Airbreathing SSTO

If polywell fusion is developed, in what ways will the world change for better or worse? Discuss.

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hanelyp
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Joined: Fri Oct 26, 2007 8:50 pm

Re: file location

Postby hanelyp » Thu Apr 17, 2008 8:45 pm

wizz33 wrote:http://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/20050170447_2005172301.pdf

those longitudinal electical waves sure are intersting for ftl comm.


Reading that paper, the writer is neglecting the difference between phase and group velocity. Phase velocity (wavelength/frequency) may exceed free space light speed with impunity. Group velocity, the speed at which signal and energy propagate, must be <= C, unless a whole lot of physicists are wrong.

Buried deep in the text I found this gem, placing 'scalar waves' within a well documented sub field of electromagnetism:
According to this definition, the Tesla experiments were near-field (characterized by longitudinal waves) and those of Hertz were far-field (characterized by transverse waves).

I also found many statements clearly the result of drinking kookaid.

93143
Posts: 1131
Joined: Fri Oct 19, 2007 7:51 pm

Postby 93143 » Thu Nov 27, 2008 11:03 pm

I wonder if it is reasonably possible to use an MHD turbine on a scramjet exhaust in order to obtain large quantities of electrical power at a reasonable voltage?

In a QED engine, you'd probably want it in between the hot hydrogen injection and the electrical heating section, so that it would be operating with a reasonable plasma but wouldn't interfere with the magnetic shielding required downstream of main power input. You could use some of the resulting low-voltage power to run a heat pump to jack the hydrogen coolant temperature up past 2000 - 2500 K, in order to increase the effective Isp without having to run the magrid that hot (the refrigeration power ends up back in the engine anyway), and maybe use some of it to run an MHD or ion thrust system or something in an intake bypass, increasing efficiency the same way a turbofan does (more mass, less velocity).

I have no idea if MHD systems can be made efficient enough, when dealing with hypersonic partially-ionized airflow, for this to be useful. Historically, MHD hasn't performed to theoretical efficiencies... I don't personally like the idea of seeding the flow with metals, but it might help...

...I think I'm just about convinced that expelling hydrogen coolant is a good idea. It avoids having to get a DLC-coated tungsten/CNT composite radiator up to 3500 K or so (nickel-based reverse Rankine cycle anyone?), which is much more difficult materials-wise and results in not only the reactor waste heat but also the very substantial refrigeration power being pretty much completely wasted. This massive refrigeration power would thus be even more difficult to extract from the engine via MHD, since it would be a significant chunk of the total engine power. The combined losses could easily exceed half the reactor output, and unless large MHD pumps and turbines can be made really efficient, this scheme might not end up power-positive at all. Indefinite atmospheric flight at Mach 24 would be nice, but overall I think ARC wins...

IntLibber
Posts: 747
Joined: Wed Sep 24, 2008 3:28 pm

Postby IntLibber » Tue Dec 30, 2008 4:11 am

Actually if you read my proposals at lorrey.biz, you'd see that SHARP materials (hafnium diboride and zirconium diboride) as are used as steering vanes on MIRVs are more than adequate TPS for hypersonic vehicles.

They allow mach 7 at sea level, mach 11 at 100k feet altitude, and there is no radio interference at any reentry speed.

93143
Posts: 1131
Joined: Fri Oct 19, 2007 7:51 pm

Postby 93143 » Mon Jan 05, 2009 1:14 am

Heh... looks like boron really is good for just about anything... 'Quintessential', almost...

I actually hadn't done a heat transfer balance to find out the critical altitude for a tungsten-CNT composite at near-orbital velocity. That isn't what I'm complaining about; my problem is with my earlier idea with the radiator.

If you don't dump coolant, you need to radiate the excess heat from the reactor at very high temperature (unless you're in space, using low thrust/high Isp engines, and can afford to deploy a huge set of panels). This entails expending a very large refrigeration power, which is also lost through the radiator. This power has to be at a usable voltage, which means it needs to be collected with a magnetohydrodynamic turbine or something, which will probably be very heavy (though not as heavy as the power electronics that would be required in order to draw it straight from the reactor). Basically you lose a huge chunk of power and add a lot of weight for a capability you don't, strictly speaking, actually need.

But it's good to know about other materials that can take those kinds of temperatures. Tungsten is heavy...


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