why do spacecraft travel at such high speed when reentering the atmosphere?

Answer 1

Any spacecraft in orbit around the earth has to travel at speeds of up to around 18000 mph (28,800kph). The lower the orbit, the higher the speed that is necessary to remain in orbit. Spacecraft in low orbits (below about 250 miles (400km)) are slowed by the extremely thin upper atmosphere of the earth. When the spacecraft are slowed below what is needed to stay in orbit, they fall into the atmosphere, but are still traveling at "high" speeds. Satellites in geosynchronous orbits travel at around 1000mph (1600kph), the speed necessary to stay above a point on the earth's equator. Those satellites, far beyond the atmosphere, will stay up "forever" as far as we're concerned. To bring them down, a rocket motor has to slow them below the 1000mph. When that happens, the satellite begins to "fall" toward the earth. As it does so, it accelerates, not enough to stay in orbit, because it's already heading toward the earth. During the 22000 mile fall, the satellite will accelerate to about 18000 miles per hour again, then hit the atmosphere, where, without a heat shield, it will begin to burn up.

The short answer is, as the first answer said, "gravity".

Answer 2

The "strange" answers are essentially correct. A spacecraft in low orbit is travelling fast relative to the Earth's surface. Slowing it causes it to drop out of orbit and it then hits the Earth's atmosphere at a high speed.

It would be theoretically possible to slow the spacecraft more so it did not hit the atmosphere quite so fast. To do so, the spacecraft would need more powerfull retro thrusters and more fuel which would mean it would weigh significantly more and would hence take a lot more fuel and thrust to launch. Atmospheric drag is in fact a very energy efficient way of slowing down a spacecraft. to landing speed.

Answer 3

They travel that fast all the time when in space, not only when entering the atmosphere. The reason they don't slow down before entering the atmosphere is that they do not have enough fuel. The reason they don't carry more fuel is that it is heavy and would require a bigger engine to lift off the Earth. But a bigger engine would USE more fuel, which would require taking along even more in order to have some left when coming back, which would be even heavier requiring an even bigger engine that uses even more fuel..... You get the idea. The more fuel you take along the more you need to use. It is summed up in the rocket equation.

But it doesn't take any fuel to use friction with the air to slow down.

Answer 4

The problem is, fuel. If you could carry enough fuel with you to reduce your speed, you could - and avoid the heat of reentry... But, all rockets - from the shuttle to Mercury, from Vostok to Space Ship 1 - expend their fuel on the trip up. If it's an orbital flight, or a return from the moon - they use the atmosphere to bleed off speed as they come in.

Answer 5

That's a rather strange question, which has spawned two even stranger answers. The answer is, there are no spacecraft as yet, unless the rumours about Roswell in 1956 are true!

The only vehicles which have returned to Earth from space are rocket pods and shuttles and shuttles cannot be classified as real spacecraft; they are more re-uasable planes which have been ferried out into space, or to be more precise beyond gravity's pull, on the back of chemical-fired rockets.

Come the day when real spacecraft enter (unlikely) or re-enter Earth's atmosphere, then they will firstly use the Earth's outer layers, the Van Allen belts, as a form of barking system. However, at some point they will have to use their own braking system, most likely retro-rockets of some sort, otherwise Earth's gravity will pull them in and cause them either to catch fire, again unlikely due to shieding systems, or to break up, again unlikely, or to create enormous sonic booms.

Answer 6

you are able to't pass previous the universe, whether you will possibly desire to holiday at greater advantageous then the fee of light. As you progression the universe expands with you, the presence of skill, rely, and the passage of time is what defines the universe, you are able to merely be helping to make it larger via moving those 3 in some direction.

Answer 7

They are already moving at 17.500 MPH when they slow down using retro rockets to cause them to enter the Atmosphere, their speed then rises to about 25.000 MPH as they are accelerated by gravity.

Answer 8

They are falling towards the Earth, initially with very little resistance from any air, so they accelerate rapidly.

Answer 9

Gravity!

Answer 10

Because they have an long way to fall