Author Topic: Long cables to power plasma rockets to orbit.  (Read 42684 times)

Offline RGClark

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Long cables to power plasma rockets to orbit.
« on: 01/12/2008 03:05 pm »
Magnetoplasmadynamic thrusters have the advantage that they can be
scaled up to produce large amounts of thrust, while still maintaining
the high ISP of ion drives:

Magnetoplasmadynamic Thrusters.
"Testing for these thrusters has demonstrated exhaust velocities of
100,000 meters per second (over 200,000 mph) and thrust levels of 100
Newtons (22.5 pounds) at power levels of 1 megawatt. For perspective,
this exhaust velocity will allow a spacecraft to travel roughly 11
times the top speed of the space shuttle (18,000 mph)."
http://www.nasa.gov/centers/glenn/about/fs22grc.html

MY ELECTRIC ROCKET ENGINE.
http://www.waynesthisandthat.com/mpd.htm

 The problem is the high amount of power required. However high
electrical power has been delivered up to hundreds of kilometers on
Earth over power lines. Then this could be used to deliver the
required electrical power to the thrusters from the ground.

  Bob Clark

c.f.,
Newsgroups: sci.astro, sci.space.policy, sci.physics
From: "Robert Clark"
Date: 20 Mar 2006 20:23:18 -0800
Local: Mon, Mar 20 2006 11:23 pm
Subject: Long cables to power arcjet rockets to orbit?
http://groups.google.com/group/sci.physics/msg/0cd3fba4a33a6d13
Single-stage-to-orbit was already shown possible 50 years ago with the Titan II first stage.
In fact, contrary to popular belief, SSTO's are actually easy. Just use the most efficient engines and stages at the same time, and the result will automatically be SSTO.
Blog: exoscientist.blogspot.com

Offline Jim

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RE: Long cables to power plasma rockets to orbit.
« Reply #1 on: 01/12/2008 03:46 pm »
Quote
RGClark - 12/1/2008  11:05 AM

 The problem is the high amount of power required. However high
electrical power has been delivered up to hundreds of kilometers on
Earth over power lines. Then this could be used to deliver the
required electrical power to the thrusters from the ground.


Engineering in terrestrial power lines have no applicability in this application.  They are static and under constant tension.

This concept has many holes in it, that may be too big to be plugged

Offline khallow

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Re: Long cables to power plasma rockets to orbit.
« Reply #2 on: 01/12/2008 05:12 pm »
Terrestrial power lines also have considerable weight. You'd need something light weight and able to unreel at supersonic speeds. Maybe leave twin trails of somewhat conductive ionized air though I don't know how you'd keep those seperated (remember, crossing the streams is bad). I'm fond of beamed microwave power. You don't need to complete an electric circuit to make that work.
Karl Hallowell

Offline Jim

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RE: Long cables to power plasma rockets to orbit.
« Reply #3 on: 01/12/2008 08:46 pm »
Quote
RGClark - 12/1/2008  4:28 PM
 You could have a cable lying on the
ground and a short length of cable extending from the craft to the
cable on the ground, say 10 to 100 meters long. Keep in mind, just as
for the magnetic launch proposal, the main thing is getting that
horizontal velocity component required for orbit. To get to the
altitude for LEO is just a small proportion of extra velocity and
energy of that required for orbital velocity.

Still not viable.   Aero heating loads would be higher than for a reentry vehicle

Offline kkattula2

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Re: Long cables to power plasma rockets to orbit.
« Reply #4 on: 01/15/2008 02:30 am »
I've thought for a while that you could power launch vehicles electrically from the ground, for short distances at least, maybe 20 to 30 km. Balloons have been tethered at these altitudes. A balloon or blimp could be used to support the weight of the cable, and keep it away from the exhaust.

The LV could use electrical power to run high pressure pumps for conventional engines, or (more mass effectively) run ducted electrical lift fans until at sufficient altitude for high expansion ratio, lower pressure engines. An SSTO RLV could use the same fans in auto rotation mode to slow a descent, and even charge up an on-board battery for a few seconds of powered flight at touch down.

Offline tnphysics

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Re: Long cables to power plasma rockets to orbit.
« Reply #5 on: 01/15/2008 02:59 am »
Use Al cables. Cu has lower resistance but is much heavier.

Offline Lampyridae

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Re: Long cables to power plasma rockets to orbit.
« Reply #6 on: 01/15/2008 03:02 am »
A laser launch system would be a much more direct way of going about beamed power propulsion.

Some kind of pellet / particle launcher firing into a bucket/thrust chamber underneath the LV would offer the highest energy efficiency overall.

Offline khallow

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Re: Long cables to power plasma rockets to orbit.
« Reply #7 on: 01/15/2008 06:24 am »
As I see it, under normal rocket-like acceleration, the vehicle will go supersonic (in atmosphere, of course) shortly into the flight. I see no way to keep cables attached to the vehicle under those circumstances or keep the cables intact even if the connections were somehow unbreakable. Even if the cables were unbreakable and zero mass, we still have the matter of the drag from air resistance. And even if we ignore that, we still have the matter of how much power these cables are supposed to be carrying. For example, if somehow you could attack 500kV lines to a rocket, that would still need 8 amps of current to generate the equivalent power of an Atlas V first stage (which happens to be around 4 million newtons). This bothers me since we're speaking of  8 amps through a very long line which handles extraordinary aerodynamical stresses (and its own weight) and somehow won't arc under the voltages we're going to need.
Karl Hallowell

Offline A_M_Swallow

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Re: Long cables to power plasma rockets to orbit.
« Reply #8 on: 01/16/2008 12:58 am »
Would it be simpler just to fire several mega-watts of laser power at a solar thermal rocket?
ISP 900 s
Lasers are reusable and their weight does not form part of the mass.

http://en.wikipedia.org/wiki/Solar_thermal_rocket

Offline Lampyridae

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Re: Long cables to power plasma rockets to orbit.
« Reply #9 on: 01/16/2008 02:04 am »
Various types of laser propulsion:

http://en.wikipedia.org/wiki/Laser_propulsion

Offline TyMoore

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Re: Long cables to power plasma rockets to orbit.
« Reply #10 on: 01/16/2008 01:05 pm »

khallow wrote: "...For example, if somehow you could attack 500kV lines to a rocket, that would still need 8 amps of current to generate the equivalent power of an Atlas V first stage (which happens to be around 4 million newtons)...'

 

You are mixing your units here. Dimensions for Power is defined to be energy per unit time--the rate at which work is done, and energy can be thought of in terms of a force acting through a displacement. Newtons have dimensions of Force...

 

From:

http://www.astronautix.com/engines/rd180.htm

 

An Atlas V, using an RD-180 rocket engine generates a sea level thrust of about:

4,152 kN (933,333 lbf) with a sea-level Isp=338 sec which corresponds to a sea-level exhaust velocity of about: 338 s * 9.80665 m/s^2 = 3315 m/s.

 

We can estimate the mechanical power of the 'exhaust jet' by finding the kinetic power of the mass throughput of the RD-180:

The kinetic energy of a freely moving mass can be found from:

 

K=1/2*m*v^2, and differentiating with respect to time holding v constant gives:

P=1/2*mdot*v^2 where P is the kinetic power of a mass stream, and mdot is the mass flow rate.

The propellant consumption rate for an RD-180 can be estimated from dividing the thrust in newtons with the exhaust speed in meters per second:

mdot = 4.152 x 10^6 N / (3315 m/s) 

        = 1253 kg/s

Thus the kinetic power of the exhaust gasses exiting the engine at sea-level is about:

P=1/2*1253 kg/s * (3315 m/s)^2

 = 6890 MW.

Assuming of course that the energy conversion from electrical supply to delivered thrust is 100%, and you have a light-weight, beefy 500KV line supplying power, the current must be atleast:

I=P/V

I=6890 MW / 500 KV

 = 13800 Amps.

So it would seem that either a bundle of such cables must be present, or the voltage must be higher, or maybe a superconductor would have to be used...

Either way, I would imagine that the utilities would find delivering nearly 7GW to a single customer challenging, let alone delivering it to something as small as an Atlas V--let alone have that Atlas V actually flying at the same time! 


Offline A_M_Swallow

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Re: Long cables to power plasma rockets to orbit.
« Reply #11 on: 01/16/2008 04:37 pm »
Quote
TyMoore - 16/1/2008  2:05 PM
Either way, I would imagine that the utilities would find delivering nearly 7GW to a single customer challenging, let alone delivering it to something as small as an Atlas V--let alone have that Atlas V actually flying at the same time!

The utilities would find it even more challenging supplying the power to a descending lander on the moon or Mars.  A laser beam can be considered a "wire" with zero mass and no air resistance.

On the moon a reusable lander's propellant could be ISRU liquid oxygen and a Mars lander say liquid CO2.

One reason for investigating this is the saving in fuel weight.  A round trip moon surface to EML2 (delta_v 2.52 * 2) takes 2.58 times as much propellant at ISP 338 than ISP 900.  A mass saving of many tons.

Getting the generator and laser to the planet can be performed using conventional rockets and can be reused for several landings.

Offline TyMoore

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Re: Long cables to power plasma rockets to orbit.
« Reply #12 on: 01/17/2008 12:40 am »
All is not just Isp--there is thrust to weight to consider. Very high Isp with very low thrust is useless as a launch vehicle--just tip a flashlight on its end, turn it on, and wait for it to fly up in the air!

High exhaust velocity is important, but the thrust generated must also be considered.

Offline kkattula2

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Re: Long cables to power plasma rockets to orbit.
« Reply #13 on: 01/17/2008 02:56 am »
Supersonic speed is NOT required to reach high altitude if power is coming from the ground. Even 50 m/s is plenty.  Thrust to weight ratio only needs to be slightly over one.

Power for ducted electrical fans is going to be a LOT less. They would be moving a large mass of air at low velocity, not a small mass of propellant at high velocity. Assumming a duct exhaust speed of 250 m/s, power is about 500 MW for RD-180 equivalent thrust. My BOTE says that would require four 5m diameter ducted fans.

Offline Lampyridae

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Re: Long cables to power plasma rockets to orbit.
« Reply #14 on: 01/17/2008 03:39 am »
http://en.wikipedia.org/wiki/Laser_propulsion

http://www.mypq.net/tools/voltagedrop.asp

http://mc-group.ca/download.htm

A cable is about the worst way to transmit power over great distances. I presume the thrust to lift the cable is coming from the propulsion system? OK, let's have a look at the numbers.

Let's look at the case for 1GW of electricity available.

For 1MV (and believe me that's frighteningly high), you need a copper cable approximately 1 inch in diameter carrying 1000 Amps. Actually, you need two: so that's about 1.4 square inches of copper cable. That's about 4cm2 for one cable or 8cm2 for two. Multiply that by the length of cable and the density of copper. Let's be generous and assume aluminium (magically imbued with the conductivity of copper): 2.7gm/cm3. That's 2.7x4 = 10.8g/cm or 1.08kg per metre, 2.16 for two cables. Multiply by one kilometre: 2.16 tonnes, excluding insulation and cable armouring. Can you accelerate your plasma rocket to orbital velocity in one kilometre? Unlikely. Call it ten kilometres - ignoring sonic booms and the fact that your cables are sheathed with high temperature plasma, both from your exhaust and atmospheric friction.

So, let's assume you have a lightweight vehicle: with payload and engine it comes to 30 tonnes. If launched roughly horizontally (it isn't), it has to attain about 8000 m/s, ignoring drag losses. 1GW of power is available, and you quite an eV of 100 000m/s. Assuming 100% efficiency this translates to 10 000N of thrust, or enough to launch an average human male upwards at 9g; far short of the acceleration you require.

By reducing the eV to the final velocity, you achieve a much more workable solution: final mass is about 1/3 the initial mass. But you have a problem because this now requires 90 tonnes to be launched. So be it.

Let's calculate the power required to achieve orbital velocity (OV) over your 10km run. To reach 8kps in 10km requires you to accelerate.

v2 = u2 + 2as
v2/2a = s = 10 000
64 000 000 /2a = 10 000
6 400 = a
or, approximately 640 gravities.
6 400 x 30 000 = 192 MN

Out of the available 1GW, that requires an Isp of about 8m/s, comfortably worse than a bottle rocket, which would probably require the mass of a small planet to get into orbit in a single stage. Hrmmm. This is a bit of a mess.

Offline Lampyridae

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Re: Long cables to power plasma rockets to orbit.
« Reply #15 on: 01/17/2008 03:55 am »
So, let's make the cables stationary somehow, hanging from an aerostat or ducted fans or whatever. Now we only need 6.4MN of thrust (our payload, rocket and fuel is only 1 tonne for ease of calculation). How much power must go through those cables? Answer: lots. We match our exhaust velocity (eV) to our orbital velocity; let's call it 10kps eV to keep it simple. Increasing eV beyond your mission deltaV is a bit pointless.

