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Comment by bagels | Hacker News Reader

Let's assume gps disappeared. Will starlink still operate?

Good question. Also consider that most of the threats to GPS are ground based jamming. It is fairly easy and cheap to make a jammer out of hobbyist parts and knock out a large area of GPS coverage. However, just because someone jams GPS for an entire city doesn't mean that they are able to jam the LEO satellites flying over that city.

The Pentagon is (plausibly) Starlink's by-far most valuable potential customer. It seems pretty safe to assume that Starlink was designed to keep working after anti-satellite weapons, jammers, hackers, etc. knocked out GPS.

It should. It does not depend on GPS, only on ground stations, to correct its orbits.

I don't have any concrete knowledge to say Starlink satellites rely on GPS, but based on what I know about satellites with thrusters and autonomous formation flying capabilities, they almost certainly have one or more GPS receivers onboard.

My understanding is that the SpaceX ground stations uplink the orbital parameters of other satellites and/or debris and it is mostly up to the satellites to avoid a collision. You need very precise onboard location knowledge for that. Also, I bet they are using GPS time to synchronize the fleet.

Of course you can still synchronize and maneuver the satellites manually from ground stations if necessary. And they probably do that when a satellite is misbehaving. But overall the Starlink operations concept is probably tailored to mostly automated operations.

So IMO they would definitely have big issues if GPS went away suddenly.

> they almost certainly have one or more GPS receivers onboard.

Wait, GPS works in space (LEO)?! Will that have required customisation?

From the point of view of the GPS satellites, LEO and the Earth's surface are almost the same thing. The GPS constellation is a lot further away.

Fair point about relative distances.

It does require special receivers, but AFAIK the only special thing in them is the removed speed/altitude limitation that exists in regular of the shelf receivers - https://en.wikipedia.org/wiki/Coordinating_Committee_for_Mul...

The commercial GPS receiver are just software disabled not to work at certain speed and altitude. There used to be a receiver you can buy that does not have those restriction. You can also build your own GPS receiver and not have the restriction.

One of the design goals for GPS was munitions guidance, including missiles with suborbital flights. So yes, at least in LEO.

A design goal? Good point.

It works up to 3000km with full precision, you just need a receiver without CoCom limits. (actually, precision should be better without atmosphere). It also works all the way up to geostationary orbit, but with some limitations.

https://www.gps.gov/multimedia/presentations/2011/09/ICG/mil...

GPS orbits at 20,200km from the surface. Starlink orbits at 550km from the surface. So, relatively, they're basically on the ground, just moving really fast!

> My understanding is that the SpaceX ground stations uplink the orbital parameters of other satellites and/or debris and it is mostly up to the satellites to avoid a collision.

That is almost certainly not how that is implemented. Why would they run the orbit maneuver planning in space when they could do the whole thing comfortably on a simple server PC on earth?

> But overall the Starlink operations concept is probably tailored to mostly automated operations.

I agree with that. They are most definietly not hand-flying their birds. But this autonomy is most likely implemented on the ground.

> That is almost certainly not how that is implemented. Why would they run the orbit maneuver planning in space when they could do the whole thing comfortably on a simple server PC on earth?

That's a great question, but SpaceX is, apparently, doing much of the processing onboard[1].

[1] https://ecfsapi.fcc.gov/file/1081071029897/SpaceX%20Orbital%...

Probably because the purpose of SpaceX is to build a city on Mars, and Starlink is a prototype for a communications and positioning system to be put in place around Mars before there are any facilities on the Martian surface. Remember this is an Elon Musk company.

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