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Dumb question: why don't they launch rockets from the tops of mountains?

mLuby 9y ago
Not a dumb question—Saddam Hussein was trying to do this. https://www.wikiwand.com/en/Project_Babylon https://www.wikiwand.com/en/Project_Babylon It's prohibitively expensive and logistically challenging to build on a mountain, and mountains on Earth don't go nearly as high as planes can.
countryqt30 9y ago
Building a mountain is expensive and not scalable
mikeash 9y ago
I think it's mainly that the difficulty of building infrastructure up there, and hauling rockets and payloads up every time you launch, isn't worth the benefits. If you could magick a launch pad and rocket to the top of Mount Everest and launch it from there, you'd get a small but decent performance improvement.
adt2bt 9y ago
I imagine it's a mix of mountainous terrain making it hard to transport launch vehicles to the top and most mountains aren't next to the sea (so the payload would have to travel over land, raising the stakes of an unplanned early failure).
vit05 9y ago
Being close to the equator is more important. And mountains that could be used to construct a base are not so high.
- the8472 9y ago
  Those are not mutually exclusive, you could build one on some plateau in the andes near the equator. But I guess the economics still don't work out for that.
renega3 9y ago
Rockets require cryogenic fuels, workers and large launch complexes. In contrast, Everest is a mere 9km and the first stage of a rocket will take it to something along the lines of 100km at 2000m/s. It is much easier just to throw more fuel in the first stage (or move to the equator) than try and relocate around the relatively smooth surface of Earth.
- blorsh 9y ago
  Cryogenic fuel is a reason to use a mountain. Florida's air is humid and dense. You get lots of heat gain from that. The density itself matters. Condensation is a huge source of heat. Freezing is another huge source of heat. So you boil off cryogenics and maybe worse. We lost a space shuttle due to a chunk of ice hitting the wing. Falcon 9 rockets need unusually cold filler; if it warms then it expands and won't even fit in the rocket. It probably pours out and gets drained away, the alternative being a rupture. The USA would do better launching from near Tuscon, Arizona. It's decently high up and dry, which helps keep the cryogenic content cold. We used to do this in fact, before the Mexican embassy complained about defective rockets crashing in Mexico. We chose to move to Florida instead of making a liability payment deal with Mexico.
jcfrei 9y ago
Related question: Couldn't we create some sort of rocket elevator with huge and very high balloons?
- monk_e_boy 9y ago
  Here are some interesting ideas: https://en.wikipedia.org/wiki/Non-rocket_spacelaunch https://en.wikipedia.org/wiki/Non-rocket_spacelaunch
- mLuby 9y ago
  Yeah it's called a rockoon! https://www.wikiwand.com/en/Rockoon https://www.wikiwand.com/en/Rockoon You get the benefit of altitude, but not of horizontal velocity.
- adrianmacneil 9y ago
  https://what-if.xkcd.com/58/ https://what-if.xkcd.com/58/
  - Symmetry 9y ago
    The point isn't to get higher up, the point is to get out of the damn atmosphere so you can use wider bells, lower chamber pressure, and lighter weight tankage.
- Symmetry 9y ago
  That's currently impractical with large rockets but there's one smallsat launcher which looks like it's making a serious bid to launch that way. http://www.zero2infinity.space/bloostar/ http://www.zero2infinity.space/bloostar/ The low pressure lets them get away with toroidal tanks, pressure fed booster engines, and a relatively large faring. Or at least that's the plan, they haven't launched anything close to orbital class yet.
InclinedPlane 9y ago
Because doing stuff from the tops of mountains is very difficult. The logistical complexity and cost of doing something from the top of a mountain swamp out the comparatively small advantages. Also, the best places to launch from are near the equator where there is a large body of water Eastward. And there are very few mountains in such spots.
Tuna-Fish 9y ago
Altitude is much less important than velocity.* The extra altitude you'd get from launching from a top of a mountain would not be worth the expense of having to lug the rocket up there in the first place. * https://what-if.xkcd.com/58/ https://what-if.xkcd.com/58/
- jeffdavis 9y ago
  Thank you, very interesting. But what is the point of a space elevator then?
  - marcosdumay 9y ago
    A space elevator gets you velocity too. Every time you get some altitude, you also get a minuscule amount of velocity because the Earth is rotating. A space elevator gets you so much mind blowing altitude that you'll also get all the velocity you need.
gruturo 9y ago
> Dumb question: why don't they launch rockets from the tops of mountains? Not a dumb question at all. It would actually give you some non-trivial advantage - but altitude matters considerably less than speed when trying to achieve orbit. Starting a mile higher would allow you to avoid the densest parts of atmosphere, giving you less air resistance and helping with the Max Q, or maximum dynamic pressure (rockets sometimes need to reduce their engine output until they have cleared the denser atmospheric layers, or they would break up due to air resistance stresses). This does unfortunately not outweigh the cost and complication of moving your launch site on top of a mountain. If you're really after every scrap of advantage, moving your launch site closer to the equator is way better than moving it up (until you already have it at the equator, that is).

