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Doubt in a scene from the movie Gravity

by k.udhay
Tags: doubt, gravity, movie, scene
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k.udhay
#1
Apr17-14, 10:57 PM
P: 79
In the movie gravity, there is a scene where Dr. Ryan Stone (Sandra Bullock) detaches herself from the broken but moving arm of space shuttle (till 0:45 in the following link):

https://www.youtube.com/watch?v=OiTiKOy59o4">https://www.youtube.com/watch?v=OiTiKOy59o4" type="application/x-shockwave-flash" width="425" height="350">

As soon as she does, she spins so fast because of her inertia and movies far away from her place. But just in few minutes, she comes to a halt. In space, where there is no friction, air resistance and no obstacles (until met), shouldn't she keep spinning forever? Or at least for years (assuming some loss because of low gravity from different planets / satellites / asteroids?
Thanks.
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paisiello2
#2
Apr18-14, 01:23 AM
P: 558
You're right of course, the spinning should go on continuously. There would probably still be some minimal air resistance that might slow you down slightly after a few days or weeks.

However, if you watch the actual film you would see she doesn't halt. Although she does seem to slow down somewhat, I think this is just some artistic license to show it from her perspective: initially fast when she panics and slower when she calms down and concentrates on trying to get her bearings.
k.udhay
#3
Apr18-14, 03:32 AM
P: 79
Yeah, probably I should have watched more artistically than scientifically... :)

mfb
#4
Apr18-14, 04:29 AM
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Doubt in a scene from the movie Gravity

Looks like a stable rate of one rotation every ~2-3 seconds to me. Once the camera switches to her perspective, you can see the earth spinning around with the same rate.
k.udhay
#5
Apr18-14, 04:59 AM
P: 79
Thanks, mfb. But I feel the deceleration of her speed is bigger than an acceptable value. Do you have a similar opinion too?
mfb
#6
Apr18-14, 09:12 AM
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I don't see any deceleration. I did not analyze the video frame by frame, but if there is a deceleration in the movie it has to be very small.

Her rotation gets slowed down by her collegue at some point, but he has rockets in his space suit.
D H
#7
Apr18-14, 09:55 AM
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Quote Quote by mfb View Post
Her rotation gets slowed down by her collegue at some point, but he has rockets in his space suit.
And that is a much bigger problem with the movie. The MMU (http://en.wikipedia.org/wiki/Manned_Maneuvering_Unit) worn by Clooney was last used in 1984. Another big problem is the SAFER (http://en.wikipedia.org/wiki/Simplif...for_EVA_Rescue) that Bullock *wasn't* wearing. That's SOP now. One of the key features of the SAFER is that it automatically stops the astronaut's rotation.
DHF
#8
Apr18-14, 01:16 PM
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Add the fact that they were in a space shuttle but this clearly wasn't set in the past because there is a completed Chinese space station which would make this a future event. I suppose its possible they could have reintroduced the Shuttle program in the years to come but it seems unlikely and there was no dialog to support that.

remember: best viewed....artistically ;)
mfb
#9
Apr18-14, 04:41 PM
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... and that Hubble, the ISS and the chinese station have nearly the same orbit, and that the extreme dense debris cloud hits them in exactly the right order for the story, and so on.

I think an extended shuttle program is not an issue.
paisiello2
#10
Apr18-14, 04:59 PM
P: 558
Quote Quote by D H View Post
And that is a much bigger problem with the movie. The MMU (http://en.wikipedia.org/wiki/Manned_Maneuvering_Unit) worn by Clooney was last used in 1984.
Since it is set in the future, could it have been an updated new version he was using?

Quote Quote by D H View Post
Another big problem is the SAFER (http://en.wikipedia.org/wiki/Simplif...for_EVA_Rescue) that Bullock *wasn't* wearing. That's SOP now. One of the key features of the SAFER is that it automatically stops the astronaut's rotation.
That is a problem for sure. Is it possible that an astronaut would not use it if it somehow got in the way of specific work they were doing?
paisiello2
#11
Apr18-14, 05:02 PM
P: 558
Quote Quote by mfb View Post
... and that Hubble, the ISS and the chinese station have nearly the same orbit...
How did you infer that?

Quote Quote by mfb View Post
... and that the extreme dense debris cloud hits them in exactly the right order for the story, and so on.
Wasn't there some kind of a chain reaction? So presumably there were multiple debris clouds.
D H
#12
Apr18-14, 05:39 PM
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Quote Quote by paisiello2 View Post
How did you infer that?
Apparently Clooney's and Bullock's characters went from one vehicle to another to another. That's just impossible. Altitude changes are hard enough. Plane changes, they're very very hard.

One of the post-Columbia flight rules was to have a safe haven option, and that restricted the Shuttle missions after Columbia to going to the ISS. For a while NASA had cancelled the final Hubble repair mission because if something bad had happened to the Shuttle during the repair mission, there would have no choice but to have the damaged Shuttle reenter the atmosphere. They could not have gone to the ISS. The Shuttle didn't have enough oomph.

