Asymmetrical LV

There are several limitations on the ability to expand a launch vehicle past certain sizes. One of them is tank diameter. On the smaller launchers, diameter limits might be dictated by available pipe sizes. A step up from there and tank diameter might be limited by available tooling. A couple of steps up from there and ground transport becomes an issue. Too large and it becomes somewhere between inconvenient and prohibitively expensive to transport from factory to launch site. Another limitation is height and fineness ratio. A launch vehicle gets into problems when the stack length is too large a multiple of tank diameter. 8″ irrigation tubing might be a good basis for a 10′ rocket, but gets into trouble before it reaches 20′. By the same token, the Atlases, Falcons, and similar vehicles are probably very close to the limits of length in relation to diameter. The standard build for a launch vehicle is, starting from the bottom, engines, fuel tank, inter tank structure or common bulkhead, LO2 tank, inter stage adapter, engine, fuel tank, inter tank structure or common bulkhead, LO2 tank, and payload. This is all in one long skinny cylinder except for a hammerhead shroud. To make the launch vehicle larger requires either more diameter, more length, or both, with the  manufacturing and transport problems from the diameter increase, or the structural problems from the length increase. There might be a way to double the size of a given vehicle class while holding the costs and other problems down. This idea is to build a vehicle that is asymmetrical around existing tooling. Also use a modular assembly technique to avoid both transport problems and the necessity of new tooling or construction techniques. Asymetrical LV   I still don’t have a computer that lets me draw cartoons all that well. The sketch is two possibilities for the vehicle concept. A stretched LOX tank built on existing tooling  that is as long as the original entire first stage. A stretched Kerosene tank proportionate to the LOX tank also built on existing tooling. These tanks are trucked separately to the launch site where they are clamped together along with the thrust structure. On the left the sketch has the helium tanks, avionics and such in the space above the shorter Kerosene tank with the second stage above the center line of the vehicle. The figure on the right has the second stage nested above the Kerosene tank with the helium tanks and such moved elsewhere. If this concept is feasible, a first stage could effectively double in size without causing problems in manufacturing and ground transport. Engines would double in number, but dome tank ends would not. The increased cost of the larger vehicle would be dominated by the engines. Eliminating the inter tank structures would eliminate a place for fumes to gather and possibly cause problems. The tank connectors could easily be lighter and cheaper than the normal inter tank structure. There would be no place at all for potentially explosive fumes to gather, which means that a leaking tank might be less of a problem. By going modular, any problem section could be swapped out with relatively little effort. The four modules being LOX tank, Fuel tank, thrust structure, and second stage. Two of these units could be flown together in a quad layout. Three of these units could act as boosters/first stage for a conventional  vehicle centered between them in the seven tank hexagon layout.

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I do construction for a living and aerospace as an occasional hobby. I am an inventor and a bit of an entrepreneur. I've been self employed since the 1980s and working in concrete since the 1970s. When I grow up, I want to work with rockets and spacecraft. I did a stupid rocket trick a few decades back and decided not to try another hot fire without adult supervision. Haven't located much of that as we are all big kids when working with our passions.

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About johnhare

I do construction for a living and aerospace as an occasional hobby. I am an inventor and a bit of an entrepreneur. I've been self employed since the 1980s and working in concrete since the 1970s. When I grow up, I want to work with rockets and spacecraft. I did a stupid rocket trick a few decades back and decided not to try another hot fire without adult supervision. Haven't located much of that as we are all big kids when working with our passions.
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14 Responses to Asymmetrical LV

  1. born01930 says:

    Or, why not have the LOX tank in the center, built with the structural matrix around it and engine plate under, then have the RP1 tank built in 2 C shaped pieces for easier construction and transport. They bolt on at the pad. No worries now about ice, the RP1 will help insulate so you can save some weight in LOX insulation.

  2. john hare says:

    I’m having a bit of trouble understanding your concept.

    Would the C shaped tank pieces also have an inner skin or would the RP be in direct contact with the uninsulated LOX tank. What would prevent the RP from freezing to the LOX tank? What would prevent the slightest tank imperfection from allowing one of the propellants into the other tank?

    How would the tooling up and manufacture of the C shaped tank halves be comparable in cost to using existing tooling by an experienced work force?

    A quick BOTE suggests to me that the C shaped tank halves could be nearly 40% larger diameter and travel by the same ground transport. Since this would nearly double the volume for a given length of tank, why not just make both tanks in this manner so that a semi-conventional layout launch vehicle could be built even longer with the extra diameter available for stiffening?

    How would the C shaped pieces attach at the launch site. Most of the joining methods I can think of off hand would be heavier and more leak prone than conventional monolithic tanks.

    All that being said, it would be interesting to find out if you are onto something here. Saturn class LV with a dozen long segments per tank that are truck transport capable. It would seem to lend itself to mass production and easy modular swap out of tank components.

