By 1970, the project was under a perceived economic threat from America's offer to fly satellites for foreign powers on a reimbursable basis. That agreement had been signed between ESRO and NASA on 30 December 1966 and by 1970 it was becoming clear that the advantage in having a national launch vehicle was insufficient to justify the cost. In 1972, NASA approved development of the reusable Space Shuttle, which at that time was largely perceived to eventually offer greater savings over the launching of satellites using an expendable system. These hopes the Shuttle delivering lower costs would ultimately prove to be hollow. By 1971, over £250 million had been spent on the Europa programme; the Europa 2 itself cost over £4 million.