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Author
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Topic: Use of pressure suits on shuttle missions
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Jim_Voce
Member Posts: 273
From:
Registered: Jul 2016
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posted 04-29-2018 06:30 PM
   
I believe it was the STS-5 mission which was the first operational shuttle mission and this was the first of the shuttle missions where the crew did not wear pressure suits of any kind.The crew wore crash helmets however and it looked like these helmets had the ability to provide the crew with oxygen in the event of a depressurization. Is this correct? The overall decision to not fly with pressure suits I thought was odd. And I always wondered what the reasoning was with this. Was it thought that the air volume in the shuttle was such that in the event of a cabin leak, that the leak would be slow enough to get a crew home? Does anyone have any thoughts on this? |
Robert Pearlman
Editor Posts: 42988
From: Houston, TX
Registered: Nov 1999
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posted 04-29-2018 06:46 PM
The decision to wear pressure suits on STS-1 through STS-4 was primarily driven by the use of ejection seats at the commander and pilot stations. When the shuttle went "operational" with STS-5, there were now crew members who could not eject and had no means of escape. From Dennis Jenkins' "Dressing for Altitude: U.S. Aviation Pressure Suits—Wiley Post to Space Shuttle": NASA believed that all of the crew should have "equal access" to escape; therefore, if the astronauts on the middeck could not have ejection seats, then nobody would. It was a contentious argument in the astronaut office but one that ultimately concluded there would be no escape provisions for the operational flights. Hence, NASA did away with the pressure suits. The Launch Entry Helmet (LEH) did not provide protection for a decompression, as Jenkins further describes: Given that the astronauts did not wear any counter-pressure clothing, the LEH could not function as a pressure-breathing mask (at least not under any meaningful pressure) and since there were no contingency plans to bail out of the orbiter (and indeed, no parachutes), the helmet did not provide windblast protection. In reality, the only protection the helmet provided was against ambient noise during ascent, incidental bumping of the head against the inside of the crew module, and possible smoke in the cockpit. NASA returned to using a pressure suit after the loss of space shuttle Challenger in 1986 as a result of developing a bailout procedure for the crew. |
OV-105
Member Posts: 816
From: Ridgecrest, CA
Registered: Sep 2000
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posted 04-30-2018 12:03 AM
I thought they could get a good seal with the launch and entry helmets. They were used for emergency air for the crew on the pad if they had to get to the slide wires and also for the EVA pre breathing. |
DG27
Member Posts: 173
From: USA
Registered: Nov 2010
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posted 04-30-2018 04:31 AM
The LEH was basically an oxygen helmet, not a pressure helmet. It provided oxygen to the face cavity which was separated from the rest of the helmet by a light weight rubber face seal. The remainder of the helmet (and the head) was unpressurized. Although the wearer received oxygen at low pressures, the helmet could not function as a pressure helmet, and thus provided no depressurization protection. However, the helmet can be used like an oxygen mask for pre-breathing or hazardous gas inhalation protection, but not for low pressure exposure protection. Probably the main reason suits were not used in the shuttle was that the shuttle was designed to provide a shirt sleeve environment. As such, the shuttle environmental control system was not designed to operate with crew pressure suits during launch, re-entry or on-orbit. That was the design that was built and flown. No suits for operational use. I don't have the history on why the decision was made to design the shuttle to not use suits, but the required systems to operate the suits take up some payload capability. Also, familiarity and success can breed overconfidence. As Robert pointed out, during the early test flights they added the ejection seats and the SR-71 derived pressure suits. After the early flights the seats and suits went away, as they could not provide escape for larger crews. The shuttle had entered its shirt sleeve environment operational phase. The LEH and flight coveralls may have given some look of safety, and they kind of looked cool, but as Jenkins describes in his excellent book, the ensemble did not provide any depressurization protection. Even after the return to using suits, with both the S1032 partial pressure suits and the S1035 full pressure suits, the shuttle ECS was still not designed to operate with suits.
Closed loop suits like what was used on Mercury, Gemini, and Apollo would require a major ECS redesign. The open loop suit design that was chosen was a bit easier to implement, (only need to provide a source and a supply line to each suit) but still not compatible with the cabin ECS, as the exhaust of the suits dumped into the cabin environment. The result was undesirable oxygen enrichment of the cabin environment which resulted in the sometime practice of not putting on gloves and not closing the helmet visors, making the suits ineffective in an emergency.
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Fra Mauro
Member Posts: 1587
From: Bethpage, N.Y.
Registered: Jul 2002
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posted 04-30-2018 07:25 AM
I wonder why there would be an argument in the Astronaut Office over the use of pressure suits only on the flight deck after the first four mission. why should the people on the mid-deck be abandoned (or incinerated from the ejection seats) while the others had a chance of escaping? |
oly
Member Posts: 905
From: Perth, Western Australia
Registered: Apr 2015
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posted 04-30-2018 09:10 AM
It may not have been a choice of abandoning the mid deck crew, it may have been a case of being able to remain conscious so that the flight crew could attempt to bring the thing back. During launch the SRB sep altitude was approximately 150,000 feet, far too high for crew survival without full pressure suits if the shuttle suffered full cabin pressure loss. However, if a partial pressure loss (leak) was detected, the flight crew would need to be conscious for an RTLS, TAL or ATO abort. Should a hatch seal failure or structural leak warrant abort, someone needs to drive. While not the same conditions, this is a similar method used in commercial airliners. The crew dons pressure oxygen so they remain alert during depressurization until they can descend to safe altitude. The passengers get LP masks without a seal to keep them alive (but not necessarily conscious). |
Jim Behling
Member Posts: 1463
From: Cape Canaveral, FL
Registered: Mar 2010
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posted 04-30-2018 10:43 AM
quote:
Originally posted by OV-105:
...for the EVA pre breathing.
The LEH was not used for EVA rebreathing. There was a separate mask for that. |
OV-105
Member Posts: 816
From: Ridgecrest, CA
Registered: Sep 2000
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posted 04-30-2018 09:24 PM
They used them on 61-B.  |
Greggy_D
Member Posts: 977
From: Michigan
Registered: Jul 2006
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posted 04-30-2018 09:29 PM
And 41-C. |
David C
Member Posts: 1015
From: Lausanne
Registered: Apr 2012
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posted 04-30-2018 11:24 PM
quote:
Originally posted by oly:
It may not have been a choice of abandoning the mid deck crew...
It certainly was about not deserting crewmates. Even on STS-5 which still had ejection seats, Vance Brand was adamant that they would be pinned and unusable. quote:
The crew dons pressure oxygen so they remain alert during depressurization until they can descend to safe altitude.
Standard Boeing and Airbus equipment provides airmix to flight crew with oxygen proportion varying with altitude up to 100% but this is on demand not pressure. For smoke protection there is an emergency selection of 100% oxygen under slight positive pressure. This merely reduces the chances of smoke leaking into the mask, it is not pressure breathing. It is possible that some nations/airlines have their own requirements, but it is not the current norm. |
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