SpaceX F9 : Starlink v0.9 : May 23, 2019 - DISCUSSION

[AC in NC]

I don’t understand the replacement strategy for Starlink,  assuming planes of 66 sats. I don’t see how SpaceX can insert the required 10 or so satellites necessary to go from the current 56 working sats to 66.

They could launch 10.

[speedevil]

I don’t understand the replacement strategy for Starlink,  assuming planes of 66 sats. I don’t see how SpaceX can insert the required 10 or so satellites necessary to go from the current 56 working sats to 66.

There need to be quite a lot of launches to fill out a constellation.
During this period, some of the satellites launched can not raise orbit for a period, so they experience different precession and can swap planes.
This is without considering if direct plane changes with ion thrusters are an option.

[Danderman]

I don’t understand the replacement strategy for Starlink,  assuming planes of 66 sats. I don’t see how SpaceX can insert the required 10 or so satellites necessary to go from the current 56 working sats to 66.

They could launch 10.

Or they could launch 1.

My question is about what they will really do to replace a small number of satellites in one plane, not what is theoretically possible.

[Danderman]

I don’t understand the replacement strategy for Starlink,  assuming planes of 66 sats. I don’t see how SpaceX can insert the required 10 or so satellites necessary to go from the current 56 working sats to 66.

There need to be quite a lot of launches to fill out a constellation.
During this period, some of the satellites launched can not raise orbit for a period, so they experience different precession and can swap planes.
This is without considering if direct plane changes with ion thrusters are an option.

If the failed sats to be replaced are near the plane that the Falcon is being launched to, sure.

Otherwise, it’s a long haul.

[marsbase]

If the failed sats to be replaced are near the plane that the Falcon is being launched to, sure.

Otherwise, it’s a long haul.

Starlink has had one launch and has 57 satellites in good orbits.  Their nearest competitor has had one launch and has 6 satellites in orbit.  Who has a long haul?

[gongora]

Starlink has had one launch and has 57 satellites in good orbits.  Their nearest competitor has had one launch and has 6 satellites in orbit.  Who has a long haul?

SpaceX has 53 in good orbits and another really close, and one more may get there.  They've already said 3 don't work and 2 more are being deorbited.

The first flight for OneWeb carried six sats.  The rest of the flights for OneWeb's deployment should be 32+ sats (other than a couple token Virgin flights), and their initial constellation is half the size of the first shell of SpaceX's initial constellation.

[envy887]

If the failed sats to be replaced are near the plane that the Falcon is being launched to, sure.

Otherwise, it’s a long haul.

Starlink has had one launch and has 57 satellites in good orbits.  Their nearest competitor has had one launch and has 6 satellites in orbit.  Who has a long haul?

It's a long haul to precess 90+ degrees. However, SpaceX has a LOT of launches to do before a hole of a few satellites in one plane becomes an issue, so 6 months to drift several planes over isn't really a problem.

If they actually want 66 satellites per plane, the obvious answer is to add 2 more layers to the stack, assuming they fit in the volume and mass requirements. That gives 34 per launch, so 2 launches populates each plane plus adds 2 spares.

If they can only fit 30 per launch, then every 3rd plane will get 3 launches of 30. Drifting 10 sats one plane over, and 10 more sats 2 planes over, only takes a few months, and they end up with 4 spares in each plane.

[marsbase]

Starlink has had one launch and has 57 satellites in good orbits.  Their nearest competitor has had one launch and has 6 satellites in orbit.  Who has a long haul?

SpaceX has 53 in good orbits and another really close, and one more may get there.  They've already said 3 don't work and 2 more are being deorbited.

Ok, thanks for the correction.  I thought the two to be deorbited were from 550 km.  The point remains that SX has a demonstrated capability to launch more satellites than competitors.  And SX is buying their launches wholesale, not retail.  I don't think anyone has a better cost/satellite.  Not even if they bought their launch services from SpaceX.

[AC in NC]

I don’t understand the replacement strategy for Starlink,  assuming planes of 66 sats. I don’t see how SpaceX can insert the required 10 or so satellites necessary to go from the current 56 working sats to 66.

They could launch 10.

Or they could launch 1.

My question is about what they will really do to replace a small number of satellites in one plane, not what is theoretically possible.

Is it not the case that your dissonance about replacing a small number of satellites comes from the artificial and perhaps unjustified presumption that small plane augmentations will be performed in the context of a 60 satellite tranche?

Launch costs are cheap.  10 isn't theoretically possible.  It's totally possible.  ISTM.

