SpaceX Falcon 9 historic landing thread (1st landing attempt & most recent missions)

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georgegassaway

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So, this is an interesting twist. Elon Musk responding to a question:



Saw it in a discussion on NSF: https://tinyurl.com/4jgudzmy

The consensus is he was not being sarcastic. Implying that they may very well work on igniting three to start the flip then shut off one if all three are running well (otherwise shut off one that's not working well, or at all).

Certainly a lot simpler, faster, and safer than igniting the third one only if one of the first two have a problem, at not very much cost in fuel.. That presumes the plumbing can handle that much of a brief surge (150%) in fuel flow, unless they start up the three at say 2/3 throttle of the throttle level they have previously used for two for the same fuel flow as with two (if they did do 2./3 throttle before shutting the 3rd engine down, then it might not even use much extra fuel. Though it *might* be safest once vertical to get all three to full throttle before shutting one down, to be sure at least two are working at 100%. It does occur to me now that at say 2/3 throttle, the ISP (efficiency) of the the engines probably take a hit compared to 100%, so a bit of cost in fuel regardless).

Update - I saw in a Facebook group, that many are assuming Musk WAS being sarcastic and making fun of the guy who asked the perfectly valid question (and some fanbois piling on). Oh I hope Musk is not that much of an A-hole to have really meant that sarcastically. I had taken it as a self-humbling response, implying that in retrospect they should have thought more about that kind of thing. Why the h*** come out of a self-imposed Twitter "time out" to be an A-hole? I will note that the people on NSF who think he was not being sarcastic are more technically oriented and less fanboi-ish than the Facebook group. One literally said it's his company and his money....he can do as he wants.... as though THAT entitles anyone to treat anyone badly (and this is why I hate the "Elon can do no wrong" Fanboi cult mentality). Anyway, I did want to add this counterpoint that he might have been sarcastic and therefore no 3rd engine for the flip.

Update two - It occurred to me that they might not have installed plumbing from the header tanks (landing fuel) to the third engine's plumbing, since they didn't plan to ignite it for landing. In that case, even if they do go for a 3rd engine for landing, it would not be tested on SN-10, or the other prototypes that are too far along in assembly to retrofit them for that capability. It would have to be added in for later prototypes. I hope they do have the plumbing capable of doing that already though, if they wanted to try it.
 
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neil_w

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I although thought while watching that it seemed crazy to have no redundancy in the landing configuration. But it sounds like they're already planning to evolve it in the future.

Starting up three and shutting one off sounds good, but recall that they have to do some rather sharp vectoring during the ascent when they shut one motor off, to deal with the shift in thrust axis. Can they do that safely in the middle of the flip?

It's a very interesting problem, there seem to be many ways to approach it.
 

mach7

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So, this is an interesting twist. Elon Musk responding to a question:



Saw it in a discussion on NSF: https://tinyurl.com/4jgudzmy

The consensus is he was not being sarcastic. Implying that they may very well work on igniting three to start the flip then shut off one if all three are running well (otherwise shut off one that's not working well, or at all).

Certainly a lot simpler, faster, and safer than igniting the third one only if one of the first two have a problem, at not very much cost in fuel.. That presumes the plumbing can handle that much of a brief surge (150%) in fuel flow, unless they start up the three at say 2/3 throttle of the throttle level they have previously used for two for the same fuel flow as with two (if they did do 2./3 throttle before shutting the 3rd engine down, then it might not even use much extra fuel. Though it *might* be safest once vertical to get all three to full throttle before shutting one down, to be sure at least two are working at 100%. It does occur to me now that at say 2/3 throttle, the ISP (efficiency) of the the engines probably take a hit compared to 100%, so a bit of cost in fuel regardless).

Thanks very much George for your last 3 posts (All of them really), A very nice summation of the issues!
It helped me sort out what all was going on.
You are approaching Steely Eyed Missile Man status.
 

Huxter

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2/4/2021 - Starlink L18 - SPOT ON landing! Are these landings getting boring! NOT!

Starlink V1.0-L18.jpg


Would love to see more of the fairing catches - those were some good videos!
 

davel

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Happy they brought back the telemetry on the first stage reentry. And that landing was appearently pushing the limits on winds and high seas.
 

Nytrunner

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As far as Musk goes, I give it a 50/50 chance of being sincere vs sarcastic, but it's still a lose/lose.

Sarcastic: That fits his personality
Sincere: Also possible, but his technical team will be made to eat crow for not seeing it coming
 

georgegassaway

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Sincere: Also possible, but his technical team will be made to eat crow for not seeing it coming
He acts like he's the smartest person in the room. So if he was sincere, he should eat the first crow (rather than the team) for not thinking of it himself.
 
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Reinhard

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Apparently Elon was sincere. He is already discussing the details on Twitter (adapting SN10 is possible; preferably shutting down the engine with the least lever arm; can't keep all 3 engines running if all work well because of minimum throttle point and thrust to weight issues).

