The most complete plan for this was proposed by JPL's Slava Turyshev and team. It has been selected for Phase III of NASA Innovative Advanced Concepts. [0]
> In 2020, Turyshev presented his idea of Direct Multi-pixel Imaging and Spectroscopy of an Exoplanet with a Solar Gravitational Lens Mission. The lens could reconstruct the exoplanet image with ~25 km-scale surface resolution in 6 months of integration time, enough to see surface features and signs of habitability. His proposal was selected for the Phase III of the NASA Innovative Advanced Concepts. Turyshev proposes to use realistic-sized solar sails (~16 vanes of 10^3 m^2) to achieve the needed high velocity at perihelion (~150 km/sec), reaching 547 AU in 17 years.
> In 2023, a team of scientists led by Turychev proposed the Sundiver concept,[1] whereby a solar sail craft can serve as a modular platform for various instruments and missions, including rendezvous with other Sundivers for resupply, in a variety of different self-sustaining orbits reaching velocities of ~5-10 AU/yr.
Here is an interview with him laying out the entire plan.[2] It is the most interesting interview that I have seen in years, possibly ever.
Sadly ,the last reference I see to this project is from 2022, from his own CV on his JPL profile page. What happens after stage 3 with NIAC? Is there even a stage 4, or does it need to get selected by some committee or something?
Well, one single long exposure would literally generate a regular sized image. Though I do guess they’ll be doing multiple exposures if only to avoid saturating their dynamic range.
Does anyone know what a typical number of acquired frames is for a space telescope?
Orbiting instruments typically transmit raw instruments data blocked into lines or segments that are are each surrounded by checksums.
It might be compressed for transmission, but raw data (warts and all) is king .. once it's "processed" and raw data is discarded .. there's no recovering the raw.
Years later raw data can be reprocessed with new algorithms, faster processes and combined with other sources to create "better" processed images.
Onboard hardware errors (eg: the historic Hubble Telescope erros) can be "corrected" later on the ground with an elaborate backpropagated trandfer function that optimally "fixes" the error, etc.
Data errors (spikes in cell values, glitches from cosmic rays, etc) can be combed out of the raw in post .. if smart people have access to the raw.
Baking processing into on board instrument processing prior to transmission isn't a good procedure.
But this wouldn’t be in orbit; it would be in what NASA calls “deep space”, which relies on the Deep Space Network [1]. The DSN is severely bandwidth constrained, due primarily to a lack of ground antennas. Indeed, for instruments that are located outside Earth’s orbit (e.g. SOHO, which is at Sun-Earth L1 [2]), bandwidth is often a limiting constraint in the design.
My understanding is that some newer instruments do both compress and select data to be downloaded (i.e. prioritizing signal over noise), and that there is more and more consideration of on-board processing for future missions, as well as possibly introducing the capability within DSN itself to prioritize which instruments get bandwidth based on scientific value of their data.
Source: A presentation from people at NASA Heliophysics last week, where this very topic came up.
The DSN is a radio network. In its present form, this is going to be ineffective for receiving a meaningful amount of imagery data from signals emitted by a lightweight space probe at 500AU. At ~150AU the current 25-70m dishes are getting less than 40 bits per second from Voyager 1.
Instead, we would use lasers with a far superior gain to what radio communication is capable of. The divergence on even a decent pocket laser pointer diode is less than 0.1 degree. This is a gain of 10*log10(41,253/(0.1*0.1)) = 66 degrees. Launch telescopes of modest size can increase this further. Then receiver telescopes fitted with narrowband filters can hone in on that laser signal.
> "First, transmitted beams from optical telescopes are far more slender than their radio counterparts owing to the high gain of optical telescopes (150 dB for the Keck Telescope versus 70 dB for Arecibo)." - https://www.princeton.edu/~willman/observatory/oseti/bioast9...
From the interview linked, it sounds like the current plan doesn't involve the DSN at all: they're effectively out of transmission range past a certain point, and the transmission back is optical, using a big earth or space-based telescope. Which is one of the scary things he mentioned: they're going to be entirely autonomous when collecting the data.
You could store all the data on the satellite, upload new code to process it differently, and download the resulting image. Then, the communications link just has to handle code (several MB up) and images (several MB down) instead of petabytes of data.
The launch mass of a petabyte of SSD is under 10 kg. I don't know if it would survive 17 years of space radiation though.
Just as a thought experiment, would it be viable to send up an array of traditional hard drives? Arrange them all for use as reaction wheels, then spin them up to persist/de-stage data while changing/maintaining targets.
Probably worse than sending up well-shielded flash, but I don't think the Seagate/WD warranty expressly forbids this usage.
Sure, it would discard a lot of data / noise, and would send a preview over first, but like with the Pluto probe, they do want to get as much data as possible, as an image is only a representation thereof.
The Wikipedia article uses the name "Slava".
His homepage on JPL website too (https://science.jpl.nasa.gov/people/turyshev/)
I opened a random paper of his from arxiv and there too he uses "Slava".
Would it be possible that Mr. Turyshev uses that name as his preferred name (at least when writing in English) and that we should just respect his decision?
Sure, but is it his decision to make, and if yes - are we ok to respect it?
I'm from a slavic country myself and my name is almost impossible to pronounce correctly in English - but I continue to use it anyway. If he wanted to do that, he could have done it.
My name is "Pavel", and usually ask Americans to put the accent on the second syllable - which is incorrect, but they can't pronounce my name correctly anyway when they put the accent on the first syllable, and it sounds more wrong to me than the way I prefer to have it pronounced.
Apologies to all the other Pavels out there; I've been training everyone I've met to pronounce it wrong. But it's the way I prefer to be addressed.
Even if somebody puts a gun to your head and orders you to change your name, you'd still have a choice and it would be your decision what to do. That's not much of an argument though.
No one put a gun to his head though. Discomfort of English speakers isn't enough reason to not use your real name if that's your preference. Again, speaking from experience.
Many Chinese (speaking) students in the US pick an English language name like “William” or “Wendy” because they know people they meet will struggle with a name which could be several short words with unfamiliar vowels and consonants and tone that matters.
Of course - and I support their choice. People struggle with my name every day and I could change it to make it easier for English speakers - but I don't think that's quite the same as being "forced" to change it.
That's not quite the same as having a gun to your head. Again, I have a slavic name that's extremely difficult to English speakers and I live in the UK - no one is forcing me to change it. I understand some people chose to change their name so it's "easier" for English speakers - and I respect that choice. But let's not pretend that Mr Turyshev was "forced" to change his name - he wasn't.
Did you mean that English speakers don't pronounce Russian names the way Russians do?
Ask your local Russian to pronounce rural Worcestershire the way that English speakers do.
Your typical Russian speaker cannot. Is it that they aren't "bothering"? The idea is absurd. Let people approximate foreign names in their own tongue. Or, if the way that they naturally pronounce something is truly atrocious, give them a name that is easier to pronounce.
Okay, that was about as rude on my part as ordering me to stop was on yours. My apologies.
But the point is that most people won't bother to google the pronunciation, listen to it and make an effort to repeat close enough. By the way, Dr. Turyshev's name is the easy part, the surname is the real challenge)
How would this kind of thing work in practice? You move the telescope out to 500AU, and then... what? I assume the telescope would have to line up a potential star system with our sun in a direct line. So the telescope would have to move around until everything is lined up. Then I presume it would need to take a wide angle view of that star system to look for a likely planet. Would it need to move closer or farther away from our sun to get a wider field of view? Once it found a suitable planet, I presume it would need to collect light from that planet over an extended period of time, say 6 months. But, the planet is moving during those six months. How does the telescope keep the planet in view? Is the telescope constantly moving to keep pace with the planet? How much fuel would we have to send out there with the telescope?
If you want to use this method, you're basically going to require one spacecraft per target and a decade of lead time for a very short-duration observation. This is not necessarily a deal-breaker; Meaningful scientific inquiry would just require we mass produce them.
We already sabotage ourselves in astronomy by refraining from mass production approaches for political reasons.
