How satellite ‘megaconstellations’ will photobomb astronomy images • Hacker News Board

Re: How satellite ‘megaconstellations’ will photobomb astronomy images

#181

Post by sobellian » Thu, Aug 27, 2020, 1:56 PM UTC

acqq wrote: post #123

LatteLazy wrote: post #107

Earlier quoted context omitted.

Is that true? What are they missing? I thought Hubble, JWST etc could do basically everything a ground based one could do only better? Excluding radio telescopes which are huge but not effected by satellites anyway.

> Is that true? Absolutely. > What are they missing? Everything. Whatever one can do on Earth which requires big optics and maintenance is many millions times more expensive to do in the orbit. And the many million times higher expenses of all astronomical projects in the world are certainly not going to be covered by the operators of the "cheap and small" satellites. Optics, for the purposes we talk about, just does…

SpaceX has absolutely taken steps to reduce the albedo of Starlink satellites. New satellites have sunshades that drastically reduce their visibility. It's just not as simple as changing the coating, a modification that has huge thermal implications.

Re: How satellite ‘megaconstellations’ will photobomb astronomy images

#182

Post by sreevisakh » Thu, Aug 27, 2020, 1:59 PM UTC

thdrdt wrote: post #26

Could a country (or a continent) in theory remove satellites hanging above their area? What if countries decide to extend the airspace to the aerospace?

There is a very important distinction between airspace and plain space. Violation of a country's airspace is a wilful act (unless of course you're lost). But you will inevitably have to fly over another country if you want to be in orbit. Even geosynchronous slots are limited to the equator (GSO insertion also requires phasing). This doesn't prevent countries from claiming 'aerospace' and destroying invading crafts. However, other countries could do the same and space exploration will be a non-starter for humanity as a whole. This is probably the reason why countries agreed to space treaties allowing overflight - and it will probably remain the same.

Of course, this logic doesn't apply to suborbital flights. Any country with the means will probably just shoot down unauthorized objects on suborbital trajectory into their airspace.

Re: How satellite ‘megaconstellations’ will photobomb astronomy images

#183

Post by liability » Thu, Aug 27, 2020, 2:02 PM UTC

BurningFrog wrote: post #159

simion314 wrote: post #45

Earlier quoted context omitted.

Will those american billionaires pay say for more European satellites to compensate? What if this were Chinese satellites would you have the same opinion? It would be great if this billionaires would also launch scientific satellites payed from their pocket to compensate, then I would change my mind.

SpaceX is lowering satellite launch cost by 90% for anyone, Chinese or otherwise. This should start a golden age of space astronomy, even if Elon doesn't give away some telescope launches as PR.

> SpaceX is lowering satellite launch cost by 90% for anyone, Chinese or otherwise.

Are you sure SpaceX is allowed to do business with China? As I understand it NASA is forbidden by Congress from collaborating with China. Since NASA and SpaceX work together, might that limitation extent to SpaceX as well?

Re: How satellite ‘megaconstellations’ will photobomb astronomy images

#184

Post by dylan604 » Thu, Aug 27, 2020, 2:12 PM UTC

51Cards wrote: post #114

verytrivial wrote: post #15

The article covers the mitigations already in place and how they only partially resolve the issue. These satellites are low, bright (at dawn/dusk) and very soon to be incredibly numerous. Yes, it is possible for data workflows to post-process these streaks away, but not all configurations allow this, and whereas previous intrusions were somewhat rare and could be ignored that simply won't be the case due to three com…

As I noted on a similar thread the issue is not removing the streaks, it's what data is lost behind those. If you take a look at this image you'll see that it can be a non-trivial amount of interference in some cases and that data can't just be filled in with "black". https://i.imgur.com/Qdt0N2g.png The interference also causes a "glow" effect on the CCD which corrupts the data well beyond the edges of the main strea…

I love all of the comments about using software to filter out the images. This response is so obvious that it is from someone who has never worked with data from imaging the sky, and probably have never thought about it more than a drive-by comment. "Just filter it out" they say. And replace it with what? An average of near by pixels? An AI background replacement? That's just bollocks. Every single dot in the sky is another star, galaxy, planet, asteroid, etc. They are not blemishes in the image. To just write them off would be like drawing a map of the earth without New Zealand on it.

