Long cables to power "ioncraft" to orbit?

[bz]

[email protected] wrote in @g44g2000cwa.googlegroups.com:

Just as with electrical power transmission over long distances, you
will use very high voltage, probably in the megavolt range, that is, if
you want to lift megakilos.

Unforetunately, you almost certainly can't scale up the voltage
significantly.

You will get arcing if you go up on the voltage, rather than ions.

Even if you could scale up the voltage, you would have two MAJOR problems.

1) arcing between the cables, the cables to the grid, or from the discharge
points to the grid.

2) xrays radiation generation. When you have voltages over about 33 kV, you
start getting significant soft x-ray generation when electrons accelerated
by such a potential are stopped. Dental x-ray machines use 70 kV. If you go
to mega volts, you will be making very hard x-rays.

In the demonstrations for small lifters, kilovolts were used to lift
only a few grams a few feet.
Since the lifter uses air for its reaction mass, you could use a
higher acceleration than that normally used for rockets to reach
orbital velocity at a lower altitude so the air is at sufficient
density. But this would reduce the lift capacity. That is, if you
accelerated at 3.6 g's, you could lift one third the mass than at 1.2
g's.
Or you could use a shallower trajectory than that used by rockets so
that most of the acceleration phase stays in the lower atmosphere. But
this would necessitate a longer and heavier cable.
Probably a combination of these would be optimal.

That reminds me of one other problem. Weather. Humidity.
The launch site will need to be in an area with very dry climate.

High humidity, clouds, or rain, will be very bad for such a device.



--
bz

please pardon my infinite ignorance, the set-of-things-I-do-not-know is an
infinite set.

[email protected] remove ch100-5 to avoid spam trap

 

[Gary Williams]

It's not actually scifi. There are lots of advocates of orbital tethers.
The one in Red Mars was constructed out of one of the moons, by
'growing' the tether in both directions. I guess they had to shift the
orbit of the moon first, so it was geostationary, but hey, it was scifi.

Also, that means my 'centrifugal force' explanation was bogus. It would
be, effectively, orbiting with the planet, with the center of mass in a
geostationary orbit.

In the story, when the tether was cut, something caused it to contact
the ground, which created friction, effectively bringing the entire mass
down over a period of a few hours or days. I can't remember many of the
details, and somebody seems to have 'borrowed' my copy of the book.

Those interested in this might like to follow up the following links:

http://www.liftport.com/
(See the FAQ for discussions of disaster scenarios)

http://www.space.com/businesstechnology/technology/edwards_boldly_050218.html

http://liftwatch.org/tiki-view_articles.php



Gary Williams

 

[Rich Grise]

I don't recall a detailed explanation being in the book, but friction due to
atmospheric drag would slow the bottom of the tether pretty quickly so as to
cause problems, then once it's unstable it's manure and impellor time.

What air friction? It's already moving at zero speed relative to the
surface of the Earth before it's cut, so "slow the bottom of the tether"
doesn't really mean anything. What's slower than zero?

I did read a story or essay, where the guy actually treated a tether
seriously, and he did some numbers, and they were mind-boggling. To do it,
he started with a BIG geostationary satellite, and started feeding
tether lines from the near and far sides simultaneously, so that they'd
balance. But at any place except that orbit, the tethers are subjected
to tidal forces - they're being pulled on. Eventually, by the time they
had 22,500 miles of Kevlar unreeled, there was so much tension on it
that it had to be like thousands of feet thick. This is one of the
problems they have with cables to deep-diving submersibles - the cable
has to be made neutrally buoyant, because otherwise it can't support
its own weight.

Once, when I was a kid, we tied a whole ball of string to a helium
balloon, figuring it would go as high as how much string we had. It
didn't go higher than maybe 100 feet, and the string just went slack.
(gradually, of course.) The weight of the string itself held the balloon
at sort of an equilibrium height.

Cheers!
Rich

 

[Joe Strout]

I did read a story or essay, where the guy actually treated a tether
seriously, and he did some numbers, and they were mind-boggling...
Eventually, by the time they
had 22,500 miles of Kevlar unreeled, there was so much tension on it
that it had to be like thousands of feet thick.

