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

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On the pad at Vandenberg:

hbLLb1E.jpg


The grid fins look black. They are changing the grid fins from aluminum with an ablative coating, to Titanium. So these may be the new Titanium ones. But they are supposed to be bigger (to allow for a shallower semi-lifting reentry to reduce heating), hard to tell from this if they are bigger.

Weather is 100% "Go".

Iridium-2 Patch:

index.php


Couple of tweets from Elon confirm.
"Flying with larger & significantly upgraded hypersonic grid fins. Single piece cast & cut titanium. Can take reentry heat with no shielding."
"
Slightly heavier than shielded aluminum, but more control authority and can be reused indefinitely with no touch ups"
 
Musk tweeted this about the new grid fins:

Flying with larger & significantly upgraded hypersonic grid fins. Single piece cast & cut titanium. Can take reentry heat with no shielding.

Edit - Ah, SpaceManMat beat me to that.

I made the image comparison below from two Falcons on the pad at Vendenberg. At left is the one that launched Iridium-1 in January (that same booster also launched Bulgariasat on Friday, first one to land on two different ASDS's). At right, from the one to be launched Sunday with the bigger grid fins (Original image was not very big, so not great quality when enlarged).

QhQZmJz.jpg


The chord seems the same, so no increased frontal area during boost. Span is increased. I expected them to be bigger than that... not huge, but bigger.


Update about the Bulgariasat booster landing.


Elon Musk was asked on Twitter:

Was the hard landing due to improper preprogrammed parameters or needing a fourth engine to decelerate from higher velocity?

His reply:

Rocket was suddenly slammed sideways right before landing. Heavy gust or something malfunctioned onboard. Reviewing telemetry.

Would be interesting to know if the two outboard engines were aligned with the axis where it went “sideways”. If so, that could mean that when they shut down the outer two engines so it could land on the center engine, that both did not shut down equally so the unequal thrust “slammed” it.
 
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Nice forgings :)

Because these are grid fins the chord is effectively the thickness of the paddle. They could keep the same paddle area and grid spacing, but increasing the thickness of the paddle would increase the control authority. Some complexities involving shock waves probably complicate matters, but thickening the paddle is the equivalent of more fin area.
 
Nice forgings :)

Because these are grid fins the chord is effectively the thickness of the paddle. They could keep the same paddle area and grid spacing, but increasing the thickness of the paddle would increase the control authority. Some complexities involving shock waves probably complicate matters, but thickening the paddle is the equivalent of more fin area.

They would have more "control authority" when deployed, but they spend time "one the way up" stowed against the body where they would stick out into the airstream more than original fins. This is going to mean more drag at the top of the rocket, probably changing the CG/CP relationship.
 
Nice forgings :)

Because these are grid fins the chord is effectively the thickness of the paddle. They could keep the same paddle area and grid spacing, but increasing the thickness of the paddle would increase the control authority. Some complexities involving shock waves probably complicate matters, but thickening the paddle is the equivalent of more fin area.

Ah, yes, of course. Just like taking a conventional rocket fin that is 2 x 2 and increasing chord from 2 to 3.

Would increase the frontal area a bit when folded, but not too badly. Also they are downstream of the large diameter fairing when flying payload missions ( as opposed to Dragon missions).

Doesn't mean they did increase the depth (chord when deployed), but they may have. It'll be interesting to find out once they provide more info or much better photos (If things go well, a nice close-up photo on the dock in a few days would be nice. Though I'm not sure there's as many SpaceX Fans hanging out at the Port of Los Angeles dock taking quality non-selfie photos, as there are at Port Canaveral )
 

Thanks for posting it, Rex.

Launch is less than 3 hours (1:25 PM Pacific, 4:25 Eastern, 3:25 Central for me). Webcast usually starts 20 minutes or so before launch.

This is an instantaneous launch, so it either goes at 1:25 PM or it's scrubbed for the day.

The Forum software is finicky about previewing Youtube, so after tweaking here it is:


[video=youtube;7tIwZg8F9b8]https://www.youtube.com/watch?v=7tIwZg8F9b8&feature[/video]
 
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Here's a side by side image posted on NSF by "AC in NC", cropped a bit:

I7t4VQ8.jpg


The booster on left is the Bulgariasat Falcon that launched Friday.

Looks like the grid fin thickness is about the same.