So:

6.4MN x 10 000 = 64 GW.

About the power requirements of a small country. Still, now it's doable.



Offline khallow

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Re: Long cables to power plasma rockets to orbit.
« Reply #16 on: 01/17/2008 08:06 am »
Quote
Lampyridae - 16/1/2008  8:55 PM

So, let's make the cables stationary somehow, hanging from an aerostat or ducted fans or whatever. Now we only need 6.4MN of thrust (our payload, rocket and fuel is only 1 tonne for ease of calculation). How much power must go through those cables? Answer: lots. We match our exhaust velocity (eV) to our orbital velocity; let's call it 10kps eV to keep it simple. Increasing eV beyond your mission deltaV is a bit pointless.

So:

6.4MN x 10 000 = 64 GW.

About the power requirements of a small country. Still, now it's doable.

I still don't see why we're doing this when we can just beam power with less losses and breakable infrastructure. Hmmm, I suppose though that some of the schemes for powering climbers on a space elevator use something similar.
Karl Hallowell

Offline A_M_Swallow

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Re: Long cables to power plasma rockets to orbit.
« Reply #17 on: 01/17/2008 06:50 pm »
State of the art on mobile lasers.
http://news.bbc.co.uk/1/hi/sci/tech/6380789.stm

To transmit a mega-watt 1 MW / 67 kW = 14.9 lasers are needed.  Surround the launch pad with 16 lasers and you have a spare.  If the rocket has a 10 metre diameter the lasers would need a tracking accuracy of about 5 metes at 100 km.

A 1 GW would require lasers that are 1000 times as powerful.


Redoing the above calculations for 100 km
To reach 8kps in 100km requires you to accelerate.

v2 = u2 + 2as
v2/2a = s = 100 000 m
64 000 000 /2a = 100 000
320 = a
or, approximately 33 gravities.
320 m/s/s x 30 000 kg = 9.6 MN

33 g can be used for cargo but I suspect that human launches would need 1,000 km, possibly in several boost sessions.

Offline khallow

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Re: Long cables to power plasma rockets to orbit.
« Reply #18 on: 01/17/2008 07:15 pm »
Quote
RGClark - 17/1/2008  1:40 AM

Khallow, we don't have lasers at multi megawatt to gigawatt power currently. Also to focus the lasers at hundred kilometer distances would require unacceptably large mirrors.

It's still a far more feasible problem than what has been presented here. Also, I'm a bit puzzled. It should be pretty easy to illuminate, for example, a 10 meter target at 100 km with any visible light laser system. Running some numbers, I see that a perfect laser system would need to have an apperature of at least 6mm (by calculating the Rayleigh diffraction limit). Real systems are somewhat worse with spread problems, but it still strikes me that you have a pretty easy problem here with respect to illuminating a large target. Even if you shrink the target size considerably to 0.1 m, that's still a minimum apperture of 0.6 m.

Beam power is a more significant problem since I gather continuous lasers still haven't broken 100 kW. But I don't see the need for a single laser of the desired power level. It should be reasonable for multiple systems to illuminate the same target. So here the goal for any beamed power system would probably be a certain number of $/watt infrastructure costs. I will wildly guess for a high launch system in the gigawatt range, that $1 per watt is probably the necessary target and I have the  impression that we're at least three orders of magnitude off from achieving that with lasers.
Karl Hallowell

Offline TyMoore

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Re: Long cables to power plasma rockets to orbit.
« Reply #19 on: 01/18/2008 01:17 am »
Gas dynamic lasers use a heated mixture of carbon dioxide or carbon monoxide gas and helium, with just a smidgeon of neon, and run through a special deLevaal nozzle to produce an expansion shock which results in a population inversion and stimulated emission of radiation--mostly in infra-red. This has been tested at multi hundred kilowatts power level.

http://en.wikipedia.org/wiki/Gas_dynamic_laser

What is so interesting about this is this:

imagine scaling this up so that instead of 100 KW we can achieve 1 GW beam power.

The efficiency is probably in the neighborhood of 20-30% which is phenominal for lasers.

For a 1 GW beam laser system we would need just about 4 or 5 GW of thermal power: imagine a nuclear plant: four high pressure, gas cooled pebble bed reactors each operating at 1250 MWt power, using a Brayton Cycle gas turbine system: probably composed of about 4 Gas turbine systems operating in parallel for each reactor, 16 in total for the beam station. Each Brayton gas turbine compressor loop will serve a single optical amplifier, so 16 operating in parallel will give just about 62.5 MW each, which is comparable to the power processed by each engine of a Boeing 747 at takeoff.

This would be a very big laser station--and for a manned launch you would probably need atleast two more stations downrange to keep the accelerations to manageable levels.

Offline Lampyridae

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Re: Long cables to power plasma rockets to orbit.
« Reply #20 on: 01/18/2008 02:56 am »
You could probably use some kind of rocket engine or gas turbine burning charcoal dust with LOX to get the required power levels, and be a lot cheaper than building a few dedicated nuke plants! The article I read spoke about using fibre lasers since they're cheap, modular and therefore "stackable" to high power levels, but their prices are something like $20 a watt.

Lasers are probably better off as a second stage solution, or a second propulsion system once the main lifting work has been done by, say, a Kero/LOX engine.

Offline Lampyridae

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Re: Long cables to power plasma rockets to orbit.
« Reply #21 on: 01/18/2008 06:00 am »
Quote
RGClark - 17/1/2008  6:37 PM

Quote
Lampyridae - 16/1/2008  11:55 PM

So, let's make the cables stationary somehow, hanging from an aerostat or ducted fans or whatever. Now we only need 6.4MN of thrust (our payload, rocket and fuel is only 1 tonne for ease of calculation). How much power must go through those cables? Answer: lots. We match our exhaust velocity (eV) to our orbital velocity; let's call it 10kps eV to keep it simple. Increasing eV beyond your mission deltaV is a bit pointless.

So:

6.4MN x 10 000 = 64 GW.

About the power requirements of a small country. Still, now it's doable.



 You wouldn't have to be restricted to a distance over which you are accelerating of 10 km, necessitating that large acceleration of 640 g's. Overhead electric power lines a few centimeters wide routinely run over hundred kilometer distances. If you allowed the distance to be a few hundred kilometers, then the acceleration could be in the 10 g's range. This would also mean you could transport larger mass for the same power.
 Then for a 1000 kg total mass, the thrust would only have to be 100,000 N.

I felt this wasn't worth pointing out, but here goes anyway:

The sonic boom would blow roofs off houses for several kilometres around the launch track. It would have to suspended high up in the atmosphere. Not to mention what a *slight* wobble in the cable would do to a launch vehicle travelling at near orbital velocities. Basically, you run into the same problems as a mass driver just with even more complications.

Quote
BTW, the MPD thrusters I've seen always give these high exhaust velocities of 60,000 to 100,000 m/s, desirable for planned uses of carrying several tons on manned planetary missions.
 However, power scales as the square of the exhaust velocity. I don't know if they've been tested or it they can work at low exhaust velocities. This would require much larger fuel loads at low exhaust speeds, if you were carrying fuel. However, would they work with just the surrounding air? Then you could use low exhaust speed to minimize power and get high thrust by having large volume of air being accelerated.


   Bob Clark

What kind of thrust-to-weight ratio are you expecting from MPDs? The best that can be currently expected is something like 200N, and that from a device which probably weighs a couple of tonnes. Even VASIMIR can't crank out that kind of performance.

At GW power levels, you'll need huge magnets to contain plasma, and lots of structural material to brace them. Without miracle materials, there's just no way around that. There's also the slight problem of your gigawatt plasma plume causing massive short circuits behind you in the power lines. Or vapourising them.

Cable power is a nice idea, but what I'm trying to tell you is that materials and the real-world problems around it are very very very very very difficult. In fact, laser propulsion which is a lot more feasible is still difficult and currently will be extremely expensive to do. Beamed power propulsion is just a lot more plausible, look at what everybody else is offering. Anyway, even though cable power doesn't really work, you can still mine the fallout of your research efforts for ideas in other applications.

Offline khallow

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Re: Long cables to power plasma rockets to orbit.
« Reply #22 on: 01/18/2008 04:00 pm »
We need to keep in mind that incredible acceleration rates in the lower atmosphere are a really bad idea. Not just because of the sonic boom mentioned by Lampyridae nor just because of aero heating loads as jim mentioned, but because things come off when you fly at high supersonic speeds in dense atmosphere. Important things. Fins, engines, upper stages.

You really need to design this so that the big accelerations aren't in atmosphere. It's not that bad, given that we're looking at lengths up to 240 km already. Just don't start serious acceleration until 30 or so km into the flight.
Karl Hallowell

Online edkyle99

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RE: Long cables to power plasma rockets to orbit.
« Reply #23 on: 01/18/2008 04:34 pm »
Cable-wise, this might be of interest - a three mile-long Kevlar cable used at White Sands.  

http://www.wsmr.army.mil/pao/whatsUp/wu1.htm

Now, could similar lightweight materials be impregnated with a conductive substance to carry power?  Others have considered this idea, apparently.

http://www.patentstorm.us/patents/7049522-claims.html

 - Ed Kyle

Offline A_M_Swallow

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Re: Long cables to power plasma rockets to orbit.
« Reply #24 on: 01/18/2008 06:51 pm »
Quote
RGClark - 18/1/2008  6:04 PM

Magnetoplasmadynamic Thrusters.
"Testing for these thrusters has demonstrated exhaust velocities of
100,000 meters per second (over 200,000 mph) and thrust levels of 100
Newtons (22.5 pounds) at power levels of 1 megawatt.

{snip}
 I estimate the weight of these thrusters as less than 100 kg. You can get the engine thrust-to-weight ratio be high by giving the same thruster more power.
On the Earth

The other thing to remember is F = m a or m = F/a
On launch acceleration a has to be greater than gravity

mass m = 100 N / 9.81 m/s/s = 10.19 kg

The thruster would need 10 times as much thrust just to lift itself.
Magnetoplasmadynamic thrusters are useful once you are in orbit but not before.


On the Moon

Lunar gravity is 1.622 m/s/s
m = 100 / 1.622 = 61.7 kg
or m = 200 /1.622 = 123 kg

Double the thrust per kg and it may be possible to launch from the moon, possibly with booster rockets.

Offline khallow

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Re: Long cables to power plasma rockets to orbit.
« Reply #25 on: 01/20/2008 04:05 pm »
Quote
RGClark - 18/1/2008  1:19 PM


 Then a large helium balloon could keep the longer cable aloft if the
cable were say 1 mm wide. But you might need a cable 1 cm wide or
larger to carry sufficient current to power the craft. Possibly
several helium balloons along its length would work to keep it aloft
in this case.

As I understand it, balloons are only good to around 60 km (and it's very hard to get past 30 km). You would need something like the plasma thrusters you mention to maintain the cables past that point.
Karl Hallowell

Offline Lampyridae

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Re: Long cables to power plasma rockets to orbit.
« Reply #26 on: 01/21/2008 01:42 am »
Quote
RGClark - 21/1/2008  1:05 AM

It is known that if subjects are immersed in water they can survive higher accelerations. On this page at the bottom is given a table of durations for accelerations while water immersed:

Adventuring hazards.
http://hiddenway.tripod.com/hero/hazards.html

 At 28 g's it's given as .5 min, 30 seconds. At this acceleration you could achieve 280*30 =8,400 m/s in 30 seconds. The distance it would take to get to 8,000 m/s would be 8,000^2/(2*280) = 114,285 m =114 km.

28g for 30 seconds is a bit optimistic in my book. For a start, the astronaut would be blind for days because the blood vessels in his eyes would burst. Lung tissue is also particularly vulnerable and the aorta is apt to simply tear off because it is in an air-filled space. Rats have survived 1800G but they suffered permanent damage. Experiments have been done with dogs breathing liquid fluorcarbons but I don't know the results of these.

http://www.projectrho.com/rocket/rocket3b.html

http://ntrs.nasa.gov/search.jsp?R=724043&id=7&qs=Ns%3DHarvestDate%257C0%26N%3D4294922851

http://ntrs.nasa.gov/search.jsp?R=228741&id=6&qs=Ntt%3Dacceleration%252Bimmersion%26Ntk%3Dall%26Ntx%3Dmode%2520matchall%26N%3D0%26Ns%3DHarvestDate%257c1

http://ntrs.nasa.gov/search.jsp?R=837659&id=10&qs=Ntt%3Dacceleration%252Bimmersion%26Ntk%3Dall%26Ntx%3Dmode%2520matchall%26N%3D0%26Ns%3DHarvestDate%257c1

Offline Jim

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RE: Long cables to power plasma rockets to orbit.
« Reply #27 on: 02/03/2008 03:38 pm »
Quote
RGClark - 3/2/2008  11:20 AM

While doing a web search I found a report on creating inflatable vacuum chambers, where the walls are filled with pressurized gas for strength. Such chambers could even be buoyant if the walls were filled with a lighter than air gas such as helium.
This then could be used to extend a vacuum travel path from the ground all the way to high altitude for orbital rocket launch.

