TES-11 GOES DCS Demonstration: A Novel LEO-to-GEO Communication System for Nanosatellites

A satellite in any low Earth orbit (LEO), with access to various geostationary Earth orbit (GEO) satellites, could have a near constant, low bandwidth, real-time link back to Earth during most of an orbit. These GEO satellites could include the two GOES, steadily refreshed since 1974, the European Space Agency (ESA) Meteosat, and the Japanese Space agencies (JAXA) Himawari satellite. These satellites implement the GOES Data Collection System (DCS), or analog, with applications which include meteorology, oceanography, hydrology, ecology, and remote sensing of Earth resources. The relatively compact DCS ground stations used by thousands of researchers transmit data at 100, 300, and 1200 bps at 402 MHz. A full-time link during much of an orbit, even at low data rate, would be useful for reporting internal spacecraft health, hazard avoidance for a future space traffic control system, and an augmentation of the GEO satellite monitoring capability (by monitoring, for example, polar regions not accessible to the system) including real-time events requiring immediate attention. A joint effort between NOAA and the NASA Ames Research Center began such an effort using the TechEdSat (TES-n) -8, -10 and -11 missions. This required a miniaturization of the basic DCS transmitter such that it could fit within the constrained volume of the cubesat standard (i.e., 100 x 100 mm cross-section). In addition, the transmitted signal needs a different Doppler correction depending on the orbit position or velocity, which represented a significant part of the mission development. The transmitted power levels were varied from 1-10 Wrf, to assess the success of the acquired message string. Even at low power, the message success was greater than 40% and found to be adequate for some applications, particularly if the message were repeated. While not a replacement for high data downlink capability, it is an attractive option for long-lived thermosphere sensing, quick command and control of the basic spacecraft avionics, and rapid identification protocols, which has become increasingly important in the crowded 400-600 km altitude band. For geostationary transfer orbits (GTO) and cis-Lunar space including the Lunar surface, the addition of this rapid command and control capability can help assure the success of the mission with the simple addition of an extra communication link. In addition, the system frequency is the same standard for the UHF Mars relay satellites, allowing for future Mars ‘nanosat-class’ ground science stations. – Thus, this process may permit the extension of the basic DCS concept, enabling a significant augmentation of Mars weather predictions for the upcoming series of missions.