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Comment by dmitrygr | Hacker News Reader

between this and Elon's stuff, how long till it is impossible to do astronomy or safely launch anything into space?

If you spread 50,000 cars over the surface of the planet, how much of the Earth's surface do you think would be blocked from view by the ISS? Because we have millions of cars scattered all across the Earth and from space, you can't even tell they're there.

>how long

I'd say at least until there are more satellites than cars. In other words, not gonna happen.

This is a poor comparison. The contrast of a cars to the background of Earth is low, ofcourse we can not see any. Remove Earth and let these cars fly on orbits 500km below ISS and, oh boy, would you suddenly see car roofs and windows glinting in the dark everywhere.

Amazing for satellite watchers and annoying for astronomers were e.g. Iridium flares. See [0][1]. Worst case for Iridium flares was them being about 50x as bright as planet Venus. Starlink satellites have the advantage of orbiting far lower which puts them into Earth's shadow on part of their orbits. Around midsummer, though, satellites in an orbit at 550km, like Starlink's lowest shells, will be lit by sunlight as soon as they cross northwards over ~ 45° latitude (their orbits have an inclination of 53°, so they definitely do this). I'm going out on a limb here but they might interfere with infrared observations because of emitted heat (being exposed to bright sunlight every half orbit heats them up).

Parent poster was most likely also referring to the Kessler Syndrome [2] when talking about safety.

[0] https://youtu.be/MTGVuPr9Epg?t=100

[1] https://en.wikipedia.org/wiki/Satellite_flare#Iridium_flares

[2] https://en.wikipedia.org/wiki/Kessler_syndrome

What percentage of the sky do you envision will be occupied by man made objects?

Very small, but that's not a useful measure. For astronomy, remember that bright, fast-moving objects will leave sizable streaks in images that halo a lot[1]. OTOH, intensity varies with time and satellite height. With regards to how much space we have, note that a satellite is taking up an orbit, not a point, and it's a lot harder to fit things in those safely, since they have a tendency to overlap.

[1]: https://nationalastro.org/news/starlink-satellites-imaged-fr...

To put this question into perspective:

The Iridium flare which you saw in video [0] so nicely next to what looked like a full-moon was produced by a flat, reflective surface of less than 2m² area at a distance of over 600km. Percentage does not matter here.

> and let these cars fly on orbits 500km below ISS

I understand the point you are trying to make, but the ISS orbits at an average height of only 400 km.

Most astronomy is done with computers. It should be easy for a computer to ignore or subtract all known satellites. If you only get 900 exposures of some new comet instead of 1000, that's still plenty. And we'd need many orders of magnitude more satellites to make 10% of astronomical photos unusable.

I hear the astronomy argument all the time, but I just don't believe it. If satellites are ever cheap and plentiful enough to make that kind of difference, the astronomers can launch a thousand Hubble-style space telescopes and timeshare on those.

I believe GP was talking about the ever growing space debris.

https://www.esa.int/Safety_Security/Space_Debris/Space_debri...

These satellites should be in low enough orbits that any junk from them burns up in the atmosphere as their orbits decay. Maybe there could be an issue from collisions in low orbit pushing objects into higher orbits but those likely would be erratic orbits with low points that still subject it to decay.

OneWeb's constellation is high enough that it'll take a lot more than 25 years for any satellite that fails to deorbit itself to decay. On the way down, these debris will cross the ISS orbit and the most popular sun-synchronous orbits.

Starlink is lower, but still above the ISS and the SSO at 282km.

All astronomy can’t be done from space. Space has many issues such as maintainability, heat, reflector sizes and the list goes on. I have friends and former colleagues who do astronomy.

I’ll trust the experts who’s profession are actually impacted.

>the astronomers can launch a thousand Hubble-style space telescopes

Who pays? The public pays for telescopes and Elon and other billionaires make more money from the internet satellites and now from putting this new telescopes up , I would be fine if SpaceX and the others would have to pay a tax that will fund astronomical telescopes on Earth and space.

About the astronomy is done with computers, there are problems that you can't jsut solve by throwing a computer at it and if there is a solution it probably costs.

I propose: LEO satellites are not a problem for astronomy.

• Atmosphere distorts observations.

• Astronomers do not like distortion.

• Astronomers like dark backgrounds.

• For a satellite to be illuminated, it must be visible to the sun.

         a 
  - - - - - 
       b/  \
        | E|           SUN
        \  /
  - - - - -

Here is the Earth (E), the Sun, and two satellites in low earth orbit, a and b. The dashed lines are the earth’s shadow.

LEO satellites are really low, like 1/20th of a diameter of the earth. That means that in order to be illuminated in a night sky, they have to be on the dark side of the Earth (left of center here), but not so far that they have dipped into the shadow. “a” is in position for that, but “b” is not. Illuminated, dark side satellites are all in a band around the Earth at the twilight line.

Astronomers don’t like lit skies, so they wait until local dark. Once you get to local dark, the twilight lit satellites are off toward the horizon where you don’t want to observe because there is a huge pile of atmosphere.

If you are making a cool picture of Orion rising out of a desert lake, well, yeah, you may need to edit out some satellites depending on the time of year, but astronomers can do their job just fine.

