Long cables to power "ioncraft" to orbit?

Mon May 23, 2005 1:48 am   

George Dishman wrote:


If you look at the pages describing the drive, the electrical power is
a means to create airflow. The thrust is due to this airflow. I'm
calculating the thrust as you do with the rocket equation.
What would be dependent on the speed is the drag. That would be a
rather complicated dependence on the shape of the vehicle. As a first
guess you could give the craft the aerodynmic shape of a supersonic or
hypersonic vehicle and use the same type of intakes on those vehicles.


Bob Clark

Mon May 23, 2005 12:25 pm   

N:dlzc D:aol T:com (dlzc) wrote:

They beam the energy to the craft using lasers or microwaves. Same
drive just different source for the power.

Bob Clark

Mon May 23, 2005 2:11 pm   

Has there actually been any tests at low pressures ? If the pressure
was halved, then there would be less ions, but that would mean less
current. This means lower thrust but also lower power.

Is the effect that the ion keeps hitting off uncharged particles as it
is accelerated, using them as reaction mass? This also means that when
it finally hits the other terminal, it is moving very slowly.

Mon May 23, 2005 3:38 pm   

N:dlzc D:aol T:com (dlzc) wrote:


You can call it MHD if you want. I'm referring to any method of
propulsion that uses either electrical or magnetic fields to propel air
that has been ionized by electrical means or otherwise.
Lifters also can work on AC current. Then in addition to the force
produced by the asymmetric electric field you could get a force due to
the Lorentz force arising from the magnetic field.


Bob Clark

Tue May 24, 2005 11:50 am   

Robert Clark wrote:

I was attempting to encourage extending the work done by amateurs with
lifters to the kilowatts of power range. However, I am informed that
using high voltages while at the same time having high wattage means
the amperage would also be high. This can potentially be lethal.
There are relatively inexpensive ways of transforming the low voltage
put out by electrical generators to the tens of thousands of volts you
need for the lifters. If you have experience working with high voltage
and amperage, then you already know what they are.
It should not be attempted unless you are already well experienced
with working on and in high power electrical supplies.


Bob Clark

Tue May 24, 2005 1:06 pm   

Robert Clark wrote:

A 3250 watt generator will weigh a lot more than 7 pounds.
The simple approach needs a lift greater than the weight
including the fuel. What you have then is an engine
(generator plus lifter) which derives thrust from fuel
using the air as reaction mass. You would get far better
efficiency from a simple jet engine.

So your idea is to leave the engine and fuel on the ground
which sounds good. However you then have the problem of
getting the power to the vehicle. Unless the mass of the
cable is less than the mass of the generator and fuel, you
gain nothing.

You are limited by voltage so assuming you use the maximum
feasible, the current is proportional to the power and the
cable mass per unit length is proportional to current for
a flat thin ribbon (maximum surface area to dissipate heat).

Information on the conductor parameters and a bit of maths
should then give you the maximum cable length, or distance
between cable-supporting lifters and so on.

All of this will let you gently raise your payload to some
altitude but won't get any appreciable speed and the need
for reaching orbit is horizontal speed, not height.

A balloon remains more practical and cheaper.

George

Fri May 27, 2005 2:49 pm   

rgregoryclark_at_yahoo.com wrote:
[snip]

Sigh. And how much does a 100 km cable weigh under 32 g? And what
is going to support that? Certainly not the cable. We don't have
cables that can support their own weight at 100 km length under
1 g, never mind 32 g. Suddenly, you are back to the effective
length of 3000 km or so.
Socks

Fri May 27, 2005 4:10 pm   

Puppet_Sock wrote:


Yeah, you probably would not want to operate at 32 g's, unless you
found some way of coming up with a super-lightweight cables (I have an
idea about that.)
But we several materials that can support their own weight at over 100
km, Kevlar, Spectra, carbon fibers, etc:

From: Dani Eder <ederd_at_worldnet.att.net>
Subject: Re: space elevator / cable
Date: May 08 1997
Newsgroups: sci.space.tech
"Peter Hanely wrote:

T-1000G carbon fiber has a strength of 924,000 psi and a density of
0.0654 lb/cu inch. Therefore it has a characteristic length of
14.1 million inches, or 359 km."
http://yarchive.net/space/exotic/carbon_fiber.html

The simplest way would probably be to have the horizontal track be
covered by cable lying on the ground and only the vertical distance of
cable be supported by the propulsive method. This would result in a
much lower acceleration because it takes place over a longer distance
and also a much lower weight of cable that had to be supported.
Keep in mind that whatever the mass of the cable that had to be
supported in the air, quite likely you would want the cable to have its
own propulsion all alongs its length rather than having it come totally
from the spacecraft itself.