[mulp]

Reading an article on my news feed about SpaceX needing a longer fairing for the disputed dod contract, how many more starlink pizza boxes could be on one flight with a 50% longer fairing?

Ie, would starlink pay for the longer fairing by reducing the number of launches by 10 out of hundreds?, 100 out of thousands???

Also, does enough S2 fuel remain to do a plane change? The certainly was no need to change planes for the first launch.

Bunch of tradeoffs on how much fuel S1 expends/where it lands, how much fuel S2 has to maneuver, how many pancakes in the stack.

[speedevil]

Launch costs are cheap.  10 isn't theoretically possible.  It's totally possible.  ISTM.

This assumes that radical plane changes from the satellites themselves is not possible.
For Elons tweets about repurposing starlink as an interplanetary probe to make any sense, where he mentions adding a 250kg tank of propellant - the possible delta-v per day needs to be quite high, or you can't easily use that propellant before you get beyond where the sun dims. This lets you do radical plane changes quite fast. However, the starlink sats have not exhibited close to the ~100m/s/day that would be naively calculated from ISP and power.

Completely nominal starlink sats that were designed to the original spec would let the satellites do moderately significant plane changes  relying on precession.
Moving up 1000km, over 550km nominal gets you 2+ degrees/day, or one plane over in under a month.
This leaves plenty of room for any extended schedule for filling holes and adding extra ones without launches of 10.

[envy887]

Reading an article on my news feed about SpaceX needing a longer fairing for the disputed dod contract, how many more starlink pizza boxes could be on one flight with a 50% longer fairing?

Ie, would starlink pay for the longer fairing by reducing the number of launches by 10 out of hundreds?, 100 out of thousands???

Also, does enough S2 fuel remain to do a plane change? The certainly was no need to change planes for the first launch.

Bunch of tradeoffs on how much fuel S1 expends/where it lands, how much fuel S2 has to maneuver, how many pancakes in the stack.

The Starlink-1 mission was already a very hot reentry. They might be able to trade some upper stage margin to recover the booster, but the current design seems to nearly max out F9's payload mass capability to that orbit so a larger fairing probably wouldn't help much on F9.

[gongora]

General Starlink discussion should go in the Starlink thread, not this mission thread.

[Danderman]

I have the impression that SpaceX wants each satellite to have a more or less equal propellant load when reaching operational altitude. Using differential precession to change planes would mean that the satellites arriving at the next plane would have different prop loads. That causes operational headaches down the road.

Remember that satellites remaining at 440 km altitude to change planes are going to have to fight drag for extended periods.

[speedevil]

I have the impression that SpaceX wants each satellite to have a more or less equal propellant load when reaching operational altitude. Using differential precession to change planes would mean that the satellites arriving at the next plane would have different prop loads. That causes operational headaches down the road.

Remember that satellites remaining at 440 km altitude to change planes are going to have to fight drag for extended periods.

The drag of a feathered solar panel would be considerably less than one that is sun-tracking.

[Joffan]

I have the impression that SpaceX wants each satellite to have a more or less equal propellant load when reaching operational altitude. Using differential precession to change planes would mean that the satellites arriving at the next plane would have different prop loads. That causes operational headaches down the road.

Remember that satellites remaining at 440 km altitude to change planes are going to have to fight drag for extended periods.

SpaceX looking to have equal propellant on satellites would be a surprising requirement, at odds with typical SpaceX operating philosophy. They usually want the equipment to be good enough for the purpose, not seeking some beautiful perfection or trying to squeeze every drop of performance out of the machines regardless of cost or convenience. In any case they will definitely be dealing with orbits of satellites that have a varying prop loads over the course of time, so this wouldn't be a typical operating setup.

[Jcc]

I don’t think the Starlink design is going to remain static, there will be tweaks to the components, size weight and balance. In the end they could have a design that easily fits 66 in a reusable F9 fairing.

I don’t consider the test deployment as attempting to complete a plane (unsuccessfully) for final deployment. It’s just a test, they may use some of the sats to develop initial operating capability, but they will all be replaced as soon as possible with updated designs.

[Danderman]

From a practical operating standpoint, it would be desirable for satellites in the shame plane to have similar propulsion requirements. Otherwise, there would be a constant process of satellites exhausting their working propellant, and needing to be replaced.

If there are going to be tweaks to Starlink design, I suspect it will be to allow 66 sats plus some spares to be flown on one F9.

[Danderman]

Even with a feathered solar panel, drag at 440 km altitude is significantly higher than at the operational altitude.

[speedevil]

Even with a feathered solar panel, drag at 440 km altitude is significantly higher than at the operational altitude.

Not if that operational altitude is 340km, for which they are also designed.