Pulse Detonation Engines - Tomorrow's propulsion, available today?

Mark S · 2002-05-23 13:49:25

NASA has mentioned "Pulse Detonation Engines" on some of its websites as a future propulsion technology. If I'm not mistaken, this type of engine is allegedly used to propel the "Aurora" Mach 6 spyplane. I've seen a patent drawing for such an engine before but I've heard several different explanationson how one would operate. I also don't understand why an airbreathing engine would be adapted for space travel. Can anybody shed some light on the situation?

Phobos · 2002-05-23 17:29:28

Do the engines generally work the way a nuclear pulse engine does but without using nuclear explosives? I've seen model rockets launched by detonating charges one a time beneath it, even though that's probably not anything like the way pulse detonation engines work.

Canth · 2002-05-23 20:21:58

There is some data about it Here. Just scroll down to the last entry. There is some good, albeit limited information about advanced propultion concepts on the Marshal Space Flight center's Advanced Space Transportation website. Some of the things they are working on are facinating. I think some of the advanced chemical designs are especially interesting. My favorite advanced chemical propulsion method is the one involving monoatomic versions of various light elements suspended in hydrogen ice contained in liquid helium. It could supposedly have a specific impulse of 750 or so. I am not sure how practical it is, however it is quite "cool" and by nature a pulsed propulsion system. I unfortunatly cannot find the reference to it although I am sure it was on some official nasa site. Pulsed propulsion of any kind is useful because it is simpler to run and maintain than a constant thrust system. Most suffer a proformance hit of some kind though. The first jet engine was an airbreathing pulse detonation system used by the nazis for the v-1 flying bomb.
P.S. I am sorry for my posts fragmentedness, I am very sleepy.

Mark S · 2002-05-30 20:28:41

Canth, thanks for the link to that site. The info was good, especially the section about high-ISp, high-density hydrocarbons.

My only question is why anybody would use a PDE, with an ISp of 600 seconds, whan a ramjet or combined-cycle has an ISp of 1500 seconds. Perhaps the PDE is lighter and can operate in all flight regimes from takeoff to orbit.

Canth · 2002-06-01 08:34:38

Pulsed detonation engines are cheaper and simpler to design and build than ramjets. Getting a reliable ramjet could take decades while reliable pulsed detonation engines will take years. Lack of complexity are pulsed detonation engines biggest (and pretty much only) advantage.

Preston · 2002-06-02 16:27:19

Firstly, hello to all you Mars Society (and OTHER) peoples.

Pulse detonation engines are also a good way to give fusion propulsion more thrust, as magnetic mirrors are typically low thrust if you dont add any propellant to the fusion products. In fact, you can get enough thrust with PDE fusion to launch a rather massive craft to LEO as an SSTO vehicle. The PDE system I refer to is called MICF or magnetically insulated inertial confinement fusion, wherein a laser, ion, or preferably an (10^13 particle) antiproton beam ignites a few-mm pellet of deuterium-3helium (a pellet with a metal shell). This gives a lot less neutrons than deutrium-tritium fusion, though I'm unsure if it can be considered safe enough for launch to LEO.

Shaun Barrett · 2002-06-02 19:48:16

Hi Preston, and a warm welcome to New Mars!
Just thought I'd mention that last night, here in Australia on Austar cable TV, the "History Channel" showed a documentary about Project Orion. Some of the guys who worked on it, including Freeman Dyson, were interviewed and they showed original footage of the early attempts to achieve controlled pulse detonation propulsion.
The first versions of the experimental craft suffered unsustainable damage to the "plate" which bore the brunt of the explosions. But with some patient redesigning, they achieved a superb result and captured it on colour film. They organised a meeting with Werner Von Braun to give a presentation of their work but he fell asleep during the theory part of it! However, no sooner had they screened the film of their successful multi-detonation launch, pushing the experimental vehicle in a controlled fashion to a height of 100 metres, than Von Braun was wide awake and firing questions at them!! Thereafter, he became an enthusiastic proponent of pulse detonation engines. (Just goes to show that theory is one thing, but you can't beat a good practical demonstration.)
Anyway, in the end, the prospect of launching a one thousand ton vehicle with dozens of people on board, using the repeated detonation of miniature fission bombs, was just too much to comprehend! The US backed away from it and ... the rest is history.
The idea, especially today, of using any form of nuclear detonation in the atmosphere, fission or fusion, to propel a spacecraft, has a zero chance of acceptance. But out in interplanetary space, who knows, maybe it could still have a part to play in solar system exploration(? ). I'm still in awe of its theoretical Isp of anywhere from 10,000 to 1 million seconds!!! That's what I call "PROPULSION" !!

Preston · 2002-06-02 21:10:19

Papers by Terry Kammash and others seem to suggest that the fusion based PDEs can direct the explosion with a magnetic nozzle[1] since you end up with a plasma. This is an important difference between MICF and the project orion-style systems of the past, which I assume used a chunk of high explosives to ignite the fissile material. Ideally, an antiproton beam is used, but if that cant be made precise enough, a single ion or laser beam will do(but a 2-3 megajoule laser or ion driver is much more massive).

By my calculations, you get a specific impulse of approximately 7e5 seconds using a tin shell with d-helium-3, or about half that with a tungsten shell (other authors tend to use tungsten...tungsten might be necessary for other reasons), so it's something that deserves more attention!

[1]Kammash, Terry. "Pulsed Fusion Propulsion Systems for Rapid Interstellar Missions." Journal of Propulsion and Power, 16.6 (2000)

p.s. theoretical designs tend to fall in the 200-300 tonne range.

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#1 2002-05-23 13:49:25

Re: Pulse Detonation Engines - Tomorrow's propulsion, available today?

#2 2002-05-23 17:29:28

Re: Pulse Detonation Engines - Tomorrow's propulsion, available today?

#3 2002-05-23 20:21:58

Re: Pulse Detonation Engines - Tomorrow's propulsion, available today?

#4 2002-05-30 20:28:41

Re: Pulse Detonation Engines - Tomorrow's propulsion, available today?

#5 2002-06-01 08:34:38

Re: Pulse Detonation Engines - Tomorrow's propulsion, available today?

#6 2002-06-02 16:27:19

Re: Pulse Detonation Engines - Tomorrow's propulsion, available today?

#7 2002-06-02 19:48:16

Re: Pulse Detonation Engines - Tomorrow's propulsion, available today?

#8 2002-06-02 21:10:19

Re: Pulse Detonation Engines - Tomorrow's propulsion, available today?

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