Starlink Thread (split from SpaceX)

[StrandedonEarth]

12 hours ago, tater said:

We'll need more space telescopes

We need FarSide optical and radio telescopes, although that two-week day might be a bummer

[tater]

Just now, StrandedonEarth said:

We need FarSide optical and radio telescopes, although that two-week day might be a bummer

Makes sense for radio, less sense for optical in many ways, particularly when we start landing more on the Moon (dust).

[Guest]

Do note that space telescopes have their own limitations. For one, making them as big as the largest Earth-based ones would require the BFR just to fit the mirror assembly in. Adaptive optics practically eliminate the effects of atmosphere, so the only way of making a space telescope with the same capabilities as recent terrestrial ones would be to use a mirror of the same size. The largest telescope currently under construction will have a 30m mirror, even with a folding mechanism, that's a lot mirror for a rocket to carry.

EDIT: Looks like the 40m one has already started and is actually further along. There was also a 100m diameter telescope under serious consideration. Matching that with a spaceborne telescope would be rather though.

Edited December 5, 2019 by Guest

[kerbiloid]

Astronomers should attach a gigawatt laser to the telescope at the ocular end.

Let the star wars begin!

Edited December 5, 2019 by kerbiloid

[Raven Industries]

14 hours ago, mikegarrison said:

If I had a dime for every time some corporation CEO promised they were working on fixing something that never ended up getting fixed, I would already be retired and driving around in my Ferrari.

Heh, true. I'm a bit more optimistic though. If that does happen, then I'll be happy to lambaste SpaceX with everyone else. 

[mikegarrison]

6 hours ago, tater said:

Makes sense for radio, less sense for optical in many ways, particularly when we start landing more on the Moon (dust).

The moon is not dusty in the way that this implies. With no atmosphere, particles will settle immediately rather than being transported around.

[tater]

57 minutes ago, mikegarrison said:

The moon is not dusty in the way that this implies. With no atmosphere, particles will settle immediately rather than being transported around.

I understand the Moon quite well. The issue is twofold. One, any nearby landings will scour the telescopes, as ejecta from the landing engines is thrown laterally at near engine exhaust velocity (a few km/s). Optics are highly sensitive to this, obviously. Two, given the high velocities and small particulates, they can travel vast distances before settling. So even landings on the other side of the Moon are an issue. They never lose their lateral velocity, they stop via hitting terrain (or the telescope) since it's an airless world. Lunar orbital velocity is ~2.something km/s. Dust could literally never come back in some instances, or be in a VERY low orbit and slam into things on the other side of the Moon. Not a big deal for many structures, but bad for optics.

Surveyor 3 was badly etched on the side facing the LM, for example.

 

EDIT: I'd add that "settling" implies dust that looks like what we see on landings like Starhopper or F9 on Earth. What actually happens is that the particles are blasted out in straight lines close to the lander, and are only bent into their curved trajectories by the low gravity of the Moon. To the extent they settle (what goes up must come down), it's actually slower than on Earth, where the lateral velocity is killed almost immediately by air resistance.

 

Edited December 5, 2019 by tater

[mikegarrison]

Fair enough. I did think about the particles actually getting put into a low orbit, but I didn't think it was all that likely. If evidence says otherwise, then so be it.

[tater]

Just now, mikegarrison said:

Fair enough. I did think about the particles actually getting put into a low orbit, but I didn't think it was all that likely. If evidence says otherwise, then so be it.

Yeah, This was discussed at meetings even back in the 80s and 90s that I went to. A prof of mine was all in for radio astronomy farside, but optical made less sense. No reason not to just put it in space, really. Also, the thermal issues are just as bad on the surface, but different---in space, you have the day/night temp issues across the spacecraft (one side in sun, the other freezing), but at least it's constant. You get the same temp range on the surface, but 14 days at a time. So deeply cold, then incredibly hot. You could use heat pipes and use the surface for some level of thermal management, I suppose, but I think it ends up coming out in the wash, or it might even be better in space. Radio is not as picky, since the wavelengths are so much longer that it takes a lot of expansion/contraction to be a decent % of a wavelength.

[StrandedonEarth]

On 12/4/2019 at 5:39 PM, Jacke said:

StarLink is already wrecking Astronomy.  I fear nothing will be done about it.

https://www.forbes.com/sites/startswithabang/2019/11/20/this-is-how-elon-musk-can-fix-the-damage-his-starlink-satellites-are-causing-to-astronomy/

And since it's in Forbes, this issue also made it onto TV's Global News National edition.

