How is Spaceshuttle pressurised?

[capster]

Hi ,

Just woke up with this thought in my head. If I understand correctly space is a virtual vacuum, so where does the air come from to pressurise, and is there a compressor permanently running to compress it?? Also the delta P must be way up in the 800-900 bracket i assume - impressive!

Thanks to everyone cleverer than me

[Wyle E Coyote]

How does the guy who drives the snow plough get to work in the morning?

......So many unanswered questions

[csd]

My uneducated guess would be a cabin differential pressure of about 15 psi to hold an equivalent sea level pressure in the cabin (1013mb is about 15 psi)

Regards

csd

[deltayankee]

I think astronauts usually take bottled air with them. Might wind up Greenpeace but there's nothing else up there. The bottled stuff gets sent up by automatic cargo ships.

And I don't know about ISA conditions. In some space flights they used oxygen at a low pressure so that it was as breathable as earth air.

[capster]

That makes sense, but where does the air come from that gets pressurised?? I feel like i am missing something obvious

[Wyle E Coyote]

where does the air come from that gets pressurised??

it was already in there when they closed the doors.

It's a pressure vessel, close the doors and the ambient pressure remains the same no matter where you put it - under the sea or in space. all you need to worry about is the makeup of gasses changing due to respiration

[hedgehopper]

Crew Compartment Cabin Pressurization

The cabin is pressurized to 14.7 psia, plus or minus 0.2 psia, and maintained at an average 80-percent nitrogen and 20-percent oxygen mixture by the air revitalization system. Oxygen partial pressure is maintained between 2.95 and 3.45 psi, with sufficient nitrogen pressure of 11.5 psia added to achieve the cabin total pressure of 14.7 psia, plus or minus 0.2 psia.

The pressurization system consists of two oxygen systems and two gaseous nitrogen systems. The two oxygen systems are supplied by the PRSD oxygen system, which is the same source that supplies oxygen to the orbiter fuel cell power plants. The PRSD cryogenic supercritical oxygen storage system is controlled by electrical heaters within the tanks and supplies the oxygen to the ECLSS pressurization control system at a pressure of 835 to 852 psia in a gaseous state. The gaseous nitrogen supply system consists of two systems with two gaseous nitrogen tanks for each system. The nitrogen storage tanks are serviced to a nominal pressure of 2,964 psia at 80º F. If the auxiliary gaseous oxygen supply tank is installed, it is serviced to 2,440 psia at 80º F and stores 67.6 pounds of gaseous oxygen to provide high flow along with gaseous nitrogen. It would maintain the crew cabin at 8 psi with oxygen partial pressure at 2 psia. For normal on-orbit operations one oxygen and nitrogen supply system is used. For launch and entry both oxygen and nitrogen supply systems are used in addition to repressurization of the airlock.

The heart of the cabin pressurization is the nitrogen/oxygen control and supply panels, the PPO 2 sensor, and crew cabin positive and negative pressure relief valves. The nitrogen/oxygen control panel selects and regulates primary (system 1) or secondary (system 2) oxygen and nitrogen. The primary and secondary nitrogen/oxygen supply panels are located in the lower forward portion of the midfuselage. The primary and secondary oxygen supply systems have a crossover capability, as do the primary and secondary nitrogen supply systems. If installed, the auxiliary oxygen supply system is also controlled by the supply panel.

The oxygen and nitrogen supply systems provide the makeup cabin oxygen gas consumed by the flight crew and nitrogen for pressurizing the potable and waste water tanks and repressurizing the airlock. An average of 1.76 pounds of oxygen is used per flight crew member per day. Up to 7.7 pounds of nitrogen and 9 pounds of oxygen are expected to be used per day for normal loss of crew cabin gas to space and metabolic usage. The potable and waste water tanks are pressurized to 17 psia.

