Author Topic: Starlink satellites (Read 3757 times)

αdαmsκι · « **Reply #25 on:** 22 April, 2020, 09:08:54 am »

Last night I was outside for 15 or 20 minutes watching them march across the London sky. It was quite humbling and mesmerizing. Tonight there are more being launched from Cape Canaveral. They'll be a live stream online and then ~20 minutes later they'll be hurtling across our skies. https://twitter.com/VirtualAstro/status/1252720313005158403

I also tried to look for meteorites later on but failed.

Jaded · « **Reply #26 on:** 22 April, 2020, 09:15:28 am »

Is this the end of clear night skies? If so it is ironic that it is occurring at at time of unprecedented clear skies because of a reduction in pollution.

Jurek · « **Reply #27 on:** 22 April, 2020, 11:02:18 am »

It's all kicking off tonight with the first one passing over my house at 20:52.
Looking down the chart on Heavens Above, it next comes over at 22:31.
So that's one orbit of the planet in just under 40 minutes.
Can anyone with more maths in their head than me, work out the speed it's travelling at?

FWIW there was a good view of them here in SE London last night.

Greenbank · « **Reply #28 on:** 22 April, 2020, 11:28:52 am »

Starlink satellites orbit at 550km.

Earth has a radius of 6370km (it varies by latitude but this is good enough).

So the circumference of a circle that has radius 550+6370 km is 2 * pi * r = 2 * pi * 6920 =~ 43500 km

43500 km in 40 minutes =~ 62250km/hr or 18125m/sec

Jurek · « **Reply #29 on:** 22 April, 2020, 11:34:22 am »

Thank you.

andyoxon · « **Reply #30 on:** 22 April, 2020, 12:29:39 pm »

Infographic of the Falcon9 launch... https://twitter.com/GeoffdBarrett/status/1252803563798986759/photo/1

Launch apparently @20:37 BST

Quote

If all goes according to plan, the Falcon 9’s second stage will shut down its engine nearly nine minutes after liftoff, injecting the Starlink satellites into a preliminary elliptical orbit ranging more than 200 miles (300 kilometers) above Earth.

The 60 Starlink spacecraft will deploy from the Falcon 9 upper stage all at once over the North Atlantic Ocean around 14 minutes into the mission.

Each of the quarter-ton Starlink satellites is expected to unfurl a solar array wing and activate a krypton ion propulsion drive to begin climbing to an operational orbit 341 miles (550 kilometers) in altitude, where they will join hundreds other Starlink nodes launched since last May.

https://spaceflightnow.com/2020/04/21/spacex-modifies-starlink-network-design-as-another-60-satellites-gear-up-for-launch/

quixoticgeek · « **Reply #31 on:** 22 April, 2020, 02:27:36 pm »

Quote from: Basil on 21 April, 2020, 10:43:20 pm

OK, I don't get this. I can go out on any clear night and within a few minutes I'll see a satellite moving in the skys. How is this any different? Shan't bother going out again.

Eventual aim is for something in the order of 4,425-11,943 from space X. Then a further 800-1500 from Oneweb, and another 1300-2600 from boeing.

To put that in perspective, the total amount of satellites launched to date is about 4000. We're not talking about being able to wait a few minutes to see one, we're talking about them going over every few seconds. For many it will be more satellites in the sky than stars. It's going to really bugger up ground based astronomy, you can kiss goodbye to nice astrophotography shots. We are literally talking about destruction of the night sky.

Why? Because it will speed up the transmission speed for financial transactions. Getting a signal across the Atlantic a few milliseconds faster, is what this is about.

J

jiberjaber · « **Reply #32 on:** 22 April, 2020, 02:43:33 pm »

Quote from: quixoticgeek on 22 April, 2020, 02:27:36 pm

Quote from: Basil on 21 April, 2020, 10:43:20 pm
OK, I don't get this. I can go out on any clear night and within a few minutes I'll see a satellite moving in the skys. How is this any different? Shan't bother going out again.

Eventual aim is for something in the order of 4,425-11,943 from space X. Then a further 800-1500 from Oneweb, and another 1300-2600 from boeing.

To put that in perspective, the total amount of satellites launched to date is about 4000. We're not talking about being able to wait a few minutes to see one, we're talking about them going over every few seconds. For many it will be more satellites in the sky than stars. It's going to really bugger up ground based astronomy, you can kiss goodbye to nice astrophotography shots. We are literally talking about destruction of the night sky.

Why? Because it will speed up the transmission speed for financial transactions. Getting a signal across the Atlantic a few milliseconds faster, is what this is about.

J

Exactly this - esp now I have just resurected my astro gear!

Pedal Castro · « **Reply #33 on:** 22 April, 2020, 03:04:58 pm »

Quote from: Jurek on 22 April, 2020, 11:02:18 am

It's all kicking off tonight with the first one passing over my house at 20:52.
Looking down the chart on Heavens Above, it next comes over at 22:31.
So that's one orbit of the planet in just under 40 minutes.
Can anyone with more maths in their head than me, work out the speed it's travelling at?

FWIW there was a good view of them here in SE London last night.

Generally satellites are either geostationary (stay over a fixed point) for communication purposes and orbit every 24h for which they have to be quite high, or spy/survey/weather satellites which normally are polar orbiting (i. e. North to South) and for greatest detail need to be as low as possible and orbit in 90'. I can't remember off the top of my head why that was the lowest technically achievable from when I last taught this stuff but I suspect that the SpaceX ones will end up with a similar orbit period.

