Why do they rocket straight up instead of fly?

[Devalon]

I was wondering why NASA use rocket on their spacecraft to go straight up while using tons of fuel, instead of flying up with wings and using their momentum or rockets to get the rest of the way. Wouldn't this use less fuel then going straight up?

I don't see jets carrying huge tanks and they can reach space. =/

 

[MeteorWayne]

Well, jets don't get anywhere near space. The get about 7 miles up at speeds of a few hundred miles an hour.

To reach orbit, you have to get more than 100 miles up, and reach speeds of 17,500 mph. To leave orbit and travel to other objects or solar orbit, the required speed is > 25,000 mph.

Rockets launch straight up to get above as much of the atmosphere as quickly as possible, since if you wre traveling at those speeds in the atmosphere, you'd burn to a crisp like a meteor.

Wayne

 

[Andorfiend]

What he said.

It is a vaild question, and for some small craft on tight budgets they do launch by droppping from conventional aircraft 'motherships'. Burt Rutans' Spaceship One works that way for example. But for large spacecraft the size of the mothership rapidly becomes enourmous and it is a practical impossibility to do it. Besideswhich the gains are comparatively small compared to the overall cost of the flight and it's simply not worth the effort.

But for small spacecraft the economies work out and it is done, sometimes.

 

[MeteorWayne]

Just should point out, though, that SS1 is suborbital, though it does technically briefly reach "space" (defined as 100 km, 60 miles).

 

[csmyth3025]

I was wondering why NASA use rocket on their spacecraft to go straight up while using tons of fuel, instead of flying up with wings and using their momentum or rockets to get the rest of the way. Wouldn't this use less fuel then going straight up?

I don't see jets carrying huge tanks and they can reach space. =/

At present, going "straight up" on an expendable rocket is the only practicle way of getting to low earth orbit. It's been pointed out that SpaceShip I and SpaceShip II by Scaled Composites are air launched to sub-orbital trajectories that technically reach "space". These vehicles basically go "straight up" once they're released by the mothership.

The only currently proposed vehicle that I know of that fits into the category of "flying" into space is the Skylon by Reaction Engines, Ltd. It's still in the design concept stage - a prototype vehicle has not yet been built. You can find the Wikipedia article on it here: http://en.wikipedia.org/wiki/Skylon

Chris

 

[molecsur]

The atmosphere is a barrier to achieving orbit. They go straight up in order to get through it ASAP. They do not actully go straight up, just close to it. If you try to make it so the atmosphere is your friend and not your enemy you end up with a whole bunch of stuff (wings, scramjets, etc) that weighs you down more than it helps you. Wings do you no good once you are in orbit above the atmosphere. Neither do jet engines that cannot work without an atmosphere.

 

[believer_since_1956]

Actually the trajectory of the booster stage is not totally vertical it starts vertical but rotates to a slight angle such that by the time it clears the atmosphere the rocket is maneuvering to achieve an orbital orientation i.e. parallel to the ground. Consider the launches when they call out altitude and down range distance. By the time of main engine cutoff the rocket's "horizontal" velocity exceeds it's vertical velocity.

 

[csmyth3025]

Actually the trajectory of the booster stage is not totally vertical it starts vertical but rotates to a slight angle such that by the time it clears the atmosphere the rocket is maneuvering to achieve an orbital orientation i.e. parallel to the ground. Consider the launches when they call out altitude and down range distance. By the time of main engine cutoff the rocket's "horizontal" velocity exceeds it's vertical velocity.

You make a very good point. Going "straight up" won't put you into LEO. The best you can hope for by going straight up all the way is to achieve Earth escape velocity (~11.2 km/s starting from the surface of the Earth) and keep on going. To achieve low Earth orbit you'll need a horizontal velocity (relative to the Earth's surface) of ~7.5 km/s.

Chris