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In case anyone is wondering, we are (sadly) very far from getting an image of this planet (or any extra-solar planet) that is more than 1 pixel across. At 110

In case anyone is wondering, we are (sadly) very far from getting an image of this planet (or any extra-solar planet) that is more than 1 pixel across. At 110 light-years distance you would need a telescope ~450 kilometers across to image this planet at 100x100 pixel resolution--about the size of a small icon. That is a physical limit based on the wavelength of light. The best we could do is build a space-based optical interferometer with two nodes 450 kilometers apart, but synchronized to 1 wavelength. That's a really tough engineering challenge.

nico 1y ago
How big would the telescope/mirror/lens need to be to get a picture of something in the Alpha Centauri system, 4.37 light years away? Also, could the image be created by “scanning” a big area and then composing the image from a bunch of smaller ones?
- GMoromisato 1y ago
  It's linear, so if it is 25 times closer then the telescope can be 25 times smaller. At 4.37 light-years we'd need an 18 kilometer telescope to image at Jupiter-sized planet at 100x100 pixel resolution. If you only wanted 10x10 resolution you could get by with a 1.8 kilometer telescope. Wikipedia has more: https://en.wikipedia.org/wiki/Angular_resolution https://en.wikipedia.org/wiki/Angular_resolution. The Rayleigh criterion is the equation to calculate this.
- joshvm 1y ago
  It's a lot easier to reason about this using angular resolution, because that's normally what the diffraction limit formula is in reference to. If you know the angular diameter of the system (α) and the wavelength (say λ=500 nm for visible), you can use α ≈ λ/d and solve for the aperture of the telescope (d). That puts a basic limit on the smallest thing you can resolve with a given aperture. You can use the angular diameter of the planet and the resolution you're after. For Alpha Centauri A it's 8.5 milli arc-second, so O(1 μas) for a 100px image? That's just for the star! The Event Horizon Telescope can achieve around 20-25 μas in microwave; you need a planet-scale interferometer to do that. https://en.wikipedia.org/wiki/Event_Horizon_Telescope https://en.wikipedia.org/wiki/Event_Horizon_Telescope It's possible to do radio measurements in sync with good clocks and fast sampling/storage, much harder with visible. I'm not super up to date on visible approaches, but there is LISA which will be a large scale interferometer in space. The technology for synchronising the satellites is similar to what you'd need for this in the optical. https://www.edmundoptics.com/knowledge-center/application-notes/imaging/limitations-on-resolution-and-contrast-the-airy-disk/ https://www.edmundoptics.com/knowledge-center/application-no... https://arxiv.org/abs/astro-ph/0303634 https://arxiv.org/abs/astro-ph/0303634
  - schobi 1y ago
    How far off are we still for doing this with visual light? Let's say you build single photon detectors and ultra precise time stamping. Would that get us near? Today, maybe we don't have femtosecond time stamping and detectors yet. But that is something I can imagine being built! Timing reference distribution within fs over 100s of km? Up to now, nobody needed that I guess.
    - joshvm 1y ago
      The biggest issue is the sheer separation required. EHT operates in mm wave light, visible is 4-6 orders of magnitude shorter wavelength. There are several smaller scale interferometers. They can already do quite impressive things because even a 50m baseline is better than any optical telescope that exists. The way that timing works for EHT is each station has a GPS reference that's conditioned with a very good atomic clock - for example at SPT we use a hydrogen maser. The readout and timing system is separate from the normal telescope control system, we just make sure the dish is tracking the right spot before we need to start saving data (sampling around 64 Gbps). I'm not sure what the timing requirements are for visible and how the clock is distributed, but syncing clocks extremely well over long distances shouldn't be insurmountable. LISA needs to solve this problem for gravitational waves and that's a million+ km baseline. Some problems go away in space. You obviously need extremely accurate station keeping (have a look how LISA Pathfinder does it, very cool), but on Earth we also have to take continental drift into account.
  - kadoban 1y ago
    Is there another limit in terms of just: how many photons from X object even hit an area of Y telescope apeture size from distance Z in like, say a year? We can't see the thing if no photons from it even intersect our telescope, right? Or maybe that limit is way way less restrictive than the other...
    - hnaccount_rng 1y ago
      The number of photons themselves is not too restrictive (i think the voyager probe still emits 6ish photons per second directed at the receiving dish). And we easily build sensors that detect every photon (far above 99% levels). The tricky part will be differentiating between “source photons” and “background photons” (for Voyager we exactly know what to look for, here we wouldn’t have any baseline for distinguishing)
bravesoul2 1y ago
L2 is moving though right? Or does it need to be simultaneously receiving at the 2 points?
- GMoromisato 1y ago
  Sadly, it has to be simultaneous. My (tenuous) understanding of interferometry is that you receive light from two points separated by a baseline and then combine that light in such a way that the wavelengths match up and reinforce at appropriate points. Wikipedia has a decent summary: https://en.wikipedia.org/wiki/Aperture_synthesis https://en.wikipedia.org/wiki/Aperture_synthesis
  - littlestymaar 1y ago
    > Sadly, it has to be simultaneous. I don't know the details of how it works, but synthetic aperture radar works thanks to the motion of the satellites, so there must be some situations for which simultaneity isn't required.
behnamoh 1y ago
Yet another reminder that space is huge and no matter how big we can imagine, due to the realities of physics, there is a good chance that we might never be able to reach the far stars and galaxies.
- grues-dinner 1y ago
  The depressing, if that's the right word, counterpoint to all the "oh my god it's fun of stars" deep fields crammed with millions of galaxies per square arcsecond is that the expansion of the universe means that nearly all of them are permanently and irrevocably out of reach even with near-lightspeed travel: they'll literally wink out of observable reality before we could ever get to them, leaving only a few nearby galaxies in the sky. At best you can reach the handful of gravitationally-bound galaxies in the local group. Not that the Milky Way is a small place, but even most sci-fi featuring FTL and all sorts of handwaves has to content itself with shenanigans confined to a single galaxy due to the mindblowing, and accelerating, gaps between galaxies.
  - sho_hn 1y ago
    It's a shame, but in a glass-falf-full sense the fact that this planet is our little boat in the ocean and all that we got is also a quite helpful focusing reminder and scope constraint. That the stars are beyond reach might be depressing, how aggresively we are gambling our little boat is on the other hand actively scary and perhaps the dominant limit on humanity's effective reach.
- UltraSane 1y ago
  Biological humans won't reach the stars but our immortal robotic offspring can.
  - runarberg 1y ago
    Unlikely. There are both economical and moral reasons to never build a self replicating robotic fleet of probes. I think a sufficiently advanced civilization will always prefer telescopes over probes for anything more distant then the nearest couple of solar systems. Just to ring the point home, we are technically (but not yet economically) capable of creating small telescopes which use our sun as a gravitational lens, which would be able to take photographs of exoplanets. In the far future we could potentially build very large telescopes which can do the same and see very distant objects with a fine resolution. That would be a much better investment then to send out self replicating robotic probes.
m3kw9 1y ago
Didn’t China able to shoot lasers to the moon orbit for comms?
GolfPopper 1y ago
We can do better than that! Using the Sun as a gravitation lens[1], and a probe at a focal point of 542 AU, we could get 25km scale surface resolution on a planet 98 ly away. [2] This would be an immense and time-consuming endeavor, but does seem to be within humanity's current technological capabilities. 1. https://en.wikipedia.org/wiki/Solar_gravitational_lens https://en.wikipedia.org/wiki/Solar_gravitational_lens 2. https://www.nasa.gov/general/direct-multipixel-imaging-and-spectroscopy-of-an-exoplanet-with-a-solar-gravitational-lens-mission/ https://www.nasa.gov/general/direct-multipixel-imaging-and-s...
- JumpCrisscross 1y ago
  Do we have a recent cost estimate?
  - twothreeone 1y ago
    "We used to look up at the sky and wonder at our place in the stars. Now we just look down, and worry about our place in the dirt."
    - sho_hn 1y ago
      It's cynical to assume OP was gunning for "it's too expensive". They might just want to know the size of the challenge to get it done.
      - twothreeone 1y ago
        And it's ironic to scold others for missing a point while missing their point. All good though.
        amanaplanacanal 1y ago
        I missed it too. What was your point?
      - JumpCrisscross 1y ago
jmyeet 1y ago
Take this even further and it eliminates a whole bunch of possible explanations for the Fermi Paradox. If, like me, you believe the future of any civilization (including ours) is a Dyson Swarm then you end up with hundreds of millions of orbitals around the Sun between, say, the orbits of Venus and Mars. It's not crowded either. The mean distance between orbitals is ~100,000km. People often ask why would anyone do this? Easy. Two reasons: land area (per unit mass) and energy. With 10 billion people, that'd be land about the size of Africa each with each person having an energy budget of about the solar output hitting the Earth, a truly incomprehensibly large amount of energy. So instead of a telescope 450km wide (fia optical interferometry), you have orbitals that are up to ~400 million kilometers apart. The resolution with which you could view very distance worlds is unimaginably high. Why does this eliminate Fermi Paradox proposed solutions? One idea is that advanced civilizations hide. There is no hiding from a K2 civilization.
vlovich123 1y ago
I thought modern telescopes use software to merge images across a period of time / from multiple telescopes to get a significantly higher resolution than that achieved through the physical limitation of light. At least that’s how all the spy telescopes work and how various ground based telescopes collaborate afaik. That’s in addition to gravitational lensing effects.
yongjik 1y ago
LIGO (the famous gravity wave detector) is made of two 4-kilometer arms. According to its website: https://www.ligo.caltech.edu/page/facts https://www.ligo.caltech.edu/page/facts > At its most sensitive state, LIGO will be able to detect a change in distance between its mirrors 1/10,000th the width of a proton! This is equivalent to noticing a change in distance to the nearest star (some 4.2 light years away) of the width of a human hair. So I think two telescopes at 450km distance synchronized to "merely" (haha) a visible light's wavelength should be doable, if we throw a fuckton of money on that.
fsckboy 1y ago
>In case anyone is wondering, we are (sadly) very far from getting an image of this planet (or any extra-solar planet) that is more than 1 pixel across. the image on the linked website is more than 1 pixel across: what are you saying? it's false/fake?
- quailfarmer 1y ago
  The resolution of the image (the ability to resolve two points) is greater than the size of the planet, thus it appears as a point spread function, no detail can be resolved.
shit_game 1y ago
I just wanna say that this an exemplary comment. This is the kind if thing i read hn coments for.
- GMoromisato 1y ago
  Thank you!
gsliepen 1y ago
If you drop the requirement that the image has to be taken with wavelengths our eyes are sensitive to, you could image it using radio telescopes. We already have this capability, the problem though with radio interferometry is that while you can get an effectively huge aperture, the contrast level will be very low, and I am guessing that after subtracting the signal from the star, the signal from the planet will not be above the noise level. Note that optical interferometers would have the same problem.
whitehexagon 1y ago
Even a single pixel in the IR range is pretty cool, but something inside me wants the RGB pixel color in visible light range. Is that a case of un redshifting this pixel, or needing the optical inferometer you mentioned with multiple single frequency filters. Or something new? like a LHC style accelerator, or space based rail gun, to fire off a continuous stream of tiny cube sats towards the target, and using the stream itself as a comms channel back. Yeah I know, this planet is burning, and all that effort for a RGB wallpaper seems crazy, but 'space stuff' also brings knowledge and hope.
perlgeek 1y ago
It would be really cool to have an array of space-based telescopes spaced out evenly in the Earth's orbit around the sun, and use each as relay for the others that cannot directly communicate with Earth, because the path is blocked by the Sun. Then you could do observations outside the solar system's orbital plane with a 2 AU synthetic aperture. And maybe even do double duty as a gravitational wave observatory. (And yes, this is currently more science fiction than science, but it's at least plausible that we can build such a thing one day).
- alex_young 1y ago
  If you can put an ugly sports car in an earth / mars orbit, surely you can put a few telescopes in some large orbit and figure out a timing source. Seems very much inside the realm of the possible.
throw0101c 1y ago
> At 110 light-years distance you would need a telescope ~450 kilometers across to image this planet at 100x100 pixel resolution--about the size of a small icon. Or use two (or more) telescopes that are 450km apart: * https://en.wikipedia.org/wiki/Aperture_synthesis https://en.wikipedia.org/wiki/Aperture_synthesis * https://www.nature.com/articles/ncomms7852 https://www.nature.com/articles/ncomms7852
drgiran 1y ago
Synchronization is solvable, and why stop at two? You could have a three-dimensional array of them, spread over very large distances. We have the technology now to pull this off.
parpfish 1y ago
Do these scientist know they can just say “enhance”?
- le-mark 1y ago
  As someone who’s sat in meeting with nontechnical people and having heard this exact request (“can’t you just enhance the image?”) I felt this.
littlestymaar 1y ago
Why can't we use the motion of the telescope in space to make a synthetic aperture like SAR imagery satellites do?

nico 1y ago

How big would the telescope/mirror/lens need to be to get a picture of something in the Alpha Centauri system, 4.37 light years away? Also, could the image be created by “scanning” a big area and then composing the image from a bunch of smaller ones?

GMoromisato 1y ago
It's linear, so if it is 25 times closer then the telescope can be 25 times smaller. At 4.37 light-years we'd need an 18 kilometer telescope to image at Jupiter-sized planet at 100x100 pixel resolution. If you only wanted 10x10 resolution you could get by with a 1.8 kilometer telescope. Wikipedia has more: https://en.wikipedia.org/wiki/Angular_resolution https://en.wikipedia.org/wiki/Angular_resolution. The Rayleigh criterion is the equation to calculate this.
joshvm 1y ago
It's a lot easier to reason about this using angular resolution, because that's normally what the diffraction limit formula is in reference to. If you know the angular diameter of the system (α) and the wavelength (say λ=500 nm for visible), you can use α ≈ λ/d and solve for the aperture of the telescope (d). That puts a basic limit on the smallest thing you can resolve with a given aperture. You can use the angular diameter of the planet and the resolution you're after. For Alpha Centauri A it's 8.5 milli arc-second, so O(1 μas) for a 100px image? That's just for the star! The Event Horizon Telescope can achieve around 20-25 μas in microwave; you need a planet-scale interferometer to do that. https://en.wikipedia.org/wiki/Event_Horizon_Telescope https://en.wikipedia.org/wiki/Event_Horizon_Telescope It's possible to do radio measurements in sync with good clocks and fast sampling/storage, much harder with visible. I'm not super up to date on visible approaches, but there is LISA which will be a large scale interferometer in space. The technology for synchronising the satellites is similar to what you'd need for this in the optical. https://www.edmundoptics.com/knowledge-center/application-notes/imaging/limitations-on-resolution-and-contrast-the-airy-disk/ https://www.edmundoptics.com/knowledge-center/application-no... https://arxiv.org/abs/astro-ph/0303634 https://arxiv.org/abs/astro-ph/0303634
- schobi 1y ago
  How far off are we still for doing this with visual light? Let's say you build single photon detectors and ultra precise time stamping. Would that get us near? Today, maybe we don't have femtosecond time stamping and detectors yet. But that is something I can imagine being built! Timing reference distribution within fs over 100s of km? Up to now, nobody needed that I guess.
  - joshvm 1y ago
    The biggest issue is the sheer separation required. EHT operates in mm wave light, visible is 4-6 orders of magnitude shorter wavelength. There are several smaller scale interferometers. They can already do quite impressive things because even a 50m baseline is better than any optical telescope that exists. The way that timing works for EHT is each station has a GPS reference that's conditioned with a very good atomic clock - for example at SPT we use a hydrogen maser. The readout and timing system is separate from the normal telescope control system, we just make sure the dish is tracking the right spot before we need to start saving data (sampling around 64 Gbps). I'm not sure what the timing requirements are for visible and how the clock is distributed, but syncing clocks extremely well over long distances shouldn't be insurmountable. LISA needs to solve this problem for gravitational waves and that's a million+ km baseline. Some problems go away in space. You obviously need extremely accurate station keeping (have a look how LISA Pathfinder does it, very cool), but on Earth we also have to take continental drift into account.
- kadoban 1y ago
  Is there another limit in terms of just: how many photons from X object even hit an area of Y telescope apeture size from distance Z in like, say a year? We can't see the thing if no photons from it even intersect our telescope, right? Or maybe that limit is way way less restrictive than the other...
  - hnaccount_rng 1y ago
    The number of photons themselves is not too restrictive (i think the voyager probe still emits 6ish photons per second directed at the receiving dish). And we easily build sensors that detect every photon (far above 99% levels). The tricky part will be differentiating between “source photons” and “background photons” (for Voyager we exactly know what to look for, here we wouldn’t have any baseline for distinguishing)

bravesoul2 1y ago

L2 is moving though right? Or does it need to be simultaneously receiving at the 2 points?

GMoromisato 1y ago
Sadly, it has to be simultaneous. My (tenuous) understanding of interferometry is that you receive light from two points separated by a baseline and then combine that light in such a way that the wavelengths match up and reinforce at appropriate points. Wikipedia has a decent summary: https://en.wikipedia.org/wiki/Aperture_synthesis https://en.wikipedia.org/wiki/Aperture_synthesis
- littlestymaar 1y ago
  > Sadly, it has to be simultaneous. I don't know the details of how it works, but synthetic aperture radar works thanks to the motion of the satellites, so there must be some situations for which simultaneity isn't required.

behnamoh 1y ago

Yet another reminder that space is huge and no matter how big we can imagine, due to the realities of physics, there is a good chance that we might never be able to reach the far stars and galaxies.

grues-dinner 1y ago
The depressing, if that's the right word, counterpoint to all the "oh my god it's fun of stars" deep fields crammed with millions of galaxies per square arcsecond is that the expansion of the universe means that nearly all of them are permanently and irrevocably out of reach even with near-lightspeed travel: they'll literally wink out of observable reality before we could ever get to them, leaving only a few nearby galaxies in the sky. At best you can reach the handful of gravitationally-bound galaxies in the local group. Not that the Milky Way is a small place, but even most sci-fi featuring FTL and all sorts of handwaves has to content itself with shenanigans confined to a single galaxy due to the mindblowing, and accelerating, gaps between galaxies.
- sho_hn 1y ago
  It's a shame, but in a glass-falf-full sense the fact that this planet is our little boat in the ocean and all that we got is also a quite helpful focusing reminder and scope constraint. That the stars are beyond reach might be depressing, how aggresively we are gambling our little boat is on the other hand actively scary and perhaps the dominant limit on humanity's effective reach.
UltraSane 1y ago
Biological humans won't reach the stars but our immortal robotic offspring can.
- runarberg 1y ago
  Unlikely. There are both economical and moral reasons to never build a self replicating robotic fleet of probes. I think a sufficiently advanced civilization will always prefer telescopes over probes for anything more distant then the nearest couple of solar systems. Just to ring the point home, we are technically (but not yet economically) capable of creating small telescopes which use our sun as a gravitational lens, which would be able to take photographs of exoplanets. In the far future we could potentially build very large telescopes which can do the same and see very distant objects with a fine resolution. That would be a much better investment then to send out self replicating robotic probes.

m3kw9 1y ago

Didn’t China able to shoot lasers to the moon orbit for comms?

GolfPopper 1y ago

We can do better than that! Using the Sun as a gravitation lens[1], and a probe at a focal point of 542 AU, we could get 25km scale surface resolution on a planet 98 ly away. [2] This would be an immense and time-consuming endeavor, but does seem to be within humanity's current technological capabilities. 1. https://en.wikipedia.org/wiki/Solar_gravitational_lens https://en.wikipedia.org/wiki/Solar_gravitational_lens 2. https://www.nasa.gov/general/direct-multipixel-imaging-and-spectroscopy-of-an-exoplanet-with-a-solar-gravitational-lens-mission/ https://www.nasa.gov/general/direct-multipixel-imaging-and-s...

JumpCrisscross 1y ago
Do we have a recent cost estimate?
- twothreeone 1y ago
  "We used to look up at the sky and wonder at our place in the stars. Now we just look down, and worry about our place in the dirt."
  - sho_hn 1y ago
    It's cynical to assume OP was gunning for "it's too expensive". They might just want to know the size of the challenge to get it done.
    - twothreeone 1y ago
      And it's ironic to scold others for missing a point while missing their point. All good though.
      - amanaplanacanal 1y ago
        I missed it too. What was your point?
    - JumpCrisscross 1y ago

jmyeet 1y ago

Take this even further and it eliminates a whole bunch of possible explanations for the Fermi Paradox. If, like me, you believe the future of any civilization (including ours) is a Dyson Swarm then you end up with hundreds of millions of orbitals around the Sun between, say, the orbits of Venus and Mars. It's not crowded either. The mean distance between orbitals is ~100,000km. People often ask why would anyone do this? Easy. Two reasons: land area (per unit mass) and energy. With 10 billion people, that'd be land about the size of Africa each with each person having an energy budget of about the solar output hitting the Earth, a truly incomprehensibly large amount of energy. So instead of a telescope 450km wide (fia optical interferometry), you have orbitals that are up to ~400 million kilometers apart. The resolution with which you could view very distance worlds is unimaginably high. Why does this eliminate Fermi Paradox proposed solutions? One idea is that advanced civilizations hide. There is no hiding from a K2 civilization.

vlovich123 1y ago

I thought modern telescopes use software to merge images across a period of time / from multiple telescopes to get a significantly higher resolution than that achieved through the physical limitation of light. At least that’s how all the spy telescopes work and how various ground based telescopes collaborate afaik. That’s in addition to gravitational lensing effects.

yongjik 1y ago

LIGO (the famous gravity wave detector) is made of two 4-kilometer arms. According to its website: https://www.ligo.caltech.edu/page/facts https://www.ligo.caltech.edu/page/facts > At its most sensitive state, LIGO will be able to detect a change in distance between its mirrors 1/10,000th the width of a proton! This is equivalent to noticing a change in distance to the nearest star (some 4.2 light years away) of the width of a human hair. So I think two telescopes at 450km distance synchronized to "merely" (haha) a visible light's wavelength should be doable, if we throw a fuckton of money on that.

fsckboy 1y ago

>In case anyone is wondering, we are (sadly) very far from getting an image of this planet (or any extra-solar planet) that is more than 1 pixel across. the image on the linked website is more than 1 pixel across: what are you saying? it's false/fake?

quailfarmer 1y ago
The resolution of the image (the ability to resolve two points) is greater than the size of the planet, thus it appears as a point spread function, no detail can be resolved.

shit_game 1y ago

I just wanna say that this an exemplary comment. This is the kind if thing i read hn coments for.

GMoromisato 1y ago
Thank you!

gsliepen 1y ago

If you drop the requirement that the image has to be taken with wavelengths our eyes are sensitive to, you could image it using radio telescopes. We already have this capability, the problem though with radio interferometry is that while you can get an effectively huge aperture, the contrast level will be very low, and I am guessing that after subtracting the signal from the star, the signal from the planet will not be above the noise level. Note that optical interferometers would have the same problem.

whitehexagon 1y ago

Even a single pixel in the IR range is pretty cool, but something inside me wants the RGB pixel color in visible light range. Is that a case of un redshifting this pixel, or needing the optical inferometer you mentioned with multiple single frequency filters. Or something new? like a LHC style accelerator, or space based rail gun, to fire off a continuous stream of tiny cube sats towards the target, and using the stream itself as a comms channel back. Yeah I know, this planet is burning, and all that effort for a RGB wallpaper seems crazy, but 'space stuff' also brings knowledge and hope.

perlgeek 1y ago

It would be really cool to have an array of space-based telescopes spaced out evenly in the Earth's orbit around the sun, and use each as relay for the others that cannot directly communicate with Earth, because the path is blocked by the Sun. Then you could do observations outside the solar system's orbital plane with a 2 AU synthetic aperture. And maybe even do double duty as a gravitational wave observatory. (And yes, this is currently more science fiction than science, but it's at least plausible that we can build such a thing one day).

alex_young 1y ago
If you can put an ugly sports car in an earth / mars orbit, surely you can put a few telescopes in some large orbit and figure out a timing source. Seems very much inside the realm of the possible.

throw0101c 1y ago

> At 110 light-years distance you would need a telescope ~450 kilometers across to image this planet at 100x100 pixel resolution--about the size of a small icon. Or use two (or more) telescopes that are 450km apart: * https://en.wikipedia.org/wiki/Aperture_synthesis https://en.wikipedia.org/wiki/Aperture_synthesis * https://www.nature.com/articles/ncomms7852 https://www.nature.com/articles/ncomms7852

drgiran 1y ago

Synchronization is solvable, and why stop at two? You could have a three-dimensional array of them, spread over very large distances. We have the technology now to pull this off.

parpfish 1y ago

Do these scientist know they can just say “enhance”?

le-mark 1y ago
As someone who’s sat in meeting with nontechnical people and having heard this exact request (“can’t you just enhance the image?”) I felt this.

littlestymaar 1y ago

Why can't we use the motion of the telescope in space to make a synthetic aperture like SAR imagery satellites do?