UPDATED at 9:50 pm

WASHINGTON — Orbital Sciences Corp. is proposing a new lifting-body spacecraft capable of carrying at least four passengers to orbit by 2015 in the competition for a second round of NASA commercial crew taxi development contracts slated for award in March, according to industry sources.

The spacecraft, designed to launch atop an Atlas 5 rocket and dock with the international space station, could be ready for test flights as early as 2014. The remotely piloted spacecraft would be able to carry four passengers initially, including three astronauts and one paying ticketholder, though based on market demand the number of private rides aboard the vehicle could grow to two, with four astronaut seats available, sources said. In the works at Orbital for the past year, the reusable spacecraft would be built using existing materials and technologies, employ standard hypergolic propellants and rely on a pusher escape system in the event of a launch mishap, sources said.

Dulles, Va.-based Orbital is teaming with Virgin Galactic of New Mexico on the Commercial Crew Development 2 (CCDev 2) project. Virgin Galactic will market commercial rides on the spacecraft, conduct drop tests of the orbital space vehicle using its WhiteKnightTwo aircraft and offer transport services for the space vehicle, industry sources said. Although Orbital expects to launch and land the spacecraft at Cape Canaveral Air Force Station, Fla., in the event of an abort, WhiteKnightTwo would be used to ferry the spaceship between its landing location and the Cape.

Virgin is also expected to announce this week a separate CCDev 2 bid led by Sierra Nevada Corp., the big winner in NASA’s first round of Commercial Crew Development awards earlier this year. The Sparks, Nev.-based firm garnered $20 million in CCDev 1 funds to mature its Dream Chaser orbital spacecraft, a six-passenger lifting-body vehicle based on NASA’s HL-20 concept from the early 1990s that the company has been working on for several years.

In October, NASA announced it expects to award roughly $200 million next year to multiple contractors seeking to refine designs for launchers and spacecraft that would transport astronauts to and from low Earth orbit on a commercial basis. Proposals are due Dec. 13, though money available for the CCDev 2 effort will depend on congressional approval of funds anticipated in a continuing appropriations bill the Senate plans to take up this week.

NASA started the CCDev program in 2009 with $50 million in economic recovery funds. The agency awarded the first round of contracts this past February to a mix of five new and established aerospace firms that are using the money to work on technology supportive of U.S. President Barack Obama’s commercial space transportation vision.