Stability Analysis of an Inflatable Vacuum Chamber.
http://arxiv.org/abs/physics/0610222v4


Bob Clark

What won't work on USENET won't work on this forum, physical laws are the same across the internet. There is no way to keep a vacuum in an open vessel.  The walls would need to be too high, which would be impractical. Also an orbital rocket doesn't fly straight up.

Offline colbourne

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RE: Long cables to power plasma rockets to orbit.
« Reply #28 on: 02/04/2008 04:32 am »
You could have the  top sealed with a thin film that could be punctured by the rocket/ or by other means as the rocket reached that point.

Offline khallow

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Re: Long cables to power plasma rockets to orbit.
« Reply #29 on: 02/04/2008 08:31 am »
Or you could use a better way of delivering power to the launch vehicle that doesnt't require a physical connection to the vehicle.

What are the advantages supposed to be? I really don't understand why people are considering this. At least with things like beamed power or a space elevator, it doesn't take that much extension of current technology and materials to make the idea possible. But we have no idea how to make cables that can withstand for long enough the turbulence of an atmospheric launch, the force from the exhaust of the rocket in vacuum, electromagnetic forces interacting on the cables from each other, and even tidal forces from nearby moons and planets. Even if you get around the stability problem, you still are limited by both how much power the cable can carry since you have to worry about heating and arcing. And we ignore how you can get an electrical connection when you're moving at several kilometers per second.

I have to side with Jim here. The physics doesn't appear to support this sort of thing. Nor does it seem to have a notable advantage over other methods of accelerating in space or atmosphere.
Karl Hallowell

Offline kevin-rf

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RE: Long cables to power plasma rockets to orbit.
« Reply #30 on: 02/04/2008 01:54 pm »
Quote
RGClark - 3/2/2008  11:20 AM

While doing a web search I found a report on creating inflatable vacuum chambers, where the walls are filled with pressurized gas for strength. Such chambers could even be buoyant if the walls were filled with a lighter than air gas such as helium.
This then could be used to extend a vacuum travel path from the ground all the way to high altitude for orbital rocket launch.

Stability Analysis of an Inflatable Vacuum Chamber.
http://arxiv.org/abs/physics/0610222v4


Bob Clark

For the chamber to be lighter than air the enclosed volume of vacuum just has to be large enough to offset weight of the Inflatable Chamber. You do not need helium, air will do. In english the mass of the volume enclosed has to be less than the mass of an equiv. volume of air. Google archimedes, just don't share the pic's of you running through the street when done ;)

It has always been a dream (pipe dream) to make a lighter than air vacuum chamber. Thanks for an idea that may work. Now I can tell the voices in my head I am not all that crazy :laugh:
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Offline sandrot

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Re: Long cables to power plasma rockets to orbit.
« Reply #31 on: 02/04/2008 02:23 pm »
Quote
khallow - 4/2/2008  4:31 AM

Or you could use a better way of delivering power to the launch vehicle that doesnt't require a physical connection to the vehicle.

What are the advantages supposed to be? I really don't understand why people are considering this. At least with things like beamed power or a space elevator, it doesn't take that much extension of current technology and materials to make the idea possible. But we have no idea how to make cables that can withstand for long enough the turbulence of an atmospheric launch, the force from the exhaust of the rocket in vacuum, electromagnetic forces interacting on the cables from each other, and even tidal forces from nearby moons and planets. Even if you get around the stability problem, you still are limited by both how much power the cable can carry since you have to worry about heating and arcing. And we ignore how you can get an electrical connection when you're moving at several kilometers per second.

I have to side with Jim here. The physics doesn't appear to support this sort of thing. Nor does it seem to have a notable advantage over other methods of accelerating in space or atmosphere.

Here at work we just installed cables for a 3 phase 300 kw motor. For 10 m of cables we had to use the crane. Long cables to power plasma rockets to orbit are unfeasible on several counts (weight, and the impossibility to reel/unreel them to say some).

A Mars mission vehicle powered by VASIMR would require 10 MW.

http://spaceflight.nasa.gov/shuttle/support/researching/aspl/vasimr.html

Do the math...
"Paper planes do fly much better than paper spacecrafts."

Offline khallow

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RE: Long cables to power plasma rockets to orbit.
« Reply #32 on: 02/04/2008 04:27 pm »
Quote
kevin-rf - 4/2/2008  6:54 AM

Quote
RGClark - 3/2/2008  11:20 AM

While doing a web search I found a report on creating inflatable vacuum chambers, where the walls are filled with pressurized gas for strength. Such chambers could even be buoyant if the walls were filled with a lighter than air gas such as helium.
This then could be used to extend a vacuum travel path from the ground all the way to high altitude for orbital rocket launch.

Stability Analysis of an Inflatable Vacuum Chamber.
http://arxiv.org/abs/physics/0610222v4


Bob Clark

For the chamber to be lighter than air the enclosed volume of vacuum just has to be large enough to offset weight of the Inflatable Chamber. You do not need helium, air will do. In english the mass of the volume enclosed has to be less than the mass of an equiv. volume of air. Google archimedes, just don't share the pic's of you running through the street when done ;)

It has always been a dream (pipe dream) to make a lighter than air vacuum chamber. Thanks for an idea that may work. Now I can tell the voices in my head I am not all that crazy :laugh:

One thing to keep in mind is that vacuum chambers don't have a large advantage over helium or hydrogen filled balloons. You'll only get a little more lift. Let's consider an example. Suppose we have a balloon filled with 4 grams of helium (that's roughly a mole of helium and that the balloon is zero pressure and noninsulating. Then the helium is at the same pressure and temperature as the outside atmosphere and automatically displaces a mole (roughly 29 grams) of atmosphere. You get lift from the 25 grams of atmosphere that are displaced. In comparison, a vacuum of the same volume would displace at most 29 grams (in the case of a perfect vacuum with zero mass walls). So you can get at best a 16% greater lift from a vacuum chamber balloon than you can from a helium filled balloon. The difference between hydrogen and vacuum is even weaker at less than 8% greater lift from the vacuum.

Now add in the additional structure you need to maintain the vacuum. In comparison, for a helium or hydrogen filled balloon, you can get away with a pretty thin plastic or latex layer. Plus the latter balloons can scale to different heights better. Glancing through the paper, it confirms that you need mostly rigid walls (some elasticity can be managed). That means your chamber with a fixed level of vacuum generates different lift at different altitudes. It can be managed (say either by carrying ballast or adjusting the quality of the vacuum) to give you more constant lift, but the standard latex weather balloon gives you virtually constant lift over most of its range (up to the last part where the latex stops stretching). If latex could somehow stretch indefinitely (even at the frigid conditions of the atmosphere at this point),one could easily send standard helium weather balloons all the way up to the top of the buoyant portion of Earth's atmosphere (as I understand it somewhere in the mesosphere, 50km to 80-90 km).
Karl Hallowell

Offline Jim

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Re: Long cables to power plasma rockets to orbit.
« Reply #33 on: 02/04/2008 08:12 pm »
Quote
RGClark - 4/2/2008  3:41 PM
 Keep in mind that the hundred kilometer long fixed electrical cable carrying hundreds of megawatts is something that already exists now and has existed for decades.
 

Not the same thing.  You can't use that as a valid comparison.  

This concept is not based on reality.  It will never be doable

1.  They are fixed
2.  The cable isn't moving 1000's of mph
3 The towers are non aerospace designs, over built
4.  the vehicle still would have to lift full weight of the cable, regardless of "ballon"

Offline Jim

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Re: Long cables to power plasma rockets to orbit.
« Reply #34 on: 02/04/2008 08:44 pm »
Quote
RGClark - 4/2/2008  4:20 PM

 Fundamental to the proposal is that the hundred kilometer long power cable is not being carried by the rocket. It is fixed in position supported at altitude by either balloons or its own thrusters.
 The rocket only has to carry a short conducting tether perhaps a few hundred meters long  to transmit the electrical power from the power line to the rocket.


    Bob Clark

3 things still undoable

1.  the interface between the tether and the cable.  Won't be able to maintain it at 1000's of mph due forces and heat

2.  suspending the cable above 30km.  not with thrusters, they need propellant mass.  How are they going to be refueled?

3.  LV's move a lot more than a few hundred meters from the planned trajectory

this cable is going to strung out for 1000's of miles from the launch site?  Going straight up won't work, the vehicle has to be going horizontal at orbital insertion

Offline Lampyridae

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Re: Long cables to power plasma rockets to orbit.
« Reply #35 on: 02/05/2008 04:24 am »
Quote
Jim - 5/2/2008  6:44 AM
3 things still undoable

1.  the interface between the tether and the cable.  Won't be able to maintain it at 1000's of mph due forces and heat

2.  suspending the cable above 30km.  not with thrusters, they need propellant mass.  How are they going to be refueled?

3.  LV's move a lot more than a few hundred meters from the planned trajectory

this cable is going to strung out for 1000's of miles from the launch site?  Going straight up won't work, the vehicle has to be going horizontal at orbital insertion

1. Plasma armatures work well enough for railgun projectiles, basically just arcing across the gap.

2. and 3. You could solve this by hanging the launch cables from a space elevator. Hey, I never said this would be practical or feasible! LOL

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Re: Long cables to power plasma rockets to orbit.
« Reply #36 on: 02/05/2008 04:37 am »
Quote
Lampyridae - 5/2/2008  12:24 AM

1. Plasma armatures work well enough for railgun projectiles, basically just arcing across the gap.


There still is something that holds it in place

Offline pippin

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Re: Long cables to power plasma rockets to orbit.
« Reply #37 on: 02/05/2008 08:34 am »
Quote
Lampyridae - 5/2/2008  6:24 AM

Quote
Jim - 5/2/2008  6:44 AM
this cable is going to strung out for 1000's of miles from the launch site?  Going straight up won't work, the vehicle has to be going horizontal at orbital insertion
If I got my gravity right, it will be almost vertical at the top end because it's hanging through... Doesn't fit well
Quote
1. Plasma armatures work well enough for railgun projectiles, basically just arcing across the gap.
They don't transfer electrical power to the projectile through arcs, the just induce a current within the projectile. Arcs are accidental and cause losses. You could theoretically do inductive coupling for  power transfer to your cable and you could even use inductive repelling force to keep your power line away from the collector ("pantograph") but to get the power up there then you would need a closed loop, high frequency AC power transmission with what probably has to be a superconducting cable.
Hmmm... Quite a bit of onobtainium in use here.

Offline Lampyridae

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Re: Long cables to power plasma rockets to orbit.
« Reply #38 on: 02/05/2008 11:24 pm »
Quote
pippin - 5/2/2008  6:34 PM

Quote
Lampyridae - 5/2/2008  6:24 AM

Quote
Jim - 5/2/2008  6:44 AM
this cable is going to strung out for 1000's of miles from the launch site?  Going straight up won't work, the vehicle has to be going horizontal at orbital insertion
If I got my gravity right, it will be almost vertical at the top end because it's hanging through... Doesn't fit well
[/QUOTE][/QUOTE]

It might do if the projectile was launched at escape or near-escape velocities. Or maybe straight up into geosynch... although that notion vaguely offends me.

Quote
Quote
1. Plasma armatures work well enough for railgun projectiles, basically just arcing across the gap.
They don't transfer electrical power to the projectile through arcs, the just induce a current within the projectile. Arcs are accidental and cause losses. You could theoretically do inductive coupling for  power transfer to your cable and you could even use inductive repelling force to keep your power line away from the collector ("pantograph") but to get the power up there then you would need a closed loop, high frequency AC power transmission with what probably has to be a superconducting cable.
Hmmm... Quite a bit of onobtainium in use here.

What I've been alluding to is that building a gigantic railgun is much easier than the mental contortions of this idea!

Regarding atmospheric drag, the Russians have done research into using plasma as a sort of anti-heating buffer, sonic boom suppressor and drag inhibitor. The theory seems to work for small vehicles (maybe 3m diameter). Maybe a railgun with an evacuated tunnel up the side of a mountain, as per usual, firing these packages up to orbital velocity and then they bore through the atmosphere with their low-drag devices.

