RF Communications Subsystem for the Radiation Belt Storm Probes Mission
- Paper number
IAC-08.B2.3.2
- Author
Mr. Dipak Srinivasan, Johns Hopkins University Applied Physics Laboratory, United States
- Coauthor
Mr. Robert Wallis, United States
- Coauthor
Mr. David Artis, The Johns Hopkins University Applied Physics Laboratory, United States
- Coauthor
Mr. Robert Stilwell, United States
- Coauthor
Mr. Ben Baker, The John Hopkins University Applied Physics Laboratory, United States
- Year
2008
- Abstract
The NASA Radiation Belt Storm Probes (RBSP) mission, currently in Phase B, is a two-spacecraft, Earth-orbiting mission that will launch in September 2011. The spacecraft’s S-band radio frequency (RF) telecommunications subsystem has three primary functions: provide spacecraft command capability, provide spacecraft telemetry and science data return, and provide highly-accurate Doppler data for navigation. The primary communications link to the ground is via the Johns Hopkins University Applied Physics Laboratory’s (APL) 18-m dish, with secondary links to a backup ground network and the Tracking and Data Relay Spacecraft System (TDRSS) in single-access mode. The on-board RF subsystem features the the APL-built coherent transceiver and canted-turnstile antennas. The coherent transceiver, with design heritage from the New Horizons, CONTOUR, and TIMED missions, provides coherency by digitally locking onto the uplink signal and digitally synthesizing the downlink signal. Downlink frame packets are sent from the spacecraft command and data handling subsystem to the transceiver, which controls the downlink data rate and encoding within its field-programmable gate array (FPGA). The transceiver also provides a critical command decoder (CCD) function, which is used to protect against box-level upsets in the C&DH subsystem. Because RBSP is a spin-stabilized mission, the antennas must be symmetric about the spin axis. Two low-gain antennas point along both ends of the spin axis, providing communication coverage from boresight to 70º. An RF splitter excites both antennas; therefore, the mission is designed such that no communications are required about 90º from the spin axis due to the interferometer effect from the two antennas. To maximize the total downlink volume from the spacecraft, the CCSDS File Delivery Protocol (CFDP) has been baselined for the RBSP mission. During real-time ground contacts with the APL ground station, downlinked files are checked for errors. Handshaking between flight and ground CFDP software results in requests to retransmit only the file fragments lost due to dropouts. This allows minimization of RF link margins, thereby maximizing data rate and thus data volume.
- Abstract document
- Manuscript document
IAC-08.B2.3.2.pdf (🔒 authorized access only).
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