Author Topic: ASAP still has concerns over Commercial Crew LOC risks  (Read 49191 times)

Offline punder

  • Full Member
  • ****
  • Posts: 476
  • Liked: 379
  • Likes Given: 239
Re: ASAP still has concerns over Commercial Crew LOC risks
« Reply #60 on: 01/17/2018 05:01 PM »
The logic of prop-loading the F9 after crew boarding is absolutely unassailable. How could working near a fueled, pressurized rocket, and boarding crew on a fueled, pressurized rocket, be safer than evacuating the pad and securing the crew in a LES-equipped capsule before any prop begins to flow? How???

The Titan II killed or injured several pad workers in this exact scenario--while they were working on or near a fully fueled, pressurized rocket.
« Last Edit: 01/17/2018 05:07 PM by punder »

Offline mn

  • Full Member
  • ***
  • Posts: 339
  • United States
  • Liked: 169
  • Likes Given: 66
Re: ASAP still has concerns over Commercial Crew LOC risks
« Reply #61 on: 01/17/2018 06:07 PM »
The logic of prop-loading the F9 after crew boarding is absolutely unassailable. How could working near a fueled, pressurized rocket, and boarding crew on a fueled, pressurized rocket, be safer than evacuating the pad and securing the crew in a LES-equipped capsule before any prop begins to flow? How???

The Titan II killed or injured several pad workers in this exact scenario--while they were working on or near a fully fueled, pressurized rocket.

I suspect this has been discussed many times here (I did read it here at least once before no idea which thread).

The process of loading can easily be considered more dangerous than after loading is complete. There is lots of things going on during loading, once you are done you are in a stable state.

(this has been argued back and forth, I'm not saying absolutely one way is right, but there is certainly enough doubt that you cannot say 'How???')

I suspect that historically there were more anomalies during loading than after loading and before launch (if there is even enough incidents to create a meaningful statistic).

Offline deruch

  • Senior Member
  • *****
  • Posts: 2324
  • California
  • Liked: 1856
  • Likes Given: 4125
Re: ASAP still has concerns over Commercial Crew LOC risks
« Reply #62 on: 01/17/2018 06:25 PM »
The logic of prop-loading the F9 after crew boarding is absolutely unassailable. How could working near a fueled, pressurized rocket, and boarding crew on a fueled, pressurized rocket, be safer than evacuating the pad and securing the crew in a LES-equipped capsule before any prop begins to flow? How???

The Titan II killed or injured several pad workers in this exact scenario--while they were working on or near a fully fueled, pressurized rocket.

Because the highest danger is during fueling.  It's a dynamic process both in terms of the propellants themselves flowing but also the vehicle hasn't reached thermal stasis.  The danger that something goes wrong and causes an accident is much higher during this period than that it is during the relatively static period of topping-off/replenishment.  So, that added risk has to be weighed against the lower risk of fewer man minutes of exposure to a loaded rocket.  Exactly which one turns out to have the true lower risk is dependent on the variables: number of astronauts and ground crew exposed, loading duration, etc.
Shouldn't reality posts be in "Advanced concepts"?  --Nomadd

Offline envy887

  • Senior Member
  • *****
  • Posts: 4737
  • Liked: 2640
  • Likes Given: 1423
Re: ASAP still has concerns over Commercial Crew LOC risks
« Reply #63 on: 01/17/2018 06:42 PM »
The logic of prop-loading the F9 after crew boarding is absolutely unassailable. How could working near a fueled, pressurized rocket, and boarding crew on a fueled, pressurized rocket, be safer than evacuating the pad and securing the crew in a LES-equipped capsule before any prop begins to flow? How???

The Titan II killed or injured several pad workers in this exact scenario--while they were working on or near a fully fueled, pressurized rocket.

No rocket is pressurized for flight until the final seconds of countdown, as far as I know. So crew weren't working on a pressurized, fueled rocket with either Shuttle or Titan II. There is only head pressure at the bottom of the tanks from the weight of the propellant higher up, but no flight pressurants.