Offline Lampyridae

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Re: Long cables to power plasma rockets to orbit.
« Reply #39 on: 02/05/2008 11:27 pm »
Quote
Jim - 5/2/2008  2:37 PM

Quote
Lampyridae - 5/2/2008  12:24 AM

1. Plasma armatures work well enough for railgun projectiles, basically just arcing across the gap.


There still is something that holds it in place

...from a Mach 25 sonic boom... plus plasma exhaust with heating power of a gigawatt or so... cables held up with balloons in the mesosphere... this is such fun.  :laugh:

Offline pippin

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Re: Long cables to power plasma rockets to orbit.
« Reply #40 on: 02/08/2008 01:22 pm »
Quote
Lampyridae - 6/2/2008  1:24 AM
It might do if the projectile was launched at escape or near-escape velocities. Or maybe straight up into geosynch... although that notion vaguely offends me.

With good reason: it's wrong. Going straight up into GSO wouldn't work since you don't have the necessary (horizontal) speed. The angular rate is the same for earth' surface and a satellite in GSO but not the velocity!

The theoretical construct of an space elevator works because it would actually accelerate it's payload during the way up!

Offline Jim

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RE: Long cables to power plasma rockets to orbit.
« Reply #41 on: 02/08/2008 02:28 pm »
Quote
RGClark - 7/2/2008  4:26 PM

1.  This idea might also work for transmitting the electrical power from the long power line to the rocket's conducting tether in my proposal without the extreme friction at the highest Mach speeds. The tether would have slippers at its end sliding along the power cable. At the very highest speeds the air between the slippers would likely become ionized and therefore highly conducting. Then even though the slippers would not be touching the power line, the thin layer of ionized air would still conduct the electrical power to the tether.
 
2.  If the inflatable vacuum chamber can indeed be made to work (it has not yet been successfully demonstrated in experiments), then it might be used around the Holloman track rather than the helium shroud. This might allow orbital velocity to be reached with just the multi-stage rockets now being used.

3  This though would remove the advantage that exists now with the slippers riding on a thin layer of gas. Perhaps a very low density residual gas would be sufficient to raise the slippers above the rails. As it is now you have to have the helium at the same pressure as the surrounding air since the thin tent would not be strong enough to hold back the outside pressure without the equalizing pressure of the helium.

 

1.  Still not viable, there still is friction. The cable isn't rigid like the track, it will have have a centenary shape.  The shoe will bang on it all the way up.  Also since the shoe can't completely enclose the cable, it must have a "C" shape to it, to avoid a cable supports (much like the rail supports on the track).   With a floating/suspended cable, it will be impossible to keep the shoes aligned to avoid hitting the supports

2.  A small chamber has yet to be demonstrated, so why do you think one, tens of miles long and miles wide is going to work.

3.  Not enough helium to fill it

This concept is not viable, and ignores physics

Offline pippin

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Re: Long cables to power plasma rockets to orbit.
« Reply #42 on: 02/08/2008 02:55 pm »
Oh, and then there's the issue with how to support the cable. The theoretical maximum for the length of an Al structure to be able to support itself (theoretical, perfect structure, no outside forces) is 26 km (at 700 MPa strength and 2700 kg/m3) so realistically let's assume something like 5 km. So how do you support that? Oh, yes: now is the time when somebody will have to mention carbon nanotubes...

Offline Jim

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Re: Long cables to power plasma rockets to orbit.
« Reply #43 on: 02/08/2008 03:18 pm »
Have we yet to build a mile high structure?

Offline pippin

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Re: Long cables to power plasma rockets to orbit.
« Reply #44 on: 02/08/2008 03:42 pm »
I'm afraid: no. There ARE mile high cables and they do even carry loads (such as cable cars), but they are made from steel (~3.000 MPa, 7850 kg/m3, this as well as the values for Al are the theoretical max. values, practical values range around 450 MPa for exotic Al alloys and 1600 MPa for steel)
Oh..., and they are typically supported by mountains made of SiO2 which is quite good at supporting high loads.

Offline TrueBlueWitt

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Re: Long cables to power plasma rockets to orbit.
« Reply #45 on: 02/08/2008 04:35 pm »
Interesting if flawed ideas.. As long as people are throwing stuff out there, this is my personal pet launch setup.

Build a lightweight launch platform that can be lifted by balloons(at the end of long cantilevered trusses off the corners).. possilby augmented by a number of highly efficient 100,000+ lb thrust Commercial Aircraft Turbofans(or take the VTOL system out of the F35?)...  Take the platform up above 40,000-50,000ft and launch from there.  Then you could vacuum optimize your first stage nozzles to get higher ISP.  Also greatly reduces issues with maxQ.  Take the thing out over water for launch.. would help reduce size/mass requirements of launch abort system on manned rockets as well.  Of course not as much fun to go watch a rocket launch.

Crazy?  I'd be interested to hear everyone's thoughts.

Offline sandrot

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Re: Long cables to power plasma rockets to orbit.
« Reply #46 on: 02/08/2008 05:27 pm »
And if the rocket blows up at liftoff the whole structure will come down as the balloons will be punctured.
"Paper planes do fly much better than paper spacecrafts."

Offline TrueBlueWitt

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Re: Long cables to power plasma rockets to orbit.
« Reply #47 on: 02/08/2008 05:46 pm »
Quote
sandrot - 8/2/2008  1:27 PM

And if the rocket blows up at liftoff the whole structure will come down as the balloons will be punctured.

Structure's unmanned.. other than crew(if manned launch).. If rocket blows up  You're having a bad day anyway.

Can always add some huge cargo parachutes  to be deployed if you lose the Balloons.. at least bring it down a little softer(and you'll be over water anyway.. could be floating platform for that matter that's lifted off water instead of land.

Offline pippin

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Re: Long cables to power plasma rockets to orbit.
« Reply #48 on: 02/08/2008 06:31 pm »
Quote
RGClark - 8/2/2008  8:09 PM
This would also eliminate the problem of it pointing straight up at the end if you had several balloons along its length. You could instead have it be relatively straight near its end.
No, it wouldn't.
Your helium balloons would line up vertically.

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Re: Long cables to power plasma rockets to orbit.
« Reply #49 on: 02/08/2008 09:08 pm »
Quote
RGClark - 8/2/2008  2:09 PM

 True if there were only a single helium balloon supporting it at the one end. However, you could have several different ones supporting it along its length, say every 5 km if you wanted. This would also eliminate the problem of it pointing straight up at the end if you had several balloons along its length. You could instead have it be relatively straight near its end.
 

still have the catenary curve.  Still not viable

There are more issues with this concept than it solves

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Re: Long cables to power plasma rockets to orbit.
« Reply #50 on: 02/08/2008 11:55 pm »
Quote
RGClark - 8/2/2008  7:34 PM

 1.  The bend of the catenary depends on how far apart the supports are.

2. Also, if the cable was made buoyant itself by making it hollow filled with helium then you could make it be straight.



1.  The bend will always be there, no matter the tension. Since your supports are spaced by many kilometers, the bend is going to be hundreds of meters
2.  Hollow?   The buoyancy would negligible.  The volume of helium required would need a cable diameter range in feet, not inches.   and again helium won't work above 30km

also it is impossible to make any suspended cable straight, a catenary will always exist.

I am sorry, but you seem to have no grasp of physics, and keep proposing impossible things

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RE: Long cables to power plasma rockets to orbit.
« Reply #51 on: 02/09/2008 12:20 am »
Quote
RGClark - 8/2/2008  8:02 PM

 In correspondence with the developer of this idea, a physicist at Florida State University, I understand the impetus of this was specifically to produce arbitrarily long lightweight vacuum chambers to serve, for example, as long, vacuum travel paths for rockets.
 

Not vertically, maybe for horizontal sleds.

Still can't get by that we haven't built anything approaching a mile high.  And then there is the jet stream

and what diameter do you proposed?  How many hundreds of meters?

Don't flatter yourself with that company.   Also Von Braun didn't ignore physics.  They didn;t propose kludges

Offline pippin

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Re: Long cables to power plasma rockets to orbit.
« Reply #52 on: 02/09/2008 07:36 am »
Bob, you are still ignoring my point. If you want this even remotely straight, then your HORIZONTAL force will be much bigger than the vertical one, the vertical one being the weight of a few 1000 mT of Al cable plus fixtures. Cable cars have massive concrete sledges with fixtures that anchor deep into mountains to cover these forces while your end will be open up in the air.
No matter how many  balloons you use, your cable will point more or less straight upwards.
The cables for your tethered balloons only have to go straight upwards.
How do you solve this?

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Re: Long cables to power plasma rockets to orbit.
« Reply #53 on: 02/09/2008 12:36 pm »
All that documentation is for 'plain" tethers, i.e anchors.  Doesn't mean squat.  The purpose of those tethers is to support balloons and aerostats.  They are a means and not the end.  None of those documents are not applicable to  your scheme.   Those tethers don't take side loads nor conduct power to a sliding "slipper'.  And all those tethers are not straight.   I have worked near an aerostat.  The high building analogy is a applicable for the vacuum chambe

"Ridiculing his idea without taking a look at the underlying theory is analogous to that (in)famous New York Times editorial ridiculing Robert Goddard's theories on space flight because in space "there is nothing to push against".
 am not ridiculing his idea.  I am ridiculing your use of his idea and tethers.  Major point:

********Actually the analogy  is directly applicable to your idea because you intend to put helium balloons in a vacuum. ********************

Also, the article talks about horizontal applications wrt transportation, not vertical  Additionally, your scheme has major disadvantages. (assuming that it overcomes the real world physics)

1.  It only launches to one azimuth
2.  "insertion" would at only one altitude

Offline Jim

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Re: Long cables to power plasma rockets to orbit.
« Reply #54 on: 02/10/2008 04:34 pm »
still not viable, you keep added more and more to it making it more complex angd unworkable.  At every problem, you proposes a marginal or nonviable solution
Heated air air through nozzles?  there isn't enough air pressure to do that, and won't propellers above 15km
Still, what is going to hold the cable above 30km?


No matter all the websites you link, the sag will always be there.  

Power cable microns thin?  it won't be able to handle the loads of the "slipper" or power transfer device.  Also any arcing would melt through the skin.  Helium filled?  It won't evenly "lift" the cable, since the volume is vertical.  the heluim will go to the top.  It will also permeate the container


This idea is hopelessly flawed


Offline A_M_Swallow

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Re: Long cables to power plasma rockets to orbit.
« Reply #55 on: 02/10/2008 05:14 pm »
If you are using cables you are building a train.  Trains have a maximum speed but so does the stage 1 of rockets.  The fastest trains use magnetic levitation.  To get to orbit build a 5 mile maglev up the side of a mountain, reaching 800 km/h and then use an ordinary stage 2 rocket.  Bob Clark you may wish to calculate how much an Ares-1 would be able to lift using this arrangement.
http://nasaexplores.nasa.gov/show2_5_8a.php?id=01-027&gl=58

Offline Jim

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Re: Long cables to power plasma rockets to orbit.
« Reply #56 on: 02/10/2008 05:19 pm »
Quote
A_M_Swallow - 10/2/2008  1:14 PM

To get to orbit build a 5 mile maglev up the side of a mountain, reaching 800 km/h and then use an ordinary stage 2 rocket.


Another flawed idea.  How many 5 mile mountains how the proper slope and are situated in the proper orientation .

Offline A_M_Swallow

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Re: Long cables to power plasma rockets to orbit.
« Reply #57 on: 02/10/2008 05:47 pm »
Quote
Jim - 10/2/2008  6:19 PM

Quote
A_M_Swallow - 10/2/2008  1:14 PM

To get to orbit build a 5 mile maglev up the side of a mountain, reaching 800 km/h and then use an ordinary stage 2 rocket.


Another flawed idea.  How many 5 mile mountains how the proper slope and are situated in the proper orientation .

We only need one, preferably in the tropics.  If the angle is too steep add electric motors, there are advantages in having a Stage 1 that never leaves the ground.

Mount Mauna Kea on Hawaii has a peak 10,200 metres (33,500 ft = 6.3 miles) above the sea.

p.s. Although only 2.6 miles may be usable.
http://en.wikipedia.org/wiki/List_of_peaks_by_prominence

Offline DMeader

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Re: Long cables to power plasma rockets to orbit.
« Reply #58 on: 02/10/2008 06:22 pm »
This reminds me of a passage from "The Moon Is A Harsh Mistress" by Heinlein. One of the main characters, while trying to drum up sympathy for the lunar colonies to be free, sells the idea of a magnetic escape-speed catapult to various countries. He always has nice things to say about whatever local high mountain is available. His estimate for lunar injection is 20G acceleration for a length of 323Km. 11 km/sec at the ejection end.

