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Why don't we focus and reflect the sun's rays instead? Or even combine this and the traditional rocket method by putting the emitters in space to catch the sun

Why don't we focus and reflect the sun's rays instead? Or even combine this and the traditional rocket method by putting the emitters in space to catch the sun and push these tiny craft after they've been shot from the Earth by the zillions in a single satellite. That way we deal with two big problems at once: generating laser energy sufficient for escape velocity, and focusing lasers through an atmosphere layer. Better yet, we can use SpaceX's reusable rockets and save even more on launch costs.

eanzenberg 11y ago
My guess is the sunlight reaching the earth's atmosphere is already too diffuse. This could maybe work if the collector + launchpad were closer to the sun.
david-given 11y ago
Apparently you can't collimate sunlight because it's not a point source. But I've been unable to find an explanation as to exactly why which I can understand, because this aspect of optics is deeply unintuitive, but the magic phrase to search for is 'conservation of éntendue'. If you find one, let me know.
- vilhelm_s 11y ago
  Also, it's easier to make mirrors to reflect monochromatic laser light than broad-spectrum sunlight. You don't want to vaporise your probe.
- XaspR8d 11y ago
  Have you seen the XKCD What If on this topic? [1] It doesn't get into the details of éntendue, and even makes a joke about the topic's complexity, so it probably won't satisfy your technical demands. But I've found the arguments about reversibility (light paths through lenses are reversible, so how could one point map back to multiple points?) and area increase (lenses do not intensify image values but can change the overall image size) intuitive enough to help quell myself and my friend's arguments about the matter. [1] - https://what-if.xkcd.com/145/ https://what-if.xkcd.com/145/
imron 11y ago
> by putting the emitters in space They cover this somewhat in the article by saying that emitters powerful enough to power the craft, and that are essentially able to position themselves to point in any direction pose a potential military threat and they're unlikely to get approval for launching such things. Presumably other space-faring nations would also take issue and look to destroy them (China has already demonstrated it's capable of destroying satellites in orbit using ground based lasers).

eanzenberg 11y ago

My guess is the sunlight reaching the earth's atmosphere is already too diffuse. This could maybe work if the collector + launchpad were closer to the sun.

david-given 11y ago

Apparently you can't collimate sunlight because it's not a point source. But I've been unable to find an explanation as to exactly why which I can understand, because this aspect of optics is deeply unintuitive, but the magic phrase to search for is 'conservation of éntendue'. If you find one, let me know.

vilhelm_s 11y ago
Also, it's easier to make mirrors to reflect monochromatic laser light than broad-spectrum sunlight. You don't want to vaporise your probe.
XaspR8d 11y ago
Have you seen the XKCD What If on this topic? [1] It doesn't get into the details of éntendue, and even makes a joke about the topic's complexity, so it probably won't satisfy your technical demands. But I've found the arguments about reversibility (light paths through lenses are reversible, so how could one point map back to multiple points?) and area increase (lenses do not intensify image values but can change the overall image size) intuitive enough to help quell myself and my friend's arguments about the matter. [1] - https://what-if.xkcd.com/145/ https://what-if.xkcd.com/145/

imron 11y ago

> by putting the emitters in space They cover this somewhat in the article by saying that emitters powerful enough to power the craft, and that are essentially able to position themselves to point in any direction pose a potential military threat and they're unlikely to get approval for launching such things. Presumably other space-faring nations would also take issue and look to destroy them (China has already demonstrated it's capable of destroying satellites in orbit using ground based lasers).