Business, Space, Technology and Society, Weird

“Landing” A Super Heavy

27 Comments

Elon issued a crazy tweet yesterday.

And someone has already come up with a render.

27 thoughts on ““Landing” A Super Heavy”

  1. It’s very interesting that tweet. But upon reflection it does make a good deal of sense. Creating landing support infrastructure for Super Heavy adds a lot of dead weight to the vehicle. This would minimize that with likely minimal change to the grid fin infrastructure. Fascinating.

    1. It does complicate landing logistics a bit because remote landing sites at sea will require a landing tower type infrastructure instead of just a large floating platform. Which begs the question is the plan for Super Heavy RTLS landings only?

  2. There was a time when landing a booster on a drone ship in the middle of the ocean was thought to be crazy. Now it’s SpaceX standard procedure. If anyone can do it, Musk can.

  3. Strengthening the grid fin support structure to take the load will require mass, increasing the landing accuracy to allow landing directly back on the launch pad will require more return fuel (slower final approach to allow time to make last second precise corrections to landing spot) hence more mass. At some point the legs are simpler, cheaper, lighter.

    Happy to be proven wrong though.

    1. I think the structural area around the grid fin is already beefed up for aerodynamic loading that is highest, for return, a few hundred feet above the ground just before the landing burn lightens the load. It may already be sufficient for carrying the booster empty weight. But then, that’s the only way this makes sense to me.

      1. It may be strong enough to support static booster weight but I doubt it is strong enough to support that mass at any landing velocity exceeding a very small fraction of m/s.

        1. The landing velocity of Falcon 9 is effectively zero m/s, otherwise it’s a crash. Because there’s a possibility of some residual the F9 legs have crush cores which are usually not crushed. There’s no reason to suppose the SH landing velocity won’t normally be zero m/s, with the “catcher” likely a cable system that will function in lieu of crush cores (much like a carrier landing arrester cable, or the reel system on your seatbelts). It only sounds impossible. But it’s not.

          1. I tend to think a cross cabled system to snare the grids fins also likely. Maybe unreeled from a capture ring that gets extended over the pad post launch. Gimbaled Raptors are key recovery elements. This is being proven out on Starship now.

      2. Combined response to Ctrot and Leland:

        I think the most stress on the grid fins comes at high Mach numbers high in the atmosphere where they support the whole weight of the stage and remaining propellant at multi-G deceleration. Compared to that, free-falling low-down at a subsonic crawl is next to being stress-free. So is hanging from a “catcher” at 1G and practically zero propellant mass. I don’t see a single gram of extra structural mass on Super Heavy being required to pull this off.

  4. I get David Spain’s point about decreasing weight of landing structure. However, if that render is near accurate, then you’ll need extra fuel to stop, translate, and then lower at a force that won’t rip the tower arm off. So why the tower arm? It’s not like that is designed to carry much of a load beyond it’s own weight.

    I would think an above ground silo configuration would be better, such that the rocket slides into a hole, rather than translates to a U frame. Essentially you raise the alignment and landing point a few hundred feet in the air, but the silo requires only one alignment versus two with the U frame.

    And if you do either, then I also wonder why you would do that on floating platforms? There, I think I have an answer. Some boosters will land on the grid fins and others will have landing legs. If you need more performance, then you use the grid fins. Perhaps only the side boosters land grid fin and the center booster lands on legs?

    I’m still not impressed with the folks at NSF. They still seem stuck in the mindset that only the whip and buggy works.

    1. I don’t get the render. It seems far simpler to use the silo/ring approach. On launch the booster translates through the ring unobstructed while for landing catch arms extend from the inside of the ring for the booster to translate and drop into. Aligns directly with the pad so simple vertical motions reorient for launch. Also the render shows fins / landing legs on booster. If a ring is employed those aren’t necessary, assuming gimbaled Raptors. I suspect the operational launch tower won’t look much like the one employed at LC-39A. Why should it? Will Super Heavy ever be positioned horizontally and “erected”? I doubt it. Why do that?

    2. If the SH is descending with enough force to rip down the tower, it’s already crashing and the computer will divert to a nearby flat spot where it can make a nice crater. SH will only descend into the catcher if the descent is good.

      I received a lifetime ban from NSF for a bit of backtalk to one of their supergenius experts. That was 11 years ago. It was a terrible timesink and I was glad to go. A hundred years from now, regarding antigravity and FTL starships, NSF experts will be proclaiming that methane fueled rockets are the only way to go.

