20 thoughts on “SSTO Hype”

  1. The article is remarkably content free. Agreed that it seems to be strictly a suborbital platform. One quote was odd:

    “former Boeing official who oversaw that company’s X-33 spaceplane program”

    That seems a bit of a contortion as the X-33 was a LockMart screw-up. I didn’t think they needed Boeing experience to help with that. But maybe there are a few degrees of Kevin Bacon that can explain this.

        1. Yes, conformal tanks, and a linear aerospike engine. It violated Pournelle’s law of X vehicles: Don’t have more than one new technology at a time. Dave Urie still swears it would have worked, though.

          1. What I heard (from a coworker whose former boss was in a lead role on LM’s X-33) was that the basic aero S&C work pre-proposal was all screwed up, and the surfaces were going to have to grow much bigger. Then the engine was coming in much heavier than planned, which when combined with all the extra weight in the aft section for the upsized surfaces, pushed the CG too far aft and made the design not really feasible, again from a basic S&C perspective.

          2. Yes, the fins on the “lifting body” were evolving into wings. It was a fiasco. It set us back over a decade, because it “proved” “reusability doesn’t work.”

          1. S&C is stability and control, in this case, referring specifically to aerodynamic stability and control. For successful controlled flight, all aircraft need a combination of inherent aerodynamic stability – the tendency to return toward an equilibrium condition when perturbed – and sufficient control power – typically provided by aerodynamic control surfaces – to augment the natural aerodynamic stability as required over the flight envelope.

            One of the challenges of aircraft design is that pretty much all aircraft have a fairly narrow range of center of gravity locations that yield sufficient stability (or at least not excessive instability) to be controlled over the required flight envelope. The LM X-33 was initially designed with control surfaces that were much too small to provide either sufficient aerodynamic stability, or sufficient aerodynamic control power, to be capable of controlled flight at the design flight conditions and design center of gravity range. To attempt to fix this, LM had to increase the size of the control surfaces; this added weight at the back of the aircraft, moving the CG farther aft – which made the aircraft less stable, in addition to reducing the mass margin. Then, the linear aerospike engine, at the back of the vehicle, kept getting heavier, moving the CG even more aft. This is a positive feedback loop – more aft CG is more unstable, needs more control power for active stabilization, so bigger and more massive control surfaces and actuators at the aft end, which moves the CG further aft, which…you get the picture.

            Eventually, you reach fundamental limits on how much an active control system can stabilize an unstable vehicle, and you’re done – the design cannot close and you have to start over. I have to say, IMHO this was typical sloppy LockMart work to be so over-optimistic in their conceptual design.

          2. I’m happy to blame Lockmart, but do you have no criticism of NASA for choosing their concept, that was uncompliant with the RFP? The other contractors had legitimate complaints about the selection.

          3. So in other words, not an RCS all the way down. 🙂

            I remember when I built my first Estes V2 and they cautioned me about using the “to scale fins” not having enough area for proper stability. Spin testing it proved them right. IIRC I kept messing with nose weight to get it stable. Then of course trying to launch it with an ‘A’ engine would simply cause a 30 ft spiral. Not very impressive. But when not absolutely certain about its S&C still a terror rocket, particularly as a model.

          4. Rand, my comments were mostly about how LM’s design was a poor design; I recently taught a class in S&C/GNC in conceptual design, so that experience and the material I prepared had some influence on these comments 🙂

            You are of course correct that NASA shares plenty of blame in the X-33 fiasco. Similarly, NASA is co-culpable (if that’s a word) in the ongoing CST-100 mess; after the first flight near-disasters, whenever I’d encounter people roasting Boeing, I’d remind them that NASA signed off on all of those test procedures, results, designs, etc., that produced the ridiculous results. I am in no way, shape, or form an apologist for NASA; in fact, I just wrapped up a small program with NASA, and they had smart people but the bureaucracy and general lack of urgency in everything, combined with “we know best” attitude…in all honesty, I hope to never have to work with them again.

      1. Boeing didn’t; McDonnell-Douglas had a concept. This was during the acquisition of McDD by Boeing, so nomenclature confusion is to be expected. Then Boeing bought Rockwell, and had two X-33 concepts that didn’t win.

  2. I saw this article about 2 weeks ago on the UPI website and basically assumed more vaporware/PR than content, that’s why I didn’t email it to you Rand. I can’t see this being just a LCH4/LOX design that would be a match for Starship esp. w/o the Super Heavy. So that leaves Reaction Engines. I wonder if they are doing a cross-licensing deal, with the idea that they have the bona-fides chops to raise enough money to actually build a US-based prototype. It’s the only “new technology” I see that makes any sense at all for an SSTO.

    From what I’ve read from Kelly Johnson & Ben Rich liquid hydrogen is basically a non-starter.

    1. I’ve seen rocket sleds referred to as a 0-stage. It’s not going to be able to get to any significant velocity, it’s more so the landing gear doesn’t have to support all the fuel.

          1. Musk refers to the SH/SS launch tower as a stage zero, and since this is a runway rocket sled (no rails) and has fuel that feeds the orbiter engines, it’s also kind of like a a zero-altutude droptank stage zero. How much advantage? I dunno. Say you have a really long runway and accelerate halfway down it before lifting off, and popping the sled chute. I don’t think you could get supersonic, but maybe high subsonic? And where would MaxQ be then? Or maybe it could land on the sled when it got back? I imagine watching the sled catch it at high subsonic would at least look cool enough…

  3. . . . because it “proved” “reusability doesn’t work.”

    Ha. Excellent point. To be blunt, NASA only proved that NASA couldn’t do it.

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