system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: At what point can an astronaut take off their helmet and why do they need to wear one for take off? (Asked by an actual 5 year old)
gpt
Once the dangerous part of the launch is over.

The first thing the spacecraft has to do it to get into orbit by riding on top of a huge rocket. This is very dangerous as rockets are known do spontaneously explode on occasion (as you would expect from a vehicle made of 98% fuel and riding a explosion at 10 times the speed of sound).

Once into orbit and clear of the rocket the risk of an accident requiring a helmet becomes basically 0.

**[edit]** They'll have to put their suit and helmet back when approaching the space station, because it is also dangerous (the main risk is a loss of control and collision with the station)

**[edit]** For those confused: the helmet isn't here to protect them from an explosion directly, but from the potential decompression that comes with a failure of the vehicle and/or the violent shaking and acceleration that happen in an abort scenario.