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Comment by ufmace | Hacker News Reader

What I want to know is how they plan on steering these things. How do you get a multi-gigawatt laser on Earth to not only hit a ping-pong ball sized thing in space, but propel it in a particular direction, precisely enough that it will pass through the inner solar system of a star system 4 light-years away? Wouldn't an encounter with a tiny bit of gas or something near our solar system cause it to be like a few billion miles off target?

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Recommend reading TFA:

>Think of it as a large pingpong ball with computers and cameras pointing in different directions. The big advantage? The spherical shape, coupled with a "hollow" laser beam that's stronger toward its outside edge, could be naturally centered on the beam throughout the acceleration.

>"Imagine blowing a piece of paper straight up. It's going to fly off the beam unless it's perfectly aligned," says Zac Manchester, a Stanford professor and Starshot engineer who's researched the subject and already launched a 1.4-inch square spacecraft into Earth's orbit.

But also from TFA, the lasers will stop after the spacecraft travels about ten times the distance between the Earth and moon. I think the question still stands, is it possible to expect anywhere near the needed precision without some kind of active steering over the four light years (minus ten moons) of space that must be traversed? It certainly must be a limiting factor in the utility of this scheme. I can't imagine using this tech to execute a planned fly-by of an extra-solar moon, for example.

10 times the distance to the Moon at an average speed of 0.1c takes about two minutes. So you would launch thousands of these crafts in the general direction of the target system and hope that at least one survives the micrometeorite onslaught and passes close enough to the target planet to snatch a few pictures. Or maybe even aero brake in the very thin heliosphere or gas giant upper atmosphere and enter a highly elliptical Centauri-centric orbit.

Or accidentally start an interstellar war.

I did read it. That's why I asked the question. That all sounds rather vague and hand-wavey compared to what I expect it to take to come near the inner planets of a solar system 4 light-years away.

If they're passively propelled, then it can just become a numbers game. Send a thousand and hope for the best maybe?

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