Mach Effect progress

Point out news stories, on the net or in mainstream media, related to polywell fusion.

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Barry Kirk
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Postby Barry Kirk » Tue Jan 15, 2013 8:26 pm


chrismb
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Postby chrismb » Tue Jan 15, 2013 8:32 pm


GIThruster
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Postby GIThruster » Tue Jan 15, 2013 8:34 pm

"Courage is not just a virtue, but the form of every virtue at the testing point." C. S. Lewis

GIThruster
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Postby GIThruster » Tue Jan 15, 2013 8:39 pm

"Courage is not just a virtue, but the form of every virtue at the testing point." C. S. Lewis

chrismb
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Postby chrismb » Tue Jan 15, 2013 8:47 pm


dkfenger
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Postby dkfenger » Tue Jan 15, 2013 8:56 pm

OK, here's some calculations. I dug up the datasheet for Busek high-power hall effect engines:
Busek BHT-20k Hall Effect Thruster
Discharge Input Power: 20kW
Discharge Voltage: 500V
Discharge Current: 40.5A
Propellant Mass Flowrate: 40.0 mg/sec
Thrust: 1.08N
Specific Impulse: 2750 sec
Propulsive Efficiency: 70%


Let's build a hypothetical microsatellite around this with a handwavium on-board power source.
10kg craft, 4kg is propellant. Round the numbers, thrust is 1N at 40mg/sec.

Exhaust velocity = 9.8066 m/s^2 * 2750s = 26,968.15 m/s. Call it 27km/s for simplicity.
Back-check delta-p: 40mg * 27km/s = 0.00004 kg * 27000m/s = 1.08 N s, so 40mg/sec produces 1.08N of thrust. Good.


Examine the effects of 1s of thrust (should not change frame enough to matter):
a = F/m = 1N/10kg = 0.1 m/s^2. Over 1s, change velocity of craft by 0.1m/s.
Energy dissipated: 20kJ.
Change in KE of craft:
KE0 = 0.5*v0^2*10kg
KE1 = 0.5*(v0+0.1m/s)^2*(10kg - 40mg)

Measure in different frames based on v0 of craft:
v0 KE0 KE1 delta-KE
0m/s 0J 0.0499998J 0.05J
1e4 m/s 5e8J 5.00008e8J 8kJ
2e4 m/s 2e9J 2.000012e9J 12kJ
4e4 m/s 8e9J 8.000008e9J 8kJ
5e4 m/s 1.25e10J 1.25e10J 0kJ

The hypothetical Hall Effect rocket above *never* goes over-unity.

Let's try again with a 1kg craft instead: delta-V is now 1m/s for 1s of thrust. delta-m is 40mg, still.
at 1e4 m/s delta-KE is 8kJ
at 2e4 m/s delta-KE is 12kJ
at 2.5e4 m/s delta-KE is 12.5kJ
at 3e4 m/s delta-KE is 12kJ and falling

Note that at the peak, the KE of the exhaust fuel is approximately zero. This shouldn't come as much of a surprise, but was something I wasn't familiar with.

KE of exhaust fuel when craft is at 0m/s: 0.5*(2.7e4m/s)^2*40mg = 14.58kJ
Plotting fuel+craft delta-KE produces a straight line, starting at 14.58kJ at v0=0m/s, hitting 0 at v0=1.82e5m/s. [Which suggests that if you fire the craft backward while at high velocity, the *propellant* violates energy conservation. Perhaps this negates my point, perhaps not. Or perhaps I've done this entirely wrong. I would welcome any corrections.]

Note 14.58kJ / 20kJ = about the 70% propulsive efficiency claimed on the datasheet.

Would anyone care to present the same math for a 10kg Mach Effect spacecraft? How much thrust could one expect from a 20kW Mach Effect thruster under realistic assumptions about the new ceramics, assuming the effect is real?

GIThruster
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Postby GIThruster » Tue Jan 15, 2013 8:56 pm

No chris. It has been illustrated by GoatGuy, Andrew and you, but you all make the same mistake. There is no onus upon me to do your math for you. Do it yourself and do it with a chemical thruster on an arm with sufficient fuel provided. You'll see the same conservation violation arises which should be no surprise because GRT is the correct scientific theory to explain such motion--not newtonian theory.
"Courage is not just a virtue, but the form of every virtue at the testing point." C. S. Lewis

GIThruster
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Postby GIThruster » Tue Jan 15, 2013 8:59 pm

dkfenger, I just glanced at your calculation but just noting, you take propulsive efficiency as a constant or invariant, which is wrong, It is not. Your method cannot give the proper result. Thrust is not relativistically invariant.
"Courage is not just a virtue, but the form of every virtue at the testing point." C. S. Lewis

chrismb
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Postby chrismb » Tue Jan 15, 2013 9:01 pm


chrismb
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Postby chrismb » Tue Jan 15, 2013 9:08 pm

Last edited by chrismb on Tue Jan 15, 2013 9:10 pm, edited 1 time in total.

GIThruster
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Postby GIThruster » Tue Jan 15, 2013 9:10 pm

"Courage is not just a virtue, but the form of every virtue at the testing point." C. S. Lewis

dkfenger
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Postby dkfenger » Tue Jan 15, 2013 9:11 pm


chrismb
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Postby chrismb » Tue Jan 15, 2013 9:12 pm


dkfenger
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Postby dkfenger » Tue Jan 15, 2013 9:18 pm


GIThruster
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Postby GIThruster » Tue Jan 15, 2013 9:18 pm

"Courage is not just a virtue, but the form of every virtue at the testing point." C. S. Lewis


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