Offline gospacex

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Re: Long cables to power plasma rockets to orbit.
« Reply #59 on: 02/10/2008 07:29 pm »
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A_M_Swallow - 10/2/2008  12:47 PM
We only need one, preferably in the tropics.  If the angle is too steep add electric motors, there are advantages in having a Stage 1 that never leaves the ground.

Mount Mauna Kea on Hawaii has a peak 10,200 metres (33,500 ft = 6.3 miles) above the sea.

?! The highest spot on Earth is 8848 meters only, and it is in Himalaya. You meant 10 km for the (submerged) base?

Offline pippin

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Re: Long cables to power plasma rockets to orbit.
« Reply #60 on: 02/10/2008 07:35 pm »
This starts to be fun...

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RGClark - 10/2/2008  6:22 PM
 You see that when the applied horizontal force is large, the sag at the center is lowered.
That was my point. To put it the other way 'round: If you want your sag low the force has to be high. Much higher than the vertical force (weight), which is equal to 1000s of mT.
Oh, and since I was assuming the cable to be so thin it could just support itself, it will not be able to carry these forces. So you have to make it, say, twice as thick aka twice as heavy. Plus you add the cables that carry the loads to the ground. They have to hold the same load so they have to be of the same strength. Aka the same weight. Please add that to your 1000s of mTs of stuff that you are liting with helium balloons to whatever height and hold in place with cables.
Question: What is the Helium volume needed for that?
Quote
The formula for the sag at the center of a beam freely supported at its ends is given here:

Deflection.
http://www.cda.org.uk/megab2/elecapps/pub22/sec8.htm#Deflection

[blah blah I remeber well from my mechanics classes erased]

I calculate using 70 gigapascals for the modulus of aluminum, that for a horizontal beam 10 meters long, 10 centimeters vertical width, and 1 millimeter horizontal width, the sag at the center would be 40 centimeters.
 If that recent announcement about an aluminum composite stronger than carbon fiber at lighter weight is correct and if this strength also applies to its modulus then since carbon fiber has a modulus ten times that of aluminum, the sag should be less than 4 centimeters for this composite for the same dimensions.
So you are putting a balloon every 10m? Over a distance of 100miles that would be 16.000 balloons.
You are not? Than do the calculation again with, say 100m and write back what you find :)
(Hint: The formula you presented is to the 4th order!)
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Also, if the power cable were to provide its own buoyancy by being microns thin and meters wide filled with helium, then it would be straight because at each point it is providing its own lift rather than only being lifted at the endpoints. Then you wouldn't need the ground tether wires to provide horizontal tension. You would still need them though to keep the lighter than air cable stable against winds.
Nice one. Good for experimenting.
Please build a prototype. Take some household aluminum foil (it's much thicker but will do for this experiment), build a structure with a diameter of several meters and report back on how much load you succeeded in putting on that.
Quote
Note if you used electrically powered thrusters or even propellers to keep the power cable stable against winds then you wouldn't need the ground tethers at all.

 Remember back on page 3, I suggested using the principal of the hot air balloon to provide buoyancy for the power cable instead of helium? Interestingly such balloons can be run on solar power alone:

Solar hot air balloons.
http://pagesperso-orange.fr/ballonsolaire/en-index.htm
Again: What volume do you need to carry, say, 50.000t to 30km?
Quote
You could also provide stability against the winds by venting the heated air through nozzles. This would also dispense with the need for ground tethers.
Bob, you are talking about forces that are several times the power of even the larges aircraft turbines or rocket engines!!!

Offline A_M_Swallow

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Re: Long cables to power plasma rockets to orbit.
« Reply #61 on: 02/10/2008 08:32 pm »
Quote
gospacex - 10/2/2008  8:29 PM

Quote
A_M_Swallow - 10/2/2008  12:47 PM
We only need one, preferably in the tropics.  If the angle is too steep add electric motors, there are advantages in having a Stage 1 that never leaves the ground.

Mount Mauna Kea on Hawaii has a peak 10,200 metres (33,500 ft = 6.3 miles) above the sea.

?! The highest spot on Earth is 8848 meters only, and it is in Himalaya. You meant 10 km for the (submerged) base?

When I copied the hight I did not realise that someone would measure a mountain from underwater.  That is why I added the p.s.

Offline Jim

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Re: Long cables to power plasma rockets to orbit.
« Reply #62 on: 02/11/2008 07:23 pm »
Quote
RGClark - 11/2/2008  1:57 PM

Quote
A_M_Swallow - 10/2/2008  4:32 PM
...
When I copied the hight I did not realise that someone would measure a mountain from underwater.  That is why I added the p.s.

 Another point to consider is that it is really the trajectory length that has to be 5 km, not the vertical height.


Then that is less of an advantage

Offline Jim

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Re: Long cables to power plasma rockets to orbit.
« Reply #63 on: 02/11/2008 10:23 pm »
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RGClark - 11/2/2008  5:38 PM
 

1.  Thanks for such a thoughtful response.  I see no problem with putting the helium balloons every 10 meters or every 1 meter. That just means you could use much smaller balloons. You won't break the world market in small helium balloons by using several thousand of them. If  it sufficed for the required current capacity to make the cable  have a 1 sq. mm cross-sectional area (while keeping the strong rectangular shape) then just a couple of those little party helium balloons sold at dollar stores would be sufficient to lift a 10 meter long segment. See this page:

2.  For the weight of the power cable itself, a cable of cross-section of 1 sq. cm and 10 meters long made of aluminum weighs about 2.7 kilos. So one 100 km long would be 27,000 kilos. It would not be thousands of metric tons. And if a 1 sq. mm cable sufficed it would be 1/100th this weight or only 270 kilos. Note also such lengths would be necessary only for manned craft that needed low accelerations . For unmanned craft that could be hardened to withstand hundreds to thousands of g's the length would be only in the 10's of kilometers range, or less.
 

You are making the classic amateur engineering design mistake.  Because you assume # 1 is feasible, you automatically #2 is a given.  

There are big problems in using balloons (#1) which makes this not feasible

1.  attachment to the cable (that alone blows out your weight estimates)  
2.  cable attachment interference with power transfer device
3.  balloon management (they can't be just attached and forgotten, they will leak)

But it is not just #1, the idea has holes everywhere.  Horizontally strung cables are not applicable to this application.  Your cross sections assumptions are based on the this, which is wrong.

Later you skip all the "standard"  cable stuff and assume that the cable can be hollow and thin membraned.  and you conveniently ignore the issues with the power transfer mechanisms

You are designing a house of cards.  Making gross (and wrong) assumptions that make this not viable.  I wouldn't want anyone who thinks this works to be involved with any engineering.




Offline pippin

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Re: Long cables to power plasma rockets to orbit.
« Reply #64 on: 02/11/2008 10:45 pm »
OK, I agree you don't need to have a strong cable if you are supporting it along the whole line with balloons. However, you still have a few wrong assumptions:

1. On horizontal forced: I didn't say "many times the vertical force" I said "much higher than..." Your factor of 2 qualifies for "much higher".
2. Where did you get the notion, that a rectangle structure is strong? It is much weaker than a round structure because it has edges where the tension gets extremely strong. Rectangle profiles are only good on a) HARD materials (such as steel) and b) if your vertical dimension is much bigger than the horizontal one to give you a strong bending module.

3. Your lift figures are for sea level. You want to go to 60km, where your atmospheric pressure is only 1/1000 so you need 1000 times the volume!

4. The problem with your aluminum foil is that you need a perfect structure to get to that tensile strength, as soon as you got an dent or ding in it it will tear (as you can see with your household foil). Can't avoid that with your this film cable. Polyethylene is much stronger in that respect since it doesn't have an atomary crystalline structure but consists of long molecular chains. Metals are generally very bad at that. Oh and you are trying to send POWER up through your cable, please keep that in mind.

Go get yourself a 1mm aluminum cable and test how "strong" it is!

5. I still don't see how you handle your power transfer to the rocket, without frying the balloon assy, and how you attach your "pantograph" to the thin cable with a string attached to it every 10m at speeds of a few 1000 km/h and where you get the power from to keep your gigantic balloon cross section from drifting away with the high winds that can be over 100km/h fast.

Sorry, face it: this ain't gonna work, there are easier ways to get to space. And if you solve all the problems you will find out that the losses are bigger than the gains.

Offline Lampyridae

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Re: Long cables to power plasma rockets to orbit.
« Reply #65 on: 02/12/2008 03:00 am »
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pippin - 8/2/2008  11:22 PM

Quote
Lampyridae - 6/2/2008  1:24 AM
It might do if the projectile was launched at escape or near-escape velocities. Or maybe straight up into geosynch... although that notion vaguely offends me.

With good reason: it's wrong. Going straight up into GSO wouldn't work since you don't have the necessary (horizontal) speed. The angular rate is the same for earth' surface and a satellite in GSO but not the velocity!

The theoretical construct of an space elevator works because it would actually accelerate it's payload during the way up!

Ahhh, thank you. I thought something was wrong with my assumption! The only other alternative really is L1... again, there are angular velocity issues. I guess, short of an escape trajectory, there really is no way to avoid two burns... unless perhaps you skip/glide at periapsis, but all that gets you is a steadily decaying orbit!

Offline Lampyridae

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Re: Long cables to power plasma rockets to orbit.
« Reply #66 on: 02/12/2008 03:11 am »
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TrueBlueWitt - 9/2/2008  2:35 AM

Interesting if flawed ideas.. As long as people are throwing stuff out there, this is my personal pet launch setup.

Build a lightweight launch platform that can be lifted by balloons(at the end of long cantilevered trusses off the corners).. possilby augmented by a number of highly efficient 100,000+ lb thrust Commercial Aircraft Turbofans(or take the VTOL system out of the F35?)...  

F-35 VTOL system uses a gearbox and crank shaft that gives me nightmares to look at that drives a lift fan, coupled with a thrust deflecter at the back. Boeing proposal derived from Harrier was more sensible IMHO but then I'm biased towards the Pegasus engine! :)

Quote
Take the platform up above 40,000-50,000ft and launch from there.  Then you could vacuum optimize your first stage nozzles to get higher ISP.  Also greatly reduces issues with maxQ.  Take the thing out over water for launch.. would help reduce size/mass requirements of launch abort system on manned rockets as well.  Of course not as much fun to go watch a rocket launch.

Crazy?  I'd be interested to hear everyone's thoughts.

Turbofans have a lousy, lousy T/W ratio. I would not put one on a launch platform unless it was a flying wing. You would have to custom-design ones that operate at zero airflow at 40 000 ft. Off-the-shelf designs would suffer. Much easier to just build a BIG flying wing and plonk engines on it.

If you want to work air-launch into it, much better to use rotors. Put some ramjets on the tip of some VERY big rotors and you have a much more effective VTOL launch platform. Better yet, use the ramjets directly as a first stage because they have good T/W ratio compared to other air-breathing engines.

Offline Lampyridae

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Re: Long cables to power plasma rockets to orbit.
« Reply #67 on: 02/12/2008 04:17 am »

Quote
RGClark - 12/2/2008 7:38 AM



For the weight of the power cable itself, a cable of cross-section of 1 sq. cm and 10 meters long made of aluminum weighs about 2.7 kilos. So one 100 km long would be 27,000 kilos. It would not be thousands of metric tons. And if a 1 sq. mm cable sufficed it would be 1/100th this weight or only 270 kilos. Note also such lengths would be necessary only for manned craft that needed low accelerations . For unmanned craft that could be hardened to withstand hundreds to thousands of g's the length would be only in the 10's of kilometers range, or less.
To give a real world example of how light long distance power lines can be, the Ekibastuz-Kokshetau power line runs 432 km carrying 1 megavolts and only weighs 50,000 kilos.

Look, you are making loads and loads of basic assumptions, and you know what assumptions are the mother of.

1 megavolt is NOT the same thing as 1 megawatt, and that is not quite the same thing as 1 megaVA. I could build a 483km line of hair-thin copper wire that carried 1 megavolt but I would only get enough current out of it to turn on a lightbulb.

