[AR] Re: to the stars, soon

  • From: Henry Spencer <hspencer@xxxxxxxxxxxxx>
  • To: Arocket List <arocket@xxxxxxxxxxxxx>
  • Date: Wed, 30 Mar 2016 12:40:34 -0400 (EDT)

On Wed, 30 Mar 2016, Uwe Klein wrote:

I may have missed it but how will the craft slow down after reaching
destination? A mirror?

Larry Niven: you will have to dive into the sun :-)

You don't literally head straight for the Sun -- aiming for a close flyby is just as good in terms of the amount of gas or light encountered.

In any case, most of the decelerating has to be done long before the solar wind and/or light is dense enough to be useful -- at near-relativistic speeds, the final approach to the sun is just too quick. Useful rule of thumb: an acceleration of 1G is roughly c/year. So if your interstellar cruising speed is 0.25c, you need about three months of 1G deceleration, and you need to start about 300 billion km (3e14 m) out.

( Isn't there some relativistic advantage to brakeing against some stars radiation at relativistic speeds than accelerating away from it ? :-)

There is, but it's unimportant at the slothful pace of only 0.25c. :-) At that speed, while relativistic effects are certainly detectable, they're still fairly small. Don't know what the ratio for this effect would be, offhand, but most relativistic effects scale with the factor sqrt(1-(v/c)^2). You need to be at 0.87c to get a factor of 2, and 0.995c to get a factor of 10.

Henry

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