Talk-Polywell.org

It's (3).

Hint: Define "expended"...

You could in principle be describing a magsail.

That reminds me - sfuerst is complaining (again) about mass-energy dipoles being impossible in tensor GR; that the lowest-order arrangement possible is a quadrupole, and that this invalidates M-E.

Did that ever get a satisfactory public answer?

Accelerate at 1 gee half way and decelerate at 1 gee the second half of the trip. Time to the Moon is about 5 hours. To Mars at its furthest approach to Earth is 2 days. Jupiter is 7, Saturn is 9... At the time when Paul and I did this, just after STAIF '06, Jim warned us that this needs a relativi...

I don't think you need to account for propellant when you're not driving a wormhole condition. You're wrong. Jim showed that if you use the GR tool, you get the right numbers for anything. What GR tool? The issue is really that dV is linear and dE is quadratic, so whenever we do these calculations ...

My whole point about exhaust velocity is that the exhaust is part of the problem that you can't neglect without getting an apparent conservation violation. This is why GoatGuy and chrismb get an apparent violation from M-E - they don't consider the reaction mass. It's the exact same reason you got a...

GIThruster, what's "wrong with the math" in your example is that the propellant kinetic energy is unaccounted for. The propellant question is not a red herring; it's central to the issue. That's why I suggest one do the calculations with a Hall or Ion thruster, because the energy into the thruster ...

So just look at the kinetic energy of the rocket. That, alone, cannot be greater than the sum energy expended, let alone some propellant floating around too. That only works if you're hauling propellant around, and/or the propellant used throughout the acceleration is known to be initially stationa...

If you're going to assess energy conservation in a thruster, you have to account for both the thruster (and whatever's attached to it) and its propellant. This is what makes rockets conserve energy - the chemical energy in the propellant is converted into a fixed amount of kinetic energy inherent in...

Skylon's max takeoff weight was about 325 tonnes, last I heard of the in-progress D1 design (last year). The C1 used in the pictures was 275 tonnes. It's mostly liquid hydrogen, in nonstructural tanks in an airship-style structural frame covered in a nonstructural composite skin; it's a lot lighter ...

The shielding thickness for a 60 MW P-B11 reactor verses a 6 GW reactor would be less. My understanding of radiation shielding is that a certain thickness of a material would be required to stop 90% (or some other selected portion) of the radiation. An additional same thickness of material would st...

I'm not refering to The Exponential Function but rather what are generally known as exponential functions which are indeed as I described, one that grows exponentially. http://oregonstate.edu/instruct/mth251/cq/FieldGuide/exponential/lesson.html I noted the general case myself - but you used the ex...

@Dio & Blank: You're both wrong. ... An exponential function is y = a^x. The most common one is y = e ^x, where e is a fundamental irrational constant roughly equal to 2.718. Interestingly, d(e^x)/dx is also e^x. y = x^2 and the position of a falling object in a uniform gravity field are both quadra...

Do I remember correctly from a while back someone stating that a 100MW p+B11 Polywell would need about a foot of concrete (or equivalent) for shielding? Not concrete. Lead. At least 10", possibly as much as 14" IIRC. That's mostly to deal with the high-energy gammas, assuming human workers spend a ...

williatw wrote:After all you would need distance & time to decelerate anyway, after you disengaged the drive

Why?

It ain't me buddy. Dammit, I knew you would jump on that, but I was in a hurry and couldn't be bothered to rewrite the sentence. You were the one who brought it up to try to make a point, and you plainly concur, not only about the judgment but about the underlying value assumptions (some of which m...