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Comment by tectonic | Hacker News Reader

We've been covering this issue frequently in Orbital Index (https://orbitalindex.com). With around 10,000 stars visible with the naked eye, there will be significantly more satellites than stars, even from a single constellation like Starlink or Project Kuiper. Granted, most of those satellites won't be visible at any given time, but I do worry about the ability of LSST and other wide-field observatories to do their (very expensive & important) jobs—one of those jobs is spotting near Earth asteroids with a collision potential.

Here's a recording of the recent 'Impacts of Satellite Constellations on Optical Astronomy' webinar that discussed this and had someone from SpaceX: https://www.youtube.com/watch?v=LaR6v0p6pB4

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Just wanted to chime in and say I love Orbital Index and read it every week.

I understand this is a bit of a selfish request and entirely a matter of personal preference given my job, but I do wish you guys would talk a little bit more about up and coming companies in the Space industry so I'd know who to keep my eyes on. Not sure if the rest of readership would care but thought I'd throw the idea out there on the off chance others would also be interested.

I don't see any other newsletters / research articles out there that are anywhere near as knowledgeable and I expect more and more people to turn their attention to startups in this space (no pun intended..)

Anyway, thanks again for the incredibly high quality content!

This is super feedback. Glad you like the newsletter. I feel like we often find it hard get a view into when startups hit what they consider important milestones—those seem to get lost in the noise of flying grain silos and such. Some attempt at aggregation of space startup press releases or similar might be place to start… I'll have to give this a bit more thought. -Ben (co-editor of OI)

As a side note, let me say that Orbital Index is a fantastic service. It's the only newsletter that I read every week without fail.

I'm so glad you're enjoying it!

+1, I look forward to it every week

Do the satellites impact more than a single pixel at a time for a brief moment? Can't the normal image stacking and pixel masking resolve this?

Seems like a bigger threat to astronomy is clouds.

Depends on exactly what type of observation you're doing and how big your telescope is. A lot of telescopes use CCD sensors which are more sensitive but have a bad side effect in that once a pixel saturates it starts to bleed into adjacent pixels causing massive horizontally or vertically oriented blooms that white out a bunch of pixels.

What is the latest news on starlink? A friend of mine had a perfect observation chance for the last launch and said he couldn't see a thing, did they "fix" them?

The satellites were only human eye visible because SpaceX let them tumble for a while right after launch. They changed operations and now they're no longer visible to the human eye (generally).

See here: https://www.spacex.com/updates/starlink-update-04-28-2020/

They did two things for two phases of the satellites' lifetimes. In the first phase the satellites are raising their orbits to their final position over a period of a month or two, and SpaceX started rotating the solar panels to reflect less light toward the Earth. But they can still be visible sometimes, until they reach the operational phase when they are in their final, higher orbit.

For the operational phase SpaceX added a sunshade which reflects light away from the Earth. This plus the higher orbit makes the satellites dim enough that they cannot be seen with the naked eye. This sunshade was designed with feedback from astronomers at the often mentioned LSST, which is the single telescope most affected by large satellite constellations. It will prevent artifacts from the imaging sensor's pixels becoming saturated, which is the main concern. The satellites will be visible to the telescope but can be filtered out with standard techniques already in use to filter out the thousands of other satellites already in orbit. See https://www.spacex.com/updates/starlink-update-04-28-2020/

> one of those jobs is spotting near Earth asteroids with a collision potential

What actually happens if they spot an asteroid with collision potential? Is there anything we can do about it?

If it's a week away and massive? Not much.

If it's years or decades away, we could try.

If only there were some way to lift a bunch of cheap kill vehicles into orbit that could be used for both detection and interdiction of incoming rocks with little notice...

(I know, it's not exactly that simple. But still.... ;) )

Any rock you can tackle on little notice is a rock that wouldn't have done much anyways. Anything with the size to have significant impact on Earth is gonna require years of lead time to tackle; you'd need to start changing its orbit well in advance.

No disagreement that less delta-V is needed for big rocks far out in their orbit, so early detection is cheaper.

... but in terms of whether stopping is possible, I believe that depends on the amount of kinetic energy you can apply to it. I'd have to sit down and do some real math to determine the practical stopping power of a kill fleet, but to give a thumbnail comparison: each Starlink sat is about 500 lbs, which is about the weight of one B57 nuclear bomb, with a yield of 5-20kt. There are about 660 Starlinks in orbit now... A constellation of kill vehicles of the same size could have the ability to deliver an upper-bound of 13.2 megatons of explosive energy. According to one source (https://www.space.com/39971-asteroid-destruction-nuclear-bom...), 3 megatons should be sufficient (though the parameters for individual delivery of smaller payloads vs. one big nuke would of course be different).

This is, of course, all a terrible idea; nobody's gonna be comfortable with a mega-constellation of nukes in orbit.

I'm pretty skeptical of this experimental approach scaling up:

> The scientists found that a 500-joule-per-gram laser blast was required to break apart a model space rock 0.3 inches to 0.4 inches in diameter (8 to 10 millimeters), if that blast were directed at a premade cavity in the "asteroid." Without the cavity, the necessary energy was about 650 joules per gram.

Really cheap heavy-lift launch capability would be a big help. Developing that capability is exactly what Starlink is intended to fund.

Let me do that and I will ready it to drop on your head whenever I want and then I'll hold that threat over you constantly.

I mean, I already live under the constant threat of nuclear armageddon from "conventional" ICBMs. So if you're going to suspend kill vehicles over my head that can also save the world from an asteroid... There's gonna be a lot of international politics to work out, but I'm not gonna be the one stopping you. ;)

I've got to be honest. I'm not going to bother with the asteroid part. I'm just going to tell you that what they're for. After all, you can't check.

There's lots of things I can't check. I delegate.

I would assume the "working out the international politics" part includes "a multinational effort among nuclear-armed countries that spot-checks the kill vehicles can actually do the thing claimed to do."

With sufficient time there are plenty of realistic options, ranging from evacuating the impact zone, to nudging it off-course with a "gravitational" space tug (surprisingly feasible), all the way to deflection with nuclear weapons. (Pushing the asteroid enough to nudge it off-course is always a lot easier than blowing it up, Armageddon-style.)

Or build 11,000 city scale engines on one side of the earth!

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