Oxygen from the respective PRSD cryogenic oxygen supply system is routed to the atmosphere pressure control oxygen sys tem 1 and system 2 supply valves. The atmosphere pressure control oxygen system 1 and system 2 supply valves are controlled by a switch on panel L2. When the switch is positioned to open, the corresponding oxygen system valve opens to permit oxygen to flow through an oxygen restrictor at a maximum flow of 20 pounds per hour and to a heat exchanger in the Freon-21 coolant loop (oxygen system 1 through Freon coolant loop 1 and oxygen system 2 through Freon coolant loop 2), which warms the oxygen supply to the oxygen regulator of that system. A talkback indicator next to the switch indicates op when the valve is open. When the atm press control O 2 sys 1 or sys 2 switch is positioned to close, the valve is closed, isolating that oxygen supply system. The talkback indicator indicates cl . A check valve downstream of the heat exchanger prevents oxygen from flowing from one supply source to the other if the crossover valves are open. Downstream of the oxygen check valve is a manifold with an oxygen systems 1 and 2 crossover valve that would permit system 1 to system 2 or vice versa. The crossover valves are controlled by the atm press control O 2 xovr sys 1 and sys 2 switches on panel L2. When the respective switch is positioned to open, that oxygen supply system is directed to airlock supply oxygen 1 and 2 manual valves, airlock oxygen 1 and 2 extravehicular mobility unit, and eight face mask outlets. If both atmosphere pressure control oxygen pressure system 1 and system 2 crossover valves are opened, oxygen supply systems 1 and 2 are interconnected. When the respective atm press control O2 press sys 1 or sys 2 xover switch is positioned to close, that oxygen supply system is isolated from the crossover feature.

The oxygen supply systems are directed to their corresponding oxygen regulator inlet manual valve. When the valve is manually positioned to open on panel M010W, the oxygen supply system is directed to its oxygen regulator, which reduces that oxygen supply source pressure to 100 psi with a minimum flow rate capability of 75 pounds per hour. Each regulator is a two-stage regulator with the second stage functioning as a relief valve when the differential pressure across the second stage is 215 psi. The relief pressure is vented into the crew cabin. This regulated pressure passes through another check valve and is directed to its 14.7-psi cabin regulator inlet manual valve, 8-psi regulator and payload oxygen manual valve for Spacelab (if the Spacelab pressurized module is installed in the payload bay) on panel M010W. The check valve on each oxygen supply system between the oxygen regulator and 14.7-psia cabin regulator prevents the reverse flow of oxygen and nitrogen into the oxygen system since the 14.7-psi and 8-psi regulators in each system control the oxygen and nitrogen flow to the cabin as required to maintain the desired cabin pressure.

The two primary and two secondary gaseous nitrogen supply tanks are constructed of filament-wound Kevlar fiber with a titanium liner. Each nitrogen tank is serviced to a nominal pressure of 3,300 psia at 80º F with a volume of 8,181 cubic inches. The two nitrogen tanks in each system are manifolded together. The primary and secondary nitrogen supply systems are controlled by the atmosphere pressure control nitrogen supply valves in each system. Each valve is controlled by its corresponding atm press control N 2 sys 1 and 2 supply switch on panel L2. When a supply switch is positioned to open, that nitrogen supply system is directed to its corresponding atmosphere pressure control system regulator inlet valve. An indicator adjacent to the switch indicates barberpole when the motor-operated valve is in transit and op when the supply valve is open. When the supply switch is positioned to close, that nitrogen supply system is isolated from the nitrogen system regulator inlet valve, and the talkback indicator indicates cl.

The inlet valve in each nitrogen system is controlled by its respective atm press control N 2 sys 1 and 2 reg inlet switch on panel L2. When a reg inlet switch is positioned to open , that system's nitrogen source pressure is directed to the system's nitrogen regulator. A talkback indicator next to the reg inlet switch indicates barberpole when the motor-operated valve is in transit and op when the valve is open. When the reg inlet switch is positioned to close, the nitrogen supply pressure is isolated from the system's nitrogen regulator, and the talkback indicator indicates cl.

The nitrogen regulators in the primary and secondary supply system reduce the pressure to 200 psi. Each nitrogen regulator is a two-stage regulator with the second stage functioning as a relief valve. The second stage relieves pressure overboard at 245 psi.

