why do space rockets take off from a upright position instead of taking off of a runway like a plane, reach 40,000 ft and entering space from there.
In: Engineering
My geuss is that u need a surface to push off of. Like how it’s easier to jump off of a rigid surface
Two complementary reasons:
1. Rocket engines are not air breathing. That is, they do not and cannot use the atmosphere to generate thrust. In fact, they generate more thrust and are more fuel efficient in a vacuum.
2. Rockets need to accelerate to a speed of ~8 km/s (~17,900 mph, ~Mach 23) to stay in orbit. Doing that inside any substantial amount of atmosphere results in incredible amounts of drag and heat, making it practically impossible to sustain.
Taking these facts together, the best launch trajectory from Earth is to head up, and only start motoring sideways in earnest once above 50-100km altitude.
However, if you can change one of these facts then you can change the launch profile. A spaceplane with air-breathing engines, such as the planned [Skylon](https://en.m.wikipedia.org/wiki/Skylon_(spacecraft)), could make a more lateral ascent through the atmosphere, using wings for lift.
On bodies without thick atmospheres, such as the Moon, rockets can turn sideways to gain speed as soon as sufficient height above the ground is reached (that is, enough height to avoid hitting mountains, etc). [This glorious chart](https://www.christies.com/en/lot/lot-6214825) shows the ascent profile for Apollo 11 from the moon’s surface. Nearby crater ridges are plotted, and it is seen that the ascent module is tilted 60° away from vertical by the time it is just 4 N.Mi. (4.6 mi, 7.4 km) from the ground; and 90° from vertical (i.e. fully horizonal) by the time it is 10 N.Mi (11.5 mi, 18.5 km) from the ground.
How would a rocket fly horizontally? You’d have to add wings to create lift. At that point you’d basically have a rocket powered plane. The great thing about planes is that (due to a good lift-to-drag ratio) they need relatively little forward thrust to stay in the air and gain altitude. Apparently it’s easier/cheaper for a rocket to just increase thrust and launch vertically. There are some rockets which are launched from planes but that’s only really feasible for small rockets and adds complexity for relatively little gain (the great thing about launching a rocket from a plane is actually that you can choose where you launch the rocket, e.g. exactly at the equator, over the ocean, instead of having to build a launch pad there).
For a rocket to reach *orbit* the hard part is gaining enough *horizontal* velocity (about 7.8 km/s (28,080 km/h) for low Earth orbit). To go to space you just have to go up by ≥100km, which is not *that* hard. To quote xkcd: “getting to space is easy. The problem is staying there.” https://what-if.xkcd.com/58/
Lot of good answers here, but one more thing to consider:
To get into orbit, you have to get to a *certain height* and a *certain speed*. Of those two , the *second* is — unintuitively — the dominant hurdle, by a huge margin. Getting to the height is *easy*. Getting to the speed is a *huge* expenditure of energy.
A rocket wants to get as high as possible as quick as possible in order to do its flight in thiner atmosphere with less air resistance then it turns to the side and puts most its effort into sideways movement.
Orbiting a planet is just a high-tech version of the looney toons hitting a baseball around the world and it hitting them in the back, if you throw somthing really really fast then it actually happens as the earth curves away from you faster than you can fall. And if you do this high enough up there’s so little air resistance that whatever you throw will stay up there for years like satellites do.
Air resistance, the biggest enemies to getting to orbit are gravity and drag, you’ve gotta go 10 x faster than any aircraft to get into orbit and your engines don’t have the benefit of using the oxygen in the air as an oxidizer, therefore you want to get above as much of the air as fast as possible so as little as possible of the energy you’re putting in to go fast gets wasted as air resistance. Some small rockers do launch from a carrier aircraft but there’s only so big you can carry on a plane. Another sub category of this is a spaceplane or an ssto (single stage to orbit) aircraft that uses either seperate air breathing and rocket engines it if possible a hybrid that can breath air then turn into a rocket, this is what skylon is attempting and it’s super cheap because no expended hardware, just fuel
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