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Aviation History
1979
1979 - 1050.PDF
1008 FLIGHT Inurnattenal, 3/ March 1979 Skylab to hit Earth this summer SKYLAB, Nasa's disused orbiting lab oratory, is now due to re-enter the Earth's atmosphere in June or July this year. The new date is due to the craft's recently adopted solar in- ertial attitude (solar arrays continually pointing at the Sun) and increased Sunspot activity. Skylab was placed in its new atti tude during January to ensure suffi cient electrical power, following the deterioration of batteries and other systems. High Sunspot activity causes the Earth's upper atmosphere to ex pand, thereby increasing the drag on spacecraft in low Earth orbit. Skylab had been kept in a low drag attitude with its axis parallel to the Earth's surface, giving an esti mated re entry in the spring of 1980. This would have allowed time for Nasa's Teleoperator Retrieval System (TRS) to have flown on the second Space Shuttle flight and docked with Skylab. The TRS would then have been used to boost Skylab into a higher orbit or to brake it to a con trolled re-entry over an uninhabited part of the Earth. Delays in the Shuttle programme however, increased Sunspot activity and the deterioration of Skylab's sys tems, made the chances of a success ful rendezvous remote and Nasa aban doned these plans in December last year. Nasa now has no control over where the debris from Skylab will fall, but because the craft's orbital inclin ation is about 50° it will be between the latitudes 50°N and 50°S. This portion of the globe encompasses Skylab as seen by the departing first crew in 1973. Some of the orbital workshop's thermal protection and one solar array were lost during launch, but astronauts managed to rig up a "parasol" shield (bright square at centre) THE European Space Agency (ESA) has announced a two year study of optical and microwave sensors, culmi nating in satellite observations of the Earth in the mid 1980s. An example of a microwave sensor, is the Syn thetic Aperture Radar (SAR) currently being developed by Germany for Spacelab, Europe's manned orbiting laboratory. Sensors like this can pro duce information about the Earth's surface despite cloud cover, which could hinder or prevent optical obser vations. Nasa has already flown an SAR aboard Seasat, which did not how ever last long in orbit, but the results, some of them of the seabed, were encouraging. Europe's remote sensing satellites will also be able to draw on the multi-mission platform, currently being developed by France for its Spot Earth observation satellite. The plat- North and South America, Africa, Australia and the southern half of Asia, but effectively rules out Britain. Skylab was last visited by US astronauts in 1974, but since then at mospheric drag has been slowing it down causing its orbit to decay. The orbiting laboratory's present altitude is about 345Km. Nasa has already studied the use of an Atlas or Delta launcher for placing a payload simi lar to TRS close to Skylab, but con cluded that such a mission had even a less chance of success than the original Shuttle proposal. Suggestions that a missile could be fired at Skylab to break it up into small bits, thereby reducing the size of pieces that penetrate the atmos phere, have been dismissed because form is similar in concept to the common satellite bus. The ESA study was approved by the Agency's remote sensing programme board earlier this month. Member states already committed include France, Britain, Denmark, Italy, Sweden and the Netherlands. Others are expected to join soon. Overall budget for the sensor work is $9-7 million. ESA plans to begin develop ment work on a remote sensing satel lite some time next year, and the cur rent study will complete some of the groundwork. One of the advantages of the two- year study is that it ensures continued development of national programmes already under way. Spot, for example, is currently funded by the French space agency (CNES). ESA's commit ment to a remote sensing satellite will probably be made next year. the debris would have been spread over a much larger area. When the 80 tonne Skylab does re-enter, it is estimated that the debris will come down in a strip 150km by 6,500km. Nasa has suggested that the chances of anyone being hit by debris are less than the risk of being struck by light ning. As Skylab enters the final stages of orbital decay, it should be possible to predict the date and place of im pact a little more precisely, Skylab's attitude can still be controlled at present, partly by the remaining con trol moment gyros and partly by the control thrusters. Nasa is currently studying the possibility of influencing Skylab's attitude in the early stages of re-entry so that some control can be exercised over the impact area. Spaceshots . . . Cosmos 1081-1088 were launched by the Soviet Union on March 15. The eight craft, believed to be military communications satellites, were orbited by a single launch vehicle. Mitsubishi has been awarded a £14-3 million contract to build a communications satellite ground station in Saudi Arabia. The company is also setting up a similar terminal, worth £4-8 million, in Malaysia. India's space budget for 1979-80 is worth about £44-2 million, an increase of £12-6 million on the current year. Roughly £7-7 mil lion of this increase will be absorbed by the domestic com munications satellite, Insat 1, which is being built by the US. Europe's window on Earth
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