Small update from Lawrenceville Plasma Physics

Aero · Post by **Aero** » Sat Oct 09, 2010 10:12 pm

40 megawatt = 53 640.883 698 horsepower [international] .
Kind of anemic for a starfighter. Its on the order of the Space Shuttle fuel pump.

GIThruster · Post by **GIThruster** » Sat Oct 09, 2010 10:32 pm

Lets suppose you built something like a Millenium Falcon. It's about 27 meters long, and has a thruster assembly about 20 meters wide and 2.5 meters high. If you have about 50 FF thrusters/square meter, at 10 MW@, that's about 25 GW, yes?

Will that fly?

Betruger · Post by **Betruger** » Sat Oct 09, 2010 10:52 pm

Was about to say, you could stack a few of them for a good enough power/weight ratio for a bare bones racer, for some short length (don't expect people would go for endurance out in space just yet) course.. e.g. quickest circumlunar or something.

rcain · Post by **rcain** » Sat Oct 09, 2010 11:02 pm

Great news!

Now they're getting repeatable runs there should be lots of lovely data. Also encouraging, all their graphs so far seem to be going in the right direction and according to plan (although they've still got several orders of magnitude to go IIRC).

Keep up the good work Dr Lerner and team. Here's hoping for some big news in 2011.

nice vid of their recent experimental runs hree - http://www.youtube.com/watch?v=70e5UGnd ... r_embedded

Aero · Post by **Aero** » Sat Oct 09, 2010 11:53 pm

GIThruster wrote:Lets suppose you built something like a Millenium Falcon. It's about 27 meters long, and has a thruster assembly about 20 meters wide and 2.5 meters high. If you have about 50 FF thrusters/square meter, at 10 MW@, that's about 25 GW, yes?

Will that fly?

Of course it depends on the mass of the combined ship structure, payload, engines, and for the Millenium Falcon, armament. But it most likely could be made to fly. Consider this:

The SSME exhaust gas velocity is about 4444 m/s, with a total exhaust stream flow rate of about 492 kg/s; thus the kinetic energy () of the exhaust stream is approximately 4.85 GJ/s which is about 76% of the energy released during the reaction of the propellants. This energy is the total enthalpy flow rate of the fluid output of the combustion chamber.

Three main engines, gives 14.55 GW not counting the substantial contribution of the two solid boosters. But the shuttle is most likely heavier, so yes, your Millenium Falcon probably could be made to fly if one wants 2500 engines. At that, you should have a pretty reliable engine system, 25 engines out is only a 1% power loss. IMO, better to stick a couple of Polywells in there, they should be a lot less massive than 2500 FF thrusters.

Brian H · Post by **Brian H** » Sun Oct 10, 2010 2:09 am

Aero wrote:
GIThruster wrote:Lets suppose you built something like a Millenium Falcon. It's about 27 meters long, and has a thruster assembly about 20 meters wide and 2.5 meters high. If you have about 50 FF thrusters/square meter, at 10 MW@, that's about 25 GW, yes?

Will that fly?
...
At that, you should have a pretty reliable engine system, 25 engines out is only a 1% power loss. IMO, better to stick a couple of Polywells in there, they should be a lot less massive than 2500 FF thrusters.

Assuming the Falcon's cooling tech is up to maxing the FFs at 25MW, that cuts the number to 500. Which is a 10x10x5 cluster - not all that massive.

Aero · Post by **Aero** » Sun Oct 10, 2010 4:12 am

Assuming the Falcon's cooling tech is up to maxing the FFs at 25MW, that cuts the number to 500. Which is a 10x10x5 cluster - not all that massive.

25 MW x 500 thrusters = 25 GW hmm - new math...Unless you're powering the space shuttle, then that's about right.

Need 1000 thrusters at 25 MW to get 25 GW. Can anyone estimate just how massive that would be?

My BOE numbers indicate that a 25 GW Polywell would mass upwards of 200 metric tons. (316 mtons is my calculated result, but that is very conservative, it will be smaller than that.) My question boils down to this,"What is the engine mass where a Polywell generates more power than ganged FF thrusters?" I have a 33 oz coffee can that is 6 inches tall and 6 inches in diameter. If that is the size of one FF thruster, what is it's density?

Edit: Add - My coffee can volume is 0.00278 cubic meters and using the same density as for a Polywell coil that I used before, 5 metric tons per cubic meter, results in FF thruster mass of 0.0139 metric tons or 13.9 kilograms. For any reasonable FF thruster power, the Polywell comes in overweight. That is because you get from 10 to 40 MW out of the first 14 kg of FF thruster, where as with a Polywell you get nothing until you are in the 10 ton range. I don't know what numbers to assume to calculate the power of 10 tons of FF thrusters, but 1000 FF thrusters would mass 13.9 metric tons from above.