Edit: it appears these will be much lower, 351 miles instead of 516 miles. I suspect that means they'll have a much shorter life span.

andyoxon · « **Reply #34 on:** 22 April, 2020, 09:09:03 pm »

Saw something bright elongated/irregular moving at 'satellite speed' across the sky @ 20:52pm. Very tight cluster of the satellites? Anyone else see it?

ETA. Looks like all 60 sats launch as 2 blocks initially... https://twitter.com/SpaceX/status/1253047783457619969?s=20

Hot Flatus · « **Reply #35 on:** 22 April, 2020, 09:14:00 pm »

It was the rocket, launching more of them.

Impressive, wasnt it.

Basil · « **Reply #36 on:** 22 April, 2020, 09:15:26 pm »

Just watched the Falcon rocket that delivered tonight's payload. Passed over Llandysul at 9.50. Sky was still very light but it stood out well. I wasn't able to see the trail of its payload satellites behind it due to the thin hazy cloud and the remaining light.

andyoxon · « **Reply #37 on:** 22 April, 2020, 09:21:19 pm »

Yes, impressive.

2nd stage + sats...

https://space.stackexchange.com/questions/17878/why-does-the-spacex-falcon-9-rocket-do-a-180-flip-for-reentry

Greenbank · « **Reply #38 on:** 22 April, 2020, 09:24:55 pm »

Quote from: Basil on 22 April, 2020, 09:15:26 pm

Just watched the Falcon rocket that delivered tonight's payload. Passed over Llandysul at 9.50. Sky was still very light but it stood out well. I wasn't able to see the trail of its payload satellites behind it due to the thin hazy cloud and the remaining light.

What kind of time machine is this?

Basil · « **Reply #39 on:** 22 April, 2020, 09:53:05 pm »

Ah yes. Sorry 8.50

Basil · « **Reply #40 on:** 22 April, 2020, 09:56:18 pm »

Just been out to view the 9.34 group passing over. Saw precisely nothing. (Not counting pipistrelles)

Vernon · « **Reply #41 on:** 23 April, 2020, 09:40:59 am »

Quote from: Jurek on 22 April, 2020, 11:02:18 am

It's all kicking off tonight with the first one passing over my house at 20:52.
Looking down the chart on Heavens Above, it next comes over at 22:31.
So that's one orbit of the planet in just under 40 minutes.
Can anyone with more maths in their head than me, work out the speed it's travelling at?

FWIW there was a good view of them here in SE London last night.

Correction - that's about 100 minutes, which is about normal for Low Earth Orbit (Leo) satellites. This means they are moving at around 7 km/sec

Jurek · « **Reply #42 on:** 23 April, 2020, 11:11:10 am »

Quote from: Vernon on 23 April, 2020, 09:40:59 am

Quote from: Jurek on 22 April, 2020, 11:02:18 am
It's all kicking off tonight with the first one passing over my house at 20:52.
Looking down the chart on Heavens Above, it next comes over at 22:31.
So that's one orbit of the planet in just under 40 minutes.
Can anyone with more maths in their head than me, work out the speed it's travelling at?

FWIW there was a good view of them here in SE London last night.

Correction - that's about 100 minutes, which is about normal for Low Earth Orbit (Leo) satellites. This means they are moving at around 7 km/sec

Oops!
My bad

Basil · « **Reply #43 on:** 23 April, 2020, 01:40:12 pm »

Ah. This is why they're getting less bright.
They are 'fixing' the brightness.

https://www.bbc.co.uk/news/technology-52391758?at_custom2=twitter&at_custom1=%5Bpost+type%5D&at_custom4=7D9970EA-8503-11EA-9EEB-23BD4744363C&at_campaign=64&at_custom3=%40BBCTech&at_medium=custom7

Vernon · « **Reply #44 on:** 23 April, 2020, 08:53:38 pm »

They should be rising in wnw and up past venus in about 4 minutes

Jurek · « **Reply #45 on:** 23 April, 2020, 09:18:02 pm »

Quote from: Vernon on 23 April, 2020, 08:53:38 pm

They should be rising in wnw and up past venus in about 4 minutes

CBA. Bed's looking good

Tim Hall · « **Reply #46 on:** 23 April, 2020, 09:24:52 pm »

Went outside to to see them, but no luck.

This was the so called "string of pearls", or as someone on the VirtualAstro twitter feed asked "can you refer to them as 'The Pearl Necklace' please."

jiberjaber · « **Reply #47 on:** 22 May, 2020, 05:43:08 pm »

Quote from: Basil on 23 April, 2020, 01:40:12 pm

Ah. This is why they're getting less bright.
They are 'fixing' the brightness.

https://www.bbc.co.uk/news/technology-52391758?at_custom2=twitter&at_custom1=%5Bpost+type%5D&at_custom4=7D9970EA-8503-11EA-9EEB-23BD4744363C&at_campaign=64&at_custom3=%40BBCTech&at_medium=custom7

They haven't yet, but are trialing a coating to be less reflective... It's still going to be a royal pain even when not visible to the eye...

Here's from a session looking at M65 a single 300s frame!

andyoxon · « **Reply #48 on:** 22 May, 2020, 06:00:03 pm »

Zoom?

ETA. impressive jj - to be able to see the shape of the galaxies on your setup.