Commercial Crew Schedule Analysis

[SWGlassPit]

(snip)
Hell, the area-time product of ISS as a whole only barely approaches a statistically significant sample for a lot of the relevant particles.

That's by design
The ISS is flown at an altitude in the exosphere that minimizes the population of debris.  Light objects, even up to the several kilograms of cubesats, have very short orbital lifetimes at those altitudes.

On the other hand, there are hundreds of square meters of surface on the ISS that can be watched.   If that's not "statistically significant" then it doesn't seem like it would be THE driving safety requirement for commercial crew.

MMOD for ISS (among others) is literally what I do for a living, and the ISS does get struck quite frequently, albeit mostly by very small particles.

The difficulty of statistical significance vs requirements is that when the requirement is probabilistic in nature -- particularly when the requirement is something on the order of one critical penetration per thousand flights, you can't make observations to test whether the fluxes in the models you are using are correct.  You can't make a determination of whether the true flux is closer to, say, 0.1 or 0.01 when you observe zero.  It's not until you are predicting a handful of strikes that an observation of zero is significant.

[speedevil]

https://directory.eoportal.org/web/eoportal/satellite-missions/s/space-fence - I strongly recommend if interested in MMOD. Space Fence is an ongoing project to upgrade the capability of tracking MMOD.



There are _lots_ more unobserved particles of course that this will not be able to track, but it's at least a start.

As mentioned above, monitoring impacts on your spacecraft is a limited way of predicting the future, if it's not happening regularly - we have good understanding of big debris and tiny debris due to being able to observe it and monitor regular impacts respectively.
There is an unfortunate gap in knowledge of the distribution of 1mm-3cm sized particles or so.

[SWGlassPit]

<snip>
There is an unfortunate gap in knowledge of the distribution of 1mm-3cm sized particles or so.

Bingo.  Incidentally, this is also the size range in which things start becoming really devastating to hardware.

[erioladastra]

I have not been following closely the development of crew capsules, but the possible delay of another year or two does not make any sense to me. These capsules are not that complicated, and the current Dragon has been flying for years without, I think, major problems that would have threatened the survival of a live passenger (animal, or human).  Capsules from Mercury and Apollo to the current Dragon have accumulated an impressive number of successful flights, and I think much is known of the unbreakable Soyuz capsules, so the requirements should be well documented. Are the developers facing continuing changes of specs from NASA in search of ever increasing reliability, after the Shuttlle fiasco ( much more dangerous than thought at the time?). In my career I faced several times the problem of project managers less competent than developers that simply did not have the knowledge and the brains for judging solutions and to develop clear and final specs, the balls for pulling the trigger, or the honesty to admit that the technical issues were over their heads and hence constantly chasing windmills...

As they say, it's complicated.  Spec changes are definitely a part of it.  NASA often doesn't realize that when you have small teams (even the Boeing team is smaller than traditional) to evaluate this or that, or make this change (even when you pay for it) you introduce delays.  Then as the reports note, you have a small set of people that have to review and evaluate the partners.  Even agreeing on what level of review to conduct can slow the NASA side down.  Then the partner's themselves still have to build it and challenges (read surprises) still happen.  Yes, Dragon is based on the cargo vehicle...but they are make a huge number of changes.  So the displays and controls are all new.  Boeing is using stuff that has flown on the X-37, but the software is all new.  And when you code new software for a vehicle, whether for displays or operations, you run into issues.

And yes Dragon had some issues that could have been life threatening as has been accounted for in books and articles.

As to your comment that capsules are pretty basic and known so how can they have problems - well cars have been around for 100+ years and we still have problems.  Yeah, you are basically make the same thing but your computer is slightly different, their environmental control is a little different and for a spacecraft for humans you have to make damn sure they work right.

[erioladastra]

It's not clear whether Boeing or SpaceX is more prepared for commercial crew certification than the other. But what seems increasingly clear to me is that NASA is less prepared than either of the providers.

So this would mean that if (big if) the providers could pull off crewed missions in the first half next year, they would have to wait a year to fly again on a certified mission?

I think you mean CFT.  OFT will still be an unmanned test flight.  CFT may be 3 crew and may be up to 6 months.

Perhaps. But if the crewed test missions are successful, NASA will be under an incredible amount of pressure to move to operational flights as soon as possible. Why do you think they are moving towards making the Boeing OFT an "operational" mission?

