747 in space

[bloodgusher]

Many years ago I read a very bad SF novel in which a 747 was put into space. Seemed pretty silly to me at the time but I always wondered what would happen if you strapped some really big boosters onto a 747 and tried it.

According to the web, the cabin pressure in a 747 is set at about 6000 to 8000 feet and the max altitude of a 747 is around 45000 feet. So the hull has to withstand a pressure difference of something like 8.8 psi. This means that if you put it in space, you could have 8.8psi cabin pressure, equivalent to normal air pressure at around 13000 feet. Some ski resorts have peaks this high.

I wonder how leaky the cabin is in a 747. In space, you can't compress exterior air and inject it into the cabin so you might have to carry air tanks to replace leaked air.

And then there's radiation, but never mind that.

Apart from that, seems like it might actually work.

[Brotoro]

If you increase the percentage of oxygen in your air, you can use lower pressure without the problem of altitude sickness that some people experience at 13000 feet.

But there is an increase in fire danger.

[Nibb31]

Cabin pressure would be the least of your problems, I think.

The whole airframe would rip itself as soon as it hits Mach 1.

Edited June 25, 2013 by Nibb31

[Canopus]

Yes how would you even get it into space and why?

[PakledHostage]

I wonder how leaky the cabin is in a 747.

Very. The outflow valves near the tail are almost always a little bit open. They're about the size of a dinner tray. The pressurisation system regulates pressure in the cabin by modulating those valves. So much air flows through that the cabin air refresh rate is about 15 times an hour.

[tavert]

I wonder how leaky the cabin is in a 747. In space, you can't compress exterior air and inject it into the cabin so you might have to carry air tanks to replace leaked air.

Quite. The way jet aircraft control cabin pressure is via a controlled leak. There's a very fast, accurate valve called the outflow valve, usually mounted on the right side of the airplane, lowish and behind the cockpit (sometimes multiple, plus an extra emergency relief valve in case the main one stops working). The environmental control system uses pressurized bleed air from the engines (taken after the compressor stage but before the burner), runs it through an air-cycle cooling system (like a fancy turbocharger with some heat exchangers around it) and into the cabin. The outflow valve regulates how much airflow is allowed to vent the cabin to keep the cabin pressure at the desired value. There are also leaks around windows and door seals and such, that are typically much smaller than the effective area of the outflow valve.

The 787 is slightly different since it uses ram air intakes and electric compressors instead of engine bleed air, but the cabin pressure is controlled the same way with an outflow valve. The main determining factor in how high cabin pressure can be is structural - the 787 and new business jets like the Gulfstream G650 can use lower, more comfortable pressure-altitudes in the cabin because their fuselages can stand a few more psi of sustained differential pressure.

Edit: damn, ninja'd. Looks like outflow valves are near the tail on a lot of airliners, side of the fuselage on smaller planes, depends.

Edited June 25, 2013 by tavert

[bloodgusher]

Hmmm, yes I guess you would need to get it up there gradually to avoid tearing the wings off. Who needs wings in space, anyway?

It would take about 30sec at cruising speed (300 m/s) to get past most of the atmosphere if you go straight up.

But wait, in the spirit of KSP, just add struts!

Why put it up there? This was bad SF, I don't think this question is relevant. And the idea of a 747 in translunar orbit appeals to me for some reason.

[DerekL1963]

And then there's radiation, but never mind that.

Apart from that, seems like it might actually work.

Thermal control is going to be a stone cold b too... The cabin will be below freezing in fairly short order.

[kahlzun]

Actually, it would be very hot: the engines would not run (obviously) and sitting in the full glare of the sun would warm it up quickly.

Imagine standing in the middle of a parking lot, on a clear, hot, day. That's how much heat the plane would be receiving.

[Nibb31]

Of course, none of the seals or hydraulics or electrics are rated for vacuum, so the whole thing would be dead after a couple of minutes. It has no RCS, so it would just tumble uncontrollably. And of course, there is no way of bringing it back home.