AMOS-6 is a pretty good example of why exposure time and risk are not correlated. The LOX tank and the COPVs were being filled, with pressures, fill levels, and temperatures constantly changing until they reached an unstable point that hadn't been reached before, resulting in the explosion.

Once filled, everything on a non-sub-cooled rocket is basically in steady state and can sit with occasional topping for boiloff for as long as you want with nothing really changing. This doesn't really work for a subcooled rocket.

SpaceX wants to make the process inherently safe and controlled. Every other type of vehicle is fueled with passengers and crew aboard. But they have a lot of work to do to prove that Falcon 9 is just as safe as other vehicles, since the fuels are inherently more dangerous.
« Last Edit: 01/17/2018 06:45 PM by envy887 »

Offline punder

  • Full Member
  • ****
  • Posts: 476
  • Liked: 379
  • Likes Given: 239
Re: ASAP still has concerns over Commercial Crew LOC risks
« Reply #64 on: 01/17/2018 07:06 PM »
Difficult to see how pad crew that have evacuated the pad, can be injured by a prop-loading mishap, when the prop-loading begins only after they have evacuated the pad.

So right there, the number of personnel exposed to danger has been halved or more than halved.

The remaining personnel still in danger--the flight crew--are sitting in a fully armed launch escape system that necessarily features, as part of its fundamental design, successful operation upon detection of a sudden, unanticipated booster explosion on the pad. Of course the LES doesn't eliminate the risk of LOC but without it, the LOC probability is 1.


Offline punder

  • Full Member
  • ****
  • Posts: 476
  • Liked: 379
  • Likes Given: 239
Re: ASAP still has concerns over Commercial Crew LOC risks
« Reply #65 on: 01/17/2018 07:19 PM »
The logic of prop-loading the F9 after crew boarding is absolutely unassailable. How could working near a fueled, pressurized rocket, and boarding crew on a fueled, pressurized rocket, be safer than evacuating the pad and securing the crew in a LES-equipped capsule before any prop begins to flow? How???

The Titan II killed or injured several pad workers in this exact scenario--while they were working on or near a fully fueled, pressurized rocket.

No rocket is pressurized for flight until the final seconds of countdown, as far as I know. So crew weren't working on a pressurized, fueled rocket with either Shuttle or Titan II. There is only head pressure at the bottom of the tanks from the weight of the propellant higher up, but no flight pressurants.

AMOS-6 is a pretty good example of why exposure time and risk are not correlated. The LOX tank and the COPVs were being filled, with pressures, fill levels, and temperatures constantly changing until they reached an unstable point that hadn't been reached before, resulting in the explosion.

Once filled, everything on a non-sub-cooled rocket is basically in steady state and can sit with occasional topping for boiloff for as long as you want with nothing really changing. This doesn't really work for a subcooled rocket.

SpaceX wants to make the process inherently safe and controlled. Every other type of vehicle is fueled with passengers and crew aboard. But they have a lot of work to do to prove that Falcon 9 is just as safe as other vehicles, since the fuels are inherently more dangerous.

The Titan II fatalities occurred in operational silos where the Titans were fully fueled and capable of being brought to flight pressures within minutes.

http://www.themilitarystandard.com/missile/titan2/accident_374-7_1976.php
http://www.themilitarystandard.com/missile/titan2/littlerockaccident.php
http://www.themilitarystandard.com/missile/titan2/accident_533-7_1978.php


Offline Rocket Science

  • Senior Member
  • *****
  • Posts: 9025
  • NASA Educator Astronaut Candidate Applicant 2002
  • Liked: 2905
  • Likes Given: 7577
Re: ASAP still has concerns over Commercial Crew LOC risks
« Reply #66 on: 01/17/2018 07:26 PM »
Wow this thread is like Deja vu all over again from AMOS-6... :o
"The laws of physics are unforgiving"
~Rob: Physics instructor, Aviator, Vintage auto racer

Offline punder

  • Full Member
  • ****
  • Posts: 476
  • Liked: 379
  • Likes Given: 239
Re: ASAP still has concerns over Commercial Crew LOC risks
« Reply #67 on: 01/17/2018 08:09 PM »
Wow this thread is like Deja vu all over again from AMOS-6... :o

Sorry if I'm annoying people. I just can't wrap my head around the idea that working around, riding an elevator beside, climbing into etc. an empty shell might be considered more dangerous than doing the same things when the empty shell has been transformed into a very large bomb.