Let me give you some good advice from the point of a non-expert and an armchair engineer that will make your time on this forum much more productive and enjoyable. Although I am not an engineer, I have read engineering books, over and above my usual studies. Sometimes I actually am qualified to offer a good opinion, whenever the discussion wanders into territory that I know. If you look at my posts, you'll notice that I've largely commented on stuff relating to aerodynamics. That's 'cause it's what I know, because I studied a bit of related stuff at university, but also because I got myself a nice intro textbook on Aeronautical Engineering and read it. Also, and maybe more importantly, I have actually gotten my hands dirty wrestling with diesel engines and electrical cables. I have stripped threads off of bolts, electrocuted myself and blown things up. Not nearly as much as the real engineers and techs here, but the point is that you get an intuitive feel for the strengths of materials and the viability of options. Earlier on, I mentioned "going straight into GEO" from the ground up, but something bugged me about it and pippin told me why I was wrong. I then thought about L1, and again realised that it's a dumb idea (going on pippin's logic).

Now, you've had your cable proposal savaged by several aeronautical engineers (Jim is actually giving you a detailed analysis of why it won't work instead of half a sentence, you should be honoured), but the idea is just full of holes. You've probably learned a bit about cables (and me too), but the idea is just not worth sticking to!

If I were you, I would go and investigate the properties of cables. What are they good for? What can they be made to do? What does DC current do? I've thought of a couple of ideas based on the initial premise of a current-carrying cable, because I believe it is an interesting concept and worth exploring. I'll do a bit more work on them and then bring them to this thread to be torn apart by the experts.


Offline A_M_Swallow

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Re: Long cables to power plasma rockets to orbit.
« Reply #68 on: 02/12/2008 07:18 am »
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RGClark - 11/2/2008  6:57 PM

 BTW, I don't understand why such a low speed of 800 km/hr would be beneficial. The Saturn V first stage for instance took the Apollo missions to 10,000 km/hr 2,700 m/s before cutoff.
   Bob Clark

There are high mountains in South America and the Himalayas, just not in so nice a place.

Any speed is an advantage, it saves the weight of fuel on Stages 2 and 3.  As for the 800 km/hr - since it is on a rail/cable Stage 1 is a train not a plane.   See the land speed records for practical limits.

Offline pippin

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Re: Long cables to power plasma rockets to orbit.
« Reply #69 on: 02/12/2008 09:22 am »
Quote
Quote
To give a real world example of how light long distance power lines can be, the Ekibastuz-Kokshetau power line runs 432 km carrying 1 megavolts and only weighs 50,000 kilos.

Look, you are making loads and loads of basic assumptions, and you know what assumptions are the mother of.

1 megavolt is NOT the same thing as 1 megawatt, and that is not quite the same thing as 1 megaVA. I could build a 483km line of hair-thin copper wire that carried 1 megavolt but I would only get enough current out of it to turn on a lightbulb.


Very good point, the whole power transmission issue is another can of worms. And of course you can have a megavolt and not transmit any power at all...even cat fur and plastics get you to thousands of volts...

Yet also the first assumption is grossly wrong, I suppose.
You got the 50t from Wikipedia, don't you? There's just a small statement there and it does NOT say that the OVERALL weight is 50t. Instead I suspect that each conductor section has that weight. Typical conductor cables are made from steel reinforced aluminum (that's the lightweight version compared to copper) and have a cross section of 60mm2 steel plus 260mm2 aluminum. 1m of that weighs roughly 1 kg (bit more but just for calculus...), so 483 km make 483t. Plus that power line has 6 conductor cables, so that would be around 3000t. I don't see how they would gain a factor of 10 to get to 50t (there's also no need to and the Soviet Union was not famous for wasting money on useless overengineering - that's why their rockets and spacecraft are so good) so I think that's either an Wikipedia myth or the weight of the heaviest section of the powerline or something - it's easy to get much heavier if you have to span long distances or use copper.

Offline pippin

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Re: Long cables to power plasma rockets to orbit.
« Reply #70 on: 02/12/2008 01:30 pm »
Quote
Thanks for all the detailed responses. The feedback is appreciated.
 I forgot to  give the web link for that 1 megavolt powerline:

Powerline Ekibastuz-Kokshetau.
http://en.wikipedia.org/wiki/Powerline_Ekibastuz-Kokshetau

Yep. And that's a literal quote from a page that refers to the pylons.
EACH PYLON carries 50t!!!

Offline pippin

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Re: Long cables to power plasma rockets to orbit.
« Reply #71 on: 02/12/2008 02:56 pm »
They are not fully made of aluminum. They have a steel core. Please read your own link. Aluminum is not strong enough. The example I gave is from a real cable, yet for a 110KV one.

BTW, how do you transmit power? Closed loop? Got two cables? Or three for High power AC (as described in your link)? You will find it difficult to ground a rocket.

Offline Jim

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Re: Long cables to power plasma rockets to orbit.
« Reply #72 on: 02/12/2008 03:17 pm »
Quote
RGClark - 12/2/2008  10:21 AM
 So you would need, for example, helium balloons of twice the diameter to lift these than that needed for 1 cm wide cables.


 

Balloons are going to work.   period!

Offline Jim

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Re: Long cables to power plasma rockets to orbit.
« Reply #73 on: 02/12/2008 05:37 pm »
Quote
RGClark - 12/2/2008  1:22 PM

 For instance instead of many separate small balloons, we could have a single long, hollow helium balloon all along the length of the cable.



Again, not viable.  Balloons lift from beneath and not from the side.  Your long balloon would want for be horizontal and have a large tension at the base of the cable

Honestly and bluntly, you don't have any concept of engineering, physics or reality.  You keep kludging together all these disconnected concepts,  in the hope of making it  work.  You are fixating on balloons, which have too many strikes against them and you have nothing to lift the cable from 30km to orbital altitude

Do you have any engineering degree or technical certificate?

Offline DMeader

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Re: Long cables to power plasma rockets to orbit.
« Reply #74 on: 02/12/2008 06:49 pm »
Mr. Clark,

Actually, he IS a rocket scientist!

I'd suggest you let this go.

Offline Jim

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Re: Long cables to power plasma rockets to orbit.
« Reply #75 on: 02/12/2008 07:00 pm »
Quote
RGClark - 12/2/2008  2:33 PM
  1.You could have the power cable running along the top of the long balloon. This might make it top heavy though so you might want to have a counterweight hanging down from the balloon as well. If the counterweight was the same weight as the weight of the cable this would increase the weight that had to be supported only by a factor of two. Then the diameter of the long balloon would only have to be larger by a factor of 1.4.

 2.  You can make the volume of the long balloon at each point along its length correspond to the altitude and air density at that point so that the structure is neutrally buoyant along its length.
 
3.The cable does not have to go to orbital altitude. The key aspect in getting to orbit is achieving orbital velocity, 7,000 to 8,000 m/s. The energy and velocity needed to get to 100 km or 200 km altitude is small in proportion to that needed for orbital velocity. So once the rocket reached orbital velocity at, say, 30 km altitude you just point it upward and give it a little extra velocity to place it at the desired orbital altitude.

4.My background is in pure math, what's yours?


Bob Clark

1.  Another kludge fix.  Now how is the rocket now suppose to "access" the conductor?  You keep trying to solve all these issue by adding more problems.  You aren't looking at the big picture.  Also it would be 1.4, you have to account for attach hardware

2.  What length?  The cable is vertical!

3. And you are going burn up your vehicle by going that fast in the atmosphere.

4.  That explains everything.  No practical experience.

My experience has been documented over and over on this forum.
http://forum.nasaspaceflight.com/photos/photo-thumbnails.asp?albumid=25&Page=2&sortdir=desc


I am out of here.  you just can't convinces some people that they are wrong despite over whelming evidence.  They stubbornly hold on to  misconceptions.  This  idea is just like a perpetual motion machine and its "inventor"

Offline DMeader

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Re: Long cables to power plasma rockets to orbit.
« Reply #76 on: 02/12/2008 07:41 pm »
I've read enough of his posts for long enough that I thoroughly respect his knowledge and expertise.

Also I may add that this is the wrong board to so strenuously defend such wild, impractical scheme and try to get a flamewar going.

While I've followed this thread since its beginning, I'm now out of here as well.

Offline pippin

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Re: Long cables to power plasma rockets to orbit.
« Reply #77 on: 02/12/2008 08:00 pm »
Quote
RGClark - 12/2/2008  9:29 PM

Quote
DMeader - 12/2/2008  2:49 PM

Mr. Clark,

Actually, he IS a rocket scientist!

I'd suggest you let this go.

 No offense. But after the Columbia accident, to those of us in other technical fields being called a rocket scientist is not regarded as a ringing endorsement.
Also no offense, but that fits my notion of somebody who does not have a clue about things, thinks everything is easy and people who don't follow these easy solutions are just morons.

I suggest you try out some of my suggestions and report back with your results in another thread (PRACTICAL results, please!)

I think this thread has had enough...

Offline A_M_Swallow

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Re: Long cables to power plasma rockets to orbit.
« Reply #78 on: 02/12/2008 11:02 pm »
Quote
RGClark - 12/2/2008  7:33 PM
 My background is in pure math, what's yours?

Then do the maths.  There are formulas for the mass of towers.  There are good reasons why pyramids and the electrical pylons are that shape.

Offline Lampyridae

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Re: Long cables to power plasma rockets to orbit.
« Reply #79 on: 02/12/2008 11:46 pm »

Quote
RGClark - 12/2/2008  9:29 PM
 No offense. But after the Columbia accident, to those of us in other technical fields being called a rocket scientist is not regarded as a ringing endorsement.

That's rich to pin the blame bad management and political decisions 30 years ago on the people who were kids at that time and now have to deal with it. You are not entrusted with people's lives, they are.

Quote
pippin - 13/2/2008  6:00 AM
Also no offense, but that fits my notion of somebody who does not have a clue about things, thinks everything is easy and people who don't follow these easy solutions are just morons.

I suggest you try out some of my suggestions and report back with your results in another thread (PRACTICAL results, please!)

I think this thread has had enough...

I'm sorry to say this, Mr. Clark, but I also agree. This is getting silly. There is a reason engiineers need to have practical experience - and armchair engineers too. Go make friends with a mechanic or electrician and help them out on weekends and you'll learn a lot. Other than that, I'm outta here.

Offline Sid454

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Re: Long cables to power plasma rockets to orbit.
« Reply #80 on: 02/13/2008 12:21 am »
I agree with Lamprydae on this it's just not workable and beaming the power with lasers or even microwaves would be far more practical.

Other issues you missed the cables carrying very high voltage of lets say  500KV will be very prone to arcing and in the upper atmosphere they will leak just like a big neon bulb as the break down voltage gets lower.

The cables also will be subject to magnetic field generated by the current passing though them which will tend to force them apart and even make them whip around in all sorts of undesirable ways.

Also the voltage conversion equipment to down convert 500KV down to 150 volts for your arcjet will weigh several tons there's a lot of reasons why this stuff is heavy.

Best type of person to talk to about on this would be someone in the power industry they can explain this better then anyone else including a rocket scientist.

I haven't even covered the mechanical and aerodynamic end of this but then that already has been covered.

Offline GSE pad rat

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Re: Long cables to power plasma rockets to orbit.
« Reply #81 on: 02/13/2008 05:32 pm »
At 62 lbs/ft for 500KV cable per conductor, two conductor at LEO 2000Km would be about 406,823 tons with required aviation beacons intermediate supports (to prevent cable damage) this could easily triple in weight. Conversion equipement adds about 20 to 40 tons.

That makes the space platform without its own weight would be supporting about 1.2 Megatons (109 Megatonnes) in orbit.

The international requirements for liablity and political considerations of having 2000Km of cable falling to earth will keep lawyer occupied for years.

Use a nuclear reactor to power it on orbit.


Offline Patchouli

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Re: Long cables to power plasma rockets to orbit.
« Reply #82 on: 02/13/2008 05:54 pm »
Looking at those numbers why not just build Bono's rombus yes I know it's just a really big chemical SSTO RLV and isn't as sexy but it's all sound engineering we can do now.
For a lot less then such a massive infrastructure you could fly probably a Rombus mission every few days each one taking 400tons to LEO.

Now said plasma engine might be great on a solar electric tug to take the stuff you just launched into LEO elsewhere as plasma arc rockets can use just about any volatile substance be it CO2,Water H2 etc as propellant.

Also once in orbit you don't need gigawatt's a hundred KW will be enough and we know how to make around that level of power in space we're doing it right now with ISS.

Offline Jim

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Re: Long cables to power plasma rockets to orbit.
« Reply #83 on: 02/14/2008 03:19 pm »
Quote
RGClark - 13/2/2008  11:56 AM

Windmills in the Sky.
A bold plan to tap the jet stream and boost our nation's energy supply.
By Michael Behar  Posted 11.21.2005 at 2:00 am.
http://www.popsci.com/scitech/article/2005-11/windmills-sky


yeah, right, that is a valid source

Offline pippin

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Re: Long cables to power plasma rockets to orbit.
« Reply #84 on: 02/21/2008 07:53 am »
So what is different with that?
Still need to support the needed force.
End will still point upwards (as you can see in your sketch).

