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Aviation History
1961
1961 - 0106.PDF
106 PLIGHT, 21 January 1%! Missiles and Space flight MINITRACK IN BRITAIN F LIGHT' PHOTOGRAPHS THE satellite-tracking and telemetry station at Winkfield,near Windsor, which forms part of the worldwide Mini-track network of the US National Aeronautics and Space Administration, is now ready to track satellites transmitting on the"new" space frequency of 136-7Mc/s. Equipment has been pro- vided on loan by NASA and has been installed; the station ismanned by staff of the Radio Research Station at Ditton Park, Slough; and the tracking-aerial system was calibrated last monthwith the help of a Canberra aircraft of the Royal Aircraft Establishment, Farnborough. Telemetry-reception aerials for both 108 and 136-7Mc/s areincluded in the Winkfield equipment: that for the former fre- quency has already been used (to receive data from Explorer 8,launched last November), while the 136-7Mc/s aerial is not yet complete. The accompanying photographs were taken during avisit to the station last week. The tracking system uses the interferometer principle to deter-mine the direction of the satellite from the station. The phase difference between radio signals received at two accurately spacedaerials represents the difference in time taken by the radio waves to reach the aerials. By making simultaneous measurements ontwo pairs of aerials, one set up along a north-south line and one east-west, the phase differences can be converted to give the anglein space of the satellite. There are two separate interferometers at Winkfield, each havingcomponent aerials located at the four corners of a square whose diagonals are about 50 wavelengths (approximately 360ft) in lengthand directed along north-south and east-west lines. One, known as the equatorial system, responds to signals arriving from a fewdegrees on either side of a north-south vertical plane; and the other, known as the polar system, to signals from a correspondingzone across an east-west plane (see photograph of site model). These are known as "fine" aerials and are used to detect phasedifference as a fraction of 360°; the installation is completed by a set of five closely spaced "ambiguity" aerials which give theintegral multiple of 360°. Inside the main building is the associated receiving and control equipment, much of which isNASA-designed and Bendix-built, plus two Sanborn 350 recorders (one digital and one analogue). To check the accuracy of the system a combined optical andradio method is used. At the centre of the aerial system a Naval Research Laboratory calibration camera (focal length 40in) ismounted in a small brick enclosure. This is used to photograph a flashing light carried by an aircraft which flies over the station,simultaneously transmitting on the appropriate radio frequency. 108Mc/s telemetry aerial at Winkfield. In the left background are some of the ground screens on which the tracking aerials are mounted The photographs taken will show the position of the aircraftagainst a star background and so give a reference against which the radio measurements can be checked.For the reception of telemetred data the appropriate remotely controlled beamed aerial is employed together with an Airtronicsreceiver and an Ampex FR600 eight-channel, magnetic tape recorder. A transmitter is used as required to command the play-back and transmission of recorded data from the satellite. The final link in the chain of information is provided by a directteleprinter circuit from Winkfisld to NASA's Goddard Space Flight Center at Greenbelt, Maryland, and other US space estab-lishments. Summarized results from each satellite transit recorded at Winkfield will be transmitted to Goddard by this method. Inthe reverse direction, up-to-date orbital information on all relevant satellites is provided, and Winkfield is alerted for forthcoming Left, a mods/ of the Winkfield aerial installation, showing central fan-shaped beam from polar tracking system and directional beams from the two telemetry aerials. The pairs of white blocks at the north, south, east and west extremities of the system represent the "fine" aerials (see text) and the group of five smaller blocks are the "ambiguity" aerials. Right, Dr B. G. Pressey (right) and Mr Charles Nicolson, who is station manager at Winkfield, in front of the Minitrack control console. All Minitrack equipment at Winkfield is on loan from NASA
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