The regulated pressure of each nitrogen system is directed to the nitrogen manual crossover valve, the water tank regulator inlet valve and the oxygen and nitrogen controller valve in each system.

The nitrogen crossover manual valve connects both regulated nitrogen systems when the valve is open and isolates the nitrogen supply systems from each other when closed. A check valve between the nitrogen regulator and nitrogen crossover valve in each nitrogen-regulated supply line prevents flow from one nitrogen source supply pressure to the other if the nitrogen crossover valve is open.

The partial pressure of oxygen in the flight crew cabin can be controlled automatically by one of two oxygen and nitrogen controllers. Two PPO2 sensors are located under the crew cabin flight deck mission support console. The PPO 2 A and B sensors provide inputs to the PPO2 control systems 1 and 2 controller and switches, respectively.

When a PPO2 contr switch is positioned to norm on panel M010W and the atm press control PPO 2 snsr/vlv switch on panel L2 is positioned to norm, electrical power is supplied to the corre sponding atm press control O 2 /N 2 cntlr vlv switches on panel L2 for system 1 or 2. When the atm press contlr vlv switch is positioned to auto, electrical power automatically energizes or de-energizes the corresponding nitrogen control valve and nitrogen-regulated supply. When the corresponding PPO 2 sensor determines that oxygen is required in the crew cabin to maintain the level at 3.5 psi, the nitrogen supply valve is automatically closed. When the 200-psi nitrogen supply in the manifold drops below 100 psi, the corresponding oxygen supply system flows through its check valve and 14.7-psi cabin regulator into the crew cabin. When the PPO2 sensor determines that the oxygen in the crew cabin is at 3.2 psi, the corresponding nitrogen supply system valve is automatically opened, the 200-psi nitrogen enters the oxygen and nitrogen manifold and closes the corresponding oxygen supply system check valve, and nitrogen flows through the 14.7-psi regulator into the crew cabin. The open and close positions of the O 2 /N 2 cntlr vlv sys 1 and 2 switch on panel L2 permit the flight crew to control the nitrogen valve in each system manually, and thus cabin pressure is controlled manually. The reverse position of the PPO 2 snsr/vlv switch on panel L2 allows controller B to system 1 and controller A to system 2.

If the 14.7-psi cabin regulator inlet manual valves of systems 1 and 2 are closed on panel M010W, the crew module cabin pressure will decrease to 8 psi. The PPO2 contr sys 1 and sys 2 switches on panel M010W are positioned to emer for the corresponding nitrogen system, which selects the 2.2-psi oxygen partial pressure. The corresponding PPO 2 sensor and controller, through the corresponding PPO 2 contr switch and the PPO2 snsr/vlv switch positioned to norm , provide electrical inputs to the corresponding O 2 /N 2 cntrl vlv switch. The electrical output from the applicable O 2 /N 2 cntrl vlv switch controls the nitrogen valve in that supply system in the same manner as in the 14.7-psi mode except that the crew module cabin oxygen partial pressure is maintained at 2.2 psi.

The oxygen systems 1 and 2 and nitrogen systems 1 and 2 flows are monitored and sent to the O 2 /N 2 flow rotary switch on panel O1. The rotary switch permits system 1 oxygen or nitrogen or system 2 oxygen or nitrogen flow to be monitored on the flow meter on panel O1 in pounds per hour.

PPO2 sensors A and B monitor the oxygen partial pressure and transmit the signal to the PPO 2 sensor select switch on panel O1. When the switch is positioned to sensor A, oxygen partial pressure from sensor A is monitored on the PPO 2 meter on panel O1 in psia. If the switch is set on sensor B, oxygen partial pressure from sensor B is monitored. The cabin pressure sensor transmits directly to the cabin press meter on panel O1 and is monitored in psia.