You need to read some of the more recent studies. There are materials
much better than kevlar, though none quite good enough yet to make a
space elevator practical -- but progress towards that material is being
made pretty rapidly, and this is no longer an idea to be dismissed
lightly. At least one company is actively pursuing it (and is now
working with NASA to spur the development of appropriate climbers via
the Centennial Challenges program).

,------------------------------------------------------------------.
| Joseph J. Strout Check out the Mac Web Directory: |
| [email protected] http://www.macwebdir.com |
`------------------------------------------------------------------'

 

[SioL]

I did read a story or essay, where the guy actually treated a tether
seriously, and he did some numbers, and they were mind-boggling. To do it,
he started with a BIG geostationary satellite, and started feeding
tether lines from the near and far sides simultaneously, so that they'd
balance. But at any place except that orbit, the tethers are subjected
to tidal forces - they're being pulled on. Eventually, by the time they
had 22,500 miles of Kevlar unreeled, there was so much tension on it
that it had to be like thousands of feet thick. This is one of the
problems they have with cables to deep-diving submersibles - the cable
has to be made neutrally buoyant, because otherwise it can't support
its own weight.

http://seattlepi.nwsource.com/business/221576_liftport26.html

I wonder if these guys are serious or perhaps just using publicity to
sell their nanotubes for other purposes.

 

[Robert Clark]

[email protected] wrote in @g44g2000cwa.googlegroups.com:



Unforetunately, you almost certainly can't scale up the voltage
significantly.

You will get arcing if you go up on the voltage, rather than ions.

Even if you could scale up the voltage, you would have two MAJOR problems.

1) arcing between the cables, the cables to the grid, or from the discharge
points to the grid.

2) xrays radiation generation. When you have voltages over about 33 kV, you
start getting significant soft x-ray generation when electrons accelerated
by such a potential are stopped. Dental x-ray machines use 70 kV. If you go
to mega volts, you will be making very hard x-rays.


That reminds me of one other problem. Weather. Humidity.
The launch site will need to be in an area with very dry climate.

High humidity, clouds, or rain, will be very bad for such a device.

You would locate the launcher at the gigawatt scale at very dry areas.
While transmission lines typically carry hundreds of kilovolts some do
go up to a million volts.
Using voltages in the hundreds of kilovolt range, power stations
already exist that transmit gigawatts of power over hundreds of
kilometers:

Quebec - New England Transmission.
http://www.answers.com/main/ntquery...+New+England+Transmission&gwp=8&curtab=2222_1


Bob Clark

 

[Puppet_Sock]

than

Aluminum is almost always used for high voltage power lines. This is
because of its lower weight:

Aluminium's Electrical Uses.
http://www.world-aluminium.org/applications/electrical/

At 2700 kg/m^3, it's weight is only 50% more than carbon fiber. So a 4
cm wide, 100km long aluminum cable would only weigh 340,000 kg. This
compares to 2 million kg for the space shuttle with solid rocket
boosters.

As Al says, getting to 100km is a no-brainer. You can use lots of
fairly simply methods to get that high. IIRC, it's not *that* much
higher than balloon records.

But the shuttle, which you want to compare to, thrusts for something
like 5 or 6 minutes to reach orbit. It goes *MUCH* farther than 100km
while still under thrust. You should be thinking more like 3000km
than 100km. IIRC, engine shutoff is someplace over Europe or so.
Multiply that 3.4E5 kg by 30 and it don't look so good any more.

In addition, the strongest cable yet manufactured is not going to
hold its own weight at 100km. (It's probably not going to do it at
10km, though I won't take any bets on that.) Do you feature a 4cm
cable holding 340,000 kg? Never mind doing it while this vehicle
is blasting away at many g's through the air.

Can you say "twang?" Knew you could. Cables have some stretch,
and then they snap. That would be pretty impressive for all
concerned. This many km long cable snaps someplace in the
middle, and both ends coil back to their connections. The
ground end snaps back pulverizing anybody silly enough to
be watching from the launch site. The sky end smacks into
the vehicle, at a relative velocity of "too many I'm sure,"
slicing it neatly into dozens of chunks. This shrapnel then
finishes up falling onto whoever happens to be downrange,
all at a velocity of several km/s. In 100 tonne amounts.

