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No, we wouldn't know today. But this is knowable in about 50 years or so, if we send probes to ~550AU and use the Sun as a gravitational lens; we will then be a

No, we wouldn't know today. But this is knowable in about 50 years or so, if we send probes to ~550AU and use the Sun as a gravitational lens; we will then be able to get high-res (1km resolution?) photos/videos of nearby extrasolar planets themselves. This may be enough to find a spacefaring civilization. (sure, rockets aren't 1km big, but they do leave big traces. maybe we could see that)

Qem 3y ago
> if we send probes to ~550AU and use the Sun as a gravitational lens; we will then be able to get high-res (1km resolution?) photos/videos of nearby extrasolar planets themselves. It doesn't scale well. The probe would be able to observe a carefully chosen extrasolar planetary system in the opposite direction in relation to the sun. If you want to observe a second system, it's necessary to launch a second probe 550 AU in another direction. You can't change targets just by rotating the probe, given its lens is the sun.
- cryptoz 3y ago
  Oh yeah, I'm aware that you'll need multiple probes - but I imagine we could send 50 or 100 of these things starting in like 20-30 years once some of the required engineering on propulsion systems etc is done. Assuming we have the will and money to send 1, I think we'd have the will and money to send dozens.
defrost 3y ago
As Qem mentioned, and as laid out on page 7 of the source paper: A significant difference of the solar gravitational lens from a conventional telescope is that the gravitational lens telescope is not in any practical sense pointable. For the telescope at a distance F from the sun to be re-aimed to image a new target 1° away, it would have to move a distance of (π/180°)F, which is 10 astronomical units at the minimum focal distance-- a lateral distance equivalent to the distance from Earth to Saturn. This means that, in practice, such a telescope is not able to be repointed. Thus, a telescope at the gravitational focus is necessarily going to be a singlepurpose telescope, with the target of observation selected before the mission is launched. A gravitational focus mission can’t be used as a telescope to search for a target: such a mission must be with the objective to observe a target whose position is already known. Mission to the Gravitational Focus of the Sun: A Critical Analysis Geoffrey A. Landis, NASA John Glenn Research Center https://arxiv.org/ftp/arxiv/papers/1604/1604.06351.pdf https://arxiv.org/ftp/arxiv/papers/1604/1604.06351.pdf
p1mrx 3y ago
That seems like a good match for this nuclear sail concept: https://www.nasa.gov/general/thin-film-isotope-nuclear-engine-rocket/ https://www.nasa.gov/general/thin-film-isotope-nuclear-engin... > The basic concept is to manufacture thin sheets of a radioactive isotope and directly use the momentum of its decay products to generate thrust. Actually it's mentioned at the end of the article: > Novel ability to reach deep space (> 150 AU) very quickly and then continue aggressive maneuvers (> 100 km/sec) for dim object search/rendezvous and/or retargeting telescopes at the solar gravitational focus over a period of years.

Qem 3y ago

> if we send probes to ~550AU and use the Sun as a gravitational lens; we will then be able to get high-res (1km resolution?) photos/videos of nearby extrasolar planets themselves. It doesn't scale well. The probe would be able to observe a carefully chosen extrasolar planetary system in the opposite direction in relation to the sun. If you want to observe a second system, it's necessary to launch a second probe 550 AU in another direction. You can't change targets just by rotating the probe, given its lens is the sun.

cryptoz 3y ago
Oh yeah, I'm aware that you'll need multiple probes - but I imagine we could send 50 or 100 of these things starting in like 20-30 years once some of the required engineering on propulsion systems etc is done. Assuming we have the will and money to send 1, I think we'd have the will and money to send dozens.

defrost 3y ago

As Qem mentioned, and as laid out on page 7 of the source paper: A significant difference of the solar gravitational lens from a conventional telescope is that the gravitational lens telescope is not in any practical sense pointable. For the telescope at a distance F from the sun to be re-aimed to image a new target 1° away, it would have to move a distance of (π/180°)F, which is 10 astronomical units at the minimum focal distance-- a lateral distance equivalent to the distance from Earth to Saturn. This means that, in practice, such a telescope is not able to be repointed. Thus, a telescope at the gravitational focus is necessarily going to be a singlepurpose telescope, with the target of observation selected before the mission is launched. A gravitational focus mission can’t be used as a telescope to search for a target: such a mission must be with the objective to observe a target whose position is already known. Mission to the Gravitational Focus of the Sun: A Critical Analysis Geoffrey A. Landis, NASA John Glenn Research Center https://arxiv.org/ftp/arxiv/papers/1604/1604.06351.pdf https://arxiv.org/ftp/arxiv/papers/1604/1604.06351.pdf

p1mrx 3y ago

That seems like a good match for this nuclear sail concept: https://www.nasa.gov/general/thin-film-isotope-nuclear-engine-rocket/ https://www.nasa.gov/general/thin-film-isotope-nuclear-engin... > The basic concept is to manufacture thin sheets of a radioactive isotope and directly use the momentum of its decay products to generate thrust. Actually it's mentioned at the end of the article: > Novel ability to reach deep space (> 150 AU) very quickly and then continue aggressive maneuvers (> 100 km/sec) for dim object search/rendezvous and/or retargeting telescopes at the solar gravitational focus over a period of years.