It's not even bad sci-fi. It's drivel.

[Henri von Braun]

Of course, none of the seals or hydraulics or electrics are rated for vacuum, so the whole thing would be dead after a couple of minutes. It has no RCS, so it would just tumble uncontrollably. And of course, there is no way of bringing it back home.

It's not even bad sci-fi. It's drivel.

It's not drivel, it's UTTERLY drivel.

[Tommygun]

I think in Earth's orbit it's something like 250F/121C degrees in direct sun light and around -250F/-156C below in the shade.

[WestAir]

I don't believe getting into space is part of the OP's question, because obviously an airliner would never make it to space. Let's assume Boeing had a factory in LEO and they built a 744 and pushed it out of the hangar doors, fully pressurized at one of the commentators 13,000 feet atmospheric pressure.

I'm not sure about the 747-400 series, but I hear the Airbus 320 and newer families have a "ditching" button that will seal all of the various valves and ports and holes in the fuselage. Let's also pretend our space 747 has that, and the crew push the button to try and maintain cabin pressure. What happens next?

Let me be the first to say "dunno" - I want to think the fuselage fails, because nothing ever seems to go right on an airplane when I fly one, but I digress.

[Themohawkninja]

Cabin pressure would be the least of your problems, I think.

The whole airframe would rip itself as soon as it hits Mach 1.

I feel that this would be the worst problem to deal with.

Funny story about this idea though. Before rockets in KSP needed an oxidizer, I put a mainsail engine on the back of a conventional jet-liner style plane, and the force of the acceleration ripped the wings off instantly. I needed a webbing of struts to keep the wings on.

[Nibb31]

"Pushing a button" assumes that systems are functional, which they wouldn't be.

Electronic components would overheat and fail in a matter of seconds. Rubber and plastic would outgas and become brittle and lose their sealing properties. Lubricants and other fluids would freeze or sublimate. Hydraulic systems would leak and fail. The cabin would probably rupture due to the pressure differential. The escaping fluids would make the whole thing tumble out of control, knocking anyone inside unconscious, assuming their blood isn't boiling and their lungs aren't collapsing already.

Space is a very inhospitable place. NASA makes it look easy, but it's hard to comprehend how hard it is to keep everything working up there. Using an airliner as a spacecraft is akin to using a motorcycle as submarine.

[WestAir]

"Pushing a button" assumes that systems are functional, which they wouldn't be.

Electronic components would overheat and fail in a matter of seconds. Rubber and plastic would outgas and become brittle and lose their sealing properties. Lubricants and other fluids would freeze or sublimate. Hydraulic systems would leak and fail. The cabin would probably rupture due to the pressure differential. The escaping fluids would make the whole thing tumble out of control, knocking anyone inside unconscious, assuming their blood isn't boiling and their lungs aren't collapsing already.

Space is a very inhospitable place. NASA makes it look easy, but it's hard to comprehend how hard it is to keep everything working up there. Using an airliner as a spacecraft is akin to using a motorcycle as submarine.

That's disturbingly awesome.

[PakledHostage]

The cabin would probably rupture due to the pressure differential.

I fully agree that it probably would survive about as long in space as a motorcycle would underwater, but they do have both positive pressure and negative pressure relief valves in the fuselage.

Edited June 25, 2013 by PakledHostage

[Mr Shifty]

Many years ago I read a very bad SF novel in which a 747 was put into space.

Was this the book where one of the stewardesses backed into a floating ball of hot coffee and got burns all over her face? And one of the other ones somehow got ejected into vacuum? I think I read that one too.

[DerekL1963]

Actually, it would be very hot: the engines would not run (obviously) and sitting in the full glare of the sun would warm it up quickly.

Imagine standing in the middle of a parking lot, on a clear, hot, day. That's how much heat the plane would be receiving.

