is it the exosphere or the trosposphere that is a problem for earth returning spacecrafts?

Question

what part of the atmosphere is very hot?

Answer 1

Neither........spacecraft start heating up around 80 or 70 miles above the ground. The spacecraft then experiences rapidly increasing outer hull temperatures and decceleration until it's hits maxium deceleration. At these altitudes, the spacecraft is in the lower ionosphere, not the exosphere. By the time a spacecraft enters the troposphere, it's no longer moving fast enough for a heat shield to be necessary. The exosphere and ionosphere are very hot, but because the gasses are so rarified, there is very little "heat." Spacecraft re-entering the atmosphere heat up because they are moving so fast, they create a bowshock of compressed gasses ahead of them. When gasses are compressed or shocked by an object passing through them at 18,000 mph or more, they heat up to 20,000 degrees or more. The radiant heat from these gasses then starts melting and vaporizing the outside of the spacecraft. If a spacecraft does not have a heatshield, or enters the atmsophere at too steep an angle for it's heat shield, the spacecraft will be destroyed by areodynamic forces and extreme heating.

Answer 2

It is not the atmosphere that is hot. A spacecraft that is in the process of reentry encounters the thin but increasing density of the upper atmosphere. The craft is moving at many thousands of miles an hour, and this creates a compression shock along the leading edges of the craft. Compression generates the heat which must be shielded against until the air resistance slows the spacecraft to safer speeds.

Answer 3

Neither. It is not a hot layer in the atmosphere that makes returning space craft heat up. It is friction from the high speed of the space craft that causes the heating. If space craft had enough rocket power to stop completely in space and then lower themselves slowly to the ground, there would be not any heating at all. But real space craft use almost all their fuel to get into space and up to orbital speed, which is 17,500 MPH. Then they just use friction with the air to come back down. They use a very small amount of fuel to change course to enter the atmosphere, and then friction does the rest of the breaking from 17,500 MPH orbital speed to zero speed.

Answer 4

it is exosphere because it burns spsce crafts surface .
for protection against heat produced due to friction in exosphere craft is covered by special type of heat resisting tiles.
but exosphere is most imp. layer of atmosphere as it protecets earth from meteors and asteroids.