Nasa is looking for more proposals from US industry to further advance commercial crew space transportation concepts.
The proposals will also mature the design and development of system elements such as launch vehicles and spacecraft.
Multiple awards are expected to be announced by March 2011 for terms of up to 14 months, worth a total of about $200m.
Nasa aims to accelerate the availability of US commercial crew transportation capabilities and reduce the gap in the nation's human spaceflight capability through the new proposals.
With the proposals, the space agency may be able to spur economic growth as potential new space markets are created.
