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

[ArbitraryConstant]

I have no idea if any of the satellites have unfixable problems but if any do they might be useful if brought down to a much lower orbit and their engines run until propellant exhaustion just to get some data on propulsion performance. It could expose problems soon enough to fix them for the next batch.

[Barley]

Maybe that will be SOP in the future, perform all checkout in the lower orbit and then only raise when all issues are resolved.

If you leave them in the low orbit for too long they will precess out of plane.

Possibly the low satellites are deliberately testing that to help plan future deployments, or because there is some other test that requires multiple planes.

[ArbitraryConstant]

Maybe that will be SOP in the future, perform all checkout in the lower orbit and then only raise when all issues are resolved.

If you leave them in the low orbit for too long they will precess out of plane.

Possibly the low satellites are deliberately testing that to help plan future deployments, or because there is some other test that requires multiple planes.

If they plan to do checkout in a lower orbit presumably they would launch them into a slightly out of phase orbit such that they'll be right on the money after the checkout period.

[Barley]

Maybe that will be SOP in the future, perform all checkout in the lower orbit and then only raise when all issues are resolved.

If you leave them in the low orbit for too long they will precess out of plane.

Possibly the low satellites are deliberately testing that to help plan future deployments, or because there is some other test that requires multiple planes.

If they plan to do checkout in a lower orbit presumably they would launch them into a slightly out of phase orbit such that they'll be right on the money after the checkout period.

Yes, you can schedule time for the check out.  But you can't take extra time to resolve issues.  If a problem satellite doesn't start raising orbit at the same time as its peers it won't be in the intended plane unless further steps are taken.

With a large constellation you may not care which plane a particular satellite ends up in so you could wait a month or so till it reaches the next plane.

[envy887]

Maybe that will be SOP in the future, perform all checkout in the lower orbit and then only raise when all issues are resolved.

If you leave them in the low orbit for too long they will precess out of plane.

Possibly the low satellites are deliberately testing that to help plan future deployments, or because there is some other test that requires multiple planes.

If they plan to do checkout in a lower orbit presumably they would launch them into a slightly out of phase orbit such that they'll be right on the money after the checkout period.

Yes, you can schedule time for the check out.  But you can't take extra time to resolve issues.  If a problem satellite doesn't start raising orbit at the same time as its peers it won't be in the intended plane unless further steps are taken.

With a large constellation you may not care which plane a particular satellite ends up in so you could wait a month or so till it reaches the next plane.

Or just raise it to a higher orbit to reverse the direction of relative precession.

[Pete]

Moreover, the data we do have on potential sat misbehaving is sketchy, and preliminary.

Have you changed your mind yet?

Quite the gutsy move, calling Spacex's Gwynne Shotwell's report "sketchy, and preliminary"

Maybe take a look at this posting in the Updates thread
https://forum.nasaspaceflight.com/index.php?topic=48135.msg1952592#msg1952592

[CJ]

If I'm reading the charts in 4353's post in the updates thread
https://forum.nasaspaceflight.com/index.php?topic=48135.msg1952592#msg1952592
correctly, then it looks to me like 4 of the sats are behaving quite differently than the other 56 (which are raising their orbit). 2 seem to have not changed their orbital apogee and perigee much at all, while two seem to be lowering theirs.

My guess is that the two lowering their orbital altitude will continue to do so (if so, they are being disposed of) whole the other two either have no propulsion, or are not written off yet.

I'd wondered why the sightings of the Starlink train had a few sats way out in front. This new info fits; the leaders are the ones braking into lower orbits, followed by the two that don't seem to be under acceleration, and bringing up the rear is the main train that is under acceleration.

[Robotbeat]

Could be difference in solar array deployment state or orientation.

[Danderman]

Any indication if any of these sats are moving into different planes?

[strawwalker]

Any indication if any of these sats are moving into different planes?

As of the latest update from Space-Track the spread in RAAN was about 0.64 degrees, the low four drifting up to half a degree west of the average.

[speedevil]

Now some above 500 km:

If we take a crude average, it seems 5km raising per day is approximately correct to within +-20% or so.

This is of the close order of 3m/s/day, or 33um/s^2.
If this was a continual thrust on a 1600s ion engine, the approximate power would be of the order of 400W.
This is very under the 3kW estimates that have been made.
Either those are very wrong, or this cluster is intentionally dawdling while gaining experience, as it is intended to be used in conjunction with more launches before major testing occurs.

[EspenU]

This is of the close order of 3m/s/day, or 33um/s^2.
If this was a continual thrust on a 1600s ion engine, the approximate power would be of the order of 400W.
This is very under the 3kW estimates that have been made.
Either those are very wrong, or this cluster is intentionally dawdling while gaining experience, as it is intended to be used in conjunction with more launches before major testing occurs.

3kW is the total output of the solar array, but do we know that all of it is available for the thruster?
During operation they only need to keep the satellites in the correct orbit, so it might not make sense to engineer them so far above what will be required during operation. The downside is just a little more time spent on getting to the correct orbit.

[speedevil]

This is of the close order of 3m/s/day, or 33um/s^2.
If this was a continual thrust on a 1600s ion engine, the approximate power would be of the order of 400W.
This is very under the 3kW estimates that have been made.
Either those are very wrong, or this cluster is intentionally dawdling while gaining experience, as it is intended to be used in conjunction with more launches before major testing occurs.

3kW is the total output of the solar array, but do we know that all of it is available for the thruster?
During operation they only need to keep the satellites in the correct orbit, so it might not make sense to engineer them so far above what will be required during operation. The downside is just a little more time spent on getting to the correct orbit.

