However, the biggest hurdle remains . A radio signal takes between 4 and 24 minutes to travel one way between Earth and Mars. In a real emergency, Earth cannot give real-time commands. The astronaut and the rescue crew must act autonomously.
Purnell’s plan was the "Sol 714" or the "Rich Purnell Maneuver." It involved using Earth’s gravity as a slingshot to fling the Hermes back toward Mars at breakneck speeds. It would add over 500 days to the crew’s mission time and risk the lives of six people to save one. the martian mision rescate