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How bad are satellite megaconstellations for astronomy?

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Re: How bad are satellite megaconstellations for astronomy?

#101

Post by shadowgovt »

SaberTail wrote: post #85
shadowgovt wrote: post #44

I'm sure it's inconvenient, but it's hard for me to believe that this isn't a solvable problem. Satellites have extremely predictable paths and are very well-tracked by every government with a space program. If you can know a source of noise is there, you can trim the noise out of the signal. Sure, this impacts the fidelity of your signal for the three-dimensional coordinates of image where the noise was present, but…

When counting photons, the noise in your signal scales with the square root of the total count. If the satellite is dumping 100 ± 10 photons in every pixel it passes through, you can no longer distinguish objects so faint that they'd only leave 10 photons in a pixel during your exposure.

But in two dimensions of space and one of time, that's only a momentary occlusion right?

Re: How bad are satellite megaconstellations for astronomy?

#102

Post by nullc »

malfist wrote: post #97
dheera wrote: post #81

Earlier quoted context omitted.

> the photo illustrations used in the article are selected to make things seem worse than they really are Exactly. I do a LOT of astrophotography and satellite trails are actually very easy to get rid of. Even the stupidest, most naive outlier rejection techniques, such as taking a stack of tracked images, finding their mean and standard deviation, throwing out any data points outside of 2 standard deviations, and th…

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.

Re: How bad are satellite megaconstellations for astronomy?

#103

Post by [deleted] »

rickydroll wrote: post #89
_dain_ wrote: post #61

Earlier quoted context omitted.

For one thing, before this decade is out we will have the lift capacity to get an ELT-worth of mass to L2. And the lack of need to correct for atmospheric distortion would simplify the design considerably. But it's beside the point. Such a singular mega-telescope would no longer be the only way to do astronomy in space. A world of radically lower launch costs gives more possibilities. We could have a fleet of thousan…

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…

[deleted]

Re: How bad are satellite megaconstellations for astronomy?

#105

Post by bmitc »

hagbard_c wrote: post #63
bmitc wrote: post #26

Earlier quoted context omitted.

That needs some citations. The James Webb Telescope's mirror is 6.5m in diameter. It took decades and billions of dollars of overruns and a prayer to launch and work correctly. There is no hope of most hardware repairs. That mirror size pails in comparison to what can be accomplished via ground based observatories for much, much cheaper. And the available modes of operation are completely different between space and…

If the promises made for new launch systems like SpaceX' Starship (and maybe even, one day, in some unknown future, Bezos' Blue Origin manages to launch something larger than a phallic pond hopper?) it should become radically less expensive to launch larger telescopes into orbit and/or to e.g. the moon.

That "should" needs a lot of backing up, and I don't understand why we need to singlehandedly rely on the same company creating the issues to apparently solve them with wishful thinking.

Re: How bad are satellite megaconstellations for astronomy?

#106

Post by bmitc »

_dain_ wrote: post #28
bmitc wrote: post #26

Earlier quoted context omitted.

That needs some citations. The James Webb Telescope's mirror is 6.5m in diameter. It took decades and billions of dollars of overruns and a prayer to launch and work correctly. There is no hope of most hardware repairs. That mirror size pails in comparison to what can be accomplished via ground based observatories for much, much cheaper. And the available modes of operation are completely different between space and…

> That needs some citations. The James Webb Telescope's mirror is 6.5m in diameter. It took decades and billions of dollars of overruns and a prayer to launch and work correctly. There is no hope of most hardware repairs. Because it had to get launched folded up, because the launch vehicles were so space- and mass-constrained. The unfolding mechanism was enormously complicated and added to much of the cost. Now we ca…

> future space telescopes will come off an assembly line. There will be thousands in orbit, pointed at every part of the heavens simultaneously.

Like I said: citations.

> Now we can send up bigger, heavier objects for much less money.

This hasn't even been demonstrated.

