Optimal Ground Station Coverage for Crew Exploration Vehicle in Low Earth Orbits
- Paper number
IAC-08.B2.3.7
- Author
Dr. Kar-Ming Cheung, Jet Propulsion Laboratory, United States
- Year
2008
- Abstract
In this paper, we describe the methodology of finding a minimal set of ground stations from a large set of candidate NASA and foreign ground stations to provide communication coverage for Crew Exploration Vehicle (CEV) in Low Earth Orbits (LEO’s) for the International Space Station (ISS) phase and for the lunar phase. The Constellation Program levies stringent requirements to ensure two-way voice communications between astronauts onboard the CEV with the Mission Operation Control Center (MOCC) on the ground. In addition to the primary S-band and Ka-band communications provided by the Space Network (SN), the Constellation Program requires the CEV to have an independent mean of two-way voice communication provided by ground stations with an availability of 10 minutes contact time every 90 minutes. This turns out to be a challenging engineering problem for the following reasons: •Due to the low altitude of the LEO orbits, the ground antenna footprint only covers a small portion of the sky. •Choosing a set of r stations from a set of n, where n >> r, is a combinatorial problem with an exponential complexity of order O(n^r). The main results of this paper are as follows: •We show geometrically that the maximum contact time per contact is around 8 minutes, with an average contact time per contact around 5 minutes. •We apply a heuristic rejection algorithm that takes into account the stations’ locations with respect to the CEV’s trajectories to down-select from a large set of ground stations to a minimal set of seven, while still meets the communication gap requirements of less than 90 minutes. This rejection algorithm also generates a satisfactory statistics of contact time provided by the optimized set of 7 stations within a 90-minutes time span.
- Abstract document
- Manuscript document
IAC-08.B2.3.7.pdf (🔒 authorized access only).
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