The red cabin atm caution and warning light on panel F7 is illuminated for any of the following monitored parameters:

Cabin pressure below 14.0 psia or above 15.4 psia.
PPO2 below 2.8 psia or above 3.6 psia.
Oxygen flow rate above 5 pounds per hour.
Nitrogen flow rate above 5 pounds per hour.
A klaxon will sound in the crew cabin and the master alarm push button light indicators will be illuminated if the change in pressure versus change in time decreases at a rate of 0.05 psi per minute or greater. The normal cabin dP/dT is zero psi per minute, plus or minus 0.01 psi, for all normal operations.

The temperature and pressure of the primary and secondary nitrogen and emergency oxygen tanks are monitored and transmitted to the systems management computer. This information is used to compute oxygen and nitrogen quantities.

The two cabin relief valves are in parallel to provide overpres surization protection of the crew module cabin above 16 psid. Each cabin relief valve is controlled by its corresponding switch on panel L2. The cabin relief A switch controls cabin relief A, and the cabin relief B switch controls cabin relief B. When the switch is positioned to enable, the corresponding motor-operated valve allows the cabin pressure to a corresponding positive pressure relief valve that relieves at 16 psid and reseats at 15.5 psid. The relief valve maximum flow capability is 150 pounds per hour. A talkback indicator above the respective switch indicates barberpole when the motor-operated valve is in transit and op when the motor-operated valve is open. When the switch is positioned to close , the corresponding motor-operated valve isolates cabin pressure from the relief valve, and the talkback indicator indicates cl.

The crew module cabin vent isolation valve and cabin vent valve are in series to vent the crew cabin to ambient pressure. Approximately one hour and 30 minutes before lift-off, the crew module cabin is pressurized to approximately 16.7 psi for leak checks of the crew cabin. The cabin vent isolation valve is controlled by the cabin vent , vent isol switch on panel L2, and the cabin vent valve is controlled by the cabin vent, vent switch on panel L2. Each switch is positioned to open to control its respective motor-operated valve. When both valves are open, the cabin pressure is vented into the midfuselage. The maximum flow capability through the valves at 0.2 psid is 900 pounds per hour. A talkback indicator above each switch indicates the position of the respective valve-barberpole when the valve is in transit and op when it is open.

If the crew cabin pressure is lower than the pressure outside the crew cabin, two negative pressure relief valves in parallel will open at 0.2 to 0.7 psid, permitting flow of ambient pressure into the crew cabin. The maximum flow rate at 0.5 psid is zero to 654 pounds per hour.

Source: NASA.


Hedgehopper.

[Wyle E Coyote]

..............please tell me you didn't just type all that

[mgTF]

but how can they seal the ship? and why our planes compared to, look more like swiss emmental?

[flyr767]

As Porky Pig would say "Th-th-th-that's all folks!" hedgehopper took it away on that one. The space shuttle is a weird vehicle anyway. I'll stick to aircraft.

[capster]

Thanks hedgehopper! Now once ive deciphered that (should only take 5 weeks:}) I'll be satisfied!!:D

[chksix]

Great info here:
http://spaceflight.nasa.gov/shuttle/reference/sodb/

The cabin of the shuttle is actually a capsule inside the outer skin of the orbiter. All windows are double glassed and the outer skin has an outer pane of glass also so in total three layers.

[BRS_flyer]

In some space flights they used oxygen at a low pressure so that it was as breathable as earth air.

Yeah, pre space shuttle US space program flights all used pure O2 pressurised at about 5psi, as the lower pressure meant less strain on the pressure compartment. This caused additional complications during ASTP (First Docking of US and Soviet spacecraft in 1975) as Soviet Craft used 14 PSI mix of Oxygen and Nitrogen. They went with this mix for the space shuttle as it is more like the earths atmosphere and so more suited to longer flights.

Not sure about the Space Shuttle but Russian space stations have employed forms of Oxygen Generating units, not sure of how they work exactly and Lithium Hydroxide cannisters for removing CO2 form the atmosphere.

Also, if anyone is interested; additional oxygen is carried in tanks to power spacecraft fuel cells. They burn Hyrogen and Oxygen to generate electricity for the ships systems and a byproduct is Water, which can be drunk by the crew.

