Engineers Just Tested an 'Impossible' Detonation Engine For The First Time - And It Works

HUH ?

 

While reading the article, I can't help remembering what Scotty said.

https://www.wired.com/story/after-60-years-explosion-powered-rockets-are-nearly-here/

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However, this is clearly a benefit:

"Ahmed estimates that eliminating all the turbopump machinery could reduce a rocket’s weight by around 30 percent. It’d also make the engine far less complicated and more fuel-efficient than a conventional one."

 

Cliff Notes Version:

 

Wired has great tech writers.

Here's another from a different source - https://newatlas.com/space/rotating-detonation-engine-ucf-hydrogen-oxygen/

This is important:

Ahmed tells us this engine design is being evaluated as a possible replacement for Aerojet Rocketdyne's RL-10 rocket, which was first developed in 1962. Modern versions are still in production for the upper stages of Atlas V and Delta IV rockets, with further versions under development for the Exploration, OmegA and Vulcan rockets, but a proven rotating detonation rocket engine could be a real game-changer.

"The U.S. Air Force is targeting a rocket launch flight test by 2025," says Ahmed, "and we are contributing to achieving that goal."​

 

I will be interested to see what the specific impulse (Isp) is that these engines develop compared to the 460 or so seconds the RL10 provides. Isp is a measure of how efficiently a rocket engine uses its propellants. Not sure how the propellants are injected if there is no turbo-pump. Pressure fed engines usually are lighter weight than pump fed engines, but you give back part of that advantage because of the extra weight of the propellant tanks to take the extra pressure.

 

A unique feature of the Centaur upper stage was the fact the pressurized tanks were designed as structural members of the complete stage. This provided wt benefits to the upper stage, boosting its payload capability. Without pressure in the tanks they were very weak.

 

So, as fuel was used, they became weaker?

 

Jim- The Centaur was powered by pump fed RL10s so the tanks did not need much pressure, only about 70 psi normally. They were plenty strong enough to provide the structure for the upper stage, though. With a pressure fed engine, tank pressure is the same as chamber pressure, so the walls have to be built up substantially to take up to 500 psi of pressure.

T- No, in this case the pressure in the tank, usually provided by helium and regulated, was low so not much difference as fuel was used. In some vehicles, like the Atlas series of launch vehicle with very light structures, the stage has to be pressurized when empty or it will collapse. You can actually tap on an Atlas III stage and watch a ripple flow all the way down the stage. Very light structure.

 

I remember seeing a video of the first Atlas-Centaur launch in 1962. The launch went fine until the vehicle was passing thru the zone of maximum dynamic pressure, when the Centaur apparently suffered structural failure and the vehicle exploded.

 

Jim- Max Q is usually the most dangerous time for any launch vehicle, assuming nothing goes catastrophically wrong before that.

 

Was the shuttle the only launch vehicle to throttle down during passage through Max Q?

 

But of course. But it seems that as originally designed, the Centaur wasn't strong enough to make it through there.

 

Isp! Man, that brings back memories.
As a young scientist, I had a summer job that included calculating specific impulse for proposed new propellant formulations for scientists @ Edwards AFB.
The Isp code was ages old, even 20+ years ago, and I don't think anyone one really knew how it worked. Just pop in some chemical properties
- molecular weight, enthalpy of formation, I think, and some others long forgotten - and after a little chugging, the predicted Isp popped out!
T

 

Jim- No, it was standard on several launch vehicles to keep Q (psf) down until the atmosphere thinned and full throttle could be applied again.

Tom- Isp for rockets is pretty simple, but it gets more complicated for air breathers. Max theoretical Isp for conventional rocket engines comes from the combination with the lowest molecular weights, hydrogen and oxygen, at slightly above 500 secs, while something like a turbofan engine can reach 7000 secs of Isp using free oxygen in the atmosphere. Mixture ratios to get 500+ secs of Isp, though, would burn up the combustion chamber so are in practice nowhere near stoichiometric.

 

Thanks Taz!
T

 

All of our launch vehicles that used solid propellant strap on motors, the grain design were tailored to minimize Max Q effects on the vehicle.

 

Darryl- Affirmative, kind of hard to throttle a solid rocket motor, so you did the next best thing.

 

Of course Max Q is a relative term and really just a design point on the ascent profile. The vehicle could be designed to be at max q for an extended (relatively speaking) period of time, and each flight of a particular launch vehicle will be different depending on payload.

Thanks, wasn't sure how throttleable (sp?) other engines were. I thought the SSME's were some of the first to have this capability, or maybe it was just the range that they had.

Definitely not an easy thing to do and makes each solid motor unique for each flight. I wonder though if on the shuttle the SSME's were used to provide all the vehicle thrust level control and the solids were just full bore from start.

 

Jim - the Shuttle solid motor grain was designed to produce max thrust at lift off then lower thrust so that at 50 seconds, which was the time of MAX Q, then build back up. The same was for the solids on Delta. The grain designs for the solids were not changed for every mission and remained constant for the life of the program.

 

Jim- In theory, the SSME could be throttled quite a bit lower than the 65% NASA used and Rocketdyne quoted. We were using a version of the SSME on XSP/Phantom Express and needed deeper throttling for initial tests at light gross weight. Program cancelled by Boeing, though, so a moot point. We did have extensive engine tests on the modified SSME AR-22 engine to validate the 10 sorties in 10 days requirement and the engine performed admirably during those tests.

Throttling has often been an issue with liquid rocket engines. TRW had to use a pintle injector to make the LEM (later LM) sufficiently throttleable for the lunar landings.

 

Just after the 2 minute mark you can barely hear it mentioned about throttling back. 60% percent I think. And throttle up around 2:40 - "Standing by for the throttle up call..."