F9 Block 5 Updates and Discussion

[john smith 19]

Every component has a different lifetime, so it doesn't matter if the titanium grid fins last beyond the life of the first booster they are attached to because there will be plenty more components (Merlin engines as more expensive items) that will also be transferred from the booster body after it has reached the end of it's useful life.

A fair point but I'm reminded of Masten's comments that they didn't reuse flight computers after a crash because it was too easy to end up with a board with a missed hairline crack that would destroy the next vehicle it was controlling as well. Obviously that's a specific situation but the hover slam landing is pretty harsh on structure (I think the only thing that comes close is an aircraft carrier landing, and such aircraft have substantially heavier landing gear than land based aircraft, or even land based variants of the same aircraft).

Actually the titanium grid fins are forgings, not machined. Both are expensive and hard, but just wanted to point that out.

Noted.
That was a loose use of English, treating machining as a simile for any mfg process.
However AFAIK, with the exception of diffusion bonding (people say it can be done in Aluminum but the limitations seems quite severe. Hard vacuum or brazes seem to be needed) all methods of working Titanium are more effort than Aluminum, either in terms of time (CNC programmers I've spoken to say it tends to "stick" to cutters, so many more light cuts than eveny high grade Aluminum alloy) or energy. IIRC Titanium needs at least warm working for forging and that "warm" is above the melting point of Aluminum.

I was just reading about the first A380 that was going to be put into flyable storage, and they were talking about how most of the value of the aircraft was in it's engines, since they can be pulled and used on another aircraft. So using commercial aircraft as analogies, there will be lots of parts that will move around onto new and used boosters. Titanium grid fins are just one of the parts.

Which sounds like the thinking that underlies the ULA SMART plan for Vulcan. Obviously that changes when you have the whole stage to strip, but then that's a chicken and egg question.

Something else to keep in mind is that it probably matters to the Falcon 9 control software whether the aluminum grid fins are used or the titanium ones, and history is littered (literally) with hardware that failed because updates were not done properly. So standardizing on one type of control surface likely makes a lot of sense, and not having to replace them all the time would likely be the least expensive option too.

Now that's a very good point. 

IIRC the Ti fins were bigger than the Al ones and with it's higher density that suggest quite different aerodynamic and mass properties. Fitting those to a stage programmed to expect Aluminum fins (or vice versa) would be a very bad day. 
It might still work, as the GNC system desperately tries to compensate for control surfaces that are bigger and heavier than it expects, but it's simpler to put control constants for both sets in memory and simply set a variable to the correct type.

Knowing SX's fondness for minimizing multiple variants I still expect them to go Titanium permanently for bkl 5.

We have no real insight into the costs.

It doesn't need to get very expensive for the labour of a guy spending a week sandblasting/recoating the fins to be cheaper than the cost of shiny new titanium fins.
If the labour costs $5K, and the forged Ti finset 250K, ...

True.

Also IIRC Musk said those were some of the biggest of their kind Ti forgings ever.  That strongly suggests they were not done in house. The list of vendors who can do that work is short and SX would be dependent on their schedule wheather they can get more of them made. One set might have been reasonably easy, but getting it as a regular order may be much more difficult.

It wouldn't even slow down the flow perhaps as the fins don't have to go back on a reflight.

For the case of one or two reuses per stage, especially as they have quite a lot of nonreflown stages to pull parts off if they choose, light repairs could be significantly cheaper.

Exactly. But what's not an issue at 2-3 reflights may be a major PITA at 10.

Or perhaps they've just found something more productive in the future for their Ti forging of large billets capabilities to do, and they'd rather have the few guys experienced in that area do that, rather than 'fix' what they now realise is a problem that now doesn't seem as bad once they've got experience.

Equally possible.

I don't have a real good quantitative feel for CNC Vs forging.
My instinct is that cycle time for forging and waste material will be quite low (good because while Titanium has gotten cheaper it's still several times the cost of Aluminum) as it's (mostly) a near net shape process.

But getting that machine time is the tough part.  If those fins need the press sizes I think they need those machines are booked up months (years?) in advance. While it's not a particularly deep part it has a lot of surface area, so the tooling is going to be big as well. It has to resist high loads and either withstand intermittent heating or run hot (isothermal forging). The joker here is wheather the tooling is the final design (good for all future fin sets) or if flight testing showed it needs modifying. Not a problem if they need to make the holes bigger (just shave some off the dies) but more awkward if they have to make them smaller.

Ideally you want to make these in batches. Not 4 at a time, multiples. Again I've no feel for an economic batch quantity. As many can be made in a working day, including tooling installation and removal (so the presses are ready for the next product to be processed)?

