Iridium satellite clock using satellite-to-ground and satelliteto-satellite measurements. And the satellite clock bias estimates are based on a Kalman filter that incorporates code-type observations from the measurements at 10 s intervals.
Abstract: The High Integrity GPS program seeks to provide enhanced navigation performance by combining conventional GPS with a communications and ranging broadcast from the Iridium® Communications System. Through clock and message aiding, it would enable existing GPS receivers to acquire and track in more challenging environments. As is the case for standard GPS, accurate and precise timing is key to performance. An approach is presented for estimating the bias of each Iridium satellite clock using satellite-to-ground and satellite-to-satellite measurements. The satellite clock bias estimates are based on a Kalman filter that incorporates code-type observations from the measurements at 10 s intervals. Filter parameters are set based on the expected behavior of the clocks, allowing for discontinuous bias and frequency adjustments due to ground commands. Typical results show the current filter to be accurate to within 200 ns while always meeting the initial system specification of half a microsecond.
17 citations
01 Sep 2013
TL;DR: In this paper, the authors investigated the benefits of using an optical telescope placed in geosynchronous transfer orbit (GTO) to estimate the area and mass of objects in GEO.
Abstract: Space-based space surveillance (SBSS) is required to observe objects in geosynchronous orbit (GEO) without weather restriction and with improved viewing geometry. SBSS satellites have thus far been placed in Sun-synchronous orbits (SSO). This paper investigates the benefits to GEO orbit determination (including the estimation of area and mass) gained by using an optical telescope placed in geosynchronous transfer orbit (GTO). Precise ephemerides of Galaxy 15 and a fictitious debris object are used with sparse, simulated astrometric and photometric measurements to analyze capabilities of a standalone GTO-based SBSS platform as well as in combination with an SSO sensor. Results show that the use of a GTO improves velocity and mass estimation as compared to an SSO. Together, the two sensor platforms significantly reduce the estimated covariance for position, velocity, area, and mass of GEO objects.
4 citations