There is no practical amount of fuel that can get you to 500AU on a simple trajectory. What seems to be the best option for setting massive vehicles on a solar escape is a sequence that looks something like:
* Launching to Jupiter propulsively
* Cancelling out most solar-orbital velocity there using a gravity assist in order to dive down into a sun-skimming orbit
* Burning through a large solid state rocket kick stage while at close approach to the sun from behind a heat shield. The Oberth Maneuver.
* (optional) unfurling an electric sail or solar sail once the rocket has finished as you're speeding away from Sol
Together that gets you the required ~100AU/year escape for a mass fraction that is tractable for our civilization.
Christian Ready made a great video on his Youtube channel, Launch Pad Astronomy, about NASA's plans for a solar gravitational lens. It's got some great graphics and visualisations, and is accessibly narrated. I was inspired and learnt a lot of new ideas.
I can highly recommend this video, and in case people do not know, Christian Ready is actually a person, not an organization run by religious fundamentalists.
Is there anything stopping you from putting 2+ satellites out "closer" but in the path of the lensed light, capturing the light simultaneously, and then resolving the image via async computation later? I think this is called interferometry and I know it's hard because you need _very_ precise timing, but I'm curious if that would be possible or not. (Maybe you can get the timing in sync with atomic clocks, or by sending a laser to both from a central point that lets them keep time with some very tight tolerance?)
Weird idea but I wonder if there are ways to take this from "crazy tech" to "hard tech".
> Is there anything stopping you from putting 2+ satellites out "closer" but in the path of the lensed light
The Sun. Literally.
Satellites have to be that far for the Einstein ring to be bigger than the apparent size of the solar disk.
Edit: to make it a bit more clear, the gravitational lens does not quite behave like a normal lens. Instead, you see the light from _behind_ the object. So if you're too close to the lensing object so that the Einstein ring is not larger than it, you'll just see a part of the object to be a bit more bright.
Also, the gravitational lens does not actually _focus_ the image, it distorts it into a band around the lensing object.
But if the light is "warping" around the object then would you be able to grab the light from either side by intercepting it there? If you are at the X AU required for lending, but you sit at X/2 AU with some slight offset, you would be in the path of the light that would be traveling to X AU eventually.
I understand if what I'm trying to describe is impossible, I just don't fully understand why. (Is it out of focus? Is the sun too big/bright?)
I'm no expert here.
You mention "either side" as if the light came from both the left and the right. But I think the light would be coming along a circle all around the sun depending on exact position.
So the trick here is that if you are at the focus point, you get all that light in a small area "for free". But if you try to catch the light on the way, you now need to catch eveywhere in a whole massive circle, which is basically impossible, so you only catch a minuscule amount of the light. And then have to deal with interferometry.
Stronger gravity around massive objects causes slow down of the part of a light wave closer to object, compared to outer part.
This difference in speed, caused by _interaction_ between the photon and gravitational field of the body, results in the bending of the light's trajectory.
Bending of spacetime is just a simplification of this process to model that easier.
from what I understand, slowing down would be true for a non-massless particle, but speed of light in vacuum is still the same around massive objects. What changes is the frequency of the light in this particular direction, and that "turns" it, probably because of self-diffraction?
Parts of photon cannot have different frequencies than whole photon. Both inner and outer parts of photon will make exact same number of fluctuations for the same period of time, but inner part will travel slightly smaller distance.
It's the same effect as in reflections, except that speed difference between air and solid objects is much much bigger, which results in sharp turning radius.
The speed of light is constant as measured from any observer. This has been verified experimentally to a very high precision and motivated the development of special and general relativity.
Otoh there is no requirement for a wave front to have the same frequency as when it started. A gradient in the gravitational field can cause a gradient in the gravitational redshift and thus "parts of photon" can very well have slightly different frequencies. If you recombine the paths and have the photon to interfere with itself, the interference pattern will capture the shape of such a wave function as affected by the distortion in the gravitational field.
IIRC this is the "standard" way of thinking about what's going on although marrying quantum mechanics and general relativity is still a work in progress.
If you buy into another theory that involves a variable speed of light, I'd love to hear more about what exact theory are you talking about since it seems to me that the burden of proof is on who makes the most extraordinary claims.
LIGO/Virgo/KAGRA found that speed of light in vacuum is affected by gravitational waves. This is verified experimentally to very high precision (1.2E-20m). If merge of neutron stars 200 megaparsec away can affect propagation of light here, on Earth, then why it cannot affect it near to the star?
ok I think we're talking past each other. let's take a step back.
Let's imagine two points in space A and B, that are let's say 10 light minutes distant from each other. A signal going straight from A to B will thus take 10 minutes.
If point A sits in a strong gravitational field (e.g. it's orbiting a very heavy star), the signal will still take 10 light minutes to reach point B. (please tell me if you disagree with this assumption).
Now, let's place another heavy star at the midpoint between points A and B.
How long will it take for a photon emitted by A to reach B? Well, it won't reach it because it will hit the start that's in between.
But another photon whose direction wasn't directly in the path from A to B will follow a longer path, be deflected around the star and reach point B.
It will take longer than 10 minutes to reach point B because it will move along a longer path.
The speed of light in vacuum is constant and is not impacted by gravity, AFAIK. Really the light is travelling in a straight line in space but gravity bends space and time.
LIGO/Virgo/KAGRA found that speed of light in vacuum is affected by gravitational waves. This is verified experimentally to very high precision (1.2E-20m).
Light doesn't travel in a straight line because, to change trajectory of photon, photon must interact with something to exchange momentum. You are talking about mathematical model[1].
> Stronger gravity around massive objects causes slow down of the part of a light wave closer to object, compared to outer part.
That only matters in areas with _really_ high fields, this effect is negligible for areas far away from a singularity of a black hole.
Instead, it's really the space that curves. The light does not slow down, it always moves at the speed of light. In the general relativity there is no "gravity field", gravity is a fictitious force.
Edit: also, gravitational lensing applies to massive point-like particles as well. For slow-moving particles and weak fields, it's negligible compared to regular Newtonian orbits, but if a particle moves at a speed that is close to lightspeed, it'll be lensed just like the light.
You forgot about conservation of momentum. Photon cannot change it's direction without interaction with something to exchange momentum.
"Bending of spacetime" is just computational trick to increase precision of the model.
Bending of trajectory because of change of speed of light is negligible, yes. It's only visible on light-year long distances.
Photon is very wide. Dual slit experiment show that single single photon interacts with two slits up to millimetre apart. Even small difference in speed/frequency at such large distance will accumulate to noticeable change of course at light year long distances.
> You forgot about conservation of momentum. Photon cannot change it's direction without interaction with something to exchange momentum.
No. I'm not forgetting anything. Photons _do_ _not_ change direction. They always move in straight lines (from their "point of view"). It's just that if you step a bit away, these straight lines are not actually "straight" globally.
A classic example is a 2D ant crawling on a surface of a sphere. From the ant's point of view, it moves in a straight line, but a 3D observer will see that a straight line is actually a 3D circle.
Conservation laws are not violated. A photon (or another particle) will cause its own slight bending of the space-time, that in turn will slightly bend the star's trajectory.
It does sound like an interaction between gravitational fields, but the models give different numeric predictions.
> "Bending of spacetime" is just computational trick to increase precision of the model.
It really is not.
> Photon is very wide.
Facepalm. Sorry dude, but you have no idea what you're talking about. Lensing and time dilation also happen for point-like particles like electrons.
> Photon cannot change it's direction without interaction with something to exchange momentum.
Doesn't the entire photon simply exchange momentum with the star, without needing to invoke any higher-order effects? Just as the star exerts a gravitational pull on the entire photon, the entire photon exerts a (very miniscule) gravitational pull on the star.
The precision you need for interferometry depends on the wavelength, and being able to do this over astronomical distances at visible wavelengths would indeed be a challenge. I think the scale is timing more accurate than 0.1 nanoseconds and distance accuracy on the order of 100 nanometers. Near those orders of magnitude at least and over astronomical distances that might be measured in AU.
Then again the precision of the gravitational wave instruments measure distance on the order of the width of a proton, so who knows.
Terrestrial infrared and optical interferometry telescopes are on the bleeding edge right now.