[erioladastra]

It's not clear whether Boeing or SpaceX is more prepared for commercial crew certification than the other. But what seems increasingly clear to me is that NASA is less prepared than either of the providers.

So this would mean that if (big if) the providers could pull off crewed missions in the first half next year, they would have to wait a year to fly again on a certified mission?

Not really.  Much of the certification gets bought off in the unmanned and manned test flights.  yes NASA has to evaluate the results but they are doing that as they also go along.  Then there will be a full cert review before the regular missions start.  Now how long that will take will be depend on a number of factors...how much is left for the (small) NASA team to review, how much is left for the providers to analyze/verify...  and surely not every requirement will be totally 100% satisfied so then there will be debate/negotiations on what is good enough to start, what has to be fixed/completed before flying again and how much can be phased in.  As we are seeing where CFT for Boeing may be more than a test fight the odds are there will still be some verifications open even when we are flighting Post Certification Missions.

[Arb]

And yes Dragon had some issues that could have been life threatening as has been accounted for in books and articles.

Must have missed those; which books and articles?

[Ike17055]

Excessive Water intrusion into the spacecraft on splashdown, to begin with...

[woods170]

Excessive Water intrusion into the spacecraft on splashdown, to begin with...

That only applied to early-series cargo Dragon and was solved even before NASA switched the preferred landing of Crew Dragon to water (instead of land).
As such that issue has no bearing on Crew Dragon, which is one of the subjects of this thread.

[Welsh Dragon]

Excessive Water intrusion into the spacecraft on splashdown, to begin with...

Life threatening amounts? Do stop concern trolling.

[ncb1397]

Excessive Water intrusion into the spacecraft on splashdown, to begin with...

Life threatening amounts? Do stop concern trolling.

Anybody knows how many amps/volts/duration the crew dragon batteries are capable of outputting? Not to mention, water can potentially cause a fire via electrical arcing in places. Let's be real here for a second. NASA isn't going to just be fine with the crew dragon shorting out and losing power either. And there is also all the potential computer triggered events as they die including firing of engines, etc. Then there is the cause of water intrusion: unplanned exposure of the pressure vessel environment to the outside environment which exposes a whole new can of worms if this occurs in space. People not thinking about these kinds of events are what led to Apollo 1, Challenger, Columbia, etc. Let's not let water intrusion be the next tile loss situation. That wasn't life threatening amounts either, until it was.

[erioladastra]

And yes Dragon had some issues that could have been life threatening as has been accounted for in books and articles.

Must have missed those; which books and articles?

For example,

http://www.latimes.com/business/la-fi-spacex-trouble-book-20180316-story.html

[woods170]

And yes Dragon had some issues that could have been life threatening as has been accounted for in books and articles.

Must have missed those; which books and articles?

For example,

http://www.latimes.com/business/la-fi-spacex-trouble-book-20180316-story.html

The stuck valve problem was not life-threatening. It was solved long before the spacecraft got in any real trouble.

You want life-threatening problems? Here's a few potential ones:

- Solar arrays failing to deploy. Guess what: no need to deploy solar arrays on Crew Dragon. They are conformal to the trunk.
- Failure to pressurize the propulsion systems. Guess what: Crew Dragon has four independent propulsion groups. Two of them can fail completely and even than Crew Dragon can still come home safely.
- Failure of the primary heat shield. Guess what: the sensitive part of the primary heat shield is protected by a whipple shield, with alternating layers of Kevlar, inside the trunk.
- Complete failure of the ECLLS. Guess what: not gonna happen. It is the best tested system of the entire Crew Dragon spacecraft.

None of the real potentially life threatening problems has ever occurred on cargo Dragon.

On the water intrusion problem: the largest amount of water that ever got into one of the early cargo Dragons, before it was lifted out of the water, was less than 200 liters. Dragon needs to take on at least 10 times that amount of water to be even remotely in jeopardy of sinking.

The water intrusion in itself was not the problem. The electrical system shorting out, because of the water, was the real problem. And that was solved by making it completely water-tight.

[ncb1397]

And yes Dragon had some issues that could have been life threatening as has been accounted for in books and articles.

Must have missed those; which books and articles?

For example,

http://www.latimes.com/business/la-fi-spacex-trouble-book-20180316-story.html

The stuck valve problem was not life-threatening. It was solved long before the spacecraft got in any real trouble.

How is losing control of your vehicle in an environment like space for 4 or 5 hours not life threatening? There was a real chance their fix wouldn't work.

