Comments by "Jeff Huffman" (@tejing2001) on "" video.

Karsten Hoff: Actually the storm at the start didn't bother me. True, martian atmosphere is very thin, but wind speeds are higher, so as I understand it the actual dynamic pressure isn't that much lower than what you get from winds on earth. Combine that with the low gravity and it sounds pretty plausible that a once-in-a-decade storm, say, would have enough wind force to tip the ascent rocket. What bothered me about the martian was how people didn't think about obvious issues until so late in the game, and how they ignored fairly obvious alternatives to their choices. How can they not start thinking about whether the mav can intercept the hermes until AFTER they've committed to the plan and the hermes is already on its way to do the hyperbolic flyby? Also, blowing the front hatch near the end seems like a stupid risk given that they still had more fuel. They can sacrifice some of the fuel allotted for the capture burn into earth orbit, so long as they still have enough that they stay bound to earth (and that's way more than enough delta-v). They would end up in some higher elliptical orbit around earth instead of a nice circular one, but it's not much harder for nasa to get a resupply vessel to them (than it would have been anyway) so long as they're actually gravitationally bound to earth. Also, given that they had the maneuvering backpack thing, why was disconnecting from the tether not even an option? Yes, it's risky, but it's way better than mark poking a hole in his suit.
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@DerKiesch I thought it was pretty clear that mark was on a hyperbolic trajectory during the rendezvous: as you said, the whole point of lightening the mav was to make up the difference in delta-v between orbital insertion and escape. But it actually doesn't matter, since no matter what their overall trajectories looked like, the fact that the intercept was very low velocity means they can achieve another intercept a short time later with a quite small amount of thrust. So basically the "only get one shot" idea and the "low intercept velocity" idea are mutually incompatible unless both craft have almost no maneuvering capability at all. Admittedly, however, if the hermes has to change orientation to achieve thrust in the desired direction, they might not have enough time for another intercept before mark runs out of air. With that big rotating habitat section the hermes is probably tough to turn.
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@DerKiesch When it comes to whether the mav can intercept the hermes, I wasn't so much talking about the crew's decision as the discussion of possibilities back at nasa. The whole working out of how to lighten the mav enough to make it happened after nasa had considered and rejected the plan and the crew had gone against orders to force their hand. How did the question of whether the mav could be lightened enough to make the intercept not come up far sooner, when the plan was still under initial consideration? Also, the thrust doesn't really matter much. Assuming they have almost any maneuvering capability at all, then the only real time constraint is the time till mark runs out of air. Given that it is (and must be) a very low velocity intercept, they don't have to make the first intercept, they can set up a second one with very little thrust. Also I didn't get the impression they were even considering using the ion thruster at that point. They were using some kind of maneuvering thrusters with a different fuel source. And all their discussion at the time was about having enough fuel, not about having enough thrust. Also, if the final stage of the mav really has zero delta-v, and the hermes really has so little maneuvering capability, how was a rendezvous supposed to work under normal conditions?
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@DerKiesch Yeah that seems like the most sensible option really. I don't know how much delta-v those packs have, but I have a hard time believing it's less than like 200m/s, which would do the job just fine.
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