# When Watney used the Ares IV MAV to ascend, he pulled 12 G's. But the crew used the MAV from Ares III to ascend, how come they didn't pass out?

The crew used the same type of MAV at the beginning of the movie as Mark did at the end of the movie to ascend to Hermes. Did they all pull 12 g's leaving as well? Did they pass out?

• Obie's answer is correct. But technically, it's more economical for a rocket to accelerate faster because there's less time to be affected by gravity before being in orbit and for single burn escape trajectories you can take advantage of the Oberth effect. Sorry, I've had too much Kerbal Space Program. Jul 4, 2016 at 8:26
• that, and the time in atmo, where you loose a lot of energy to drag Jul 4, 2016 at 14:20
• In an Earth orbital launch, typically less than 1% of energy is lost to atmospheric drag; with Martian atmosphere being about 1% of the density of Earth's, atmospheric losses will be negligible. Gravity losses are larger than drag, but reduction of dry mass mostly just increases the delta-v potential of the craft via the rocket equation. en.wikipedia.org/wiki/Tsiolkovsky_rocket_equation Jul 4, 2016 at 18:58

## The MAV had been modified

Watney removed excess weight from the MAV in order to get it to go fast enough. In the first part of the movie, presumably it did not have to escape Mars's gravity:

It might be a wasted effort. The MAV isn't going to have much weight allowance when I launch. To intercept Hermes, it'll have to reach escape velocity, but it was only designed to get to orbit. The only way to get it going fast enough is to lose a lot of weight.

The Martian

Also:

“Suffice it to say, ” Venkat interrupted, “It would be very difficult and dangerous. But we have a lot of clever scientists to help him trick out the rover. Also there would be MAV modifications.”

“What's wrong with the MAV?” Mitch asked.

“It's designed to get to low Mars orbit, ” Venkat explained. “But Hermes would be on a flyby, so the MAV would have to escape Mars gravity entirely to intercept.”

“It'd have to lose weight... a lot of weight. I can get rooms full of people working on these problems if we decide to do this.”

The Martian

It is specifically mentioned that the modified MAV will experience severe forces:

“He might be in bad shape when I get him, ” Beck said. “The stripped down MAV will get up to 12 g's during the launch. He could be unconscious and may even have internal bleeding.”

The Martian

The reason the Hermes could not enter orbit (as it had presumably done before) was due to fuel demands. From the film script:

MITCH: The problem is the intercept velocity. The Hermes cannot enter Mars orbit, or they’ll never have enough fuel to make it home. The MAV is only designed to get to Low Mars Orbit. So in order for Mark to escape Mars’ gravity entirely and intercept the Hermes...

• Thank you all. This makes sense. I need to read the book.... I just bought the book from Am*zon... Jul 4, 2016 at 14:48