Re: How satellite ‘megaconstellations’ will photobomb astronomy images

#185

Post by Waterluvian » Thu, Aug 27, 2020, 2:17 PM UTC

I'm not expressing a pro or con opinion here, but I'm curious. Did this same conversation happen when we started light polluting the city? Was this why observatories adapted by moving to darker locations?

On the surface this seems a wee bit absurd, but I wonder if a case could be made that it's time for more space-based telescopes.

Re: How satellite ‘megaconstellations’ will photobomb astronomy images

#186

Post by 0-_-0 » Thu, Aug 27, 2020, 2:17 PM UTC

welterde wrote: post #165

0-_-0 wrote: post #163

Earlier quoted context omitted.

(can't reply below) If you had a localised shutter covering pattern X for 6 seconds, could you compensate for that by covering the inverse pattern of X for 6 seconds to get the same exposure for all pixels? So if you covered 3 satellite streaks of 6 seconds each using non-verlapping patterns (A,B,C) you could compensate for that by ending your exposure with covering the inverse of A+B+C for 6 seconds, adding only 6 s…

If the conditions are quite stable that might work (or if one can live with limited accuracy), but conditions tend to change over time (moon position, thin clouds and of course the seeing - how much the atmosphere distorts the image) so nothing is as straightforward as one might hope for. In space that approach would work quite well indeed, but then you wouldn't need it in the first place.. Edit: Even if one still ha…

How much does the bloom extend in the image fom the streak? Can you measure it in arcminutes or is it optics dependent? Is the bloom present if you cover up the satellite exactly? (Is it caused by the sensor, or would diffraction around a shutter cause it as well?)

I think you could mitigate the problems with conditions changing if (instead of blocking out the streak in the image with some per-area shutter) you tracked the satellite in the image with a horizontal (or vertical) shutter stripe which has the right width to cover the entire satellite. This would make the data lost really minor, and changing conditions wouldn't be a problem, and the exposure would be even. Does that make sense?

Re: How satellite ‘megaconstellations’ will photobomb astronomy images

#187

Post by dylan604 » Thu, Aug 27, 2020, 2:18 PM UTC

0-_-0 wrote: post #117

51Cards wrote: post #114

Earlier quoted context omitted.

As I noted on a similar thread the issue is not removing the streaks, it's what data is lost behind those. If you take a look at this image you'll see that it can be a non-trivial amount of interference in some cases and that data can't just be filled in with "black". https://i.imgur.com/Qdt0N2g.png The interference also causes a "glow" effect on the CCD which corrupts the data well beyond the edges of the main strea…

It seems to be around 1-2%, which I would say is trivial. This can be further reduced if you use multiple exposures because then only 1 contains the streak. Getting satellite data from SpaceX about satellite positions and turning off the receiver for a few seconds would also mitigate the issue. I don't understand how this is treated as a problem that's worth halting satellite launches over.

1-2% of the size of the entire Universe is trivial to you?

Re: How satellite ‘megaconstellations’ will photobomb astronomy images

#188

Post by purple-again » Thu, Aug 27, 2020, 2:21 PM UTC

liability wrote: post #183

BurningFrog wrote: post #159

Earlier quoted context omitted.

SpaceX is lowering satellite launch cost by 90% for anyone, Chinese or otherwise. This should start a golden age of space astronomy, even if Elon doesn't give away some telescope launches as PR.

> SpaceX is lowering satellite launch cost by 90% for anyone, Chinese or otherwise. Are you sure SpaceX is allowed to do business with China? As I understand it NASA is forbidden by Congress from collaborating with China. Since NASA and SpaceX work together, might that limitation extent to SpaceX as well?

