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My understanding is that the Breakthrough Starshot approach intends to use a small RTG thermocouple of a few milligrams plutonium or americium, not solar. The o

My understanding is that the Breakthrough Starshot approach intends to use a small RTG thermocouple of a few milligrams plutonium or americium, not solar. The optics are minimal and low resolution (~2 megapixel). The uplink is slow (~2 baud) — it’s basically reflecting a laser off its own sail. That’s still going to be optically better than anything you’ll get on or near Earth because you’re near the subject. As for the time to accelerate, you may overestimate. Constant acceleration for months on end brings you to very high speeds indeed. If you’re accelerating at 1G a full year I think it’s closer to 0.9c than 0.2, I’d have to do the math to check.

BbzzbB 5y ago
Could such a probe do a round-trip if it does a 180 flip when it gets ~midway (adjusted for star brightness)?
- Someone 5y ago
  This probe isn’t solar-powered, it’s laser-powered (because solar energy/area goes down too fast at larger distances. Creating and aiming the lasers for this is a technical challenge in itself) So, it could do a round-trip only if you had a similar laser set up at the destination. If you can do that, why build this tiny spacecraft?
  - BbzzbB 5y ago
    Oh crap, silly me... It slipped me that this project is/will be laser powered. I'll go into hiding now.
- Rebelgecko 5y ago
  Changing orientation doesn't necessarily change velocity. I don't think there's a way to "tack" 180°.
Someone 5y ago
The 0.2 fraction comes from the article: “With the use of lasers, these researchers say, this tiny probe from Earth could travel up to 1/5 the speed of light.”
denton-scratch 5y ago
> it’s basically reflecting a laser off its own sail I see - thanks! But how is the sail supposed to modulate the reflected signal? At ~2 baud, you could do it with a minute attitude adjustment; but nobody's said this probe has any attitude-adjustment capability. Maybe the innovative sail material has reflectivity that can be altered electronically? But they didn't mention that in the article.

BbzzbB 5y ago

Could such a probe do a round-trip if it does a 180 flip when it gets ~midway (adjusted for star brightness)?

Someone 5y ago
This probe isn’t solar-powered, it’s laser-powered (because solar energy/area goes down too fast at larger distances. Creating and aiming the lasers for this is a technical challenge in itself) So, it could do a round-trip only if you had a similar laser set up at the destination. If you can do that, why build this tiny spacecraft?
- BbzzbB 5y ago
  Oh crap, silly me... It slipped me that this project is/will be laser powered. I'll go into hiding now.
Rebelgecko 5y ago
Changing orientation doesn't necessarily change velocity. I don't think there's a way to "tack" 180°.

Someone 5y ago

The 0.2 fraction comes from the article: “With the use of lasers, these researchers say, this tiny probe from Earth could travel up to 1/5 the speed of light.”

denton-scratch 5y ago

> it’s basically reflecting a laser off its own sail I see - thanks! But how is the sail supposed to modulate the reflected signal? At ~2 baud, you could do it with a minute attitude adjustment; but nobody's said this probe has any attitude-adjustment capability. Maybe the innovative sail material has reflectivity that can be altered electronically? But they didn't mention that in the article.