[WHBM]

As I understand it the Apollo programme (and presumably predecessors) was designed for 100% oxygen. The Apollo 1 fire showed the folly of this approach and the breathable air mixture was changed to an 80% nitrogen - 20% oxygen one (which presumaby means you need to take 5 times as much gas with you).

[capster]

Thanks guys interesting stuff. Isnt that generator that burns Hydrogen and O2 with H20 as a byproduct the answer to "global warming" or does Shell disagree?

[BRS_flyer]

Fuel cells of the type used in spacecraft use liquid hydrogen and, which must be kept below -252C. It is good for use in spacecraft as that fuel type usually needs to be present anyway to power rocket engines as does Oxygen for the breathing.

However the technology is being developed for automotive (and possibly aviation) use, see here for info: http://en.wikipedia.org/wiki/Fuel_cell#Hydrogen_transportation_and_refueling

[Check Airman]

hedgehopper gets my vote for post of the day. Thanks

[mason]

The snowplougher takes the plough home with him and parks it backwards
therefore he just hopes in in the morning...happy days

[hedgehopper]

Check Airman, Thanks for the vote, but it was a Cut 'N' Paste from Nasa::rolleyes:

http://spaceflight.nasa.gov/shuttle/reference/shutref/index.html

There is a fundamental difference between Aircraft & Space craft when one considers Pressurization.

Basically: Aircraft fly in the reservoir of air that is used for pressurization, whereas space craft (currently) need to generate (albeit a by-product of fuels) or carry reservoirs of pure gasses to create the same.

In aircraft: air is drawn from its’ surroundings by using engine driven “Blowers or Compressors” to provide a flow of air through the pressure vessel, outflow valves control the pressure and since the reservoir is effectively endless, the blowers/compressors can supply more air than is necessary just to pressurize, so leaks here and there are of no real consequence. (Obviously a bad door seals etc. have an effect)
However in a spacecraft since the source is in short supply, the pressure vessel it’s self has to be of a higher standard, NO or Very Low losses.

Hope that helps?

[B Fraser]

The apollo 1 issue was that 100% O2 was used in a capsule test at sea level pressure i.e. 1000mb of O2 in round numbers. One spark and the rest is history. They didn't stand a chance as the massive rise in internal pressure held the door shut against the outside air.

The atmospheric system in-flight was designed to supply O2 at about 200mb, about the same partial oxygen pressure as the air we breath at sea level. The result was that the capsules could be designed to be light as you could get away with extremely thin walls. The skin on the lunar module was so thin that it could be punctured by a biro. The acceleration forces experienced on the ascent from the moon would often buckle the airframe.

[chornedsnorkack]

ISA at tropopause (11 km) is about 220 mb. If you filled your plane with pure oxygen, you could fly unpressurized to FL370 or above (how high?)

[moggiee]

but how can they seal the ship? and why our planes compared to, look more like swiss emmental?
Very good seals and strong locks/latches.

There are also fewer holes built into it in the first place - aeroplanes have basin drains, outflow valves, lots more doors and hatches unlike spacecraft which are more like a baked bean tin with a single door in.

To be brutally honest, I would have thought it was obvious! :)

[mgTF]

here's another question,
how does it work when they go outside for a walk, is there a sort of mini room with a vacuum system preventing internal air to dispel outside?

[wiggy]

There have been some good replies here but the answer to most of this can be best found on the NASA shuttle pages... try typing "Space shuttle" into Google and then going into the NASA pages - I think, mgTF, that 'external airlock" might be the answer to your question.

moggiee - to be brutally honest I agree:ok:, I'm just trying to be kind:O

[B Fraser]

If you filled your plane with pure oxygen, you could fly unpressurized to FL370 or above (how high?)

You would have to pre-breath neat O2 for a couple of hours beforehand and all the way up to altitude until your body was free of nitrogen. Decompression sickness can ruin your whole day.

[Tinstaafl]

Capster, the change in pressure is not that high. Rather less than what your car tyres have to hold.