Spacex is subject to the same OFAC sanctions as every other US business. They are free to do business with most of China, however there are a number of exceptions usually having to do with the company participating in construction in the South China Sea.

Doesn’t mean new sanctions can’t be levied and certainty China seems a likely target for future increased sanctions.

Re: How satellite ‘megaconstellations’ will photobomb astronomy images

#189

Post by jeroenhd » Thu, Aug 27, 2020, 2:24 PM UTC

aga98mtl wrote: post #161

jeroenhd wrote: post #112

Earlier quoted context omitted.

> I personally believe that pervasive high speed internet even in remote locations will do more for humanity than the scientific cost of these satellites. Perhaps in the US, but other countries, even poor ones, manage to do rural internet fine without cluttering the night sky. I, for one, am not stoked about the implications of an American ISP forcing worldwide coverage for themselves. Their shady business practices…

>Perhaps in the US, but other countries, even poor ones, manage to do rural internet fine without cluttering the night sky. Most of sub-saharan Africa has slow and expensive internet. I would guess there is 1 billion people who will have access to the internet via mobile tower with starlink & competitors backhaul in a few years. This is enormous.

The same countries also have nationalized internet service providers, often run by friends or family of the government. I doubt it'd be legal to sell StarLink receivers in large parts of the continent.

There's nothing in the landscape that prevents Africa from running fiber to every house like Eastern Europe has been proven to be capable of. In fact, a lot of infrastructure is already there. Geopolitical instability, poverty and instability of the power grid makes it very unattractive to build data centers in the continent and that's what's forcing ISPs to use expensive cables to access most websites, driving up the cost and reducing the speed.

This problem can be partially mitigated by using StarLink instead of oceanic cables, but I don't imagine their system will be able to replace the fiber optics that carry most large volumes of data between governments. StarLink is fast, but still depends on ground stations for decent speed internet access. Collecting internet traffic for one entire continent on another isn't feasible in the plans I've seen.

StarLink will reduce latency and improve coverage for customers already using satellite internet connections. African people can already use those if they have the means to afford it, yet many African cities have dial-up or slower internet access because of the lack of resources.

Re: How satellite ‘megaconstellations’ will photobomb astronomy images

#190

Post by sreevisakh » Thu, Aug 27, 2020, 2:27 PM UTC

scoot wrote: post #16

I can periodically see with the naked eye what appear to be "moving stars" (about the same approximate brightness as an average star), and appearing to orbit the earth (moving in a "straight" line across the sky). Can I assume that these are satellites?

What you describe does sound like a satellite - but it could also be a rocket body. If it moves slowly enough and lasts long enough to for you to show it to another person, it probably is a satellite or rocket body. As mentioned, it also travels straight and shows up close to dawn and dusk. You can get predictions for sighting in your area from Heavens Above (https://www.heavens-above.com/).

It gets more interesting though. Most satellites have brightness that changes slowly as moves - due to change in illumination. But occasionally, you would find ones which dim and brighten in cycles. This indicates that the object has no attitude control and is tumbling in space. That could be a dead satellite or a rocket body. Rocket bodies are spent rocket stages which loiter in space for a while after completing its mission. Then there are flares. Some satellites (like the old Iridium constellation) occasionally reflect sunlight right at you (unlike diffuse reflections in normal sats). This is a very local event. Some flares can get brighter than any planet or stars.

It's also possible to identify what you are seeing. That used to be my hobby. You would record the time it appears, how high it gets, the direction in which it flies, how bright it gets and when it disappears. With experience, you can get a good enough estimate of the brightness (magnitude) and angles even without instruments. You would then compare it against satellite predictions like Heavens Above to identify the exact object. The one I was thrilled about was a Russian satellite powered by a nuclear reactor (a fission reactor, not a decay battery like RTG). Some of them are still in LEO (https://en.wikipedia.org/wiki/List_of_nuclear_power_systems_...).