This could cause the neighbours to complain.

And even if the damn thing could work, you'd wind up with
this string of wire hanging in mid air, then falling back
with a certain amount of dispatch. The neighbours might be
more seriously pissed the higher the fool thing got. What
would, say, Span have to say if a multi-thousand-km cable
were to be dropped on them at orbital speeds? I doubt it
would resemble "Ole!"
Socks

 

[bz]

You would locate the launcher at the gigawatt scale at very dry areas.
While transmission lines typically carry hundreds of kilovolts some do
go up to a million volts.
Using voltages in the hundreds of kilovolt range, power stations
already exist that transmit gigawatts of power over hundreds of
kilometers:

I haven't found any 1 MV transmission lines. 450 kV is the highest I saw,
but I did find some cool pictures of arcs and sparks.

http://teslamania.delete.org/frames/longarc.htm

Also some real neat looking pictures of the results of 'quarter shrinkers'.
Which use very high pulsed magnetic fields to shrink coins.





--
bz

please pardon my infinite ignorance, the set-of-things-I-do-not-know is an
infinite set.

[email protected] remove ch100-5 to avoid spam trap

 

[Joe Strout]

http://seattlepi.nwsource.com/business/221576_liftport26.html

I wonder if these guys are serious or perhaps just using publicity to
sell their nanotubes for other purposes.

They are very serious. Any selling of the nanotubes for other purposes
is just to fund further development of the space elevator.

,------------------------------------------------------------------.
| Joseph J. Strout Check out the Mac Web Directory: |
| [email protected] http://www.macwebdir.com |
`------------------------------------------------------------------'

 

[[email protected]]

He did.

I dropped my jaw to hear this from a dais located in Washington D. C.
He also did other things that were fraught with intelligence.

Yep. Closer to home, note that the first category above is endowed
with what we (meaning sci.physics regulars) refer to as "second order
ignorance", which is the characteristic of many of our cranks.

Anyway, Rummy did say this and many seemingly intelligent people
jumped on this as a "dumb statement", not realizing that it was their
own stupidity they were thus proclaiming.

Yes, these types fixed his behaviour. Now anything that is decided
or accomplished using brains, as they should be used, will not
be documented. I drove down to Bethesda a couple of years ago
and kept looking for the toll booth where everybody had to hand
in his/her organ that contains common sense.

I got that book. I've read the first two chapters. I spent my
dreamtime last night editing my mental data base. I'm so tired.

/BAH

Subtract a hundred and four for e-mail.

 

[[email protected]]

I dropped my jaw to hear this from a dais located in Washington D. C.
He also did other things that were fraught with intelligence. Yep.


Yes, these types fixed his behaviour. Now anything that is decided
or accomplished using brains, as they should be used, will not
be documented.

Indeed. Would be dangerous to act otherwise.

I drove down to Bethesda a couple of years ago
and kept looking for the toll booth where everybody had to hand
in his/her organ that contains common sense.
))

I got that book. I've read the first two chapters. I spent my
dreamtime last night editing my mental data base. I'm so tired.

Well, let me know what you think, when you finish.

Mati Meron | "When you argue with a fool,
[email protected] | chances are he is doing just the same"

 

[[email protected]]

fairly simply methods to get that high. IIRC, it's not *that* much
higher than balloon records.

But the shuttle, which you want to compare to, thrusts for something
like 5 or 6 minutes to reach orbit. It goes *MUCH* farther than 100km
while still under thrust. You should be thinking more like 3000km
than 100km. IIRC, engine shutoff is someplace over Europe or so.
Multiply that 3.4E5 kg by 30 and it don't look so good any more.

In addition, the strongest cable yet manufactured is not going to
hold its own weight at 100km. (It's probably not going to do it at
10km, though I won't take any bets on that.) Do you feature a 4cm
cable holding 340,000 kg? Never mind doing it while this vehicle
is blasting away at many g's through the air.