[kerbiloid]

6 hours ago, tater said:

Radio is not as picky, since the wavelengths are so much longer that it takes a lot of expansion/contraction to be a decent % of a wavelength.

And that's a purpose for the Moon. Covering it with countless antennas made of local metals. As the antennas themselves are mostly rather simple parts.

Edited December 6, 2019 by kerbiloid

[magnemoe]

11 hours ago, tater said:

I understand the Moon quite well. The issue is twofold. One, any nearby landings will scour the telescopes, as ejecta from the landing engines is thrown laterally at near engine exhaust velocity (a few km/s). Optics are highly sensitive to this, obviously. Two, given the high velocities and small particulates, they can travel vast distances before settling. So even landings on the other side of the Moon are an issue. They never lose their lateral velocity, they stop via hitting terrain (or the telescope) since it's an airless world. Lunar orbital velocity is ~2.something km/s. Dust could literally never come back in some instances, or be in a VERY low orbit and slam into things on the other side of the Moon. Not a big deal for many structures, but bad for optics.

Surveyor 3 was badly etched on the side facing the LM, for example.

 

EDIT: I'd add that "settling" implies dust that looks like what we see on landings like Starhopper or F9 on Earth. What actually happens is that the particles are blasted out in straight lines close to the lander, and are only bent into their curved trajectories by the low gravity of the Moon. To the extent they settle (what goes up must come down), it's actually slower than on Earth, where the lateral velocity is killed almost immediately by air resistance.

 

I know the particles could go kilometers but did not thought they would go so thousands of km, note that this would be very tiny dust particles, not much an problem for an spaceship, but bad for optic. 
On an base you will have an landing pad and also an barrier to stop this, but this would not work other places, but think risk is pretty low.

Micrometeorites hitting the moon would be an larger source and they can throw larger stuff if hitting at an shallow angle. 
An fun thing in KSP is to crash something on the Mun with very shallow angle and orbital speed, if its something complex it will generate an cloud of derbies on various trajectories. 

[tater]

2 hours ago, magnemoe said:

I know the particles could go kilometers but did not thought they would go so thousands of km, note that this would be very tiny dust particles, not much an problem for an spaceship, but bad for optic. 
On an base you will have an landing pad and also an barrier to stop this, but this would not work other places, but think risk is pretty low.

Yeah, they usually show bases with landing areas inside berms. Some particles bounce off the berm, and head up, away from the base (and with much reduced velocity after the impact).

Near a base, the debris can be quite large (but slower). The guy I quoted the tweet from is probably the leading expert on exhaust plume regolith interactions on Earth. He's the guy NASA is having work with SpaceX on Starship for CLPS on this subject (huge engine impact on the Moon, and how it affects landing operations, since it actually digs deep holes (which then fill in once the thrust stops)).

 

2 hours ago, magnemoe said:

Micrometeorites hitting the moon would be an larger source and they can throw larger stuff if hitting at an shallow angle. 
An fun thing in KSP is to crash something on the Mun with very shallow angle and orbital speed, if its something complex it will generate an cloud of derbies on various trajectories. 

Yeah, even natural pelting could impact optical telescopes. It's possible to mitigate the effect, obviously. Have telescopes with covers that can be stowed after landers operate for some time period, etc. The question is what is gained by putting them on the surface vs space?

[mikegarrison]

4 hours ago, tater said:

The question is what is gained by putting them on the surface vs space?

Do you mean a robotic platform? If so, probably not much is gained. People, however, might like to work in a place where there is an up and a down.

And if there is an issue of blocking all emissions from Earth, the far side of the moon is ideal.

[tater]

3 minutes ago, mikegarrison said:

Do you mean a robotic platform? If so, probably not much is gained. People, however, might like to work in a place where there is an up and a down.

And if there is an issue of blocking all emissions from Earth, the far side of the moon is ideal.

Yeah, if you want or need people. It's not like you need to manually stand in the dome and move it (our motor broke once (dead moths inside) and we had to climb onto roof and push it to move the slit to take data). The telescopes would be robotic regardless. You could have people nearby (maintenance?), but the scope would certainly be out in vacuum. Having people makes the dust situation far worse for two reasons, though. One, you have to have a local landing area (resupply, etc). You can shield the scopes for some period after landing or take off ops, and that's not a huge deal, but also any EVA at all raising a much more mundane dust issue, that matches the more normal "settling" concern. Walk or drive around, tiny dust is thrown around, and gently settles all over. I suppose you could pave the landing site, pave access to the scopes, etc, as well.

