Author Topic: NASA evaluating CCP Loss Of Crew and Mishap procedures  (Read 18690 times)

Offline Chris Bergin

http://www.nasaspaceflight.com/2015/05/nasa-evaluating-commercial-loss-crew-mishap/

Saturday night was a choice between pub, more outstanding (non-corrupt) FIFA 15 victories for my team on the PS4 or write this up. So I wrote this up ;) (Pub tomorrow night).

I personally find this interesting as much as it could be argued LOC ratios are a bit nonsensical. But I remember this being hammered into people's faces during the Shuttle extension debates and then those crazy "Ares I is so safe!!" claims, so when I saw references to that I thought I could write around the main references from the ASAP for an article.

Offline A_M_Swallow

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Re: NASA evaluating CCP Loss Of Crew and Mishap procedures
« Reply #1 on: 05/31/2015 03:14 AM »
NASA learnt to give the Space Shuttle a hull inspection before it docked to the ISS. Will the Commercial Crew vehicles be required to undergo a similar inspection?

We may be able to patch a hole at the ISS. We can certainly launch a replacement vehicle.

Offline NaN

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Re: NASA evaluating CCP Loss Of Crew and Mishap procedures
« Reply #2 on: 05/31/2015 05:36 AM »
Good choice! Interesting article on an important topic - I didn't realize MMOD was such a large factor in the estimated risk.

Is it possible to add captions or tooltips to the images? I don't always know what I'm looking at or the context to the article. Is the mouse-cursor-hand in image #6 (STS EVA) pointing out anything? Looks inadvertent, but I'm not sure.

Offline Hog

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Re: NASA evaluating CCP Loss Of Crew and Mishap procedures
« Reply #3 on: 05/31/2015 06:11 AM »
NASA learnt to give the Space Shuttle a hull inspection before it docked to the ISS. Will the Commercial Crew vehicles be required to undergo a similar inspection?

We may be able to patch a hole at the ISS. We can certainly launch a replacement vehicle.
Commercial Crew TPS isn't exposed during launch like STS was.  Shuttle vs. capsule.
Paul

Offline guckyfan

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Re: NASA evaluating CCP Loss Of Crew and Mishap procedures
« Reply #4 on: 05/31/2015 07:06 AM »
It is a great article, thanks for the valuable information.

I too am surprised that MMOD is considered a significant risk for capsules which protect their heat shields quite well. I would have expected the biggest risk might be to the windows during long stay at the station. Any problem there would easily be detected.

Offline darkenfast

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Re: NASA evaluating CCP Loss Of Crew and Mishap procedures
« Reply #5 on: 05/31/2015 10:16 AM »
I don't understand why the possibility of LOC is as high as it is.  We've had five LOC events in the history of manned spaceflight (I'm including Apollo 1).  None of those are at all likely to be repeated, because the vehicles are too different. 

The possibility of LOC during pad and launch phases is very low, because there will be a robust escape system on both spacecraft.  I would think that a person would have a much better chance of surviving an escape in a capsule than in a jet fighter ejection seat.

The possibility of LOC on re-entry is much reduced because the heat shield is mostly protected during the rest of the flight and is (yes, I'm assuming), stronger and smaller than the shuttle's tile system.  Multiple parachutes and (in the case of Dragon), Super Dracos offer more options to save a crew.

MMOD remains a possibility, but what sort of incident would actually cause an LOC?  It simply hasn't happened yet, so how do you predict it?  I think it would be harder than we might think to get to a small hole and patch it, so here's a question: can a depressurized capsule safely re-enter in an emergency with the crew in suits?  Of course, something big enough to punch through the various layers and penetrate people and equipment would be a real scary situation, but even then, would it result in loss of the whole crew?  Also, the area involved is smaller, which reduced the risk of being hit.  The pressurized volume is smaller and the rest of the vehicle is way smaller than the Orbiter.

Glad you wrote this up, Chris.  Good to think about.


Offline Chris Bergin

Thanks for the kind words folks! :)

Good choice! Interesting article on an important topic - I didn't realize MMOD was such a large factor in the estimated risk.

Is it possible to add captions or tooltips to the images? I don't always know what I'm looking at or the context to the article. Is the mouse-cursor-hand in image #6 (STS EVA) pointing out anything? Looks inadvertent, but I'm not sure.


