5mo ago

If I were traveling some near light speed percent, and hit a grain of sand, would it be catastrophic? What are the chances of violent destruction in the "vacuum" of space, when going "relatively" fast

Pun intended, but still a serious question.

Would a neutron matter? (Pun also intended, but also serious)

18 comments

- By my back-of-the -envelope math it is 4,500,000,000 joules. The Hiroshima bomb is listed at approximately 10,000,000,000,000 joules. I bet xkcd is far more accurate, though.
  
  How did you calculate that? The question didn't even mention a specific speed, just "near the speed of light".
  The kinetic energy for a grain of sand near the speed of light is somewhere between "quite a lot" and "literally infinity" (which is, in a sense, the reason you can't actually reach light speed without a way to supply infinite energy).
  
  Did you assume the sand as having no velocity relative to the object going C?
- It's the first What If?, even:
  https://what-if.xkcd.com/1/
PBS SpaceTime has a great video about this topic (see @ ~7min to get your specific question)
- Link with timestamp for the lazy: https://youtu.be/wdP_UDSsuro?t=420
It's actually a legit concern with any (hypothetical) interstellar mission. Even hydrogen atoms will hit with significant force. Dust hits like nukes, and an asteroid is just game over.
The maxim used in a lot of sci-fi is an ablative armour plate. Often in the form of ice. Interstellar ships would likely aldo be needle like, to minimise their cross section. We could also use electric and/or magnetic fields to move smaller particles out of the way.
As for densities, I believe it's a couple of hydrogen ions per m^3 . Dust is rarer, but still present. It's only bigger rocks that are rare enough to just hope to avoid.
- Didn't one of the space shuttles almost holed by a fleck of paint?
  
  The ISS has been pinholed by debris a few times. Likely paint. The shuttle was damaged by foam breaking off, amongst other events.
  By comparison orbital velocity is around 7km/s, while a bullet is around 0.367km/s. Any mismatch will push debris up to bullet speeds easily.
  As for relativistic speeds. C is 300,000km/s assuming you get up to 1/3C (barely relativistic) you are moving at 100,000km/s or 14,000x faster than the ISS moves, or 39000x faster than a bullet. A 10g rock would hit with 10kilotons of energy. About 2/3 the energy of the first atom. bombs.
  
  Challenger had a fleck of paint damage one of its windows on an early mission.
This is why Star Trek's Enterprise has that forward-facing deflector dish. It wouldn't last very long without something to prevent such collisions.
- How the hell did they think of everything in the 1960s? Like, their science is good.
  Didn't they have Arthur C Clark advising them or someone like that?
Yes. For the effects, look up pictures of the damage that space debris has on spacecrafts.
- Mind to post your favourite example?
- The fastest human made object moves at 1/1000 of the speed of light
Depends on the strength of your navigational deflector.

18 comments