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How bad are satellite megaconstellations for astronomy?

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Re: How bad are satellite megaconstellations for astronomy?

#161

Post by malfist »

DiogenesKynikos wrote: post #157
StellarScience wrote: post #121

Earlier quoted context omitted.

Thanks for providing all those links. Indeed, the key there is peak magnitude. BlueWalker 3 has a giant array that reflects light like a mirror. So when you happen to get the angle of incidence exactly equal to the angle of reflection, it shines quite brightly. Of course since it's reflecting all sunlight in one direction, that means from all other spots on earth it will be extremely dim. Also note that BlueWalker 3,…

> So one solution is to schedule astronomy for the middle of the night, when none of these low earth satellites will lit by the sun at all. Let me translate that a bit: "So one solution is to just eliminate 20% of all available observing time."

Not really. Astronomical dusk and dawn are different than civil dusk or dawn, you'd normally skip an hour or so after sunset and before sunrise anyway.

Re: How bad are satellite megaconstellations for astronomy?

#162

Post by malfist »

nullc wrote: post #102
malfist wrote: post #97

Earlier quoted context omitted.

Seriously, any time you have >3 images to stack satellites and planes are a complete non issue. The median pixel value is always going to exclude those. Five images is enough to eliminate any trails even if they overlap between images.

You're not imaging with cryogenic CCDs --- satellite trail can blow out whole rows.

No, I'm not, I'm using cooled CMOS sensors. CCD is ancient tech these days.

Re: How bad are satellite megaconstellations for astronomy?

#163

Post by inemesitaffia »

Turing_Machine wrote: post #79
shadowgovt wrote: post #54

Earlier quoted context omitted.

In many cases, the issue isn't cost to run but cost to maintain. Consider South Africa, where the largest threat to installation deployment is inability to police the entire deployment coupled with massive wealth inequality... People just dig the cables out of the ground for the copper. Cellular radio has ameliorated the issue some (harder to steal the repeater antenna out of the back yard of a shotgun-owning residen…

That specific problem should go away as more lines get replaced with fiber, which has minimal scrap value compared to copper.

No one can tell before they cut if they are outsiders

Re: How bad are satellite megaconstellations for astronomy?

#164

Post by schiffern »

labcomputer wrote: post #141
schiffern wrote: post #117

Earlier quoted context omitted.

>so just grab 5% more images. You say it like major observatory telescopes are sitting idle, but they're not. In practice what actually happens is you lose 5% of your scientific data return. >terrestrial light pollution Problem is that it's global vs local, so our normal solution for terrestrial light pollution (build telescopes in a remotely populated area) doesn't work.

So just write all grant proposals with an extra 5% slop.

Budgets are fixed, so again this also boils down to "just do 5% less science."

Believe it or not, actually using 100% capacity on the big expensive telescope you paid for isn't some brilliant unheard-of suggestion like people seem to think. This Dunning-Kruger idea always seems to crop up whenever this particular topic is in the news.

There simply isn't any "slop in the system" that lets you get that 5% (and climbing!) back "for free." If there was, then that inefficiency should be fixed regardless of the situation with megaconstellations.

Re: How bad are satellite megaconstellations for astronomy?

#165

Post by sapiogram »

TeMPOraL wrote: post #160
sapiogram wrote: post #95

Earlier quoted context omitted.

The largest filled-aperture radio telescope in the world has a 500-meter diameter, and reportedly only cost $180 million. For comparison, the International Space Station costs $3 billion per year just to operate. Doing stuff in space is expensive .

Right, but the whole reason people are so excited about SpaceX is because they're making the costs of doing stuff in space drop like a stone .

For large (>10m) telescopes, it doesn't matter much, because no one is building rockets with big enough fairings. Even if the cost of launching to LEO was $0, in-orbit unfolding/assembly is a bottomless hole of engineering complexity that you cannot avoid. Again, see JWST/ISS.

Re: How bad are satellite megaconstellations for astronomy?

#166

Post by rickydroll »

labcomputer wrote: post #146
rickydroll wrote: post #89

Earlier quoted context omitted.

It doesn't simplify the design; it increases its complexity. All the problems of telescopes on Earth become significantly more problematic in space: temperature, flexure, warping, backlash, pointing models, optical alignment, and collimation are some of the issues. Electronics, sensors, and consumables fail or run out, which means you need to be able to get there to fix things. Then, as research projects change, you…

> Electronics, sensors, and consumables fail or run out, which means you need to be able to get there to fix things. Then, as research projects change, you need to change instruments. So launch another. Launch capacity is getting cheap... let's use it. Consider that 1% of SpaceX's annual launch capacity is enough to put one Hubble in orbit every year. Instead of sending astronauts to fix the fucked-up mirror, you jus…

I agree launch capacity is getting cheaper, but the cost of making a telescope is not. For example. https://optcorp.com/products/planewave-1-meter-observatory-t...