Heh, the mouse cursor was a mistake on my part - stupid Greenshot ;) Corrected.

Captions - never been a fan as much as it doesn't really work on Wordpress. I aim to provide an image that relates to the text it is surrounded by. When that's not the case it's generic enough to work most of the time.

Online mtakala24

The Shuttle had relatively huge oxygen/N2 tanks, and the ECLSS was designed to cope with a rather large hole, giving the crew enough time to deorbit. Someone must remember that hole size, I don't..  square inches just do not stay in my head long enough vs. cm^2 :)

I don't think these commercial crew taxi vehicles have as big reserve capabilities, but they do fly shorter missions too. I wonder what the end effect is....

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Re: NASA evaluating CCP Loss Of Crew and Mishap procedures
« Reply #8 on: 05/31/2015 01:33 PM »
The MMOD thing for CC is very odd. Surely this must be an overly conservative estimate or ISS, Mir, Skylab, or the various Salyuts would've no doubt been punctured in their pressurized sections by now (considering they've been nearly permanently in orbit since the early 1970s). Even Shuttle didn't receive a fatal strike to its enormous heat shield from MMOD.
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Online spacenut

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Re: NASA evaluating CCP Loss Of Crew and Mishap procedures
« Reply #9 on: 05/31/2015 01:43 PM »
Does anyone think they may move up the time frame for the commercial crews due to recent events with the Russian failures? 

Offline Rocket Science

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Re: NASA evaluating CCP Loss Of Crew and Mishap procedures
« Reply #10 on: 05/31/2015 02:34 PM »
Thanks for the article Chris on an important and still controversial topic...
"The laws of physics are unforgiving"

Offline psloss

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Re: NASA evaluating CCP Loss Of Crew and Mishap procedures
« Reply #11 on: 05/31/2015 04:00 PM »
Even Shuttle didn't receive a fatal strike to its enormous heat shield from MMOD.
True; however, the program started flying the orbiters in attitudes to minimize exposure time of critical systems like the radiator cooling loops and the belly TPS.  Even with complex attitude tradeoffs while docked to station, the Shuttle-Station mated attitude was changed for missions after STS-107 to mitigate MMOD risk to the orbiter.

Assuming that the station attitude will not be changed for the new USOS crew vehicles, the primary docking port on Node 2 forward points the heat shield for both CCP vehicles into the velocity/ram vector.  The Soyuz vehicles are shielded to varying degrees by the Station structure, but much better than the CCP vehicles will be in the normal station attitude.

I would also assume that Shuttle orbiter MMOD risk was based on a much shorter mission duration of ~2 weeks, versus the much longer 25 or more weeks planned for these crew transport vehicles.

It would be interesting to see any information on how effectively the structure covering the heat shield for the two CCP providers mitigates the MMOD risk.

Offline MattMason

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Re: NASA evaluating CCP Loss Of Crew and Mishap procedures
« Reply #12 on: 05/31/2015 07:35 PM »
Great article. Glad that there's a clear program that's analyzing this for both crew vehicles and thinking ahead.

As for LoC events I can imagine, the two worst are a serious MMOD hit that vents the cabin and cannot be patched or a sudden LV explosion that moves too fast for LES.  Current designs, debris mapping and safeguards are far more refined than in the Apollo days (last time we used a capsule) and modes of abort with high probabilities to save the crew are all over the map for both CC. In a perfect world, it would be good for each CC to have their next LV ready as a rescue to the other. But this would require a docking adapter between the IDA types, and odds are that if you're in orbit, your spacecraft can either reenter or make it the ISS oasis. But I'm sure I'm oversimplifying.
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Offline rcoppola

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Re: NASA evaluating CCP Loss Of Crew and Mishap procedures
« Reply #13 on: 05/31/2015 07:54 PM »
Does anyone think they may move up the time frame for the commercial crews due to recent events with the Russian failures?
I'll hazard a guess over here:

http://forum.nasaspaceflight.com/index.php?topic=35717.msg1382581#msg1382581
« Last Edit: 05/31/2015 08:01 PM by rcoppola »
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Offline TrevorMonty

Have any of the recovered Dragon V1s received any MMOD of note.?

