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Aviation History
1959
1959 - 1916.PDF
FLIGHT, 28 August 1959 69 Missiles and Spaceflight. . . MAPPING OUTER SPACE By KENNETH OWEN OVERSHADOWED by the bowl and struc-ture of the world's largest steerable radiotelescope, the working site of Jodrell Bank Experimental Station resembles a village green sur-rounded by the strange shapes of the aerial tubes, wires and rods that are the esoteric tools of radioastronomy. Fringing the green also are the modest huts in which Manchester University scientists havedevised experiments, built equipment and inter- preted results leading to a wide basic knowledge ofthe universe. Almost incidentally, these men are now in the satellite and space-probe business. Director of the station and Professor of RadioAstronomy at the university is Alfred Charles Bernard Lovell, O.B.E., F.R.S., who conceived theidea of the big steerable instrument in 1947. Sup- port in the construction of the instrument wasreceived by the university from the Department of Scientific and Industrial Research and from theNuffield Foundation. Ten years later, there was a new landmark in the Cheshire countryside and thetelescope entered service. The science of radio astronomy has shown that there is muchmore in the universe than the eye can see, even when helped by the largest optical telescopes. Light waves from the stars areobscured in their passage to Earth by interstellar dust and gas, by dust and cloud in the Earth's atmosphere, and by daylight. Radiowaves, whose wavelengths are millions of times longer than light waves, can be received unhampered by cloud, dust or daylight,and radio telescopes can study a much greater volume of space than is accessible to any optical telescope. The signals received, apart from electromagnetic radiation fromthe Sun, comprise a general radio "brightness" which is maximum in the plane of the galaxy, and signals from a number of discretesources of small angular diameter. There are two ways of improving the range at which signals can be received and alsothe sharpness of focus, or resolution: (1) simply by increasing the area of the reflector, and (2) by using two spaced aerials as aninterferometer. At Jodrell Bank both methods had been used prior to theconstruction of the big steerable instrument. A 218ft reflector, in appearance rather like a wide saucer of wire netting, was (and stillis) used, but this is a simple transit type which is fixed to the ground and is not steerable. On occasion the 218ft and the 250ftinstruments are used together in interferometric techniques. The construction of the 250ft radio telescope was the mostsignificant step forward in the history of Jodrell Bank, and the value of its later applications to the tracking of artificial satellitesand space probes is now well known. The engineering problems involved in such a construction project were immense.The main reflector bowl is a paraboloid 250ft in diameter, made of welded steel plates and supported in a lattice steel cradle.Radio waves received by the bowl are reflected and concentrated at the focus of the paraboloid, and a 62^ft steel tower at the centreof the bowl is used to mount the aerial at this focus position. The bowl and cradle assembly weighs about 800 tons and is carried byroller bearings in trunnions at the top of the two 185ft side towers. Suspended beneath the centre of the bowl is a "swinging" SHORT WAVELENGTHS "Flight" photograph io-* to-6 io-8 WAVELENGTH (cm) 10-l0 PRIMARY COSMIC 'RAY CT-PARTICLE"1 WINDOW E 10-'4 10-'6 MANCHESTER UNIVERSITY'S RADIO- ASTRONOMY STATION AT JODRELL BANK laboratory which contains part of the main amplification systemfor incoming radio signals, and the entire bowl and cradle assembly is damped against swaying, flutter and vibration by the prominent"bicycle wheel" circular stabilizing girder. The entire supporting structure comprising the towers and a horizontal lattice girderrotates in azimuth, with six roller-bogies at the base of each tower running on a double circular-rail track of 352ft outer diameter. By changing the aerial mounted at the focus the frequency ofthe instrument can be altered and, for radar use, transmitters can be housed in extra laboratory space at the tops of the supportingtowers. In October 1957, as the final touches were being made to thenew radio telescope, came the amazing news of the launching by the Soviet Union of the first artificial Earth satellite. Prof. LoveUdecided to use the Jodrell Bank facilities to track the sputnik, by connecting radar transmitters (previously used to obtain Moonechoes) to the 250ft dish of the radio telescope. Radar contact with the satellite's carrier rocket was successfully obtained, andorbital data was sent to Moscow following a Soviet request. This was followed by similar radar tracking of Sputnik 2 andthe carrier rocket of Sputnik 3, and by a more ambitious joint Anglo-American effort concerned with receiving signals from thesubsequent U.S. lunar and space probes. This latter work pro- vides the explanation for the electronics trailer labelled SPACE TECHNOLOGY LABORATORIES, which is now parked at the side ofthe main radio-telescope control block. The team of U.S. electronics engineers at Jodrell Bank, led byWilliam Young of S.T.L., utilize American receiving and record- ing equipment in connection with aerials mounted on the 250ftradio-telescope dish to receive signals from the battery-powered transmitters aboard various U.S.A.F. and NASA space probes.The primary purpose is to record the telemetry signals trans- mitted by the probe during the period it is above the horizon, andthe secondary purpose is to keep track of the probe's position in space by means of the steady beacon signal. Advantages ofemploying the Jodrell Bank radio telescope are that its great sensi- tivity enables weak signals to be received up to great distances;and its beamwidth is small enough for a probe's position to be determined with considerable accuracy. The position of the probe as determined by the telescope istransmitted continuously by teletype direct to the U.S.A. from the unit at Jodrell Bank, and the magnetic tapes and paper chartscarrying the telemetry data are airmailed after a modest amount of data reduction on the spot. This information is received at theS.T.L. computing centre in Los Angeles where it is further processed and, together with data from other tracking stations, isconveyed to the U.S.A.F. and NASA. Pioneer 1, which reached 70,700 miles, and Pioneer 4, which passed the Moon to becomean artificial planet of the Sun, were both successfully tracked, and "Windows" in the radiation spectrum: A, radiation cut off by atmos- phere; B, some absorption, but atmosphere essentially transparent in this region (radar, UHF, VHF); C, radiation cut off by atmosphere gases; D, radiation cut off by atmosphere (cosmic-ray particles cut off by atmosphere and magnetic field); E, gamma rays and X-rays. The shaded area in the opticql window represents eye, sensitivity
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