I hope this is worthy of its own thread... I know there are tidbits scattered in various threads.
You see the term “Human Rated” thrown around so much. But it’s not entirely clear to me what that actually entails.
Obvious thing would be a launch escape system. But what other things are required to make a rocket human rated? And why would one engine be human rated and another not?
Example SSME vs RS-68
A launch escape system is not a requirement for human rating, see STS.
Human rated systems are designed to different safety factors and with different design controls than non human rated systems. That's why RS-68 is not human rated while SSME was.
Edit: should say that a LES was not always a requirement for human rating, as STS was human rated. However, current NASA requirements include a LES, which is why all CC vehicle designs have them.
Have the human rating standards for interplanetary transfer vehicles and landers been published?