Author Topic: SpaceX F9 : Starlink Group 4-4 : VSFB SLC-4E : 18 December 2021 (12:41 UTC)  (Read 72712 times)

Offline TJL

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Not sure if I'm missing something but is there any reason why SpaceX decided to launch this Starlink mission from the West coast (not going into polar orbit) impacting the payload capability it would have had launching from KSC? Thank you.

Offline ulm_atms

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Not sure if I'm missing something but is there any reason why SpaceX decided to launch this Starlink mission from the West coast (not going into polar orbit) impacting the payload capability it would have had launching from KSC? Thank you.

I think because it was the only pad left for Starlink.  The other two east coast pads are launching this weekend too. (Turksat 5B - SLC-40 and Spx-24 - 39A)

Offline zubenelgenubi

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Thanks, RL, for the launch thread coverage!  Congratulations to the launch campaign team!



In watching the launch after the fact, I see we got a short glimpse of the LOX dregs in the second stage during the rocketcam step-throughs via Punta Arenas at mission elapsed time +28:57 (instead of waiting until it came in range of Mauritius).



Launch time to the second or millisecond?
(Answered below.)

Edited
« Last Edit: 12/19/2021 02:41 am by zubenelgenubi »
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Online Elthiryel

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Launch time to the second or millisecond?

According to T.S. Kelso, it was supposed to be 12:41:40 UTC.

https://twitter.com/TSKelso/status/1472117225234464771
« Last Edit: 12/18/2021 04:09 pm by Elthiryel »
GO for launch, GO for age of reflight

Offline zubenelgenubi

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Historical question re: today's launch descending node launch to a 53.2 deg inclination orbit, grazing the Pacific coast of Baja California:

Is this a new use of available launch azimuths from Vandenberg?  Any similar launches from NASA or Air Force history?
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Offline russianhalo117

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Historical question re: today's launch descending node launch to a 53.2 deg inclination orbit, grazing the Pacific coast of Baja California:

Is this a new use of available launch azimuths from Vandenberg?  Any similar launches from NASA or Air Force history?
The launch used an already available azimuth which did not need a required overflight permission.

Titan-23G was proposed to keep flying out of VAFB SLC-4W to provide upto 3,600kg interim/emergency resupply capability per launch to ISS immediately following the Columbia launch and reentry disaster. It should be discussed wayback somewhere on this forum. When was it decided to keep using STS to resupply ISS, Titan-23G was retired (converted from deactivated and stored ICBM fleet) with the remaining Titan-II inventory scrapped as their saving grace proposal was shelved (not the only reason for retiring the Titan launcher family).
« Last Edit: 12/18/2021 05:58 pm by russianhalo117 »

Offline wannamoonbase

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During the webcast the presenter said that this was the third flight for one of the fairing halves an the fourth flight for another one.

I love that fairing recovery is becoming normal and so successful too. It’s t knocks about $100K off per star link to orbit.

Also raises the bar for industry too, case in point the proposed Neutron design.

Great launch by SpaceX by using the west coast.  I was hoping for fog but I’ll take it.
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Offline SPKirsch

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https://twitter.com/thejackbeyer/status/1472197309333000196
Quote
Liftoff of SpaceX Falcon 9 B1051.11, the first ever 11th flight of a booster, carrying the Starlink 4-4 group into orbit on a rare crystal clear night at Vandenberg Space Force Base in California. @NASASpaceflight
https://twitter.com/SLDelta30/status/1472247436202504195
Quote
The @SpaceX Starlink mission successfully launched from Vandenberg Space Force Base at 4:41 a.m today. The mission launched on a Falcon 9 rocket and will add 52 satellites to the Starlink satellite constellation. Job well done #TeamV!
« Last Edit: 12/18/2021 08:44 pm by SPKirsch »

Offline OneSpeed

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Here is a comparison of the telemetry from the Starlink Group 4-1 and 4-4 missions, both to an inclination of 53.2°, but launched from opposite coasts.

From the Starlink Mission Control Audio, the 4-4 launch azimuth was initially 180°, or due south. From 50s to 100s in flight, the booster yawed about 36° to the east. I was hoping to see some evidence of this manoeuvre in the telemetry, but unfortunately any difference is hidden within the noise of the available data.

Offline briantipton

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Watching the landing on the broadcast, I noticed the displayed stage 1 velocity was still 263 kph when the altitude reach 0.0 km, and was still 183 kph when the altitude flipped from 0.0 km to -0.0 km, which presumable meant effectively 0 m. Since the video had cut out (as usual) I found this telemetry disconcerting. Fortunately, a few seconds later we got confirmation of a safe landing so clearly the broadcast telemetry was inaccurate (maybe just out of synch). I haven't watched every landing, but it always seemed like the displayed telemetry converged nicely to 0 velocity and altitude at the same time in the past. Was this landing unique or have we seen misleading telemetry in the broadcast previously? Any idea why the two data streams would be so far out of synch?

Offline mkent

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Not sure if I'm missing something but is there any reason why SpaceX decided to launch this Starlink mission from the West coast (not going into polar orbit) impacting the payload capability it would have had launching from KSC? Thank you.

I think because it was the only pad left for Starlink.  The other two east coast pads are launching this weekend too. (Turksat 5B - SLC-40 and Spx-24 - 39A)

I think the question is not "Why did they launch from the Western Range?" but "Why did they launch into the 53.2 deg shell?"