This scope is not built for space travel. This model for space telescopes from NASA put a price tag on all the major components for building and operating a single space telescope is counted in billions. https://ntrs.nasa.gov/api/citations/20110015780/downloads/20...

A couple of things not covered in other comments are the costs of mission control and end-of-life deorbiting. It is far cheaper to rent a car, drive to an observatory, mount your evolving experiment on scope, and debug it on-site than to put the same experiment in orbit. Terrestrial telescope mission control is ad hoc and usually in a heated/air-conditioned shack on the mountaintop.

Re: How bad are satellite megaconstellations for astronomy?

#167

Post by agos »

labcomputer wrote: post #141
schiffern wrote: post #117

Earlier quoted context omitted.

>so just grab 5% more images. You say it like major observatory telescopes are sitting idle, but they're not. In practice what actually happens is you lose 5% of your scientific data return. >terrestrial light pollution Problem is that it's global vs local, so our normal solution for terrestrial light pollution (build telescopes in a remotely populated area) doesn't work.

So just write all grant proposals with an extra 5% slop.

if there were extra 5% budget they already would be using it

Re: How bad are satellite megaconstellations for astronomy?

#168

Post by agos »

rblatz wrote: post #116
nullc wrote: post #102

Earlier quoted context omitted.

You're not imaging with cryogenic CCDs --- satellite trail can blow out whole rows.

Just do it in space and avoid the whole atmosphere and ground based light pollution. Space is cheaper than ever now, this is a problem for amateur astronomers, and hobbyists shouldn’t hold back progress.

"just do it in space" has got to be one of the best hacker news solution to other profession's issue I've ever read.

Re: How bad are satellite megaconstellations for astronomy?

#169

Post by djao »

labcomputer wrote: post #140
whoopdedo wrote: post #134

Earlier quoted context omitted.

> these days some of the best astronomy is performed by telescopes in space, so astronomy overall benefits by having easier access to space. Public access satellites. The FCC requires broadcast licensees to demonstrate that they're acting "in the public interest". Should private rocket launches have to give a minimum amount of their payload to research and non-profit purposes?

Sure, why not? A Hubble-sized telescope is only about 12 tons, which is only about 70% the mass of what a Falcon 9 can deliver to low earth orbit, and SpaceX does that 100x per year (it's only May and they've launched 47 so far this year). For reference, Spitzer is 1 ton and Chandra is 6 tons. The elephant in the room is that launching one Hubble per year to a Hubble-like orbit only uses about 1% of SpaceX's current…

Space telescopes cost billions of dollars not because of launch costs but because of all the dedicated engineering required to fit the telescope into the size and weight restrictions required for launch. In the past we've always been willing to go to extreme lengths to meet launch requirements (hand-made parts with exotic materials, folding mirrors with intricate deployment procedures, etc.).

If we instead design something to be mass-produced at a cost more commensurate with that of a Falcon 9 launch, then it may well be much better than Hubble in terms of bang for the buck, but it won't be as capable as Hubble in absolute terms. Even so, although Falcon 9 is very cost effective per unit weight compared to past rockets, it does not have a large payload volume compared to launch vehicles used for previous large space telescopes, and volume is usually what you need for space telescopes (because big mirrors are constrained by volume, not weight).

Once Starship becomes fully operational it will completely transform the landscape because it is not only low cost but the interior payload bay volume is much larger than existing rockets in all dimensions.

Re: How bad are satellite megaconstellations for astronomy?

#170

Post by djao »

schiffern wrote: post #117
hedora wrote: post #114

Earlier quoted context omitted.

Even if they don’t know where the satellites will be, a simple motion detection algorithm in the stacker would delete the streak caused by the satellite. A given pixel will only be impacted for a few exposures, so just grab 5% more images. I’d guess terrestrial light pollution is a much bigger problem.

>so just grab 5% more images. You say it like major observatory telescopes are sitting idle, but they're not. In practice what actually happens is you lose 5% of your scientific data return. >terrestrial light pollution Problem is that it's global vs local, so our normal solution for terrestrial light pollution (build telescopes in a remotely populated area) doesn't work.

If it's just a matter of 5% inefficiency, I have to think that there must exist some possible mechanism for capturing the economic benefits of satellite internet (with a tax, perhaps) and redirecting a portion to astronomy to increase budgets there by 5% (or more) so that everybody wins.
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