Impacts of Large Satellite Constellations on Astronomy

[eeergo]

[deleted](Retweeted by Dr McDowell):

https://twitter.com/sundogplanets/status/1398344744925753349

BTW: If you drink a small amount of well-studied poison that makes you ill but doesn't kill you, you don't need to drink the full lethal amount to say "major, visible detrimental effects are already visible", even if they weren't fatal. I won't elaborate on the applicability of this metaphor here.

As for taking an interested party's (actually, the most biased and interested party of all for this topic) not-backed-by-open-analysis sweeping assurance and concluding that "this proves a wide, general concern to be non-existent", is laughable at best, purposefully misleading more realistically.

[Vultur]

Personally, I think a future of massive space industrialization (which I absolutely support) inevitably will lead to artificial objects as a major - even predominant - feature of the night sky; so I'm not sure "more satellites than stars" is automatically a bad thing.

(Actually, personally, it sounds really cool to me!)

[envy887]

Personally, I think a future of massive space industrialization (which I absolutely support) inevitably will lead to artificial objects as a major - even predominant - feature of the night sky; so I'm not sure "more satellites than stars" is automatically a bad thing.

(Actually, personally, it sounds really cool to me!)

The "most people on earth will see more satellites than stars" bit is probably quite untrue. This depends mostly on the visual brightness of the Kuiper and Chinese satellites, but at zenith the OneWeb sats average around 7.5 mag and Starlinks average about 6 mag. In the operating constellation, at most a few dozen will be anywhere near zenith at any time, and the vast majority (~80%?) are below 30 degrees and 1/4th the brightness or less. OneWeb sats are sunlit for much longer, but highly unlikely to be visible to the naked eye at any time.

There are some 4000 stars visible that are brighter than this, and they are not (nearly as affected by elevation. For any given light condition, stars will probably outnumber visible megaconstellation satellites by a factor of ~100. For people in light-polluted areas (which is the vast majority of people), it's quite unlikely that any operational satellites will be visible at all.

[Vultur]

The "most people on earth will see more satellites than stars" bit is probably quite untrue.

For these currently planned constellations, I agree (most people probably live in places where 6th magnitude is not at all visible, for one thing).

I was more talking about this as a "test case". If we end up with massive solar-electric spacecraft with square kilometer solar arrays, or solar power sats, or O'Neill cylinders in the Earth-Moon system  - and I hope we do - those will have a significant impact on how the sky looks.

This isn't a situation like Earth-surface environmental issues where there are all these complex dependencies on the existing situation. Besides the specific astronomical concerns (which in the long run IMO will be solved by relocating major astronomy to space) it's purely aesthetic - which is hard to "objectively" resolve.

[Robotbeat]

Personally, I think a future of massive space industrialization (which I absolutely support) inevitably will lead to artificial objects as a major - even predominant - feature of the night sky; so I'm not sure "more satellites than stars" is automatically a bad thing.

(Actually, personally, it sounds really cool to me!)

Yeah, we're unlikely to ever get to "more satellites than stars", but it strikes me as kind of ridiculous how NIMBYist some people are about this.

Like, we REALLY have to be stuck on one planet simply because our spaceships might be visible? Imagine it's 1000AD or something and you're angry at the Vikings or the Polynesians or the Romans or whatever simply because their merchant vessels are visible at sea and not just a pure expanse of water.

If humanity is going to be multiplanetary and generally spacefaring, we're inevitably going to have visible signs of it in the sky. It's unlikely we'll invent cloaking devices any time soon. And most certainly our spacefaring will be *detectable* by super sensitive telescopes! It's absurd to me that some people actually think that spacefaring should be stopped because it is *detectable*!

[eeergo]

Re: failure rates, constellation size, and impacts on astronomy:

https://twitter.com/cgbassa/status/1400196813290942464

[freddo411]

[deleted](Retweeted by Dr McDowell):

https://twitter.com/sundogplanets/status/1398344744925753349

BTW: If you drink a small amount of well-studied poison that makes you ill but doesn't kill you, you don't need to drink the full lethal amount to say "major, visible detrimental effects are already visible", even if they weren't fatal. I won't elaborate on the applicability of this metaphor here.

As for taking an interested party's (actually, the most biased and interested party of all for this topic) not-backed-by-open-analysis sweeping assurance and concluding that "this proves a wide, general concern to be non-existent", is laughable at best, purposefully misleading more realistically.

Couple of points:

* Low orbit sats are only visible when illuminated by the sun which is during dusk conditions on Earth.   Astronomy is almost never conducted during dusk anyway, for reasons that have nothing to do with satellites.
* Some satellites have been visible since sputnik launched.  Did these make you puke?
* Is it proper to demand that all other human beings avoid doing anything that is visible in 1/2 of the observable universe that you might be looking toward?   

[Lee Jay]

* Low orbit sats are only visible when illuminated by the sun which is during dusk conditions on Earth...

Some of these constellations are not that low - that's one of the points of the plots.

