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Comment by geocrasher | Hacker News Reader

I was okay with this list until I saw "Gravity" on it. It's preposterous and silly.

Astronaut Chris Hadfield Reviews Space Movies, from 'Gravity' to 'Interstellar': https://www.youtube.com/watch?v=3RkhZgRNC1k

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>> “If you want to know what a Spacewalk actually looks like, there is no better film than Gravity.”

Sure he had a lot of issues with it but it didn’t sound all bad.

I loved Gravity, obviously some of the science was bad but man what an experience, saw it in 3d, I haven't watched a 3d movie since some "wax museum" thing some time ago.

LOL, "House of Wax". If you saw it in the theater when I did, then you and I are very old.

heh yeah, i bet you have better retirement plans than i do tho

The visuals are stunning to be sure, and there is good reason to watch the movie. The physics, which was the focus of this list, was not one of them.

Cannot agree more. If I remembered correctly, there was such an obvious bug in 'Gravity' that in the orbit, if you want to catch up with another object in front of you, you cannot simply accelerate, or you will result in getting further from it. In stead you will have to decelerate first and then accelerate again. The result is counter intuitive, I remember that simply because I did not believe it at first and as a result we did such calculation on the blackboard while I was in high school.

Is that because you need to decelerate relative to the planet's core to get on an orbit with a smaller radius, so that you can then increase your revolutions per minute at your existing momentum, then accelerate to get back to the orbit the other object's on? I'm trying to visualize the scenario you're describing

I highly recommend you play Kerbal Space Program if you want to get an intuitive understanding for how it works. But in short, yes, and also if you accelerate towards another orbiting object your own orbit becomes more elliptical such that over sufficient distance you will actually move away from it rather than toward it.

Ah I think that's the piece I was missing, makes sense once you said elliptical. Thanks

Well, it depends. Over short distances and timescales, relative motion behaves pretty much as you would expect for objects in free-fall. It's only over significant fractions of an orbital period that counterintuitive things start happening, with orbital speed and height influencing each other. (You can think of this as a tidal or Coriolis-esque pseudoforce that appears to increase in magnitude as objects get farther from each other.)

In general, there are many possible paths you can take to achieve an orbital rendezvous, varying widely in how long they take and how much fuel they consume.

Interesting. Gravity is admittedly sci-fi but so is Interstellar and Contact. The list lost me at Back To The Future.

"Gravity" had comic book physics in a lot of places, but it was still a really good movie that opens with an amazing single shot that goes on for something like 13 minutes. I can cut it a lot of slack on the physics.

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