Seems like the added infrastructure might mean that space is just easier. If you need human access, have a space station someplace, and send crews as needed (then like ISS, you have to worry about RCS impingement, etc... never ends.

Regarding radio, yeah, farside is awesome for blocking RF.

[tater]

Quote

LOS ANGELES — One of the Starlink satellites in the next batch of 60 that SpaceX plans to launch in late December will be treated with a special coating designed to make the spacecraft less reflective and less likely to interfere with space observations, SpaceX president and chief operating officer Gwynne Shotwell said Dec. 6.

“We are going to get it done,” Shotwell said during a meeting with reporters at SpaceX’s headquarters in Hawthorne.

...

Shotwell said the next batch has one satellite “where we put a coating on the bottom.” She noted that this is just an experiment and could not predict if it will work. “We’re do trial and error to figure out the best way to get this done,” said Shotwell.

...

The experimental coating that would make the satellite less reflective could affect its performance, so that is something that will be examined, said Shotwell. “It definitely changes the performance of the satellite, thermally. It’ll be some trial and error but we’ll fix it.”

 

[tater]

https://aas.org/posts/advocacy/2019/12/aas-works-mitigate-impact-satellite-constellations-ground-based-observing

[tater]

 

[tater]

 

[Brotoro]

I watched the third batch of Starlink satellites pass over tonight at approximately 6:30 PM. This was the group launched a week ago, but this was the first night with a decent visible pass from New Mexico. I used the prediction from the Heavens Above website, and it was pretty accurate, with the satellites going from south-southwest toward the east, passing below Cetus and heading toward Orion. The pass tomorrow should be a bit higher up and easier to see. The ones today  got as high as 42 degrees before disappearing into the Earth's shadow west of Orion.

Using binoculars, I was able to count 38 of the satellites. The first one was spotted around 6:26 PM, and the last one was spotted around 6:37 PM. My wife was able to see four of then naked eye. The brightest ones were maybe 2.0 to 2.5 magnitude.

 

Edited January 14, 2020 by Brotoro

[tater]

I thought celestrak said the pass here (NM) was in the morning. Looks like evening. Better.

Looks like 5:40-ish. I'll post the results from here on the other side of the mtn . I'll have my kids with younger eyes looking as well.

 

[Brotoro]

Heavens Above shows the Tuesday pass at 6:40 PM, MST.

Rising up past the west side of Venus, past the west of the Great Square, and disappearing into Cepheus.

Edited January 14, 2020 by Brotoro

[tater]

7 hours ago, Brotoro said:

Heavens Above shows the Tuesday pass at 6:40 PM, MST.

Rising up past the west side of Venus, past the west of the Great Square, and disappearing into Cepheus.

My celestrak link I had saved had old TLEs I think.

7 hours ago, Brotoro said:

Heavens Above shows the Tuesday pass at 6:40 PM, MST.

Oh, duh, they're using Starlink - 3rd launch placeholder as Starlink 2. I looked at the wrong one.

[sevenperforce]

Funny exchange on my Medium blog:

Reader:

Quote

"Last night I saw a string of 12 unidentified lights passing our house in formation over the Caribbean Sea. My husband who is not at all interested in unidentified flying objects was stunned. They disappeared as fast as they were seen by us. There is no plausible explanation for what they were, where they came from, and how they moved the way they did.

"If we are indeed the observers of a fractal universe, creating material reality through observation, we can assume there are others who may operate differently. How about the idea of mirror universes or brane worlds?"

Me:

Quote

"Those were Starlink satellites launched on January 6 from Cape Canaveral."

Reader:

Quote

"No well after they were launched checked that! No plausible explanation I’m afraid! We asked a lot of people and they were stumped — sitings [sic] occur here fairly often!"

Me:

Quote

"Because they were launched into orbit, they circle the Earth once every 90 minutes. They take a few weeks to spread out from their initial 'train' appearance, so that’s a couple hundred possible observations.

"Depending on exactly where in the Caribbean Sea you are viewing from, I would estimate your sighting took place between 7:28 and 7:32 PM local time, in the western sky. They would have passed very close to Venus and been completely opposite in the sky from the moon.

Spoiler

"Sound about right?"

Reader:

Quote

"Yes much lower down in front of Venus in a train formation and about that time. Definitely in the Western sky. However they seemed to be in low orbit and disappeared without a trace quite fast. You are right though very possibly these satellites if they maintain train format for a few weeks after launch. We are on Bequia a small island in Grenadines part of Saint Vincent and the Grenadines."

I found it really funny. Maybe not everyone does, but.......

[tater]