Seeing that unfold on Twitter in basically real time interspersed with Dogecoin memes... Well, we're living in interesting times.

Reinhard
 

cbwho

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Apparently Elon was sincere. He is already discussing the details on Twitter (adapting SN10 is possible; preferably shutting down the engine with the least lever arm; can't keep all 3 engines running if all work well because of minimum throttle point and thrust to weight issues).

Seeing that unfold on Twitter in basically real time interspersed with Dogecoin memes... Well, we're living in interesting times.

Reinhard
I knew he was sincere at first read since he said: "we WERE dumb". Past tense. They won't make that mistake again.

Also Musk is not arrogant. If a person listens to his interviews and discussions it's obvious. Short tweets are easily mis-read.
 

georgegassaway

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So, no launch Friday. Starlink 17 has slipped to early Sunday. This will be the 8th launch of booster #49 ( the designation 1049.8).

"Launch targeting February 7, 2021 at 4:31 am EST (0931 UTC) on Falcon 9 (booster 1049.8 ) from Kennedy Space Center’s LC-39A. ASDS landing is expected on Just Read The Instructions, towed by tugboat Finn Falgout. Fairing recovery is expected."

Back to Starship landings, to start 3 engines then shut down one after the flip, another indicator they are going to do that:


And....ran across this photo of SN-9's engines and other stuff inside the tail section. This seems to be before thermal shielding was put in place. None in sight, but that had to be what some, if not all, of the pieces that came off during the flip-tastophe were. This also shows how exposed the other two engines are to damage if one has a failure that energetically spews parts, or spews very melty-hot flames at critical components like fuel lines, gimbal hydraulic, pumps, and electrical cables. Falcon-9 booster's engines are far less exposed to damage from a bad engine.

 
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neil_w

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Can someone please confirm if I have this right?
1612530190964.png

Especially, uncertain about the tank between the two Starships.
 

Nytrunner

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Also Musk is not arrogant. If a person listens to his interviews and discussions it's obvious. Short tweets are easily mis-read.
Based on Public relations appearances, I can see where you form that impression. I'll just say that there is a difference between PR Musk and business Musk
 

cbwho

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Based on Public relations appearances, I can see where you form that impression. I'll just say that there is a difference between PR Musk and business Musk
I'm not talking PR events.
For example, Musk admitted to faults in the Telsa car and talked about how they are fixing them in a discussion I saw.
Musk is very straight forward. I admire his style.

We may have to agree to disagree on Musk.
 

georgegassaway

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So, the Starlink 17 launch that was bumped to Feb 7th, has now been postponed indefinitely. The link below mentions "additional inspections". But also, the KSC weather forecast is for a LOT of rain Saturday night into Sunday morning, and rain for the next few days. Also, the downrange recovery weather seems very poor. I saw a reference to the recovery fleet coming back to port, too.


As for SN-9 and SN-10, the photo below (by "Nomadd" on NSF), a different angle, shows SN-9 at left, and SN-10 at right. A notable visible difference is that SN-10 has a larger area of black test re-entry tiles on it, plus a few smaller sets of test tiles in three places below the big set. They are being tested mostly to see if the attachment method works well enough to even survive launch and transition to belly-flop (and reaction to contraction/expansion from the cryogenic fuels).



Flyover pic from last Monday. By BocaChicaGal.


Video of work on new prototypes, and cleanup of SN-9 (SN-9 debris starts at about 14.5 minutes)

An interesting view of the last few seconds of SN-9. At first I thought wow they had to be close for the "boom" to happen so fast after the kaboom. But later realized that the first few seconds was the sound of the engine firing, not the boom with echoes. The last moment of sound might have been the crash.

OK, one last thing, but very significant. In the context of igniting 3 engines for the flip (then shut one down to land with two good ones) Elon Musk confirms they will test that out on the next flight - SN-10. So it seems either SN-10 has all the hardware to do it already, or any hardware mods must be pretty easy/quick to do.

 
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georgegassaway

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OK, one more post. Pretty neat, albeit a few problems. And no, I won't be building one. :0

...
 

rklapp

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This reminds me of the discussion of why SpaceX doesn't include an escape capsule option on the Starship. Their answer is that they'll put more time and resources into reliability by flying the rocket over and over again until landing is just as common as commercial jets. They can fly cargo around the world or into space for hundreds and hundreds of launch/landings until they get it right. I'm not sure if the FAA is okay with this approach.
 

georgegassaway

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So, the delayed Starlink 17 launch, is still delayed, with no launch date projected.

Meanwhile, Starlink 19 is scheduled to launch Friday.

