Fifty years after a Redstone rocket carried the first American astronaut, Alan Shephard, into space, NASA is getting out of the business of sending astronauts on missions using its own spacecraft.  Instead, the U.S. space agency will rely on privately designed and owned rockets to ferry cargo and crew to the orbiting International Space Station.

    The commercially built space vehicles are expected to be every bit as powerful and reliable（可靠的） as those operated by NASA, but they’ll cost American taxpayers far less. One company, Space Exploration Technologies Corporation, or SpaceX, has signed a  $1.6 billion deal with NASA for 12 unmanned delivery flights to the space station.

    SpaceX says the deal should lower the cost of launching cargo to about $1,000 per half kilogram - less than one-tenth of what it costs NASA to get a payload into outer space on the shuttle.

    President Barack Obama is asking Congress to approve $850 million to aid the development of private rockets to service the orbiting scientific outpost. NASA administrator Charles Bolden says the budget will support a public-private partnership in space.

    "We must have safe, reliable and affordable access to it for our astronauts and their supporting equipment.  That’s why this budget boosts funding for our partnership with the commercial space industry," Bolden said.

    The private sector’s role in unmanned space operations - such as the manufacture of satellites and robotic spacecraft -- is nothing new. So says former NASA executive Alan Stern, now with the Southwest Research Institute, which offers technical assistance to the aerospace industry.

    Stern says the private sector is promising to conduct space missions for a fraction of what they have traditionally cost NASA.  For example, SpaceX says it can reduce the cost of a launch, depending upon the rocket, to between $50 million and $100 million compared to the $1.5 billion price tag for each space shuttle mission.

    Stern says this savings of dimes on the dollar benefits the private sector as well as the public.

    "That’s a huge reduction in cost that’s going to allow us to have multiple space lines, and to be able to afford that. and to be able to do more things in space than we could in the past," Stern said.

    Last year, SpaceX became the first commercial aerospace company to successfully launch, place into orbit and retrieve a spacecraft -- the Falcon 9, carrying an unmanned capsule called the Dragon.

    The Dragon is being built as part of NASA’s $1.6 billion deal with SpaceX.  Company founder and CEO Elon Musk says the space agency has been pressing it to complete testing of the capsule, so it can go to the space station on a resupply mission at the end of this year.  However, news reports have quoted a top official in Russia’s manned space program as saying Russia will not allow the SpaceX rocket to dock with the space station until more extensive safety testing has been completed.(本文由在线英语听力室整理编辑)