# Tag Info

6

You are correct. There are, however, a few differences you missed. Hermes actually was going to accelerate using an ion drive type system to get to Mars, thus it wasn't actually on a direct path to Mars. Landing something on Mars is hard. At a minimum a heat shield and parachute would be required, even to have a less than perfect landing. Those can be ...

1

ok, another partial answer. I think what you have plotted there is an OPM. Introduced a while ago, it makes the station turn on all axis to change from 180 degrees to 0 (or vice versa), with minimal amount of fuel used. So, for this question: Did the ISS just turn upside-down? answer is no. NASA article on it when it was new: https://www.nasa.gov/...

15

Yes, it takes roughly the same amount of delta-v, your analysis is sound and good. But no, there is no error in the book because that's the premise of that part of the story: we can either reach Mars with food and supplies to last Watney until Ares 4 comes around and picks him up OR we resupply Hermes and they pick him up now(ish). The difference is not in ...

6

note: not an answer and too long for a comment... Did the ISS just turn upside-down? Nauka docking attitude maneuvers; did the cupola near pointing zenith and therefore show only black sky w/ stars? As @OrganicMarble points out: No. The ISS yawed 180 degrees, stayed like that for ~ a week, then yawed back around. But frighteningly, just a short time ...

5

No. The ISS yawed 180 degrees, stayed like that for ~ a week, then yawed back around. You can see a simulation of the maneuver in this official engineering video from NASA. The video is cued to start just before the maneuver. Other 180 degree yaw and 90 degree pitch maneuvers have been executed recently and are planned for ...

1

Yes, that sort of orbit is possible. It is a closed transfer orbit. It is noted in the Wikipedia article about a Cycler, a potential ferry spacecraft using that sort of orbit, that would pass close to two celestial bodies at regular intervals.

1

A direct insertion into a polar orbit gives you only one option for an orbital plane: one that's initially pointed straight at the Sun. This is sub-optimal for an observation mission, since you're more or less directly over the sunrise/sunset line, and can only see deeply shadowed ground. It will be several months before the planet moves far enough in its ...

2

Not the reference you are looking for, but a response to this: Any references and insights would be deeply appreciated! I would like to note that low-thrust phasing in elliptical orbits is "boring", in the sense that the optimal strategy is conceptually simple. For sufficiently low thrust, the phasing orbit does not have time to noticeably ...

5

This is an Oberth maneuver, getting the most out of your delta-v budget by adding velocity on top of an already high velocity. Nowhere in the solar system does one achieve greater orbital velocities than during perihelion of a Sun dive, as close as thermal management allows. At that ~100km/s velocity, every km/s of velocity added corresponds to ~14km/s at ...

1

Goal: lower Phobos's orbit. Status: ACHIEVED! By the time you read this line, Phobos' orbital altitude is already lower than when you started reading this question. Tidal deceleration is dropping Phobos by about 2cm per year, and in less than 50 million years Phobos will impact Mars. Well, actually it won't. In only about 20-25 million years, Phobos will ...

3

First, one assumptions: The acceleration is so low that instantaneous impulse solutions are out of the question, and the trajectory can be modelled as a very gentle spiral. This is quite reasonable, as an absolutely enormous amount of thrust would be necessary to provide high acceleration to a $1.0659×10^{16} kg$ rock. So let's get started then. First, we ...

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