SpaceX F9 - Starlink Group 4-18 - LC-39A

[Grendal]

Launch Date: May 18
Launch Window: 5am EDT (2am PDT, 09:00 UTC)
Launch site: LC-39A, Kennedy Space Center, Florida
Core Booster Recovery: ASDS - ASOG
Booster: B1052.5
Fairings: Reused
Mass: 53 satellites - 15.6 tonnes
Orbit: LEO

A SpaceX Falcon 9 rocket will launch the 46th group of satellites for SpaceX’s Starlink broadband network, a mission designated Starlink 4-18.

This will be SpaceX's 21st orbital launch of the year.

 

[Grendal]

Weather is good.

 

[Grendal]

 

[Grendal]

One more fully successful launch and landing. Beautiful booster shots all the way to the ASDS.

 

[HVM]

https://twitter.com/x/status/1526882451078885376

 

[ItsNotAboutTheMoney]

One more fully successful launch and landing. Beautiful booster shots all the way to the ASDS.

A lot of hard work went into building an LEO Internet network so we could get that shot.

 

[HVM]

https://twitter.com/x/status/1526895219966234626

 

[MyJoule]

It will never get old - yet they make it look so routine. Way to go SpaceX Nice camera views all the way to the landing too. Not many folks were up at 3:00AMin Hawthorne- notice how quiet it was behind Jessie? Loved the Moon images at the start of the webcast too- really put the rotation of the Earth and the Moon in perspective as the Moon moved across the camera.

 

[Cosmacelf]

It will never get old - yet they make it look so routine. Way to go SpaceX Nice camera views all the way to the landing too. Not many folks were up at 3:00AMin Hawthorne- notice how quiet it was behind Jessie? Loved the Moon images at the start of the webcast too- really put the rotation of the Earth and the Moon in perspective as the Moon moved across the camera.

Apparently Jessie never sleeps. She’s actually a Teslabot prototype, but, don’t tell anyone.

 

[ecarfan]

Way to go SpaceX Nice camera views all the way to the landing too. Not many folks were up at 3:00AMin Hawthorne- notice how quiet it was behind Jessie?

Like on the previous Starlink mission a few days ago, it sounded like just one person was clapping at stage sep. And this time Gwynne did not do the countdown. These missions are becoming like a commercial jet taking off and landing; routine.

It was really nice to have a continuous video feed from the booster all the way to touchdown, which again appeared to be as close to a bullseye as one could imagine.

 

[adiggs]

Is it just me, or does it look like the booster is taped together, top and bottom, with electrical tape?

Like maybe the stick broke and they applied a fix something like I would - tape the two pieces back together and use it anyway.

 

[JohnnyEnglish]

One more fully successful launch and landing. Beautiful booster shots all the way to the ASDS

Yes, the booster landing shots seem to improve all the time.

Looking at the telemetry it seems like the landing burn starts just above 1km. Amazing that the burn slows the booster (in a controlled manner) from freefall to almost zero in that distance.

 

[Electroman]

Looking at the telemetry it seems like the landing burn starts just above 1km. Amazing that the burn slows the booster (in a controlled manner) from freefall to almost zero in that distance.

From 500 KM/hr to Zero in less than 1000 meters.

 

[ecarfan]

From 500 KM/hr to Zero in less than 1000 meters.

I wonder how many Gs a human would experience undergoing that kind of deceleration.

 

[bxr140]

The same g’s the rocket experiences?

 

[Cosmacelf]

I wonder how many Gs a human would experience undergoing that kind of deceleration.

I think the formula is a = (vf**2 - vi**2) / (2 * (xf - xi)) where vf is final speed, vi is initial, xf is final distance, xi is initial distance.

vf = 0, vi = 138.9 m/s (1000 km/hr)
xf = 0, xi = 1000 m

It works out to 9.6 m/s**2 which is about 1G, so quite comfortable.

 

[Grendal]

Yes, the booster landing shots seem to improve all the time.

Looking at the telemetry it seems like the landing burn starts just above 1km. Amazing that the burn slows the booster (in a controlled manner) from freefall to almost zero in that distance.

Keep in mind that the booster is almost empty. It is very light compared to what it had at liftoff.

 

[Electroman]

I would pay to take a ride on the booster and back. Honestly I would. Put me up in a space suit and an oxygen tank, and strap me to the booster. 8 minutes of ride that compares to nothing.

 

[bxr140]

I think the formula is a = (vf**2 - vi**2) / (2 * (xf - xi)) where vf is final speed, vi is initial, xf is final distance, xi is initial distance.

vf = 0, vi = 138.9 m/s (1000 km/hr)
xf = 0, xi = 1000 m

It works out to 9.6 m/s**2 which is about 1G, so quite comfortable.

Can also WAG acceleration maths using time instead of distance. Using SX's tlm data I get about 8.2 m/s2 (or .84g)

Its worth pedantic-izing that this is all average acceleration. Max instantaneous acceleration on landing burn is probably a good bit higher--maybe 2-3g's? Maybe a bit less? Not totally sure how quickly Merlin can throttle--that would be one of the limiting factors on max instantaneous acceleration (Newtie's 2nd, and all). Its also worth pointing out that the above calculations are the total vehicle acceleration--the free body diagram, if you will. The acceleration from the landing burn also needs to offset gravity, so the F=ma math from just the Merlin thrust would be ~1.84g.

Leveraging that to rathole on Moar Math, its interesting to note that a single Merlin's minimum thrust on a completely empty falcon first stage results in an acceleration of ~16.2m/s2, or ~1.65g's. Its not a super useful number other than the fun thought experiment of a hovering falcon first stage: This "thrust results in more than 1g" lower bound means that once a stage is below ~4% fuel load, which is about where minimum thrust = 1g, it cannot hover--it will start to go back up. Put another way, the stage can't simply hover indefinitely until its fuel runs out.

***FTR that's not factoring momentum--obviously if the thing is still falling at 4% fuel load its a different story
***Also FTR, and of course Good Math willing, that 4% fuel load represents about 125 seconds at minimum throttle

 

[Electroman]

I think the touch downs of this booster seems much more silkier & smoother than some landings of commercial jet liners I have to experienced. Definitely much much better then any parachute landings.