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I always wondered if it was possible for planes and other aircraft to leave the Earth's atmosphere. Normal commercial transport airplanes can fly pretty high, but then they need air to get the speed boost from. Reactive engines seem like a better idea, but I don't know how much importance air has for them.

Is it possible to get to space from Earth's surface using a non-rocket aircraft?

Federico
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user1306322
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    I guess that aircraft as the name implies uses air to gain and maintain altitude. Lift is a force created by an airfoil in the air. As soon as you remove air (definition of space), you also remove lift possibility, and the object becomes a spacecraft. So an aircraft cannot go to space only using its own capabilities. – mins Apr 30 '16 at 17:08

7 Answers7

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Depends on what you mean.

Get to high altitude? Yes you can. It is really inefficient to get there, but some aircraft already do it.

Achieve a stable orbit and be able to maintain control? No, at those altitudes you do not have enough oxygen to keep your engines running, you have to bring your own (and thus use a rocket)

For the sake of clarity, some definitions:

  • reaction engine: includes both rockets and jets. The engine pushes some mass in one direction and by reaction it achieves thrust in the opposite one.

  • jet (engine): is used to refer to airbreathing engines. The aircraft carries the fuel, but not the oxidizer; that is taken from the surrounding atmosphere.

  • rocket (engine): is used to refer to non-airbreathing engines. The (space)craft carries both the fuel and the oxidizer. No atmosphere is needed.

  • space: above 100km of altitude.

  • go to space: enter image description here

  • staying in space: enter image description here
    Images from xkcd

FreeMan
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Federico
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    High altitudes aren't necessarily inefficient. Some amazing aircraft like the Lockheed U2 were very, very efficient at FL 700. Of course, the turbofans on the U2 can't get it too much further AMSL though. – shortstheory Apr 17 '14 at 07:10
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    @shortstheory U2 is efficient AT FL700, absolutely inefficient at getting there. – Federico Apr 17 '14 at 07:25
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    Can a spacecraft be merely "shot" into space, such as on an incredibility powerful railgun? I suspect the air friction would absorb all the energy too quickly. And the acceleration might be less than pleasant for the astronaughts xD – Alexander Nov 24 '17 at 14:34
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    @Alexander Why don't we use catapults to get to space? on [space.se] probably covers much of that. Full disclosure: Accepted answer is my own. – user Sep 02 '18 at 19:44
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    @Alexander-ReinstateMonica Yes, and theoretically you could achieve the same with a relatively standard jet-powered aeroplane - accelerate fast enough while within the atmosphere and momentum will carry you out. In reality the speed required is too high for current engine technology. – MikeB Sep 21 '20 at 16:09
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For certain values of "go to space", yes. The Karman line (the altitude at which an airplane cannot generate enough lift to stay aloft at any speed slower than orbital velocity) is usually considered the lower edge of outer space. This implies that with a powerful engine and enough fuel it's possible to "fly" up into space: you just keep gaining altitude and speed until you find yourself in orbit.

No aircraft has actually done this. The X-15 and SpaceShipOne were both able to reach that altitude in zoom climbs; neither went fast enough to stay there.

