NASA's Constellation Program, which was projected to develop a replacement rocket for the space shuttle, was cancelled last year.
While the government is not currently working on a shuttle replacement, potential private sector candidates include the Falcon 9-Dragon vehicle from SpaceX, which has been successful in test launches so far, but is still in early development.
Thus for the foreseeable future the USA will no longer have any human-rated launch vehicle.
Without manned spacecraft, US astronauts will now have to rely solely on the Russian Soyuz to access the International Space Station.
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