WASHINGTON — As Boeing begins work on its NASA commercial crew contract, the company is proposing to use a version of the same spacecraft to transport cargo to the international space station.

Company officials said in a Dec. 9 interview here that they submitted a proposal earlier this month for NASA’s Commercial Resupply Services (CRS) 2 competition, a follow-on to the existing CRS contracts held by Orbital Sciences Corp. and Space Exploration Technologies Corp. to ferry cargo to and from the station.

The cargo version of Boeing’s CST-100 spacecraft will be based on the crewed version the company is developing for NASA, said John Mulholland, Boeing commercial crew program manager. Boeing will remove spacecraft components not needed for crew missions, like its launch abort system and environmental controls, to free up room in the spacecraft for cargo.

The cargo version of CST-100 would, like the crewed version, launch on a United Launch Alliance Atlas 5 rocket. The cargo version will also be able to return cargo to Earth, landing in the western United States like the crewed version.

That similarity between the two CST-100 versions is intended to improve the spacecraft’s overall economics. “It gives us a chance to use the launch vehicle and capsule that are being integrated for crew and get more missions out of it to help with affordability,” said John Elbon, vice president and general manager for space exploration at Boeing.

The CST-100’s ability to come down on land, versus splashing down in the ocean, will allow it to take advantage of a new element of the CRS2 procurement for the accelerated return of cargo from the ISS. In that optional portion of CRS2, cargo is handed over to NASA within three to six hours of landing instead of 24. “We’ll be able to get access to the science that’s coming down within an hour or so,” Elbon said.

Mulholland declined to specify how much cargo the CST-100 could carry to the ISS, but said it exceeds the minimum of 2,500 kilograms per mission required by NASA.

Mulholland argued that using a vehicle already under development for crewed vehicles, launched on the Atlas 5, offers a degree of robustness that puts Boeing at an advantage in the competition. “It really helps our bid,” he said. “It will position us to have at least one of the awards.”

Boeing is facing competition from several other companies for the CRS2 contracts. Orbital and SpaceX had been widely expected to submit proposals to keep their existing ISS cargo business. Executives with Sierra Nevada Corp. (SNC) said in September they were considering a CRS2 bid using the Dream Chaser vehicle it was previously developing for NASA’s commercial crew program.

Representatives with Orbital and SNC confirmed that their companies each submitted CRS2 proposals, which were due to NASA by Dec. 2. SpaceX spokesman John Taylor said Dec. 15 that the company does not comment on bid decisions in advance of any contract awards.

NASA is expected to award CRS2 contracts by June 2015, with cargo missions scheduled to begin in 2018. NASA has not disclosed how many contracts it will award, but many in the industry expect at least two contracts to provide redundancy should one provider experience problems.

While putting together its CST-100 cargo proposal, Boeing has also started work on its Commercial Crew Transportation Capability (CCtCap) contract, awarded by NASA in September.

Mulholland said the company has completed two early milestones in that contract. One is a certification baseline review that covered what Boeing must do to win NASA certification to carry astronauts on the CST-100. The second was a critical design review of the CST-100 ground segment, including mission operations and training. A third milestone, a safety review, had just started, he said.

As Boeing ramps up its work on the CCtCap contract, it is keeping an eye on a protest filed by SNC with the U.S. Government Accountability Office. SNC, which lost the competition to Boeing and SpaceX, claims it offered a similar technical capability at a lower price than Boeing. The GAO is scheduled to render a decision on the protest by Jan. 5.

“There’s not much we can do to influence the process,” Elbon said of the protest. “I think NASA did a heck of a job and made a sound decision, and I’m hopeful those who are auditing that decision will see it that way.”