KECOMMENDA1 ION 365-3 * FREQUENCIES, BANDWIDTHS AND PROTECTION CRITERIA FOR MANNED AND UNMANNED DEEP-SPACE RESEARCH CONSIDERING (a) that suitable operating frequencies, required radio-frequency bandwidths, and limiting interference criteria for deep-space manned and unmanned research telecommunication links are determined by the technical considerations set forth in Reports 536-1, 683 and 685. (b) that cosmic noise and man-made noise militate against the use of frequencies lower than 100 MHz and that atmospheric noise and absorption allow the use of only particular frequency bands at frequencies much higher than 10 GHz; (c) that some high precision tracking techniques required for guidance of spacecraft to the Moon and the planets and for manoeuvres in their vicinity result in a preference for several widely separated frequencies above 1 GHz; (d) that two-way communication is required for all deep-space missions, and is vital for manned deep-space missions; (e) that manned deep-space missions require in particular two-way voice and also television as aids to command and control, guidance navigation and other telecommunication functions; (0 that for most deep-space missions the typical operating noise temperature of earth station receivers, operating at frequencies in the 2 GHz region will be 16 K, equivalent to -217 dB(W/Hz), in the 8 GHz region will be 23 K, equivalent to —215 dB(W/Hz), and in the 15 GHz region will be 33 K, equivalent to — 213 dB(W/Hz), with design margins of less than 6 dB; and that for reception at frequencies less than 1 GHz cosmic noise increases the system noise temperature approximately as the inverse of the square of the frequency; (g) that the typical operating input noise temperature of a receiver in a deep-space station operating at frequencies in the 2 GHz region will be 600 K, equivalent to -201 dB(W/Hz), in the 7 GHz region will be 800 K, equivalent to —200 dB(W/Hz), and in the 15 GHz region will be 1100 K, equivalent to — 198 dB(W/Hz), with design margins of less than 6 dB; and that for reception at frequencies less than 300 MHz, cosmic noise increases the system noise temperature approximately as the inverse of the square of the frequency; (h) that, at frequencies higher than 4 GHz, water vapour in the atmosphere can produce significant degradation in the quality of deep-space communications; (j) that typical deep-space systems will use directional antennae both on the Earth and on the spacecraft. These antennae will have a surface precision of between 0.24 mm and 5 mm r.m.s., regardless of diameter, so that frequencies between 1 and 20 GHz will generally be more suitable for efficient transmission; (k) that Doppler shifts can be of the order of 1 x IO-4 of the carrier frequency; (I) that interruptions in communications which aggregate to more than five minutes on any one day without prior planning, could seriously affect the success of the mission; (m) that real-time television from the lunar surface is practical with frame rates, resolutions, and qualities comparable to terrestrial television, and that photographic facsimile from the nearer planets is similarly practical; (n) that it is practical and desirable to effect telemetering, data transmission, and tracking functions on the same space-to-Earth link, and telecommand and tracking functions on the same Earth-to-space link; (o) that to effect precision tracking, a pair of coherently-related Earth-to-space and space-to-Earth frequencies with a separation of at least 7% of the higher frequency in any one band (e.g. pairs near 2 GHz, 8 GHz and the region of 15 GHz) is required, and that for more accurate correction for effects of charged particles on space propagation delays, simultaneous use of space-Earth links with coherent frequencies in two or more of these bands is required; (p) that to enable precision tracking corrections and to allow both low-rate weather-immune emergency communications, and high-rate primary communications, both Earth-to-space and space-to-Earth communications are desirable on two or more widely separated frequency bands (e.g. 2 GHz, 8 GHz and near 15 GHz); (q) that the angular spacings of the Moon and the planets are often such that the same frequency may be used for probes at different celestial coordinates, but that different spacecraft in the vicinity of the same coordinates or in the antenna beamwidth may require different frequencies; ♦ This Recommendation is brought to the attention of Study Groups i, 4, 7, 8, 9, 10 and 11.
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