It occurred to me later that the increased span could be far more effective beyond the percentage of span increase. Because of turbulence and blanking-out near the surface of the cylindrical body when flying at a significant angle of attack as they intend to do later for shallower descents. To get the most pitch effectiveness out of all four, they'd want to come in in "X" fin orientation, rather than "+" which would not get any pitch steering out of two of them. So in that case, in "X" orientation, the upper two would be blanked out a bit in the inner areas, by the airflow (shock waves) around the cylindrical tankage. So being longer in span, the outer extended portion would be in cleaner air and much more effective than the same area near the body.
 
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Oh wow, look at the scalloped edges on the underside of the grid fins.

https://www.instagram.com/p/BVxWVmelhKG/

I wonder if they come to a sharp edge as well?
Hey, thanks for that! I've been looking for details on the new gridfin, best shot I've seen so far. Surprised one side is still flat as there's some interesting sim work being done on valley or mountain configs.

I'd be willing to bet you're spot on, there's some tapering going on. If you think of this as an array of supercritical symmetric airfoils, it makes sense.

Edit: an apples-to-apples comparison
xlv3bJu_d.jpg
 
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Good launch, staging, and entry burn.

Landing burn begun.

WOW GREAT LANDING!

Had a LOT of shaking when the landing burn began. Perhaps related to going Transsonic, lots of turbulence to begin wit,h and the grid fins do not work well in that phase. They might need to tweak the control feedback/authority values for that phase. I do not recall shaking that bad from an onboard camera view, so this may be related to the improved grid fin performance/behaviour. Also do not recall seeing a grid fin move back and forth and back and forth to the extent that the left one did.

That great side by side photo that dhbarr posted, the apparent scalloping seems to indicate a very sharp leading edge (the edge once deployed, coming down), and the flat surface we see is the trailing edge. Like a wedge cross-section. Wedges work well at supersonic speeds. And flat plates do not, which is what the original F9 grid fins used.

WHOA! I knew the landing looked so soft. Well, watched it again. TOO soft - it never landed before engine shutdown!

As you may recall, the Merlin engine's minimum throttle is still more thrust than the F9 weighs during landing. So if during landing, it comes to zero downward velocity and has NOT touched down yet, it is going to go back UP. I think it may have reached zero velocity a foot or more above the deck ( and would have gone back up if the engine had not shut down). Because the legs did NOT move any to indicate they were touching the deck, when the engine shut down. Then you can see the rocket drop a bit and the leg tips move out as they contact the deck and finally support the weight of the rocket. The more I watch it the more I'm sure that's what happened. AFAIK, this has not happened before. But well within the structural design to fall from not too high

This animated gif I found shows the landing (I later found out after posting this, that others on NSF and elsewhere noticed this too). But it's more obvious in watching the youtube webcast on full screen.

giphy.gif
 
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nice onboard view of the landing. I did notice that their animation showed them launching from Florida...oops.
Rex
 
Good launch, staging, and entry burn.

Landing burn begun.

WOW GREAT LANDING!
...<snipped>
This animated gif I found shows the landing (I later found out after posting this, that others on NSF and elsewhere noticed this too). But it's more obvious in watching the youtube webcast on full screen.
In the attached graphic I made you can see how little the vertical height changes during the last 1.3 seconds or so. For almost 1 full second there is very little change in height as it appears to hover. Pretty crazy that in even the rough seas it looked like a super soft landing.


Tony

(I am assuming 30 fps)

Hover.jpg
 
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Good launch, staging, and entry burn.

Landing burn begun.

WOW GREAT LANDING!

Had a LOT of shaking when the landing burn began. Perhaps related to going Transsonic, lots of turbulence to begin wit,h and the grid fins do not work well in that phase. They might need to tweak the control feedback/authority values for that phase. I do not recall shaking that bad from an onboard camera view, so this may be related to the improved grid fin performance/behaviour. Also do not recall seeing a grid fin move back and forth and back and forth to the extent that the left one did.

That great side by side photo that dhbarr posted, the apparent scalloping seems to indicate a very sharp leading edge (the edge once deployed, coming down), and the flat surface we see is the trailing edge. Like a wedge cross-section. Wedges work well at supersonic speeds. And flat plates do not, which is what the original F9 grid fins used.

WHOA! I knew the landing looked so soft. Well, watched it again. TOO soft - it never landed before engine shutdown!