"Launch targeting February 12, 2021 at 12:25am EST (0525 UTC) on Falcon 9 (booster 10xx.x) from CCSFS SLC-40. ASDS landing is expected. Fairing recovery is expected."
 

neil_w

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This reminds me of the discussion of why SpaceX doesn't include an escape capsule option on the Starship. Their answer is that they'll put more time and resources into reliability by flying the rocket over and over again until landing is just as common as commercial jets. They can fly cargo around the world or into space for hundreds and hundreds of launch/landings until they get it right. I'm not sure if the FAA is okay with this approach.
Yes, it does seem like a very risky way to land with humans on board, and no backup plan. How many 9s of reliability can they achieve on landings, and how could they even prove it?
 

rklapp

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Yes, it does seem like a very risky way to land with humans on board, and no backup plan. How many 9s of reliability can they achieve on landings, and how could they even prove it?
By launching and landing a lot of rockets, hundreds and hundreds.

Here's a video to put the space program into perspective.

 

Marc_G

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Yes, it does seem like a very risky way to land with humans on board, and no backup plan. How many 9s of reliability can they achieve on landings, and how could they even prove it?
Well, recovering astronauts from space in an essentially unpowered glider with the flight characteristics of a brick was an unproven, bizarre idea at one time, too.
 

neil_w

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Well, recovering astronauts from space in an essentially unpowered glider with the flight characteristics of a brick was an unproven, bizarre idea at one time, too.
True, but a glide (however brick-like) still has many fewer failure modes than what Starship is trying to do.
 

boatgeek

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This reminds me of the discussion of why SpaceX doesn't include an escape capsule option on the Starship. Their answer is that they'll put more time and resources into reliability by flying the rocket over and over again until landing is just as common as commercial jets. They can fly cargo around the world or into space for hundreds and hundreds of launch/landings until they get it right. I'm not sure if the FAA is okay with this approach.
Yes, it does seem like a very risky way to land with humans on board, and no backup plan. How many 9s of reliability can they achieve on landings, and how could they even prove it?
By launching and landing a lot of rockets, hundreds and hundreds.

Here's a video to put the space program into perspective.

There's also a big difference between risks for relatively small numbers of astronauts who have signed up for the risk and a liner service for the general public. It's possible that the FAA will be OK with it eventually. On the other hand, commercial airplanes go through a lot of flight testing hours and that's with a relatively well-known risk set. I would expect FAA to require a lot of testing, particularly on the landings. We should see many tests with a variety of failure conditions to demonstrate that they can land safely with one or two allowed points of failure.

It also wouldn't surprise me to see SpaceX change their landing approach before the rocket is human-rated.
 

boatgeek

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The thing is, it is not aerodynamically stable in tail-first descent. Yes, if the nose flaps deploy out "flat", and the rear flaps folded completely up, would be stable in pitch. But it would not be stable in yaw for two reasons. For one, no equivalent flaps deployed at the nose, 90 degrees to the other set (yes I'm talking about the need for four "fins" or flaps on the nose).

The other problem in the yaw axis would come from the folded tail flaps. They would cause a yaw/roll coupling problem. Think of say a 4 finned rocket, with one fin broken off. If the rocket is super-stable enough to be stable in yaw from just one fin in the yaw axis, that fin is on one side but nothing of equal force on the other side. So, any yaw would also cause a roll. Thus, yaw/roll coupling. There's no fix for Starship for those two problems aerodynamically, without having yet even more aerodynamic surfaces added.
Sorry for going back a ways. Would Starship still have aerodynamic stability if the tail flaps were slightly deployed (say 20% from minimum drag) and the nose flaps were only mostly deployed (say 80% max)? That should provide more roll stability. I see your point on yaw-roll coupling, but it seems like the exciting forces in yaw would be pretty small in the couple of seconds between starting the flip and lighting the engines. If the Starship still had a significant tilt when the engines lit (say 30 degrees), it would still have some roll stability from the flaps as well.
 

rklapp

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There's also a big difference between risks for relatively small numbers of astronauts who have signed up for the risk and a liner service for the general public. It's possible that the FAA will be OK with it eventually. On the other hand, commercial airplanes go through a lot of flight testing hours and that's with a relatively well-known risk set. I would expect FAA to require a lot of testing, particularly on the landings. We should see many tests with a variety of failure conditions to demonstrate that they can land safely with one or two allowed points of failure.

It also wouldn't surprise me to see SpaceX change their landing approach before the rocket is human-rated.
Agreed. Seems like for the foreseeable future, there will be a cycle of test, fly, crash, investigate, test, fly, crash, investigate, test, fly, crash, investigate...

As a kid, we would camp at Coulee and Steamboat Rock every summer.
 

CPUTommy

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So, the delayed Starlink 17 launch, is still delayed, with no launch date projected.

Meanwhile, Starlink 19 is scheduled to launch Friday.

"Launch targeting February 12, 2021 at 12:25am EST (0525 UTC) on Falcon 9 (booster 10xx.x) from CCSFS SLC-40. ASDS landing is expected. Fairing recovery is expected."
Where do I go and watch this?!?
 
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