Astro Hacker News - Starlink satellites being lowered from 550 km to 480 km

Havoc |next [-]

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

montjoy |root |parent |next [-]

My take is that orbits below 500 km are “cleaned out” and during solar minimum there is less drag going on there. So, it’s a good spot to home your satellites for a while because there isn’t as much junk to maneuver around.

JumpCrisscross |root |parent |next |previous [-]

> 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.

londons_explore |root |parent |next [-]

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'.

JumpCrisscross |root |parent [-]

> you don't pay for space or power

These birds aren’t totally autonomous. They do take up “space” in a limited sense. And having your fleet be somewhat similar lets one execute maneuvers like this global plane change more efficiently.

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quailfarmer |root |parent |previous [-]

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.

Havoc |root |parent [-]

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

mikhailfranco |next |previous [-]

Presumably this reduces the beam footprint on the ground, hence increases the bandwidth available to individual users in dense urban environments (reduced sharing).

TOMDM |next |previous [-]

Is this potentially a response to Russia's posturing around anti satellite weapons?

https://www.pbs.org/newshour/world/intelligence-agencies-sus...

tristanj |root |parent [-]

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

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

jagaerglad |next |previous [-]

So instead of having to launch new satellites to replace the deorbited ones ever couple of years, do they have to send new ones every couple of months? Or can the functioning ones maintain their orbits somehow and this is only for the malfunctioning ones?

jws |root |parent |next [-]

It sounds like this corresponds to an atmospheric contraction. They are lowering to avoid extending the lifetime of possible debris, but that also probably means the regular lifetime is not shortened. They are just staying in the designed density to match their designed service lives. The field of view of the satellites will be reduced, but presumably they have enough units up there to maintain full coverage.

This is distinct from the FCC application they have made for another Starlink shell in VLEO (~330km) for another 15000 satellites to better serve cellular phones.

verzali |root |parent [-]

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.

DoctorOetker |root |parent [-]

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 steering, it could be a logical choice.

verzali |root |parent [-]

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.

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manmal |root |parent |next |previous [-]

They have ion thrusters that prevent them from losing altitude as long as they are operational.

JumpCrisscross |root |parent [-]

> ion thrusters that prevent them from losing altitude as long as they are operational

Unintentional tautology. A satellite is by definition operational as long as it can station keep.

That said, yes, they should be able to station keep with ions alone. But also, ion propulsion still requires propellant. Until we figure out orbital magnetic suspension, it’s all reaction engines.

lefra |root |parent |previous [-]

They have an ion thruster to compensate for atmospheric drag.

m4rtink |root |parent [-]

There has been some research (IIRC by ESA) for using the upper atmosphere to feed a ion engine. That way you should be able to put satellites even lower as long as they have enough power from solar panels and are functional.

GeertB |next |previous [-]

I wonder if this will improve latency and signal strength

rented_mule |root |parent |next [-]

It seems plausible that it would help with latency, but not by a game changing amount. This is 70/550 or 13% closer. Not all of the latency is caused by distance to the the satellites (e.g., terrestrial latency is not 0), so my guess would be that the latency experienced by users would improve by less than 13%.

486sx33 |root |parent [-]

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TGower |root |parent |previous [-]

Should be about half a millisecond round trip difference. 70 km / speed of light = 233.5 microseconds one way duration.

vipa123 |next |previous [-]

How much Delta-V would that take, and how much would they typically have onboard at the start of their life?

wmf |root |parent [-]

Drag is constantly pulling them down so maybe they won't have to use any propellant.

hulitu |next |previous [-]

> Starlink satellites being lowered from 550 km to 480 km

Why stop ? 200 km looks like the right orbit.

croes |next |previous [-]

Isn’t that just moving the problem?

NedF |next |previous [-]

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thot_experiment |next |previous [-]

great move, we're continually about 2 days away from kessler if we lost maneuvering control on a constellation like starlink (ofc that's vanishingly unlikely, but it's important to understand that continual maneuvering is what keeps space accessible to humanity)

anything we can do to lower that risk is a good move, and dropping 70km of elevation for the largest satellite constellation is definitely going to make a dent in the risk profile

https://arxiv.org/pdf/2512.09643

i hope to see progress with air breathing ion engine satellites in the coming years to further lower the minimum altitudes that these constellations can operate at

Veedrac |root |parent |next [-]

The paper says we are 2.8 days away from a collision. It doesn't say we're '2 days away from kessler'. In fact, the paper explicitly warns against your interpretation.

> We emphasize that the CRASH Clock does not measure the onset of KCPS, nor should it be interpreted as indicating a runaway condition.

thot_experiment |root |parent [-]

Thanks, I stand corrected. I'll do a better job reading next time.

JumpCrisscross |root |parent |previous [-]

> 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.

quailfarmer |root |parent [-]

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.

JumpCrisscross |root |parent [-]

> 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...

wmf |previous [-]

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 for "safety". Is this an emergency change to account for a design flaw that they just discovered?

JumpCrisscross |root |parent |next [-]

> 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.

wmf |root |parent [-]

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?

JumpCrisscross |root |parent [-]

> 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?

wmf |root |parent [-]

I don't think this kind of change has ever been done before so there may not be clear regulations.

quailfarmer |root |parent |previous [-]

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

wmf |root |parent [-]

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.