Your car's tyre is at something like 50 psi total pressure - more after a long drive when the tyre has been heated by friction - the atmosphere around it is at ~15 psi (slightly less & variable so rounded for convenience) so the tyre's difference is ~35 psi. That 35 psi (or 32 or whatever you usually inflate your tyre to) is what we usually think of when we think about how much pressure the tyre holds. We tend to forget this measurement is relative to the atmosphere, not absolute.

Meanwhile, both relatively & absolutely, the shuttle's interior is held at 14.7 psi, the exterior is at 0 psi (near enough) so the difference is......14.7 psi!

[moggiee]

here's another question,
how does it work when they go outside for a walk, is there a sort of mini room with a vacuum system preventing internal air to dispel outside?
You don't watch enough telly!

UFO, Space 1999, Star Wars, 2001, Alien, Solaris etc. - any of those will give you your answer.

[Tinstaafl]

You must mean they have teletransporters to beam them outside, Moggiee! Amazing. I mean, how else could it be done? :8

[rsuggitt]

In a word, airlocks.

[TURIN]

In a word, airlocks.

There's no need for that sort of language. :)

[moggiee]

You must mean they have teletransporters to beam them outside, Moggiee! Amazing. I mean, how else could it be done? :8
Transporters are "Star Trek" and "Blake's 7" - all my references are clearly airlock users!

[james ozzie]

Although a pure oxygen atmosphere allows lower cabin pressure & and solves lots of engineering problems, the fire hazard gets way too high. The deadly Apollo 1 launch pad fire ended pure oxygen cabins. By the way, track down (Wiki) the transcript of Flight Director Gen Kranz's address to the team after the accident - an excellent speech that is as good and relevant today as it was 40 years ago.

[wiggy]

"The deadly Apollo 1 launch pad fire ended pure oxygen cabins"...Er, no it didn't, or at least not immediately - all the subsequent Apollo missions flew, manned, with pure Oxygen enviroments. What did stop post Apollo 1, amongst other things, was the procedure of pumping the Cabin up to greater than 15 psi with pure Oygen pre-launch ( Or in Apollo 1's case, a launch rehearsal). That, procedure, plus the uncontrolled spread/use of infalammable material in the Command Module (e.g. velcro), played a major part in the spread of the fire in Apollo 1.

[ShyTorque]

baked bean tin

I thought baked beans were a banned substance on all space flights. :ooh:

[hedgehopper]

Parp:

Pardon me...

[Capt Pit Bull]

I'd like to take this opportunity to recommend the HBO series 'From the earth to the moon', (one episode of which, incidentally, cover the Apollo 1 accident.)

I found this to be a very interesting, well made and also deeply moving series and an absolute must for anyone interested in space flight. Each episode considers different aspects of the Gemini and Apollo programmes.

BTW I don't get a cut from HBOs DVD sales, though perhaps I ought to!

pb

[chris weston]

I'm pretty sure its Lithium Peroxide not Hydroxide that's used as the peroxide scrubs to the carbonate and oxygen in 2:1 redox stoichiometry.

The Hydroxide simply neutralises to the carbonate.

Forgive the lack of subscripts and yes I know it's ionic really but it goes like this

2Li2O2 + 2CO2 = 2Li2CO3 + O2

cf

Li(OH)2 + CO2 = LiCO3 + H2O


CW

[chris weston]

Try

2LiOH + CO2 = Li2CO3 + H2O

Clicked too fast

Sorry pardon

CW

[Spanner Turner]

From Space Shuttle Reference Manual (available at NASA website),

The cabin air from the cabin fan is ducted to the two lithium hydroxide canisters, where carbon dioxide is removed and activated charcoal removes odors and trace contaminants. An orifice in the duct directs a specific amount of cabin air through each lithium hydroxide canister. The canisters are also located under the middeck floor. They are changed alternately every 12 hours through an access door in the floor. For a flight crew of seven, the lithium hydroxide canisters are changed alternately every 11 hours. Replacement canisters are stored under the middeck floor between the cabin heat exchanger and water tanks.

