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I hope the E-cat guy is for real. Historically, our best, most dramatic advances took place when somebody upset the applecart of conventional wisdom. It's way past time this happened to the "fusion business".
GW Johnson
Actually, any practical system capable of a flight to an NEO is capable of going to Mars. You just add landers. It's not so much the delta-vee and flight times, it;'s actually crew survival that drives what you do. If you fly weightless, you have to fly fast: one year max is demo'd on the various space stations over the last few decades, and we do not know that Mar's 0.38 gee is enough to be therapeutic. Otherwise, go 9 months one-way, several months there, and about 9 months home, and provide just about 1 gee by spinning the ship end-over-end. There's no way anyone will stay sane cooped up in any capsule; we'll need a Skylab-like module to live in. The bigger, the better. Think orbital rendezvous and assembly here, and orbital rendezvous (like the Apollo missions) at Mars. You'd better start thinking nuclear thermal rockets, maybe even gas core. You might also start thinking about the real point of going there: is it flag-and-footprints like Apollo, or is it real exploration to find out what exactly is there, and where exactly is it?
GW Johnson
Hi gang:
This is GW Johnson the old aero engineer, and ramjet expert from long ago. I surely am glad to see the forums up and running again.
In recent news: I have picked up a consulting client for a possible ramjet launch effort. And, that client and I both think I may be just about the last living US all-around expert in ram propulsion (I seem to have outlived the rest).
I’m particularly glad to see LEO access under active discussion, especially with Josh and Hop talking about reusable vehicles, and perhaps ramjet assist. The last stuff I had is a posting over at http://exrocketman.blogspot.com, where I looked at horizontal takeoff and landing with a winged first stage using separate rocket and ramjet power. That article is dated August 22, 2010, so it’s way down the list (chronological, latest on top). There’s a navigation tool by date and title on the left, under my photo. It looked to me like a staging condition of near Mach 6 at around 60,000 feet altitude might well work out, including booster flyback. And, it looks like ramjet might really pay off in this scenario.
Josh is exactly right: the frontal thrust density of ramjet is too low to support vertical acceleration of a heavily-loaded vertical launch vehicle on ramjet alone. But parallel-burn of otherwise-separate rocket and ramjet might offload some of the thrust requirement temporarily onto the higher-Isp ramjet, thus swapping a smidge of rocket propellant for a smidge of extra payload. That kind of vehicle is moving only around M2 at 60,000 feet, so it’s a “low-speed” pitot inlet design, not the “high-speed” spike inlet that makes sense for the ramjet launch airplane. Whether this idea is actually technically and economically attractive in vertical launch, remains to be seen. I just dunno, yet.
You can think of “high-speed” systems being some sort of spike or ramp inlet, a dump combustor, and a very mild-expansion convergent-divergent nozzle. Min Mach number is around 1.5, and max is around M5 to 6, depending more on vehicle drag than the ramjet design itself. I looked at nose inlets, but side inlets also work. Peak performance is around M2 to 3, and frontal thrust density falls too low to provide effective acceleration above about 60,000 feet. It doesn’t matter a lot whether you analyze RP-1 or JP-5 kerosene, or even RJ-5/Shelldyne-H synthetic, they all come out similar in proportions and performance. I think liquid methane would look very similar to kerosene, too.
“Low speed” systems are a simple pitot (normal-shock) inlet, most likely a nose inlet, a dump combustor, and a convergent-only nozzle. Min Mach is a tad fuzzy, there being thrust greater than drag (in low-drag nacelles) down under Mach 0.5, although Isp is over kero-lox rocket levels only above around Mach 0.7-ish. Max Mach is around 2 to 3, depending more on vehicle drag than the ramjet, with max performance around M1.5 to 2. I think thrust densities fall too low to be useful for acceleration above around 60,000 feet, although this remains to be seen for sure. Again, specific fuel choice is not all that important.
Whatever I do come up with, I’ll let y’all know. This stuff is fun. I haven’t done any of it in almost 2 decades, now. I think I’ll turn my old how-to notebooks into a published book. Otherwise, the art will die with me. (It’s still mostly art, until I can get it all written down). That ain’t easy.
GW