Re: How bad are satellite megaconstellations for astronomy?

#107

Post by bmitc »

ggreer wrote: post #100
palata wrote: post #74

Earlier quoted context omitted.

> The economics will only become more favorable when SpaceX improves their launch capabilities with Starship. Until we start making them pay for the environmental impact, that is.

What environmental impact? So far there have been 162 Starlink launches. Each launch uses around 200 tons of RP-1, which is equivalent to the fuel capacity of a Boeing 747. In other words: A single 747 burns more fuel in a year than all the Starlink launches in the past five years.

Rocket launches are far more environmentally non-friendly than planes. You can't just look at fuel capacity. It's the composition and where the waste product gets dumped. Rockets dump their waste much higher up in parts of the atmosphere much more sensitive to it. Comparing a rocket and plane isn't an effective comparison in terms of environment impact. So this:

> A single 747 burns more fuel in a year than all the Starlink launches in the past five years.

is not an accurate summary of the environmental impact of rocket launches.

Also, rocket launches are incredibly disruptive to the local ecosystems of the launch sites.

Re: How bad are satellite megaconstellations for astronomy?

#108

Post by bmitc »

FredPret wrote: post #51
bmitc wrote: post #30

Earlier quoted context omitted.

To me, these are capitalistic solutions looking for problems. It's the whole startup mentality. Let's just throw a bunch of shit in space and see if it ends up being useful for anything. This idea of connecting the world is as false as the other hundred millions times that's been sold.

If you paid attention, "this time" and also the "other hundred million times" are true, not false. We're massively more connected than ever before. Homeless people in the third world have phones now. They should be able to get on the internet too.

> We're massively more connected than ever before.

In a certain electronic sense, yes, but emotionally and socially, we are not more connected than ever before. So like I said, this utopian promise of the Internet connecting and liberating and educating us has not happened. In fact, it's the opposite that has happened.

Re: How bad are satellite megaconstellations for astronomy?

#109

Post by bmitc »

ggreer wrote: post #65
bmitc wrote: post #30

Earlier quoted context omitted.

To me, these are capitalistic solutions looking for problems. It's the whole startup mentality. Let's just throw a bunch of shit in space and see if it ends up being useful for anything. This idea of connecting the world is as false as the other hundred millions times that's been sold.

Useful for anything? Starlink useful to its 2.7 million subscribers. And it's already profitable. As of last year, SpaceX makes more in subscription fees than it costs to build and launch the satellites. The economics will only become more favorable when SpaceX improves their launch capabilities with Starship.

I'm not sure how the existence of subscribers and profit negates the point. Their are plenty of things that have those that aren't useful beyond a capitalistic sense.

Re: How bad are satellite megaconstellations for astronomy?

#110

Post by mercutio2 »

petsfed wrote: post #47
mercutio2 wrote: post #20

Earlier quoted context omitted.

Are there really a lot of ground based telescope components larger than Starship's fairing? I'm just not seeing the argument for there being any telescope function that wouldn't be better done in orbit, at Starship payload prices.

I count 13 on wikipedia's list of the largest telescopes. There are 3 more currently under construction. The evocatively named "Extremely Large Telescope" is estimated to cost about $1 billion USD. Who knows how much it will actually cost, but for comparison, that's about $400 million less (adjusted for inflation) than the budgeted cost of the Webb telescope, which is about 1/6 the planned size (and therefore 1/36 th…

But the point is that Webb was vastly over-engineered because we needed to get value out of every ounce of mass at the very high costs of legacy launch providers, and even more compromised because of Ariane 5’s tiny fairing.

You could build Webb for vastly, vastly less money if it launched on Starship, not just per unit of mass; volume is at much less of a premium in the new regime.

You can’t quite fit ELT pre-constructed into a single Starship, it’s true. But it’s built out of segmented mirrors. It doesn’t have to arrive on station in one piece.

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