Mark
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  • to stay in orbit you need to achieve escape velocity, that is much harder then just getting up there for a bit – ratchet freak Apr 17 '14 at 09:40
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    No, to stay in orbit you need to reach orbital velocity, which is much slower than escape velocity. Fascinatingly enough, as I mentioned in my answer, the stall speed for an airplane flying at the altitude of the Karman line is orbital velocity. – Mark Apr 17 '14 at 10:00
  • I thought you had to do a particular maneuver to circularize your orbit though? And that maneuver has to be done when you are outside of the atmosphere. If you were to do it inside the atmosphere your orbital trajectory would take you back into the atmo and you'd decelerate, taking you out of orbit... I suppose I'm splitting hairs, but it seems that a true orbit requires you to be outside the atmosphere, thus requires a rocket engine. – Jae Carr Apr 18 '14 at 16:42
  • Granted, the question wasn't actually about getting into orbit, just about getting into space. So the answer still works. – Jae Carr Apr 18 '14 at 16:44
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    @JayCarr, to get a stable orbit, you need to raise both perigee and apogee to be outside the atmosphere. To do this, you need to accelerate at both the high point and the low point of the orbit. A conventional rocket needs to fire the engines twice to do this because the engines run for such a short period, but a "space plane" might not need to if it climbs into orbit gradually enough. – Mark Apr 18 '14 at 19:33
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    @Mark You'd still have to level off at the apogee though, which must be outside of the atmo if you don't want to risk de-orbiting, so you'd still need a rocket engine. Really my point is if you want a stable orbit outside of the atmosphere, you will eventually need a rocket engine, because you will have to do some sort of maneuver in a vacuum. Though, mea culpa, all my knowledge of this comes from hours of playing Kerbal Space Program, reality may differ ;). – Jae Carr Apr 18 '14 at 20:10
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    @JayCarr, in the real world, "stable" is relative. At 100km, you might manage to orbit once before re-entry; 300km will get you a few months, and 35,786km (geostationary orbit) has a decay time of millions of years. – Mark Apr 18 '14 at 20:56
  • @Mark - Ah! So it sounds like your plan will work so long as stable orbit is defined as getting around a few times but no more? Mkay, that makes some more sense now. – Jae Carr Apr 19 '14 at 01:46
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    @JayCarr obligatory xkcd: https://xkcd.com/1356/ – dalearn Sep 02 '18 at 20:32
  • X-15 and SpaceShipOne (and Two) are both winged, but they are still rocket-powered. – Jan Hudec Mar 27 '19 at 06:38
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It depends what you include in "non-rocket aircraft". Wikipedia has a whole article on "Non-rocket spacelaunch" which discusses the various options.

The short version is, there are no current space launch systems which do not use rockets. The most practical one we know of appears to be space guns, which have been successfully used for sub-orbital launches (but are not practical for human spaceflight).

Colin Pickard
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A jet engine can only accept air at around half the speed of sound. If the plane is flying faster, the inlet system needs to slow the air down before accelerating it again. Hence the higher the speed, the less thrust it can provide. It is not like a rocket engine that always pulls with comparable force.

A plane needs to accelerate to Mach 25 or about to fly into orbit as a spacecraft, and this is only possible with a new type of engine.

Scramjet that is a jet engine, not a rocket, could probably do this. However this engine seems still under development and currently a rocket is required to accelerate to the speed under that this engine can even be started.

h22
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I'm not sure how you'd classify the proposed Skylon spacecraft spacecraft. It would be an airbreathing reactive engine in lower altitudes but a rocket above 26 km.

It might be a game changer. But this time I don't give even odds that Skylon will come to pass.

HopDavid
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No aircraft powered by engines which rely on atmospheric oxygen can operate outside of Earths atmosphere, 100,000 ft is approximately the altitude limit for air breathing aircraft using conventional fuels, higher sustained altitudes might be possible using liquid hydrogen, but the utility of very high speed and altitude performance as a means of avoiding interception is questionable today. No air breathing aircraft is likely to outrun a rocket propelled Surface to Air Missile however apparently impressive it's performance statistics.

J. Southworth
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  • Related to the discussion in the last sentence, Could a SR-71 be shot down today? – user Sep 02 '18 at 19:47
  • Yes, in theory quite easily using the Surface to Air Missile systems currently in use by the United States and Russia, using as a basis the known target speed, maneuvering and altitude capabilities of these systems. As an example of the kind of dynamic performance obtainable from a missile, the Sprint missile developed for the Safeguard ABM system accelerated at 100 g to reach Mach 10 five seconds after launch, although this was a short range system. In principle though it should always be possible to design a missile system capable of downing any possible air breathing aircraft. – J. Southworth Sep 02 '18 at 20:06
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    Lockheed Martin are promoting the SR72 on the basis that it will achieve Mach 6 at 80,000 ft, so we can assume that somebody somewhere thinks that this will make it difficult to shoot down. – J. Southworth Sep 03 '18 at 08:43
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I recall hearing about F-15s making ballistic suborbital flights, by simply getting up enough of a head of steam to coast through near-space. I don't think they actually went into "space" (100 km altitude) and they certainly didn't make orbit. Does anyone else recall the specifics on this? I can find some references online to using F-15s to test launch ASAT missiles, but my recollection was that the whole aircraft actually went high enough to get well above maximum cruising altitude.

Phil Perry
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