Dr. Patricia Sanders, chair, NASA Aerospace Safety Advisory Panel: That’s a very difficult question, thank you. Right now, I believe NASA is planning to require seven launches with that configuration, and we believe that’s an appropriate number. There’s some statistical evidence—that Mr. Gerstenmaier could probably talk to a little bit better than I can—why that is a reasonable number. It is not a totally random number, it is a number that’s predicated on having more than a few, but having a timeframe in which you can actually accomplish those and still get on with certification and make the right risk decision on flying.

Space Subcommittee Chairman Brian Babin (R-Texas): Dr. Sanders, how many launches with a stable configuration should NASA require SpaceX and Boeing to achieve before certification?

This requirement grew out of concerns about SpaceX and how frequently they update the design of Falcon 9. And from where NASA stands, it’s a totally valid concern and requirement.

The problem is that it has very blatantly only ever been applied to SpaceX.

Starliner is flying on top of an Atlas V—a launch vehicle with a long, successful history. But flying crew on an Atlas V requires some changes to eliminate abort black zones—sections of flight where aborts are impossible. And doing that requires adding a second engine to Centaur, the upper stage of the Atlas V.

Dual Engine Centaur is not a new concept—Centaur flew with two engines for most of its history. But the last flight of a Dual Engine Centaur was on February 21, 2002–an Atlas IIIB launching Echostar 7. That launch was the first flight of Common Centaur, which is the version of Centaur flying today on Atlas V.

Now, I’m sure there have been design changes to Centaur in the last 16 years, but let’s say that the Echostar 7 launch counts as Dual Engine Common Centaur’s first flight. Then we have to figure out what NASA constitutes a stable configuration: is it a particular variant of a fully-integrated stack, or can first and second stages be flown independently and count towards the stable configuration flight count? From what I’ve gathered, it’s the former.

Starliner’s first flight will be the first flight of the Dual Engine Common Centaur on Atlas V. Starliner’s second flight—its first with crew—will be flying the second.

Two is a long way from seven.