Talk-Polywell.org

the rotating detonation engine is tantalizingly simple in a mechanical sense, but this self-propagating detonation wave has proven torturously difficult to achieve and sustain.

Until now, it seems. A team at the University of Central Florida, working alongside the Rotating Detonation Rocket Engine Program at the Air Force Research Laboratory, claims to have built and tested a working laboratory model. It's a 3-inch copper test rig using a mix of hydrogen and oxygen for fuel, which is the highest-performing rocket fuel for upper stage rocket engines.

https://newatlas.com/space/rotating-det ... en-oxygen/

"Japan tests rotating detonation engine in space for the first time"

https://interestingengineering.com/japa ... first-time

Very nice, I totally missed this.
There is not much data in the article but it says that results will be published soon.
I am curious to see if the ISP will match their predicted model of around 150.

I saw it earlier. Way to go Japan!
Hope this goes somewhere...

"NASA Validates Revolutionary Propulsion Design for Deep Space Missions"

https://www.nasa.gov/centers/marshall/f ... e-missions

They have a video of it operating.

a team of propulsion development engineers at NASA have developed and tested NASA’s first full-scale rotating detonation rocket engine

Very excited about those kinds of engines. They could make SSTOs possible.

Skipjack wrote: ↑

Thu Jan 26, 2023 4:37 pm

Very excited about those kinds of engines. They could make SSTOs possible.

During the X-33 period I explored the SSTO math and it come out that you will need an ISP of around 2000 to make a meaningful and practical SSTO rocket/plane.
The detonating engine design has a theoretical efficiency improvement of around 25% over conventional chemical rockets ISP.
An amazing improvement in the field that was not seen since the start of modern rocketry, but still very far from the ISP needed.

A practical SSTO will probably need a nuclear engine, but than there is the issue of those nasty neutron fluxes that complicates everything.......

Giorgio wrote: ↑

Sun Jan 29, 2023 11:01 am

Skipjack wrote: ↑

Thu Jan 26, 2023 4:37 pm

Very excited about those kinds of engines. They could make SSTOs possible.

During the X-33 period I explored the SSTO math and it come out that you will need an ISP of around 2000 to make a meaningful and practical SSTO rocket/plane.
The detonating engine design has a theoretical efficiency improvement of around 25% over conventional chemical rockets ISP.
An amazing improvement in the field that was not seen since the start of modern rocketry, but still very far from the ISP needed.

A practical SSTO will probably need a nuclear engine, but than there is the issue of those nasty neutron fluxes that complicates everything.......

Using Joe's DeltaV calculator and Starship and Raptor as a baseline:
Assuming: 410s average Isp with an RDE ( 25% would be an 87 second improvement, so 410 might be conservative)
Dry mass: 100 tonnes. That does not even account for structural mass savings through the reduced payload fairing size (one could also add more fuel in that same volume).
Payload: 10 tonnes
Landing fuel: 30 tonnes

With all that I get almost 9100 m/s DeltaV.

SSTOs would be limited to LEO destinations for sure. GEO would need some sort of kick stage and payload would be low.

That said, I think that if the capacitor mass is not too high and you can do some sort of direct conversion then, one could probably do an SSTO based on the Sheared Flow Stabilized Z- Pinch with D-He3 as fuel. There might be issues with Tritium in the exhaust through D-D side reactions. But all that is off topic here.

Skipjack po:st_id=134362 wrote:

Sun Jan 29, 2023 7:19 pm

Using Joe's DeltaV calculator and Starship and Raptor as a baseline:
Assuming: 410s average Isp with an RDE ( 25% would be an 87 second improvement, so 410 might be conservative)
Dry mass: 100 tonnes. That does not even account for structural mass savings through the reduced payload fairing size (one could also add more fuel in that same volume).
Payload: 10 tonnes
Landing fuel: 30 tonnes

With all that I get almost 9100 m/s DeltaV.

SSTOs would be limited to LEO destinations for sure. GEO would need some sort of kick stage and payload would be low.

That said, I think that if the capacitor mass is not too high and you can do some sort of direct conversion then, one could probably do an SSTO based on the Sheared Flow Stabilized Z- Pinch with D-He3 as fuel. There might be issues with Tritium in the exhaust through D-D side reactions. But all that is off topic here.

Raptor has an ISP of around 325, so 410 is a good estimate.
If you want to simulate SSTO using 140 Tons to LEO (100T Spaceship, 10T Payload, 30T landing Fuel) you get:

Lift off mass with RAPTOR Engine ISP 325 = 2500 Tons (Cannot be SSTO).

Lift off mass with Detonating Engine ISP 410 = 1400 Tons (This can barely become a SSTO (LEO) but not really practical)

Lift off mass with Nuclear Engine ISP 900 = 400 Tons (This start to become highly practical even to GEO)

Lift off mass with Nuclear Engine ISP 2000 = 230 Tons (This would enable mass commercial flights to GEO)

With an ISP of 2000 you can actually send 200Tons directly to GEO with a liftoff weight of just 400 tons.
Imagine what that could do for commercial space flight.

Off topic indeed but still a potentially exciting road for a fusion reactor if it can be made to withstand liftoff vibrations.

That is the sea level Isp. The vacuum Isp is quite a bit higher.

Indeed.
It was just a quick apple to apple comparison to evaluate what the different ISP will allow.
The logic (and the relative results) is similar if you will compare the the various technologies with their vacuum ISP.

And if you are interested you can give a look to the experiments going on in the next iteration of detonation engines, the "Oblique Detonation" engine. This has a theoretical ISP of 1800 and could give a practical ISP of 1500.

Exciting innovations while we wait for the fusion era to start.

Giorgio wrote: ↑

Wed Feb 01, 2023 8:35 am

And if you are interested you can give a look to the experiments going on in the next iteration of detonation engines, the "Oblique Detonation" engine. This has a theoretical ISP of 1800 and could give a practical ISP of 1500.

That's an air-breathing concept. You aren't getting 15 km/s exhaust out of a chemical rocket no matter how you burn the chemicals.

93143 wrote: ↑

Wed Feb 01, 2023 12:00 pm

That's an air-breathing concept.

That's true and they explain it clearly in the introduction paragraph to their paper.

It isn't a new concept. My department was doing simulations of this technology over 15 years ago.

Good to see it's making progress...

Got me thinking. Stick for a minute with ISP 410 and SSTO.

With Giorgio’s numbers of a 100T craft, 10T payload, and 30T return fuel, I calculate that if you can pick up the return fuel in LEO, you save 269 T of launch fuel.

If you can ship it there from the moon in a 5T craft, and return the craft to the moon, it costs 171 T of fuel.

Much more interestingly, the same SSTO can now take 40T to LEO instead of 10 with little more total fuel cost. The fuel per tonne to LEO drops 72%.

Not so useful at higher ISP, and very dependent on the SWAG at 30T return fuel.

Just reading Wikipedia…