Boeing may yet shelve future development of its CST-100 capsule, despite a recent award of more than $460 million from NASA's programme to transport astronauts to the International Space Station (ISS).

"Our base business case is based on transportation to ISS through 2020," says John Elbon, Boeing's vice-president of space exploration. Though not formalised, the company requires at least two flights per year from NASA to make the project viable.

"That's just for the ISS. That's kind of the basement," adds Elbon. More flights than those to the ISS are required he says, and Boeing is cautious about over-committing itself while future revenue streams are unclear.

NASA has funding for two full awards and one partial award in the commercial crew integrated capability (CCiCap) programme, to be doled out gradually according to established technical milestones. The two full grants were awarded to Boeing and SpaceX, while Sierra Nevada Corporation won the partial award.

Attached to each space act agreement, as the contracts are known, is an extensive list of optional milestones that takes the companies into flight testing.

While Boeing stands to gain at least $460 million by completing all 19 milestones during the 21-month base period, which would bring the CST-100 through the critical design review stage, an undisclosed, but significant, amount of additional funding may be gained through accomplishing 33 optional milestones.

But the base-period investment alone may not be enough for Boeing to justify continued funding, which may bring CST-100 development to an end.

While the cut-off point "wouldn't be at the end of this base period", says Elbon, it may be in the following option period.

"It's more important to have a definite market there. Obviously Boeing has significant resources, and if there's a business caseit's important that it's clear NASA is committed to the commercial crew programme going forward, that they're going to use it for flights to the ISS, and that we can grow some markets around that."

Boeing is working closely with space station manufacturer Bigelow Aerospace and orbital tourism company Space Adventures in an attempt to secure non-NASA revenue. While Bigelow and Space Adventures have racked up tangible success, neither has yet demonstrated a requirement for regular passenger trips into orbit.

The CCiCap contenders' business cases were among the criteria by which NASA evaluated their proposals. In a NASA justification document released after the selection announcement, Boeing's business case was described in "neutral" terms. It says: "Proposed corporate investment during the CCiCap period does not provide significant industry financial investment and there is an increased risk of having insufficient funding in the base period."

Boeing programme manager John Mulholland said it was difficult to compare the contributions made by companies. He said: "We are only counting things that are direct monetary contributions as an investment, we have a very conservative guideline that we use for what we call true investment. There is a lot of additional contributions we are making to the programme beyond that cash infusion."

Source: Flight International