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Starlink Orbital Decay

08/20/2020 1:30 AM

How it is possible to support a satellite based internet system in such a low orbit?
Even if given a realistically high m/CA wouldn’t the orbit decay in just a few weeks to a few months?

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Guru

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#1

Re: Starlink Orbital Decay

08/20/2020 2:46 AM

They have boosters that boost the speed every so often, they are projected to have a 5 year useful life, then need to be refueled or replaced....

..."Starlink satellites use Hall-effect thrusters with krypton gas as the reaction mass[76][132] for orbit raising and station keeping.[133] Krypton Hall thrusters tend to exhibit significantly higher erosion of the flow channel compared to a similar electric propulsion system operated with xenon, but at a lower propellant cost.[134] "...

https://en.wikipedia.org/wiki/Starlink

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#2
In reply to #1

Re: Starlink Orbital Decay

08/20/2020 3:25 AM

That is amazing.

58 Sats packed in a single bus, each with its own ion propulsion system.

How does the economics work when competing against Geostationary, Geosynchronous, and Molniya orbit systems?

The transponding and routing capabilities that would be required is mind boggling.

The scale blows my mind.

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#3
In reply to #2

Re: Starlink Orbital Decay

08/20/2020 11:55 AM

Yes, it is amazing technology but the light pollution problem for astronomy has yet to addressed.

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#4
In reply to #3

Re: Starlink Orbital Decay

08/21/2020 12:17 AM

...not to mention adding to space junk at the end of those 5 years, unless they have enough fuel and thrusters pointing in the right direction to de-orbit them. Undoubtedly at the end of life, at least a few will fail to de-orbit properly and become space junk. Even those that do de-orbit as planned will create a brief but significant light polution as they burn up in the atmosphere.

I'm well aware of the speed of technology advancing, so in 5 years there will be something better, but I hate the waste of devices that only last 5 years, or even 10.

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#5
In reply to #4

Re: Starlink Orbital Decay

08/21/2020 12:58 AM

At that altitude, without further propulsion, an orbit decays to reentry within a few weeks or months depending on a number of variables with the mass/(Coefficient of Drag * Crossectional Area) ratio being the most critical.

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#14
In reply to #5

Re: Starlink Orbital Decay

08/28/2020 12:07 PM

Cross Sectional Area on Starlink must be minimal if they orient with broadside toward Earth. Its like a waffle flying sideways...

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#7
In reply to #4

Re: Starlink Orbital Decay

08/22/2020 6:38 AM

..."The lower orbits will help ensure the satellites re-enter the atmosphere in a shorter time in case of failure, and will enable them to broadcast signals at reduced power levels, because they are closer to Earth, which SpaceX said will allow the fleet to be compliant with limits to reduce radio interference with other satellite and terrestrial wireless networks.[57]

SpaceX has said that satellites are launched at a lower altitude, and failed satellites are expected to deorbit within five years without propulsion.[14] "...

https://en.wikipedia.org/wiki/Starlink

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#15
In reply to #4

Re: Starlink Orbital Decay

04/05/2021 11:55 AM

All satellite manufacturers, including SpaceX, know about the significance of the space debris problem. Nowadays, each self-respecting space agency tries to present its own concept of a spacecraft capable of collecting or at least de-orbiting space debris. UK space manufacturer had already presented it — a space tug. I'm also concerned about light pollution caused by satellites, but I think this problem will be solved soon. Btw, I'm waiting for the solution SpaceX themselves will propose. They create a problem — they should develop a way to get rid of it, right?

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#16
In reply to #15

Re: Starlink Orbital Decay

04/05/2021 12:37 PM

I think the light pollution problem has been greatly reduced, at least for naked-eye viewing. 25 years ago, I commonly went out an hour or so after sunset to watch for satellites going over, and timed it; at that time, I saw one on average after four minutes of observation time (naked-eye). It was not unusual to see two visible at the same time, and I think I recall seeing three visible at once.

I have gone out to look several times during the last year, watching for 20 minutes or so at a time, and have not seen a single one, other than the ISS, whose visibility was known in advance.

I did read about some people seeing a string of Space-X satellites shortly after launch not too long ago, but haven't heard (or seen) anything since.

For those using large telescopes, on the other hand, these satellites may spoil, or at least degrade, quite a few images

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#11
In reply to #2

Re: Starlink Orbital Decay

08/23/2020 12:50 AM

Starlink orbits have several advantages over any of the orbits you mentioned. First, it takes less fuel to lift all those satellites to low-earth orbits. Second, since Starlink is an internet service, the travel time for data transmission is much less for low-earth orbits. Geostationary/geosynchronous orbits are typically about 22,000 miles above earth, so a round-trip data packet needs to travel 44,000 miles. Since the speed of data transmission is the speed of light (~186,000 miles/second), it takes about 250 milliseconds to make that journey. With Starlink orbits under 1,000 miles of earth, round-trip distances are cut dramatically as are transmission times, usually under 25 milliseconds.

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#12
In reply to #11

Re: Starlink Orbital Decay

08/23/2020 1:18 AM

Correct, and welcome to CR4! I love your moniker!

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#13
In reply to #11

Re: Starlink Orbital Decay

08/28/2020 2:58 AM

OHM Run - All of your points appear valid; but even with ion propulsion in each sat, and the overly optimistic orbital lifespan of 5 years, the launch cycle becomes a continuous activity; hardly more efficient than geostationary in terms of total energy input.

The data packet transmission time appears to be a reasonable argument also, until you consider the process time required for transponding and routing.

I guess we will see how well it competes?

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#8
In reply to #1

Re: Starlink Orbital Decay

08/22/2020 9:44 AM

Exactly. And then what ever makes it through fiery descent uses Our whole planet as their landfill. Something tells me there is "stuff" on the satellite that is best protected, therefore most likely to survive re-entry that We wouldn't want to put in any public use landfill let alone Our oceans and general landmasses.

I guess they could save one last boost for elevating it to our ever expanding trashosphere.

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#9
In reply to #8

Re: Starlink Orbital Decay

08/22/2020 1:09 PM
  • 100% of "all components of this design will quickly burn in Earth's atmosphere at the end of each satellite's lifecycle".
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#10
In reply to #9

Re: Starlink Orbital Decay

08/22/2020 3:07 PM

Yeah. I've heard those sorts of promises in a vast diversity of cases my entire life.

Guess what? I've seen most of those self same promises prove to be untrue. So sorry if I am more than just a little skeptical.

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#6

Re: Starlink Orbital Decay

08/21/2020 11:09 PM

There's sometimes an advantage having satellites with decaying low Earth orbits. The US Antarctic station at South Pole has access to several modern satellite systems, but only during limited windows of visibility:
https://www.usap.gov/technology/1982/
They are *way* Down Under at South Pole, and when those satellites are invisible, some of the old Iridium satellites come to the rescue ... while they're still flying:
https://spacenews.com/iridium-would-pay-to-deorbit-its-30-defunct-satellites-for-the-right-price/
At this page you will find a comprehensive list of Iridium satellites and their decay status:
https://en.wikipedia.org/wiki/Iridium_satellite_constellation
Thanks to some of those, the US Antarctic Division has (limited) 24-hour communications courtesy of clunky old satellites in quirky decayed orbits that are visible from South Pole.

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