"Boring" cesium atomic clocks can do 50 ps per day with the best cutting edge optical clocks coming in at ~739 fs per day. Optical clocks would only need to resynchronize once every ~ 135 days while cesium clocks would need to do it every 2 days to get 0.1ns of accuracy.
I think the bigger challenge may be how you would transport the clocks after synchronization to maintain it across astronomical distances since they're very sensitive to any kind of acceleration. Since you have to regularly re-synchronize them in space anyway, that feels like the engineering problem you'd have to solve - how do you synchronize two atomic; the current record is synchronizing to within 0.32fs at a distance of 300km [1].
Presumably it means that two light rays that leave the same point on the planet simultaneously (but going in slightly different directions) arrive at the two telescope satellites simultaneously
But if they want to observe planets, and planets move, wouldn't the telescope need to move too, to keep the image stable while gathering more photons? I presume very few photons reach the telescope from that far away.
That means the object's orbit need to be known before beginning it's observation, and then consuming a lot of propellant to change the telescope's speed and trajectory, possibly distance to Sun too, to track another object.
At that distance from the Sun, to track objects in another solar system, it would need to move vast distances sideways possibly taking hundreds of years.
Yes, the planet (hypothetically, a very earth-like planet with a 1-year, 1 AU orbit, 24-hour rotation, and 23-degree tilt at 4 light years' distance like Proxima Centauri b) moves at most 2 AU in a 6 month integration, and the telescope ~700 AU behind the center of the lens would have to move more to keep it opposed. But that 4 light year distance means it's 250,000 AU from the Sun, so some basic geometry says it only has to translate laterally by on the order of 2 * 700 / 250,000 = 0.0056 AU. You're right that that is far larger than an image sensor would be, and larger than the solar sails that would push this craft would be, but inconsequential for a vehicle that's just flown 700 AU.
Planets not only move relative to their star, but they also rotate and tilt. I see a number of artists' depictions of the planet (eg at [1]) that look like the satellite just flew into space, illuminated a circular planet with a giant flash bulb, and returned a pixellated photo. I've only thought about this for a minute, but I don't think it would look anything like that.
Trying to integrate an image of over the course of a 6-month exposure means not only tracking where the planet is in its orbit but also discerning the longitude on the planet from which a given photon was emitted at a particular time. Plus, if it's tilted at all, we might get many images of the north pole and none of the south pole, or an underexposed image of some polar regions that were only aligned with us for a small duration of the exposure. Finally, even though this gravitational lens is enormous and can collect many more light rays that happen to be aimed at the sun on the image sensor than a physical lens or mirror could, light still has to come from somewhere - specifically, the host star, so only half of the sphere can potentially receive photons that might bounce in our direction at any time, and that half may or may not be aligned with us. Finally, over the course of 6 months, the planet might experience seasons, with changes in the atmosphere and surface ice!
Assembling the raw data into a sharp image would be far more challenging than just opening and closing a shutter then grabbing a serial stream of X by Y pixel data from an image sensor, but the output might be much more than a single image.
Basically, it's possible to generate an image of an exoplanet, but "retargeting" the telescope(s) to observe another object is not feasible. So you'd better make sure the target that the mission will focus upon is actually worth the attention it gets - but there are other planned telescopes that will be capable of generating data that will allow selecting potential candidates.
Here's a PBS Space Time episode [1] from a couple years ago that describes a couple different proposals for how to do this that take quite different approaches. It starts getting into the specifics of those approaches at 7 minutes in if you don't need the introductory material.
Is this a similar principle to the concept in the 3 Body Problem series of books? As in, how one of the main characters is able to boost the transmission power of an earth bound antenna
In the three body problem she uses some property of the Sun's internal layers to amplify the signal. In reality we don't know of any actual property in the Sun that could do this.
The gravitational lens idea is different, it makes use of a known phenomenom where the Sun's gravity "bends" light rays moving around it, which can amplify the light coming from far away objects. In principle you could run it backwards, so the lens could amplify signals we send as well.
It wouldn't amplify them, there's no energy gain. A gravitational lenses just bends the trajectory of the waves. If you do it right it may be possible to use that to focus the signal on a directional trajectory(as in, the same energy is redirected in a single direction instead of being spread out), if I'm not mistaken.
The ability to observe at given resolution implies though that there is a lightcone of civilization discovery spreading from humanity, visible to our neighbours.
It's using the Sun as a (gravity) lens, with probes at the focal point to gather the image. Because it's a very large lens, that's allow to have a massive zoom on whatever object we are interested in.
But you should be able to use it as a "parabolic" mirror, to make a very directed ray to the planet. (Assuming diffraction is not a problem.) (Assuming no time delay, because to see the planet you should look to were it was many years ago, but to send a message you should aim to where it will be many years in the future.) (Assuming I'm not missing a few more technical problems that are not impossible to solve, but extremely difficult.)
Would space telescopes use interferometry to get a clearer picture?
If we had thousands of telescopes spread across the solar system, what sort of images of distant stars/planets/galaxies could we gather? Would such an array be scientifically worth making in our distant future, or does it suffer from diminishing returns?
There have been plans drawn up for space telescopes flying in formation to do the same kind of interferometry thing as the Keck observatory.
The problem is that even far from the Earth, there are tiny but significant forces pushing the space telescopes around. Solar wind, outgassing, gravitational influences from planets, etc...
The precision required to maintain formation is... challenging.
Why do you need to maintain formation? Can the just fly randomly and fix the problem storing the info and a software that gets the positions and calculate the delays?
For radio frequency I think it's possible.
For visible light, I guess you must do the interference using very accurate mirrors to aim to the central point and that move slightly forward and backward to get the correct phase shift. I think it's not impossible, but very difficult.
For a comparable endeavour, they combined the data of telescopes across the world to create a planet-diameter-sized telescope and with that, the first image of a black hole; extending something like that solar-system-wide would make a solar-system-wide telescope. I'm no astronomer but I'd say it's worth it.
> Light coming from an exoplanet would be gravitationally focused by the sun with a focal point in the region of about 550 AU to 850 AU,
Ouch. Does this mean we're limited to targets located in our plane of ecliptic? Also, we have to have a good target picked out don't we? There's no way to point this at a more interested planet if the first is a bust.
I think so, as long as you know how far away your target is (the focal point) to position the sender, and you need a way to send the signals at the right angles "skimming" the sun at the right distance. (note: armchair amateur, this is just conjecture / thought experiments)
One could also lens neutrinos using the Sun's core. Because neutrinos are not absorbed by the Sun, there is a critical offset from the core where they are maximally focused. This would form a caustic, and would cause increased magnification of the neutrino signal at that focal distance.
The sun is the biggest neutrino source in the sky. So we'd need some way to filter out neutrinos that are not from the sun, like we do with various photon telescopes.
Furthermore, we can barely detect neutrinos. Building neutrino detectors is extremely challenging. Usually they are extremely massive and surrounded by lots of rock (even more massive). We'd have to get all that mass to the focal point of the observatory which is extremely far away.
Lastly, the gravitational field inside the sun is much different than outside. In fact, the field is strongest at the surface (or slightly below, as it doesn't have equal density). The further inside you go, the more parts of the sun start pulling you outside, until you reach the center of mass, where the gravitational forces cancel out.
Looks like Est31 has made about 7 factual claims. I'd guess you'd get more replies if you would narrow down which of the seven you are most perplexed by.
Neutrinos could be distinguished by energy, and also from antineutrinos. There would be an upper bound to the energy that could be detected because at some energy the Sun becomes opaque to neutrinos.
Yes, they are hard to detect, so this is a massive project, not practical right now.
The last point is why there's a caustic. The focal length diverges to infinity as you get to the center; there's a radius where it's at a minimum. This radius will be well within the sun, since the center of the Sun is so much denser than outside the Sun.
What non-uniform field of neutrinos would one expect? I seem to recall that neutrinos come from every direction. Perhaps some stellar event like a nova? Otherwise the image would be the same everywhere, as the sun is relatively uniform.
I’ve put this in my “other ideas” section in YC applications for a couple rounds now. No luck yet.
Would love to send 1,000 probes to 550AU+ out in order to observe 1,000+ ‘nearby’ exoplanets, hopefully find life, make contact, start trade…haha. Or otherwise defend the solar system from invaders that are perhaps already on the way!