Of course a spacecraft in orbit isn't surrounded by hot asphalt (or concrete or whatever your parking lot is made of) - it's in the middle of a vast polar wasteland. Seriously, unless you're in LEO and thus near the (relatively warm) Earth, most of what a spacecraft 'sees' isn't the sun - the sun is a point source, it's the blackness around that dominates. (That's why Apollo 13 froze rather than boiled.) Even in LEO, you're frequently having more problems keeping warm rather than keeping cold. (That's why the hydrazine tank on USA-193 was frozen.)

[MBobrik]

Electronic components would overheat and fail in a matter of seconds. Rubber and plastic would outgas and become brittle and lose their sealing properties. Lubricants and other fluids would freeze or sublimate. Hydraulic systems would leak and fail. The cabin would probably rupture due to the pressure differential. The escaping fluids would make the whole thing tumble out of control, knocking anyone inside unconscious, assuming their blood isn't boiling and their lungs aren't collapsing already.

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I've first read the text w/o reading who has posted it. And, I thought to myself, that this kind of hyperpessimistic hyperbole looks like it was written by Nibb31. And look, it was !

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First, lots of electrical components are inside the pressurized areas. and virtually all that are outside are passively cooled and likely don't work on the edge of thermal failure as the most critical systems have to have a huge safety margin. So most would do just fine conducting the heat to the frame of the airplane.

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Second, 747 has service ceiling of 13000 m which means only 20 KPa pressure. So if rubber and plastic don't rupture going from 100 KPa to 20 KPa, then they won't suddenly explode when going the shorter distance from 20 KPa to 0 KPa. The same with the cabin. It as a lot of safety margin, and at 13000m it already experiences 70 % of vacuum forces.

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Hydraulic fluids are sealed hermetically at MUCH higher pressures than atmospheric pressure so the hydraulic system won't even notice that the pressure difference between the inside and the outside rose from 25 MPa to 25.1 MPa

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Escaping gases will diffuse out of the plane slowly from all directions, if one manages to close the damn air bleed valve, and an airplane has a LOT of inertia, so the rotation would not pick up any swiftly. ( ultimately it would, but the plane runs out of air faster than that )

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One more thing. Don't get me wrong, I don't think that 747 in space is a good idea at all, it just won't fail as swiftly as your hyper-pessimistic post suggests..

Edited June 25, 2013 by MBobrik

[DerekL1963]

Was this the book where one of the stewardesses backed into a floating ball of hot coffee and got burns all over her face? And one of the other ones somehow got ejected into vacuum? I think I read that one too.

I suspect the OP may be referring to Harry Harrison's Star Smashers of the Galaxy Rangers - which was a comedy/parody, it was *meant* to be bad, so bad it was good. (And it was, if you're familiar with the style and type of SF it was parodying.)

[tavert]

Agree with MBobrik here. Certainly not a good idea, but equipment failures probably wouldn't be as catastrophic or fast as you might think, if you ignore getting there in the first place. High altitude is most of the way to vacuum conditions in many respects.

Most systems on the plane won't work without an engine or APU to power them, and the leakage rates with all valves and intakes closed would still be too high to hold much cabin pressure for a useful amount of time.

[Mr Shifty]

I suspect the OP may be referring to Harry Harrison's Star Smashers of the Galaxy Rangers - which was a comedy/parody, it was *meant* to be bad, so bad it was good. (And it was, if you're familiar with the style and type of SF it was parodying.)

I believe this was the novel I (and perhaps the OP?) were thinking of: http://www.amazon.com/Orbit-Thomas-Block/dp/147015241X

There's also this: http://en.wikipedia.org/wiki/Starflight:_The_Plane_That_Couldn%27t_Land

[metaphor]

A 747 weighs around 400 tons. To get it into orbit, you would need the equivalent of 4 Saturn V rockets.

[MBobrik]

A 747 weighs around 400 tons. To get it into orbit, you would need the equivalent of 4 Saturn V rockets.

or one botched alien abduction attempt