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Starlink satellites being lowered from 550 km to 480 km

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Re: Starlink satellites being lowered from 550 km to 480 km

#31

Post by quailfarmer »

wmf wrote: post #7

Usually orbits are reserved years in advance. AFAIK this kind of move is unprecedented (although everything about Starlink is unprecedented since it's the first megaconstellation). Two weeks ago, a Starlink satellite exploded. SpaceX believes it wasn't caused by a collision which means the explosion was probably caused by a malfunction in the satellite itself. Now 4,400 Starlink satellites are moving to a lower orbit…

You’re comparing to GEO communication sat orbits, which are highly coordinated and expensive real estate, reserved for small numbers of vehicles.

Re: Starlink satellites being lowered from 550 km to 480 km

#32

Post by JumpCrisscross »

wmf wrote: post #24
JumpCrisscross wrote: post #18

Earlier quoted context omitted.

> Usually orbits are reserved years in advance Because planning missions took years to plan. Holidaygoers book hotels months and sometimes a year or more in advance. Business travelers don’t. That doesn’t make the latter unusual, just a different use case. > Is this an emergency change to account for a design flaw that they just discovered? Zero evidence or precedent for this.

If the existing orbit is safe enough, why bother "increasing space safety"? The cost of this reconfiguration must be quite large. And why have no public comment period?

> If the existing orbit is safe enough, why bother "increasing space safety"?

My honest guest is this is about latency more than safety.

> why have no public comment period?

Does the FAA require public-comment periods for plane changes?

Re: Starlink satellites being lowered from 550 km to 480 km

#33

Post by JumpCrisscross »

quailfarmer wrote: post #30
JumpCrisscross wrote: post #16

Earlier quoted context omitted.

> we're continually about 2 days away from kessler if we lost maneuvering control on a constellation like starlink To be clear, we’d be at risk of losing those specific orbits for a few years. Nothing would block all orbits much less access to space. And nothing above those orbits would be any more statistically likely to suffer an impact afterwards.

For these large constellations, vehicles are generally raised slowly at the beginning of their lives, and debris spreads out as it decays downwards. A significant increase in debris at 550km would have an impact on all orbits below it, including all vehicles raising through that debris zone.

> A significant increase in debris at 550km would have an impact on all orbits below it, including all vehicles raising through that debris zone

Space is huge. Try this trick: the number of satellites in orbit is about the same as the number of planes in the air at any time. (~12,000 [1][2].)

The volume of space from the ground to 50,000 feet is about 200x smaller than the volume from the Karman line to the top of LEO alone (~2,000 km).

Put another way, we approach the density of planes in the sky in LEO when there are milliions of satellites in that space alone. Picture what happens if every plane in the sky fell to the ground. Now understand that the same thing happening in LEO, while it occurs at higher energy, also occurs in less-occupied space and will eventually (mostly) burn up in the atmosphere.

Put another way, you could poof every Starlink simultaneously and while it would be tremendously annoying, most satellites orbiting lower would be able to get out of the way, those that couldn't wouldn't cause much more damage, the whole mess would be avoidable for most and entirely gone within a few years.

There are serious problems with space pollution. Catastrophic Kessler cascades that block humans from space, or knock out all of our satellites, aren't one of them.

[1] https://www.travelandleisure.com/airlines-airports/number-of...

[2] https://www.travelandleisure.com/airlines-airports/number-of...

Re: Starlink satellites being lowered from 550 km to 480 km

#34

Post by tristanj »

TOMDM wrote: post #20

Is this potentially a response to Russia's posturing around anti satellite weapons? https://www.pbs.org/newshour/world/intelligence-agencies-sus...

It's more likely because of the starlink satellite that exploded on December 19.

https://www.theverge.com/news/847891/a-starlink-satellite-se...

Re: Starlink satellites being lowered from 550 km to 480 km

#36

Post by londons_explore »

JumpCrisscross wrote: post #17
Havoc wrote: post #14

That would surely also mean their expected lifespan is shorter too? Faster decay doesn’t just affect dead satellites Idk seems like a strange move and the stated reason seems flimsy

> would surely also mean their expected lifespan is shorter too? Are Starlinks being deörbited due to propellant exhaustion? In many respects, Starlink satellites are small servers. They’re probably profitable to replace quicker than decay would force them to be.

But you don't pay for space or power - so the normal business incentives to retire old hardware don't really apply.

We are nowhere close to the sky being 'full'.

Re: Starlink satellites being lowered from 550 km to 480 km

#37

Post by [deleted] »

JumpCrisscross wrote: post #17
Havoc wrote: post #14

That would surely also mean their expected lifespan is shorter too? Faster decay doesn’t just affect dead satellites Idk seems like a strange move and the stated reason seems flimsy

> would surely also mean their expected lifespan is shorter too? Are Starlinks being deörbited due to propellant exhaustion? In many respects, Starlink satellites are small servers. They’re probably profitable to replace quicker than decay would force them to be.

[deleted]

Re: Starlink satellites being lowered from 550 km to 480 km

#38

Post by verzali »

DoctorOetker wrote: post #25
verzali wrote: post #6

Earlier quoted context omitted.

At 480km there will be increased drag, even as we get closer to the solar minimum. The trade-off may be between using propellant for collision avoidance vs using it to counter altitude loss and for station keeping. Maybe it is also linked to the falling altitude of the ISS? 480km is about the upper bound of its altitude but they seem unlikely to actually raise it that high before it is deorbited.

is it conceivable that collision avoidance maneuvers become cheaper in fuel consumption by using the slightly less thin atmosphere to steer a satellite (only use propellant for attitude control, less direct linear acceleration? i.e. if the propellant consumption for collision avoidant steering at 550 km in practice turns out to be higher than the consumption to negate the drag incurred for using atmosphere for steeri…

Yes, you can do that. But you do need to alter your attitude for long periods and that usually means you point away from the optimal position for the solar panels and for the antennas pointing towards the ground. So yes, but only at the cost of some loss of efficiency.

Re: Starlink satellites being lowered from 550 km to 480 km

#39

Post by Havoc »

quailfarmer wrote: post #29
Havoc wrote: post #14

That would surely also mean their expected lifespan is shorter too? Faster decay doesn’t just affect dead satellites Idk seems like a strange move and the stated reason seems flimsy

Yes, it’s absolutely a trade off against prop (argon) lifetime, energy spent thrusting, and atomic oxygen degradation of plastic components. The benefits of increased drag for these shells of thousands of vehicles must be worth it.

Why is drag desirable? Aside from faster decay for cleanup.

I just don’t understand why spacex would do this from a biz/strategic perspective

Re: Starlink satellites being lowered from 550 km to 480 km

#40

Post by wmf »

quailfarmer wrote: post #31
wmf wrote: post #7

Usually orbits are reserved years in advance. AFAIK this kind of move is unprecedented (although everything about Starlink is unprecedented since it's the first megaconstellation). Two weeks ago, a Starlink satellite exploded. SpaceX believes it wasn't caused by a collision which means the explosion was probably caused by a malfunction in the satellite itself. Now 4,400 Starlink satellites are moving to a lower orbit…

You’re comparing to GEO communication sat orbits, which are highly coordinated and expensive real estate, reserved for small numbers of vehicles.

No, I'm not. AFAIK there has been years of regulatory wrangling between Starlink, Kuiper, OneWeb, etc. about who gets which orbital shell. Shells aren't yet as scarce as GEO slots but companies are already planning for a future where they might be.
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