SpaceX F9 : Starlink 5 (v1.0 L4) : Feb. 17, 2020 : Master Thread

[Captain Crutch]

Are we reaching the conclusion that something frozen caused a grid fin control failure leading to an aborted safe ocean landing?

That is, it failed as designed?

Not at all. It splashed down close to the drone ship, you could see spray from the landing. A grid fin failure would mean it would land nowhere near the ship. Imo.

Another possibility is that the landing barge was in the wrong location.

I agree, the droneship could have been a bit too far to one side and the Falcon was unable to move that much, or possibly a sticky throttle valve but on one of the droneship thrusters causing it to have trouble keeping position. Obviously, this is all speculation. However, I will add that a grid fin failure could also be the culprit if it was late enough in the flight, and was the 'pitch/yaw?' fins instead of the 'roll' fins like last time. IIRC there's one set of fins for roll, and one set for pitch or yaw (whichever one it's considered in rocketry). Once again this is purely speculation, I doubt SpaceX even knows for sure yet...

[Vettedrmr]

You make a good point. But it hit so close to the barge, I can't believe it is a grid fin failure either. The booster may have have detected some issue so that it didn't do the final maneuver to target the barge. <snip>

Whatever happened, I'm sure it will be interesting.

Yeah, I don't buy the grid fin failure either.  This is one where we literally have no info other than it apparently landed more or less at its ballistic target (and that's a guess), that it was close to 0 velocity touchdown, and that the booster survived.  I don't know how they'll salvage it, but it's going to be interesting to see.

Have a good one,
Mike

[Citabria]

As long as we're speculating, it looked to me that, just before landing burn, the drone ship was pitching and rolling a lot. Will they abort a landing if ship stability goes out of bounds?

[kevinof]

As long as we're speculating, it looked to me that, just before landing burn, the drone ship was pitching and rolling a lot. Will they abort a landing if ship stability goes out of bounds?

Nope. There is no feedback from the drone ship to the stage

[ulm_atms]

As long as we're speculating, it looked to me that, just before landing burn, the drone ship was pitching and rolling a lot. Will they abort a landing if ship stability goes out of bounds?

Nope. There is no feedback from the drone ship to the stage

Add to that....that was MUCH calmer water then other successful landings by a good amount.

[photonic]

[...]
 However, I will add that a grid fin failure could also be the culprit if it was late enough in the flight, and was the 'pitch/yaw?' fins instead of the 'roll' fins like last time. IIRC there's one set of fins for roll, and one set for pitch or yaw (whichever one it's considered in rocketry). Once again this is purely speculation, I doubt SpaceX even knows for sure yet...

All 4 grid fins are identical and spaced 90 degrees apart. You can correct for pitch, yaw or roll by using them in different combinations. To correct for pitch, you would rotate 2 opposite grid fins in the same direction along one axis (so seen from inside the rocket, you rotate 1 CW, the other CCW), to correct yaw you do the same for the other two grid fins, and to correct roll you rotate all 4 in the same direction (e.g. all CCW as seen from inside the rocket), which creates a cork-screw effect. The control system needs to corrects all 3 at the same time, so you use a simple 'driving matrix' to convert from pitch/yaw/roll to fin1/fin2/fin3/fin4.

[Mandella]

[...]
 However, I will add that a grid fin failure could also be the culprit if it was late enough in the flight, and was the 'pitch/yaw?' fins instead of the 'roll' fins like last time. IIRC there's one set of fins for roll, and one set for pitch or yaw (whichever one it's considered in rocketry). Once again this is purely speculation, I doubt SpaceX even knows for sure yet...

All 4 grid fins are identical and spaced 90 degrees apart. You can correct for pitch, yaw or roll by using them in different combinations. To correct for pitch, you would rotate 2 opposite grid fins in the same direction along one axis (so seen from inside the rocket, you rotate 1 CW, the other CCW), to correct yaw you do the same for the other two grid fins, and to correct roll you rotate all 4 in the same direction (e.g. all CCW as seen from inside the rocket), which creates a cork-screw effect. The control system needs to corrects all 3 at the same time, so you use a simple 'driving matrix' to convert from pitch/yaw/roll to fin1/fin2/fin3/fin4.

Although this is true, if I am remembering correctly that is not how they are mechanically linked. Apparently both opposite pairs are slaved together but one pair reversed, effectively making it so that one pair is for pitch and the other for roll. To yaw the Falcon has to roll to the correct orientation.

