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

[Pete]

This launch's MECO is early and at a lower speed (7840 km/h vs 8078 km/s), so they're taking it easy with this booster, the landing issue is not caused by them pushing it too hard.

YES, MECO is at 240m/s slower.
It also occurs at more than 6km higher altitude, due to the more lofted trajectory.
*not* taking it easy on this booster, merely different trajectory.

[aero]

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?

[Mandella]

This launch's MECO is early and at a lower speed (7840 km/h vs 8078 km/s), so they're taking it easy with this booster, the landing issue is not caused by them pushing it too hard.

YES, MECO is at 240m/s slower.
It also occurs at more than 6km higher altitude, due to the more lofted trajectory.
*not* taking it easy on this booster, merely different trajectory.

Perhaps, but in the pre-launch commentary it was specifically mentioned that the older trajectory was very hard on the boosters, and thus one reason to change it was to ease the wear and tear on them.

IIRC.

[Lars-J]

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

Who is this "we"? No, a reasonable observer does not jump to that conclusion. Frozen ice falling of the booster is not unusual...

[Pete]

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 nearly.
That is one of a host of possibilities that might fit the facts. Really, all we have at this time are a couple of data points:
The launch happened, there was some visible ice/stuff on the S1, the landing did not complete but came very close apparently 'landing' in the failsafe destination which is just off the landing pad.

For any more detail, including actual cause and chain of events, we will just have to sit back and await info from SpaceX. They have a very good track record of telling us what actually happened.

[HVM]

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

[Stan-1967]

This launch's MECO is early and at a lower speed (7840 km/h vs 8078 km/s), so they're taking it easy with this booster, the landing issue is not caused by them pushing it too hard.

YES, MECO is at 240m/s slower.
It also occurs at more than 6km higher altitude, due to the more lofted trajectory.
*not* taking it easy on this booster, merely different trajectory.

If my BOE calculation is right, that extra 6km altitude is around 340m/s additional velocity downward, so velocity at re-entry was comparable & likely higher.  This makes me wonder what stresses the booster the most?
1. moving through it's own exhaust plume on the landing burn & late part of re-entry burn
2. plasma heating on re-entry
3. dynamic pressure at Max-Q

How does a more lofted trajectory impact these flight regimes?

[JamesH65]

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.

[AndrewRG10]

This launch's MECO is early and at a lower speed (7840 km/h vs 8078 km/s), so they're taking it easy with this booster, the landing issue is not caused by them pushing it too hard.

YES, MECO is at 240m/s slower.
It also occurs at more than 6km higher altitude, due to the more lofted trajectory.
*not* taking it easy on this booster, merely different trajectory.

If my BOE calculation is right, that extra 6km altitude is around 340m/s additional velocity downward, so velocity at re-entry was comparable & likely higher.  This makes me wonder what stresses the booster the most?
1. moving through it's own exhaust plume on the landing burn & late part of re-entry burn
2. plasma heating on re-entry
3. dynamic pressure at Max-Q

How does a more lofted trajectory impact these flight regimes?

Arabsat 6A survived re-entry of 9000km/h after entry burn. With entry burn this booster would be going in realms of 7500km/h. I'm struggling to see how entry would've hurt the booster.
I'd love to know but everyone including Musk seems to have gone offline about it. I'm kinda hoping NSF or other spaceflight news sites ask for comment on what exactly went wrong, and hopefully Elon releases video.

[FutureSpaceTourist]

https://twitter.com/spacexfleet/status/1229543005876559872

Fleet Update: Ms. Tree and Ms. Chief have traveled 90 km west and are now on-scene at the booster landing zone with support ship GO Quest.

Tug Hawk appears to possibly be leaving the area, presumably with Of Course I Still Love You.

https://twitter.com/spacexfleet/status/1229670734211014656

Ms. Tree, Ms. Chief and GO Quest are slowly moving north, presumably following the drifting booster.

Tug Hawk and OCISLY are well underway. They are completely clear of the area and en-route to Port Canaveral.

[OneSpeed]

Here is the Starlink 1.0 telemetry for flights 3 and 4. After the first 4 virtually identical launch profiles, it's nice to see some some variety.

1. As you can see from the altitude plots, flight 4 lofts the payload (and the second stage) to 216 kilometres at SECO, compared with 168 kilometres for the previous Starlink launches.

2. The extra loft is obtained by increasing the pitch of both the first stage from about T+90 seconds, and the second stage until around T+300s. You can see the divergence of the two velocity plots during this period.

3. You can also see correspondingly reduced acceleration in the flight 4 profile for the same period, i.e. increased gravity losses.

