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Talk-Polywell.org • QED-ARC Engine ISP figures
Page 1 of 2

QED-ARC Engine ISP figures

Posted: Fri Sep 18, 2009 5:46 pm
by Mindblast
Hello all,

i'm in the process of developing an addon for Orbiter, the free spaceflight-simulator. ()
What i want to do is a SSTO spaceplane using Polywell reactors, inspired by the design proposed by Dr. Bussard for example in this paper:


I have blogged about my current concept state here: I would like to invite you all to comment on it.

Now my question concerns Dr. Bussards calculations for the attainable ISPs of a QED-ARC engine. In the paper above he mentions an ISP range of 1500-5500s for the ARC engine. I have run some numbers and can't quite find out how this would be possible:

Assuming a 6GW Reactor that has an electrical efficiency of 80% (i think that was about the efficiency that was assumed in the papers), that would mean 1.2GW of energy would have do be cooled regeneratively. Assuming also (like in the paper) that the reactor could still work at a temperature of 2087K and assuming LH2 as propellant:

H2 has a heat capacity of ~14300 J/(kg*K)
so the massflow required to keep the reactor at 2087K would be
mdot = 1.2e9 / (14300 * 2087) =~ 40.2 (units W * K * kg / (J * K) = kg/s)

Now when i assume the engine can convert all 6GW of reactor power to kinetic energy of the propellant i get:

eKin = 0.5 * mdot * vexhaust^2

so

vexhaust = sqrt(eKin * 2 / mdot)

vexhaust = sqrt(6e9 * 2 / 40.2) =~ 17277 (units sqrt(W * s / kg) = m/s)

ISP = vexhaust / 9.81 = 1761s (units m * s^2 / m * s = s)

So i get an absolute maximum of 1761s ISP at a reactor temperature of 2087K. So how did Bussard figure out a maximum of 5500s ? If i take that value and do the calculation in reverse i get a reactor temperature of about 20000K (!!!).

Posted: Sat Sep 19, 2009 4:51 pm
by D Tibbets
Mindblast, if you've not yet seen it, look at :

http://www.askmar.com/Fusion_files/QED% ... tation.pdf

On page 3 SSTO is discussed.


Dan Tibbets

Posted: Sun Sep 20, 2009 3:06 pm
by Mindblast

Lateral thinking...

Posted: Tue Oct 06, 2009 12:59 am
by Nik

Posted: Tue Oct 06, 2009 10:34 am
by Mindblast

Posted: Tue Oct 06, 2009 3:45 pm
by MSimon

Posted: Tue Oct 06, 2009 8:06 pm
by KitemanSA

Posted: Tue Oct 06, 2009 11:01 pm
by MSimon

Posted: Wed Oct 07, 2009 12:59 am
by djolds1

Posted: Wed Oct 07, 2009 9:21 am
by KitemanSA

Posted: Wed Oct 07, 2009 10:40 am
by MSimon

Posted: Wed Oct 07, 2009 1:54 pm
by Mindblast

Posted: Wed Oct 07, 2009 2:13 pm
by KitemanSA

Posted: Thu Oct 08, 2009 1:22 am
by djolds1

Posted: Thu Oct 08, 2009 6:01 am
by 93143