As you may recall, the Merlin engine's minimum throttle is still more thrust than the F9 weighs during landing. So if during landing, it comes to zero downward velocity and has NOT touched down yet, it is going to go back UP. I think it may have reached zero velocity a foot or more above the deck ( and would have gone back up if the engine had not shut down). Because the legs did NOT move any to indicate they were touching the deck, when the engine shut down. Then you can see the rocket drop a bit and the leg tips move out as they contact the deck and finally support the weight of the rocket. The more I watch it the more I'm sure that's what happened. AFAIK, this has not happened before. But well within the structural design to fall from not too high

This animated gif I found shows the landing (I later found out after posting this, that others on NSF and elsewhere noticed this too). But it's more obvious in watching the youtube webcast on full screen.

giphy.gif
[/QUOkTE]

Pretty tricky business landing at sea, the barge even if kept perfectly flat, it will still be going up and down. So which height will you go for? Assuming you have one engine running its at min power there is no way you can adjust for a slightly lower barge at the exact instance you happen' it's a case of cut the power and hope it's not too high. Of course the opposite can be an issue too, if you aim even lower but the barge hits a big wave it's going to be higher than you expect and you'll still be on the way down when you hit the barge coming up. Fortunately in that case you may have enough time to tweak the thrust a bit.

Also the transition of weight onto the barge isn't zero weight instantly changing to full weight, with the thrust bearing down on the barge it is actually full supporting the weight of the rocket before it lands. Not sure how much the rocket weighs compared to the barge but the barge will be forced into the water before and after landing. But with the 1 foot drop the weight is momentarily off the barge it should in fact rise to some extent before the rocket falls on it.
 
OK, back to the new grid fins.

why are the fins not flat er the underside edges?


Elon Musk @elonmusk
More aero effectiveness to create steep spires on windward side at the grid fin intersections


From a post on NSF, a link to a report about the kind of grid fins SpaceX is now using. This link to the forum message:

https://forum.nasaspaceflight.com/index.php?topic=42097.msg1695055#msg1695055

Report title:

Novel High-Performance Grid Fins for Missile Control at High Speeds: Preliminary Numerical and Experimental Investigations

The numerical and experimental results show that the novel design of the lattice wings has distinct advantages in comparison to the conventional not-swept configurations. Compared to conventional lattice wings the maximum benefit e.g. of the zero-lift total drag for the investigated locally swept lattice wings is of the order of 30% - 40%

And this link to automatically download the pdf file (no preview)

https://tinyurl.com/y7g2co6s

This drawing from the report, normal grid fin on left.

index.php


So, this view shows the swept designs' scallops/spikes/spires/whatever, along the sides

hZH3XMU.jpg


So the average thickness (chord once deployed) may be greater than before. And for a given size, the design is a lot more effective anyway.
 
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iridium dispersion.JPG

Just after the last deployment, they entered sunlight, and five of the sats were visible all in a row.

Too bad the new iridiums won't generate flares.
 
OK, probably a dumb question, but I'm curious. Video here: https://spaceflightnow.com/2017/06/...t-lifts-off-from-vandenberg-lands-in-pacific/ . What is that 'extraneous' fire coming out the back end of the F9? Look around the :57 second time in the video clip. It's a flickering flame at the base of the cluster, orange in this video, but not coming from any of the nozzles - in slower flight it can appear fairly extensive. It's been there on every flight I've watched, and even appears to be there during the landing burn.
 
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What is that 'extraneous' fire coming out the back end of the F9?

Seen also, as I recall, on other boosters before the F9. (I think even Saturn V did this to some degree?) I also wonder where it's coming from. It's engine plume somehow, I guess... gotta be a wildly active environment right above the nozzles, right?
 
OK, probably a dumb question, but I'm curious. Video here: https://spaceflightnow.com/2017/06/...t-lifts-off-from-vandenberg-lands-in-pacific/ . What is that 'extraneous' fire coming out the back end of the F9? Look around the :57 second time in the video clip. It's a flickering flame at the base of the cluster, orange in this video, but not coming from any of the nozzles - in slower flight it can appear fairly extensive. It's been there on every flight I've watched, and even appears to be there during the landing burn.

I don't know for certain if this is the case for Falcon 9, but I think some kinds of liquid fueled rockets burn some fuel and oxidizer to run a turbo pump, and that pump is the "fuel pump" which forces the propellants into the main engines. Exhaust and flames from the turbo pump system vent off to the side and don't go out through the nozzle, so it looks like an "extraneous fire".
 
Seen also, as I recall, on other boosters before the F9. (I think even Saturn V did this to some degree?) I also wonder where it's coming from. It's engine plume somehow, I guess... gotta be a wildly active environment right above the nozzles, right?