Offline pippin

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Re: Long cables to power plasma rockets to orbit.
« Reply #85 on: 02/21/2008 03:46 pm »
Quote
RGClark - 21/2/2008  5:24 PM

Actually it points upwards at an angle which is what you want so that most of velocity component is in the horizontal direction to achieve orbital velocity and a smaller component in the vertical direction to achieve orbital altitude.


      Bob Clark
The "angle" will be close to 90°. All that has been said from the beginning of the thread applies to this. No difference whether it's wind or a turbine that pulls on the balloon.

Offline Jim

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Re: Long cables to power plasma rockets to orbit.
« Reply #86 on: 02/21/2008 05:42 pm »
Quote
pippin - 21/2/2008  11:46 AM

Quote
RGClark - 21/2/2008  5:24 PM

Actually it points upwards at an angle which is what you want so that most of velocity component is in the horizontal direction to achieve orbital velocity and a smaller component in the vertical direction to achieve orbital altitude.


      Bob Clark
The "angle" will be close to 90°. All that has been said from the beginning of the thread applies to this. No difference whether it's wind or a turbine that pulls on the balloon.

The cables goes 57km horizontally and only 8 km vertically.  Just the exact opposite of a "standard" trajectory.  It spends too much time in the atmosphere

Offline pippin

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Re: Long cables to power plasma rockets to orbit.
« Reply #87 on: 02/22/2008 12:29 am »
Quote
Jim - 21/2/2008  7:42 PM

The cables goes 57km horizontally and only 8 km vertically.  Just the exact opposite of a "standard" trajectory.  It spends too much time in the atmosphere
C'mon Jim. This is not even a trajectory. It tops out at 8km, not even airliner altitude. The other 7/8th of the cable will have to be added. And that cable will follow some form of exponential function. The ed result will be the same, of course: you burn up your vehicle in the lower atmosphere jut to shoot it's remains straight up into the sky at the end.

Will look cool, though, a reverse asteroid.

Offline Jim

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Re: Long cables to power plasma rockets to orbit.
« Reply #88 on: 03/04/2008 02:14 am »
Why are you still bothering with this.  It is still not viable

Offline Jim

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Re: Long cables to power plasma rockets to orbit.
« Reply #89 on: 03/05/2008 12:04 am »
Quote
RGClark - 4/3/2008  5:15 PM

According the U.S. patent office the idea of sending high electrical power along power lines held aloft seveal kilometers in the air is viable.
 This married with the fact that a rocket running on electrical power from the ground has essentially unlimited power makes reusable rockets easy and cheap.


   Bob Clark

That is the major hole.  It can't be married.  There is no way of getting the power to the rocket.   Also several km is not orbital altitude.

 Why can't you understand this not viable

Offline hop

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Re: Long cables to power plasma rockets to orbit.
« Reply #90 on: 03/05/2008 12:13 am »
Quote
RGClark - 4/3/2008  2:15 PM

According the U.S. patent office the idea of sending high electrical power along power lines held aloft seveal kilometers in the air is viable.
The USPTO says no such thing.

The issuance of a patent says almost nothing about the possibility, never mind practicality of the invention. In theory, they aren't supposed to issue patents for things that are obviously impossible, but in practice there's plenty of patents on all kinds of fantastic nonsense.

Charlatans and quacks have long used patents to lend an air of authenticity to their output, but is based on exploiting the publics misunderstanding.

Offline khallow

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Re: Long cables to power plasma rockets to orbit.
« Reply #91 on: 03/05/2008 07:21 am »
Quote
hop - 4/3/2008  5:13 PM

Quote
RGClark - 4/3/2008  2:15 PM

According the U.S. patent office the idea of sending high electrical power along power lines held aloft seveal kilometers in the air is viable.
The USPTO says no such thing.

The issuance of a patent says almost nothing about the possibility, never mind practicality of the invention. In theory, they aren't supposed to issue patents for things that are obviously impossible, but in practice there's plenty of patents on all kinds of fantastic nonsense.

Charlatans and quacks have long used patents to lend an air of authenticity to their output, but is based on exploiting the publics misunderstanding.

For example, there's probably  been a zillion patented perpetual motion or "free energy" machines. Not a one has been shown to work, that is to produce at least as much work as was put in.
Karl Hallowell

Offline pippin

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Re: Long cables to power plasma rockets to orbit.
« Reply #92 on: 03/05/2008 04:16 pm »
Um... this thread is not about high altitude wind power generation but about tethered plasma rockets. The former may be feasible (I don't know), the latter is not. That is what people have been referring to.

Offline Jim

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Re: Long cables to power plasma rockets to orbit.
« Reply #93 on: 03/05/2008 05:17 pm »
Quote
RGClark - 5/3/2008  12:38 PM

Quote
Jim - 4/3/2008  8:04 PM

Quote
RGClark - 4/3/2008  5:15 PM

According the U.S. patent office the idea of sending high electrical power along power lines held aloft seveal kilometers in the air is viable.
 This married with the fact that a rocket running on electrical power from the ground has essentially unlimited power makes reusable rockets easy and cheap.


   Bob Clark

That is the major hole.  It can't be married.  There is no way of getting the power to the rocket.   Also several km is not orbital altitude.

 Why can't you understand this not viable

 Not only is it viable it is fact easy.

You have proven nothing.  And you definitely can't say easy.  You don't have the engineering or knowledge to say that.

You have only strung together unrelated topics.  

For example,

high altitude to minimize air drag and heating is above 60 miles, way above balloons

Short distances? that means inches and not hundred of feet






 

     Bob Clark

Offline DMeader

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Re: Long cables to power plasma rockets to orbit.
« Reply #94 on: 03/05/2008 07:37 pm »
Perhaps we all need to just ignore this.

Since the OP does not seem receptive to criticism of the idea, it can be argued that rather than having a discussion, we are just feeding a troll.

Offline hop

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Re: Long cables to power plasma rockets to orbit.
« Reply #95 on: 03/05/2008 08:39 pm »
Quote
RGClark - 5/3/2008  9:01 AM

Quote
khallow - 5/3/2008  3:21 AM
For example, there's probably  been a zillion patented perpetual motion or "free energy" machines. Not a one has been shown to work, that is to produce at least as much work as was put in.

 KHallow, the patent office specifically disallows perpetual motion machines, or any device that appears to put out more energy than it takes in.


   Bob Clark
Specifically disallowing them doesn't actually stop patents from being granted for this sort of thing, which was the whole point of my post. It just means the obvious ones get thrown out. Yes, patented inventions are supposed to be useful which obviously implies they need to be possible. In practice, patent examiners are busy and not necessarily well qualified to evaluate each specific invention.

The existence of a patent is a very weak argument for the feasibility of an invention.

Offline Jim

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Re: Long cables to power plasma rockets to orbit.
« Reply #96 on: 03/05/2008 09:35 pm »
Quote
RGClark - 5/3/2008  4:36 PM

However, one of the main criticisms was that supporting high power lines at kilometers high altitude was not feasible. This is in fact being investigated and being funded at preliminary stages for wind power generation.
 


and the criticisms still apply.  You still haven't shown how to support the line at 60-70km.  Techniques for less than 20km are not applicable

Offline Jim

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Re: Long cables to power plasma rockets to orbit.
« Reply #97 on: 03/05/2008 09:40 pm »
Quote
RGClark - 5/3/2008  3:31 PM

1.  The conducting rocket tether could be within inches of the power line to still transmit high power from the power line to the rocket. However, there are also methods to transmit high electrical power over hundreds of feet if you wanted to avoid the use of the tether.

2.  I say implementing the proposal would be easy based on the granted patents and the papers published in peer-reviewed journals on the high altitude power generation.

3.  The parts of the proposals having to do with maintaining the power lines at altitude are the easy parts of the proposals.


1.  The rocket wouldn't follow the power line.  Winds affect the flight paths of launch vehicle greatly

2.  That doesn't mean squat.  There is theory and there is practice

3.  That hasn't been proven "easy"  I haven't seen one yet

Offline Jim

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Re: Long cables to power plasma rockets to orbit.
« Reply #98 on: 03/05/2008 09:42 pm »
Moderators please lock this thread.  The author has no concept of debate and physics for the matter.  It is a useless

Offline A_M_Swallow

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Re: Long cables to power plasma rockets to orbit.
« Reply #99 on: 03/05/2008 09:43 pm »
Quote
RGClark - 5/3/2008  8:31 PM
 The proposals for scramjets, where they are using the surrounding air for combustion, also rely on getting this air up to altitudes in the range of 30km to 50 km. Helium balloons have also been flown up to 50 km altitude; so could be used for supporting the power lines at this altitude.
 The conducting rocket tether could be within inches of the power line to still transmit high power from the power line to the rocket. However, there are also methods to transmit high electrical power over hundreds of feet if you wanted to avoid the use of the tether.

R G Clark time for the numbers.

How heavy is a 30 km long electrical power tether?
How heavy is your vehicle?
How much of a force does the accelerating vehicle apply to the cable?
How big a balloon is needed to support tether and launch force?

Offline pippin

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Re: Long cables to power plasma rockets to orbit.
« Reply #100 on: 03/05/2008 11:50 pm »
Quote
RGClark - 5/3/2008  9:31 PM
 I say implementing the proposal would be easy based on the granted patents and the papers published in peer-reviewed journals on the high altitude power generation.
   Bob Clark

As I stated a few times before:
If this is so incredibly easy and everybody else on this planet except for you is so incredibly stupid: why don't you just do it and get incredibly rich doing it?

Offline khallow

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Re: Long cables to power plasma rockets to orbit.
« Reply #101 on: 03/06/2008 12:16 am »
Quote
A_M_Swallow - 5/3/2008  2:43 PM

R G Clark time for the numbers.

How heavy is a 30 km long electrical power tether?
How heavy is your vehicle?
How much of a force does the accelerating vehicle apply to the cable?
How big a balloon is needed to support tether and launch force?

Let me add a few.

How long in duration can a cable be suspended?
How much damage are you expecting to the cable from a launch?
How many launches do you want to get out of a cable before it needs to be replaced?
Karl Hallowell

Offline Jim

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Re: Long cables to power plasma rockets to orbit.
« Reply #102 on: 03/06/2008 02:23 am »
"proposed by university professors of engineering and aeronautics. "

Who teach but not do

Offline Jim

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Re: Long cables to power plasma rockets to orbit.
« Reply #103 on: 03/06/2008 02:29 am »
Quote
RGClark - 5/3/2008  10:22 PM

Quote
Jim - 5/3/2008  5:42 PM

Moderators please lock this thread.  The author has no concept of debate and physics for the matter.  It is a useless

 On the contrary, for all the objections raised I have pointed  to specific references that show the proposal is feasible. These references are by experts in the field. I certainly don't think they are unaware of the physics involved.


   Bob Clark

Point to one feasible reference where there is a heavy cable going up to 70 nmi, is suspended without catenary dips.  

Show how a rocket can follow a cable within 1 mile

Show how a conductor can be pulled along a cable without interfering with the intermediate supports  (balloons and connections)

Show how a rocket is not going to hit the cable or the supports******



******* this is the killer

Offline pippin

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Re: Long cables to power plasma rockets to orbit.
« Reply #104 on: 03/06/2008 03:59 am »
Patents have no technical value. Patents are for claims management only.

Offline Jim

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Re: Long cables to power plasma rockets to orbit.
« Reply #105 on: 03/06/2008 10:48 am »
Quote
RGClark - 6/3/2008  4:37 AM

Quote
pippin - 5/3/2008  11:59 PM

Patents have no technical value. Patents are for claims management only.

 Yes, they do. If the invention works, then it tells other people how also to make it. You could of course do the same thing in a research publication. The key fact is they both are peer-reviewed.
 There sometimes are mistakes made with patents just as there are sometimes mistakes made with peer-reviewed journals.



   Bob Clark

patents are not peer reviewed.

Offline khallow

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Re: Long cables to power plasma rockets to orbit.
« Reply #106 on: 03/06/2008 02:58 pm »
Quote
RGClark - 6/3/2008  1:37 AM

Quote
pippin - 5/3/2008  11:59 PM

Patents have no technical value. Patents are for claims management only.

 Yes, they do. If the invention works, then it tells other people how also to make it. You could of course do the same thing in a research publication. The key fact is they both are peer-reviewed.
 There sometimes are mistakes made with patents just as there are sometimes mistakes made with peer-reviewed journals.