Offline rayleighscatter

  • Full Member
  • ****
  • Posts: 1040
  • Maryland
  • Liked: 485
  • Likes Given: 228
Re: ASAP still has concerns over Commercial Crew LOC risks
« Reply #68 on: 01/17/2018 09:02 PM »
Wow this thread is like Deja vu all over again from AMOS-6... :o

Sorry if I'm annoying people. I just can't wrap my head around the idea that working around, riding an elevator beside, climbing into etc. an empty shell might be considered more dangerous than doing the same things when the empty shell has been transformed into a very large bomb.

It's statistical analysis.

It's the same reason it's fine for them to store large amounts of fuel and oxidizer on site for months and have people working around them, but why no extraneous personnel can be around when it's transferred from the trucks.
 

Offline Negan

  • Full Member
  • ***
  • Posts: 362
  • Southwest
  • Liked: 85
  • Likes Given: 292
Re: ASAP still has concerns over Commercial Crew LOC risks
« Reply #69 on: 01/17/2018 09:24 PM »
The logic of prop-loading the F9 after crew boarding is absolutely unassailable. How could working near a fueled, pressurized rocket, and boarding crew on a fueled, pressurized rocket, be safer than evacuating the pad and securing the crew in a LES-equipped capsule before any prop begins to flow? How???

The Titan II killed or injured several pad workers in this exact scenario--while they were working on or near a fully fueled, pressurized rocket.

Sad part is SpaceX has already proved at least 38 times in a row they can safely fuel F9 without blowing it up, and that's with some flight-proven 1st stages in the mix.

Edit: Not to mention "returning helium loading operations to a prior flight proven configuration based on operations used in over 700 successful COPV loads"
« Last Edit: 01/17/2018 10:01 PM by Negan »

Offline punder

  • Full Member
  • ****
  • Posts: 476
  • Liked: 379
  • Likes Given: 239
Re: ASAP still has concerns over Commercial Crew LOC risks
« Reply #70 on: 01/17/2018 09:35 PM »
Wow this thread is like Deja vu all over again from AMOS-6... :o

Sorry if I'm annoying people. I just can't wrap my head around the idea that working around, riding an elevator beside, climbing into etc. an empty shell might be considered more dangerous than doing the same things when the empty shell has been transformed into a very large bomb.

It's statistical analysis.

It's the same reason it's fine for them to store large amounts of fuel and oxidizer on site for months and have people working around them, but why no extraneous personnel can be around when it's transferred from the trucks.

Must be a case of dueling statistical analyses.   :)

Offline Rocket Science

  • Senior Member
  • *****
  • Posts: 9025
  • NASA Educator Astronaut Candidate Applicant 2002
  • Liked: 2905
  • Likes Given: 7577
Re: ASAP still has concerns over Commercial Crew LOC risks
« Reply #71 on: 01/17/2018 10:09 PM »
Wow this thread is like Deja vu all over again from AMOS-6... :o

Sorry if I'm annoying people. I just can't wrap my head around the idea that working around, riding an elevator beside, climbing into etc. an empty shell might be considered more dangerous than doing the same things when the empty shell has been transformed into a very large bomb.
Nah, it's all good... We have to pass the time until we "finally" get to launch crews from US soil again whoever goes first! :)
"The laws of physics are unforgiving"
~Rob: Physics instructor, Aviator, Vintage auto racer

Offline mn

  • Full Member
  • ***
  • Posts: 339
  • United States
  • Liked: 169
  • Likes Given: 66
Re: ASAP still has concerns over Commercial Crew LOC risks
« Reply #72 on: 01/17/2018 11:01 PM »
Wow this thread is like Deja vu all over again from AMOS-6... :o

Sorry if I'm annoying people. I just can't wrap my head around the idea that working around, riding an elevator beside, climbing into etc. an empty shell might be considered more dangerous than doing the same things when the empty shell has been transformed into a very large bomb.