By my calculations SpaceX needs 24 launches to fill the 70 deg and 97.6 deg shells and 30 launches to fill the 53.2 deg shell.  But the higher launch cadence possible from the Eastern Range should cause the 53.2 deg shell to be filled much sooner than the higher-inclination shells.

Launching this flight into the 70 deg shell should have helped balance things out, making the question "Why didn't they do that?"  Does anyone here know?

Offline AC in NC

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Not sure if I'm missing something but is there any reason why SpaceX decided to launch this Starlink mission from the West coast (not going into polar orbit) impacting the payload capability it would have had launching from KSC? Thank you.

I think because it was the only pad left for Starlink.  The other two east coast pads are launching this weekend too. (Turksat 5B - SLC-40 and Spx-24 - 39A)

I think the question is not "Why did they launch from the Western Range?" but "Why did they launch into the 53.2 deg shell?"

By my calculations SpaceX needs 24 launches to fill the 70 deg and 97.6 deg shells and 30 launches to fill the 53.2 deg shell.  But the higher launch cadence possible from the Eastern Range should cause the 53.2 deg shell to be filled much sooner than the higher-inclination shells.

Launching this flight into the 70 deg shell should have helped balance things out, making the question "Why didn't they do that?"  Does anyone here know?
TJL's question wasn't why did they launch from the West Coast.  There were a couple typos and awkward phrasing.  If you step back and read it carefully ...

The question was "Did the decision to launch from the West Coast impact payload capacity?" thus resulting in the fewer than typical number of Starlink.
« Last Edit: 12/18/2021 11:27 pm by AC in NC »

Offline Craftyatom

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Watching the landing on the broadcast, I noticed the displayed stage 1 velocity was still 263 kph when the altitude reach 0.0 km, and was still 183 kph when the altitude flipped from 0.0 km to -0.0 km, which presumable meant effectively 0 m. Since the video had cut out (as usual) I found this telemetry disconcerting.
One factor is the rotation of the planet.  SpaceX's telemetry, certainly for the first stage, is relative to the launch site - however, since the rocket launched south towards the equator, it ended up in a position further from Earth's axis of rotation, and was thus moving from west to east slightly faster.

Vandenberg is at 34°43′58″N, or ~0.6062 radians.
Assuming a spherical earth with a radius of 6378km, that means that the launch site is about cos(0.6062)*6378 = 5242 km away from the axis of rotation.
The earth completes a rotation approximately once every 24 hours, or 0.2618 radians per hour.  Thus, the linear speed of a point 5242 km away from the axis of rotation is 5242*0.2618 = 1372 kph.
Estimating the location of the barge (if someone has the ship tracking data feel free to jump in) as about 30 degrees N, and performing the same math, we get cos(0.5236)*6378*0.2618 = 1446 kph, or a difference of 74 kph.

Obviously that's not all of it, but it's one big culprit in SpaceX telemetry that we've seen before.  Oh, and feel free to check my math, as always.
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Offline Kiwi53

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I think the question is not "Why did they launch from the Western Range?" but "Why did they launch into the 53.2 deg shell?"

By my calculations SpaceX needs 24 launches to fill the 70 deg and 97.6 deg shells and 30 launches to fill the 53.2 deg shell.  But the higher launch cadence possible from the Eastern Range should cause the 53.2 deg shell to be filled much sooner than the higher-inclination shells.

Launching this flight into the 70 deg shell should have helped balance things out, making the question "Why didn't they do that?"  Does anyone here know?

I don't know, but I'd guess that the 70° shell gives them access to Alaska, far north Canada, Greenland, Iceland, and far north Norway & Sweden, plus the adjacent seas. These are interesting, underserved and strategically important regions, but not going to be big revenue earners. And almost nothing in the southern hemisphere - the very bottom of S. America is ~56°S

True polar (97.6°) orbits with inter-satellite links allows true global coverage, but that's only going to interest those that can't see 70° orbit satellites - airlines flying trans-polar, the military and Antarctic research stations


A second (and later a third, IIRC) 53.x° shell delivers the meat of the world's population, more minutes per orbit above revenue-rich areas - i.e. better for profitability.
So for Starlink's commercial viability, it's much better to fill up the 53.x° shells than the higher-inclination orbits

Offline gongora

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So for Starlink's commercial viability, it's much better to fill up the 53.x° shells than the higher-inclination orbits

What if a single government services contract for higher inclination coverage was worth 10,000 or more consumer dishy subscriptions?  Would filling up a higher inclination shell desired by that customer be worth it?

Offline Steven Pietrobon

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In watching the launch after the fact, I see we got a short glimpse of the LOX dregs in the second stage during the rocketcam step-throughs via Punta Arenas at mission elapsed time +28:57.

Doesn't look like much was left in the tank.
Akin's Laws of Spacecraft Design #1:  Engineering is done with numbers.  Analysis without numbers is only an opinion.

Offline zubenelgenubi

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In watching the launch after the fact, I see we got a short glimpse of the LOX dregs in the second stage during the rocketcam step-throughs via Punta Arenas at mission elapsed time +28:57.
Doesn't look like much was left in the tank.
When I see the very low LOX level, I hear this in my imagination (technically, I suppose my imagination should hear this only if the tank is draining):
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Offline Lewis007

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Online Elthiryel

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Quote
This was the shortest launch turnaround at SLC-4E, just 24 days since the DART launch.

Wow, I didn't notice that!

Previous record: 35d 23h 56m (PAZ -> Iridium-5) - long time ago in SpaceX terms, March 2018!
New record: 24d 06h 20m (DART -> Starlink Group 4-4)
GO for launch, GO for age of reflight

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