From the article

"Is the vehicle even functioning enough that you can bring it back?" he wondered.

Apparently, SpaceX's director of Advanced Projects questioning whether the vehicle will come back to Earth is not life threatening. If this happened on a crew dragon, it would be the cliff notes version of Apollo 13 or equivalent to the tile heat shield damage on STS-1. 

[yg1968]

You cut the rest of the quote which is also relevant:

But as they tried to figure out what was wrong, Steve Davis, SpaceX's director of advanced projects, had begun to prepare for the worst — aborting the mission. "Is the vehicle even functioning enough that you can bring it back?" he wondered. "We weren't sure. That was the only time we had ever planned for an emergency reentry, which is like a big thing because you have to whip it through airspace. You have to reroute planes in real time. It's not awesome. And so we were in panic mode."

At that time, they didn't know what the problem was. So he had to consider all possibilities. But that doesn't mean that the vehicle was unable to come back to Earth. It just means that they had to consider all of the possibilities (including a non-functioning spacecraft). 

[abaddon]

I think it's pretty hilarious that lessons learned on cargo-only Dragon, that has successfully flown ~14 missions to date, are somehow being viewed as a negative with respect to the crew version.

[ncb1397]

You cut the rest of the quote which is also relevant:

But as they tried to figure out what was wrong, Steve Davis, SpaceX's director of advanced projects, had begun to prepare for the worst — aborting the mission. "Is the vehicle even functioning enough that you can bring it back?" he wondered. "We weren't sure. That was the only time we had ever planned for an emergency reentry, which is like a big thing because you have to whip it through airspace. You have to reroute planes in real time. It's not awesome. And so we were in panic mode."

At that time, they didn't know what the problem was. So he had to consider all possibilities. But that doesn't mean that the vehicle was unable to come back to Earth. It just means that they had to consider all of the possibilities (including a non-functioning spacecraft).

What you are basically saying is that because the vehicle came back to earth, it wasn't life threatening. If that is the case, Apollo 13 wasn't life threatening either. They had a 100% chance of survival because that is how it turned out. If a non-functioning (it was non-functioning for nearly a quarter of a full day) and non-fixable spacecraft was a possibility, then it was life threatening.

Maybe I can put this another way. If you go to your bookie and he gives you 100 to 1 odds of crew survival on a certain mission. You put $10 dollars down against crew survival with a possible pay out of $1000. After control of the spacecraft RCS is lost, you go back to your bookie and want to put down another $100 with a possible payout of $10,000 at the same odds. What do you think is going to happen? He isn't going to give you the same odds.

[whitelancer64]

You cut the rest of the quote which is also relevant:

But as they tried to figure out what was wrong, Steve Davis, SpaceX's director of advanced projects, had begun to prepare for the worst — aborting the mission. "Is the vehicle even functioning enough that you can bring it back?" he wondered. "We weren't sure. That was the only time we had ever planned for an emergency reentry, which is like a big thing because you have to whip it through airspace. You have to reroute planes in real time. It's not awesome. And so we were in panic mode."

At that time, they didn't know what the problem was. So he had to consider all possibilities. But that doesn't mean that the vehicle was unable to come back to Earth. It just means that they had to consider all of the possibilities (including a non-functioning spacecraft).

What you are basically saying is that because the vehicle came back to earth, it wasn't life threatening. If that is the case, Apollo 13 wasn't life threatening either. They had a 100% chance of survival because that is how it turned out. If a non-functioning (it was non-functioning for nearly a quarter of a full day) and non-fixable spacecraft was a possibility, then it was life threatening.

Maybe I can put this another way. If you go to your bookie and he gives you 100 to 1 odds of crew survival on a certain mission. You put $10 dollars down against crew survival with a possible pay out $1000. After control of the spacecraft RCS is lost, you go back to your bookie and want to put down another $100 with a possible payout of $10,000 at the same odds. What do you think is going to happen? He isn't going to give you the same odds.

Are you saying that a stuck RCS valve should cause an immediate abort?

[yg1968]

Good summary by Jeff Foust:
http://www.thespacereview.com/article/3535/1

[DigitalMan]

Quite a relief to see that list, I was expecting to hear of new issues with Crew Dragon or issues that had not been previously known.  Something like that could cause long schedule delays.

Seeing issues that have been solved and followed by many successful flights is encouraging to me.