Can you say "twang?" Knew you could. Cables have some stretch,
and then they snap. That would be pretty impressive for all
concerned. This many km long cable snaps someplace in the
middle, and both ends coil back to their connections. The
ground end snaps back pulverizing anybody silly enough to
be watching from the launch site. The sky end smacks into
the vehicle, at a relative velocity of "too many I'm sure,"
slicing it neatly into dozens of chunks. This shrapnel then
finishes up falling onto whoever happens to be downrange,
all at a velocity of several km/s. In 100 tonne amounts.

This could cause the neighbours to complain.

And even if the damn thing could work, you'd wind up with
this string of wire hanging in mid air, then falling back
with a certain amount of dispatch. The neighbours might be
more seriously pissed the higher the fool thing got. What
would, say, Spain have to say if a multi-thousand-km cable
were to be dropped on them at orbital speeds? I doubt it
would resemble "Ole!"
Socks

There are a couple of ways of dealing with the horizontal distance
component of the trip. Let's say the lifter craft is moving in a
straight-line, not straight-up but at some inclination, at a constant
velocity a along this straight-line. Then the speed along this
straight-line will be v=a*t and the distance along this straight-line
will be s=(1/2)*a*t^2.
Eliminate t from these two equations to get 2*a*s=v^2. If you want v to
equal orbital velocity, about 8000m/s, then a*s = 32*10^6. If you want
s , which will be the length of the cable, to be 100,000m, then a = 320
m/s^2, about 32 g's (using g as approx. 10 m/s^2). For this
acceleration you would want the payload just to be cargo. The purpose
of this is to make launches of megakilo payloads possible at low cost
remember. Electronics can easily be hardened to withstand this
acceleration. Note also the time would only be t = v/a = 8000/320 = 25
seconds.
Or you could make the distance be 5 times longer, making the cable 5
times heavier, and the acceleration would be 6.4 g's. This is probably
within the range humans can take for a few minutes:

QUESTION:
How much speed can a body's organs take in space?
"In the case of the Space Shuttle, this acceleration is around 3 times
the force of gravity - 3g - making the crew feel three times their
normal weight, but in the early days of manned space flight, the
astronauts had a rougher ride. The Mercury capsules launched by the
Atlas booster reached a peak acceleration of 8g during ascent to orbit,
then decelerated during re-entry at loads as high as 7.8g. The Titan
rockets launched the Geminis at 7.25g, and the Saturn 5 peaked at 4g.
However, the Apollo capsules returning from the Moon re-entered the
atmosphere at over 6g."
http://quest.arc.nasa.gov/saturn/qa/new/Effects_of_speed_and_acceleration_on_the_body.txt

Astronauts probably could take 15 g's acceleration for short periods:

Armstrong.
"18 June 1959 - Centrifuge program to investigate the role of a pilot
in the launch of a multi-stage vehicle.
A centrifuge program was conducted at Johnsville, Pennsylvania, to
investigate the role of a pilot in the launch of a multi-stage vehicle.
Test subjects were required to perform boost-control tasks, while being
subjected to the proper boost-control accelerations. The highest
g-force experienced was 15, and none of the test subjects felt they
reached the limit of their control capability. As a note of interest,
one of the test subjects, Neil Armstrong, was later selected for the
Gemini program in September 1962."
http://www.astronautix.com/astros/armtrong.htm

The time at this acceleration would be 8000/150 = 53.3 seconds.
The disadvantage of using such high accelerations even for cargo is
that you could lift proportionally smaller weight. That is,
accelerating at 32 g's you could lift only 1/10th the cargo as at 3.2
g's.

So another possible solution would be to allow the total cable length
to be longer but having only a smaller portion say 100 km to be in the
air, the rest lying on the ground. You could for example have a 500km
cable length laid out beforehand on the ground. The lifter would launch
with the bottom end of its tethered cable running along the portion of
the cable on the ground. Then you could have a gentler acceleration,
about the same as for a 500km long powered flight, 6.4 g's, but the
weight of the cable that had to be supported in the air would stay at
the weight of 100km of cable.
Note that during the flight and after disconnect you probably want the
cable to be supported by smaller lifter devices along its length. This
would allow it to be returned to the launch site for reuse.
Carbon fiber can support its weight up to 300 km in height. But even
if you used aluminum the weight of the cable probably would be
supported over its length by small lifter devices anyway.
Just as with shuttle launches the lifter craft launches would be
directed to not be over populated areas during the period of powered
flight.
For the power drain, a cable 600 km long would take up to 6 times as
much power. So if the drain was 5% at 100 km, it would be 30%. You
would increase the power generated to make up for this loss.