Maybe YC rejects me specifically because I put that there…hm.
What kind of ROI would attract a VC to this kind of project? How could they monetize it?
Would each image created be proceeded by ads that you can skip after 5s or would they be unskippable? Data harvesting is kind of the point of the platform, but maybe they could track that data and get the PII/deanonymized information? "This user spent 104 hours continuously staring at the sun. Maybe they would be interested in sunglasses, or maybe some sun block"
how much analysis have you done on this? I'm working on a series around Kardashev II work - space solar, asteroid mining, dyson spheres and the real work that is happening to support this now. contact me if you'd like to discuss - @bensand on X
I mean it's a great idea and all and probably not original, but it needs billions if not more in new spacecraft that can travel 3-4x as far as the furthest human-made object is (Voyagers) in a reasonable time, a scalable launch system that can launch the probes (1000x payload + fuel with the delta-V required to get there), probes that go to the destination, and a new almost interstellar communications network to get the data and commands there and back again.
Basically your idea would be the biggest, most expensive and longest undertaking in space exploration system, ever. I can see why investors would be a bit hesitant about that.
if to use existing nuclear reactor tech and already existing, as tested by NASA (and drives Starlink satellites), ionic drive - about 3500 ISP - that focal point would take about 10 years to reach. I hope that SpaceX flights to Mars will, after the probably first chemical ones, be done using ionic drive with solar as it is just faster, thus getting tech developed and with adding nuclear for beyond Mars - so in 10-20 years we'll have the stuff flying. (note that "small" reactors - 100MW - we have for submarines, and with MS, ORCL, GOOG, AMZN getting into nuclear we'll have such small reactors productized into normal commercial use which will simplify space use too as commercial use require higher reliability/etc. compare to military)
You don't need to slow down, the region where you can do the observations is basically a slowly expanding cone the further you get away from the sun. But it does sound like the current plan involves a 25 year journey before observations start.
It is the napkin scale, not precise mission calculation. Doing 2 stages you can get faster, doing higher voltage you can get faster, etc. Slow down would of course take time and delta-v, changing observation station would also take them, etc. What interesting is that increasing Isp 10x seems to be doable with the today's/near-future tech, and that would even allow 1000 year mission to the closest star using 3 stages (unfortunately even my napkin breaks though when trying to stretch to the 100 years mission to the star using the today's/near-future tech).
Right, but assuming constant acceleration, there's an enormous difference between accelerating all the way to the target and only accelerating halfway to the target, and then decelerating the rest of the way.
Silly question. Can you do a "drive by". In other words not slow down. How much time you need to "take the photo". I am using terms like Randall in Thing Explainer here!!
Maybe it has further missions in deep space after that. Or look in other directions and use other stars.
I've actually just finished watching the video linked elsewhere in this thread and a drive-by is exactly what they propose, using multiple telescopes launched on staggered schedules in order to make repeated observations and gradually refine the image.
it isn't realistic assumption. Until you're talking pure solar, the amount of acceleration is limited by the reaction mass available. Actually to get there in 10 years with the Isp 3500 3 stages are necessary, or better the Isp should be increased 2x-4x - still seems doable - to get with like 2 stages with realistic [today] parameters of the reactors/etc.
We can use solar sail for initial acceleration, then we can attract surrounding ion/particles/dust using long wires with negative charge, to have more mass for further acceleration.
i think solar sail is red herring kind of. Really slow and very big, and hardly working beyond Mars.
Compare to nuclear powered ion thruster. Say we get reactor plus generation at 5KW/kg total - takes some engineering, yet nothing unrealistic for current tech (even 10KW/kg seems pretty reachable). Reactor is on a long pole with only small protection wall directly between reactor and payload. Say 5 ton reactor, 25MW. 100 ton whole rocket, 80 ton of it reaction mass. At current NASA 40km/s ion trusters we get delta-v 80km/s in 60 days. If we get thrusters with 80km/s - wikipedia mentions that current ones reach 50km/s, so don't see why we can't increase voltage and thus ejection speed further - then it would take 240 days to reach delta-v 160km/s (i.e. current multi-year missions to Jupiter/etc. would get in well under a year, and it will be with like 10 ton payloads). Don't see solar sails coming close to that - https://en.wikipedia.org/wiki/Solar_sail#Inner_planets.
And as i mentioned earlier - let say we got thrusters with 400km/s. The same rocket will get to 800km/s - 1500 years to the nearest star - in 20 years. 3 stages - 500 years to the nearest star. 1 ton final payload if starting with 1000 ton rocket like the one described above.
Gathering reaction mass ram style - it needs big apparatus and needs to be efficient. Doesn't seem realistic with current tech, yet i'm sure will be on the table once the tech matures.
that will pass. With Starship you can deliver reactor into orbit in a "safe box" such that if anything happens with the rocket during launch and acceleration the box with the reactor will fall without breaking apart. Such box can be made in self-stabilizing shape similar to Dragon capsule so that it will slow down in atmosphere. One can imagine 10 cm thick tungsten and steel walls, etc. for the "box" to not break on fall/reentry or in the rocket explosion. And you don't need it for the whole reactor, only for the nuclear fuel.
You don't need anything at all. A reactor that has never been turned on is not radioactive. The only protection you need is to simply not start the reactor until it's on a planetary escape orbit, one that does not return.
The most complete plan for this was proposed by JPL's Slava Turyshev and team. It has been selected for Phase III of NASA Innovative Advanced Concepts. [0]
> In 2020, Turyshev presented his idea of Direct Multi-pixel Imaging and Spectroscopy of an Exoplanet with a Solar Gravitational Lens Mission. The lens could reconstruct the exoplanet image with ~25 km-scale surface resolution in 6 months of integration time, enough to see surface features and signs of habitability. His proposal was selected for the Phase III of the NASA Innovative Advanced Concepts. Turyshev proposes to use realistic-sized solar sails (~16 vanes of 10^3 m^2) to achieve the needed high velocity at perihelion (~150 km/sec), reaching 547 AU in 17 years.
> In 2023, a team of scientists led by Turychev proposed the Sundiver concept,[1] whereby a solar sail craft can serve as a modular platform for various instruments and missions, including rendezvous with other Sundivers for resupply, in a variety of different self-sustaining orbits reaching velocities of ~5-10 AU/yr.
Here is an interview with him laying out the entire plan.[2] It is the most interesting interview that I have seen in years, possibly ever.
[0] https://en.wikipedia.org/wiki/Slava_Turyshev#Work
[1] https://www2.mpia-hd.mpg.de/~calj/sundiver.pdf
[2] https://www.youtube.com/watch?v=lqzJewjZUkk
Sadly ,the last reference I see to this project is from 2022, from his own CV on his JPL profile page. What happens after stage 3 with NIAC? Is there even a stage 4, or does it need to get selected by some committee or something?
A 6 month integration time is going to generate massive amounts of data. How do they intend to receive all this back from 500 AU away?
Well, one single long exposure would literally generate a regular sized image. Though I do guess they’ll be doing multiple exposures if only to avoid saturating their dynamic range.
Does anyone know what a typical number of acquired frames is for a space telescope?
The computer onboard likely merges everything into a final image in space?
Orbiting instruments typically transmit raw instruments data blocked into lines or segments that are are each surrounded by checksums.
It might be compressed for transmission, but raw data (warts and all) is king .. once it's "processed" and raw data is discarded .. there's no recovering the raw.
Years later raw data can be reprocessed with new algorithms, faster processes and combined with other sources to create "better" processed images.
Onboard hardware errors (eg: the historic Hubble Telescope erros) can be "corrected" later on the ground with an elaborate backpropagated trandfer function that optimally "fixes" the error, etc.
Data errors (spikes in cell values, glitches from cosmic rays, etc) can be combed out of the raw in post .. if smart people have access to the raw.
Baking processing into on board instrument processing prior to transmission isn't a good procedure.
But this wouldn’t be in orbit; it would be in what NASA calls “deep space”, which relies on the Deep Space Network [1]. The DSN is severely bandwidth constrained, due primarily to a lack of ground antennas. Indeed, for instruments that are located outside Earth’s orbit (e.g. SOHO, which is at Sun-Earth L1 [2]), bandwidth is often a limiting constraint in the design.
