
Could one lase accelerated probe, slow another probe behind it down? - Pica_soO
I remember reading on HN a article on small probes, that could be accelerated to near 0.25 c with lasers. My Question is- could one such probe, aim a laser on a probe behind it, and slow it down?
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deftnerd
Laser light has very little mass but it does have some. The problem is the
immense amounts of energy created to generate the laser beam.

The idea behind using a laser to push a probe is interesting because the power
generation required can be kept on Earth.

On it's face, yes, a probe using a laser could fire it in the opposite
direction in order to slow down... But the amount of power required would
easily dwarf anything you could generate on a probe.

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Pica_soO
Could it redirect the beam it recived from earth, back unto a probe behind
itself in mid flight?

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SamReidHughes
Yes, with a giant mirror. And that's the best way to do it. But note that all
lasers spread out in a cone -- they aren't a perfect column. The angle of this
cone can only be made smaller by making very large optical equipment (I'd
guess in the form of a large parabolic mirror collimating an earlier stage as
best it can) which means far away probes only get a fraction of the energy
Earth is sending. This also means the reflection only has a small portion of
the initial light, and then the reflected beam spreads out with its own cone
as well. So the deceleration stage is _vastly_ longer than the acceleration
stage.

