Problem of the day, that pesky Starship Hoverslam.

Imagining a crazy (childish) contest to see who could flip at the lowest altitude and brake to 0 rate of descent and land, it was (hilariously) imagined one could "cheat" by braking in the horizontal with "side rockets" then flipping and landing.

Then, it was realized, could just the engines be gimballed 90 degrees for a horizontal landing. Yes, another would be needed in front.

Conceptually, the design might be a bit like the Harrier, but could control pitch just like a Chinook helicopter, and enable one to make the aerodynamic fins smaller.

Could this be practical?

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    $\begingroup$ What exactly do you want to gain by that, increasing the gimbal range tenfold, installing another set of landing gear and duplicating all the plumbing and pumping for a second engine at the top? $\endgroup$
    – asdfex
    Feb 14 at 15:51
  • $\begingroup$ Easier to disembark, for starters. Larger, more stable landing base. Better control in descent. Much wider available CG range. $\endgroup$ Feb 14 at 16:28
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    $\begingroup$ They are not duplicating any plumbing, the only added plumbing in the current approach is the downcomers from the header tanks. A nose Merlin would require an entire additional fuel tank for the RP-1, and a single Merlin would lack redundancy. And descending horizontally with rockets at nose and tail would be far, far more difficult to control and require major increases in structural mass. $\endgroup$ Feb 14 at 16:58
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    $\begingroup$ @RobertDiGiovanni umm, no? If you make the Starship shorter and wider, you greatly exacerbate the structural problems of making it capable of landing "on its side". The problem is already that the reinforcement needed to make a 9m-wide tube rigid enough and resilient enough without hugely increasing its mass. Double its diameter, and the problem becomes double^3 = 8 times as hard to solve... Thin stainless steel plating is very strong in its length, and ridiculously weak against transverse forces(denting & buckling) $\endgroup$ Feb 15 at 14:32
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    $\begingroup$ @RobertDiGiovanni This question pertains to the OP's suggestion of landing the StarShip on its side. You should respect the OP's question, why I believe he may even be a relative of yours. He has the same name, anyways. It's bad to disrespect a relative by trying to derail his question like that! $\endgroup$ Feb 15 at 15:14

Unlikely to be plausible. During belly flop descent the forces placed on the horizontal Starship are distributed over the windward side very evenly. The cylinder walls represent the majority of the frontal area and the flaps are fluttered back taking less than their full potential drag - and their mounts are still naturally broad and spread the additional force over the skin.

During flip the aft drag will reduce as the aft flaps feather, meaning off-axis force on the aft drops. The nose flaps do flare for higher drag, but they are the smallest of the flaps and their impulse will rapidly drop off as the ship rotates and the area they present to the wind reduces. The major impulse for the flip is provided by the engines through the thrust puck and typical rocket structures.

When the large deceleration for landing occurs after the flip, the engine thrust is aligned with the tank walls, distributed there by the thrust puck - again as during ascent.

Applying the thrust forces perpendicular to the tank walls would overwhelm the thin tank structure. Applying the necessary structural reinforcements to support the mass horizontally at small points would greatly increase the dry mass, reducing payload.

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    $\begingroup$ Valid answer. I submit a landing Starship would have considerably less mass, there for fewer stresses. Yes, it would have to be more robust, but with no existing $/kg to Mars parameters, a stronger build might have additional safety benefits. $\endgroup$ Feb 14 at 16:31
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    $\begingroup$ You're not adding safety margins, you're adding structure to keep it from snapping in half under stresses unlike those it encounters at any other point in its flight. That's mass that could instead be devoted to actually improving safety margins if necessary, and which could otherwise be used for useful payload. $\endgroup$ Feb 14 at 17:21
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    $\begingroup$ The flop descent does no such thing, the flaps support only a fraction of the vehicle's weight. And Starship is not a boat. $\endgroup$ Feb 14 at 18:17
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    $\begingroup$ Consider frontal area to the wind during flop. The bulk of it is the windward side of the cylinder of Starship. The flaps on the edges of the cylinder are fluttered back to take less than their full potential drag, and are smaller than the body. Then flip reduces drag at the aft, reducing off-axis forces on the structure. It flares the nose slightly which would increase off-axis force there, but the nose flaps are the smallest. Then a thrust off-axis but through the thrust puck applies hard flight-similar force. The flip-flop needs less off-axis reinforcement than horizontal landing. $\endgroup$
    – Saiboogu
    Feb 14 at 18:49
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    $\begingroup$ The Kestrel has been out of production for about a decade. It also was an upper stage engine designed with no need for fast or accurate throttle adjustments, and your proposed landing approach would be reliant on throttling for control, while also making the vehicle much more sensitive to throttling error. And it used the wrong fuel. And it wasn't reusable. $\endgroup$ Feb 15 at 21:20

You would need to bring along more rocket engines. If the thrust axis does not go through the center of mass of the craft the craft will rotate and landing while rotating is a crash. The Starship has all it's engines at the rear--incapable of pointing through the center of mass unless they're pointed virtually straight down.


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