My understanding is that some newer instruments do both compress and select data to be downloaded (i.e. prioritizing signal over noise), and that there is more and more consideration of on-board processing for future missions, as well as possibly introducing the capability within DSN itself to prioritize which instruments get bandwidth based on scientific value of their data.
Source: A presentation from people at NASA Heliophysics last week, where this very topic came up.
[1]: < https://www.nasa.gov/communicating-with-missions/dsn/> [2]: < https://science.nasa.gov/mission/soho/>
The DSN is a radio network. In its present form, this is going to be ineffective for receiving a meaningful amount of imagery data from signals emitted by a lightweight space probe at 500AU. At ~150AU the current 25-70m dishes are getting less than 40 bits per second from Voyager 1.
Instead, we would use lasers with a far superior gain to what radio communication is capable of. The divergence on even a decent pocket laser pointer diode is less than 0.1 degree. This is a gain of 10*log10(41,253/(0.1*0.1)) = 66 degrees. Launch telescopes of modest size can increase this further. Then receiver telescopes fitted with narrowband filters can hone in on that laser signal.
> "First, transmitted beams from optical telescopes are far more slender than their radio counterparts owing to the high gain of optical telescopes (150 dB for the Keck Telescope versus 70 dB for Arecibo)." - https://www.princeton.edu/~willman/observatory/oseti/bioast9...
From the interview linked, it sounds like the current plan doesn't involve the DSN at all: they're effectively out of transmission range past a certain point, and the transmission back is optical, using a big earth or space-based telescope. Which is one of the scary things he mentioned: they're going to be entirely autonomous when collecting the data.
Sounds like we need to drop little relay nodes along the way to build the first SpaceNet
"Which is one of the scary things he mentioned: they're going to be entirely autonomous when collecting the data."
With no way to send commands to the decices?
Engrave it on a hair and coilgun it towards a receiver?
You could store all the data on the satellite, upload new code to process it differently, and download the resulting image. Then, the communications link just has to handle code (several MB up) and images (several MB down) instead of petabytes of data.
The launch mass of a petabyte of SSD is under 10 kg. I don't know if it would survive 17 years of space radiation though.
Just as a thought experiment, would it be viable to send up an array of traditional hard drives? Arrange them all for use as reaction wheels, then spin them up to persist/de-stage data while changing/maintaining targets.
Probably worse than sending up well-shielded flash, but I don't think the Seagate/WD warranty expressly forbids this usage.
Well, you could.
I don't think I'd do that.
Ignoring the failure modes of a petabyte of SSD spending decades in deep space, what kinds of things are difficult and|or impossible if you were to
> store all the data on the satellite, upload new code to process it differently, and download the resulting image
?
Sure, it would discard a lot of data / noise, and would send a preview over first, but like with the Pluto probe, they do want to get as much data as possible, as an image is only a representation thereof.
It's Vyacheslav. When you say Slava it sounds like you are talking about a child or a friend.
The Wikipedia article uses the name "Slava". His homepage on JPL website too (https://science.jpl.nasa.gov/people/turyshev/) I opened a random paper of his from arxiv and there too he uses "Slava".
Would it be possible that Mr. Turyshev uses that name as his preferred name (at least when writing in English) and that we should just respect his decision?
This decision is forced by it being hard for most English speakers to pronounce Vyacheslav.
Sure, but is it his decision to make, and if yes - are we ok to respect it?
I'm from a slavic country myself and my name is almost impossible to pronounce correctly in English - but I continue to use it anyway. If he wanted to do that, he could have done it.
My name is "Pavel", and usually ask Americans to put the accent on the second syllable - which is incorrect, but they can't pronounce my name correctly anyway when they put the accent on the first syllable, and it sounds more wrong to me than the way I prefer to have it pronounced.
Apologies to all the other Pavels out there; I've been training everyone I've met to pronounce it wrong. But it's the way I prefer to be addressed.
Now I'm curious what the _right_ pronunciation is!
You can look it up on Youtube.
Stop. For whatever reason, he has people call him Slava and does not correct them when they do so.
>For whatever reason
The reason is that you won't bother to pronounce Vyacheslav so Russians have to use a short version of their name.
No, they don't have to - they are chosing to. To pretend otherwise is to say they don't have agency in this, which they do.
Even if somebody puts a gun to your head and orders you to change your name, you'd still have a choice and it would be your decision what to do. That's not much of an argument though.
No one put a gun to his head though. Discomfort of English speakers isn't enough reason to not use your real name if that's your preference. Again, speaking from experience.
Many Chinese (speaking) students in the US pick an English language name like “William” or “Wendy” because they know people they meet will struggle with a name which could be several short words with unfamiliar vowels and consonants and tone that matters.
It can also be annoying to run the 15-minute gauntlet of "but how do you really pronounce it", and you end up having to play dialect coach.
Going by an easy-to-pronounce name is much less aggravating.
Of course - and I support their choice. People struggle with my name every day and I could change it to make it easier for English speakers - but I don't think that's quite the same as being "forced" to change it.
Sure, but do you refuse to use the names those people give? This takes away their agency. It is their call, not yours.
People would want to avoid awkward situation and talk to you (or about you) less.
That's not quite the same as having a gun to your head. Again, I have a slavic name that's extremely difficult to English speakers and I live in the UK - no one is forcing me to change it. I understand some people chose to change their name so it's "easier" for English speakers - and I respect that choice. But let's not pretend that Mr Turyshev was "forced" to change his name - he wasn't.
I won't bother? But you don't know me?
Did you mean that English speakers don't pronounce Russian names the way Russians do?
Ask your local Russian to pronounce rural Worcestershire the way that English speakers do.
Your typical Russian speaker cannot. Is it that they aren't "bothering"? The idea is absurd. Let people approximate foreign names in their own tongue. Or, if the way that they naturally pronounce something is truly atrocious, give them a name that is easier to pronounce.
Or watch this fellow give foreign pronunciation his best shot: https://youtu.be/fKGoVefhtMQ Absurd, right?
Okay, that was about as rude on my part as ordering me to stop was on yours. My apologies.
But the point is that most people won't bother to google the pronunciation, listen to it and make an effort to repeat close enough. By the way, Dr. Turyshev's name is the easy part, the surname is the real challenge)
How would this kind of thing work in practice? You move the telescope out to 500AU, and then... what? I assume the telescope would have to line up a potential star system with our sun in a direct line. So the telescope would have to move around until everything is lined up. Then I presume it would need to take a wide angle view of that star system to look for a likely planet. Would it need to move closer or farther away from our sun to get a wider field of view? Once it found a suitable planet, I presume it would need to collect light from that planet over an extended period of time, say 6 months. But, the planet is moving during those six months. How does the telescope keep the planet in view? Is the telescope constantly moving to keep pace with the planet? How much fuel would we have to send out there with the telescope?
If you want to use this method, you're basically going to require one spacecraft per target and a decade of lead time for a very short-duration observation. This is not necessarily a deal-breaker; Meaningful scientific inquiry would just require we mass produce them.
We already sabotage ourselves in astronomy by refraining from mass production approaches for political reasons.
There is no practical amount of fuel that can get you to 500AU on a simple trajectory. What seems to be the best option for setting massive vehicles on a solar escape is a sequence that looks something like:
* Launching to Jupiter propulsively
* Cancelling out most solar-orbital velocity there using a gravity assist in order to dive down into a sun-skimming orbit
* Burning through a large solid state rocket kick stage while at close approach to the sun from behind a heat shield. The Oberth Maneuver.
* (optional) unfurling an electric sail or solar sail once the rocket has finished as you're speeding away from Sol
Together that gets you the required ~100AU/year escape for a mass fraction that is tractable for our civilization.
The planet is also rotating, so how do you keep a specific 10 square kilometers part of it in focus?