Nobody ever said that entering the empty vehicle was more dangerous, the danger is in the fueling process and the question is do you want the crew sitting there during that process.

Offline butters

  • Full Member
  • ****
  • Posts: 1773
  • Liked: 398
  • Likes Given: 147
Re: ASAP still has concerns over Commercial Crew LOC risks
« Reply #73 on: 01/17/2018 11:14 PM »
Loading prop after crew ingress increases the risk of a pad abort by some unknown amount. Loading prop before crew ingress might slightly increase the risk to flight and ground crew during ingress prior to LES activation. Which is safer depends on the probability of an emergency during prop load combined with the success rate of LES on pad aborts, as compared to the probability of an emergency during replenishment and the prospects for escaping such an emergency via the slidewires.

The risk of something going very wrong during replenishment should be significantly lower than the risk during prop load. But the odds of a successful escape should be significantly higher with the LES. It's not a straightforward comparison.

Offline punder

  • Full Member
  • ****
  • Posts: 476
  • Liked: 379
  • Likes Given: 239
Re: ASAP still has concerns over Commercial Crew LOC risks
« Reply #74 on: 01/17/2018 11:25 PM »
Wow this thread is like Deja vu all over again from AMOS-6... :o

Sorry if I'm annoying people. I just can't wrap my head around the idea that working around, riding an elevator beside, climbing into etc. an empty shell might be considered more dangerous than doing the same things when the empty shell has been transformed into a very large bomb.

Nobody ever said that entering the empty vehicle was more dangerous, the danger is in the fueling process and the question is do you want the crew sitting there during that process.

I see your point, but given a launch escape system, I'd say yes. Are you listening, NASA?   :D

I'm a train nut who gets nervous just standing next to old steam engines at 200 psi... they have occasionally launched their boilers into short but highly spectacular suborbital trajectories, with entirely predictable consequences for the unfortunate cab crew. (Sorry OT.)

Offline Jim

  • Night Gator
  • Senior Member
  • *****
  • Posts: 32443
  • Cape Canaveral Spaceport
  • Liked: 11188
  • Likes Given: 331
Re: ASAP still has concerns over Commercial Crew LOC risks
« Reply #75 on: 01/17/2018 11:52 PM »

The Titan II killed or injured several pad workers in this exact scenario--while they were working on or near a fully fueled, pressurized rocket.

No, not in this exact scenario. For one accident, they were disconnecting a pressurization line and a quick disconnect did not work.    The other accident, a worker dropped a large socket that punctured the fuel tank.    Not the same as loading a crew.

Online Steven Pietrobon

  • Member
  • Senior Member
  • *****
  • Posts: 17304
  • Adelaide, Australia
    • Steven Pietrobon's Space Archive
  • Liked: 5723
  • Likes Given: 729
Re: ASAP still has concerns over Commercial Crew LOC risks
« Reply #76 on: 01/18/2018 05:17 AM »
Sad part is SpaceX has already proved at least 38 times in a row they can safely fuel F9 without blowing it up, and that's with some flight-proven 1st stages in the mix.

That's 19 times in a row since the last fuelling explosion on 1 September 2016 with AMOS 6. Lets try and get some numbers. I made some engineering guestimates.

Probability vehicle fails after loading = p = 0.01 (an engineering guess upper bound)
Probability vehicle fails during loading = 2*p = 0.02 (this is twice more dangerous)
Probability escape vehicle fails = q = 0.1 (remember seeing this somewhere)
Probability fail to get away from vehicle during fuelling = 2*q = 0.2 (assume twice more dangerous)
Number of flight crew = n = 4
Number of ground crew = n = 4 (assume same as flight crew)
Assume time to load propellants is same as time to load crew (half an hour).

