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TEIF: Behind the scenes

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Re: TEIF: Behind the scenes
Post by tlb   » Mon May 02, 2022 7:06 am

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Loren Pechtel wrote:There is some ability to turn but it loses a lot of power in doing so. A building doesn't make you invulnerable, but the more it has to turn to get to you the weaker it will be.

kzt wrote:Blast barriers offer useful reduction in blast wave only if you are essentially right next to it on the protected side. If you are some distance away there is negligible benefit. IIRC, you have to be closer to the barrier than the barrier is high to get a significant benefit. But I may be remembering that wrong.

Loren Pechtel wrote:Yeah, that's what I'm talking about--near a barrier. Say, in a hole in the ground when the blast wave passes over.

You are still taking a chance on the geometry: for example you could be too close to an air burst that has some line of sight into that hole. Or that it makes the turn into your hiding spot and "loses a lot of power"; but still has enough power to damage, if you are too close.
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Re: TEIF: Behind the scenes
Post by Loren Pechtel   » Mon May 02, 2022 7:11 pm

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tlb wrote:
Loren Pechtel wrote:There is some ability to turn but it loses a lot of power in doing so. A building doesn't make you invulnerable, but the more it has to turn to get to you the weaker it will be.

kzt wrote:Blast barriers offer useful reduction in blast wave only if you are essentially right next to it on the protected side. If you are some distance away there is negligible benefit. IIRC, you have to be closer to the barrier than the barrier is high to get a significant benefit. But I may be remembering that wrong.

Loren Pechtel wrote:Yeah, that's what I'm talking about--near a barrier. Say, in a hole in the ground when the blast wave passes over.

You are still taking a chance on the geometry: for example you could be too close to an air burst that has some line of sight into that hole. Or that it makes the turn into your hiding spot and "loses a lot of power"; but still has enough power to damage, if you are too close.


I'm not "taking a chance", I'm proposing about the only scenario where the negative pressure could possibly matter. Anything else anyone at risk from the negative pressure is already dead.
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Re: TEIF: Behind the scenes
Post by tlb   » Mon May 02, 2022 7:22 pm

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Loren Pechtel wrote:I'm not "taking a chance", I'm proposing about the only scenario where the negative pressure could possibly matter. Anything else anyone at risk from the negative pressure is already dead.

Okay, I am good with that. I said all along that the only way that I could see the negative pressure being more significant than the blast front was at the very margins. We know from NASA that a person has survived an exposure to a hard vacuum for as much as 30 seconds with minimal damage.
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Re: TEIF: Behind the scenes
Post by kzt   » Mon May 02, 2022 7:38 pm

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tlb wrote:Okay, I am good with that. I said all along that the only way that I could see the negative pressure being more significant than the blast front was at the very margins. We know from NASA that a person has survived an exposure to a hard vacuum for as much as 30 seconds with minimal damage.

Nobody on Columbia got their visor down, which is all they needed to do to seal their suit. This strongly implies actual functional time in vacuum is not as long as tests suggest.
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Re: TEIF: Behind the scenes
Post by Jonathan_S   » Mon May 02, 2022 8:49 pm

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Loren Pechtel wrote:You are still taking a I'm not "taking a chance", I'm proposing about the only scenario where the negative pressure could possibly matter. Anything else anyone at risk from the negative pressure is already dead.
It would be the only chance - but I don't think it's a likely chance.

My initial guess would be that most people sufficiently protected from the overpressure blast are going to be somewhere where the low pressure that follows it also wouldn't be quickly change their surrounding atmospheric pressure down to any kind of dangerously low psi. (And that's assuming that the psi in the low pressure zone gets low enough to be dangerous in the first place; which I'm not convinced of)


Still, you could imagine hypothetical scenarios involving large one-way hatches (storm cellar doors for example) that might prevent overpressure from coming in but not air pushing out into (relative) vacuum. But even if the "vacuum" is deadly, and even if it could kill people who'd somehow survived the blast wave, the vast majority of deaths (and injuries for that matter) would come from the blast not the following vacuum.