There's a history of diffusion bonding at NAA (in the 60's and 70's) which explains one of the goals of using DB was to avoid needing to machine big billets of it (the "buy to build" ratio) while at the same time side stepping the need for the very big presses which were the only way people thought you could do near net shape mfg at the time.

BTW since then Ti casting has greatly improved. Foundries are claiming (and IIRC Airbus are using) castings with "casting factors" (ratio of weight of casting to same part made by machining or forging) of 1.0-1.1. IE 0-10% weight penalty over machined/forged parts.

With 3d printing of the shape and lost wax(lost plastic?)  casting for the mold high(ish) volume would not be a problem if the foundry can supply enough clean, molten Ti alloy. That is not a trivial issue. These parts are big and Ti alloys are more like Magnesium than Steel to cast, but it may be a future option. Forging delivers excellent quality but it has several penalties (not just the unit price) that SX may not be willing to pay long term for the kind of volumes they need.

As you say, we don't have enough insight into their costs to know what factors are influencing their decisions.

[macpacheco]

I can't help but to conclude people are just way too worked up about Ti fins.
SpaceX might be planning to use Ti fins only with Block V intended for reuse (there's still the possibility of a few expendable Block V launches).
Maybe Block V and FH launches.
There is no evidence that Al fins have to be refurbed after a LEO mission, which is the only scenario for reuse so far (booster used on a single LEO launch).
Its possible the same Al fins can fly a few times on LEO missions.
SpaceX knows their safety margins. Just because it glowed during re-entry, doesn't follow the fins are gone.
After all they have withstood a few recoveries which were hail marry attempts.

That single Ti fin launch likely was to verify its operations, and Al fins are good enough for current missions.

How about a little less obsessing, please ?

[JamesH65]

I can't help but to conclude people are just way too worked up about Ti fins.
SpaceX might be planning to use Ti fins only with Block V intended for reuse (there's still the possibility of a few expendable Block V launches).
Maybe Block V and FH launches.
There is no evidence that Al fins have to be refurbed after a LEO mission, which is the only scenario for reuse so far (booster used on a single LEO launch).
Its possible the same Al fins can fly a few times on LEO missions.
SpaceX knows their safety margins. Just because it glowed during re-entry, doesn't follow the fins are gone.
After all they have withstood a few recoveries which were hail marry attempts.

That single Ti fin launch likely was to verify its operations, and Al fins are good enough for current missions.

How about a little less obsessing, please ?

I mostly agree, but if an aluminium fin starts to glow, it's had it, since at the point of glowing it's lost all strength.

[Herb Schaltegger]

I can't help but to conclude people are just way too worked up about Ti fins.
SpaceX might be planning to use Ti fins only with Block V intended for reuse (there's still the possibility of a few expendable Block V launches).
Maybe Block V and FH launches.
There is no evidence that Al fins have to be refurbed after a LEO mission, which is the only scenario for reuse so far (booster used on a single LEO launch).
Its possible the same Al fins can fly a few times on LEO missions.
SpaceX knows their safety margins. Just because it glowed during re-entry, doesn't follow the fins are gone.
After all they have withstood a few recoveries which were hail marry attempts.

That single Ti fin launch likely was to verify its operations, and Al fins are good enough for current missions.

How about a little less obsessing, please ?

I mostly agree, but if an aluminium fin starts to glow, it's had it, since at the point of glowing it's lost all strength.

As several folks have pointed out, the glow we see in the entry footage is indicative of not necessarily "glowing white hot" aluminum. Rather, removal of a camera's IR filter combined with over-saturation of the camera sensor in the near-IR bands. Yes, the fins get hot. But not - generally speaking - hot enough to glow white to a human eye, as the camera footage appears to show.

Yes, some of the earliest landings showed fin webs eroded or even burned through in one or two cases. But it's clear SpaceX has either changed coating substances or application techniques, perhaps combined with entry trajectory shaping, since we've not seen any such obvious fin damage on recently-returned cores.

[AncientU]

I can't help but to conclude people are just way too worked up about Ti fins.
SpaceX might be planning to use Ti fins only with Block V intended for reuse (there's still the possibility of a few expendable Block V launches).
Maybe Block V and FH launches.
There is no evidence that Al fins have to be refurbed after a LEO mission, which is the only scenario for reuse so far (booster used on a single LEO launch).
Its possible the same Al fins can fly a few times on LEO missions.
SpaceX knows their safety margins. Just because it glowed during re-entry, doesn't follow the fins are gone.
After all they have withstood a few recoveries which were hail marry attempts.

