Satellite communications for manned spacecraft

Future manned spaceflight programs may require continuous real-time communications between the spacecraft and the mission control center. This paper examines the feasibility of relay satellite (RS) systems to meet these requirements. Anticipated requirements range from voice and low-speed data for the Skylab and Space Shuttle to television for the Space Station. Frequencies in S, C, X, and K bands (2, 5, 8, and GHz bands, respectively) are considered. Terrestrial radio-relay links may cause interference in the mission spacecraft (MS) and RS and vice versa. Possible remedies include better control of antenna sidelobes and judicious choice of channel frequencies. It is found that INTELSAT IV offers a technically feasible means of providing voice and data communications but not TV. A new dedicated satellite system can meet the requirements with two geostationary satellites both of which are visible to a single earth station (ES) in the United States. A shared satellite system, catering to other potential users as well as to manned spacecraft, offers the possibility of reduced cost to individual users. Satellite configurations for both dedicated and shared systems are presented. The satellites can be launched by boosters of the Thor-Delta class if the links between satellite and spacecraft operate in K band.