So it just seems weird that some reporting is so focused on the later, minor, effect rather than the former, major, one. Any why focus on the the vacuum rather than on their asphyxiating effect if used in enclosed, low airflow, spaces (like caves)? Unlike a regular explosive the thermobaric FAE consumed lots of atmospheric oxygen as oxidizer for its fuel -- in an enclosed space that wasn't blown open by the explosion that could so deplete the oxygen that survivors might asphyxiate before natural air exchange replaced the excess CO2 with fresh O2.
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Re: TEIF: Behind the scenes
Post by tlb   » Mon May 02, 2022 8:57 pm

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tlb wrote:Okay, I am good with that. I said all along that the only way that I could see the negative pressure being more significant than the blast front was at the very margins. We know from NASA that a person has survived an exposure to a hard vacuum for as much as 30 seconds with minimal damage.

kzt wrote:Nobody on Columbia got their visor down, which is all they needed to do to seal their suit. This strongly implies actual functional time in vacuum is not as long as tests suggest.

Columbia disintegrated on re-entry, so I am not sure that is a good measure. Sealing their suits was not going to be their main concern.

The NASA employee that experienced hard vacuum did it as an accident, not as a planned test.
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Re: TEIF: Behind the scenes
Post by tlb   » Mon May 02, 2022 9:08 pm

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Jonathan_S wrote:So it just seems weird that some reporting is so focused on the later, minor, effect rather than the former, major, one. Any why focus on the the vacuum rather than on their asphyxiating effect if used in enclosed, low airflow, spaces (like caves)? Unlike a regular explosive the thermobaric FAE consumed lots of atmospheric oxygen as oxidizer for its fuel -- in an enclosed space that wasn't blown open by the explosion that could so deplete the oxygen that survivors might asphyxiate before natural air exchange replaced the excess CO2 with fresh O2.

They are obviously conflating the two effects, using "vacuum" as shorthand for the consumption of the oxygen. In a cave you might get carbon monoxide production also.
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Re: TEIF: Behind the scenes
Post by kzt   » Mon May 02, 2022 10:33 pm

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tlb wrote:Columbia disintegrated on re-entry, so I am not sure that is a good measure. Sealing their suits was not going to be their main concern.
.

Most people tend to find that breathing is really, really important and doing things that allow you continue breathing tends to be top of mind. Particularly when you are not trying to, say, get the hydraulics back on line.
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Re: TEIF: Behind the scenes
Post by tlb   » Mon May 02, 2022 11:00 pm

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tlb wrote:Columbia disintegrated on re-entry, so I am not sure that is a good measure. Sealing their suits was not going to be their main concern.

kzt wrote:Most people tend to find that breathing is really, really important and doing things that allow you continue breathing tends to be top of mind. Particularly when you are not trying to, say, get the hydraulics back on line.

You are correct that NASA claimed that they "probably survived the initial breakup of Columbia, but lost consciousness in seconds after the cabin lost pressure". The statement from the following website does not state how much destruction or violent motion was occurring as the cabin lost pressure, but it was certainly much too late to "get the hydraulics back on line".

From Space.com "Columbia Disaster: What happened and what NASA learned":
On Feb. 1, 2003, the shuttle made its usual landing approach to the Kennedy Space Center. Just before 9 a.m. EST, however, abnormal readings showed up at Mission Control. Temperature readings from sensors located on the left wing were lost. Then, tire pressure readings from the left side of the shuttle also vanished.

The Capcom, or spacecraft communicator, called up to Columbia to discuss the tire pressure readings. At 8:59:32 a.m., Husband called back from Columbia: "Roger," followed by a word that was cut off in mid-sentence.

At that point, Columbia was near Dallas, traveling 18 times the speed of sound and still 200,700 feet (61,170 meters) above the ground. Mission Control made several attempts to get in touch with the astronauts, with no success.

