Jean-Luc Margot (2013 Sep 28)
From the production notes
Gravity is a 2013 American 3D film co-written, co-produced, co-edited and directed by Alfonso Cuarón. The film stars Sandra Bullock and George Clooney as surviving astronauts in a damaged space shuttle.
Medical engineer Dr. Ryan Stone is on her first Space Shuttle mission accompanied by veteran astronaut Matt Kowalsky, who is commanding his final expedition. During a spacewalk, debris from a satellite crashes into the space shuttle Explorer, leaving it mostly destroyed, and stranding them in space with limited air. Without means of communication with Earth, they must cooperate to survive.
There are many things to like about the movie, including an engaging story of adversity and survival, brilliant performances by talented actors, high-quality sound and 3D imagery, and full immersion in a superb space simulator. The film makers based their story on realistic premises and clearly made an attempt to conform to many physical principles.
Realism of movie premises
- The plot is based on a space shuttle mission to repair the Hubble Space Telescope (HST) (there have been five such servicing missions).
- The plot invokes the voluntary destruction of an artificial satellite (China did this in 2007, and the USA did this in 2008).
- The destruction of the satellite generates thousands of pieces of orbital debris (the Chinese event did this).
- The risk of orbital debris colliding with spacecraft is very real (this is a significant concern actively studied by federal agencies).
Realism of movie physics
The following physical principles were honored to a large extent:
- Sound does not propagate in space.
- Drops of liquid are spherical, not teardrop-shape, in a weightless environment.
- Conservation of momentum (but see below for exceptions). When Stone and Kowalsky collide with each other, they bounce off each other with appropriate velocities.
- Lighting that obeys the laws of optics (reflection/refraction/absorption).
- Appropriate orbital period (~90 min) for orbital height (~560 km) of Hubble Space Telescope.
- Realism of oceans/landmasses.
There are some minor inaccuracies in the movie:
- Tools for space instrumentation are very carefully calibrated to provide the correct amount of torque. An astronaut would not screw parts together with her bare hands.
- Electronics are sensitive to radiation and would normally be carefully protected in a chassis, not exposed to the space environment.
- The movie places the space shuttle, the HST, and the International Space Station (ISS) in an orbit at 600 km above the surface of the Earth. While that is approximately correct for the HST, the ISS orbits at a height of 370 km above the surface of the Earth.
There are some instances in which the movie exaggerates or departs from reality, but that is probably needed at some level to sustain the narrative:
- Many of the maneuvers during space walks are executed much too fast (approaches would purposefully be very gentle in reality).
- Communication blackouts were much more severe and extended than they would be in reality.
- The diffusion of the cloud of orbital debris was much more rapid than it would be in reality (it would take weeks, months, or years, depending on the mass-to-area ratio and altitude of the debris).
- Collision scenes have much more devastating consequences in the movie than would be expected from the impact of pieces of orbital debris.
Perhaps the most unrealistic scene in the movie occurs when the space shuttle starts to roll rapidly as a result of a collision with orbital debris. It would take the entire (undestroyed) satellite (about 1,000 kg) to hit the wing of the shuttle at the most favorable location (the tip) with a relative velocity of about 1 km/s to produce that much rotation (assuming that the shuttle remained structurally intact after that impact, which is in itself rather unlikely). Any piece of debris would be much lighter and would travel at much smaller relative velocity, so the effect on the shuttle would be nowhere near what is portrayed in the movie. It would puncture the structure for sure, but it would not dramatically affect the spin state of the shuttle.
There are a few inaccuracies and exaggerations in "Gravity", but the movie premises are sound and many physical principles are honored, which greatly enhances the quality of the movie experience. I highly recommend the movie. Short of watching actual astronaut footage, this is as close to space as you are likely to get in the next few years. It may even prompt you to investigate the promise of space tourism.
The above thoughts were condensed into a 2-minute CNN video.
Dept. of Earth, Planetary, and Space Sciences
Dept. of Physics and Astronomy
University of California, Los Angeles
595 Charles Young Drive East
5642 Geology Building
Los Angeles, CA 90095
310 206 8345