That single Ti fin launch likely was to verify its operations, and Al fins are good enough for current missions.

How about a little less obsessing, please ?

Obsessing is what we do, though... SpaceX is also obsessing about rapid turn-around after flight (if 24 hour goal isn't obsessive, not sure what is) and the Ti grid fins put that component to bed as far as rework is concerned*.

Obsessing aside, Block 5 will be manufactured for rapid reuse, end-to-end.  Expect nothing but a post-flight inspection if they are successful. 


* Probably including GTO flights.

[envy887]

I can't help but to conclude people are just way too worked up about Ti fins.
SpaceX might be planning to use Ti fins only with Block V intended for reuse (there's still the possibility of a few expendable Block V launches).
Maybe Block V and FH launches.
There is no evidence that Al fins have to be refurbed after a LEO mission, which is the only scenario for reuse so far (booster used on a single LEO launch).
Its possible the same Al fins can fly a few times on LEO missions.
SpaceX knows their safety margins. Just because it glowed during re-entry, doesn't follow the fins are gone.
After all they have withstood a few recoveries which were hail marry attempts.

That single Ti fin launch likely was to verify its operations, and Al fins are good enough for current missions.

How about a little less obsessing, please ?

I mostly agree, but if an aluminium fin starts to glow, it's had it, since at the point of glowing it's lost all strength.

As several folks have pointed out, the glow we see in the entry footage is indicative of not necessarily "glowing white hot" aluminum. Rather, removal of a camera's IR filter combined with over-saturation of the camera sensor in the near-IR bands. Yes, the fins get hot. But not - generally speaking - hot enough to glow white to a human eye, as the camera footage appears to show.

Yes, some of the earliest landings showed fin webs eroded or even burned through in one or two cases. But it's clear SpaceX has either changed coating substances or application techniques, perhaps combined with entry trajectory shaping, since we've not seen any such obvious fin damage on recently-returned cores.

Also, they appear to be covered in SPAM, which is probably a good enough insulator to be glowing on the outside while the aluminum underneath is cool enough to avoid any metallurgical changes.

[OneSpeed]

That single Ti fin launch likely was to verify its operations, and Al fins are good enough for current missions.

The Iridium-2 mission probably was intended to validate the Ti grid fins, but I'm not convinced the results were entirely satisfactory. The larger fin increases control authority, but the scalloped leading edges actually reduce drag, which may not be desirable. Perhaps there will be a further iteration of the Ti grid fin design before its usage becomes commonplace?

[ClayJar]

That single Ti fin launch likely was to verify its operations, and Al fins are good enough for current missions.

The Iridium-2 mission probably was intended to validate the Ti grid fins, but I'm not convinced the results were entirely satisfactory. The larger fin increases control authority, but the scalloped leading edges actually reduce drag, which may not be desirable. Perhaps there will be a further iteration of the Ti grid fin design before its usage becomes commonplace?

Out of curiosity, what is the lead time for setting up to manufacture a large titanium forging?  Would it be reasonable to assume that the titanium grid fins we saw demonstrated were manufactured as prototypes (e.g. machined out of billet titanium) to get real flight experience and validate the models before proceeding along toward production?  Even if the design was validated with performance matching the models, a lag between a machined prototype and a forged (and machined) production run would seem logical.  Alas, I have no manufacturing background to know how long a lead time to forecast.

[Semmel]

How do you forge a lattice structure like the grid fins anyway? Sounds like a daunting task to get the metal into that shape..

[cambrianera]

Typical process and results.

[nacnud]

Video of forging aluminium, forging starts at 8:55.

http://dmmclimbing.com/knowledge/dmm-factory-tour-vid/

[almightycat]

The grid fin is "cast and cut", not forged: https://twitter.com/elonmusk/status/878821062326198272

[ClayJar]

The grid fin is "cast and cut", not forged: https://twitter.com/elonmusk/status/878821062326198272

Musk: New design coming for Grid Fin.  Will be largest titanium forging in the world.  Current Grid Fin is aluminum and gets so hot it lights on fire... which isn't good for reuse.

Yes, the tested set of titanium grid fins we saw were machined ("cast and cut"), but the production titanium grid fins will be forged.  The fact we haven't seen titanium grid fins again yet may imply that they passed their testing, as if they needed to be altered, we may have seen a new build of test titanium fins by now.  Seeing none, my personal assumption would be that the testing was successful and they're setting up for the forged production version (which takes more to get rolling than just machining one set).