How long until the most remote and poorest populations in the world can access jobs and the worlds collective knowledge on the internet?

That’s a much better question to ask, mr negative.

Most of these people already have at least 2G cellular coverage.

Ideally with space based telescopes. Hopefully launching things up into orbit becomes dirty cheap and it's not so unreasonable.

These satellites are going to damage real science that is already costing us billions (and what's more perverse, do it for a profit). Professional astronomers already warned us about the issue, and IMHO there's no reason to think we know better. Of course we're launching telescopes into space (like the James Webb, planned for 2021 [1]), but those won't be able to replace science done by the larger terrestrial telescopes.

For reference, the ELT, which is currently being built in Chile, will be 74 meters high, 86 meters wide (with a Ø 39.3 meters primary mirror), and weighing 5,000 tonnes.

[0] https://en.wikipedia.org/wiki/European_Extremely_Large_Teles...

[1] https://en.wikipedia.org/wiki/James_Webb_Space_Telescope

Surely someone who builds an 86 meter wide telescope is able to spend a few bucks on image processing software, that even today's hand held mobile devices could do in real time...

Spreading FUD. Spacex has the most advanced satellite management and deorbiting systems ever made. Fully approved by the fcc.

That accounts for access to space.

Like it or not, there are astronomers pretty pissed off about Starlink & co.

https://twitter.com/superasassn has been pretty open about it, for example. https://twitter.com/89Marvaz/status/1196356715270291456 as well.

Do you have any details about this? As an amateur astronomer I am concerned about increased number of objects in orbit and their eventual fate. How the quality of deorbiting system measured? Have they deorbited any yet and their success rate is higher than others? Also I had no idea FCC approves satellite guidance systems, I thought they mostly supervise radio spectrum.

Every country is supposed to regulate space debris, and in the US, that happens to have been assigned to the FCC. BTW, many people in the industry thinks that the international standard of 25 years needs to be strengthened.

I came across this. Someone tried to put the facts together from original sources. If you read the links report back. I’d be curious what your opinions are.

https://pay.reddit.com/r/spacex/comments/fc9rqq/rspacex_disc...

They are mostly a problem at sunrise and sunset when they catch the sun and reflect it. Astronomy isn't much good then anyway.

How am I getting downvoted? How can satellites reflect the sun when they are in shadow?

And who is pointing their telescope up at sunrise? No one!

Let's put this to rest for once and all. The average radius of Earth is 6,371 km. Initial sats will be at 550 km height (many will be higher, many somewhat lower, but does not make much diff.) So the surface of the 6,931km radius globe is ~603,672,875 km2 (~604 million square kilometers). Don't have exact size for a Starlink sat, but a good upper bound is 3 x 2 m, i.e. 6 m2 = 0.000006 km2. Let's say there will be 40,000 such sats at peak, so altogether they occupy 0.24 km2 area. Altogether, they will occupy 0.00000003976% of the sky. QED.

Looks like you've never done astronomy. A single satellite passing through the shot can saturate the sensor and ruin a multi hour exposure.

The satellite would not be passing through the shot for the entire exposure.

If you had software to detect and delete frames with a satellite moving through them, how many frames from a multi-hour exposure would have to be deleted?

I assume it can even be done digitally in post-production, but even if you had to actually close the aperture ahead of the satellite crossing through your frame, we know exactly where the satellites are going to be so we could calculate when they would enter and exit the frame.

We studied this technique in the graduate-level observation class I took 30 years ago. It is not trivial for a lot of reasons, especially for modern wide-field telescopes with multiple satellites in the field of view at all times.

I appreciate the expert feedback. A lot of very complex things often seem trivial from an outside perspective.

I think everyone can agree this will be at least somewhat a burden on astronomy and will at least marginally increase the cost in obtaining certain imagery.

I guess it’s possible that there are certain types of images which may even become prohibitive or impossible to obtain, but I personally haven’t read a scientific analysis making this claim.

I also think most everyone is agreeing that we attack this problem from both sides. Limit the reflectivity of the satellites and work on enhancing software to mitigate the effects.

In the end there is a tremendous benefit to society both from astronomy as well as having affordable worldwide broadband internet.

I’m not going to go so far to say that we need to sacrifice one for the other, but I think the capabilities and opportunities provided by Starlink to billions of people are too great to pass up. Even if there is a significantly increased cost to perform certain observations. Even if it means some observations can only be made from orbit in the future. Even if some observations become entirely impossible? Hopefully that can be avoided.

You had digital sensors thirty years ago?

Yes. In the case of the system I used in class, it was a CCD intended for a TV camera, hence pretty low resolution. Pre-HD. But this was something appropriate for a one meter telescope, not a big one.

Er . . .

A long exposure isn't the same as frame stacking. It isn't taking a traditional video and stacking the frames. Even if a shot is made out of stacked frames, each frame may be 5+ minutes of exposure, enough time for the chance of it being ruined by a satellite to be very high.

Looks like you have never done computers. It is trivial to substract the well known light effect of the sat.

From a saturated pixel on a CCD?

I once made the mistake of shooting a twilight flat when it wasn't dark enough yet, and it took me 20 minutes to pump all of the electrons out of the CCD.

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