Just popped in to look at this group today, and I'm surprised to find there was a lively discussion on the Roton thread.
I asked Bob Truax about the Roton (motor) concept about a year ago, and he said "Oh, Goddard tried that. It blew up.".
Bob ran the (successful) project that developed the JATO rockets for PBY aircraft around 1940. Goddard was also funded to do the same thing in parallel, at the same location. Goddard built a number of things that failed (explosively), including a LOX-gasoline motor that spun on its axis, with a centrifugal pump integrated into the injector end. Neat idea. Oh, well. Truax's team made hypergolic propellant pressure-fed motors and also jet-vane powered pump motors, and succeeded where Goddard never did.
If you can stand to listen to me hold forth on rockets, you may find this interesting.
I am repeating Truax's ideas here because nobody else in the world has his long perspective on rockets. First, just to make sure you know where this is coming from, a partial resume for Truax (from memory: He ran the first government sponsored rocket research project in the country. He invented regenerative cooling (example: Space Shuttle Main Engine), started the precursor to the AIAA with Von Braun and worked with him on the V2s brought over from Germany after the war, worked on winged rocket powered missiles, invented the submarine launched ballistic missile, ran the Polaris missile project, worked on the nuclear rocket projects (NERVA, I believe), first head of the Air Force space program, ran the first project actually intended to figure out how to orbit payload cheaply (Aerojet General corp, 1963 or so: The Sea Dragon study), developed a large 100-knot surface effect ship for the Navy, and retired. Then started the "Volksrocket" project in the early 80's (to put one !
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So. To paraphrase: He says that getting into orbit is not a technological problem. The technology was solved decades ago. To get into orbit cheaply, you need to build your rockets Big and Dumb. This is called the Big Dumb Booster concept, the result of the 1963 Aerojet General study. It has never been tried. The principles are:
on up to 100KM and pay for it with the television rights), later, with new investors, "Project Private Enterprise", and after the Navy bought the project, SEALAR (SEA Launch And Recovery). A number of small research contracts since then.
Make it ultimately simple (pressure fed, two-stage, single engine per stage), make it reusable, never make it *too* reliable, and build it *big* (100,000-1 million pounds to LEO). Historical analysis of rocket projects shows that development and operational cost scales rapidly with complexity, and very slowly with size. Payload scales up rapidly with size, but not with complexity. I won't go into more details unless there is interest in it.
(My thoughts, not Bob's:)
Relevant to the current discussion, startup rocket projects constantly repeat the same old mistakes. Someone wrote a book about it. The general pattern is this. First, to get funding, they convince investors and the public that the solution is a new technology. Then, they spend the money, get part way through developing a nifty idea, go belly up. Almost any idea can be made to work, and as for the Roton concept, this project is a classic. Several nifty new ideas in one project. Of course it can be made to work, with enough money. That is not the question. The question is, can it be made to work before the money runs out?