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Re: NASA evaluating CCP Loss Of Crew and Mishap procedures
« Reply #15 on: 05/31/2015 10:10 PM »
Just about anything can be rationalized, which NASA has proven numerous times regarding safety.  And the Shuttle showed that even though it had fatal flaws, like no realistic way to survive an inflight failure, people still took the chance to fly on it.

So what I would propose is a system that simply determines if a new system is potentially more safe than the previous system, and then make sure to quantify what the dangers still are (both known and and potential) such as MMOD.

For instance, what if the crew is in the vehicle on the launch pad and something goes wrong, is there a system that can get them to safety?  During the ascent phase when the vehicle is not yet in orbit and is attached to the 1st stage, is there a system that can get them to safety in the event of a 1st stage failure?  And a 2nd stage failure?  And then what happens if they do get a hull breach in orbit?

Shuttle crews knew the answers to those questions, but they had no alternative way to orbit.  Now that we have two crew transportation systems that are likely to start service, there is choice.  And going forward as more transportation systems get added the free market forces will guide what levels of safety are acceptable.

What could stifle that though is the NASA Authorization Act of 2005 and it's requirement to impanel a Presidential Commission to investigate inflight failures.  We don't do that for any other modes of transportation, so this legacy from the Shuttle days needs to be changed - government employees are killed while working all the time, so obviously this was more about the cost of failure, not that people died per se.

If given the chance I would probably have flown on a Shuttle, but I would have been concerned for my safety.  I would have few concerns if I was going to ride on either a CST-100 or Crew Dragon, and I'm so glad we're finally making some good progress on the safety front.
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Offline edkyle99

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Re: NASA evaluating CCP Loss Of Crew and Mishap procedures
« Reply #16 on: 05/31/2015 11:39 PM »
... the Shuttle showed that even though it had fatal flaws, like no realistic way to survive an inflight failure ...
Only a catastrophic failure of an SRB during the first two minutes of flight presented this hazard.  Everything else to my knowledge had an abort mode or modes to provide a means of crew survival.  One orbiter actually did an abort-to-orbit when it lost an SSME.

But yes, those first two minutes were hard to watch, every time. 

And let's not forget that CST-100 will also be lifted by two powerful solid motors during the first 90 seconds of flight, which have some of the same failure modes present in SRBs.

 - Ed Kyle
« Last Edit: 05/31/2015 11:51 PM by edkyle99 »

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Re: NASA evaluating CCP Loss Of Crew and Mishap procedures
« Reply #17 on: 05/31/2015 11:57 PM »
... the Shuttle showed that even though it had fatal flaws, like no realistic way to survive an inflight failure ...
Only a catastrophic failure of an SRB during the first two minutes of flight presented this hazard.  Everything else to my knowledge had an abort mode or modes to provide a means of crew survival.  One orbiter actually did an abort-to-orbit when it lost an SSME.

But yes, those first two minutes were hard to watch, every time. 

And let's not forget that CST-100 will also be lifted by two powerful solid motors during the first 90 seconds of flight, which have some of the same failure modes present in SRBs.

 - Ed Kyle
....Thankfully, CST-100 has abort thrusters. But good point.
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Offline A_M_Swallow

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Re: NASA evaluating CCP Loss Of Crew and Mishap procedures
« Reply #18 on: 06/01/2015 12:04 AM »
NASA learnt to give the Space Shuttle a hull inspection before it docked to the ISS. Will the Commercial Crew vehicles be required to undergo a similar inspection?

We may be able to patch a hole at the ISS. We can certainly launch a replacement vehicle.
Commercial Crew TPS isn't exposed during launch like STS was.  Shuttle vs. capsule.

Good.

The primary TPS across the underneath of the capsules is covered but the side walls, top and windows are exposed permitting MMOD.

Offline Elmar Moelzer

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Re: NASA evaluating CCP Loss Of Crew and Mishap procedures
« Reply #19 on: 06/01/2015 12:18 AM »
How catastrophic would the effect of a small (mm size) puncture "wound" to the TPS be for
1) the Dragon and 2) the CST100
and for A) the main TPS at the bottom and B) the TPS on the side?
I am no expert but looking at the cargo dragon, with various small ridges and attachment points that are not fully covered in TPS, I have trouble seeing a small puncture that is surrounded by the relatively thick TPS to automatically result in a LOC event. But I am curious about what those with more expertise have to say about it.
Also, don't the trunks/SMs give some protection to the main TPS while the capsules are in orbit?

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