Christian Ready made a great video on his Youtube channel, Launch Pad Astronomy, about NASA's plans for a solar gravitational lens. It's got some great graphics and visualisations, and is accessibly narrated. I was inspired and learnt a lot of new ideas.
https://www.youtube.com/watch?v=NQFqDKRAROI (23 minutes)
I can highly recommend this video, and in case people do not know, Christian Ready is actually a person, not an organization run by religious fundamentalists.
LMAO at that other possibility... I hadn't even considered it but it's almost obvious in hindsight
Is there anything stopping you from putting 2+ satellites out "closer" but in the path of the lensed light, capturing the light simultaneously, and then resolving the image via async computation later? I think this is called interferometry and I know it's hard because you need _very_ precise timing, but I'm curious if that would be possible or not. (Maybe you can get the timing in sync with atomic clocks, or by sending a laser to both from a central point that lets them keep time with some very tight tolerance?)
Weird idea but I wonder if there are ways to take this from "crazy tech" to "hard tech".
> Is there anything stopping you from putting 2+ satellites out "closer" but in the path of the lensed light
The Sun. Literally.
Satellites have to be that far for the Einstein ring to be bigger than the apparent size of the solar disk.
Edit: to make it a bit more clear, the gravitational lens does not quite behave like a normal lens. Instead, you see the light from _behind_ the object. So if you're too close to the lensing object so that the Einstein ring is not larger than it, you'll just see a part of the object to be a bit more bright.
Also, the gravitational lens does not actually _focus_ the image, it distorts it into a band around the lensing object.
But if the light is "warping" around the object then would you be able to grab the light from either side by intercepting it there? If you are at the X AU required for lending, but you sit at X/2 AU with some slight offset, you would be in the path of the light that would be traveling to X AU eventually.
I understand if what I'm trying to describe is impossible, I just don't fully understand why. (Is it out of focus? Is the sun too big/bright?)
> But if the light is "warping" around the object then would you be able to grab the light from either side by intercepting it there?
Certainly. But it won't be any more focused at that location. There's no real advantage compared to just building a regular phased antenna array.
I'm no expert here. You mention "either side" as if the light came from both the left and the right. But I think the light would be coming along a circle all around the sun depending on exact position.
So the trick here is that if you are at the focus point, you get all that light in a small area "for free". But if you try to catch the light on the way, you now need to catch eveywhere in a whole massive circle, which is basically impossible, so you only catch a minuscule amount of the light. And then have to deal with interferometry.
>to make it a bit more clear, the gravitational lens does not quite behave like a normal lens. Instead, you see the light from _behind_ the object.
Or to put it another way: A gravity lens bends space so that the light from behind an object curves around it while travelling straight.
"Normal" lenses bend light more strongly farther out towards the edges. Gravitational lensing is shaped differently.
The point is you aren't bending the light, no the light is travelling straight.
You are bending the dimension, the light travels straight through a bent dimension thus coming out curved.
I think that's mindblowing.
No, light doesn't travel in straight lines.
Stronger gravity around massive objects causes slow down of the part of a light wave closer to object, compared to outer part.
This difference in speed, caused by _interaction_ between the photon and gravitational field of the body, results in the bending of the light's trajectory.
Bending of spacetime is just a simplification of this process to model that easier.
from what I understand, slowing down would be true for a non-massless particle, but speed of light in vacuum is still the same around massive objects. What changes is the frequency of the light in this particular direction, and that "turns" it, probably because of self-diffraction?
Parts of photon cannot have different frequencies than whole photon. Both inner and outer parts of photon will make exact same number of fluctuations for the same period of time, but inner part will travel slightly smaller distance.
It's the same effect as in reflections, except that speed difference between air and solid objects is much much bigger, which results in sharp turning radius.
The speed of light is constant as measured from any observer. This has been verified experimentally to a very high precision and motivated the development of special and general relativity.
Otoh there is no requirement for a wave front to have the same frequency as when it started. A gradient in the gravitational field can cause a gradient in the gravitational redshift and thus "parts of photon" can very well have slightly different frequencies. If you recombine the paths and have the photon to interfere with itself, the interference pattern will capture the shape of such a wave function as affected by the distortion in the gravitational field.
IIRC this is the "standard" way of thinking about what's going on although marrying quantum mechanics and general relativity is still a work in progress.
If you buy into another theory that involves a variable speed of light, I'd love to hear more about what exact theory are you talking about since it seems to me that the burden of proof is on who makes the most extraordinary claims.
LIGO/Virgo/KAGRA found that speed of light in vacuum is affected by gravitational waves. This is verified experimentally to very high precision (1.2E-20m). If merge of neutron stars 200 megaparsec away can affect propagation of light here, on Earth, then why it cannot affect it near to the star?
ok I think we're talking past each other. let's take a step back.
Let's imagine two points in space A and B, that are let's say 10 light minutes distant from each other. A signal going straight from A to B will thus take 10 minutes.
If point A sits in a strong gravitational field (e.g. it's orbiting a very heavy star), the signal will still take 10 light minutes to reach point B. (please tell me if you disagree with this assumption).
Now, let's place another heavy star at the midpoint between points A and B.
How long will it take for a photon emitted by A to reach B? Well, it won't reach it because it will hit the start that's in between.
But another photon whose direction wasn't directly in the path from A to B will follow a longer path, be deflected around the star and reach point B.
It will take longer than 10 minutes to reach point B because it will move along a longer path.
Do you agree this is what would happen?
The speed of light in vacuum is constant and is not impacted by gravity, AFAIK. Really the light is travelling in a straight line in space but gravity bends space and time.
LIGO/Virgo/KAGRA found that speed of light in vacuum is affected by gravitational waves. This is verified experimentally to very high precision (1.2E-20m).
Light doesn't travel in a straight line because, to change trajectory of photon, photon must interact with something to exchange momentum. You are talking about mathematical model[1].
[1]: https://en.wikipedia.org/wiki/Curved_spacetime
Aren't gravitational waves the same effect I described?
c is an universal constant and it seems that you're saying that it is not!
> Stronger gravity around massive objects causes slow down of the part of a light wave closer to object, compared to outer part.
That only matters in areas with _really_ high fields, this effect is negligible for areas far away from a singularity of a black hole.
Instead, it's really the space that curves. The light does not slow down, it always moves at the speed of light. In the general relativity there is no "gravity field", gravity is a fictitious force.
Edit: also, gravitational lensing applies to massive point-like particles as well. For slow-moving particles and weak fields, it's negligible compared to regular Newtonian orbits, but if a particle moves at a speed that is close to lightspeed, it'll be lensed just like the light.
You forgot about conservation of momentum. Photon cannot change it's direction without interaction with something to exchange momentum.
"Bending of spacetime" is just computational trick to increase precision of the model.
Bending of trajectory because of change of speed of light is negligible, yes. It's only visible on light-year long distances.
Photon is very wide. Dual slit experiment show that single single photon interacts with two slits up to millimetre apart. Even small difference in speed/frequency at such large distance will accumulate to noticeable change of course at light year long distances.
I can calculate bending radius, if you wish.
> You forgot about conservation of momentum. Photon cannot change it's direction without interaction with something to exchange momentum.
No. I'm not forgetting anything. Photons _do_ _not_ change direction. They always move in straight lines (from their "point of view"). It's just that if you step a bit away, these straight lines are not actually "straight" globally.
A classic example is a 2D ant crawling on a surface of a sphere. From the ant's point of view, it moves in a straight line, but a 3D observer will see that a straight line is actually a 3D circle.
Conservation laws are not violated. A photon (or another particle) will cause its own slight bending of the space-time, that in turn will slightly bend the star's trajectory.
It does sound like an interaction between gravitational fields, but the models give different numeric predictions.
> "Bending of spacetime" is just computational trick to increase precision of the model.
It really is not.
> Photon is very wide.
Facepalm. Sorry dude, but you have no idea what you're talking about. Lensing and time dilation also happen for point-like particles like electrons.
> Photon cannot change it's direction without interaction with something to exchange momentum.
Doesn't the entire photon simply exchange momentum with the star, without needing to invoke any higher-order effects? Just as the star exerts a gravitational pull on the entire photon, the entire photon exerts a (very miniscule) gravitational pull on the star.
