Hacker News Reader

Comment by tectonic | Hacker News Reader

Nice gravitational lens observation! We're hoping to use the same technique with the Sun to observe exoplanets by launching a fleet of small satellites to 547 AU (80 billion km / ~3 light days). The craft would sample the distorted Einstein ring around our Sun from that vantage point, then combine and reconstruct an image of the disk of an Earth-like exoplanet up to 100 light-years beyond, at a resolution of 25 kilometers / pixel.

https://orbitalindex.com/archive/2020-07-08-Issue-72/#more-o...

View on HN

25 kilometers per pixel is incredible resolution for something that far away!

That would be tremendous.

Earth is 12700 km in diameter, so such an image would be a bit more than 500px across.

Here is a picture of the Earth that is about 500px in diameter: https://cdn.mos.cms.futurecdn.net/3upZx2gxxLpW7MBbnKYQLH.jpg

Do we only get a ring or do we get the whole thing? If we only get a ring why is that? Is the thing we are bending light around in the way?

Your question seems to be sorta answered in this thread: https://news.ycombinator.com/item?id=24425595

Not the same technique, but there are similar architectures that could be implemented far sooner.

Earth's atmosphere as a refractive telescope: https://www.scientificamerican.com/article/earth-could-be-a-...

Not nearly as powerful, though.

That depends on the planet used. If it works for earth, the next step might be Jupiter or Saturn, something that might be possible by only repositioning the spacecraft. It may even be possible to use the sun's atmosphere, the transparent part, as a lens.

How does the lensing work? Why doesn't the galaxy in the middle between us and the faraway galaxy pollute the image with its own light? It it separated by frequency or some trick?

The light bends around the galaxy. You're right that looking straight at the galaxy wouldn't work, but looking just a tiny bit to the sides does.

How do you propose to power a fleet of spacecraft at 550AU? Would you be able to acquire enough RTGs? What about DSN time for the downlink?

And how would you get them out to, and stop at, 550 AU? Voyager 1 and 2 are nuclear powered with RTGs and they are respectively about 150 AU and 125 AU from the sun, and they are going really fast. The Voyager RTGs are also fairly depleted at this point. I’m guessing these spacecraft would need a faster, more efficient mode of propulsion, like a nuclear thruster or ion drive (or Epstein drive?!). One could also get a lot more fuel for the journey if the the probes didn’t have to launch fully fueled from the Earth’s surface.

No need to stop at 550AU, the gravitational lens keeps working beyond that(theoretically all the way to infinity).

As for how to get there, yes, innovative propulsion is required. My idea is that the probe would dive close to Sun and use solar energy (sail? electric propulsion?) to accelerate itself out to hundreds of km/s.

I was wondering how fast myself and found this:

https://voyager.jpl.nasa.gov/mission/status/

Voyager-1 is the fastest at 38,000 mph (61000 km/h) with respect to the Sun, but currently about 90,000 mph (144000 km/h) relative to earth (I guess this fluctuates annually).

Sun slingshot, solar sail

https://www.youtube.com/watch?v=NQFqDKRAROI

That webpage says a tech demo is due 2024, with launch in 2034 and the constellation would reach 550AU by 2064, so probably a lot of how this will work is still WIP.

The problem with dates like that is they are pure best wishes. They might have funding for a demo in 2024 – although it isn't even clear they've got that yet, it sounds like they may just have funding to develop their proposal further. Even assuming the tech demo is successful, it sounds like they don't even yet have a detailed costed proposal for a 2034 launch, and no idea how likely that it will actually get funded.

Politicians and bureaucrats want immediate results, so a "launch now and see results in 30 years" mission – by which time many of the senior decision-makers will likely be dead – is going to be less attractive than competing missions offering results much sooner.

If you go back through the history of space exploration, it is full of proposals that "by year X we will be doing Y!" which never came to pass, because the money never turned up.

> Politicians and bureaucrats want immediate results

This makes me sad. The entire point of Government is to be an enterprise spanning multiple generations.

The downside of electoral democracy, is if you are only going to be be in power for 5-10 years max, why care about the state of the country in 30 years time, except out of the goodness of your heart? And electoral politics often does a rather poor job of selecting leaders with goodness in their hearts.