The assumption that makes 3kW seem plausible is that Elon was not talking about a massively different bus with ten times the thrusters when he tweeted mentioning them as probes.
3kW is the average output of the array - it peaks at ~6kW - for 20% and 30m^2.

Mentioning starlink in the context of interplanetary stuff, when it would be essentially useless with a 15um/s^2 acceleration does not seem to make a whole lot of sense.

It is possible that some of these assumptions are wrong, for example, he considers that sticking another ten thruster modules which cost ~$0 to construct on a probe to be 'trivial'.

[niwax]

Now some above 500 km:

If we take a crude average, it seems 5km raising per day is approximately correct to within +-20% or so.

This is of the close order of 3m/s/day, or 33um/s^2.
If this was a continual thrust on a 1600s ion engine, the approximate power would be of the order of 400W.
This is very under the 3kW estimates that have been made.
Either those are very wrong, or this cluster is intentionally dawdling while gaining experience, as it is intended to be used in conjunction with more launches before major testing occurs.

There was talk about them initiating a new burn every 90 minutes, so the increase isn't continuous. The straight lines in the chart are somewhat misleading.

[EspenU]

This is of the close order of 3m/s/day, or 33um/s^2.
If this was a continual thrust on a 1600s ion engine, the approximate power would be of the order of 400W.
This is very under the 3kW estimates that have been made.
Either those are very wrong, or this cluster is intentionally dawdling while gaining experience, as it is intended to be used in conjunction with more launches before major testing occurs.

3kW is the total output of the solar array, but do we know that all of it is available for the thruster?
During operation they only need to keep the satellites in the correct orbit, so it might not make sense to engineer them so far above what will be required during operation. The downside is just a little more time spent on getting to the correct orbit.

The assumption that makes 3kW seem plausible is that Elon was not talking about a massively different bus with ten times the thrusters when he tweeted mentioning them as probes.
3kW is the average output of the array - it peaks at ~6kW - for 20% and 30m^2.

Mentioning starlink in the context of interplanetary stuff, when it would be essentially useless with a 15um/s^2 acceleration does not seem to make a whole lot of sense.

It is possible that some of these assumptions are wrong, for example, he considers that sticking another ten thruster modules which cost ~$0 to construct on a probe to be 'trivial'.

True, but that would as you say involve more thrusters. If each thruster is limited in max power draw then adding more of them would of course bring the total closer to 3kW. However, I don't know very much about ion thruster design so I don't know if it makes sense that they would be power limited in this way.

[speedevil]

Now some above 500 km:

If we take a crude average, it seems 5km raising per day is approximately correct to within +-20% or so.

This is of the close order of 3m/s/day, or 33um/s^2.
If this was a continual thrust on a 1600s ion engine, the approximate power would be of the order of 400W.
This is very under the 3kW estimates that have been made.
Either those are very wrong, or this cluster is intentionally dawdling while gaining experience, as it is intended to be used in conjunction with more launches before major testing occurs.

There was talk about them initiating a new burn every 90 minutes, so the increase isn't continuous. The straight lines in the chart are somewhat misleading.

Are you aware of any source of more frequent data? I've not found one.
And yes, there are good reasons in principle that could be invoked other than 'dawdling' for slow raising.

[ThatOldJanxSpirit]

Now some above 500 km:

If we take a crude average, it seems 5km raising per day is approximately correct to within +-20% or so.

This is of the close order of 3m/s/day, or 33um/s^2.
If this was a continual thrust on a 1600s ion engine, the approximate power would be of the order of 400W.
This is very under the 3kW estimates that have been made.
Either those are very wrong, or this cluster is intentionally dawdling while gaining experience, as it is intended to be used in conjunction with more launches before major testing occurs.

Half an orbit in darkness, plus IIRC Elon has said the arrays are not tracking the sun yet??

[ArbitraryConstant]

Seems likely they are charging batteries and then pulsing the engines to raise the orbit. That would let them avoid sunlight availability dictating the orbit raising.

[Pete]

]

If we take a crude average, it seems 5km raising per day is approximately correct to within +-20% or so.

This is of the close order of 3m/s/day, or 33um/s^2.
If this was a continual thrust on a 1600s ion engine, the approximate power would be of the order of 400W.

May we please know how you calculate this 400W figure?
What are your assumptions for thruster ionisation power losses, power conversion efficiencies, etc?
On what model of thruster's specs did you base this calculation?

[Comga]

Now some above 500 km:

If we take a crude average, it seems 5km raising per day is approximately correct to within +-20% or so.

This is of the close order of 3m/s/day, or 33um/s^2.
If this was a continual thrust on a 1600s ion engine, the approximate power would be of the order of 400W.
This is very under the 3kW estimates that have been made.
Either those are very wrong, or this cluster is intentionally dawdling while gaining experience, as it is intended to be used in conjunction with more launches before major testing occurs.

Pete:  It's obvious how speedevil does this calculation.  You can look it up.

Remember, Musk also owns Tesla and Solar City, with extensive battery and solar photovoltaic technology.
They will sell you a wall pack to store extra power generated by solar panels for later use
It might be that the power of the thrusters is limited, to keep them small, but run continuously using power stored in batteries.
Musk said that the Starlink satellites aren't tracking the sun, but is that "yet" or always?
It doesn't look like they rotate, so tracking would involve spinning and tipping the satellites from the local vertical.
If the panels and batteries are big enough they don't need to maximize power by tracking.
With such a big solar panel, it makes sense to keep it "feathered", and present the narrow edge to the exosphere to minimize drag.