Bob Clark


Bob Clark

 

[[email protected]]

Indeed. Would be dangerous to act otherwise.

This irritates the hell out of me. How am I supposed to learn
stuff if those who have the knowledge can't make it available?
Politics have already sewn distribution of certain doors shut.
When will the intelligentsia finish with mundane things like
science and personal finances?

Imposing this kind of behaviour is extremely dangerous because
one of the things that these idiots jumped on was a memo
where he asked that people speculate about scenarios that
could happen and backup plans if they did occur.

))

I personal crank theory is that Leonardo was correct about
this sense organ and the fact that none can be found proves it.

Well, let me know what you think, when you finish.

I've already used it. I have a criticism but
I wish to wait until I finish because there had to be
a purpose the author organized it the way he did.

So far, most of what he has written, I've known instinctively
but could never describe in English ASCII. I'm blessing that
man's mother because he's done this work for me.

/BAH

Subtract a hundred and four for e-mail.

 

[George Dishman]

Eliminate t from these two equations to get 2*a*s=v^2. If you want v to
equal orbital velocity, about 8000m/s, then a*s = 32*10^6. If you want
s , which will be the length of the cable, to be 100,000m, then a = 320
m/s^2, about 32 g's (using g as approx. 10 m/s^2). For this
acceleration you would want the payload just to be cargo. The purpose
of this is to make launches of megakilo payloads possible at low cost
remember. Electronics can easily be hardened to withstand this
acceleration. Note also the time would only be t = v/a = 8000/320 = 25
seconds.
Or you could make the distance be 5 times longer, making the cable 5
times heavier, and the acceleration would be 6.4 g's. This is probably
within the range humans can take for a few minutes:

For goodness sake Bob, try to inject some
common sense into your ideas. It isn't within
the tensile strength of the cable and we have
no engine capability that could produce the
thrust needed to accelerate the payload plus
the mass of the cable at that rate no matter
how much electrical power you give it.

Humans are irrelevant, try working out the
numbers to launch Cassini using your method.

George

 

[Robert Clark]

For goodness sake Bob, try to inject some
common sense into your ideas. It isn't within
the tensile strength of the cable and we have
no engine capability that could produce the
thrust needed to accelerate the payload plus
the mass of the cable at that rate no matter
how much electrical power you give it.

Humans are irrelevant, try working out the
numbers to launch Cassini using your method.

George

????

The point of this thread is the savings in power you would get by
using a lifter thruster method.
Look at the table near the bottom on this page:

Lifter Theory.
http://jnaudin.free.fr/html/lf­theory.htm

The last line in this table labled Thrust(g)/Power(W) ratio gives the
weight that could be lifted for given power with the air density
available at ground level. It is given as 0.509, or about 2 to 1 for
power in watts required to lift a weight in grams.
This is at ground level. The thrust available becomes proportionally
less as the air density decreases so you arrange your trajectory so
that most of the powered flight occurs in the lower atmosphere. Lifter
thrust ratios at this level or better have already been demonstrated
for small test cases.
Here's a case where 185g weight of the lifter plus payload was lifted
using 200 watts of power. This is about a 1 to 1 ratio:

Saviour, the WINNER OF THE 100g of PAYLOAD CHALLENGE.
http://jlnlabs.imars.com/lifters/100gwin/index.htm

The next step is to test that this thrust ratio will hold at the
kilowatt range. Many people already own electrical generators that can
put out a few kilowatts of power. They are used for example for
generators for RV's, stand-by generators, picnic trips, etc.
This page shows such generators can be had for a few hundred dollars:

Electric Generator Store - Portable Generator, Diesel Generators ...
http://www.electricgeneratorstore.com/

For example using the 1 to 1 thruster ratio, the 3250 watt generator
advertised for $500 could lift 3.25 kilos, about 7 pounds.