[freddo411]

* Low orbit sats are only visible when illuminated by the sun which is during dusk conditions on Earth...

Some of these constellations are not that low - that's one of the points of the plots.

Yes, satellite altitude is an important factor.    The graphs don't seem to tell me what altitude they used in their assumptions to plot number of sats vs. time of day.

[vanbrua]

* Low orbit sats are only visible when illuminated by the sun which is during dusk conditions on Earth.   Astronomy is almost never conducted during dusk anyway, for reasons that have nothing to do with satellites.

Since this is 50 degrees N at summer solstice, midnight is not far away from dusk and the orbits are bunching up.

[Lee Jay]

* Low orbit sats are only visible when illuminated by the sun which is during dusk conditions on Earth...

Some of these constellations are not that low - that's one of the points of the plots.

Yes, satellite altitude is an important factor.    The graphs don't seem to tell me what altitude they used in their assumptions to plot number of sats vs. time of day.

Just look up the altitudes of the systems stated.

[freddo411]

* Low orbit sats are only visible when illuminated by the sun which is during dusk conditions on Earth...

Some of these constellations are not that low - that's one of the points of the plots.

Yes, satellite altitude is an important factor.    The graphs don't seem to tell me what altitude they used in their assumptions to plot number of sats vs. time of day.

Just look up the altitudes of the systems stated.

Why bunch all those system with wildly different altitudes together?   

Why act as if all those satellites will actually be launched?   Odds are, they will not.

Why not focus on just that sats that exist?   

That would result in a much less scary looking graph.

[whitelancer64]

* Low orbit sats are only visible when illuminated by the sun which is during dusk conditions on Earth...

Some of these constellations are not that low - that's one of the points of the plots.

Yes, satellite altitude is an important factor.    The graphs don't seem to tell me what altitude they used in their assumptions to plot number of sats vs. time of day.

Just look up the altitudes of the systems stated.

Why bunch all those system with wildly different altitudes together?   

Why act as if all those satellites will actually be launched?   Odds are, they will not.

Why not focus on just that sats that exist?   

That would result in a much less scary looking graph.

The point was to project how many sats will be in the night sky in the future, not the current state of things.

[Yggdrasill]

It is definitely a worst-case for the near term. Most likely all these constellations will not coexist over time. And they will also change over time.

The more competitive constellations will drive the less competitive constellations out of business. And I get the impression OneWeb is one of the most visible constellations due to it's operating altitude. It's altitude is also exactly why OneWeb is not likely to stick around. It gives significantly worse latency, as well as worse granularity in where you point the antennas.

I don't know if even the constellations at around 550 km have any long term future. There are significant improvements to be had by replacing them with more satellites at 300-400 km altitude. It wouldn't surprise me if the internet satellites at 400+ km are all deorbited and not replaced in 10-20 years.

What would those graphs look like with say 100,000 satellites spread out at 300-400 km?

[eeergo]

It is definitely a worst-case for the near term. Most likely all these constellations will not coexist over time. And they will also change over time.

They'll most likely coexist, just because of the business model and the disparate regions of influence they'd be serving (or the gap-bridging capability, i.e. until more resilient, long-run-cheaper ground-based solutions, renders them unnecessary). The higher-orbiting constellations will be long-lived even if the model goes bust, and one could argue that even more visible (if the sats are no longer stabilized they'll flare and not keep a low-visibility orientation, while they can take decades to deorbit naturally if a disposal plan is not feasible while the business exists/has money to do something about them).

Yes, time-variability and continuous replenishment/disposal is one of the most relevant, harder-to-model concerns.

[...] I get the impression OneWeb is one of the most visible constellations due to it's operating altitude. It's altitude is also exactly why OneWeb is not likely to stick around. It gives significantly worse latency, as well as worse granularity in where you point the antennas.

Different business model (institutional vs retail). However, that's -generally- correct: the higher, the worse for the orbital and astronomical environment. Being fainter through distance doesn't outweigh longer illumination times, slower angular velocity and orbital debris/persistency after failure/deorbit difficulties.

What would those graphs look like with say 100,000 satellites spread out at 300-400 km?

Things get dicey with drag quickly below 500 km. Not only because of more fuel that you have to carry for cumulative impulse (or, alternatively shorter lifetime), but also because of the larger control authority you need to have (thrust AND electric power), and the quickly worsening impacts of large drag cross-sectional areas. Lowering a few km down from 500 km is not the same even qualitatively than lowering the same amount from 400 km; even less from 350 km.

That said, lower altitudes with serious low-visibility mitigations would be better for visible astronomy on a per-satellite basis. You'd need more satellites to have the same coverage on the ground though, because of shrinking cell size, so the overall constellation might end up being worse. That's difficult to model without input from the designers though, as it depends on the actual tech on the satellites.

