system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: Why can't the space shuttle just go slow enough to not be heated up by friction with earths atmosphere on re-entry?
gpt
Because friction is a completely free way to slow a spacecraft down. In space, the only way to slow down is to burn fuel in the opposite direction you're moving. Using the air to slow down instead means you don't need to bring as much fuel, which means you can bring a heavier payload.

Increasing the payload size by making the rocket more efficient is a goal for any rocket scientist.