Expected loss standard procedure = 2*n*2*q*p = 4*n*p = 0.016
Expected loss SpaceX procedure = n*q*2*p = 0.008

What this shows is that the SpaceX procedure is safer because less people are exposed to risk and that the crew escape system is safer than having the ground and flight crew try and get away using slide wires. As the Space Shuttle did not have an escape system, the standard procedure is the safest way.
« Last Edit: 01/18/2018 05:18 AM by Steven Pietrobon »
Akin's Laws of Spacecraft Design #1:  Engineering is done with numbers.  Analysis without numbers is only an opinion.

Offline watermod

  • Full Member
  • ****
  • Posts: 404
  • Liked: 109
  • Likes Given: 122
Re: ASAP still has concerns over Commercial Crew LOC risks
« Reply #77 on: 01/18/2018 05:40 AM »
So are the Dragon and the Starliner more dangerous for the astronauts to fly in then the Soyuz?    If not then NASA and the Congress should find other battles to quibble over.   If it is more dangerous than quibble away.

Online Steven Pietrobon

  • Member
  • Senior Member
  • *****
  • Posts: 17304
  • Adelaide, Australia
    • Steven Pietrobon's Space Archive
  • Liked: 5723
  • Likes Given: 729
Re: ASAP still has concerns over Commercial Crew LOC risks
« Reply #78 on: 01/18/2018 05:43 AM »
So are the Dragon and the Starliner more dangerous for the astronauts to fly in then the Soyuz?

I would say yes as both of these vehicles are unproven.
Akin's Laws of Spacecraft Design #1:  Engineering is done with numbers.  Analysis without numbers is only an opinion.

Offline deruch

  • Senior Member
  • *****
  • Posts: 2324
  • California
  • Liked: 1856
  • Likes Given: 4125
Re: ASAP still has concerns over Commercial Crew LOC risks
« Reply #79 on: 01/18/2018 06:22 AM »
Sad part is SpaceX has already proved at least 38 times in a row they can safely fuel F9 without blowing it up, and that's with some flight-proven 1st stages in the mix.

That's 19 times in a row since the last fuelling explosion on 1 September 2016 with AMOS 6. Lets try and get some numbers. I made some engineering guestimates.

Probability vehicle fails after loading = p = 0.01 (an engineering guess upper bound)
Probability vehicle fails during loading = 2*p = 0.02 (this is twice more dangerous)
Probability escape vehicle fails = q = 0.1 (remember seeing this somewhere)
Probability fail to get away from vehicle during fuelling = 2*q = 0.2 (assume twice more dangerous)
Number of flight crew = n = 4
Number of ground crew = n = 4 (assume same as flight crew)
Assume time to load propellants is same as time to load crew (half an hour).

Expected loss standard procedure = 2*n*2*q*p = 4*n*p = 0.016
Expected loss SpaceX procedure = n*q*2*p = 0.008

What this shows is that the SpaceX procedure is safer because less people are exposed to risk and that the crew escape system is safer than having the ground and flight crew try and get away using slide wires. As the Space Shuttle did not have an escape system, the standard procedure is the safest way.

And how do your numbers work if the probability of failure during fueling is 5 or 10 or 20 times higher than the static condition or if ground crew numbers are larger/smaller?  That's the point.  The relative safety is highly dependent on the variables and as outsiders we don't have a good idea of how they are determined/supported.  SpaceX obviously thinks their procedures are safer, NASA may remain skeptical.  But, neither position is unreasonable from their respective positions.  It's only right that SpaceX believes in their processes (so long as they have the test data to back them up) and it's right for NASA to make them prove it.  The only no-nos are for SpaceX to stick to their method "just because" or for NASA to stubbornly reject it even in the face of good supporting data because it's NIH (not invented here; i.e. not the way we've always done it).
Shouldn't reality posts be in "Advanced concepts"?  --Nomadd

Tags: