8 ms·

Funny given that Starlink itself has potential to be one giant synthetic aperture radar installation. From Casey Handmer’s excellent post (https://caseyhandmer

Funny given that Starlink itself has potential to be one giant synthetic aperture radar installation. From Casey Handmer’s excellent post (https://caseyhandmer.wordpress.com/2021/11/17/science-upside-for-starship/ https://caseyhandmer.wordpress.com/2021/11/17/science-upside...): “Starlink SAR is great for Earth observation, but the same principle can be applied looking outwards. Starlink is a network of thousands of software defined radios with highly precise PNT information and high speed data connections. It is practically begging to be integrated into a world-sized radio telescope. With 13000 km of baseline (trivially extendable with a handful of GTO Starlink launches) and the ability to point in any desired direction simultaneously, Starlink could capture practically holographic levels of detail about the local radio environment. Literally orders of magnitude better resolution than ground-based antennas like the Very Large Array. Cheaper than repairing Arecibo and independent of Earth’s rotation. Potentially capable of resolving exoplanets.”

ngcc_hk 5y ago
You just do a sensor and lens manipulated opposite to where the unwanted light source are (earth, moon and sun) and sent the info back. I am not sure the radio channel the thing operate affect this approach. Just no one seem to think of this as complement to the earth one. Synergy not fight then.
suifbwish 5y ago
Their claim is the equivalent of complaining that the weight of a large vehicle engine is bad because it makes the vehicle more difficult to carry up a hill. Get in, start the engine and drive up the hill lol. I’m curious what you mean by “holographic levels of detail” If starlink were used as an outward sensor array, with the correct software and enough compute you could generate a live 3D model of the entire sky and almost anything in it down to quite a small resolution.
- idealmedtech 5y ago
  Your second paragraph answers the first question, I think! As you probably know, more antennas spread further apart dramatically increases the effective antenna size when phased correctly.
  - ben_w 5y ago
    While that does increase the angular resolution, it does nothing for weak signals — only area can boost that.
    - thro1 5y ago
      But can we boost that signals - focusing not on observation, but on detection of objects in the solar system moving toward Earth? With such great resolution, what power, scanning frequency etc. of an active radar would be needed? Considering the area we can't use focused beams (but impulses would be nice) - right?, could the solar radio emission be used instead or the light is better? Or maybe there is some background radiation on frequency that we can detect when is covered ?
    - suifbwish 5y ago
      Wouldn’t the area of the combined sensor be the sum of the areas of each sensor?
      - ben_w 5y ago
        Yes, if that’s what you’re asking (which is not what I thought this was about). Thought as someone else said, even combined it’s still less than Arecibo.
        Dylan16807 5y ago
        > it’s still less than Arecibo Which is a huge baseline and getting anywhere near it with so much better resolution could be really impressive.
        ben_w 5y ago
        We’ve basically already got one twice the size of Arecibo, though: https://en.wikipedia.org/wiki/Square_Kilometre_Array https://en.wikipedia.org/wiki/Square_Kilometre_Array
ianai 5y ago
Yes. If Elon was as concerned about the survival of humanity as he claims with his mars initiatives then he’d outfit these with some equipment for this. There’s got to be a way to do both internet and radio astronomy.
- immmmmm 5y ago
  putting extremely sensitive RF detectors on top of extremely power RF emitters doesn't seems the best match
  - hypertele-Xii 5y ago
    Until you realize every single satellite that both transmits and receives information has solved this problem already, including Starlink.
    - emn13 5y ago
      I'm somewhat skeptical that every radio receiver is interchangable. Yes, starlink will have some kind of transceiver - but do you have any citation to back up the claim that it can be used effectively for astronomical observation? Even if the physics are fundamentally the same, all kinds of practical implementation details like orientation, bandwidth, frequency, and probably all kinds of stuff an actual expert in the field would know about may well differ.
    - Dylan16807 5y ago
      They got the signal to noise margins down enough for effective communication. That doesn't mean they'd be within orders of magnitude of optimal for measuring extremely weak signals.
- cryptonector 5y ago
  It takes enormous amounts of capital to do all of this. He's got to build some of that capital first, and to do that he has to pursue commercial interests first. Once he's got positive cash-flow and growth and demonstrated a sustainable business, then he still can't quite build a radio telescope on SpaceX's dime for fiduciary reasons, but he'd have built a launch facility that governments could use to do it.
idealmedtech 5y ago
If their primary mission was observation, they would be an incredible astronomical resource. However, I think that given the fuel constraints and SLA they aim to provide, I would be shocked if they used any fuel to orient for extraterrestrial observation.
- jillesvangurp 5y ago
  I think that SpaceX has convincingly proven that it is not that expensive to send up thousands of satellites. So, anyone interested in launching a telescope satellite could do worse than talk to them to see if they could help out. Also, given enough money, I don't see why SpaceX would not be using their satellite network for more than communication. Positioning is another interesting use case for them, for example.
  - shantara 5y ago
    Another thing that SpaceX has proven with Starlink is that the benefits of economy of scale could be applied to satellite production and the aerospace industry in general. It is so incredibly wasteful that the companies and governments keep coming up with unique designs for the satellites serving similar purposes. Imagine if we had a standard design template for an optical telescope that could be cheaply and easily mass produced and launched by the thousands.
    - mcguire 5y ago
      As someone mentioned above, weak signals require large receivers.
    - giantrobot 5y ago
      > It is so incredibly wasteful that the companies and governments keep coming up with unique designs for the satellites serving similar purposes. Common satellite chassis has been a thing for decades. StarLink and other systems like it benefit from mass production and economies of scale. Each block of StarLink satellites is identical. They also have a singular task and everything about them is optimized for it. Most satellites are not identical copies of one another even if they have "similar" roles. Mass production is less desirable as you'd end up with unoptimized designs which means wasted mass or reduced capabilities.
seventytwo 5y ago
Or… We just stop letting the broadband companies regulate themselves and nationalize the system. Then we don’t have multiple layers of bandaids.
welterde 5y ago
Even the full planned constellation has a smaller collecting area than Arecibo had (~60 000 m^2 vs ~73 000 m^2 for Arecibo) - and that's not even considering that for half the constellation the earth will be in the way, not the full dimensions of the satellite are usable as antenna, they are pointing the wrong way, etc. etc. Nevermind that one looses quite a lot of sensitivity when using these arrays..
- nuccy 5y ago
  It is not about collecting area, but about synchetic aperture [1] alike very-long baseline interferometry (e.g. used by Event Horizon Telescope [2], which is a combination of many radio telescopes to observe the accretion disk around the supermassive black hole in M87 galaxy [3]). For that you need as long as possible distance between antenas, good time synchronisation, and as many as possible pairs of antenas (i.e. baselines) [3]. Though unfortunately advances in radio don't compensate losses in optical and survey quality due to strays. Different sources emit at different wavelengths differently and usually one needs the whole picture (spectral energy distribution) from radio, ir, visible light, uv, x-rays up to gamma-rays to explain the properties of a source. 1. https://caseyhandmer.wordpress.com/2021/11/17/science-upside-for-starship/ https://caseyhandmer.wordpress.com/2021/11/17/science-upside... 2. https://en.m.wikipedia.org/wiki/Very-long-baseline_interferometry https://en.m.wikipedia.org/wiki/Very-long-baseline_interfero... 3. https://skyandtelescope.org/astronomy-blogs/black-hole-files/how-does-very-long-baseline-interferometry-work/ https://skyandtelescope.org/astronomy-blogs/black-hole-files...
  - welterde 5y ago
    Depends on what you are after. You need long baselines if you want high resolution. However if you want high sensitivity there is no way around having a large collecting area. And since we are not looking to detect the sun in super high resolution, but very far away objects that will be extremely faint we need very high sensitivity. There is a reason the VLA (and other arrays such as ALMA) move their antennas into different configurations. A more compact configuration achieves better sensitivity at the cost of lower resolution and a more spread out configuration gives the inverse. Your hypothetical Starlink telescope would always have extremely high resolution but virtually no sensitivity to detect anything at all (maybe the sun). Certainly not any NEO objects - those were the prime targets for large single-dish radio telescope like Arecibo. The closest radio telescope to the concept you have in mind is LOFAR, but even for that one each station has many times the collecting area of many dozens of Starlink satellites (total collecting area of all stations together is up to ~1km^2).
thro1 5y ago
I made that question once on HN (2020, relating to Arecibo) and it was downvoted: Couldn't it be receivers on Starlink satellites plus some computing power instead? - but I've got great feasibility study by teraflop as the answer for that: https://news.ycombinator.com/item?id=25051151 https://news.ycombinator.com/item?id=25051151 .
- deleted 5y ago
  [deleted]
- thro1 5y ago
  Parent downvoted ? Whatever, if you didn't read teraflop's answer, IMHO it's the best here so far (but missing some insight like angular resolution, synthetic aperture and baselines).
lokimedes 5y ago
Does the StarLink constellation have sufficiently accurate time synchronization and phase stability to allow it to act as a long baseline multi-static radar? I have been contemplating using it as a passive radar source, but here the limitation is its phased array nature. It is not really optimal for non-cooperative receivers.
- justinjlynn 5y ago
  One would imagine so given that the satellites are eventually meant to collaborate via peer to peer direct laser links. Time synchronisation and phase stability are required for direct links but it's a good question as to how much is available in terms of the microwave SDRs.
cronix 5y ago
You could also install cameras pointing back towards Earth and basically have 24/7 coverage of everyone's movements similar to what Darpa's ARGUS-IS[1](2013) does except using a global network of satellites instead of drones and build the greatest video surveillance platform on the planet. Instead of covering a city for a limited time with a drone stuffed with an array of off the shelf cell phone cameras, you could have "persistent stare" for the entire planet. I wonder if the NSA has thought about that. [1]https://www.youtube.com/watch?v=QGxNyaXfJsA https://www.youtube.com/watch?v=QGxNyaXfJsA
- echelon 5y ago
  I can't imagine that the NSA hasn't already had several talks with Musk.
- Retric 5y ago
  Starlink satellites are tiny which limits how much you can slip in undetected. You can’t get anything close to useful resolution from something like a cellphone camera at those altitudes. Maximum resolution really requires something the size of Hubble.
  - Teever 5y ago
    I was under the impression that spy satellites are put into much higher orbits to increase their lifespan but necessitating larger optical systems. One of the advantages of a LEO based surveillance system is that the optics could be smaller at the cost of requiring more satellites with shorter life span.
    - Retric 5y ago
      ~500km is still a common NRO orbit, and presumably that’s to take the highest resolution images possible. The earliest spy satellites where under 150km and had extremely short lifespans. By comparison the commercial KOMPSAT-3 can provide 0.7m b/w images and 2.8m multispectral images from a 980kg satellite at 685 km and a multi year lifespan, I doubt classified satellites are that much better than that. Some NRO satellites are sent to geostationary orbit, presumably for other missions. So, it really depends on the goals as not all satellites are designed for ground imaging.
mcguire 5y ago
Certainly, Starlink's ground equipment has multiple functions: https://www.smithsonianmag.com/smart-news/outdoor-cats-are-using-500-starlink-satellite-dishes-as-self-heating-beds-180979401/ https://www.smithsonianmag.com/smart-news/outdoor-cats-are-u...
hinkley 5y ago
I think it's likely there will be a dope deal at some point where low-earth satellite clusters have to offer sky observation services that offset the loss of fidelity from ground-based systems. If the satellites can swing between sky and ground scanning several times in a single orbital period, they could use off-peak hours in the early morning to scan the skies. I don't know if that practically will work out, as Starlink has lower speed of light delays than undersea cables. Accessing content on the other side of the world will become more attractive with lower latency. For instance a lot more people using VPNs to watch BBC.co.uk at 4 am GMT.
- Jtsummers 5y ago
  More likely, instead of dual purposing the satellites they'll end up finding a customer who is willing to pay for them to send up additional satellites that offer imagery, radio telemetry, or other sensor data. They'll get mixed in with the rest of the fleet, possibly acting as relays between satellites rather than downlink/uplinks themselves. Removing the downlink/uplink components would free up quite a bit of mass that could be dedicated to various sensor platforms, and the comms left would be the inter-satellite system already being used by the fleet. There are lots of potential customers for this (especially if used for terrestrial imagery or similar sensing), and piggybacking on their existing telecom fleet to handle the uplink/downlink side could be a phenomenal bit of cost savings for them. And they get the benefit of improving the inter-satellite network with the additional relays.
  - hinkley 5y ago
    If you follow that thread, it might be cheaper still for Starlink to provide bandwidth to actual orbital telescopes.
    - Jtsummers 5y ago
      Yep, I was pondering that during my workout and was going to put in an edit. If Starlink offered inter-satellite comms as a product/service, it could potentially reduce the cost of many satellites both in low orbit or any higher orbit since it would reduce both mass and energy requirements (up/downlink takes a lot of mass and energy). Reducing the weight of systems targeting higher orbits making them cheaper to launch, or allowing them to incorporate more capabilities thanks to the reduced mass. It also reduces the terrestrial-to-satellite comms requirements, you'd connect to your satellite like any other Internet enabled device. Just with higher latency than most and maybe (for a few times a day) lower than optimal latency. Of course, there's a downside. What if Starlink goes bust in 5-10 years? Even 20. Whatever the comms system is, you'd want it to be reprogrammable (at least) if not part of some more open specification that others could connect to. Which suggests the possibility of licensing the technology. That opens Starlink up to competitors, but makes the service more appealing to customers. Which brings it back to probably having the most near-term utility for other LEO satellites since longevity isn't an issue for them in general, but reduces the utility for the next JWT.
ajnin 5y ago
> Potentially capable of resolving exoplanets I was curious about that claim, so I did a bit of research and made a "back of the envelope" calculation. According to Wikipedia [1], the angular resolution of a telescope is proportional to <wavelength of light>/<diameter>. Starlink seems to operate from 10 to 40GHz, so assume the hardware has a 50% design margin so is capable of reaching 60GHz. Visible light has a frequency of 400 to 800THz, so take the middle of 600THz. Using those figures, it come out that the Starlink satellites, used as a telescope, would have the same angular resolution as a 1.3m visible light telescope. Is it enough to resolve exoplanets ? I'm not sure but I think not. Hubble is 6m and can apparently resolve some exoplanets so it's not too far off. Some launches to GEO would boost the resolution to the equivalent of 8.4m in visible. (IANAA) 1: https://en.wikipedia.org/wiki/Angular_resolution https://en.wikipedia.org/wiki/Angular_resolution
- Dylan16807 5y ago
  Your math makes sense, 60GHz and 600THz are a factor of 10000 apart, etc. But that means you mixed up meters and kilometers when you did your division. 1.3km visible light telescope
- gliptic 5y ago
  Hubble is 2.4 meter aperture.
- jcims 5y ago
  This is the one that specifically discusses telescope array (but your formula is still correct) https://en.wikipedia.org/wiki/Angular_resolution#Telescope_array https://en.wikipedia.org/wiki/Angular_resolution#Telescope_a... 60GHz has a wavelength of 5mm. Effective diameter would be ~13000km. Someone check my math but I end up with 5e-3/13e6 radians or ~.0001 arcseconds. Hubble is ~.05 arcseconds.
- peter303 5y ago
  The Event Horizon Telescope "imaged" two black hole structures down to 10 microarcsecond resolution. The create synthetic apertures from radio telescope pairs separated as much as 8,000 miles and operating up to 450 GigaHertz. (Synthetic telescopes have been created since the 1970s, but used much lower radio frequencies with a much lower computation burden.) Each telescope pair samples a small bit of spatial frequencies. So sophisticated inversions were run to compute the image that best fit these samples.

ngcc_hk 5y ago

You just do a sensor and lens manipulated opposite to where the unwanted light source are (earth, moon and sun) and sent the info back. I am not sure the radio channel the thing operate affect this approach. Just no one seem to think of this as complement to the earth one. Synergy not fight then.

suifbwish 5y ago

Their claim is the equivalent of complaining that the weight of a large vehicle engine is bad because it makes the vehicle more difficult to carry up a hill. Get in, start the engine and drive up the hill lol. I’m curious what you mean by “holographic levels of detail” If starlink were used as an outward sensor array, with the correct software and enough compute you could generate a live 3D model of the entire sky and almost anything in it down to quite a small resolution.

idealmedtech 5y ago
Your second paragraph answers the first question, I think! As you probably know, more antennas spread further apart dramatically increases the effective antenna size when phased correctly.
- ben_w 5y ago
  While that does increase the angular resolution, it does nothing for weak signals — only area can boost that.
  - thro1 5y ago
    But can we boost that signals - focusing not on observation, but on detection of objects in the solar system moving toward Earth? With such great resolution, what power, scanning frequency etc. of an active radar would be needed? Considering the area we can't use focused beams (but impulses would be nice) - right?, could the solar radio emission be used instead or the light is better? Or maybe there is some background radiation on frequency that we can detect when is covered ?
  - suifbwish 5y ago
    Wouldn’t the area of the combined sensor be the sum of the areas of each sensor?
    - ben_w 5y ago
      Yes, if that’s what you’re asking (which is not what I thought this was about). Thought as someone else said, even combined it’s still less than Arecibo.
      - Dylan16807 5y ago
        > it’s still less than Arecibo Which is a huge baseline and getting anywhere near it with so much better resolution could be really impressive.
        ben_w 5y ago
        We’ve basically already got one twice the size of Arecibo, though: https://en.wikipedia.org/wiki/Square_Kilometre_Array https://en.wikipedia.org/wiki/Square_Kilometre_Array

ianai 5y ago

Yes. If Elon was as concerned about the survival of humanity as he claims with his mars initiatives then he’d outfit these with some equipment for this. There’s got to be a way to do both internet and radio astronomy.

immmmmm 5y ago
putting extremely sensitive RF detectors on top of extremely power RF emitters doesn't seems the best match
- hypertele-Xii 5y ago
  Until you realize every single satellite that both transmits and receives information has solved this problem already, including Starlink.
  - emn13 5y ago
    I'm somewhat skeptical that every radio receiver is interchangable. Yes, starlink will have some kind of transceiver - but do you have any citation to back up the claim that it can be used effectively for astronomical observation? Even if the physics are fundamentally the same, all kinds of practical implementation details like orientation, bandwidth, frequency, and probably all kinds of stuff an actual expert in the field would know about may well differ.
  - Dylan16807 5y ago
    They got the signal to noise margins down enough for effective communication. That doesn't mean they'd be within orders of magnitude of optimal for measuring extremely weak signals.
cryptonector 5y ago
It takes enormous amounts of capital to do all of this. He's got to build some of that capital first, and to do that he has to pursue commercial interests first. Once he's got positive cash-flow and growth and demonstrated a sustainable business, then he still can't quite build a radio telescope on SpaceX's dime for fiduciary reasons, but he'd have built a launch facility that governments could use to do it.

idealmedtech 5y ago

If their primary mission was observation, they would be an incredible astronomical resource. However, I think that given the fuel constraints and SLA they aim to provide, I would be shocked if they used any fuel to orient for extraterrestrial observation.

jillesvangurp 5y ago
I think that SpaceX has convincingly proven that it is not that expensive to send up thousands of satellites. So, anyone interested in launching a telescope satellite could do worse than talk to them to see if they could help out. Also, given enough money, I don't see why SpaceX would not be using their satellite network for more than communication. Positioning is another interesting use case for them, for example.
- shantara 5y ago
  Another thing that SpaceX has proven with Starlink is that the benefits of economy of scale could be applied to satellite production and the aerospace industry in general. It is so incredibly wasteful that the companies and governments keep coming up with unique designs for the satellites serving similar purposes. Imagine if we had a standard design template for an optical telescope that could be cheaply and easily mass produced and launched by the thousands.
  - mcguire 5y ago
    As someone mentioned above, weak signals require large receivers.
  - giantrobot 5y ago
    > It is so incredibly wasteful that the companies and governments keep coming up with unique designs for the satellites serving similar purposes. Common satellite chassis has been a thing for decades. StarLink and other systems like it benefit from mass production and economies of scale. Each block of StarLink satellites is identical. They also have a singular task and everything about them is optimized for it. Most satellites are not identical copies of one another even if they have "similar" roles. Mass production is less desirable as you'd end up with unoptimized designs which means wasted mass or reduced capabilities.

seventytwo 5y ago

Or… We just stop letting the broadband companies regulate themselves and nationalize the system. Then we don’t have multiple layers of bandaids.

welterde 5y ago

Even the full planned constellation has a smaller collecting area than Arecibo had (~60 000 m^2 vs ~73 000 m^2 for Arecibo) - and that's not even considering that for half the constellation the earth will be in the way, not the full dimensions of the satellite are usable as antenna, they are pointing the wrong way, etc. etc. Nevermind that one looses quite a lot of sensitivity when using these arrays..

nuccy 5y ago
It is not about collecting area, but about synchetic aperture [1] alike very-long baseline interferometry (e.g. used by Event Horizon Telescope [2], which is a combination of many radio telescopes to observe the accretion disk around the supermassive black hole in M87 galaxy [3]). For that you need as long as possible distance between antenas, good time synchronisation, and as many as possible pairs of antenas (i.e. baselines) [3]. Though unfortunately advances in radio don't compensate losses in optical and survey quality due to strays. Different sources emit at different wavelengths differently and usually one needs the whole picture (spectral energy distribution) from radio, ir, visible light, uv, x-rays up to gamma-rays to explain the properties of a source. 1. https://caseyhandmer.wordpress.com/2021/11/17/science-upside-for-starship/ https://caseyhandmer.wordpress.com/2021/11/17/science-upside... 2. https://en.m.wikipedia.org/wiki/Very-long-baseline_interferometry https://en.m.wikipedia.org/wiki/Very-long-baseline_interfero... 3. https://skyandtelescope.org/astronomy-blogs/black-hole-files/how-does-very-long-baseline-interferometry-work/ https://skyandtelescope.org/astronomy-blogs/black-hole-files...
- welterde 5y ago
  Depends on what you are after. You need long baselines if you want high resolution. However if you want high sensitivity there is no way around having a large collecting area. And since we are not looking to detect the sun in super high resolution, but very far away objects that will be extremely faint we need very high sensitivity. There is a reason the VLA (and other arrays such as ALMA) move their antennas into different configurations. A more compact configuration achieves better sensitivity at the cost of lower resolution and a more spread out configuration gives the inverse. Your hypothetical Starlink telescope would always have extremely high resolution but virtually no sensitivity to detect anything at all (maybe the sun). Certainly not any NEO objects - those were the prime targets for large single-dish radio telescope like Arecibo. The closest radio telescope to the concept you have in mind is LOFAR, but even for that one each station has many times the collecting area of many dozens of Starlink satellites (total collecting area of all stations together is up to ~1km^2).

thro1 5y ago

I made that question once on HN (2020, relating to Arecibo) and it was downvoted: Couldn't it be receivers on Starlink satellites plus some computing power instead? - but I've got great feasibility study by teraflop as the answer for that: https://news.ycombinator.com/item?id=25051151 https://news.ycombinator.com/item?id=25051151 .

deleted 5y ago
[deleted]
thro1 5y ago
Parent downvoted ? Whatever, if you didn't read teraflop's answer, IMHO it's the best here so far (but missing some insight like angular resolution, synthetic aperture and baselines).

lokimedes 5y ago

Does the StarLink constellation have sufficiently accurate time synchronization and phase stability to allow it to act as a long baseline multi-static radar? I have been contemplating using it as a passive radar source, but here the limitation is its phased array nature. It is not really optimal for non-cooperative receivers.

justinjlynn 5y ago
One would imagine so given that the satellites are eventually meant to collaborate via peer to peer direct laser links. Time synchronisation and phase stability are required for direct links but it's a good question as to how much is available in terms of the microwave SDRs.

cronix 5y ago

You could also install cameras pointing back towards Earth and basically have 24/7 coverage of everyone's movements similar to what Darpa's ARGUS-IS[1](2013) does except using a global network of satellites instead of drones and build the greatest video surveillance platform on the planet. Instead of covering a city for a limited time with a drone stuffed with an array of off the shelf cell phone cameras, you could have "persistent stare" for the entire planet. I wonder if the NSA has thought about that. [1]https://www.youtube.com/watch?v=QGxNyaXfJsA https://www.youtube.com/watch?v=QGxNyaXfJsA

echelon 5y ago
I can't imagine that the NSA hasn't already had several talks with Musk.
Retric 5y ago
Starlink satellites are tiny which limits how much you can slip in undetected. You can’t get anything close to useful resolution from something like a cellphone camera at those altitudes. Maximum resolution really requires something the size of Hubble.
- Teever 5y ago
  I was under the impression that spy satellites are put into much higher orbits to increase their lifespan but necessitating larger optical systems. One of the advantages of a LEO based surveillance system is that the optics could be smaller at the cost of requiring more satellites with shorter life span.
  - Retric 5y ago
    ~500km is still a common NRO orbit, and presumably that’s to take the highest resolution images possible. The earliest spy satellites where under 150km and had extremely short lifespans. By comparison the commercial KOMPSAT-3 can provide 0.7m b/w images and 2.8m multispectral images from a 980kg satellite at 685 km and a multi year lifespan, I doubt classified satellites are that much better than that. Some NRO satellites are sent to geostationary orbit, presumably for other missions. So, it really depends on the goals as not all satellites are designed for ground imaging.

mcguire 5y ago

Certainly, Starlink's ground equipment has multiple functions: https://www.smithsonianmag.com/smart-news/outdoor-cats-are-using-500-starlink-satellite-dishes-as-self-heating-beds-180979401/ https://www.smithsonianmag.com/smart-news/outdoor-cats-are-u...

hinkley 5y ago

I think it's likely there will be a dope deal at some point where low-earth satellite clusters have to offer sky observation services that offset the loss of fidelity from ground-based systems. If the satellites can swing between sky and ground scanning several times in a single orbital period, they could use off-peak hours in the early morning to scan the skies. I don't know if that practically will work out, as Starlink has lower speed of light delays than undersea cables. Accessing content on the other side of the world will become more attractive with lower latency. For instance a lot more people using VPNs to watch BBC.co.uk at 4 am GMT.

Jtsummers 5y ago
More likely, instead of dual purposing the satellites they'll end up finding a customer who is willing to pay for them to send up additional satellites that offer imagery, radio telemetry, or other sensor data. They'll get mixed in with the rest of the fleet, possibly acting as relays between satellites rather than downlink/uplinks themselves. Removing the downlink/uplink components would free up quite a bit of mass that could be dedicated to various sensor platforms, and the comms left would be the inter-satellite system already being used by the fleet. There are lots of potential customers for this (especially if used for terrestrial imagery or similar sensing), and piggybacking on their existing telecom fleet to handle the uplink/downlink side could be a phenomenal bit of cost savings for them. And they get the benefit of improving the inter-satellite network with the additional relays.
- hinkley 5y ago
  If you follow that thread, it might be cheaper still for Starlink to provide bandwidth to actual orbital telescopes.
  - Jtsummers 5y ago
    Yep, I was pondering that during my workout and was going to put in an edit. If Starlink offered inter-satellite comms as a product/service, it could potentially reduce the cost of many satellites both in low orbit or any higher orbit since it would reduce both mass and energy requirements (up/downlink takes a lot of mass and energy). Reducing the weight of systems targeting higher orbits making them cheaper to launch, or allowing them to incorporate more capabilities thanks to the reduced mass. It also reduces the terrestrial-to-satellite comms requirements, you'd connect to your satellite like any other Internet enabled device. Just with higher latency than most and maybe (for a few times a day) lower than optimal latency. Of course, there's a downside. What if Starlink goes bust in 5-10 years? Even 20. Whatever the comms system is, you'd want it to be reprogrammable (at least) if not part of some more open specification that others could connect to. Which suggests the possibility of licensing the technology. That opens Starlink up to competitors, but makes the service more appealing to customers. Which brings it back to probably having the most near-term utility for other LEO satellites since longevity isn't an issue for them in general, but reduces the utility for the next JWT.

ajnin 5y ago

> Potentially capable of resolving exoplanets I was curious about that claim, so I did a bit of research and made a "back of the envelope" calculation. According to Wikipedia [1], the angular resolution of a telescope is proportional to <wavelength of light>/<diameter>. Starlink seems to operate from 10 to 40GHz, so assume the hardware has a 50% design margin so is capable of reaching 60GHz. Visible light has a frequency of 400 to 800THz, so take the middle of 600THz. Using those figures, it come out that the Starlink satellites, used as a telescope, would have the same angular resolution as a 1.3m visible light telescope. Is it enough to resolve exoplanets ? I'm not sure but I think not. Hubble is 6m and can apparently resolve some exoplanets so it's not too far off. Some launches to GEO would boost the resolution to the equivalent of 8.4m in visible. (IANAA) 1: https://en.wikipedia.org/wiki/Angular_resolution https://en.wikipedia.org/wiki/Angular_resolution

Dylan16807 5y ago
Your math makes sense, 60GHz and 600THz are a factor of 10000 apart, etc. But that means you mixed up meters and kilometers when you did your division. 1.3km visible light telescope
gliptic 5y ago
Hubble is 2.4 meter aperture.
jcims 5y ago
This is the one that specifically discusses telescope array (but your formula is still correct) https://en.wikipedia.org/wiki/Angular_resolution#Telescope_array https://en.wikipedia.org/wiki/Angular_resolution#Telescope_a... 60GHz has a wavelength of 5mm. Effective diameter would be ~13000km. Someone check my math but I end up with 5e-3/13e6 radians or ~.0001 arcseconds. Hubble is ~.05 arcseconds.
peter303 5y ago
The Event Horizon Telescope "imaged" two black hole structures down to 10 microarcsecond resolution. The create synthetic apertures from radio telescope pairs separated as much as 8,000 miles and operating up to 450 GigaHertz. (Synthetic telescopes have been created since the 1970s, but used much lower radio frequencies with a much lower computation burden.) Each telescope pair samples a small bit of spatial frequencies. So sophisticated inversions were run to compute the image that best fit these samples.