Anticipated Problems of Re-Entry Vehicle Telemetry at UHF

Abstract

Present information on missile range planning indicates that serious UHF telemetry coverage problems are likely to occur during reentry of ballistic vehicles. Flight test experience at VHF has demonstrated that receiving stations experience difficulty in tracking re-entry vehicles under conditions of rapid changes of signal strength caused by combinations of vehicle motion, vehicle antenna pattern, and plasma attenuation. Similar but greater variations at UHF coupled with narrow beamwidths and reduced sensitivity of re-entry stations portend greater problems at UHF. Conical scan systems may prove inadequate. Comparisons of similar telemetry systems at VHF and S-band are presented, demonstrating that received signal to noise ratios at re-entry stations will be 3 to 9 db below levels Presently obtained at VHF for reentry stations. The narrow antenna beamwidths (1° to 3.5°) will also cause problems in acquisition so that some form of acquisition aid will be required at each station. Omnidirectional antennas currently used in aircraft at VHF will be useless at UHF. Ships and aircraft will require stabilized or compensated antennas. Acquisition of hypersonic targets will be a particularly severe problem for aircraft receiving stations. In addition to defining the re-entry problem, system limitations, and expected effects, this paper also makes recommendations to range planners and users to minimize or correct the anticipated problems.