Author Topic: Commercial Crew providers making "significant progress" toward first flights  (Read 17464 times)

Online Lar

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Let's be excellent to each other. Not sniping at each other about who asks what questions would be part of that. There is nothing wrong with asking a question that pertains to only one of the two vehicles ASAP commented on.
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Offline yg1968

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Not that it matters but the 1 in 270 commercial crew LOC number comes from the Shuttle's LOC numbers. When the Shuttle was retired, it had a 1 in 90 LOC Probabilistic Risk Assessment (PRA) (this is a different number from the actual LOC number which was  1 in 65). It was determined that commecial crew needed to be 3 times as safe as Shuttle, thus a 1 in 270 PRA LOC ratio.

Ares I was supposed to be 10 times safer than Shuttle (so 1 in 900 or 1 in 1000 depending on what numbers you use for Shuttle). But that was determined to be unrealistic.

For more on this, see this link:
https://forum.nasaspaceflight.com/index.php?topic=35717.msg1665335#msg1665335
« Last Edit: 07/10/2017 06:07 PM by yg1968 »

Offline Jim

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Offline Hog

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Lots of convo about safety and some comparison to STS,

Starliner/Dragon-2 with their crewed duration being tiny compared to operational, orbit attaining Shuttle missions which probably averaged around a week, not including the ALT or STS-1-4 test or failure to attain orbit missions), with 17 days15hours(STS-80) being the longest, and STS-51C being the shortest 03d 01h DoD mission.
Starliner apparently has a crewed duration design of 60 hours(launch/dock/undock/landing) with 210 days docked.

Is there any consideration or allowance for the duration a crew is being exposed to risk? 
60 hours max. as in Starliner(launch/dock-undock/landing, compared to 423 hours actual exposure during STS-80(launch to landing), with a max design duration of 28days(672hours with a second EDO pallet, 13 tank sets).

If I have to live in an enclosure which, at any time, can be destroyed by high speed penetrants, I would think that the shortest time within said enclosure would be the safest, all else equal.

Spacecraft safety discussions/studies must be hugely complicated.  the safest spacecraft is one that doesn't leave the pad. But staying on the ground doesn't make that crafts safety absolute.
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Offline envy887

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AIUI, the majority of the risk comes from MMOD damage to the heatshield causing an entry anomaly. This is roughly proportional to total time on orbit (which is much longer than Shuttle), not crewed time on orbit (which is much shorter than Shuttle).

Offline robert_d

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AIUI, the majority of the risk comes from MMOD damage to the heatshield causing an entry anomaly. This is roughly proportional to total time on orbit (which is much longer than Shuttle), not crewed time on orbit (which is much shorter than Shuttle).

I'm not clear how this could be proportional to time on orbit since the trunk will be attached? Also, total surface area of Shuttle was so much larger and somewhat more fragile than PICAX.

Can anyone point to a source for the Soyuz calculation and result? I would like to know if the Orbital module was hit, could the command module still detach and land? How much damage could the service module take before undocking and retro-propulsion was not possible?


Offline clongton

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MMOD damage to the heatshields of vehicles that still have their trunks or service modules attached should be non-existent. Therefore this should not be a factor in calculating LOC numbers.
Chuck - DIRECT co-founder
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Offline envy887

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MMOD damage to the heatshields of vehicles that still have their trunks or service modules attached should be non-existent. Therefore this should not be a factor in calculating LOC numbers.

That's not what I gather from:
https://www.nasaspaceflight.com/2015/05/eft-1-orion-inspections-vital-mmod-information/
and
https://www.nasaspaceflight.com/2016/08/nasa-mmod-primary-threat-crew-vehicles/

Backshell TPS is also at risk. I could be misinterpreting those though.

Offline RonM

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MMOD damage to the heatshields of vehicles that still have their trunks or service modules attached should be non-existent. Therefore this should not be a factor in calculating LOC numbers.

That's not what I gather from:
https://www.nasaspaceflight.com/2015/05/eft-1-orion-inspections-vital-mmod-information/
and
https://www.nasaspaceflight.com/2016/08/nasa-mmod-primary-threat-crew-vehicles/

Backshell TPS is also at risk. I could be misinterpreting those though.

There have been 50 Soyuz missions to ISS and 30 Soyuz missions to Mir. These missions typically last about 5 to 6 months. How many of them were severely damaged by MMOD? AFAIK, none. It doesn't look like ASAP is using any of that data.

Offline whitelancer64

MMOD damage to the heatshields of vehicles that still have their trunks or service modules attached should be non-existent. Therefore this should not be a factor in calculating LOC numbers.

That's not what I gather from:
https://www.nasaspaceflight.com/2015/05/eft-1-orion-inspections-vital-mmod-information/
and
https://www.nasaspaceflight.com/2016/08/nasa-mmod-primary-threat-crew-vehicles/

Backshell TPS is also at risk. I could be misinterpreting those though.

There have been 50 Soyuz missions to ISS and 30 Soyuz missions to Mir. These missions typically last about 5 to 6 months. How many of them were severely damaged by MMOD? AFAIK, none. It doesn't look like ASAP is using any of that data.

