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In the movie version of The Martian, Mark Watney pre-blows the escape hatches and removes the heat shield from the Aries IV MAV. What were the benefits of doing this compared to simply leaving the heat shield in place and blowing the hatches when he was outside of the Martian atmosphere? It seems to me like these would increase wind resistance and also greatly add to the chances that something goes wrong (debris whipping around the cabin and cracking his helmet, for example) while only producing a negligible decrease in mass.

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    IIRC the team on Earth gave him a set of instructions on how light he had to make the craft to get him high enough to meet with his team. So I guess shedding any weight necessary would make the difference. Also he attempted to deal with air resistance my covering the top in a tarp, which didn't wholly succeed. – Edlothiad Aug 2 '16 at 5:44
  • In addition there wouldn't have been much in terms of space debris to get in through the doors, as they hadn't really left anything in orbit around Mars. Most things were either flown over to drop things of or dropped to the surface. In the MAV, they would've expected him to remove almost everything that wasn't needed, so in that sense they wouldn't have expected him to be hit by any debris – Edlothiad Aug 2 '16 at 6:09
  • @Edlothiad I wasn't thinking of space debris so much as the screws/bolts/etc. that were flying around in the cabin, left over from the disassembly efforts. – fluffy Aug 2 '16 at 8:00
  • Any loose nuts and bolts (as in ones he'd removed) would've been expected to be discarded of, due to every gram being of the essence. – Edlothiad Aug 2 '16 at 8:11
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"We'll remove the nose airlock, the windows, and Hull Panel Nineteen"

"You're taking the front of the ship off?"

"Sure, the nose airlock alone is four hundred kilograms. The windows are pretty damn heavy too. And they're connected by Hull Panel Nineteen, so may as well take that too."

As seen here. And in addition to these large components he removed everything else that wasn't nailed down and much of the stuff that was (e.g., extra chairs for crew, life support, backup control systems, etc. etc. etc.).

The book (and movie too, I thought) make it clear that without removing a metric shitload of mass from the MAV there was no chance at all of making a rendezvous with the Hermes. They also had to add more fuel.

The cost of putting mass into orbit (or in this case, rendezvous) is high, see, e.g., here. You can't wait until you get to a high altitude before jettisoning mass - you've got to get rid of it before you start - because the rockets have to push it all the way up.

(Update: A major part of the problem was that the MAV was designed to take the entire crew up to Low Mars Orbit where the Hermes would be waiting for them. But for Mark, the Hermes was on a fly-by and the MAV had to get to Mars escape velocity ... much much faster.)

  • Makes sense. I must have missed those important lines while watching the other night. Thanks! – fluffy Aug 3 '16 at 2:19

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