[NA]Starlink tracking and general sat info[NA]

[Let'sgoflying!]

So there was plenty of talk recently in the local area about the string of beads in the night sky which was an array of SL satellites. (photos looked impressive)
I found a tracker app, and this website tells me to expect to see a bunch of them Oct9.
Wiki says there are 2300 up there. Below the link is an image for my location, well it shows all the SL sats. I was mildly shocked about the sheer number of these objects (I realize they are depicted many times larger than real life, but still that is a ton of hardware up there.)

Any simplified explanation of why they have chosen the orbits they have, why they *sometimes* appear in lines, why there are so many over the (uninhabited) poles (I realize they are not geosynchronous), how they avoid collisions (do they all share the same altitude?), are astronomers affected by them during their scientific work, what about rocket launches; are their routes easy to avoid, what is the effect of the effete satellites- do they head to the nearest playground or burn up completely?

https://www.heavens-above.com/StarLink.aspx

 

[Brad W]

wow, nice visual.. thanks for posting
I've been wondering the same questions.
It's very cool....but also very disturbing...and maybe even a little creepy.

 

[DaleB]

I, for one, welcome our new orbiting overlords.

 

[Cap'n Jack]

Astronomers are sometimes affected by them. Current models are made to reduce reflections from them. Amateurs often see trails across their images

The rest of your questions...I'm not qualified to answer other than guesses.

 

[eman1200]

starlink came thru here 2 nights this past week. I missed them the first time but went chasing them the second night, but also used that opportunity to get night current. it ended up being cloudy so I couldn't see any stars at all, forget about starlink, but got night current, so there's that. was a lil ****ed but still went flying around for fun so whadyagonnado. this was me wandering around chasing orbiting satellites.

 

[wanttaja]

So there was plenty of talk recently in the local area about the string of beads in the night sky which was an array of SL satellites. (photos looked impressive)
I found a tracker app, and this website tells me to expect to see a bunch of them Oct9.
Wiki says there are 2300 up there. Below the link is an image for my location, well it shows all the SL sats. I was mildly shocked about the sheer number of these objects (I realize they are depicted many times larger than real life, but still that is a ton of hardware up there.)

Any simplified explanation of why they have chosen the orbits they have, why they *sometimes* appear in lines, why there are so many over the (uninhabited) poles (I realize they are not geosynchronous), how they avoid collisions (do they all share the same altitude?), are astronomers affected by them during their scientific work, what about rocket launches; are their routes easy to avoid, what is the effect of the effete satellites- do they head to the nearest playground or burn up completely?
View attachment 110874

Not that familiar with the system, but:

They sometimes appear in lines, because about 46 satellites are inserted into orbit by a single booster. Once released, each satellite uses its thruster to achieve its targeted position. The line stretches out over time as the satellites achieve their spots. Think of a single launch forming a large ring...the individual satellites adjust their orbit to make them equally spaced out around the ring. The thrusters they use are hall-effect (e.g., very low thrust, long operating time) so it takes a while to get everything in its final position.

The maximum latitude/longitude achieved by a given satellite depends on its launch azimuth. If the launch vehicle goes directly north or south, the satellites can go into a polar orbit (orbit plane 90 degrees offset from the equatorial plane) and the satellites go directly over the poles. Crank on a littttlllle bit more inclination (~98 degrees, depending on altitude) and you end up in a sun-synchronous orbit, which puts you over the Earth with the same solar angle each orbit. Lovely for taking pictures.

Whether the launch vehicle can be launched into the 90 degree/98 degree orbit depends on what is downrange of the launch site. Launch south from Vandenberg SFB or south from Kodiak, and you can get that pilot orbit. However, launching from the east coast is far more constrained. Don't want to drop your boosters on anybody.

This is a very, VERY old diagram showing the problem. Note that the Western Test range can launch due south.

Notice how badly ETR (e.g., Cape Canaveral) is constrained for launch azimuths.

"Why not launch into a ~60 degree orbit from ETR and just curve the orbit?" Because that uses a prohibitive amount of fuel. You're flying at ~24,000 FPS, calculate how much delta-v is required for a 30-degree inclination change. About 12,000 fps, and that's about half of what it took just to get you into orbit.

As far as "why not in Geo"...well, there's a lot going on, there. First off, you're looking at a distance from the user to the satellite of about 24,000 miles... vs. ~700 or so. Obviously can get buy with a lot smaller comm system. Neither the user or the satellite will have to point big unwieldy dishes and actively track the other component.

Available orbit slots in Geo are tight...you have to have one assigned to you, and the frequencies you're allowed to operate on will set how big your "slot" will have to be.

Putting satellites in Geo is expensive (big launch vehicle) and since getting a slot is difficult, the press is on to launch the most reliable, longest-landing satellite you can afford. Compared to the Starlink model, which features cheap satellites, cheap launches, and (especially) cheap replacements.

Ron Wanttaja

 

[Let'sgoflying!]

When I open the SL tracking app now, it says that the company has reduced the sat brightness to help astronomers.
(thus crippling any utility of the app; a fair tradeoff imo)
I’m presuming it’s not just a matter of adjusting the nav lights down a smidge.
Isnt the brightness from sunlight reflection? If so, what does it take to keep rotating all these satellites?

Recently I read that they can change their location or orbit.
In view of how small they are, I’m surprised they have an engine (with fuel) large enough to do this .
Is the Hall Effect device which Ron mentioned the one?

 

[Capt. Geoffrey Thorpe]

 

[wanttaja]

When I open the SL tracking app now, it says that the company has reduced the sat brightness to help astronomers.
(thus crippling any utility of the app; a fair tradeoff imo)
I’m presuming it’s not just a matter of adjusting the nav lights down a smidge.
Isnt the brightness from sunlight reflection? If so, what does it take to keep rotating all these satellites?

It's pretty easy to compute where your solar arrays will reflect the sun. Just adjust your attitude to minimize the reflection onto populated surfaces on the Earth. You might lose a bit of total solar array power, but normally one has pretty good margins.

The Iridium satellites are the opposite of this; they reposition and put a huge flash or flare onto the surface. If you've been looking up into the sky at night and see a real bright spot lasting several seconds....you probably saw an Iridium flare.

http://www.satobs.org/iridium.html

Third parties even publish the data so you can predict them.

Recently I read that they can change their location or orbit.
In view of how small they are, I’m surprised they have an engine (with fuel) large enough to do this .
Is the Hall Effect device which Ron mentioned the one?

Hall effect thrusters are hugely efficient. You can drive a satellite around with them.

It just takes a while.

A nominal conventional thruster has, say, 50 pounds of thrust, with a Specific Impulse (ISP) of, say, 200. ISP tells you how much fuel you burn for a given change in velocity. So, for instance, you can adjust the orbit the way you like with a ~100-second burn, that'll use propellant in the hundreds of pounds.

A Hall effect thruster has an ISP closer to 5,000! It will make the same change in velocity using a trivial amount of fuel...a few pounds.

The trouble is, the Hall thruster might have about 0.001 pounds of thrust. It'll take hours, even days or weeks to achieve the same change in velocity.

*If* you don't mind waiting, a Hall Effect thruster is a good solution.

(Note that the values above are just approximate strawman estimates...I didn't actual run the numbers).

Even so, a very small spacecraft may not carry enough propellant for a major orbit change, even with a hall effect engine.

Ron Wanttaja

 

[donjohnston]

The ones you see in a line all bunched up are from recent launches. It takes time for them to spread out.

Here's the most recent launch:




And one from 18 months ago.