As Jim pointed out, patent claims aren't peer reviewed. I also suspect that one can withhold considerable information from a patent and still have something legally viable. Certainly, I don't see your assertion that there will be enough information contained in the patent to build a working device.

Finally, I really don't see the feasibility of attaching cables to rockets. First, you've discussed in relative detail how to suspend cable in atmosphere via balloons. That only works to around 30 km. Past that, then you have to use some sort of active no-atmosphere system (like rocket propulsion) or have something like a space elevator. That means either the system is limited in how long it stays up or we have better mechanisms for getting things to space than using rockets.

Second, you don't explain how the rocket can maintain an electrical connection with the cables. Last we saw, the cables were spaced a mile away from the rocket (to avoid damage from the rocket's turbulence and exhaust). Now the rocket has to drag at least a couple of miles of connecting cable at hypersonic speeds. I don't see it happening. Too much closer and the cables will break from the passage of the rocket and then you lose connection to the power source which looks to me like it has to be on the ground.

Even if the cable is far enough away from the rocket, it isn't far enough away from the electrical connection to the rocket. At some point there is a stationary cable electrically connected to a rapidly accelerating cable that soon will be travelling at hypersonic speeds. I don't see a cable staying structurally intact under those circumstances.

Third, those cables have to carry enough power to be relevant. You are voltage limited (since you're trying to avoid arcing between cables and arcing from the cable to ground). I doubt copper cable would work, too much mass per unit length.

Fourth, the rocket and the cable will have different aerodynamic characteristics in wind. The cable is going to be blown in different directions at different altitudes. It's not going to be straight enough without some degree of active correction.

Fifth, the arcing between the cable and the connector to the rocket is going to damage the cable no matter what else happens. That means you are pretty limited in how many times you can use that cable before it needs repair (at least of the surface).

As I see it, you're lifting a considerable structure using some sort of suspension that doesn't depend on ground or atmosphere support. Then you somehow electrically connect it to a rocket that quickly reaches hypersonic speeds. Finally, you either need to do this repeatedly to drive down the cost per launch, or make the structure extraordinarily cheap so that it can be disposed after each launch.

That just doesn't seem physically possible much less competitive with beamed power or regular no frills chemical power.
Karl Hallowell

Offline 2.71

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Re: Long cables to power plasma rockets to orbit.
« Reply #107 on: 03/06/2008 06:32 pm »
On top of that, you need 2 cables. One for return current, unless you plan on using an ion thruster;) And don't forget the magnetic field generated by the high current. And forget about setting this up near any storm clouds, because then you need a lightning protection system.

2.71
"Your political views are so interesting to me!"

Offline Jim

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Re: Long cables to power plasma rockets to orbit.
« Reply #108 on: 03/06/2008 09:56 pm »
That is totally unrelated to the topic, 15,000 feet (4600 m) is no where near what is needed.   This can't be extrapolated to 20-30 times higher.

This is exactly what I said, you link unrelated topics which is bogus.  

Here is a premise:  
Let's say you can string a cable to orbit and you can transfer the power to the rocket.    The rocket can't follow the cable.  Launch vehicles don't correct for wind disturbances during the climb thru the atmosphere.  They let the winds buffet them around to keep the loads low.  Aside from the winds there is nothing that will keep the rocket from hitting the cable.  there is nothing on the rocket to sense where the cable is

So this is still not viable.

Just let it go.  It is a dead end.  You clearly show that you don't know the physics involved


Offline Jim

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Re: Long cables to power plasma rockets to orbit.
« Reply #109 on: 03/06/2008 11:47 pm »
Quote
RGClark - 6/3/2008  6:47 PM

 I could argue that you yourself are setting up a "straw man". As I said and you are well aware of you don't have to maintain powered flight to orbital altitude. You just attain sufficient velocity to achieve orbit, point it upward

That minimum altitude is around 70km, still too high for a cable.  It would be too much aeroheating below that.   still to high for an anchor.  So still not viable.

It is not even worth testing.  

Offline hop

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Re: Long cables to power plasma rockets to orbit.
« Reply #110 on: 03/07/2008 12:19 am »
Quote
RGClark - 6/3/2008  3:47 PM
This is how all proposed methods for launch that accelerate the satellite at ground level work, such as gun launch, magnetic launch, etc.
And all of them suffer greatly from need to fly near orbital velocity in the lower atmosphere ("lower atmosphere" here being anything below several hundred thousand feet.)

This isn't a minor detail.

Offline hop

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Re: Long cables to power plasma rockets to orbit.
« Reply #111 on: 03/07/2008 12:55 am »
Quote
RGClark - 6/3/2008  5:29 PM
 True. As far as I know all such ground level orbital velocity systems, like gun launch for example,  are only envisioned for small micro satellites, 10 kg or so, shaped like thin, compact missiles.
The credible ones use multiple rocket stages after gun launch.
Quote
But proposed hypersonic scramjets reach their high Mach speeds at altitudes in the range of 30km to 50 km, still within the atmosphere, to support combustion.
Proposed. Notice that these proposals have generated a lot of viewgraphs/powerpoints and not much flight hardware. The only flown scramjets were boosted on rockets, didn't fly close to orbital velocity, and at best produced enough thrust to be detectable with sensitive instrumentation!

Pointing to paper vehicles to support the credibility of your proposal isn't very convincing.

Offline Jim

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Re: Long cables to power plasma rockets to orbit.
« Reply #112 on: 03/07/2008 01:13 am »
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RGClark - 6/3/2008  8:38 PM

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Jim - 6/3/2008  7:47 PM

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RGClark - 6/3/2008  6:47 PM

 I could argue that you yourself are setting up a "straw man". As I said and you are well aware of you don't have to maintain powered flight to orbital altitude. You just attain sufficient velocity to achieve orbit, point it upward

That minimum altitude is around 70km, still too high for a cable.  It would be too much aeroheating below that.   still to high for an anchor.  So still not viable.

It is not even worth testing.  

 No, the orbital scramjet proposals have to remain in the atmosphere during powered flight since they get their oxygen from the air. They reach their highest Mach speeds at the altitude range of 30 km to 50 km.


Again, totally unrelated.  So what about scramjets.  
Doing a horizontal test is still not viable.   the cable would have to many catenary curves

Now I know what perpetual motion machine "inventors" are like

Offline Jim

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Re: Long cables to power plasma rockets to orbit.
« Reply #113 on: 03/07/2008 01:14 am »
Here is another nail in the coffin.  Launch vehicle trajectory is in the lower corner.

The cables are shaped wrong and spend too much time in the lower atmosphere.  Also the multiple balloon has catenary curves that would go up and down several KM.

End of story






Offline Jim

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Re: Long cables to power plasma rockets to orbit.
« Reply #114 on: 03/07/2008 02:34 am »
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RGClark - 6/3/2008  9:57 PM

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Jim - 6/3/2008  9:14 PM

Here is another nail in the coffin.  Launch vehicle trajectory is in the lower corner.

The cables are shaped wrong and spend too much time in the lower atmosphere.  Also the multiple balloon has catenary curves that would go up and down several KM.

End of story



 Obviously, there wouldn't be a great dip in the cable if the balloon supports were only separated by for example 10 meters, or if the cable was supported continuously along its length.

Obviously that is impossible.  

You just negated any power transfer capability.  The lift system would interfere with it.  Whether is it by direct contact or transmitted.

Balloon every 10m?  how is the deployment and maintenance of over 120km/10m or 12000 balloons be done?

Where is the concept of practically?

You just keep digging a hole deeper and deeper in the willful suspension of physical reality

Also how is the issue  for the need for 2 conductors  ( one for power and the other for return) resolved

Obviously this concept is not going to work on any level

Offline Avron

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Re: Long cables to power plasma rockets to orbit.
« Reply #115 on: 03/07/2008 03:07 am »
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Jim - 6/3/2008  10:34 PM

Obviously this concept is not going to work on any level

Come now Jim.. it will work on the ground..

Offline Jim

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Re: Long cables to power plasma rockets to orbit.
« Reply #116 on: 03/07/2008 03:09 am »
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Avron - 6/3/2008  11:07 PM

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Jim - 6/3/2008  10:34 PM

Obviously this concept is not going to work on any level

Come now Jim.. it will work on the ground..

that is called a train

Offline pippin

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Re: Long cables to power plasma rockets to orbit.
« Reply #117 on: 03/07/2008 08:33 am »
Jim, Rob, you are both wrong. The cable would point more or less straight upwards. I still didn't see the concept on how to apply the horizontal force necessary to keep a bend. Any bend will be at the low end of the cable the top end will point 90° into the sky no matter how many balloons you apply.

But a train going 7km/s, wow, THAT would be something... Would LOVE to see the plasma trail it generates...

Offline sandrot

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Re: Long cables to power plasma rockets to orbit.
« Reply #118 on: 03/07/2008 12:22 pm »
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pippin - 7/3/2008  4:33 AM

[...]

But a train going 7km/s, wow, THAT would be something... Would LOVE to see the plasma trail it generates...

We've got to PM vt_hokie on this...
"Paper planes do fly much better than paper spacecrafts."

Offline khallow

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Re: Long cables to power plasma rockets to orbit.
« Reply #119 on: 03/07/2008 04:15 pm »
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pippin - 7/3/2008  1:33 AM

Jim, Rob, you are both wrong. The cable would point more or less straight upwards. I still didn't see the concept on how to apply the horizontal force necessary to keep a bend. Any bend will be at the low end of the cable the top end will point 90° into the sky no matter how many balloons you apply.

But a train going 7km/s, wow, THAT would be something... Would LOVE to see the plasma trail it generates...

At that point, I think it'd be wise to stick the thing inside a tube with vacuum. Even though it breaks the totally-cool plasma trail effect.
Karl Hallowell

Offline pippin

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Re: Long cables to power plasma rockets to orbit.
« Reply #120 on: 03/07/2008 04:29 pm »
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At that point, I think it'd be wise to stick the thing inside a tube with vacuum. Even though it breaks the totally-cool plasma trail effect.
Actually there was a (seriously considered) project in Switzerland for an underground maglev that proposed to do exactly that...

Offline sandrot

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Re: Long cables to power plasma rockets to orbit.
« Reply #121 on: 03/07/2008 04:32 pm »
I remember reading of an underground train in vacuum that would have taken from NY do San Francisco in 25 minutes... something like 20 years ago.

(vt_hokie, where are you?)
"Paper planes do fly much better than paper spacecrafts."

Offline sandrot

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Re: Long cables to power plasma rockets to orbit.
« Reply #122 on: 03/07/2008 04:40 pm »
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RGClark - 7/3/2008  12:13 PM

[...]. The SR-71 Blackbird uses jets that can operate to 100,000 ft, 30 km:

LOCKHEED SR-71 BLACKBIRD.
http://www.abovetopsecret.com/pages/sr71.html

 and the NASA's Helios solar powered plane can operate at nearly 100,000 ft:

NASA Solar Aircraft Sets Altitude Record; Communications And Environmental Breakthroughs Expected.
http://www.sciencedaily.com/releases/2001/08/010815081052.htm



   Bob Clark

Yes, I would suggest using chemical rockets to keep the cable leveled as needed. It's doable and it makes sense. We saw DC-X and Pixel could do leveled flight...
"Paper planes do fly much better than paper spacecrafts."

Offline pippin

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Re: Long cables to power plasma rockets to orbit.
« Reply #123 on: 03/07/2008 05:14 pm »
here it is: http://www.swissmetro.ch/eng-home-startseite.html
For practical reasons I suggest we just build a 60km mountain, drill a hole into it and have out great maglev launcher. No issues with balloons and at least as doable. We now how this works, just need lots of soil

Offline sandrot

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Re: Long cables to power plasma rockets to orbit.
« Reply #124 on: 03/07/2008 05:24 pm »
Pippin, you've got do deal with outgassing from the soil, you will not have vacuum in the hole. It's not doable. (devil is in the details)
"Paper planes do fly much better than paper spacecrafts."

Offline Jim

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Re: Long cables to power plasma rockets to orbit.
« Reply #125 on: 03/07/2008 05:25 pm »
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RGClark - 7/3/2008  12:25 PM

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Jim - 6/3/2008  9:13 PM

...

Now I know what perpetual motion machine "inventors" are like

 No, what you are experiencing is what it's like to argue against a proposal that can actually work.


You haven't haven't proven anything.  

This is just a fool's folly

Offline Chris Bergin

RE: Long cables to power plasma rockets to orbit.
« Reply #126 on: 03/07/2008 05:37 pm »
This is becoming very pointless as a thread. We won't allow threads here to turn into sci.space type discussions.

Locked.
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