Previous Abstract Return to Session C10 Next Abstract

Session C10: GPS in Military Applications/NAVWAR

Effects of Cycling GPS IIR-M M-Code During Eclipse
John Coggi, The Aerospace Corporation; John Baker, MD-31/STS; Anne Le, The Aerospace Corporation
Location: Ballroom D
Date/Time: Wednesday, Jun. 4, 2:50 p.m.

There are currently 25 M-Code SVs in the GPS constellation: 7 GPS IIR-M, 11 GPS IIF, and 7 GPS III. The oldest of these are the 7 GPS IIR-Ms launched 2005-2009. 2025 will mark the 20th birthday of the GPS IIR-Ms whose initial design life was 10 years. An attempt to further extend the useful life of the aging GPS IIR-Ms was proposed: power management of individual GPS IIR-Ms by turning M-code off for brief periods during earth eclipses, thereby reducing the SV battery amp-hour discharge. Just prior to entering the eclipse, the SV would be commanded to switch from broadcasting Alternate M-Code Flex Power (AMFP) mode to broadcasting just legacy signals + L2C, and prior to the end of the eclipse, the SV would be commanded to resume broadcasting AMFP.
An initial on-orbit test was successfully performed to demonstrate the feasibility of power managing the GPS IIR-Ms. However, global GPS users may be impacted if M-Code availability is decreased. An analysis was performed to determine the impact to global M-Code users due to turning off M-Code on GPS IIR-Ms during the earth eclipses.
The analysis parameters included two earth eclipse seasons for each of the 7 GPS IIR-M per calendar year, which generally do not overlap with the other GPS IIR-Ms. Each earth eclipse season averages 35 days. Additionally, during the earth eclipse season, each GPS IIR-M will enter deep eclipse twice per day, 12 hours apart per the GPS SV orbit. Deep eclipse duration starts at a few minutes and increases each day during the eclipse season to a maximum of 58 minutes long and then decreases again until the end of the eclipse season.
The analysis was performed using Aerospace-developed Satellite Orbit Analysis Program (SOAP). The results of the analysis will show how many usable M-Code SVs are visible and the effects on PDOP with the GPS IIR-M power management in operation.

Previous Abstract Return to Session C10 Next Abstract