Author Topic: Starlink : General Discussion - Thread 1  (Read 1217436 times)

Offline Joseph Peterson

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Re: SpaceX - now a satellite manufacturer (Starlink)
« Reply #2440 on: 12/09/2018 10:42 pm »
I could use some math help.  What I want to know is the minimum number of Starlink satellites needed so that a ground station always has one 550 km satellite in view at various latitudes with various numbers of planes partially populated.
« Last Edit: 12/09/2018 10:58 pm by Joseph Peterson »

Offline Robotbeat

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Re: SpaceX - now a satellite manufacturer (Starlink)
« Reply #2441 on: 12/10/2018 01:56 am »
I could use some math help.  What I want to know is the minimum number of Starlink satellites needed so that a ground station always has one 550 km satellite in view at various latitudes with various numbers of planes partially populated.
I guesstimate about 500-800 satellites.
Chris  Whoever loves correction loves knowledge, but he who hates reproof is stupid.

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Offline gongora

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Re: SpaceX - now a satellite manufacturer (Starlink)
« Reply #2442 on: 12/10/2018 02:15 pm »
For those wanting an example of what RF inter-satellite links look like in FCC documents, here are a couple of constellation filings that have them:

Iridium NEXT (SAT-MOD-20131227-00148)
Audacy (SAT-LOA-20161115-00117)

Look for Inter-Satellite Service or ISS beams in the documentation (both narrative and Schedule S).  If you find similar entries in the SpaceX filings then please let me know, I must have overlooked them.

Offline IainMcClatchie

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Re: SpaceX - now a satellite manufacturer (Starlink)
« Reply #2443 on: 12/11/2018 12:28 am »
I could use some math help.  What I want to know is the minimum number of Starlink satellites needed so that a ground station always has one 550 km satellite in view at various latitudes with various numbers of planes partially populated.

I can't give you a simple equation for that.  I wrote a matlab script to figure it out (attached).  You set some parameters: orbit altitude, number of rings, number of satellites per ring, and orbital inclination, and it generates plots like the one attached, which is for the following parameters.
  orbit altitude: 550 km
  orbit inclination: 53 and 37 degrees
  number of planes: 20
  number of satellites per plane: 30

This configuration gives continuous coverage from 25 to 56 degrees N, but has minimum coverage gaps around 10 N and 22 N.

From there, you just have to fool around with the numbers a bit.  This config is the minimum number of sats I came up with at 550 km altitude.  The minimums are fairly sensitive to the relative phasing of the satellites within their rings, and there may be some optimization there I haven't figured out.

Offline speedevil

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Re: SpaceX - now a satellite manufacturer (Starlink)
« Reply #2444 on: 12/11/2018 09:19 am »
I could use some math help.  What I want to know is the minimum number of Starlink satellites needed so that a ground station always has one 550 km satellite in view at various latitudes with various numbers of planes partially populated.

I can't give you a simple equation for that.  I wrote a matlab script to figure it out (attached).  You set some parameters: orbit altitude, number of rings, number of satellites per ring, and orbital inclination, and it generates plots like the one attached, which is for the following parameters.
  orbit altitude: 550 km
  orbit inclination: 53 and 37 degrees
  number of planes: 20
  number of satellites per plane: 30

This configuration gives continuous coverage from 25 to 56 degrees N, but has minimum coverage gaps around 10 N and 22 N.

Interesting!

The above gives average sats visible - is it possible to simply plot minimum sats? (no matlab)

If you are assuming a mixed constellation of planes at different inclinations, it probably makes more sense at least initially to ask about coverage of a constellation at 550km, with only 53 degrees. In other words, when can a partially launched constellation be of use.

A back of the envelope calculation indicated that you can get a fair coverage down to approaching 30N or so with 53 degree inclination satellites, but with only 12 of the 24 nominal planes populated.
Covering most of the population of the USA and Europe.
Spherical geometry hurts my head.

Offline Joseph Peterson

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Re: SpaceX - now a satellite manufacturer (Starlink)
« Reply #2445 on: 12/12/2018 01:48 am »
I could use some math help.  What I want to know is the minimum number of Starlink satellites needed so that a ground station always has one 550 km satellite in view at various latitudes with various numbers of planes partially populated.

I can't give you a simple equation for that.  I wrote a matlab script to figure it out (attached).  You set some parameters: orbit altitude, number of rings, number of satellites per ring, and orbital inclination, and it generates plots like the one attached, which is for the following parameters.
  orbit altitude: 550 km
  orbit inclination: 53 and 37 degrees
  number of planes: 20
  number of satellites per plane: 30

This configuration gives continuous coverage from 25 to 56 degrees N, but has minimum coverage gaps around 10 N and 22 N.

From there, you just have to fool around with the numbers a bit.  This config is the minimum number of sats I came up with at 550 km altitude.  The minimums are fairly sensitive to the relative phasing of the satellites within their rings, and there may be some optimization there I haven't figured out.


Thanks.  This appears to be what I need. 

