Considering a suited human space explorer, in free space with no means of thrust or acceleration aside from their dexterity, their own mass, and that of a sledge hammer, what possibilities exist for altering their initial state?

Let's presume for this question, that throwing the hammer is a drastic and potentially foolhardy maneuver, as is venting suit pressure.

  • Could the person rotate freely, controlling their orientation?
  • Would it be at at all possible to accelerate in a desired direction, within these parameters?
  • $\begingroup$ Does "drastic and potentially foolhardy" mean that for the purposes of your question can't/won't do it? $\endgroup$
    – uhoh
    Jan 13, 2019 at 7:54
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    $\begingroup$ Yes, my intent was to explore any possibilities beyond the laws of momentum. $\endgroup$ Jan 13, 2019 at 18:36
  • $\begingroup$ sounds good, interesting question! $\endgroup$
    – uhoh
    Jan 13, 2019 at 22:19

1 Answer 1


A person in a free fall environment can rotate and change their orientation with complex body movements, similar to how a cat can rotate mid-air so that it always lands on it's feet.

However, it is impossible to permanently gain acceleration in any direction without 'throwing' something away. Without an EVA manuverability pack or other thruster system, the ways the astronaut could gain acceleration are basically limited to:

  • Venting a gas
  • Throwing parts of his suit or his hammer

If the astronaut is immortal, they can start

  • Shining flashlights (effect would be almost immeasurably small)
  • Waiting for solar wind or radiation to push him somewhere (also an extremely small effect)
  • Waiting for gravity of a nearby station or rock to pull him in

The astronauts could shift their center of gravity further away from it's natural point by extending the hammer as far away from them as possible but even this would only extend the astronauts reach a tiny bit.

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    $\begingroup$ Along the lines of an immortal astronaut - might a traditional space suit's transparent face shield also provide a (immeasurable) means of acceleration from directional radiative heat loss? $\endgroup$ Jan 13, 2019 at 18:48
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    $\begingroup$ @CrystallineEntity potentially, yes. There's other small possible forces that could also cause acceleration. For example, the suits wiring could generate a magnetic field which interacts with any magnetic fields in the surrounding area. The astronaut could also generate a static potential assuming the materials in his suit/hammer allow them to build up a charge. $\endgroup$
    – Dragongeek
    Jan 13, 2019 at 19:05

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