      1. I was never a big fan of the moderated web forums, coming from the wild west days of USENET News. I think it is better to be heard regardless of how badly informed one might be than bans and censorship. I believe Web Forums were a progenitor of cancel culture, which is not good for civilization at large. Wear your ban as a badge of honor. I had finely honed filters I used to prune USENET news of the trolls. Regrettably, traffic there (mostly due to its inability to host graphical and multimedia content) has shrunk to the point that what transpires there isn’t very interesting, at least to me. The ARocket mailing list is very good, but tends to flip over at times to the super-technical that I’m not qualified to comment upon nor understand without a few semesters of college courses for which I don’t have the time and tends to focus particularly on what is of interest to its members in amateur rocketry (as one would expect).

        1. One of the greatest annoyances I had with NSF was the continuous silo-ing of information. Make a comment slightly off-topic and boom, if it isn’t removed outright it gets binned somewhere that, unless a link is provided, good luck finding it.

          Also happens when an argument gets a little heated. But sometimes that’s precisely the tipping point where the information gets interesting. Esp. when 3rd parties chip in. But alas, often information is sacrificed in the name of comity. At least that doesn’t happen here. 😀

    3. Side boosters? Center booster? This discussion is about Super Heavy, which is a single-core booster, not a 3-core deal like Falcon Heavy.

  5. This reminded me of the Brodie systems used to launch and recover aircraft with an LST during WW2. Necessity is the mother of invention.

  6. They will have to call it, Big Pappa, or something similar because no one catches a falling baby like a dad.

  7. Well, since we are talking crazy.
    So it seems problem is size of legs to land without being
    instable.
    So have simple idea of using a big pipe which has one end
    capped- call it pipelauncher. And powered liquid air and water displacement.
    And made more complicated by having it have stages, ie, two stage or three stage pipelauncher {mainly to use less liquid air}.
    And then with starship I added what call a pit- mainly cause starship is so massive and tall- and to use less liquid air.
    And with the pit, the legs are a complication and wasn’t thinking catching spent stage with pipelauncher, though consider the problem of having abort option with a launch.
    And having abort option of launch is slightly similar to catching a spent stage.
    So, aborted is pipelauncher is going up {vertical} and at some point lits rocket engine, and if can’t lit engine, you have recover with fully fueled rocket {and try again}.
    And catching spent stage is having pipelauncher high above waterline, having spent stage “land” in the pit, while pipelauncher is coming down {like aborted recovery}.
    But as with those legs, with a recovering of spent stage, the pit needs the larger diameter.

  8. Three poles, cables, inertial reels. Keep it simple, stupid, Isn’t that the way engineering is supposed to work? Or we can just have the rocket catcher designed by modernst free verse poets.

    1. His first design was what I was thinking related to silo. It doesn’t need to be a solid cylinder, but the vehicle would slide vertically into a ring. His second option of two arms that rotate to either side is interesting.

    2. As Scott points out keeping the Raptors at a safe distance off the deck minimizes the chance of kicking up debris that would damage them. Also, as he points out, it allows a sound suppression system to operate underneath the returning booster. Seems like good trade-offs to me. You’ll need confidence in your GNC anyway whenever trying to pull off powered descents. Pad infrastructure should be made modularized for quick replacement with hard to replace items (like tankage) kept at a safe distance or in underground bunkers. Assume pads will be damaged due to failed recovery attempts. Hopefully not too many RUDs.

  11. A couple of points to remember: The SH grid fins are nine meters long, which means the “finspan” is 27 meters across (counting the nine meter hull diameter). The landing accuracy of Falcon 9 is in the 1 – 2 meter range, and there’s no reason to expect SH will be worse. Then, the grid fins fold down to the hull (a 90 degree range of movement) and a actuated by hydraulics. That suggests the hydraulics themselves can take the place of a crush core. Rather than cables, angle the fins down a bit and thread the needle of a 18 meter ring, letting the ring slide up as the fins absorb the residual, if any. The ring doesn’t move during landing and the rocket does all the work. If the ring has movement, it would be to lower the rocket to the launch mount and drop down to get below the folded grid fins. No reason you can’t launch through the ring on the way back up.

    1. Yup a ring or a ring of cables would work. It might even have the ability to do sone shock absorption. Yes also to the idea of the ring fixed in place even at launch because the retracted grid fins should pass through easily.

      I don’t think Musk is trolling anybody. Pushing the recovery mass back onto the pad infrastructure just makes such a tremendous amount of sense. Starship pads aren’t going to look much like your grandfather’s pads at the Cape. In fact they may end up being multi-story structures (or the service bays) to allow roll-on roll-off attachment of Starships. The less screwing around with cranes the better. In fact I wouldn’t be surprised to see an eventual race-track processing pathway for supporting multiple service structures that are in various stages of Starship or SuperHeavy booster deploy modes. Mobile rocket factories.

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