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Throughout history soldiers have fought bloody battles inorder to control the high ground．There is no doubt that thisis a tactical（戰(zhàn)術(shù)的）necessity．Standing abouve your enemy isan advantage that often leads to vietory．
Nowadays，high ground does not just mean hill tops．Italso means space,which has become an increasingly importantpart of military strategy（軍事戰(zhàn)略）．
With its more advanced satellite technologies,America isthe major power in space．And now the US Air Force has putinto service a new weapon designed to jam enemy satellite communications．It is an important step toward US control of space．
The so-called Counter Communications System（反衛(wèi)星通信系統(tǒng)）was declared operational on November 1．The ground-based system uses electromagnetic radio frequencites（無線電磁波）to stop enemy satellites working on a shortterm basis．
“A short-term effect ensures that during the time of need,the enemy's space-based capability（能力）is reduced,”said a US military official．“Following the time of need，their capabilities can return to its original state．”
The system is made up of an antenna（天線）,transmitters（發(fā)射機(jī)）and receivers and can be easily transported around in a vehicle．
To control space was one of four aims of a national space policy started by former president Bill Clinton in 1996．The goal is to make sure US forces can rely on space-based services and to deny an enemy any similar benefits．
The US military has experimented with several“anti-sat-ellie”weapons,including lasers,to destroy or damageenemy units．
Theresa Hitchens,vice president of the Centre for Defence Information in Washington,welcomed the new systemas long as it does not create rubbish that could threaten globaluse of space．She believed it should not destroy satellties．only stop them working for a while．
“Unfortunately，it seems we are not going to limit ourgoal for‘space control’to non-violent systems,”she said，rai sing the danger of a space arms race．
To change the balance of power in space the EU and China are working together on the Galieo project．By 2008 the system will be in place as an alternative to the Americans'global positioning service．
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