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Vertical takeoff requires disposable rockets (would it a satellite rocket), which is a money loss, and also a lot of fuel, because initial velocity is zero. Also vertical takeoff seems risky, involves huge pieces of equipments, launch pads, to diminish risk.

Horizontal takeoff are done with a reusable aircraft, like a modified 747. Initial velocity not being zero, there are much less risk, and the fuel spent in a 747 is much less expensive than a disposable rocket.

So, Why are there more vertical takeoff than horizontal for spacecrafts?

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semi-on topic: en.wikipedia.org/wiki/Space_elevator –  Andrew Apr 30 '12 at 1:32

4 Answers 4

Sabre engine-powered skylon aircrafts are the only horizontal takeoff spacecraft in the horizon that will be able to go into LEO and back in a single stage.

I expect that we will see a prototype of this aircraft doing its first test flights in the next 10 years, but there are many financial and political roadblocks that need to be surmounted first

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one more corporate video: youtube.com/watch?v=0UL4rgq6glE –  lurscher Dec 20 '12 at 16:32

Actually, just a few weeks ago NusSTAR was launched from a Pegasus rocket on a modified 747.

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A 747 moves at approximately 1,000 km/h, a satellite in orbit travels at 28,000 km/h. So, after your rocket is released from the 747 it still needs enough fuel to accelerate a further 27,000km/h. That requires a lot more fuel than the 747 is capable of carrying. Remember that the shuttle lift-off weight is about 2,000 tons - far more than the 747 can carry.

In addition, you need to get above the atmosphere. Going 28,000 km/h at 10,000 m will burn up any spacecraft, so you need to get up very high before you start going at extreme speeds.

It is possible to reach orbit after horizontal take-off, but we're not there yet

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So the fuel saving is not worth a horizontal takeoff, if I understand well. I thought escaping earth's gravity required a lot of energy, and that's why I'm thinking about planes... –  jokoon Apr 30 '12 at 17:26
Apart from the fact that you can't escape earth's gravity, yes it takes lots of energy to get into orbit. Horizontal take-off would imply using jet engines, hence using oxygen from the air; that will save quite a bit in take-off weight. Nevertheless, it's still not really feasible. Skylon claim to be ready to unveil a space plane, but I'll need some convincing. –  hdhondt May 1 '12 at 0:14
What I was thinking was like any vehicle, the energy required to make a vehicle move from no speed at all to small speed was the greatest energy taker. –  jokoon May 1 '12 at 10:37
It's the change-of-speed (delta-V) that determines the energy required. To change from 0 to 100 km/h takes the same amount of energy as the change from 10,000 to 10,100. The current speed of the vehicle has nothing to do with the energy required - except for the fact that a rocket (or jet) engine has highest efficiency when it is moving at the same speed as the exhaust gases, so the exhaust becomes stationary when exiting the engine. –  hdhondt May 3 '12 at 23:28

A 747 - can get you to around 35,000 feet. Still very much within the atmosphere.

So what do you do then? Launching a rocket from that point still requires an awful lot of kit, so while you have reduced your propellant requirements a little, the 747 still has to carry a launch platform, so you're not really getting anything out of this.

New technologies, such as that used by Virgin Galactic is managing to make this work, hopefully, with a hybrid model that does fly up to around 50,000 feet before launching the spacecraft section, but this is very new.

enter image description here

So the simple answer is - it used to require vertical rocket launches, and all the associated paraphernalia, but modern technology is moving towards fully reusable methods such as this.

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I'm sure it's not that much new... there was other kind of projects like this... –  jokoon Apr 28 '12 at 19:42
Yes, but they couldn't do it successfully, which is why it is only recently beginning to work. –  Rory Alsop Apr 28 '12 at 20:00
It's worth pointing out that the craft you've pictured (SpaceShipTwo) is a sub-orbital one. It's much harder to launch orbital craft that way, although Virgin Galactic say they're working on it. I suspect it will only be for small payloads, at least with this generation of technology. –  Nathaniel Dec 20 '12 at 11:52
True - it's all about progress, and this is a step. –  Rory Alsop Dec 20 '12 at 12:21

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