> 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
I learned this doing engineering trades on the Aldrin cycler idea; Ultimately it doesn't add much to a mission because getting there and getting back into the transfer sacrifices more than you could really hope to gain. You're likely better off just launching what you need attached to everything else at the Earth escape burn.
Does anyone know what a typical number of acquired frames is for a space telescope?
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.
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.
Probably worse than sending up well-shielded flash, but I don't think the Seagate/WD warranty expressly forbids this usage.
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
?
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/>
With no way to send commands to the decices?
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...
Put a relay at the Lagrange point.
Stick a relay at the midpoint between earth / Voyager 1 so it gets a signal that’s 4x as strong. Unfortunately that’s still really weak so it needs a huge dish, and orbital mechanics means it can’s stay in that position.
We’re better off sending out probes that send stronger signals and just build huge ground based systems. At least until space based manufacturing becomes practical.
PS: Where relays make sense is for probes on the surface of a planet etc communicating with something in orbit which then sends signals to earth.
https://www.youtube.com/watch?v=NQFqDKRAROI (23 minutes)
Weird idea but I wonder if there are ways to take this from "crazy tech" to "hard tech".
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.
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?)
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.
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.
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.
You are bending the dimension, the light travels straight through a bent dimension thus coming out curved.
I think that's mindblowing.
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.
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.
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.
That is not true. The "speed of light" in vacuum is not constant for all observers in the _general_ relativity. It is constant only _locally_, Lorentz invariance is a local symmetry in GR. Special relativity thus simply becomes an edge case of GR, where the Lorentz invariance is also a global symmetry.
That's how we get lensing, regions of space near a massive object are more "viscous" and the light moves slower through them.
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?
Now imagine that it's not a star, but a black hole with a small radius to make arguments easier. You shoot a photon slightly off the axis, and it gets deflected.
You can try to treat a photon as a moving object, and integrate the forces acting on it. Taking Lorentz transformations into account, of course.
But the thing is, your calculations will be off, and the experimental results won't match your predictions. You will need to take into account that the lightspeed near massive objects is _slower_ for distant observers.
Another example, suppose that you have a star surrounded by a massive cloud of fog. Somebody shoots a laser beam from one side of the fog bank to another, while you are far away from the star. The fog is there just to allow you to see the beam as it moves, it does not by itself slow the light.
But you will actually see the light moving _slower_ than lightspeed!
Or equivalently, you can take a clock that ticks every second. And if you lower that clock to the surface of a planet, you will see the clock ticking slower. And this is a very real effect, we have to correct for it in the GPS satellites.
The speed of light is the same in both frames of reference. What you think is going affect the speed is actually the slowing of the proper time which effectively causes the photon to redshift.
No. You can drop a ruler onto the surface of Earth and measure from the Moon the time it takes the light to travel from one end of the ruler to the other. It will be slower than the lightspeed from your point of view. This is a real effect, we've measured it.
However, it will be lightspeed from the point of view of an Earth observer.
And this effect falls out directly from the warping of space-time described by general relativity
am I understanding correctly that you claim that the warping of space-time is just a mathematical trick and that the phenomena are better explained by just postulating they light slows down in a gravity well?
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].
c is an universal constant and it seems that you're saying that it is not!
I cannot read your mind.
> c is an universal constant and it seems that you're saying that it is not!
Yep, c is universal constant for many physical models.
In physical world, c is constant as long, as properties of physical vacuum (permitivity and permeability) are constant, which in turn depends on α (Fine-structure constant[1]), which, in turn, variates at higher energies[2].
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.
"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.
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.
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.
It's not possible, because EM field doesn't affect all particles.
> Lensing and time dilation also happen for point-like particles like electrons.
If we stick 2E15 electrons together in a long line, then it will start to rotate too due to differences in gravitational field at inner and outer segments of the line. Something like that must happen to an 1mm wide photon too. I'm not talking about orbit of those electrons around object, but about rotation alone.
It's not the EM field, but gravity.
> If we stick 2E15 electrons together in a long line, then it will start to rotate too due to differences in gravitational field at inner and outer segments of the line.
Just look at an individual electron. Why would it curve? It's sufficiently point-like for the gravitational field gradient to be negligible.
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.
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
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.
Sounds like several near impossible problems on top of each other though.
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.
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.
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...
And based on their proposal docs, just a few telescopes would be able to image at 100km resolution. Bonus, it'd be able to image a lot more targets since it wouldn't need the sun to be in the right place. https://newworlds.colorado.edu/info/ http://newworlds.colorado.edu/info/documents/gsfc_February%2... https://newworlds.colorado.edu/info/documents/FinalReportNew...
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'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.
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?
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.
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.
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.
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...
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.
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"
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.
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.
Picking a good target is also a good idea for the same reason.
Is this taking into account the time needed to slow down?
Maybe it has further missions in deep space after that. Or look in other directions and use other stars.
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.
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.
Take into account much much harder radiation in interstellar space, which will require much heavier radiation shield. We can make as many circles around Sun as we need, like a commet.
say at the Mercury orbit we unfurled the large sail and got strong boost, and we'll come back for the next round in like 100 years. It is something we'd have to do if there weren't better alternatives. Nuclear or solar panels + ion thruster inside the Mars orbit, nuclear + ion thruster outside Mars seems to beat pure solar. Interstellar - nuclear + ion or my favorite Orion project seems to be again better than pure solar. It is like sailboats vs powerboats - while we love sailboats, the powerboats are really more practical in all the cases except for the lazy relaxed cruising.
>Take into account much much harder radiation in interstellar space, which will require much heavier radiation shield.
Until we have a way of getting like 0.1c, any interstellar takes hundreds of years and will be done either by pure robots or cyborgs and beside some shielding the main way of dealing with radiation damage is to catch/repair ECC memory style.
For 0.1c we have either project Orion - though nobody seems to be willing to go that way (we'll see how it goes once we have operations established on the Moon and Mars, may be somebody will turn to it as 1. they would have a business case for it and 2. it isn't really possible to do such experiments and development on Earth anymore) - or today it looks more like the fusion-exploding small pellets like NIF at Livermore does is the way to go. We can reasonably expect continuing improvement in the gain in those experiment, and while Earth based energy generation requires higher gain and efficient conversion of that small explosion into electric energy which is still a problem to be solved, the space drive application requires exactly such a small explosion, and thus i think such fusion drive will come much sooner than an Earth based fusion power station.
A 1 ton payload is probably not enough to even stick a sufficiently powerful laser on to see at all over those distances.
2. 1 ton is starting from 1000 ton rocket. The Saturn V and Startship are on the scale of 5000 ton and assembled on Earth. That interstellar rocket will be assembled in space anyway, so not being subject to any meaningful gravitational nor accelerational stresses, we can easily build a 100000 or even 500000 ton rocket - basically just the reactors and tanks of acceleration mass - and thus get 100-500 ton payload. If we get any [semi]hybernation going (may be combined with 3d printing or CRISPR-like repair of organs, whatever we get in 20-30 years) or more probably some brain [partial] upload integrated with AI into some capable cyborg, may be even some people or those merged human/AI cyborgs would be able to go.
And by collecting some additional reaction mass ram-style over that distance and time (as long as we have enough reactor power to use part of the collected mass to avoid slow down resulting from the collection) we'd probably be able to slow down some small probes to land and orbit various objects in the target star system.