The precision you need for interferometry depends on the wavelength, and being able to do this over astronomical distances at visible wavelengths would indeed be a challenge. I think the scale is timing more accurate than 0.1 nanoseconds and distance accuracy on the order of 100 nanometers. Near those orders of magnitude at least and over astronomical distances that might be measured in AU.
Then again the precision of the gravitational wave instruments measure distance on the order of the width of a proton, so who knows.
Terrestrial infrared and optical interferometry telescopes are on the bleeding edge right now.
"Boring" cesium atomic clocks can do 50 ps per day with the best cutting edge optical clocks coming in at ~739 fs per day. Optical clocks would only need to resynchronize once every ~ 135 days while cesium clocks would need to do it every 2 days to get 0.1ns of accuracy.
I think the bigger challenge may be how you would transport the clocks after synchronization to maintain it across astronomical distances since they're very sensitive to any kind of acceleration. Since you have to regularly re-synchronize them in space anyway, that feels like the engineering problem you'd have to solve - how do you synchronize two atomic; the current record is synchronizing to within 0.32fs at a distance of 300km [1].
[1] https://spectrum.ieee.org/atomic-clock-femtosecond-accuracy
On a cosmic scale what does simultaneously mean? Two object in a distinct orbit will be in different planes of reference
Presumably it means that two light rays that leave the same point on the planet simultaneously (but going in slightly different directions) arrive at the two telescope satellites simultaneously
But if they want to observe planets, and planets move, wouldn't the telescope need to move too, to keep the image stable while gathering more photons? I presume very few photons reach the telescope from that far away.
That means the object's orbit need to be known before beginning it's observation, and then consuming a lot of propellant to change the telescope's speed and trajectory, possibly distance to Sun too, to track another object.
At that distance from the Sun, to track objects in another solar system, it would need to move vast distances sideways possibly taking hundreds of years.
Yes, the planet (hypothetically, a very earth-like planet with a 1-year, 1 AU orbit, 24-hour rotation, and 23-degree tilt at 4 light years' distance like Proxima Centauri b) moves at most 2 AU in a 6 month integration, and the telescope ~700 AU behind the center of the lens would have to move more to keep it opposed. But that 4 light year distance means it's 250,000 AU from the Sun, so some basic geometry says it only has to translate laterally by on the order of 2 * 700 / 250,000 = 0.0056 AU. You're right that that is far larger than an image sensor would be, and larger than the solar sails that would push this craft would be, but inconsequential for a vehicle that's just flown 700 AU.
Planets not only move relative to their star, but they also rotate and tilt. I see a number of artists' depictions of the planet (eg at [1]) that look like the satellite just flew into space, illuminated a circular planet with a giant flash bulb, and returned a pixellated photo. I've only thought about this for a minute, but I don't think it would look anything like that.
Trying to integrate an image of over the course of a 6-month exposure means not only tracking where the planet is in its orbit but also discerning the longitude on the planet from which a given photon was emitted at a particular time. Plus, if it's tilted at all, we might get many images of the north pole and none of the south pole, or an underexposed image of some polar regions that were only aligned with us for a small duration of the exposure. Finally, even though this gravitational lens is enormous and can collect many more light rays that happen to be aimed at the sun on the image sensor than a physical lens or mirror could, light still has to come from somewhere - specifically, the host star, so only half of the sphere can potentially receive photons that might bounce in our direction at any time, and that half may or may not be aligned with us. Finally, over the course of 6 months, the planet might experience seasons, with changes in the atmosphere and surface ice!
Assembling the raw data into a sharp image would be far more challenging than just opening and closing a shutter then grabbing a serial stream of X by Y pixel data from an image sensor, but the output might be much more than a single image.
[1] https://www.nasa.gov/general/direct-multipixel-imaging-and-s...
This video linked by another commenter explains it quite well: https://www.youtube.com/watch?v=NQFqDKRAROI
Basically, it's possible to generate an image of an exoplanet, but "retargeting" the telescope(s) to observe another object is not feasible. So you'd better make sure the target that the mission will focus upon is actually worth the attention it gets - but there are other planned telescopes that will be capable of generating data that will allow selecting potential candidates.
Here's a PBS Space Time episode [1] from a couple years ago that describes a couple different proposals for how to do this that take quite different approaches. It starts getting into the specifics of those approaches at 7 minutes in if you don't need the introductory material.
[1] https://www.youtube.com/watch?v=4d0EGIt1SPc
Is this a similar principle to the concept in the 3 Body Problem series of books? As in, how one of the main characters is able to boost the transmission power of an earth bound antenna
In the three body problem she uses some property of the Sun's internal layers to amplify the signal. In reality we don't know of any actual property in the Sun that could do this.
The gravitational lens idea is different, it makes use of a known phenomenom where the Sun's gravity "bends" light rays moving around it, which can amplify the light coming from far away objects. In principle you could run it backwards, so the lens could amplify signals we send as well.
It wouldn't amplify them, there's no energy gain. A gravitational lenses just bends the trajectory of the waves. If you do it right it may be possible to use that to focus the signal on a directional trajectory(as in, the same energy is redirected in a single direction instead of being spread out), if I'm not mistaken.
The ability to observe at given resolution implies though that there is a lightcone of civilization discovery spreading from humanity, visible to our neighbours.
It's not a way to boost a signal.
It's using the Sun as a (gravity) lens, with probes at the focal point to gather the image. Because it's a very large lens, that's allow to have a massive zoom on whatever object we are interested in.
But you should be able to use it as a "parabolic" mirror, to make a very directed ray to the planet. (Assuming diffraction is not a problem.) (Assuming no time delay, because to see the planet you should look to were it was many years ago, but to send a message you should aim to where it will be many years in the future.) (Assuming I'm not missing a few more technical problems that are not impossible to solve, but extremely difficult.)
Wouldn't you have to have very accurate information about where the planet is going to be when the light arrives?
From my layman understanding, yes, this concept should be bidirectional.
Here's a little project looking at a related concept using multiple stars
https://github.com/celestiary/mglt
Sort of related question:
Would space telescopes use interferometry to get a clearer picture?
If we had thousands of telescopes spread across the solar system, what sort of images of distant stars/planets/galaxies could we gather? Would such an array be scientifically worth making in our distant future, or does it suffer from diminishing returns?
There have been plans drawn up for space telescopes flying in formation to do the same kind of interferometry thing as the Keck observatory.
The problem is that even far from the Earth, there are tiny but significant forces pushing the space telescopes around. Solar wind, outgassing, gravitational influences from planets, etc...
The precision required to maintain formation is... challenging.
E.g.: https://arxiv.org/abs/1907.09583
Why do you need to maintain formation? Can the just fly randomly and fix the problem storing the info and a software that gets the positions and calculate the delays?
For radio frequency I think it's possible.
For visible light, I guess you must do the interference using very accurate mirrors to aim to the central point and that move slightly forward and backward to get the correct phase shift. I think it's not impossible, but very difficult.
For a comparable endeavour, they combined the data of telescopes across the world to create a planet-diameter-sized telescope and with that, the first image of a black hole; extending something like that solar-system-wide would make a solar-system-wide telescope. I'm no astronomer but I'd say it's worth it.
> Light coming from an exoplanet would be gravitationally focused by the sun with a focal point in the region of about 550 AU to 850 AU,
Ouch. Does this mean we're limited to targets located in our plane of ecliptic? Also, we have to have a good target picked out don't we? There's no way to point this at a more interested planet if the first is a bust.
aiming it and keeping it on target would be pretty hard, though. And time-consuming, to say the least.
This is almost the plot of Three Body Problem. Could we use a Solar Gravitational Lens in reverse and project signals out of the lens in reverse?
I think so, as long as you know how far away your target is (the focal point) to position the sender, and you need a way to send the signals at the right angles "skimming" the sun at the right distance. (note: armchair amateur, this is just conjecture / thought experiments)
But why? Sending signal this way does not amplify the signal. Just point lasers directly at that point.
Protector by Larry Niven (1973) also features a gravity-powered telescope.
Could we do a less extreme version of this with a planet in the solar system? Or would a probe have to be too far away from it?
If you use Earth, you can use atmospheric lensing (rather than gravitational) to get a focal point inside the Earth–Moon system: https://www.scientificamerican.com/article/earth-could-be-a-...
