As a dual-frequency (frequencies L1 and L2) receiver, IGOR is available in two versions for low-Earth orbit: as a receiver for precision orbit determination (POD) only, or as a receiver for both POD and radio occultation. “IGOR provides orbit determination, which is similar to other GPS receivers on the market. However, the unique feature is that IGOR has the radio occultation science capability,” says Smith.
IGOR also features a solid state recorder that allows the recording of extra data in case there are problems with the downlink at ground stations, and a payload controller that can control additional instruments on the satellite. “We repackaged it a little bit, but we didn’t touch any of the JPL items such as the signal acquisition and tracking algorithms. We focused on the hardware,” says Smith.
Designed to meet all of the requirements of occultation science experiments, IGOR is currently being used by NASA, as well as by German, Korean, and Brazilian organizations. To date, nine IGOR receivers have been deployed on orbit: six flight units for COSMIC, one flight unit for the German TerraSAR-X, one flight unit for the German Tandem-X, and one flight unit for the U.S. Air Force Research Laboratory’s TACSAT-2 (which is no longer operational). Two additional flight units have been delivered, including one to Korea for KOMPSAT-5, and one to Brazil for LATTES. While BRE is currently working on a flight build for the Spanish PAZ, company personnel are also in discussions with Japanese customers.
“Some of the international agencies collaborate with NOAA or UCAR, and they are basically building the global dataset for radio occultation,” says Smith. “As they input the radio occultation data into the operational NOAA weather models, the severe weather forecasting has improved significantly. The data is indicating that hurricane tracking predictions are improving.”
According to UCAR, data from COSMIC has proven valuable for weather forecasting, hurricane forecasting, and investigation of the atmospheric boundary layer (the lowest part of the atmosphere). The data has also proven useful for testing ionospheric models, is being used for space weather models, and can potentially benefit climate studies, due to its high precision and global and daily sampling coverage. As Franklin describes, “Temperature, pressure, water vapor, and electron content can be retrieved in a widely distributed way as each of the 31 GPS spacecraft signals are observed by the six COSMIC spacecraft, cutting though Earth’s atmosphere on average of 1,500 times per day.” This is the first time such large amounts of data have been obtained on a global scale.
After introducing the benefits of IGOR to the satellite industry, BRE licensed additional technology from Goddard Space Flight Center in 2011. Called Navigator, the NASA-derived GPS receiver can acquire and track the weaker signals broadcast by GPS satellites to enable navigation in geosynchronous orbits (GEO) and highly elliptical orbits (HEO), where typical GPS receivers fail to pick up a signal. “Goddard provided the software, algorithms, and Kalman filtering. Again, we repackaged the hardware and coordinated initial bench-top performance testing with Goddard. This effort allowed us to make it part of our IAU, creating another hardware option for satellites considering these type of missions,” says Smith.
The first use of BRE’s version of Navigator will fly on the Air Force Research Laboratory’s Nanosatellite Guardian for Evaluating Local Space (ANGELS) mission, planned for 2012.
While Smith looks forward to continued collaborations with NASA to make the next generation of GPS receivers for tracking additional frequencies, in the meantime, he says, “As we continually look for options in the best interest of flight hardware, we have a good product line based on NASA technology.”