Bob Clark

Sun May 29, 2005 6:48 pm   

Key for lifter drive becoming a generally useful propulsion method is
an electrical power source lightweight enough to be lifted by the
lifter dirve. Electrostatic high voltage generators may prove to an
answer for such a power source.
Electrostatic high voltage generators have existed since the 18th
century. They were earlier called electrostatic influence machines.
This page of Antonio Carlos M. de Queiroz calcutes the current that can
be generated by an electrostatic influence machine:

Maximum electric field.
http://www.coe.ufrj.br/~acmq/efield.html

(For anyone who had the same problem as I did opening this site, you
can get the Google cached version here:

Maximum electric field.
http://64.233.161.104/search?q=cache:Su6AOXBIC9EJ:www.coe.ufrj.br/~acmq/efield.html)

Note that it is dependent on the product of the dielectric constant
of air and the breakdown voltage of air.
Then since the dielectric constant of the air and vacuum are about
the same but the breakdown voltage of the vacuum is immeasurably
high, you can achieve much higher currents enclosing the device in a
vacuum.
Various types of electrostatic generators are described on this page
of de Queiroz:

Electrostatic Machines.
http://www.coe.ufrj.br/~acmq/electrostatic.html

Especially useful for our methods might be the Wimhurst, Wehrsen,
Holtz, or Bonetti machines. I believe these devices would be able to
deliver more current and therefore greater wattage for our application
than a Van de Graaff generator.
Another interesting possibility might be the voltage doubler. As the
name implies it doubles the applied voltage with each cyclic turn of
the rotors:

The Bohnenberger machine.
http://www.coe.ufrj.br/~acmq/bohnenberger.html

Take a look at the graph on this page to see how the voltage is
doubled at each cycle. The doublers are limited in voltage in air by
the sparking that is produced. The voltage possible in vacuum should be
markedly higher.
Another possibility might the generators that use a vertical cylinder
as a rotor. From de Queiroz "Maximum electric field" page you see the
current produced is proportional to the surface area of the rotor and
the speed of rotation. But there are limits to the rotational speed for
real materials since they would fall apart from the internal stresses.
Keeping the speed low but increasing the radius of a flat disc raises
the same problem because the speed on the edge of the disk will be
higher. However, a vertical cylinder solves this since you get
increased surface area by making the cylinder long while the internal
stresses from the rotation are only operating radially.
The key factor in using an electrostatic generator for the power
supply is that they can serve as both the source of the electrical
power and the source of the high voltage generation - you don't need
separate power supply and transformer.
That they act as source for high voltage is known, but the reason they
can act as the power source for our application is they are in effect
flywheel batteries. Then at launch you induce the rotors to spin at
high speed by either mechanical or electrical means and as with any
flywheel they would act as a means of power storage. Note that with the
most advanced flywheel batteries you enclose the flywheel in vacuum to
keep the time the flywheel spins to a longer period by reducing air
friction, and they also use magnetic bearings to reduce the friction
from the support of the rotor. Then this dovetails nicely with the
requirement to have them in vacuum to increase voltage attained.
A file in the Yahoo Lifters group calculates remarkable power
generation for a moderately sized vacuum electrostatic generator:

Lifters.
http://groups.yahoo.com/group/Lifters/

The file named "Electrostatic HV Supply.PDF" appears in the Files
section in that group. It was copied from a book on high voltage
generation and claims for a generator operating in high vacuum with 50
rotors, 4 feet in diameter rotating at 4,000 RPM could generate 1 MV
and 7 megawatts of power. Note that key in its being able to deliver
this power is the rotors operating in vacuum where much higher voltage
gradients are possible, 1 MV/cm or 100 MV/m in this case. In air you
might be able to get only 3 MV/m. Then assuming approx. a 1 to 1
thrust(in grams) to power(in watts) ratio, this could lift 7,000 kg.
Key would be making the rotors light weight. Then work on advanced
flywheel batteries that use carbon composites for the flywheel would be
helpful here:

Composite Rotor Lifetime Testing.
http://www.utexas.edu/research/cem/composite%20rotor%20testing.html

Flywheel Energy Storage.
http://www.upei.ca/~physics/p261/projects/flywheel1/flywheel1.htm

Flywheel Basics Tutorial.
http://rpm2.8k.com/basics.htm




Bob Clark


Robert Clark wrote:

Mon May 30, 2005 11:55 am   

Robert Clark wrote:

It seems to me the efficiency can't get any worse at
high power, where efficiency is thrust to power ratio. For
example Blaze Labs was able to lift 185 grams using
200 watts. Therefore all you would have to do with
3000 watts would be to distribute this power equally
to 15 lifters of the Blaze Labs design physically
connected together in a single layer and you would be
able to lift 15*185 = 2775 grams. You might be able to
maintain safety by making sure the wires for separate
lifters do not touch. A good way to do this is in fact
to use completely separate but identical power supplies
for each lifter and ensuring that though the lifters
are physically connected, none of the conducting parts touch.
Since drag increases in proportion to cross-sectional
area the drag would also only increase in proportion
to the size. You might also be able to get less drag by
stacking the lifters on top of one another. However,
Blaze Labs believes their experiments show this would
*reduce* the thrust to power ratio.
But the key question that needs to be answered is how
does the thrust change at high air speed.


Bob Clark