A planet would be a weaker lens so you'd have to be even farther away, and you'd have less collecting area as well.
Cool worlds YouTube channel has a great video about Earth sized telescopes:
https://youtu.be/jgOTZe07eHA?si=0veG99yEbLQTKs4I
One could also lens neutrinos using the Sun's core. Because neutrinos are not absorbed by the Sun, there is a critical offset from the core where they are maximally focused. This would form a caustic, and would cause increased magnification of the neutrino signal at that focal distance.
The sun is the biggest neutrino source in the sky. So we'd need some way to filter out neutrinos that are not from the sun, like we do with various photon telescopes.
Furthermore, we can barely detect neutrinos. Building neutrino detectors is extremely challenging. Usually they are extremely massive and surrounded by lots of rock (even more massive). We'd have to get all that mass to the focal point of the observatory which is extremely far away.
Lastly, the gravitational field inside the sun is much different than outside. In fact, the field is strongest at the surface (or slightly below, as it doesn't have equal density). The further inside you go, the more parts of the sun start pulling you outside, until you reach the center of mass, where the gravitational forces cancel out.
Can you please elaborate? I find myself making up reasons why but I am certainly wrong.
Looks like Est31 has made about 7 factual claims. I'd guess you'd get more replies if you would narrow down which of the seven you are most perplexed by.
Neutrinos could be distinguished by energy, and also from antineutrinos. There would be an upper bound to the energy that could be detected because at some energy the Sun becomes opaque to neutrinos.
Yes, they are hard to detect, so this is a massive project, not practical right now.
The last point is why there's a caustic. The focal length diverges to infinity as you get to the center; there's a radius where it's at a minimum. This radius will be well within the sun, since the center of the Sun is so much denser than outside the Sun.
The neutrino gravitational focus should be somewhere between the orbits of Uranus and Pluto: https://www.nasa.gov/general/cube-sat-space-flight-test-of-a...
What non-uniform field of neutrinos would one expect? I seem to recall that neutrinos come from every direction. Perhaps some stellar event like a nova? Otherwise the image would be the same everywhere, as the sun is relatively uniform.
There should be many concentrated neutrino sources, for example active galactic nuclei.
I’ve put this in my “other ideas” section in YC applications for a couple rounds now. No luck yet.
Would love to send 1,000 probes to 550AU+ out in order to observe 1,000+ ‘nearby’ exoplanets, hopefully find life, make contact, start trade…haha. Or otherwise defend the solar system from invaders that are perhaps already on the way!
Maybe YC rejects me specifically because I put that there…hm.
What kind of ROI would attract a VC to this kind of project? How could they monetize it?
Would each image created be proceeded by ads that you can skip after 5s or would they be unskippable? Data harvesting is kind of the point of the platform, but maybe they could track that data and get the PII/deanonymized information? "This user spent 104 hours continuously staring at the sun. Maybe they would be interested in sunglasses, or maybe some sun block"
how much analysis have you done on this? I'm working on a series around Kardashev II work - space solar, asteroid mining, dyson spheres and the real work that is happening to support this now. contact me if you'd like to discuss - @bensand on X
Sadly I am still at very early stages of this idea. However I will save this thread and contact you if I make progress!
I mean it's a great idea and all and probably not original, but it needs billions if not more in new spacecraft that can travel 3-4x as far as the furthest human-made object is (Voyagers) in a reasonable time, a scalable launch system that can launch the probes (1000x payload + fuel with the delta-V required to get there), probes that go to the destination, and a new almost interstellar communications network to get the data and commands there and back again.
Basically your idea would be the biggest, most expensive and longest undertaking in space exploration system, ever. I can see why investors would be a bit hesitant about that.
*the daily mail has entered the chat*
Spoiler: the focal point is 3.5x the distance to Voyager 1.
if to use existing nuclear reactor tech and already existing, as tested by NASA (and drives Starlink satellites), ionic drive - about 3500 ISP - that focal point would take about 10 years to reach. I hope that SpaceX flights to Mars will, after the probably first chemical ones, be done using ionic drive with solar as it is just faster, thus getting tech developed and with adding nuclear for beyond Mars - so in 10-20 years we'll have the stuff flying. (note that "small" reactors - 100MW - we have for submarines, and with MS, ORCL, GOOG, AMZN getting into nuclear we'll have such small reactors productized into normal commercial use which will simplify space use too as commercial use require higher reliability/etc. compare to military)
> that focal point would take about 10 years to reach
Is this taking into account the time needed to slow down?
You don't need to slow down, the region where you can do the observations is basically a slowly expanding cone the further you get away from the sun. But it does sound like the current plan involves a 25 year journey before observations start.
It is the napkin scale, not precise mission calculation. Doing 2 stages you can get faster, doing higher voltage you can get faster, etc. Slow down would of course take time and delta-v, changing observation station would also take them, etc. What interesting is that increasing Isp 10x seems to be doable with the today's/near-future tech, and that would even allow 1000 year mission to the closest star using 3 stages (unfortunately even my napkin breaks though when trying to stretch to the 100 years mission to the star using the today's/near-future tech).
Right, but assuming constant acceleration, there's an enormous difference between accelerating all the way to the target and only accelerating halfway to the target, and then decelerating the rest of the way.
Silly question. Can you do a "drive by". In other words not slow down. How much time you need to "take the photo". I am using terms like Randall in Thing Explainer here!!
Maybe it has further missions in deep space after that. Or look in other directions and use other stars.
I've actually just finished watching the video linked elsewhere in this thread and a drive-by is exactly what they propose, using multiple telescopes launched on staggered schedules in order to make repeated observations and gradually refine the image.
>but assuming constant acceleration
it isn't realistic assumption. Until you're talking pure solar, the amount of acceleration is limited by the reaction mass available. Actually to get there in 10 years with the Isp 3500 3 stages are necessary, or better the Isp should be increased 2x-4x - still seems doable - to get with like 2 stages with realistic [today] parameters of the reactors/etc.
We can use solar sail for initial acceleration, then we can attract surrounding ion/particles/dust using long wires with negative charge, to have more mass for further acceleration.
i think solar sail is red herring kind of. Really slow and very big, and hardly working beyond Mars.
Compare to nuclear powered ion thruster. Say we get reactor plus generation at 5KW/kg total - takes some engineering, yet nothing unrealistic for current tech (even 10KW/kg seems pretty reachable). Reactor is on a long pole with only small protection wall directly between reactor and payload. Say 5 ton reactor, 25MW. 100 ton whole rocket, 80 ton of it reaction mass. At current NASA 40km/s ion trusters we get delta-v 80km/s in 60 days. If we get thrusters with 80km/s - wikipedia mentions that current ones reach 50km/s, so don't see why we can't increase voltage and thus ejection speed further - then it would take 240 days to reach delta-v 160km/s (i.e. current multi-year missions to Jupiter/etc. would get in well under a year, and it will be with like 10 ton payloads). Don't see solar sails coming close to that - https://en.wikipedia.org/wiki/Solar_sail#Inner_planets.
And as i mentioned earlier - let say we got thrusters with 400km/s. The same rocket will get to 800km/s - 1500 years to the nearest star - in 20 years. 3 stages - 500 years to the nearest star. 1 ton final payload if starting with 1000 ton rocket like the one described above.
Gathering reaction mass ram style - it needs big apparatus and needs to be efficient. Doesn't seem realistic with current tech, yet i'm sure will be on the table once the tech matures.
They're hesitant to put nuclear reactors in a rocket though, in case it goes wrong.
that will pass. With Starship you can deliver reactor into orbit in a "safe box" such that if anything happens with the rocket during launch and acceleration the box with the reactor will fall without breaking apart. Such box can be made in self-stabilizing shape similar to Dragon capsule so that it will slow down in atmosphere. One can imagine 10 cm thick tungsten and steel walls, etc. for the "box" to not break on fall/reentry or in the rocket explosion. And you don't need it for the whole reactor, only for the nuclear fuel.
You don't need anything at all. A reactor that has never been turned on is not radioactive. The only protection you need is to simply not start the reactor until it's on a planetary escape orbit, one that does not return.