[Yggdrasill]

They'll most likely coexist, just because of the business model and the disparate regions of influence they'd be serving (or the gap-bridging capability, i.e. until more resilient, long-run-cheaper ground-based solutions, renders them unnecessary). The higher-orbiting constellations will be long-lived even if the model goes bust, and one could argue that even more visible (if the sats are no longer stabilized they'll flare and not keep a low-visibility orientation, while they can take decades to deorbit naturally if a disposal plan is not feasible while the business exists/has money to do something about them).

They'll coexist, for a while, but as the good constellations get cheaper and better, and the less good constellations stagnate, due to lack of additional demand, there will come a point where everyone involved just say enough is enough and deorbit the constellation. No agency or government will be fine with paying say $100 million/year for an inferior service, if the retail option is $1 million and much better. Not in the long run.

And the constellations that are able to compete and coexist will continually try to improve their services, so they will add more and more satellites in as low orbits as they can, while the satellites in higher orbits eventually are obsolete and can be deorbited with no consequences for the constellation as a whole.

And I actually think the trend you suggest will be opposite. As the satellite constellations become cheaper and cheaper, more and more of the ground based infrastructure will become more expensive to maintain and operate than simply relying on satellites, and the reliance on the satellite constellations will only increase.

This is a bit like how the copper phone lines are rotting away. Replaced by fiber and 4G/5G.

Things get dicey with drag quickly below 500 km. Not only because of more fuel that you have to carry for cumulative impulse (or, alternatively shorter lifetime), but also because of the larger control authority you need to have (thrust AND electric power), and the quickly worsening impacts of large drag cross-sectional areas. Lowering a few km down from 500 km is not the same even qualitatively than lowering the same amount from 400 km; even less from 350 km.

That said, lower altitudes with serious low-visibility mitigations would be better for visible astronomy on a per-satellite basis. You'd need more satellites to have the same coverage on the ground though, because of shrinking cell size, so the overall constellation might end up being worse. That's difficult to model without input from the designers though, as it depends on the actual tech on the satellites.

You need more propellant and power to stay in orbit for many years at 300-400 km, but at the same time the cost of putting mass into orbit is decreasing. Adding 100 kg extra propellant to a satellite becomes fairly trivial if it costs $50/kg to LEO.

When Starship is flying three times a day, it can deliver something like 600 half ton satellites per day into LEO. With a 5 year life per satellite that allows for a continuous presence of 1.1 million satellites. Exactly how many will be placed into orbit remains to be seen, but it really just depends on demand. More demand means more capacity is required so they put more capacity into orbit.

[edzieba]

The higher-orbiting constellations will be long-lived even if the model goes bust

Of the 95 original 'flaring' Iridium constellation:
- 65 have been actively deorbited
- 15 have deorbited after failure
- 11 are still in orbit (failed or unable to actively deorbit)
- 1 destroyed in collision with Kosmos 2251

That's an 88% real-world cleanup rate for an end-of-life constellation.

[eeergo]

The higher-orbiting constellations will be long-lived even if the model goes bust

Of the 95 original 'flaring' Iridium constellation:
- 65 have been actively deorbited
- 15 have deorbited after failure
- 11 are still in orbit (failed or unable to actively deorbit)
- 1 destroyed in collision with Kosmos 2251

That's an 88% real-world cleanup rate for an end-of-life constellation.

*Naturally* long-lived, as is obvious from the context in the rest of the post.

Legacy Iridium is actually quite a peculiar example, on the other hand: it was small by today's standards (95 satellites is not a lot), the company "went bust" BUT crucially was bailed out and kept operating through the hardship with little deleterious effects on the hardware, which was mostly a consequence of its uniqueness and strategic importance (Motorola roots etc), and the new company that took care of the assets was willing and able to perform most of the decommissioning operations at a later time (70%). The satellites also operated at a more benign altitude than the high-flying megaconstellations I referenced - almost half of the altitude than OneWeb, for instance.

It is also a peculiar example in that, as you mention in your last point, it created one of the largest and most dangerous debris clouds out there, close to orbit-denying and generated while the constellation was still operational, along with the first recorded orbital collision between two large objects. In that sense, that's a 100% real-world catastrophic collision probability for an at-the-time-operational LEO constellation.

In any case, ignoring all the bells and whistles that make legacy Iridium such a peculiar example, and just using the numbers you quote, if you extrapolate from the 100-satellite constellation to a single 10000 "underdeveloped" megaconstellation, that's 1100 uncontrollable, highly visible, stranded failures, **and 100 LEO collisions**, expectable from "real-world" rates, just during the operational lifetime of the systems. Precisely why tens of hundreds, or an environment on the order of hundreds of thousands of LEO sats, are such a concern.

[rubicondsrv]

It is also a peculiar example in that, as you mention in your last point, it created one of the largest and most dangerous debris clouds out there, close to orbit-denying

This is rather exaggerated. there was not even one secondary event due to that collision, that is hardly "close to orbit denying"

[zubenelgenubi]

Moderator: Deletions and edits.  Play the ball, not the man.