WASHINGTON — Nearly six months after winning high-profile NASA contracts, the two companies developing commercial crew transportation systems are still in some sense competing with each other, playing up their strengths and highlighting the other’s perceived weaknesses.

At a U.S. House Science space subcommittee hearing on NASA’s commercial crew program Feb. 27, representatives of Boeing and SpaceX politely sparred with each other about which company was in the best position to meet NASA’s goal of transporting astronauts to the International Space Station by the end of 2017.

Much of that debate focused on the companies’ choices of launch vehicles for their crewed spacecraft: Boeing’s use of the United Launch Alliance Atlas 5 versus SpaceX’s Falcon 9.

“The Falcon 9 is, in our opinion, the best way for the U.S. to wean itself off its Russian dependency,” said Garrett Reisman, director of crew operations for SpaceX, noting that unlike the Atlas 5 and its Russian-built main engine, the Falcon 9 is “100 percent American-made.”

Reisman argued that the Falcon 9, which performed its 16th launch March 1, is catching up in experience to the veteran Atlas 5, which has flown 52 times to date. “By the time in 2017 when we strap somebody in, we’ll be well over 50 missions,” he said.

John Mulholland, vice president and program manager of commercial programs at Boeing Space Exploration of Houston, responded with some skepticism about that flight rate. “As Dr. Reisman mentions, they expect to be over 50 missions by the time the [commercial crew] launch services are provided,” he said, “which would be a significant increase in their schedule reliability to be able to achieve that number of missions.”

Mulholland also pointed out Falcon 9 had gone through “different design changes,” including the introduction of the Falcon 9 v1.1 in 2013 and plans to increase the thrust of the Falcon 9’s first-stage engines starting later this year. “So it will be interesting to see the stability and scale as they perform” that increased number of launches, he said.

The different values of the contracts also became a topic for debate at the hearing. Boeing’s contract is worth $4.2 billion, compared with SpaceX’s $2.6 billion, assuming all options for later operational flights are exercised. One subcommittee member, Rep. Bill Johnson (R-Ohio), asked about that apparent disparity.

“There is a difference in approach,” Mulholland responded. “I think the only objective evidence is the NASA evaluation from the source selection board.” That board’s report, he said, contained “many instances of statements about the increasing confidence that NASA has in the Boeing plan because of the detailed understanding of the certification requirements.”

He compared that with SpaceX, which he said “did not demonstrate as good an understanding of the certification products or have effective systems for the development of these key products.”

Reisman countered that the technical difference between the two companies’ proposals was not that large. “If you look in detail at the source selection official’s statement, it was neck-and-neck when it came to technical and mission suitability,” he said. “There was a 7 percent difference in the scores that were awarded, but there was a 70 percent difference in price.”

In data released by the U.S. Government Accountability Office in January, SpaceX received 457 of 525 points in the technical evaluation of its commercial crew proposal, while Boeing received 488 points, or about 7 percent higher than SpaceX. Boeing’s proposal price, excluding the flight services included in the NASA contract value, was $3.01 billion, about 70 percent higher than the $1.75 billion price offered by SpaceX.

Reisman said the price difference was caused in large part by difference in maturity between SpaceX’s Dragon v2 vehicle and Boeing’s CST-100. “We’re so much ahead in terms of development of the vehicle,” he said, citing SpaceX’s experience with the cargo version of Dragon currently in service. “We had a lot of runway behind us, and at the same time we’re also very efficient.”

While Mulholland and Reisman debated their relative strengths and weaknesses, the two left room for potential future collaboration. Mulholland noted that Boeing has had discussions in the past with SpaceX about the technical compatibility of the CST-100 with the Falcon 9 as a backup to the Atlas 5. “We were not given a bid for the Falcon 9 in this previous phase of the proposal, but we’ve had discussions with SpaceX,” he said.

“We have had some discussion” about using Falcon 9 for the CST-100, Reisman agreed, but added that any decisions about bidding were “above my pay grade.”

“I don’t get a commission, so I can’t sell you one of those today,” Reisman told Mulholland.