SpaceX F9 : Starlink v1.0 L19 : CCSFS SLC-40 : 15/16 Feb 2021 (0359 UTC)

[OneSpeed]

Both L18 and L19 execute a g-limiting throttle reduction about 10 s prior to MECO.
I assume the spike in 18's acceleration plot immediately prior to that is an artifact of noisy telemetry.
But what do you make of 19's ~ 1.6X  greater reduction in acceleration?

The point of the boost phase is to get the second stage to a particular velocity and altitude at a particular time. The point of the terminal guidance phase is not just to limit gs, but also to converge on the desired boost parameters. If you examine the telemetry, you can see that both L18 and L19 reach the same altitude and velocity at the same time, so both boost phases went to plan.

Although there are always small differences in engine performance, I suspect the main reason L19 had to throttle down further to meet its goals was because it had a larger tailwind from the jet stream than L18. I don't have the wind speeds aloft for the days in question, but speeds as high as 100m/s have been recorded. Perhaps someone could look those numbers up?

Is this throttle reduction done by shutting down the center engine?
Have we ever actually seen this in video, or are the plumes too diffuse by then?

The throttle down needs to be continuously variable to precisely match the effect of the jet stream, so although Falcon Heavy sometimes shuts down individual engines prior to terminal guidance, as did L5 (unexpectedly), I've only ever seen F9 throttle down for terminal guidance, as it does for MaxQ.

[AndrewRG10]

Slightly off-topic but this flight hit a cool milestone. This is the tenth failed landing on a droneship.
A bit more off-topic, three out of the four Block 5 boosters which flew CRS missions have now crashed. So keep B1058 close while she's still here

[FutureSpaceTourist]

[eeergo]

Deorbit burn over the Western Mediterranean was observed from two meteor-hunting observatories in Spain:

https://twitter.com/Marco_Langbroek/status/1362036254813151232

[wannamoonbase]

Those birds were my tell tale sign that the booster was lost.  They were not concerned about a darn thing.

[FutureSpaceTourist]

https://twitter.com/kyle_m_photo/status/1362124675149688833

Ms. Tree's fairing half is damaged with a fairly big crack in the side. #SpaceXFleet #SpaceX

https://twitter.com/kyle_m_photo/status/1362125942651518980

Ms. Tree has spun around and there is a lot more damage visible now. #SpaceXFleet #SpaceX

[FutureSpaceTourist]

twitter.com/nasaspaceflight/status/1362123678041993220

They didn't get the booster back, but there's a few million dollars worth of fairing recovered. Both fairing catchers back into Port Canaveral at the same time!

NSF Fleetcam: youtube.com/watch?v=gnt2wZ…

https://twitter.com/nasaspaceflight/status/1362123961283264522

Active side looks intact. Passive side looks like it'll need buffing out (won't be reused).

[FutureSpaceTourist]

https://twitter.com/kyle_m_photo/status/1362132185336143881

Ms. Tree's damaged fairing half has been lifted off and onto the dock. #SpaceXFleet #SpaceX

[hektor]

My paranoid self has always a question in such a case.

What prevents another space power, let us call it Freedonia, to send a submarine, retrieve the avionics units of the F9 and try to decipher the flight software to improve Freedonian rockets?

[darkenfast]

My paranoid self has always a question in such a case.

What prevents another space power, let us call it Freedonia, to send a submarine, retrieve the avionics units of the F9 and try to decipher the flight software to improve Freedonian rockets?

I'm not quite sure where the edge of the continental shelf is in relation to the impact point, but the depth in that area ranges from about 200m to about 1000m meters.  There is only one candidate that I know of that currently operates nuclear-powered submarines that have the capability to deploy smaller deep-diving submersibles for "sneaky" operations.  The Atlantic has been wired for sound for decades. The odds of pulling something like that off without being caught at it are very, very slim. For one thing, how do you find the pieces, evaluate them and recover them, without making any noise?

[gaballard]

My paranoid self has always a question in such a case.

What prevents another space power, let us call it Freedonia, to send a submarine, retrieve the avionics units of the F9 and try to decipher the flight software to improve Freedonian rockets?

They'd probably save more time and money Googling various interviews and talks the SpaceX software team has done and reverse engineering from there. They've shared a lot of good information on the broad strokes, e.g. what algorithms they use for things like avionics redundancy and landings, what languages/platforms they use, etc.

[Comga]

https://twitter.com/kyle_m_photo/status/1362132185336143881

Ms. Tree's damaged fairing half has been lifted off and onto the dock. #SpaceXFleet #SpaceX

And this damaged fairing half appears to be in the net, as if it was caught on the fly.
It would be ironic if SpaceX’s method evolved from trying to catch the descending fairings to retrieving them from the water as a preferred method.

[edkyle99]

Has anyone noticed/discussed the fact that 1059 flew three return-to-launch-site missions?  That may be more than any other booster.  Life leader 1051, for example, has only flown one RTLS mission.  Those return flights involve a long boost-back burn that the down-range landings do not require.  So 1059 would probably have accumulated more firing time for its recovery engines than any other booster with its number of flights.

 - Ed Kyle

[ZachS09]

https://twitter.com/kyle_m_photo/status/1362132185336143881

Ms. Tree's damaged fairing half has been lifted off and onto the dock. #SpaceXFleet #SpaceX

And this damaged fairing half appears to be in the net, as if it was caught on the fly.
It would be ironic if SpaceX’s method evolved from trying to catch the descending fairings to retrieving them from the water as a preferred method.

Cross-posting from SpaceX Reusability’s fairing reuse thread:

Has SpaceX given up on catching the fairings in Ms. Chief and Ms. Tree's nets?