Just because there hasn't been a loss of a Soyuz from MMOD doesn't mean there is no risk.

Also the debris environment around the ISS / LEO in general is worse now than it ever has been, which is a part of the issue. There are MMOD models that output different risk factors depending on assumptions made about the amount and location of debris hazards. For example, fine debris from the Chinese ASAT test is slowly coming closer to Earth, but exactly where it is, how big the particles are, and how fast the orbital decay rate for the debris is a matter of some guesswork. How you model those parameters can change the risk level.
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Online Lars-J

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MMOD damage to the heatshields of vehicles that still have their trunks or service modules attached should be non-existent. Therefore this should not be a factor in calculating LOC numbers.

That's not what I gather from:
https://www.nasaspaceflight.com/2015/05/eft-1-orion-inspections-vital-mmod-information/
and
https://www.nasaspaceflight.com/2016/08/nasa-mmod-primary-threat-crew-vehicles/

Backshell TPS is also at risk. I could be misinterpreting those though.

There have been 50 Soyuz missions to ISS and 30 Soyuz missions to Mir. These missions typically last about 5 to 6 months. How many of them were severely damaged by MMOD? AFAIK, none. It doesn't look like ASAP is using any of that data.

Just because there hasn't been a loss of a Soyuz from MMOD doesn't mean there is no risk.

Also the debris environment around the ISS / LEO in general is worse now than it ever has been, which is a part of the issue. There are MMOD models that output different risk factors depending on assumptions made about the amount and location of debris hazards. For example, fine debris from the Chinese ASAT test is slowly coming closer to Earth, but exactly where it is, how big the particles are, and how fast the orbital decay rate for the debris is a matter of some guesswork. How you model those parameters can change the risk level.

Who said it was no risk? The point - unless I am misunderstanding - was merely that after ~100 flights we starting to have a decent sample to give us data to see if the cited danger is as dangerous as claimed.

Offline Robotbeat

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Um, not just no loss of Soyuz (which would require more than just what we might call major MMOD), but no major damage to any Soyuz OR Progress from MMOD EVER. There have been hundreds of flights.

Shuttle's black, fragile and exposed heatshield is 400 times the area of the little bit of Dragon's tougher PICA heatshield that is protected by a metal covering but isn't covered by the trunk. Also, you can see at least half of it clearly from at least one window.
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Offline woods170

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Um, not just no loss of Soyuz (which would require more than just what we might call major MMOD), but no major damage to any Soyuz OR Progress from MMOD EVER. There have been hundreds of flights.

Shuttle's black, fragile and exposed heatshield is 400 times the area of the little bit of Dragon's tougher PICA heatshield that is protected by a metal covering but isn't covered by the trunk. Also, you can see at least half of it clearly from at least one window.
Forget it. That argument will never turn ASAP. If it was up to ASAP all CCP vehicles would be equipped with tripple-layer whipple shields over the entire backshell. And then they would still would voice strong concerns over the LOC/LOM numbers.
Given the energies and velocities involved in spaceflight there will never be "safe" spaceflight. But that is a fact that ASAP is not readily willing to accept. As QuantumG once voiced: the only safe manned spaceflight is no manned spaceflight.

Offline clongton

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Well shucks, buttercup. If there's the slightest chance that someone might get hurt by riding one of these things then maybe we should just skip this and go fishing instead. Be careful of that there hook young fella. It's got a sharp pointy end on it that could hurt if you stuck yourself with it. Come to think about it, let's just forget about fishing and go take a nap. What could go wrong with that?  ::)
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Offline Robotbeat

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Could get trapped and suffocated by the blankets.
Chris  Whoever loves correction loves knowledge, but he who hates reproof is stupid.

To the maximum extent practicable, the Federal Government shall plan missions to accommodate the space transportation services capabilities of United States commercial providers. US law http://goo.gl/YZYNt0

Online jg

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Could get trapped and suffocated by the blankets.
Particularly if you put baby face down...

Offline Jim

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Quote
“The other provider has placed a value on agility and rapid problem solving with beneficial results.  They are also showing signs of evolving to reconcile their approach with the benefits and need for discipline and control.

“However, they need to ensure that the evolution reflects an inherent desire to adopt the tenets of systems engineering.”

Uh, yeh.  I'm glad that SpaceX is never going to adopt the "tenets of systems engineering" while Musk is in charge.

And that is why they had and will have more failures

Online abaddon

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Being too expensive is its own kind of failure.  And no guarantee, space is hard and all providers have mishaps.

Offline AbuSimbel

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Quote
“The other provider has placed a value on agility and rapid problem solving with beneficial results.  They are also showing signs of evolving to reconcile their approach with the benefits and need for discipline and control.

“However, they need to ensure that the evolution reflects an inherent desire to adopt the tenets of systems engineering.”

Uh, yeh.  I'm glad that SpaceX is never going to adopt the "tenets of systems engineering" while Musk is in charge.

And that is why they had and will have more failures
ULA will too.
Failure is not only an option, it's the only way to learn.
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Offline Steve D

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The attitude at NASA seems to be "Failure is not an option". ISTM that attitude stifles the kind of creativity needed to really advance. The Spacex attitude seems to be "Failure is an option, quitting is not". 

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