GIThruster · Post by **GIThruster** » Sun Oct 10, 2010 4:53 am

Aero wrote:. . .so yes, your Millenium Falcon probably could be made to fly if one wants 2500 engines. At that, you should have a pretty reliable engine system, 25 engines out is only a 1% power loss. IMO, better to stick a couple of Polywells in there, they should be a lot less massive than 2500 FF thrusters.

Agreed. FF thrustsers really would work best with something too small for a Poly and a Poly might fit in a light transport like the Falcon. FF is good for those craft too small for a Poly. Either way the trouble with making something fly isn't in the power density of a fusion drive. It's in the mass of the propellant, the shielding, the cap banks--mostly still though, the propellant.

That's because rockets suck.

GIThruster · Post by **GIThruster** » Sun Oct 10, 2010 5:15 am

A better use for a FF reactor for flight would be an air breather. Suppose you were to fit an MV22 with a pair of 10MW reactor/turbofans. If you captured just half the energy and used it (which is being generous with all that air to heat) you'd have about the same power as the huge fans on the Osprey. They put out 4,590 KW each. The difference is, you don't need fuel. You feed it Boron with a teaspoon so suddenly your craft has almost unlimited range. Not a bad application.

Aero · Post by **Aero** » Sun Oct 10, 2010 5:24 am

Check the edit to my post above. The FF thruster is so low mass that it may beat Polywell all across the envelope for flight vehicles. What is the upper limit on Polywell power based on cooling requirements, because at the low end, FF thrusters wins hands down. Polywell starts out way behind on power to mass ratio, and it may never catch up.

Brian H · Post by **Brian H** » Sun Oct 10, 2010 5:28 am

Aero wrote:
25 MW x 500 thrusters = 25 GW hmm - new math...Unless you're powering the space shuttle, then that's about right.
...

Not new, just error -- missed that you were working with 10MW since I'm used to thinking of the FF as a 5MW machine. So the count would be 1000, which is 10x10x10.
Which makes me wonder whether waste heat from that many FFs in clusters might be usable.

This whole exercise is very speculative, of course. I'm more interested in the nearer-term uses in conjunction with such drivers as the VASIMR.

Brian H · Post by **Brian H** » Sun Oct 10, 2010 5:33 am

GIThruster wrote:A better use for a FF reactor for flight would be an air breather. Suppose you were to fit an MV22 with a pair of 10MW reactor/turbofans. If you captured just half the energy and used it (which is being generous with all that air to heat) you'd have about the same power as the huge fans on the Osprey. They put out 4,590 KW each. The difference is, you don't need fuel. You feed it Boron with a teaspoon so suddenly your craft has almost unlimited range. Not a bad application.

Some interesting ideas about SSTO vehicles using MHD have been floated. In combo with VASIMR that might make for a one-vehicle-does-all solution. Except for high-G space dogfights.

DeltaV · Post by **DeltaV** » Sun Oct 10, 2010 5:55 am

Assume REB heating of propellant (QED/ARC) is used for the boost to orbit, using only air as propellant at boost start (say 70-100K ft at M2.5-3.5), transitioning smoothly to using only onboard propellant at boost end.

What is the fraction of total output power available for the REB, DPF vs. Polywell?

GIThruster · Post by **GIThruster** » Sun Oct 10, 2010 6:24 am

Aero wrote:Check the edit to my post above. The FF thruster is so low mass that it may beat Polywell all across the envelope for flight vehicles. What is the upper limit on Polywell power based on cooling requirements, because at the low end, FF thrusters wins hands down. Polywell starts out way behind on power to mass ratio, and it may never catch up.

Hard to make an educated guess. With 1,000 FF, you need 1,000 fuel injectors. Even though they're small, these things add up.

I think the coffee-can sized electrode on the FF is Beryllium. It probably has a significantly higher density than the YBCO one expects you'd make a poly coil out of.

GIThruster · Post by **GIThruster** » Sun Oct 10, 2010 6:53 am

DeltaV wrote:Assume REB heating of propellant (QED/ARC) is used for the boost to orbit, using only air as propellant at boost start (say 70-100K ft at M2.5-3.5), transitioning smoothly to using only onboard propellant at boost end.

What is the fraction of total output power available for the REB, DPF vs. Polywell?

Have you looked at LACE? Liquify the air and separate it or not, store some for high altitude, dump the rest as liquid into the alpha stream for cooling and thrust. The best work I've ever seen comparing the various possible continuous cycles is certainly this:

http://www.amazon.com/Future-Spacecraft ... 301&sr=8-1

With the FF, because it's not intended to run in stasis but is pulsed, you actually have an opportunity for a pulsed detonation of liquid air. Czysz and Bruno talks quite a bit about about pulse engines too. It's an excellent book and easily worth the price if you're seriously interested in this.