How do he astronauts attach themselves to the rocket in space?

Astronauts do not attach themselves to the rocket in space; instead, they are secured within the spacecraft or module that is part of the launch vehicle. During launch, they are strapped into their seats with harnesses designed to keep them safe under the forces of acceleration. In space, if they need to conduct spacewalks or move outside the spacecraft, they use tethers and safety lines to prevent drifting away. Communication and coordination with the spacecraft's systems ensure their safety while in orbit.