However, even if we stick to a two staged kerolox ballistic rocket, I fail to see how using an air augmented ejector cowling around the rocket engine would not significantly improve the rockets performance and orbital payload. The proof of concept at least suborbitally is the GNOM missile, the development program tested its PR-90 rocket: http://www.astronautix.com/lvs/gnom.htm

“The concept was evidently been proved on a subscale tactical missile, the PR-90, now on display at MAI’s museum at Orevo, north of Moscow. The PR-90, with a launch mass of only 1500 kg, of which 550 kg was payload, could reach an altitude of 40 km and a range of 100 km. The booster unit used 200 kg of RAM-10 ballistite with a specific impulse of 180 seconds to get the missile up to ram-air ignition speed. Then the air-augmented unit, with a specific impulse of 550 seconds, cut in and used 300 kg of propellant to boost the vehicle to its 1 km/s cut-off speed. An equivalent liquid propellant missile (such as the American Lance) weighed over twice as much. A solid propellant equivalent (such as the French Pluton) would weigh three times more. ”

When it comes down to the nuts and bolts, other than Gnom and the French Onera program, as well as retirees from Marquardt, I don’t see anybody testing hardware today. The examples that have been flown IMHO disprove the unsupported claims of detractors.

Would staying in the atmosphere for long enough really be a problem? If at some stage during ascent you use only ramjets and no rockets that sounds plausible. But what if you only used ramjets simultaneously with rockets? That wouldn’t give you a spectacular Isp improvement, but it might make cheaper, lower performance propellants and engines competitive and reduce mass fraction constraints on your orbiter stage.

Now, there may be some niche orbital situations where small airbreathing engines for landing purposes or such might make sense, but I’m completely unconvinced that a ramjet is going to be of any real use for ascent. It’s more pain than it’s worth. Isp isn’t everything.

~Jon

The NewSpace industry needs more players. I look forward to seeing your ramjet fly.

Mike

I think you are dead on about the analysis. The guys that are getting things done are getting their hands dirty.

Have you gone to any conferences to discuss ramjets with the rocket guys? It seems to come up a time or two at every one I’ve been to and the conclusions are that it doesn’t close. You just might be bringing new insight to the problem. I have bought the papers on disk from the conferences of the ISOABE and several hardback references on inlets and ABE high speed engines. Many of the people that attend those conferences have more.

I won’t fight over the cagejet or any other concept to the point of heated arguement. I throw ideas out there to see if there’s any meat on them. When something useful comes up, I look for ways to push it a bit further.

There’s plenty of ramjet production models out there that work just fine. The Russian GNOM missile, for instance, uses an air augmented rocket ejector to boost its range 80% for only a 20% weight penalty. The French have solid fuelled ramjets using boron fuels to propel their equivalent of the Pheonix missile (Russians do the same thing with their Adder missile, at over mach 5), and the USAF is looking to adopt the same propulsion module for an extended range AMRAAM.

I agree compared with simple ammunition like ballistic rockets, ramjet propelled lifting vehicles can more complex, if you think too much, but they don’t have to be. Looking at the market, I see VG and XCOR as the leaders and both work with winged vehicles. If that pattern holds there has to be a place for ramjets to boost average trip Isp.

But talking complexity, this cage jet concept is taking that to new heights.

However, compared with multistaging of liquid fuelled systems, ramjets are a lot simpler, even with adaptive intakes and exhaust.

Investors want something that turns profits and the simpler, the faster, which is good for ROI. Strike two.

Very few of the newspace people I know have left major contractors, and none at all from NASA.

Many of them though have run the numbers on ramjets just as I have though and found them not useful. It is almost the first alternative we all look at to get out from unther the rocket equation. The problem is that the engine sounds simple and cheap, but isn’t. New engine cost is largely in the testing and debugging. Ramjets are far more expensive to test than rockets. Ramjets are also very finicky about the incoming air, which makes the inlet a major engineering project. Ramjets give you five mach numbers if you really stretch them, and the integration issues will kill you. That ‘simple’ engine requires a sophisticated and relatively heavy airframe and constricted flightpath compared to a pure rocket vehicle.

Just because ramjets aren’t on the list doesn’t mean it’s because we are all close minded. We’ve looked.