1. The first flight of the JPL microGPS receiver was on the Student Nitric Oxide Explorer (SNOE) spacecraft which was launched on February 26, 1998. See figure 14. Preflight simulations indicated post-process navigation errors on the order of 100 m (Icr)when the receiver acquires data approximately every 30 minutes. Flight operation of the microGPS was quite successful. Specific results of the microGPS operations and performance on SNOE are described in a paper that will be presented in the Space Applications session of the IONGPS-98conference [13].
2. The SHUCS experiment flew on the Space Shuttle Discovery STS-91 mission that was launched on June 2, 1998. From a GPSperspective, the SHUCS experiment wasquite successful. The SPACEHAB team was able to initialize the GPS receiver and autonomously point the L-band antenna array to the INMARSAT satellites several times during this mission. The experiment demonstrated for the first time a spaceborne pointing system, which used GPS to steer ah antenna to a target. Duringthe flight, the GPSteam expected to receive realtime high rate data from the SHUCS experiment through INMARSAT and through the NASA high rate Ku-band communications system. Unfortunately, a problem with the Ku-band system exacerbated the troubleshooting of an issue with the SHUCS communication system. These two independent issues prevented a full 2-way high speed communications hook up using SHUCS. A reflight of SHUCS (currently dubbed SHUCS-II) is tentatively planned for the STS-96 mission. Currently GSFC and SPACEHAB have not decided whether this will be a TANS Vector receiver reflight or a flight of the new Trimble/GSFC GPSreceiver that was developed for SIGI. STS-96 is currently scheduled for launch in May 1999.
3. TMSAT, launched on July10,1998,represents the first flight of the SSTL SGR receiver. TMSAT is a Technology Transfer Micro-satellite being constructed for Thailand. [14] The primary objective of this flight experiment is to validate the use and autonomous operation of the SSTL SGR receiver for navigation and timing functions. TMSAT utilizesthe SGR receiver in a 2 antenna configuration. Ifthe primary objectives of the experiment are successful, the GPS team at SSTL expects to perform some limited phase difference measurements with the SGR to understand the abilities and limitations of this receiver to sense vehicle attitude. A similar flight experiment isplannedtobe launched onboard the TIUNGSAT microsatellite that SSTL is developing for Malaysia. TIUNGSAT is currently awaitingshipment forlaunch. The next step in the SSTL SGR development process is the first flight of the full-up 4/5antenna receiver. This is planned for installation on theUoSAT-12 satellite that is expected to be launched early in 1999.