--- snip ---

Much later, in 2008, NASA released a crew survival report detailing the Columbia crew's last few minutes. The astronauts probably survived the initial breakup of Columbia, but lost consciousness in seconds after the cabin lost pressure. The crew died as the shuttle disintegrated.
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Re: TEIF: Behind the scenes
Post by kzt   » Tue May 03, 2022 2:53 am

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However, the R2 panel, to the immediate right of the PLT on the flight deck (figure 3.3-2), warranted further investigation. This panel contains the primary controls for the auxiliary power units (APUs). The APUs drive the hydraulic pumps that provide hydraulic pressure to the flight control surface actuators. During entry, these surfaces become increasingly important to vehicle control, and loss of hydraulic pressure can have catastrophic results. Reconstructed general purpose computer (RGPC)-2 data revealed that the hydraulic systems failed prior to GMT 14:00:03 while the crew was conscious and capable of taking action.

When recovered, the R2 panel was folded back in on itself (figure 3.3-3), protecting the innermost switches from manipulation during recovery operations. The switch positions were considered to be unaltered by external factors, making the switches valuable in determining crew actions.

The panel was pried open during the investigation and switch positions were reviewed. In figure 3.3-4, all out-of-position switches are outlined with a pink box and noted with a pink dot.

The APU 2 and APU 3 Operate switches (“lever lock” switches that require two independent actions to change the switch position) were found in the “injector cool” position as opposed to the nominal “start/run” position. These switches are used when starting and stopping the APU. The “injector cool” position is used to cool down the APU after a shutdown prior to restarting it.

The remaining out-of-position switches are paddle-type switches that require just a push to move out of position. The switches on the left side of the panel are main engine-related switches that are not used during entry.5 The two paddle-type switches in the lower center of the panel are the circulation pump switches for
hydraulic systems 2 and 3. These were found in the “on” position as opposed to the normal “off” position. The circulation pump is used for thermal conditioning of the hydraulic fluid while the orbiter is on orbit. The pump also is used to keep the hydraulic reservoir pressurized. This pump is not powerful enough to
deploy the landing gear, but it can provide some hydraulic pressure if activated. The pump is neither used nominally on entry nor is it used in off-nominal procedures.

At the end of RGPC-2 (GMT 14:00:05), all three APUs were operating but the hydraulic systems pressures and quantities were zero, presumably due to a loss of hydraulic fluid from damage to the left wing. While the crew members could not know the reason for the low hydraulic pressure, they would know from training that a loss of hydraulic pressure would result in a vehicle LOC such as they were experiencing.

In response to a hydraulic system failure, the procedures require shutting down the APUs by placing the APU Operate switches in the “off” position, then moving the APU Operate switches into the “injector cool” position to cool down the APUs before attempting a restart of the APUs. RGPC-2 data indicate that the APU Operate and hydraulic circulation pump switches were in their nominal, expected positions.6 Therefore, these switches changed position after GMT 14:00:05, 13 seconds prior to the Catastrophic Event (CE).

Because the R2 panel was recovered folded in half and the APU Operate switches were not accessible, it is concluded that these switch positions were not altered during recovery operations. While the possibility exists for the lever lock switches to move due to random debris-debris interaction, the requirement for specific physical actions to enable switch movement makes it much more probable that the PLT deliberately moved the switches in an effort to regain hydraulic pressure and control of the vehicle. The paddle switches for the circulation pumps would be more subject to movement due to debris contact. However, the switches that were out of position (for hydraulic systems 2 and 3) correspond to the same APUs (APUs 2 and 3), lending credence to the theory that the actions were deliberate.

The catastrophic events that led to the loss of Columbia are not simulated in training or covered by existing systems procedures. The crew’s attempt to recover at least two APUs by selecting the “injector cool”position and, in the interim, providing some hydraulic pressure to the flight control surfaces through the use of the circulation pump demonstrates remarkable aplomb. Their effort to regain hydraulic pressure to recover vehicle control shows excellent knowledge of the orbiter systems and problem-resolution techniques. This also indicates that deliberate crew actions (such as manipulating specific switches) were possible for some period of time after GMT 14:00:05, indicating that the CM was still pressurized and the dynamics of the out-of-control vehicle were not incapacitating.
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