Nasa contractor United Space Alliance (USA) is preparing a bid to continue flying the shuttle as a commercial service after the space agency completes its last three planned missions this year.
By 2013, the contractor proposes to fly twice a year with Atlantis and Endeavour at a cost of under $1.5bn a year, following the construction of a new external tank.
If the plan receives support, it is expected to reduce an anticipated gap of at least four years between launch of the last shuttle mission this year and availability of new privately run crew taxis, a period during which astronauts will depend on Russian spacecraft to reach the International Space Station.
USA has proposed a six-month study of the commercial shuttle option, and urged Nasa to help fund the study under a programme set up to speed the development of new rockets and spacecraft able to carry people, according to usatoday.com.
