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Wayward satellite clambers towards orbit

作者:贺学    发布时间:2019-03-06 10:05:00    

By Nicola Jones The $850 million European satellite that was delivered to the wrong orbit on 12 July is now fighting its way up to the right one. The experimental communication satellite, called Artemis, is using its chemical and ion propulsion thrusters to push it up 18,000 kilometres from its initial position into a geostationary orbit. Ironically, one of the main missions of the satellite was to test two different kinds of ion thrusters. Now they will be asked to do far more than they were designed to achieve. The rescue mission will use up considerable fuel for both kinds of thrusters. That will lower the 10 year life expectancy of the satellite, though no one yet knows by how much. “We will not make it for 10 years for sure,” says European Space Agency spokesman Franco Bonacina. “But if we get six to seven years, we’re still happy.” Artemis was mis-delivered by an Ariane 5 rocket, which also carried a Japanese TV satellite – now unrecoverable. All Ariane 5’s have now been grounded by their operator Arianespace until investigators can determine what went wrong. Their report is due on 1 August. They currently believe the rocket simply ran out of one of its propulsion fuels, possibly because of a leak. ESA expects this inquiry will affect the scheduled launch of its satellite, called ENVISAT, in October. “We will have a minimum three to four weeks delay,” says Bonacina. Artemis’s recovery mission began on Thursday with a chemical thruster burn that increased the high point of its elliptical orbit from 17,487 km to 19,164 km. Another two burns followed and two more are scheduled for Friday. That should successfully end the first stage of the mission, placing the satellite in a highly elliptical orbit with a high point of 31,000 km. The chemical thrusters will then be used to make the orbit circular, still at 31,000 kilometres. By then the solar arrays and antenna should be fully deployed, and the satellite will start the three month process of activation. ESA says all the satellite’s systems are responding well. To get the satellite into geostationary orbit – 35,853 km – Artemis will have to use its electrical ion propulsion thrusters, helping to conserve chemical fuel. But since the engines were originally designed only to nudge the satellite back into orbit or to perform small turning manoeuvres, this will not be simple. “We were supposed to use the ion thrusters for orientation of the satellite, not propulsion, so this is a bit tricky,” says Bonacina. He says the process will be slow and Artemis will not be in its final position for at least six months. But, if all goes well, ESA will be extremely glad they chose Artemis as their first satellite to carry these new engines. “The ion propulsion is no longer a ‘nice to have’ – they need it” says Dave Gibbon, a propulsion expert from Surrey Satellite Technology in Guildford,

 

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