Boeing's Starliner

[Meecrob]

15 hours ago, tater said:

I don't pretend to understand all of the complexities behind NASA's communication strategy regarding Starliner. But from the outside it appears poor, and non-responsive. What I'm hearing is not great news, so that may explain the reticence to engage.

— Eric Berger (@SciGuySpace) May 21, 2024

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I suspect that if they say anything, they will get bombarded with jokes about how the helium actually keeps the door attached (or some other joke about the door blowing off the MAX). Whether this is fair or not, the message of the press release will be overshadowed.

 

 

[tater]

 

[tater]

(what I was hearing earlier, but it was not for public consumption)

Guess I will watch on my phone (or wife's laptop) from London.

[tater]

This ticking clock issue reminds me of the SLS round trips from/to VAB issue, FTS battery replacement, etc. Seems plausible.

[kerbiloid]

Quote

We have slightly modified the valves

Before

Spoiler

After

Spoiler

[AckSed]

Summary (from here):

They didn't want to give updates before now because information was changing too quickly as they were working through the issues

There were three issues: the Centaur O2 leak, the Starliner helium leak, and a deorbit burn scenario that they found when considering the helium leak.

For the Centaur leak, they find that the valve had exceeded its rated number of cycles.

It was a complicated activity to change the valve, as Centaur is only stable under pressure or under tension, and they needed to depressurize it to change the valve

To put it under tension, they attached a crane to Starliner, which is how they install it so not an issue, but since, in addition to its own weight, it also had to apply tension to Centaur to stabilize it, they had to confirm it was capable of handling the extra strain.

For the helium flange, it sounds like it's a defective rubber seal (but they're not sure). After a few cycles, the leak rate got worse, but then stabilized. The flange is part of an assembly that is exposed to NTO, so they can't replace the seal without destacking Starliner and moving it to a place where that hazard can be neutralized.

The leak rate is low enough and stable enough that they are comfortable launching; even if the seal failed completely, they would still be comfortable with the leak rate. No other seals are leaking.

They had no way of noticing the leak during launch; they only noticed it during post-scrub operations. If they had launched, the mission would still have been safe and successful.

Nonetheless, they will fix it for Starliner-1.

The de-orbit scenario that they discovered is a rare one (0.7% of failure modes). They have two pairs of OMAC thrusters and would need to lose one of each pair, so that they had to deorbit using only RCS thrusters. On top of that, they would need to lose two helium manifolds immediately adjacent to each other. They did not have a plan for if this scenario occurred; now they do (instead of an 8-RCS-thruster burn, this scenario would require two 4-RCS-thruster burns).

Part of the delay until the next launch opportunity is so that the team, who have been working long hours and seven day weeks the past two weeks, get the long weekend off.

Nothing on the rocket or Starliner should expire until late June at the earliest (at which point the FTS pyrotechnics would need to be changed out). They're good to remain stacked until then.

The changes have impacted Starliner's interim human rating for CFT, so they're holding a Delta Flight Readiness Review to make sure that it still qualifies for human rating with the changes. The FRR will be Wednesday, May 29.