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Re: Mag brake

I appended my web pages mass in space calculations on the end in case your

Oh, the plasma is probably swirling around with the rest of the galaxy in a
slightly different orbit that us and the other local stars.


At 10:55 PM 2/14/96, KellySt@aol.com wrote:
>Forwarded message:
>From:	T.L.G.vanderLinden@student.utwente.nl (Timothy van der Linden)
>To:	KellySt@aol.com, stevev@efn.org, jim@bogie2.bio.purdue.edu,
>zkulpa@zmit1.ippt.gov.pl, hous0042@maroon.tc.umn.edu, rddesign@wolfenet.com,
>David@InterWorld.com, bmansur@oc.edu
>Date: 96-02-12 12:54:50 EST
>>Are their any numbers on how much power per thrust the magnetic break would
>I'm not certain if you understood the mechanism. It seems that I didn't
>Now looking at the formulas again, I notice that the plasma needs to move
>traverse to the flightpath and my assumption of towing the wires behind the
>ship is probably not right either. They need to be in a network in front of
>the ship (the plane of the net is perpendicular to the direction of
>The interstallar plasma is moving, don't ask me why or whereto but the book
>says it does. What we do is use the magnetic field component that is
>traverse to the velocity of the ship.
>       /\
>       ||
>---------------- moving conducting wire
>X O X O X O X O  magnetic field lines going up or down or aside
>If the field lines are perpendicular to the direction the wires are moving,
>then an electric current will start to flow in these wires. The electric
>resistance turns this current into heat and radiates it away in all
>directions. All that heat comes from the kinetic energy of the starship and
>thus the ship slows down.
>They use the following formula:
>Drag force= rho V Va A
>rho=mass density of the plasma
>V=ships velocity
>Va="Alfven" velocity=Sqrt[B^2/(4 Pi rho)]=10 km/sec
>B=traverse magnetic field
>A=frontal area of the net
>They use also another way of writing:
>Drag force = Sqrt(Dh Dm)
>Dh=hydronamic drag= rho V^2 A       (Dh=normal drag due to mass-collisions)
>Dm=magnetic drag = A B^2/(4 Pi)
>This system looks a lot like the solid plate in front of the ship catching
>the ISM to decelerate. The book tries to explain that this magnetic sister
>may be more usefull due to the size:mass ratio. While one can use thin wires
>to make use of the magnetic field, one needs a rather thick plane to stop
>fast moving particles.
>By the way, Steve, would it be possible for you to explain how a normal
>magnetic scoop could be constructed.

Ram Scoop collector

1000 km diameter scoop 200 tons. The speed of light is 300,000 kilometers
per second Assuming your moving at 1/3rd the speed of light (100,000
kilometer per second, or 1E10 cm/sec) with a scoop area of 1000 km
(pi*R^2=pi(50,000,000cm)^2 = 7.854E15 cm^2). You'd be scooping up the mass
in 7.854 E25 cubic centimeters of space.

A big question is the composition of interstellar space. A classic
assumption is that there is nothing but about 1 atom of hydrogen in a cubic
centimeter of space. More recently, people guess it might be less than .054
atoms per cubic centimeter or as many as 10. Even more recently than that
(say the last few months) it has been proposed that there may be a lot of
long-chain carbon molecules in space. Perhaps 60-200 atoms / molecules.
These small, dark, heavy molecules might be the missing 90-99% of the mass
of the galaxy (euphemistically called "dark matter").

So far, no one really knows. This is unfortunate, because the composition
of the interstellar medium makes a hell of a difference in the design of a
RAIR-based starship. Since we don't know one way or the other, let's assume
one atom per cubic centimeter at a proton mass of 1.673 E-27 Kg. At 0.333c,
using the above design figures, our 1000 km in diameter scoop, scoops up a
ram flow of 131.4 grams per second.

Note that this number might be off by a factor of 10 or even 100!


Kelly Starks                       Internet: kgstar@most.fw.hac.com
Sr. Systems Engineer
Magnavox Electronic Systems Company
(Magnavox URL: http://www.fw.hac.com/external.html)