Yes, it's exhaust plume recircularization. The base of the rocket has a lower pressure than the air aorund it (due to the high speed airflow), which for our models we often call "Base drag". It sucks up some of the exhaust flame from the engines. It's an issue for almost any rocket, just a matter of degree. And happens to most of our models too. Ever notice on some models that the bottom centering ring is dirty, of that fin trailing edges near the root are dirty or even charred?

Saturn-V had it:

1294_20_the-apollo-11-saturn-v-space-veh~t-apollo-11-pictures-that-amazed-us.jpg


Space Shuttle had it. The base of the ET had a massive amount of flame recirculating under its aft dome. So much so that the foam insulation was about 3 times as thick for the aft dome as it was for the sides, acting as an ablative to keep the aft dome from overheating. Can't find a photo of it. Here's a cool video, period. It does not show a more direct side view where the flames would be as obvious as some video I have seen, but at about 1:30 you can see it faintly start to happen in the left frame, as the yellow/orange aft dome foam begins to darken. When the SRB's sep, in the upper right frame, you can see how most of the aft dome is charred black.

[video=youtube;DXXrAiXUeXE]https://www.youtube.com/watch?v=DXXrAiXUeXE[/video]

Thirstybarbarian mentioned turbopump exhaust. A lot of rockets used to do that, and some still do. I did not recall if Falcon9 did or not (some engine designs route the turbopump exhaust into the engine nozzle). Seems that the Falcon-9's Merlin 1D has external exhaust. The photo below, the blue caps are likely pre-flight covers over the exhaust ports (and the protective base panels have not been installed yet)

index.php


So, the Falcon is dumping exhaust that is visible then becomes more visible as it gets moving faster for lower pressure at the base, peaking by Max-Q. After all, when it is taking off at first, all those exhaust port flames are hidden inside of the exhaust of the outer 8 engines. But since the exhaust is not a high velocity stream flow, it is easier for the lower pressure at the base to expand it outwards, recirculate, and become more visible.
 
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That was an awesome video!!! It's been so long since I have seen a Shuttle launch, I kind of forgot how cool they were.
 
On a lot of the flights, I've noticed a small amount of flame near the base of the rocket that does not seem to be recirculation. I'm having a problem uploading a screen capture from my "device", but if you watch the video, as soon as they cut back to the zoomed in shots after clearing the clouds at around 40 - 45 seconds into the launch, you see small flames around the base of the rocket, above the nozzles.
 
Something that's been bugging me, is how the hydraulic piston assembly fits inside the legs when stowed. They just don't look like they'll fit. Found a good video showing how they deploy.

[video]https://forum.nasaspaceflight.com/index.php?action=dlattach;topic=33526.0;attach=562 376;sess=0[/video]
 
Here's a photo of a leg at SpaceX HQ.

YXCrb.jpg


I have heard several times that the final deployment of the legs is by falling into place due to gravity, but even so would need some method to help push them down at first. A google search on the web found very little except for one reference repeated elsewhere that it uses pressurized helium to deploy the legs pneumatically. Probably both, pressure to pneumatically get them moving down, then gravity taking over the rest of the way (technically not gravity but the landing burn deceleration under thrust at more than 1G).

No hydraulics, those are heavy and would require powerful pumps and a lot of fluid. The Falcon has lots of pressurized helium onboard to fill the inside of the tank volume as the fuel is pumped out. OK, so they do have a hydraulic system for steering the grid fins, but that is a relatively small pump system and limited hydraulic fluid compared to what it would take to rapidly 100% deploy and hold rigid four big legs if they did not have lockouts. BTW - the Grid Fin hydraulic system was changed from open loop (dumping the hydraulic fluid) to closed loop to recirculate the fluid (they changed that 2 years ago but Musk only broke that news with this flight).

Legs have lock-outs so that as they fully deploy, the lockouts click in place to keep them from folding back. On the Jason-3 mission's booster landing (January 2016), the booster landed safely on the ASDS barge, but one leg did not lock out, so it fell over and kaboomed. It was launched from Vandenberg when there was a lot of fog, and it was suspected that the moisture from the foggy conditions, and the extreme cold of the Lox inside the uninsulated tank, had caused ice to form in the lockout to prevent it working properly, allowing the leg to fold back. They made some changes to the lockouts, perhaps including some electrical warmers to prevent icing.
 
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