I'm a fan of the project of putting a telescope in the gravitational focus point of the Sun (at 542 AU from it). It's the kind of almost sci-fi, large scale project that would make me proud of our civilization.
So about 3 times further away than the Voyager probes, and you need the fuel to slow down once you get there. Yep, large scale all right. It's hard enough securing the funding for a 10 year build with 5 year mission for a regular planetary probe.
You'd do this, and a century later when it gets there, something will be spotted and it's not in the direction the telescope is pointing.
You don't really have to circularise the orbit when you get there (counter-intuitively this means speeding up, not slowing down), because you'll have enough time to observe a single point. Changing the direction the telescope is pointing at means waiting for the telescope to move along the orbit around the Sun, which might take a very long time indeed. If it's too long you might as well not bother with circularisation, drastically simplifying the mission.
Of course, you have to choose what you're going to observe before launch, and you need to be certain it will still be there when the telescope arrives. Perhaps an exoplanet?
I was curious what this meant - long enough for an observation? Long enough to check an exoplanet for annual Doppler shifts? Long enough for the telescope technology to become obsolete?
Well, it would still actually be slowing down, since it's only speeding up if you do a hohmann transfer (or something close to it), which would take literal millenia; in actuality you'd be on a highly hyperbolic unbound trajectory to get there sometime in the same century, in which case you would indeed need to slow down if you intended to keep the telescope for multiple observations.
You are still right that it wouldn't steictly be necessary if you just have it fly by for a bit, though, I think many SGL proposals don't slow down and just continue flying off into the void
Fair enough. I think the only plausible design for such a mission would be a light sail. The trajectory would be a spiral, but your point stands: if we don't want to wait millennia it will be going too fast at the focal point, and one would need to slow down if orbit circularisation is desired.
Are you aware of a concrete SGL proposal that includes circularisation? I'd be curious to see the numbers of how hard it is to bring enough fuel to do it.
I can't think of any circularizong ones offhand, though I do vaguely remember hearing of a proposal for a fission fragment rocket based one (something we have the technology to build, just not much of a reason to; FFRE would have the same regulatory issues as NTR, and its thrust makes ion drives look punchy, so it's only really uaeful for far outer solar system). That's potentially able to pull it off, with a longer transit at least
And yeah, whatever you use if it's got the Isp it'll likely be low thrust and have to start as a spiral, but only until you reach escape velocity, and most of your acceleration will be after that point, since you're gonna want to go several times that speed
Seems like ionic thrusters could be practical too. Voyager got a decent chunk of the way in 50 years from a 17km/s gravity slingshot. a 2500s Isp ion thruster could beat that with a mass ratio of less than 10.
Voyager is way too slow for such a mission. It travels at 3.57 AU/y, so it would take 150 years to arrive. Even being double as fast is not enough. I don't think there's any hope without sidestepping the Tsiolkovsky equation.
Resolution depends on one thing, the size of your receptor. You're talking about noise, which fortunately can be solved with longer exposures and statistical analysis
Title text: I'm trying to buy a gravitational lens for my camera, but I can't tell if the manufacturers are listing comoving focal length or proper focal length.
If we ignore aerodynamic forces, then a liquid spinning along an axis that is parallel to gravity would form a paraboloid. However, since you can’t tilt the liquid mirror to point it at observation targets, you would need to have another mirror to reflect the light from the target onto the liquid mirror.
I'm a fan of the project of putting a telescope in the gravitational focus point of the Sun (at 542 AU from it). It's the kind of almost sci-fi, large scale project that would make me proud of our civilization.
So about 3 times further away than the Voyager probes, and you need the fuel to slow down once you get there. Yep, large scale all right. It's hard enough securing the funding for a 10 year build with 5 year mission for a regular planetary probe.
You'd do this, and a century later when it gets there, something will be spotted and it's not in the direction the telescope is pointing.
You don't really have to circularise the orbit when you get there (counter-intuitively this means speeding up, not slowing down), because you'll have enough time to observe a single point. Changing the direction the telescope is pointing at means waiting for the telescope to move along the orbit around the Sun, which might take a very long time indeed. If it's too long you might as well not bother with circularisation, drastically simplifying the mission.
Of course, you have to choose what you're going to observe before launch, and you need to be certain it will still be there when the telescope arrives. Perhaps an exoplanet?
