Author Topic: Commercial Crew LOM scenario  (Read 4769 times)

Offline A_M_Swallow

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Re: Commercial Crew LOM scenario
« Reply #20 on: 05/15/2017 11:31 PM »
Such damage could occur as a result of an MMOD strike hitting near the docking adapter.
Yes and an MMOD strike can hit any spacecraft. Not just the CCP providers.

True but this is a Commercial Crew thread. Orion is NASA's problem. Each CCP provider needs a solution for its own spacecraft.

Offline docmordrid

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Re: Commercial Crew LOM scenario
« Reply #21 on: 05/16/2017 05:14 AM »
ISTM there is no full solution, only mitigations, and those mitigations (Whipple shields etc.) are pretty well understood.
« Last Edit: 05/16/2017 05:16 AM by docmordrid »
DM

Offline woods170

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Re: Commercial Crew LOM scenario
« Reply #22 on: 05/16/2017 08:44 AM »
Such damage could occur as a result of an MMOD strike hitting near the docking adapter.
Yes and an MMOD strike can hit any spacecraft. Not just the CCP providers.

True but this is a Commercial Crew thread. Orion is NASA's problem. Each CCP provider needs a solution for its own spacecraft.
It is slightly more subtle than that. CCP requirements, issued by NASA btw, also include requirements for MMOD protection.

Offline Hog

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Re: Commercial Crew LOM scenario
« Reply #23 on: 05/22/2017 08:22 PM »
Unlike Shuttle, Dragon and Starliner can go up fully autonomously... I guess that doesn't solve a crew rotation problem, but it does highlight that Shuttle isn't a good comp here.
Are you meaning that Shuttle couldn't launch to ISS without a crew?  Shuttle could launch with its normal flight crew compliment of 4, and still pick up a full ISS crew for de orbit.  Of course it wouldn't be doing the on station stay of 180 days.
Perhaps I am comprehending this poorly?
Paul

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Re: Commercial Crew LOM scenario
« Reply #24 on: 05/22/2017 08:38 PM »
If I recall correctly, Columbia flew with a two crew only on its debut mission.

Offline woods170

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Re: Commercial Crew LOM scenario
« Reply #25 on: 05/22/2017 08:55 PM »
If I recall correctly, Columbia flew with a two crew only on its debut mission.
That was the minimum required. Very much later in the program it became possible to re-enter and land an orbiter unmanned. But, launching it unmanned and have it dock with the ISS unmanned, was never in the realm of possibilities.

Offline Hog

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Re: Commercial Crew LOM scenario
« Reply #26 on: 05/27/2017 11:27 AM »
If I recall correctly, Columbia flew with a two crew only on its debut mission.
Correct, the 4 test missions, STS-1 through STS-4 were conducted with a crew of 2.

I stated a crew of four as that's what the Columbia Accident Investigation Board (CAIB) stated as the launch crew size would have been aboard Atlantis for the rescue.  Commander, Pilot and a couple EVA crew. In January, seven commanders, seven pilots, and nine spacewalk-trained astronauts were available. Downmass would have been 11 souls, 4 on the flight deck, and 7 on the middeck, if the rescue option would have been exercised.
Paul

Re: Commercial Crew LOM scenario
« Reply #27 on: 05/30/2017 09:13 PM »
http://spacenews.com/commercial-crew-vehicles-may-fall-short-of-safety-threshold/

Commercial crew vehicles may fall short of safety threshold

Quote
“The number one safety-related concern for the program is the current situation with respect to the estimate of loss of crew,” Donald McErlean, a former engineering fellow at L-3 Communications and a member of the panel, said at the meeting. “The threshold values were considered to be challenging, and both contractors currently have a challenge to meet that precise number.”

Quote
If either or both companies can’t meet the LOC requirement with the spacecraft, NASA may have to issue waivers for that requirement. “That remains a risk to the program that will have to be addressed, in all likelihood, by a risk acceptance waiver,” McErlean said.

“It may be necessary to do a formal risk acceptance of the variance from the stipulated goal,” he said later in the meeting. “We would remind NASA that that risk acceptance, including a complete presentation of the alternatives and the consequences, should be made formally, and that risk acceptance signed off by appropriate authorities.”






Offline woods170

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Re: Commercial Crew LOM scenario
« Reply #28 on: 05/31/2017 06:57 AM »
From the same article these important take-aways:

http://spacenews.com/commercial-crew-vehicles-may-fall-short-of-safety-threshold/

Quote from: Jeff Foust
He (Donald McErlean, a former engineering fellow at L-3 Communications and a member of the ASAP panel) also warned against placing too much emphasis on the LOC metric alone. “One has to be judicious in how one applies these statistical estimates,” he said. “One has to look at whether or not the contractors have expended the necessary effort and engineering activity to make the system as safe as they conceivably can and still perform the mission.”

He added that he was ”very positive” both companies were doing so. “There was no known or indicated area where with, by spending even a small amount of money, the contractor could have made their systems considerably safer.”

Bill Gerstenmaier, NASA associate administrator for human exploration and operations, has also warned against focusing too much on the LOC statistic alone in weighing risks of flying crewed spacecraft.

Offline ChrisGebhardt

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Re: Commercial Crew LOM scenario
« Reply #29 on: 05/31/2017 04:08 PM »
From the same article these important take-aways:

http://spacenews.com/commercial-crew-vehicles-may-fall-short-of-safety-threshold/

Quote from: Jeff Foust
He (Donald McErlean, a former engineering fellow at L-3 Communications and a member of the ASAP panel) also warned against placing too much emphasis on the LOC metric alone. “One has to be judicious in how one applies these statistical estimates,” he said. “One has to look at whether or not the contractors have expended the necessary effort and engineering activity to make the system as safe as they conceivably can and still perform the mission.”

He added that he was ”very positive” both companies were doing so. “There was no known or indicated area where with, by spending even a small amount of money, the contractor could have made their systems considerably safer.”

Bill Gerstenmaier, NASA associate administrator for human exploration and operations, has also warned against focusing too much on the LOC statistic alone in weighing risks of flying crewed spacecraft.

And Kathy Lueders said the same thing this morning at the CCP Q&A media event.  Final LOC estimates for Dragon and Starliner might not match the 1-in-270 benchmark at the outset, but she's happy with where both companies are.

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