Again, working from memory, but apparently I saw the same explanation as Captain Crutch...

[zubenelgenubi]

I think the new flight plan and the missed landing are evidence the sats are getting heavier. launching 59 or 54 is apparently not an option.

I'd wager satellite weight had exactly zero to do with the missed landing.

I'm going to wager you are wrong. I think they gave the satellites a little extra boost for the new orbital insertion, using just a little more fuel. My guess is, they ran out of fuel on the landing burn. I'm sure we will know something soon.

Satellite mass (weight is a force) does not equal fuel mass or a launch vehicle change in velocity (speed and direction).

[PaulKerrisdale]

Just after the entry burn, around T+00:07:28, someone says "Stage 1 LOS expected". What does LOS mean in this context?

If it stands for "Loss Of Stage" then they were expecting to miss the landing just after the entry burn finished. It does seem to make the main commentator hesitate a little before she talks about the landing burn.

It could also mean "Loss Of Signal" referring to the downlink though, or lots of other things.

[zubenelgenubi]

Just after the entry burn, around T+00:07:28, someone says "Stage 1 LOS expected". What does LOS mean in this context?
<snip>
It could also mean "Loss Of Signal" referring to the downlink though, or lots of other things.

Your final guess is correct.  LOS in this context = Loss Of Signal

Welcome aboard!

[Mandella]

Normally Elon would post some update or reason for missed landing, but not now. So we can assume that there were no failures at booster, they just pushed the envelope and risk didn't pay off this time.

"...heaviest payload we fly so putting them directly into this orbit requires more vehicle performance and makes recovery more challenging..." -Jessica Anderson

I just rewatched to make sure, and while Anderson did use the phrase "directly into this orbit," in context it seems clear that she is talking about the earlier launch profile where they had to perform a circularization burn. By implication this launch was supposed to make recovery easier.

Now of course the reality is that perhaps the steeper re-entry did uncover a wear state they were not anticipating, but nonetheless they were trying to be easier on the booster, not harder.

[HVM]

Ok, checking OneSpeed's telemetry graph, staging happened at lower speed -> easier reentry for
L4. So you're correct.

And from Scott Manley's YouTube comment (I didn't see posted this before here):
"Update: I have heard from multiple sources confirmation that the fairing were not recovered, and that the booster has broken in half after falling over, so we're not sure what will ultimately be recovered."

_{Also I miss update only threads...}

[PaulKerrisdale]

Just after the entry burn, around T+00:07:28, someone says "Stage 1 LOS expected". What does LOS mean in this context?
<snip>
It could also mean "Loss Of Signal" referring to the downlink though, or lots of other things.

Your final guess is correct.  LOS in this context = Loss Of Signal

Welcome aboard!

Thanks!
So the loss of the downlink signal at that point wasn't unexpected, which could be for a number of different reasons.

[ChrisC]

From three weeks ago in the Starlink F3 thread:

This mission's thread was never split between updates and discussion. Is that a new thing, or just an oversight?

It is a new thing we're trying for the Starlink launches.  The threads aren't quite as long as they used to be, and the Starlink launches will be very frequest and very similar.  It's basically how the forum works outside of the SpaceX section.

A Starlink Master Updates thread is a possibility.  The Starlink threads in the SpaceX General section are a work in progress right now.  All of the main Starlink threads should be listed in the Starlink Index thread.

As a reminder for the Mission section, the SpaceX Manifest thread kinda serves as an index.  The first two posts in the thread have links to a Discussion/General/Master thread for each mission.  The top post has recent and future flights, the second post has older flights.  If there is an Update thread for a mission it will be linked in the top post of the Discussion thread (at least for the last few years).  The third and fourth posts in the manifest thread are also maintained with additional information.

Given the chatter in this thread, generally resulting from the landing failure, I'd like to respectfully suggest that we resume splitting these threads into Updates vs Discussion

But I understand mine may be a minority opinion.  Carry on!

[meberbs]

Although this is true, if I am remembering correctly that is not how they are mechanically linked. Apparently both opposite pairs are slaved together but one pair reversed, effectively making it so that one pair is for pitch and the other for roll. To yaw the Falcon has to roll to the correct orientation.

Again, working from memory, but apparently I saw the same explanation as Captain Crutch...

