In "The Martian", Rich Parnell uses a supercomputer to calculate a life saving slingshot trajectory that allows Watney to be saved.

The entire film is renowned for its scientific care, so I was really surprised at this. The Hermes is travelling between Earth and Mars, so even allowing for an extended journey and slingshot, there are very few bodies that are materially relevant to its journey. The time scale is short by cosmology standards. Flight and delta-v calculations don't seem like they need supercomputing capability for something like this, as the calculations just don't seem complex enough to need that level of resources. The main question would be risk evaluation (excess fuel, risk of incidents) not trajectory calculations or simple flight viability.

Would a calculation like this really have needed a supercomputer? It seems like something that wouldn't be unreasonable to expect to be calculable on a much more mundane computer.

Hard science answers appreciated! It won't spoil the film to be told if this was a minor exaggeration for effect, or to learn it's actually a lot harder in real life than it seems!

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    And did Rich Purnell really need to camp out between the supercomputer stacks while it was computing the trajectory, instead of remotely accessing the computer?
    – RobertF
    Oct 27 '19 at 19:57
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    @RobertF: No; most clusters don't even have a GUI installed on the head / master node. So he'd almost certainly be accessing it over a network, in which case anywhere with ethernet or even wifi would be fine. I think the search was supposedly done fully on the supercomputer, not interactively / visually / human evaluation of candidate trajectories at all. Oct 27 '19 at 21:15
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    "The entire film is renowned for its scientific care". On a scale of zero to Hollywood, sure, maybe. Oct 28 '19 at 15:43
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    @duct_tape_coder. Those two are not mutually exclusive :) Being the most scientifically accurate in Hollywood doesn't take much... Oct 28 '19 at 19:23

The consensus on Space Exploration.SE where this same question was asked is...


Answer by Mark Adler

Well, developing low-thrust trajectories does take more computation than impulsive trajectories (e.g. like Voyager, which was done with rather primitive computers). You have no choice but to run many fully integrated trajectories. However it would not take a supercomputer of the future, or even a supercomputer of the present to search for and find trajectories like that.

In fact, Andy Weir used his home computer (whatever that was, but likely not even a small cluster) to find and check his trajectories.

Answer by DuffBeerBaron

The short answer is no, the calculations do not require a supercomputer. Any modern laptop has the computing power to handle the scenario.

The long answer is that the particular orbit depicted in the movie is what's called a Planetary Cycler, which cycles between two bodies (Earth/Mars). You can use gravity assists at each body to put your spacecraft on a return trajectory to the other body. These gravity assists can be augmented with maneuvers as needed.


Answer by Loren Pechtel

Calculating an energy-optimal orbit for a simple thing like Earth->Mars is no big deal. Even using low-thrust engines doesn't add much to it. It would be tedious but you could do it on a calculator.

However, that's not what they needed in the book & movie. The objective wasn't to get there as cheap as possible, the objective was to get there as fast as possible given the available energy. There's no standard solution for this, you're simply going to have to try a huge range of possible orbits and see what's best. That's why you want a supercomputer.

Modern deep space craft often use paths that take some pretty extreme calculating. Consider Messenger: 6 planetary encounters and 5 deep space burns. They obviously simulated a huge number of possible paths to find the one that got them there the cheapest.

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    So.... YES. Oct 27 '19 at 14:21
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    So the answer isn't no, then, is it? Loren would be the only one with a correct answer. It doesn't matter if one calculation is sufficient. The question is about parallel processing in which case the supercomputer was necessary. Oct 27 '19 at 17:59
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    That link had a lot of info. But nothing there or in the movie suggests a situation that needed a supercomputer. Yes some situations would,but this one doesn't seem like one of them (only few bodies "on rails", rough paths capable of refinement, no evidence of finessing extremely tight delta-v or time (an extra 50 days is easy), and the film's already taken license with him needing to be in the datacentre rather than remotely logged in. So I'm pretty happy the answer is "no" from that Q, although other people may make up their own minds. Its a movie after all. But that link is the key. Thanks!
    – Stilez
    Oct 27 '19 at 23:31
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    There are a lot of calculations in the world that can be solved either by the development and application of clever mathematics or by brute forcing a solution using a shedload of monte-carlo simulations. For example you can work out pi either by running an infinite series or by using a computer to 'throw' a few million darts at a circle. One of them needs an intellectual leap or two and one requires nothing but a shedload of computational capacity. If you absolutely need a solution and have a computer that can do it there's no reason not to brute force, even though it's not strictly needed.
    – Joe Bloggs
    Oct 28 '19 at 15:37
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    Computations could be done on a laptop in an unreasonably long amount of time. Not only did they have a limited time to get to Mars, but Parnell had a very limited window in which to complete the computations, so yes, he did need a cluster. His laptop would have gotten there, but a few days too late. Oct 28 '19 at 19:28

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