Not a dumb question—Saddam Hussein was trying to do this. https://www.wikiwand.com/en/Project_Babylon https://www.wikiwand.com/en/Project_Babylon It's prohibitively expensive and logistically challenging to build on a mountain, and mountains on Earth don't go nearly as high as planes can.

countryqt30 9y ago

Building a mountain is expensive and not scalable

mikeash 9y ago

I think it's mainly that the difficulty of building infrastructure up there, and hauling rockets and payloads up every time you launch, isn't worth the benefits. If you could magick a launch pad and rocket to the top of Mount Everest and launch it from there, you'd get a small but decent performance improvement.

adt2bt 9y ago

I imagine it's a mix of mountainous terrain making it hard to transport launch vehicles to the top and most mountains aren't next to the sea (so the payload would have to travel over land, raising the stakes of an unplanned early failure).

vit05 9y ago

Being close to the equator is more important. And mountains that could be used to construct a base are not so high.

the8472 9y ago
Those are not mutually exclusive, you could build one on some plateau in the andes near the equator. But I guess the economics still don't work out for that.

renega3 9y ago

Rockets require cryogenic fuels, workers and large launch complexes. In contrast, Everest is a mere 9km and the first stage of a rocket will take it to something along the lines of 100km at 2000m/s. It is much easier just to throw more fuel in the first stage (or move to the equator) than try and relocate around the relatively smooth surface of Earth.

blorsh 9y ago
Cryogenic fuel is a reason to use a mountain. Florida's air is humid and dense. You get lots of heat gain from that. The density itself matters. Condensation is a huge source of heat. Freezing is another huge source of heat. So you boil off cryogenics and maybe worse. We lost a space shuttle due to a chunk of ice hitting the wing. Falcon 9 rockets need unusually cold filler; if it warms then it expands and won't even fit in the rocket. It probably pours out and gets drained away, the alternative being a rupture. The USA would do better launching from near Tuscon, Arizona. It's decently high up and dry, which helps keep the cryogenic content cold. We used to do this in fact, before the Mexican embassy complained about defective rockets crashing in Mexico. We chose to move to Florida instead of making a liability payment deal with Mexico.

jcfrei 9y ago

Related question: Couldn't we create some sort of rocket elevator with huge and very high balloons?

monk_e_boy 9y ago
Here are some interesting ideas: https://en.wikipedia.org/wiki/Non-rocket_spacelaunch https://en.wikipedia.org/wiki/Non-rocket_spacelaunch
mLuby 9y ago
Yeah it's called a rockoon! https://www.wikiwand.com/en/Rockoon https://www.wikiwand.com/en/Rockoon You get the benefit of altitude, but not of horizontal velocity.
adrianmacneil 9y ago
https://what-if.xkcd.com/58/ https://what-if.xkcd.com/58/
- Symmetry 9y ago
  The point isn't to get higher up, the point is to get out of the damn atmosphere so you can use wider bells, lower chamber pressure, and lighter weight tankage.
Symmetry 9y ago
That's currently impractical with large rockets but there's one smallsat launcher which looks like it's making a serious bid to launch that way. http://www.zero2infinity.space/bloostar/ http://www.zero2infinity.space/bloostar/ The low pressure lets them get away with toroidal tanks, pressure fed booster engines, and a relatively large faring. Or at least that's the plan, they haven't launched anything close to orbital class yet.

InclinedPlane 9y ago

Because doing stuff from the tops of mountains is very difficult. The logistical complexity and cost of doing something from the top of a mountain swamp out the comparatively small advantages. Also, the best places to launch from are near the equator where there is a large body of water Eastward. And there are very few mountains in such spots.

Tuna-Fish 9y ago

Altitude is much less important than velocity.* The extra altitude you'd get from launching from a top of a mountain would not be worth the expense of having to lug the rocket up there in the first place. * https://what-if.xkcd.com/58/ https://what-if.xkcd.com/58/

jeffdavis 9y ago
Thank you, very interesting. But what is the point of a space elevator then?
- marcosdumay 9y ago
  A space elevator gets you velocity too. Every time you get some altitude, you also get a minuscule amount of velocity because the Earth is rotating. A space elevator gets you so much mind blowing altitude that you'll also get all the velocity you need.

gruturo 9y ago

> Dumb question: why don't they launch rockets from the tops of mountains? Not a dumb question at all. It would actually give you some non-trivial advantage - but altitude matters considerably less than speed when trying to achieve orbit. Starting a mile higher would allow you to avoid the densest parts of atmosphere, giving you less air resistance and helping with the Max Q, or maximum dynamic pressure (rockets sometimes need to reduce their engine output until they have cleared the denser atmospheric layers, or they would break up due to air resistance stresses). This does unfortunately not outweigh the cost and complication of moving your launch site on top of a mountain. If you're really after every scrap of advantage, moving your launch site closer to the equator is way better than moving it up (until you already have it at the equator, that is).