Bob Clark

 

[N:dlzc D:aol T:com \(dlzc\)]

Dear Robert Clark:

....

The point of this thread is the savings in power
you would get by using a lifter thruster method.
Look at the table near the bottom on this page:

Lifter Theory.
http://jnaudin.free.fr/html/lf­theory.htm

The last line in this table labled
Thrust(g)/Power(W) ratio gives the weight that
could be lifted for given power with the air
density available at ground level. It is given as
0.509, or about 2 to 1 for power in watts
required to lift a weight in grams.

Lift that is not countered in any sense by "V^2" of drag through
the atmosphere. An atmosphere that becomes increasingly
conductive as it is heated, further reducing your thrust.

This is a waste of time and effort. Rocket engines are more
efficient than 50% at turning power into velocity, or even in
sustaining position.

David A. Smith

 

[Robert Clark]

Dear Robert Clark:

...

Lift that is not countered in any sense by "V^2" of drag through
the atmosphere. An atmosphere that becomes increasingly
conductive as it is heated, further reducing your thrust.

This is a waste of time and effort. Rocket engines are more
efficient than 50% at turning power into velocity, or even in
sustaining position.

David A. Smith

I agree the calculation does not include the effect of drag. It would
probably be analogous to the drag encountered by air-breathing methods
of space access, hypersonic craft for instance.
Rockets are efficient but you have the problem of the huge amount of
fuel mass they have to carry. At the very least lifters could provide a
low cost lower stage that could lift the craft to high altitude and to
high velocity before a final rocket stage carried the craft to orbit.
This would result in signficant levels of fuel savings.


Bob Clark

 

[N:dlzc D:aol T:com \(dlzc\)]

Dear Robert Clark:

Dear Robert Clark:

...

I agree the calculation does not include the
effect of drag. It would probably be analogous
to the drag encountered by air-breathing
methods of space access, hypersonic craft for
instance.
OK.

Rockets are efficient but you have the problem
of the huge amount of fuel mass they have to
carry. At the very least lifters could provide a
low cost lower stage that could lift the craft to
high altitude

High altitude? No, since their thrust capacity is dependent on
gas density.

and to high velocity

High velocity? No, since their ability to thrust is dependent on
the gas being non-conductive. Heating destroys that.
Additionally, their thrusting capacity is dependent on the gas
pressure being uniform over the charged surface, which is
definately not true for something moving at more than a few tens
of miles per hour.

before a final rocket stage carried the craft to
orbit. This would result in signficant levels of
fuel savings.

Only in your dreams.

David A. Smith

 

[bz]

The next step is to test that this thrust ratio will hold at the
kilowatt range. Many people already own electrical generators that can
put out a few kilowatts of power. They are used for example for
generators for RV's, stand-by generators, picnic trips, etc.
This page shows such generators can be had for a few hundred dollars:

Electric Generator Store - Portable Generator, Diesel Generators ...
http://www.electricgeneratorstore.com/

For example using the 1 to 1 thruster ratio, the 3250 watt generator
advertised for $500 could lift 3.25 kilos, about 7 pounds.

You need 30,000 VDC. That generator puts out 110 VAC.





--
bz

please pardon my infinite ignorance, the set-of-things-I-do-not-know is an
infinite set.

[email protected] remove ch100-5 to avoid spam trap

 

[N:dlzc D:aol T:com \(dlzc\)]

Dear bz:

You need 30,000 VDC. That generator puts out
110 VAC.

That is the least of his problems. AC to high-VDC conversion is
not trivial, but it can be done. Getting ~3000 watts is slightly
more difficult. Getting flexible, light, cabling that can
deliver it at great length? Priceless...

His problems start with his belief that "lift" equates to
"overcoming air friction due to velocity through the very medium
being used to produce lift".

And the USAF charged the skin of an aircraft for the purpose of
being stealthy. No improvement in flight characterisitics was
noted. So I suspect that if we aren't talking MHD, then we are
talking about repelling the lifting body with the Earth as one
"capacitive plate". Anything else is window dressing, mere
slight-of-hand to distract the unwary.

David A. Smith