Of course, non-democratic systems have their own, equally serious downsides. Consider China: a system which is arguably much better at making long-term investments in public infrastructure than most democratic countries are (witness China's high-speed rail system), but also a system which ruthlessly suppresses dissent and locks up over a million of its citizens in "re-education camps"

Even without politicians, the effective limit to most enormous projects is a human life span. Even if you look at projects that spanned 100-200 years like some cathedrals, they tended to be built in chunks: the main hall might be the first and largest, but things like trancepts, side chapels etc. would come later

In a hereditary absolute monarchy, the son (or more rarely daughter) may feel motivated to continue to the projects of his father (or more rarely mother), out of a sense of filial duty. In principle, it seems like hereditary absolute monarchy may avoid the problem you describe.

In practice, hereditary absolute monarchy suffers from the problem of the dud heir: Marcus Aurelius is remembered as one of the greatest Roman Emperors, his son and successor Commodus is remembered as one of the worst.

>This makes me sad. The entire point of Government is to be an enterprise spanning multiple generations.

Not in a democracy. The point of a government in a democracy is to serve the current will of the people. The government itself might last many generations, but its goals and motivations change with every election cycle.

The point of democracy is to create AI powered propaganda to tell the people how to vote and make the rich even richer?

rich people are not a problem; if anything, they are more likely to finance this kind of project

The esoteric among them.

the recommendation is RTG + rad-hardened battery, naturally the question of will there be enough RTGs is a perfectly valid one.

https://arxiv.org/ftp/arxiv/papers/2002/2002.11871.pdf

for downlink can't they launch a few extra sats that just sit around the Sun and form a big virtual dish (via baseline interferometry or what's that occult DSP magic called these days)?

> it’d still take 25 to 30 years for them to reach a vantage point .... > mission designers would have to pick carefully because they could observe only a single target

It will take 30 years to get in position but then we can only look at one target? While it sounds very neat, I'd rather fund something we can use more than once, and sooner.

Still valuable as a way to observe a potentially habitable planet in more detail. If we wanted to launch a probe there, it would take a lot more time!

We should build one for each target we want to observe.

Starship is going to open so many opportunities.

You CAN use for more than 1 target, you just need to reposition the telescope a bit. See [1], is a great great video on the subject. I can't recommend enough

[1]: https://www.youtube.com/watch?v=NQFqDKRAROI

The whole concept is that we should launch a fleet of them every few months. Very lightweight semi-autonomous smart lightsails with some optics.

The first fleet helps targeting the second, and all those who come after them.

https://www.youtube.com/watch?v=NQFqDKRAROI (already linked by a sibling comment, but yes, can't recommend this enough!)

20 AU per year is a tremendous distance. Pluto is apparently right around 25 AU. Is this speed actually feasible even with solar sails?

Big layman here. I only skimmed this link but this stood out to me.

If that can be done, it means the light and the info is there. Meaning here. The lensing and the 550 AU are just ways to catch it. I should be highly surprised if we do not - long before 2064 - have optical and computational trickery to catch such resolution with snapshots from somewhere very close to home.

That's four times as far away as Voyager 1 is. I see from the link that it would take 25 to 30 years to reach that distance, and only one target could be observed: we would have to have one particular exoplanet we want to image and go to the right point for the sun to focus the image to.

Your link suggests the satellites word need to be around 2000 AU to avoid the corona, though I suppose the delta v requirements would be pretty small for such a large change so far from the sun (but my only source for the intuition is kerbal so take it with a grain of salt).

That's really cool. If it's good enough to detect geographic features, will it be possible to photograph the same planet from the night side later in its orbit?

That's completely mad! I'd love to be part of that.

> 547 AU

For comparison Voyager-1 is now at a distance of 40 AU only.

Is that number correct? Why not just launch at those starts at that point?

For comparison, the nearest star to us is 268,770 AU away, or around 491 times further away. It would take quite a bit longer to get there!

i guess i was thinking more about the complexity of arranging a constellation of telescopes around sol versus just sending one much closer to a target star.

Is Voyager-1 still accelerating?

Nope, both are slowly decelerating as they leave the solar system: https://upload.wikimedia.org/wikipedia/commons/0/0c/Voyager_...

That is not correct... it is 150 AU away from earth.

https://voyager.jpl.nasa.gov/mission/status/

That is incorrect. It's approximately at 150 AU[0]. For reference, that's about three times the distance of Pluto at aphelion. 547 AU is about 11 times the distance of Pluto at perihelion.

[0] - https://voyager.jpl.nasa.gov/mission/status/

Wow.

It's not a new idea... I first heard of it in the intro segment of this Cool Worlds Lab vid

https://www.youtube.com/watch?v=jgOTZe07eHA

Reply on news.ycombinator.com