For those wanting an example of what RF inter-satellite links look like in FCC documents, here are a couple of constellation filings that have them:

Iridium NEXT (SAT-MOD-20131227-00148)
Audacy (SAT-LOA-20161115-00117)

Look for Inter-Satellite Service or ISS beams in the documentation (both narrative and Schedule S).  If you find similar entries in the SpaceX filings then please let me know, I must have overlooked them.

I'll keep my eyes open.   

Offline IainMcClatchie

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Re: SpaceX - now a satellite manufacturer (Starlink)
« Reply #2446 on: 12/12/2018 11:15 pm »
The above gives average sats visible - is it possible to simply plot minimum sats? (no matlab)

Yup.  The dashed line shows minimum sats visible, and the solid line is average sats visible.

Quote
If you are assuming a mixed constellation of planes at different inclinations, it probably makes more sense at least initially to ask about coverage of a constellation at 550km, with only 53 degrees. In other words, when can a partially launched constellation be of use.

I tried that first.  You have to choose between covering Europe with at least 1, covering the US with at least 1, or using a lot more satellites.

550 km is a lot harder than 1050 km.  At 1050 km the spots are so much bigger that the number of satellites to get min 1 coverage goes way down.

Quote
A back of the envelope calculation indicated that you can get a fair coverage down to approaching 30N or so with 53 degree inclination satellites, but with only 12 of the 24 nominal planes populated.
Covering most of the population of the USA and Europe.
That's not what my Matlab script shows.  At 12 planes you'd open up a lot of gaps at the equator that would continue up through at least San Francisco.

Offline saliva_sweet

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Re: SpaceX - now a satellite manufacturer (Starlink)
« Reply #2447 on: 12/13/2018 08:20 pm »
Look for Inter-Satellite Service or ISS beams in the documentation (both narrative and Schedule S).  If you find similar entries in the SpaceX filings then please let me know, I must have overlooked them.

I wonder if they could use their customers as ground stations to create faux inter satellite links. Not sure whether that would make sense.

Offline northstar

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Re: SpaceX - now a satellite manufacturer (Starlink)
« Reply #2448 on: 12/19/2018 05:25 pm »
The above gives average sats visible - is it possible to simply plot minimum sats? (no matlab)

Yup.  The dashed line shows minimum sats visible, and the solid line is average sats visible.

Quote
If you are assuming a mixed constellation of planes at different inclinations, it probably makes more sense at least initially to ask about coverage of a constellation at 550km, with only 53 degrees. In other words, when can a partially launched constellation be of use.

I tried that first.  You have to choose between covering Europe with at least 1, covering the US with at least 1, or using a lot more satellites.

550 km is a lot harder than 1050 km.  At 1050 km the spots are so much bigger that the number of satellites to get min 1 coverage goes way down.

Quote
A back of the envelope calculation indicated that you can get a fair coverage down to approaching 30N or so with 53 degree inclination satellites, but with only 12 of the 24 nominal planes populated.
Covering most of the population of the USA and Europe.
That's not what my Matlab script shows.  At 12 planes you'd open up a lot of gaps at the equator that would continue up through at least San Francisco.

Iain,

Could you run the Matlab script again for the higher orbital plane satellites?  It will IIRC be the first one put in place, and for those of us at higher latitudes provides better coverage.

Offline Lars-J

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Re: SpaceX - now a satellite manufacturer (Starlink)
« Reply #2449 on: 12/19/2018 07:20 pm »
The guy that did the nice 3D routing analysis of the Starlink constellation recently posted an updated version for the new proposal with the new ~500km orbit:



My apologies if this has been posted already.
« Last Edit: 12/19/2018 07:20 pm by Lars-J »

Offline gongora

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Re: SpaceX - now a satellite manufacturer (Starlink)
« Reply #2450 on: 12/19/2018 11:32 pm »
Could you run the Matlab script again for the higher orbital plane satellites?  It will IIRC be the first one put in place, and for those of us at higher latitudes provides better coverage.

The higher inclination planes are not going up first.  Northern Alaska/Canada and parts of Northern Europe won't get coverage from the initial deployment.

Offline smoliarm

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Re: SpaceX - now a satellite manufacturer (Starlink)
« Reply #2451 on: 12/20/2018 04:09 pm »
I'm not sure this news bit is about Starlink. But it is definitely not about rockets or launches.
However, it's 29 millions - so should be some place for it here :)

DoD Contracts for Dec. 19, 2018:

