arstechnica looks at Breakthrough Starshot, the goal to send a spaceship to the nearest star at 20% the speed of light. While this would mean visiting another solar system — we could visit Alpha Centauri in 20 years — travelling at those speeds means that impact with a stray atom or — worse — a dust particle, would have some catastrophic consequences.
Dust presents a somewhat different problem. Small dust particles will essentially act like a simultaneous bombardment by a lot of gas atoms. That's because the energy binding things together in a dust particle is tiny compared to the energy of the collision itself, and the dust is largely composed of heavier atoms. But a sufficiently large dust particle will create a collision energetic enough to destroy a craft. And "sufficiently large" isn't very big; the authors estimate that it only has to be 15 micrometers across to kill off the craft. Fortunately, dust particles this size are rare, and the authors calculate the odds of running into one at 1050 to one against.
Overall, the authors find the effect of gas to be minor and only likely to cause damage down to a depth of 0.1 millimeters. Dust, however, is a different story. It will evaporate about 1.5 millimeters off the surface of the spacecraft, and melting will happen at depths of up to 10 millimeters. When every gram counts, this could be significant.
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