That final repair mission was restored to the manifest and it did occur. The astronauts who performed that mission gladly volunteered to take the risk.


Wasn't there some kind of a chain reaction? So presumably there were multiple debris clouds.
That's another problem. Space debris is tracked. Spacewalks don't happen if there's any kind of imminent threat.
paisiello2
#13
Apr18-14, 06:51 PM
P: 558
Quote Quote by D H View Post
Apparently Clooney's and Bullock's characters went from one vehicle to another to another. That's just impossible. Altitude changes are hard enough. Plane changes, they're very very hard.
Why do you say that? I assume that it only takes a small delta V to transfer from a higher orbit to a lower one. And apparently Hubble is at an altitude of 559km and the ISS is at an altitude of 370km. So they had a height advantage at least.

Quote Quote by D H View Post
That's another problem. Space debris is tracked. Spacewalks don't happen if there's any kind of imminent threat.
Not a problem in this case. The sequence of events in the film were:
1) Space walk
2) Russians destroy one of their own satellites. Warning issued and situation continuously monitored.
3) Debris from the destroyed satellite hits another satellite causing a chain reaction. Immediate abort of mission declared.
mfb
#14
Apr18-14, 07:32 PM
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Quote Quote by paisiello2 View Post
Why do you say that? I assume that it only takes a small delta V to transfer from a higher orbit to a lower one. And apparently Hubble is at an altitude of 559km and the ISS is at an altitude of 370km. So they had a height advantage at least.
"Small" relative to orbital velocities of km/s, sure. But huge compared to the delta_v the SAFER or even the MMU could deliver (a few m/s). Even height changes require several 10 m/s to get anywhere, changes of the orbital plane are more in the range of several hundred m/s. Height is not a significant advantage.

Not a problem in this case. The sequence of events in the film were:
1) Space walk
2) Russians destroy one of their own satellites. Warning issued and situation continuously monitored.
3) Debris from the destroyed satellite hits another satellite causing a chain reaction. Immediate abort of mission declared.
Tons of problems.
While such a chain reaction is possible, it would take months, not hours. And it would generate debris in many different orbits. And the big targets (space stations) would certainly not be the last objects to get hit. And not in that synchronized way, and not in the right order for the plot.

If you want to continue to discuss that, please open a new thread, this went far away from the initial question about rotation.
D H
#15
Apr18-14, 11:10 PM
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Quote Quote by paisiello2 View Post
Why do you say that? I assume that it only takes a small delta V to transfer from a higher orbit to a lower one. And apparently Hubble is at an altitude of 559km and the ISS is at an altitude of 370km. So they had a height advantage at least.
That alone requires a delta V of over 80 meters/second, well beyond what a jet pack can do.

There's a much bigger problem than this altitude change. The Hubble has an inclination of 28.47 degrees; for the ISS it's 51.65 degrees. Plane changes are ridiculously expensive. That 23.18 degree change in inclination would mean a delta V of over 3000 meters/second.

There's an even bigger problem: The Hubble's right ascension of ascending node right now is 72.81 degrees, for the ISS it's 33.24 degrees. Changing the line of nodes makes changing inclination look like child's play. The cheapest way to do that might well involve transferring to an orbit whose apogee is beyond the Moon, doing a maneuver at apogee, and inserting back into a circular orbit at perigee (a bi-elliptic transfer). It would be cheaper to send the vehicle to Mars.


Not a problem in this case. The sequence of events in the film were:
1) Space walk
2) Russians destroy one of their own satellites. Warning issued and situation continuously monitored.
3) Debris from the destroyed satellite hits another satellite causing a chain reaction. Immediate abort of mission declared.
That's a big problem in this case. The Flight Dynamics Officers (FIDOs) would have been working like crazy as soon as the first incident occurred. The abort would have been called in minutes, not a situation continuously monitored.
paisiello2
#16
Apr19-14, 12:54 AM
P: 558
Quote Quote by D H View Post
That's a big problem in this case. The Flight Dynamics Officers (FIDOs) would have been working like crazy as soon as the first incident occurred. The abort would have been called in minutes, not a situation continuously monitored.
I'm skeptical on this. Was the ISS abandoned in 2007 when the Chinese blew up one of their satellites?
D H
#17
Apr19-14, 01:59 AM
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There was no immediate threat.

Big pieces ("big": 5 centimeters or more across) of orbital debris are tracked and their orbits are predicted. NASA takes notice when there's even a 1 in 100,000 probability of a collision. There was a potential threat to the Space Station four years after that Chinese anti-satellite test. NASA considered moving the space station out of the way of a chunk of the debris from that test, but didn't do so when they concluded it would pass about six kilometers below the station.

Orbital debris is a problem, but it's a long term, death by 1000 cuts kind of problem, rather than an acute one as depicted in the movie. The movie was unrealistic in that regard. Things don't happen in space at Hollywood speed. It's a lot faster and at the same time, a lot slower.
paisiello2
#18
Apr19-14, 02:06 AM
P: 558
So then, there was technically no immediate threat in the movie either. At least not until the chain reaction started. The movie got that aspect right anyway.


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