I have never heard of such a thing, and it would make very little sense. Pitch and yaw axes as defined here are basically symmetric, and you would generally want equal control in both. I have seen no evidence of shared axles in the interstage, which while it would eliminate 2 actuators, the remaining actuators would need double the power, and would otherwise add significant complexity, and serve no purpose other than to reduce functionality by removing an axis of control authority.

[CorvusCorax]

The unified thread idea was under the impression of expected rapid launch cadence and boring routine.

Unfortunately (or fortunately for those who like stuff to stay "interesting") booster landings on barges are not as boring routine yet as we'd all assumed after 50 49 + 2 splashdowns of them.

Since this is likely a rare occurence, we could make a new thread about the booster-splashdown+recovery(maybe)+causes (in the hope that we will ever get to know these), move all the post splashdown posts there and keep this one clean for the next launch.

This might be a good precedent on what to do if stuff on a routine launch doesn't go as planned.


To add to the speculation - a dead easy cause for either barge or rocket not being where it's supposed to be would be a GPS malfunction.

GPS can be prone to outages and drift, and in this case you rely on two autonomous vessels to hold respectively reach the correct position in space independently from each other. If something was wrong with GPS sats, signal paths, receivers or modules on either vehicle could lead to this with no hardware issue whatsoever.

Not saying that is it, but without knowing any other suspect, this is among the most obvious plausibilities.

[HVM]

Although this is true, if I am remembering correctly that is not how they are mechanically linked. Apparently both opposite pairs are slaved together but one pair reversed, effectively making it so that one pair is for pitch and the other for roll. To yaw the Falcon has to roll to the correct orientation.

Again, working from memory, but apparently I saw the same explanation as Captain Crutch...

I have never heard of such a thing, and it would make very little sense. Pitch and yaw axes as defined here are basically symmetric, and you would generally want equal control in both. I have seen no evidence of shared axles in the interstage, which while it would eliminate 2 actuators, the remaining actuators would need double the power, and would otherwise add significant complexity, and serve no purpose other than to reduce functionality by removing an axis of control authority.

4 actuators, no linking and it would not make sense.

[FutureSpaceTourist]

https://twitter.com/spacexfleet/status/1229875301179588608

Ms. Tree, Ms. Chief and GO Quest were all inching north up until 11:30am EST today. At this time, GO Quest peeled away and is now heading west at speed.

The fairing catchers are still circling around their 11:30 position some 4 hours later.

Tug Hawk and OCISLY are halfway home.

Not sure what to make of it, has the booster sunk and they’re watching for debris?

[AndrewRG10]

https://twitter.com/spacexfleet/status/1229875301179588608

Ms. Tree, Ms. Chief and GO Quest were all inching north up until 11:30am EST today. At this time, GO Quest peeled away and is now heading west at speed.

The fairing catchers are still circling around their 11:30 position some 4 hours later.

Tug Hawk and OCISLY are halfway home.

Not sure what to make of it, has the booster sunk and they’re watching for debris?

If it sunk then they're wasting money chasing worthless scrap. If it's compromised its structure in any way, the parts that will sink first are grid fins. The only thing they can salvage are grid fins. They're following the booster keeping marine traffic away while they figure out a way to get the grid fins off or tow it somewhere to take them off.

[whitelancer64]

The unified thread idea was under the impression of expected rapid launch cadence and boring routine.

Unfortunately (or fortunately for those who like stuff to stay "interesting") booster landings on barges are not as boring routine yet as we'd all assumed after 50 49 + 2 splashdowns of them.

Since this is likely a rare occurence, we could make a new thread about the booster-splashdown+recovery(maybe)+causes (in the hope that we will ever get to know these), move all the post splashdown posts there and keep this one clean for the next launch.

This might be a good precedent on what to do if stuff on a routine launch doesn't go as planned.


To add to the speculation - a dead easy cause for either barge or rocket not being where it's supposed to be would be a GPS malfunction.

GPS can be prone to outages and drift, and in this case you rely on two autonomous vessels to hold respectively reach the correct position in space independently from each other. If something was wrong with GPS sats, signal paths, receivers or modules on either vehicle could lead to this with no hardware issue whatsoever.

Not saying that is it, but without knowing any other suspect, this is among the most obvious plausibilities.

My understanding is that terminal guidance is done with radar during the landing burn. Since the splashdown was very near the ASDS, if GPS location was the issue for either the booster or the ASDS, the radar should still have been able to pick up the ASDS and the booster should have been able to correct to the ASDS's true position.

Unless, of course, my understanding is not correct.