# Debris in interstellar flight

If we are ever able to built a spacecraft that can travel near the speed of light, how can we make it to our destination in one piece? I mean at such speed a tiny tiny rock (even space dust?) would completely destroy the spacecraft. At such speed, you can't really dodge them either, so how would it be possible?

• Thankfully, interstellar space is phenomenally empty, so it's not so much of a worry. Commented Jul 9, 2016 at 22:20

Here is a fairly recent paper by Crawford on this topic. He considers the case of a probe traveling for 6 years at 0.1c. It appears that the most problematic material is relatively large dust grains in the 100 μm range. Most interstellar dust particles are orders of magnitude smaller than this, but the distribution has a tail of large particles. Although the tail is poorly characterized, it appears that such a probe would experience something like 2-200 impacts per square meter with particles of this size. Each of these grains would have a kinetic energy of millions of joules, which is equivalent to about a kilogram of TNT. Material shielding works for smaller particles, but can't protect against impacts this energetic.

There is some discussion in the paper of how to solve the problem. It seems extremely speculative, but then, boosting a space probe to relativistic speeds is itself extremely speculative, and is not likely to be something humans can achieve for centuries into the future.

• Apart from the damage potential, seems like it would be a non-trivial drag on a spacecraft. Commented Jul 11, 2016 at 1:09
• @AnthonyX: The drag force is proportional to velocity squared, while the rate of energy dissipation is proportional to velocity to the third power. So at high velocities like this, the latter is the big issue.
– user687
Commented Jul 11, 2016 at 3:46

## Wear protection

• it's a joke, just build proper interstellar ship.

Most times, when people talk about destroying ship by particles at 0.9c speed, people forget about what happens with that little(or big) particle.

What happens with that particle when it meets a cloud of particles on 0.9c?

If that cloud is gas let say Hydrogen, just take enough of it and it will evaporate most particles you might encounter. I mean it might not be able to evaporate 1km asteroid (depends on how big is shield) but it might work as early detection system too, in that case, so it probably good idea to launch it(or light detection version of it) some light hours ahead.

Make ship which is able to generate such cloud from gas or dust upfront. One of possibilities, if you relay on reactive propulsion for slowdown at arrival point - just let work braking engines for enough time to form such cloud. With conventional reactive engines, one day after making of that bubble, bubble will be upfront at distance 1 light second, and each day it will be 1 more light second farther. With ION propulsion systems 1 light second per each 2 hours(70 km/s exhaust velocity).

There will be some effective pressure of interstellar media, it will slow down that cloud, and after some time "return" it back in form of plasma at almost same relative velocity, as velocity you have launched that cloud - catch it, launch back.

I took it as simple way to demonstrate, but it's not only way to implement such protection. Also you will collect some heavy elements during your journey, nice, mining "gold" with interstellar space ship.

There are other ways to retain that shield and implement whole system, as I said, but over all in general it's simple idea.

## Clarification and reference and cites

Similar concept proposed in (link is just abstract of it) A. Bond, Project Daedalus: target system encounter protection, in: A. Bond et al., Project Daedalus: Final Report, JBIS Suppl. (1978) S123-S125

A concept for protecting the Daedalus vehicle against destructive impacts with large particulate debris during the stellar encounter phase of the mission is presented. In the concept a cloud of fine particles would fly ahead of the vehicle so that any large masses passing through the cloud would be heated and vapourised before the arrival of the main vehicle. Such a protective shield is made possible by virtue of the high specific kinetic energy of the cloud relative to the target star.

Although I do not have access to that report, and being unable to determine similarity and difference in details, but proposed principle is the same.

But overall it's maybe simpler understand in case of thin foil, or cloud of pieces of such foils, let say same 50 mkM thickness - which may evaporate bodies of significant size and mass on impact.

As I said above, this principle may be implemented in different ways, and efficient in therms of mass needed for that.

• I don't understand this answer at all. This seems like speculation with no scientific basis that I can detect.
– user687
Commented Jul 10, 2016 at 16:53
• @BenCrowell thanks for feedback, you may consider to formulate what is not clear and what looks like speculation, so I may add clarification about that aspect. Although you may have to keep in mind it is brief description of idea to how can we make it to our destination in one piece? which I wished to keep brief and straightforward about concept. Also I do not work in NASA, I'm not familiar how they solve travel near the speed of light problems at the moment. Commented Jul 10, 2016 at 18:45