[john smith 19]

Yes, the tested set of titanium grid fins we saw were machined ("cast and cut"), but the production titanium grid fins will be forged.  The fact we haven't seen titanium grid fins again yet may imply that they passed their testing, as if they needed to be altered, we may have seen a new build of test titanium fins by now.  Seeing none, my personal assumption would be that the testing was successful and they're setting up for the forged production version (which takes more to get rolling than just machining one set).

I did not realize this.

I did recall Musk saying they were (will be?)s ome of the biggest Titanium forgings ever. To put this in perspective the book "Diffusion bonding of Titanium Metal Structures" by Joe Melill described teh forging of the H53 helicopter rotor hub in Titanium (in the late 60's)

This 1200lb of Ti to be hot forged to give a 350lb finished part (after a lot of machining).  It took the biggest press on the North American continent, Govt owned but operated by Wyman Gordon and was (is?) rated to 50 000 tons. Interestingly the DB assembled structure had better material properties than forging and isn't the Octoweb fabricated in Titanium?

The upside is the mfg should be fairly fast. Essentially you're looking at a tool and die set like a monster waffle mold, that can cope with hot Titanium.  Once  you've got the billet in place a relatively small number of smacks should do most of the work before finish machining (although the CNC's for this will also be quite large).

[intrepidpursuit]

https://twitter.com/elonmusk/status/878821062326198272

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

They are cast to an approximate shape and then machined to an exact shape. You can't really forge complex shapes directly, totally different process (hammers and folding).

[Coastal Ron]

https://twitter.com/elonmusk/status/878821062326198272

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

They are cast to an approximate shape and then machined to an exact shape. You can't really forge complex shapes directly, totally different process (hammers and folding).

Forging is in no way related to casting, so I tend to believe Musk when he says the new grid fins will be forged.

As to "hammers and folding", I think you're thinking of smithing-type forging (i.e. ironworking). 20th century metalworking can do a lot more. An example of titanium forging (smaller parts than grid fins though):



An interesting article about titanium forgings at forging.org:

4.6 Titanium Alloys | Forging Industry Association

[gongora]

The "cast & cut" comment came several months after the forging comment, and he had other comments about the grid fins in that conversation on twitter.  I wouldn't count on the earlier one being the most accurate.

[intrepidpursuit]

https://twitter.com/elonmusk/status/878821062326198272

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

They are cast to an approximate shape and then machined to an exact shape. You can't really forge complex shapes directly, totally different process (hammers and folding).

Forging is in no way related to casting, so I tend to believe Musk when he says the new grid fins will be forged.

As to "hammers and folding", I think you're thinking of smithing-type forging (i.e. ironworking). 20th century metalworking can do a lot more. An example of titanium forging (smaller parts than grid fins though):



An interesting article about titanium forgings at forging.org:

4.6 Titanium Alloys | Forging Industry Association

I just quoted Elon, he said CASTING. Where are you getting forging from? I understand that modern forging doesn't use a smith hammer anymore, but it is still working with hot but solid metal and pressure rather than molten metal and cast. Making holes, thin shapes and fine 3D elements is not a strong suit of forging.

By casting the rough shape and then machining, you have little material waste and the fewest steps to a finished product. Forging provides extra strength compared to casting, but it would seem that was not an issue in this case.

[intrepidpursuit]

https://twitter.com/elonmusk/status/878821062326198272

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

They are cast to an approximate shape and then machined to an exact shape. You can't really forge complex shapes directly, totally different process (hammers and folding).

Forging is in no way related to casting, so I tend to believe Musk when he says the new grid fins will be forged.

As to "hammers and folding", I think you're thinking of smithing-type forging (i.e. ironworking). 20th century metalworking can do a lot more. An example of titanium forging (smaller parts than grid fins though):



An interesting article about titanium forgings at forging.org:

I just quoted Elon, he said CASTING. Where are you getting forging from? I understand that modern forging doesn't use a smith hammer anymore, but it is still working with hot but solid metal and pressure rather than molten metal and cast. Making holes, thin shapes and fine 3D elements is not a strong suit of forging.

By casting the rough shape and then machining, you have little material waste and the fewest steps to a finished product. Forging provides extra strength compared to casting, but it would seem that was not an issue in this case.

Perhaps this is where you are getting forging:

Musk: New design coming for Grid Fin.  Will be largest titanium forging in the world.  Current Grid Fin is aluminum and gets so hot it lights on fire... which isn't good for reuse.

That quote was forward looking, verbal, and off the cuff in March. In June, he said the current fins are cast and cut in writing. I'd believe the later quote.

[cscott]

Why not both: prototype ("current") Ti fins cast and cut, forthcoming fins same shape but forged?

It would explain the long gap (to set up a forging process) between the flight of the prototype and production use of the new fin design.