  3. momerathe says:

    I would worry about the centre of mass shifting laterally as the propellants were burnt. It needs to balance both when empty – so structural mass must be the same on both sides – and when full; which given relative density and fuel-oxidizer ratio, I don’t see how you’d do it.

  4. john hare says:

    There would be concerns about a shifting center of mass, which would be addressed by making sure there is enough Thrust Vector Control to handle the problem. TVC on the asymmetrical Shuttle stack was handled by gimbaling the main engines as propellant was depleted and center of mass shifted from the LOX tank toward the orbiter.

    Thrust modification would be different for different companies.

    An Atlas mod would gimbal slightly to the right at launch and slightly to the left at near depletion of propellants. Additionally the left engine would throttle down when it came time to limit gee forces.

    A Delta mod would have a LOX shorter tank than the Hydrogen tank and so would have a nearly unchanging center of thrust. Or if even more lift was needed, a full length LOX tank with full length Hydrogen tanks on each side for a triple configuration that should be cheaper than the stock Delta IV heavy. For extra points, a hydrogen tank could be dropped on the way up.

    For a Falcon mod, the extreme left engines would be shut down for both throttling and to keep the thrust through center of mass.

    I don’t get your concern about structure being the same on both sides. The whole vehicle requires enough structure to support the loads that must be carried at any point in the launch profile. It seems unlikely to me that this would result in equal structures on both sides from a structural engineering point of view. For financial and manufacturing ease it may be desirable.

  5. Paul451 says:

    Any reason you don’t repeat the side-by-side design for the upper-stage? Especially for left-side version in your image. You could continue the same diameter tanks as the first stage (shorter length) to make manufacture easier/cheaper. The overall vehicle would have a biamese look.

  6. Paul451 says:

    (Staging for the right-side version might be… exciting.)

  7. johnhare johnhare says:

    iPhone comment will be short. Makes good sense continuing the pair on the left I don’t see the staging problem on th right. Expand?

  8. Paul451 says:

    I don’t see the staging problem on th right.

    You not only have the burnt out first stage behind the second stage, you have it simultaneously alongside. That separation trajectory will need to be very precise, down and to the left. Boosters/etc that run alongside can pull away to the side, and stages behind can drop back, but you have to do both at the same time.

    [The alternative is separating the individual parts. MECO, then jettison the engines/thrust-frame, then drop the LOx tank like a booster, then finally the Kero tank. All before firing the second stage engine.]

    [[Alternative alternative is to have the second stage on a rail. Shunting it forward during staging. But adds mass/complexity.]]

    [[[Aside: For the left-side version, I’d put that spare-void under the kero tank, then use the space for fuel pumps and other plumbing. If you also run a truss up the centre, you can hang the load of the second stage directly onto the thrust-frame of the first-stage, allowing the both first and second-stage tanks to be light, weak balloon tanks. Should also make connecting the tanks during assembly after delivery easier.]]]

  9. Paul451 says:

    “during assembly after delivery easier”

    By which I mean pre-launch integration at the pad.

  10. johnhare johnhare says:

    I like your aside. Mind if I expand on that in another post?

  11. Paul451 says:

    Sure, go nuts.

    [I should point out that the reason I suggested balloon (thin-walled pressure-stabilised) tanks is to make up for the extra mass of a truss up the spine.]

  12. Peterh says:

    “I still don’t have a computer that lets me draw cartoons all that well.”
    Try .

    The idea of horizontally parallel tanks extends to a larger number of tanks, such as one center and a pair to either side. As I recall the Saturn I first stage used a cluster of 8 smaller diameter tanks around a central tank, based on existing tooling for much smaller rockets. As an extreme variant of this principle look at Otrag.

  13. Paul451 says:

    Speaking of Otrag, that’s a potential stepping stone to SpaceX’s BFR. Once they develop Raptor, convert the F9 core to a single Raptor engine, fly it as a single core Falcon 9 with dummy/discount payloads to test the engine. Then fly it as FH, to test multiple engines and cross-feed. Then modify the thrust-frame design on each core to be able to bolt nine F9-Raptor cores together during integration at the pad, fly without cross-feed in order to test the 9-engine configuration (and aerodynamics) in the simplest possible configuration, along with the inevitably larger second stage. Then finally bring back the cross-feed between cores to allow re-flowing of the fuel if one engine fails and you need to burn others longer using that engine’s fuel.

  14. born01930 says:

    My thoughts were that the LOX tank would be constructed inside a lattice that could support the 2nd stage and payload. Since RP1 isn’t terribly reactive it should be able to be in contact with the insulation of the LOX tank. I am not sure what pressure the RP1 tank typically sees in a standard rocket, but since the RP1 tank is not supporting anything other than itself it doesn’t need to be stout. Assuming the halves are carbon fiber there is no reason they couldn’t be epoxied together onsite.
    I was thinking of standard high rise construction around a central core. The core being the lattice, the lox filling the center, then strap on the RP1 sections

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