 F, p. 356. include provision for low orbiting satellites, which would have Free, B.A. (1980) North-south station keeping with electric propul- advantages for service to road vehicles and in particular to hand sion using on-board battery power, 1980 JANNUF Propulsion portable radio telephones. Meeting, 5 p. 217. Development of high definition television (HDTV) is in progress Fuenzalida, J.C. Rivalan, P. and Weiss H.J. (1977) Summary of the in many countries. Most of the systems that have been announced INTELSAT V communications performance specifications, so far require much more information to be transmitted than is COMSAT Tech. Rev. 7 No.1 p. 311. needed for standard definition TV. In consequence there are no Hall, G.C. and Moss P.R. (1978) A review of the development of the ready means, terrestrial or satellite, of distributing such signals INTELSAT system, Post Office Elect. Eng. J, 71 p. 155. widely and there is interest in securing a new frequency allocation Hayn, D., Braitinger, M. and Schmucker, R.H. (1978) Performance for satellite broadcasting of HDTV, probably around 20GHz. A prediction of power augmented electrothermal hydrazine thrus- second broadcasting development looks towards multi channel ters, Technische Universitaet Lehrstuhl fur Raumfahrttechik, sound broadcasting of 'CD-quality' that could be received in motor Munich, W. Germany. cars; for this purpose another new frequency allocation is being Hills, M.T. and Evans B.G. (1973) Telecommunications System sought, but this would have to be much lower in the spectrum, Design, Vol.1 Transmission Systems, pp. 176-198, George Alla- probably below 3GHz. The ITU Conference in 1992 will consider nand Unwin. proposals for both of these developments. INTELSAT (1972) TDMA/DSI system specification (TDMA/DSI Traffic terminals), INTELSAT Document BG 42/65 (Revl) June 1981. 51.8 Acknowledgements INTELSAT (1977) Standard A performance characteristics of earth stations in the INTELSAT IVA and V systems having a G/T of The author wishes to thank the Commission o