:ok:

[Wyle E Coyote]

This'll keep the boys and girls happy,

......activated charcoal removes odors and trace contaminants

"change the filter lads, it baked beans tonight"

[crushenator]

in my mind, if you were to put a 747 into orbit, the internal air pressure and the outside vaccum would surely make it rip open? the space shuttle must be made of some strong stuff :8

[chksix]

Here you can see how they were built up:
http://forum.nasaspaceflight.com/forums/thread-view.asp?tid=4538&start=1
http://forum.nasaspaceflight.com/forums/thread-view.asp?tid=7231&start=1

There's a pressure hull like on a submarine that is placed inside the outer unpressurised hull that we see. The cabin is a capsule and is connected to the airlock with the docking mechanism.

Good view of the capsule:
http://forum.nasaspaceflight.com/forums/get-attachment.asp?action=view&attachmentid=13200

And the outer hull where it will be placed:
http://forum.nasaspaceflight.com/forums/get-attachment.asp?action=view&attachmentid=13206

Hope it helps :8 :O

[wiggy]

I can't do the chemistry but all the sources I've seen over the years state that Lithium Hydroxide, not Peroxide, that has been used as the Carbon Dioxide "scrubber" in US spacecraft, right back to the days of Mercury.

[Old Aero Guy]

"...in my mind, if you were to put a 747 into orbit, the internal air pressure and the outside vaccum would surely make it rip open? the space shuttle must be made of some strong stuff..."

Not really. When things were going slow for Boeing in the early 1970's, they proposed the 737 fuselage to NASA as the basis of an orbiting laboratory to be carried to orbit by the space shuttle.

The differential pressure capability of the basic 737 fuselage would have been fine for pure O2, partial pressure environment.

[chornedsnorkack]

"...in my mind, if you were to put a 747 into orbit, the internal air pressure and the outside vaccum would surely make it rip open? the space shuttle must be made of some strong stuff..."

Not really. When things were going slow for Boeing in the early 1970's, they proposed the 737 fuselage to NASA as the basis of an orbiting laboratory to be carried to orbit by the space shuttle.

The differential pressure capability of the basic 737 fuselage would have been fine for pure O2, partial pressure environment.

Look at it this way: a jet which flies at 40 000 feet has about 4/5 of the atmosphere below and only 1/5 above. At 12 000 m, ISA is 194 mbar

The passenger planes are normally not pressurized to sea level - it would make them too heavy, and humans do have some ability to deal with lower pressure in mountains and elsewhere. Roughly 3/4 of the sea level pressure is regarded as enough: at 2500 m, ISA is 747 mbar.

This leaves 553 mbar differential to be borne by the fuselage. 553 mbar pressure can be found between 4500 and 5000 m.

People live at that height - sleep, drive cars, bear children, without additional oxygen. People who have just travelled there suffer mountain sickness, though. But oxygen can fix that completely.

[crushenator]

nah i didnt mean it as in anything to do with being able to live in a partial atmosphere with breathable air, i meant that because the cabin of the shuttle is pressurised (wether it be to sea level or 3/4 of sea level), and a few inches outside of that pressurised cabin is just a pure vaccum of nothingness, then the shuttle has to be structurally very strong. :ok:

[Tinstaafl]

That depends what you mean by "...very strong." In comparison to other pressure shells it's not a hugely enormous must-add-another-inch-of-steel-plate step. Even if SL pressure is maintained in space, the max differential is only ~15 PSI ie around half of what your car tyre contains. Some Gulfstream business jets have a max differential of ~10 PSI. so the shuttle would only require another 50% gain (ignoring any other structural requirements). If the shuttle's cabin pressure was kept at half sea level pressure then the pressure differential would be ~7 or 8 PSI - less than the Gulfstream's maximum ability and in the same range as many other jets.

[stilton]

All impressive stuff, she flew over my house tonight with 2 loud bangs.

It's not Apollo but will certainly be missed when she's gone.

[gr8shandini]

Keep in mind that the max delta p on an airframe is based on fatigue life and not ultimate load. Therefore, the structure required to support pressurizing the space shuttle over its 100 flight life cycle might not be significantly heavier than that required to pressurize a 737 tens of thousands of times.