Per https://www.elonx.net/fairing-recovery-attempts/, there hasn't been that many catch attempts lately.

I don't think they've given up on it. They've recently been testing the nets in port, for example. But lately there simply haven't been many opportunities for catch attempts. Seems to me SpaceX only attempts to catch fairings when:

1) Both Ms. Chief and Ms. Tree are present
2) The weather is very good (possibly because a failed catch attempt increases the chance the fairing will get damaged)
3) The ships aren't needed for two missions in quick succession (without going to port in between them)

And in the past few months, these "requirements" have rarely been met for various reasons. For example, after Starlink v1-14, both Ms. Tree and Ms. Chief were damaged and needed repairs and maintenance. Ms. Tree was out of service for two months, so Ms. Chief had to deployed either on her own or with a non-catcher ship.

After Ms. Tree was repaired, the weather has been mostly bad. And in those few cases where the weather might have been fine, the ships were deployed for two missions at once. And from what I understand, once either ship catches a fairing in the net, it cannot scoop up another half from the water. So if you need to recover four fairing halves from two missions with only two ships, they all need to be recovered from the water (unless the ships have time to unload in port in between the two launches).

In the last launch, Elon tweeted the caught one of the fairing halves.  The primary one with the controls.  Don't know about the other one.  Sometimes they fish them out of the sea. 

The fairing Elon was talking about was recovered from the water. SpaceX said in the webcast that they weren't attempting to catch them in the nets on that mission.

[spacenut]

Does SpaceX still do a static fire before every launch to check out the engines? 

[skater]

Has anyone noticed/discussed the fact that 1059 flew three return-to-launch-site missions?  That may be more than any other booster.  Life leader 1051, for example, has only flown one RTLS mission.  Those return flights involve a long boost-back burn that the down-range landings do not require.  So 1059 would probably have accumulated more firing time for its recovery engines than any other booster with its number of flights.

 - Ed Kyle

I would also assume it faced harsher reentry aerothermal conditions?

[ChrisC]

Does SpaceX still do a static fire before every launch to check out the engines? 

Let's keep this thread focused on the L19 mission.  Fortunately, your question is discussed in glorious detail here: https://forum.nasaspaceflight.com/index.php?topic=51340.0

[leetdan]

And this damaged fairing half appears to be in the net, as if it was caught on the fly.
It would be ironic if SpaceX’s method evolved from trying to catch the descending fairings to retrieving them from the water as a preferred method.

Incorrect.  The 'catch net' is much larger, reaching all the way from tip to tip of the four booms.  This is the much smaller 'scoop net' that is used for water recoveries.  A midair catch was not attempted - whenever it has in the past, the 'catch net' will be rigged and visible when the ship leaves port.

[kdhilliard]

Has anyone noticed/discussed the fact that 1059 flew three return-to-launch-site missions?  That may be more than any other booster.  Life leader 1051, for example, has only flown one RTLS mission.  Those return flights involve a long boost-back burn that the down-range landings do not require.  So 1059 would probably have accumulated more firing time for its recovery engines than any other booster with its number of flights.

 - Ed Kyle

I would also assume it faced harsher reentry aerothermal conditions?

Reentry on RTLS missions is much more benign than on ASDS missions, as can be seen from the speed & altitude telemetry of two recent flights.

___________________	RTLS: NROL-108 (2020-12-19) ___	ASDS: Starlink L18 (2021-02-04) _	ASDS: Starlink L19 (2021-02-15)
MECO	T+02:22 6010 km/h @ 73.9 km	T+02:38 7955 km/h @ 63.9 km	T+02:38 7929 km/h @ 65.0 km
Apogee	T+04:12  831 km/h @ 148 km	T+04:27 7099 km/h @ 115 km	T+04:27 7073 km/h @ 116 km
Start Entry Burn	T+06:31 4757 km/h @ 57.6 km	T+06:25 8066 km/h @ 55.2 km	T+06:26 8063 km/h @ 55.2 km
End Entry Burn	T+06:58 2244 km/h @ 31.1 km	T+06:46 5750 km/h @ 36.7 km	T+06:50 5879 km/h @ 33.4 km
Max V post Entry Burn	T+07:13 2495 km/h @ 21.2 km	T+06:49 5756 km/h @ 33.8 km	T+06:50 5880 km/h @ 33.1 km

Not only is MECO earlier on RTLS missions, but the stage isn't that far downrange, so it can make a leisurely boosted-back return to the Cape, as reflected by the speed at apogee (which represents the horizontal component of the stage's velocity during its free fall).

Data from the webcasts: NROL-108 & Starlink L18 & Starlink L19
(Linked to 5 seconds prior to apogee.)
OneSpeed's Telemetry Charts: NROL-76 v. NROL-108 & Starlink L18 v. L19

Edit: Added in L19 for good measure.

^{(BBCode table formatting advice gladly accepted.)}

[TorenAltair]

Has anyone noticed/discussed the fact that 1059 flew three return-to-launch-site missions?  That may be more than any other booster.  Life leader 1051, for example, has only flown one RTLS mission.  Those return flights involve a long boost-back burn that the down-range landings do not require.  So 1059 would probably have accumulated more firing time for its recovery engines than any other booster with its number of flights.

 - Ed Kyle

I'm not sure if a specific engine remains tied to a certain booster or if they are swapped between boosters. Additionally it might be that a center engine does not stay the center engine for the next flight. As far as I understand is the only difference between the booster engines is a larger supply of TEA-TEB for the "re-entry engines" which should be "external" to the engines.