This is a short term (less than one-year) effort to develop a software- defined radio ground station (SDRGS) for use by future geospace research and operational CubeSat missions employing high data rate downlinks (i.e., >1 Mbit/sec).The SDRGS will be based on a prototype version that the proposing team has already developed on the NSF Dynamic Ionosphere CubeSat Experiment (DICE) space weather mission. With this effort, the team will: 1) perform a site survey and feasibility of use study for radio frequencies (UHF and S-band) that are relevant for government frequency allocations at two 18-meter dish sites : the Wallops Flight Facility (WFF) and SRI (Santa Clara, CA); 2) develop a real-time SDRGS architecture that has the capability of acquiring data rates >1 Mbit/second at UHF and S-band; and 3) demonstrate the performance of the SDRGS at UHF at both sites via on-orbit communications with DICE.
When completed and tested with DICE, the SDRGS design and source code will be made publicly available and distributed for use by the CubeSat and nano-satellite communities. The resultant SDRGS will not be limited to use at Wallops or SRI; those two sites were simply chosen for this proposed work given their high-gain, 18-meter dishes and the team's familiarity with both sites. The project will promote education and learning in that two graduate students and two undergraduate students from the department of Electrical and Computer Engineering at USU will perform the majority of the code and hardware development and testing.
The Dynamic Ionosphere Cubesat Experiment (DICE) is one of the first NSF Cubesat missions to be selected and flown. The DICE project consists of two CubeSats, weighing less than 2.2 kg each, which were launched into a highly eccentric low Earth orbit on October 28, 2011. Together the DICE CubeSats measure gradients of electric fields and electron densities in the ionosphere. The main science goal of the DICE project is to study the causes of storm enhanced densities (SED), which is a major space weather disturbance and concern.
The goal of this project was to develop a low-cost, portable, real-time ground station (GS) software defined radio (SDR) for use by the general CubeSat community on upcoming geospace research and operational CubeSat missions that require multi-megabit data rates, based upon the prototype version USU-SDL developed for the on-orbit DICE mission. This goal was achieved. Because DICE was licensed as a secondary user in the 460-470 MHz band, signals transmitted from space-to-Earth arrive at the ground station antenna mixed with interference from primary users of the band, which consist of maritime mobile, public safety radio, private land mobile, and personal radio. The presence of the interfering signals prevents the DICE signal from being successfully demodulated. Therefore, a significant portion of the research was devoted to developing algorithms for interference cancellation. These algorithms enable successful demodulation of nearly 100% of the packets transmitted by the spacecraft. At the time of this writing, nearly 20 Terabytes of raw data has been archived at USU/SDL facilities. This has allowed us to achieve this nearly 100% data capture level from overpasses since the beginning of the mission (Nov. 2011). All of the ground-breaking work done with the communications system has allowed the program to downlink ~ 65 Gbits of data from the two sensor sats. This data volume is significantly more than that of a standard CubeSat. This opens up a door to science-intensive missions achieved with these miniature sensor sat platforms. SDL-USU made the SDR ground station design publicly available, including open source code, and distributed it for use by the CubeSat (nano-satellite) community. We have already been involved with supplying designs and code so that others CubeSat missions can duplicate the functionality in the DICE communication system. This work paved the way for and provided continued operational environment for six recently awarded CubeSat programs. Three of the programs are NASA sponsored, one is NSF sponsored, one is DOD sponsored, and the final is sponsored by MIT. Each program will use the CADET radio developed on DICE by USU and L-3. Three of the six programs will use the GS and Wallops communication infrastructure as improved on RAPID.