4. Both flights released their fairings at an altitude of 104 kilometres, flight 3 at T+207s, flight 4 at T+194s.

5. Despite jettisoning the fairings some 13 seconds earlier in the flight, the flight 4 S2 had to burn for an additional 6 seconds to achieve a comparable median altitude. This left insufficient propellant for an S2 de-orbit burn. It will be interesting to see how quickly the satellites can circularise their elliptical orbits.

Edit: changed kms to kilometres

[woods170]

One thing that people should keep in mind: SpaceX still expects that - even with booster landing "perfected" - a certain percentage of boosters will be lost during landing attempts. Margins for error are extremely small.

[CorvusCorax]

One thing that peeves me. Plural of km is km. Not kms,  kms would be SI unit for "kilo meter second" which might be relevant as a unit of spacetime but doesn't make sense in this context. It also makes it prone to confusion with "kilo meter per second" (km/s) as a unit of speed

1. As you can see from the altitude plots, flight 4 lofts the payload (and the second stage) to 216 kms at SECO

It's 1 kilo meter, 2 kilo meter, 3 kilo meter, 216 kilo meter.  If it ever were "kilo meters" then you'd also have to say "one kilo meters" because kilo means literally "thousand"

[Vettedrmr]

My guess is, they ran out of fuel on the landing burn. I'm sure we will know something soon.

You literally can't both run out of fuel AND make a soft landing.  And the fact that EM hasn't said anything (especially with a survived booster) implies to me that SpaceX doesn't know yet, either.

Going to be very interesting to see if they can salvage any/all of the booster.

Have a good one,
Mike

[LouScheffer]

My personal speculation (knowing only that it was close, but not quite) is that one of the grid fins got stuck in one position.  Assuming the opposite one is behaving normally, this would reduce the course correction capability by roughly half, and (depending on the position the grid fin got stuck in) change the center point of the dispersion as well.   Then the booster simply did not have the control authority needed to get to the center of the barge.

This seems plausible since recovery hardware is single-string, actuators could conceivably have wear from previous missions, and they don't seem to test grid fin actuators during countdown, unlike engine actuators.  But again, this is only a guess based on almost no data.  SpaceX will know.

[Captain Crutch]

Do we know if SpaceX is going to use their fleet of 3 ships with supposedly 2 more on the way to bring the booster home or are they basically just going to keep track of it until it becomes target practice for some new Air Force pilot? Furthermore, if they're going to recover it, how are they planning to do that? I would assume so since according to SpaceXFleetUpdates there may have been 2 tugs dispatched to the booster...

[alienmike]

My guess is, they ran out of fuel on the landing burn. I'm sure we will know something soon.

You literally can't both run out of fuel AND make a soft landing.  And the fact that EM hasn't said anything (especially with a survived booster) implies to me that SpaceX doesn't know yet, either.

Going to be very interesting to see if they can salvage any/all of the booster.

Have a good one,
Mike

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. I can only assume that it was coming in a little too fast, so it failed to divert to the barge. There could be lots of causes for this, so we will wait and see. SpaceX/Elon is usually pretty open about such failures. Whatever it is, they will learn from it and move on. I still think it has something to do with the new launch profile and that these launches are pushing the limits of the F9 due to the mass of the Starlink satellites. I also suspect that the mass of these satellites has increased slightly, as they iterate the design.

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

[jak Kennedy]

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.

[abaddon]

One thing that peeves me. Plural of km is km. Not kms,  kms would be SI unit for "kilo meter second" which might be relevant as a unit of spacetime but doesn't make sense in this context. It also makes it prone to confusion with "kilo meter per second" (km/s) as a unit of speed

1. As you can see from the altitude plots, flight 4 lofts the payload (and the second stage) to 216 kms at SECO

It's 1 kilo meter, 2 kilo meter, 3 kilo meter, 216 kilo meter.  If it ever were "kilo meters" then you'd also have to say "one kilo meters" because kilo means literally "thousand"

Reminds me of a very animated discussion at a pub after work with some mates about "math" versus "maths" in Guildford a few years ago...

[Alastor]

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.

They would have known that prior to landing.
It happened previously that one of the barge thrusters failed shortly before a launch, and they brought the barge back home and expended the booster (can't remember which one).
If the barge booster had failed minutes before the landing, you could imagine they might not have been able to change the plan and remove the barge enough, but then, they would have told on stream that due to a barge issue, they expected the booster to miss the barge.

So I don't think this scenario is realistic.

Generally, it's probably best not to speculate too much right now, since we have literally no indication of what has failed.
For all we know, the booster might have been fine if it had attempted the barge landing.
The fact that Elon hasn't said anything yet, means they probably don't know exactly yet either.