A very long time indeed!
I was curious what this meant - long enough for an observation? Long enough to check an exoplanet for annual Doppler shifts? Long enough for the telescope technology to become obsolete?
So I checked the solar orbit calculator at http://www.hyperphysics.phy-astr.gsu.edu/hbase/solorb.html.
It says that for a 542 AU orbital diameter, the time to complete an orbit is 12,541 years.
That's a long time.
But focusing on one spot would be close to instant.
Well, it would still actually be slowing down, since it's only speeding up if you do a hohmann transfer (or something close to it), which would take literal millenia; in actuality you'd be on a highly hyperbolic unbound trajectory to get there sometime in the same century, in which case you would indeed need to slow down if you intended to keep the telescope for multiple observations.
You are still right that it wouldn't steictly be necessary if you just have it fly by for a bit, though, I think many SGL proposals don't slow down and just continue flying off into the void
Fair enough. I think the only plausible design for such a mission would be a light sail. The trajectory would be a spiral, but your point stands: if we don't want to wait millennia it will be going too fast at the focal point, and one would need to slow down if orbit circularisation is desired.
Are you aware of a concrete SGL proposal that includes circularisation? I'd be curious to see the numbers of how hard it is to bring enough fuel to do it.
Unless it's made from asteroids, concrete would be a terrible material for building a space probe. 😉
I can't think of any circularizong ones offhand, though I do vaguely remember hearing of a proposal for a fission fragment rocket based one (something we have the technology to build, just not much of a reason to; FFRE would have the same regulatory issues as NTR, and its thrust makes ion drives look punchy, so it's only really uaeful for far outer solar system). That's potentially able to pull it off, with a longer transit at least
And yeah, whatever you use if it's got the Isp it'll likely be low thrust and have to start as a spiral, but only until you reach escape velocity, and most of your acceleration will be after that point, since you're gonna want to go several times that speed
Seems like ionic thrusters could be practical too. Voyager got a decent chunk of the way in 50 years from a 17km/s gravity slingshot. a 2500s Isp ion thruster could beat that with a mass ratio of less than 10.
Voyager is way too slow for such a mission. It travels at 3.57 AU/y, so it would take 150 years to arrive. Even being double as fast is not enough. I don't think there's any hope without sidestepping the Tsiolkovsky equation.
The faster you arrive, the more velocity you have to shed, or you don't slow down and have a shorter observation window.
There are plans to do with with the Earth and atmospheric refraction instead.
I'm interested, do you have a source?
https://en.wikipedia.org/wiki/Terrestrial_atmospheric_lens
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Resolution depends on one thing, the size of your receptor. You're talking about noise, which fortunately can be solved with longer exposures and statistical analysis
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Title text: I'm trying to buy a gravitational lens for my camera, but I can't tell if the manufacturers are listing comoving focal length or proper focal length.
Don't get it? explain xkcd
Don't drink that! Rude.
Also, it’s mercury
I was worried I wouldn't recognise the joke telescopes
I honestly can't tell if the Gregorian and Cassegrain telescopes are real or jokes.
They're some of the most common. The liquid mirror is real too.
But most liquid-mirror telescopes use liquid mercury, so the bendy straw is a bit of a joke.
Cassegrain is real, so I'm guessing Gregorian is too, although I'm not sure.
I laughed way too much at the comoving vs proper focal length lol
I think with buying gravitational lens a problem would be shipping, as the shipping companies charge both per kilogram and per kilometer.
Actually not a problem for very large deliveries, as they just bend the space enough to create a temporary wormhole.
Do you think the beancounters will let that get in the way of charging for full distance?
The core slander never stops
now i'm wondering what type of curve that liquid spin would make, and what effects that'd have on it as a mirror
It exists IRL. https://en.wikipedia.org/wiki/Liquid-mirror_telescope
https://en.wikipedia.org/wiki/Large_Zenith_Telescope
https://www.youtube.com/watch?v=GLURSGpgahQ
If we ignore aerodynamic forces, then a liquid spinning along an axis that is parallel to gravity would form a paraboloid. However, since you can’t tilt the liquid mirror to point it at observation targets, you would need to have another mirror to reflect the light from the target onto the liquid mirror.
You can just tilt the Earth instead (i.e., wait for it to rotate).
No love for the Yolo.