Quote
Space Exploration Technologies Corp., Hawthorne, California, has been awarded a $28,713,994 competitive, firm-fixed-price, other transaction agreement for experimentation per the advanced research announcement, FA8650-17-S-9300. This agreement allows for experimentation in the areas of establishing connectivity, operational experimentation, and special purpose experimentation. Experimentation will include connectivity demonstrations to Air Force ground sites and aircraft for experimental purposes. For the proposed Phase 2, the awardee proposes to perform experiments in two other key areas: early versions of a commercial space-to-space data relay service and mobile connectivity directly from space to aircraft. Work will be performed in Hawthorne, California, and is expected to be completed by June 18, 2021.  Fiscal 2019 research, development, test and evaluation funds in the amount of $19,167,989 will be obligated at the time of award. Air Force Research Laboratory, Wright-Patterson Air Force Base, Ohio, is the contracting activity (FA8650-19-9-9320). (Awarded Dec. 19, 2018)

https://dod.defense.gov/News/Contracts/Contract-View/Article/1718270/

Offline docmordrid

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Re: SpaceX - now a satellite manufacturer (Starlink)
« Reply #2452 on: 12/20/2018 05:08 pm »
I'm not sure this news bit is about Starlink. But it is definitely not about rockets or launches.
However, it's 29 millions - so should be some place for it here :)

DoD Contracts for Dec. 19, 2018:

Thank you!!

This ties into earlier reports of Air Force Research Lab interest and preliminary tests, FCC issuing permits for same, and the DARPA Blackjack program looking into using LEO constellation satellite buses for milsats (implied: wolves hiding among the sheep)
« Last Edit: 12/20/2018 05:24 pm by docmordrid »
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Offline gongora

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Re: SpaceX - now a satellite manufacturer (Starlink)
« Reply #2453 on: 12/20/2018 08:42 pm »

Offline su27k

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Re: SpaceX - now a satellite manufacturer (Starlink)
« Reply #2454 on: 12/21/2018 12:52 am »
I'm not sure this news bit is about Starlink. But it is definitely not about rockets or launches.
However, it's 29 millions - so should be some place for it here :)

DoD Contracts for Dec. 19, 2018:

Thank you!!

This ties into earlier reports of Air Force Research Lab interest and preliminary tests, FCC issuing permits for same, and the DARPA Blackjack program looking into using LEO constellation satellite buses for milsats (implied: wolves hiding among the sheep)

I don't think this is related to Blackjack, Blackjack is DARPA and more about using production line to build DoD's own satellites, this is Air Force Research Lab testing the bandwidth. So there is the potential for SpaceX to win more in Blackjack.

Offline docmordrid

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Re: SpaceX - now a satellite manufacturer (Starlink)
« Reply #2455 on: 12/21/2018 01:07 am »


I'm not sure this news bit is about Starlink. But it is definitely not about rockets or launches.
However, it's 29 millions - so should be some place for it here :)

DoD Contracts for Dec. 19, 2018:

Thank you!!

This ties into earlier reports of Air Force Research Lab interest and preliminary tests, FCC issuing permits for same, and the DARPA Blackjack program looking into using LEO constellation satellite buses for milsats (implied: wolves hiding among the sheep)

I don't think this is related to Blackjack, Blackjack is DARPA and more about using production line to build DoD's own satellites, this is Air Force Research Lab testing the bandwidth. So there is the potential for SpaceX to win more in Blackjack.

The DARPA presentation shows Blackjack birds co-orbiting within a same-bused LEO constellation, hence my comment about wolves hiding among the sheep.

http://fiso.spiritastro.net/telecon/Thomas_8-22-18/Thomas_8-22-18.pptx
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Offline Johnnyhinbos

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Re: SpaceX - now a satellite manufacturer (Starlink)
« Reply #2456 on: 12/21/2018 03:27 pm »
IEEE seems to think that there's a 45% chance a SpaceX satellite will cause death or injury every six years...


https://spectrum.ieee.org/tech-talk/aerospace/satellites/the-odds-that-one-of-spacexs-internet-satellites-will-hit-someone
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Online Kenp51d

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Re: SpaceX - now a satellite manufacturer (Starlink)
« Reply #2457 on: 12/21/2018 03:42 pm »
I read that a couple days ago. Thought it was hit piece journalism.
I seriously question that the FCC would allow anything to fly with that great a chance in any time frame coming down on some one.
But then, I'm just an arm chair coach, what do I know?

Ken

Offline gongora

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Re: SpaceX - now a satellite manufacturer (Starlink)
« Reply #2458 on: 12/21/2018 03:52 pm »
The FCC doesn't currently enforce the casualty numbers for the constellation as a whole.  I thought the IEEE article was pretty well written.  The headline isn't great.

Offline gdjacobs

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Re: SpaceX - now a satellite manufacturer (Starlink)
« Reply #2459 on: 12/21/2018 03:58 pm »
The conclusions of the assessment are somewhat questionable considering our historical experience base.
https://mysteriousuniverse.org/2017/06/in-the-line-of-fire-people-that-were-injured-or-killed-by-falling-space-debris/

My tally thus far for people actually hurt by falling orbital debris is presently zero. There was that guy in Kazakhstan whose house was set on fire by launch debris and he died in the fire. The lady hit by Delta debris might qualify if it was part of a de-orbited second stage. Also, didn't Skylab kill a cow when it came down?

If they're able to target de-orbit and breakup, this will even more be a non issue.
« Last Edit: 12/21/2018 04:02 pm by gdjacobs »

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