There have been several general critiques of the realism some of the physics depicted in the movie "Gravity" notably regarding the the orbital mechanics of the transition from the Hubble Space Telescope to the International Space Station. I understand that these center around the energetic requirements of getting from the orbits occupied by HST to the ISS, but am foggy on the details. In particular, I'm curious what steps would be involved, and how much energy would be required at each, and whether it would be possible, with any practicable technology, to carry an source that could provide sufficient energy.

My (vague) intuition, from what I can gather, is that one would first need to (1) decelerate from the HST orbit and begin to fall towards the ISS orbital altitude (I'm never clear on whether one also acquires a higher orbital velocity as one falls) (2) accelerate to the orbital velocity for the ISS orbital once one arrives at the ISS orbital altitude, and then maneuver to (3) catch up with the ISS and (4) change direction to match its different orbital inclination.

What are the actual steps involved in getting from the HST to the ISS? How much energy would be required at each step? How big a fuel tank or other energy source would be required to provide this energy? Could a human possibly carry such a source, or survive its use?


1 Answer 1


Hubble is at around 590km altitude, the ISS is at 380km, so the dV needed is only around 0.13km/s.

A lot more energy is needed to shift the inclination from the Hubble's 28deg to the ISS 51deg. (The ISS is in a very high inclination orbit, to allow it to be reached from the Russian launch site). In a classic Hohmann change of inclination ( dV = 2v sin beta/2 ) this needs about 3.2km/s, HST has a mass of around 11,000kg and so this along with the mass of the booster means a considerable amount of fuel.

There is also the problem of building something that can reach HST.

Finally, there isn't really a lot of point. HST is obsolete, it is in a poor orbit for doing science (an effect of having to be reachable by the shuttle) and moving it down to an even less favourable ISS orbit wouldn't be worth it.

  • 2
    $\begingroup$ So if HST is obsolete & poorly positioned for science, why is it very hard to get observation time on it? $\endgroup$
    – Kyle Kanos
    Commented Oct 6, 2013 at 18:58
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    $\begingroup$ @KyleKanos - because there is only one of them. It's very difficult to get a seat on old fashioned, slow, dangerous and dirty trains into work in the morning as well $\endgroup$ Commented Oct 6, 2013 at 22:39
  • $\begingroup$ have a google for gravity movie on the reference frame. $\endgroup$
    – Jitter
    Commented Dec 5, 2013 at 18:58

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