Why does a spaceship heat upon re-entry to Earth?

Friction against the atmosphere heats up the craft, the heat resistant tiles reflect some of the heat.

@canidmajor Thanks. Can a spacecraft approach at a different angle or speed velocity?

Slowing it down against the pull of gravity would require a lot of fuel. They’re working on it, though! I would check and see if any of the NASA sites have interactive Q&A areas.

@canidmajor Ok thanks.

Be smoother (less friction), lighter (less dense, so causes less friction), or slower (so less friction).

If a spaceship can maneuver to a position just outside the atmosphere, and not orbiting nor hurtling toward the planet, the fall straight down through the atmosphere can not cause all that much friction.

The reason something like a Space Shuttle or low-orbit space station or satellite burns up, is because it’s in orbit – that is, it’s going so fast perpendicular to the planet, that it doesn’t fall. Since it’s also so close to the atmosphere, slowing down causes it to fall into the atmosphere, but at that great sideways (near-orbital) speed.

It is actually the pressure on the surface facing the atmosphere, not the friction. It is called the bow shock.

Despite thousands of hours on Kerbal Space Program, basically making me qualified to work for NASA, I wasn’t entirely sure of the answer.

The heat is from the rapid compression of the air.

Spaceships use the atmosphere to slow down without expending fuel. It’s already mitigated by ablative shielding and heat resistant materials.

@ragingloli
I don’t know the answer just inquiring:
So it’s basically the boundary of the solar wind/plasma hitting the earth’s magnetosphere?

Similar to a gust of wind hitting a wall?

I had thought it was air friction, so I did Web search and found this answer on Quora

If you come in too steep (@ about 17,000 MPH) the rapid increase in air resistance isn’t enough to slow you down gradually, and you burn up.
If you come in too shallow you skip off the atmosphere like a flat stone on a flat pond with no fuel you get you back into a proper orbit for another try.

But again, that’s only if you are coming in from low orbit (which is where the 17,000 MPH comes from).

If you have a Sci-Fi propulsion system, you can decelerate prior to hitting the atmosphere. Then you won’t get that compression heating.

the tyranny of the rocket equation. It’s not really avoidable.

@Zaku Which is the orbit you have to come in from if you don’t want to burn up being too steep or skip off if too shallow. It’s what I meant by “proper orbit.”

@kritiper Only if you are coming in from an orbit. If you land in sync with the earth’s rotation, or at the poles, you wouldn’t have that lateral velocity.