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#1 2005-08-25 20:52:58

SpaceNut
Administrator
From: New Hampshire
Registered: 2004-07-22
Posts: 21,706

Re: ION Engines

The topic of ION engine push has come up but they were more or less about the power supply used for them and not the engine.
The back ground of which is well stated by the deep space probe and others for small to medium cargo push slowly from earth orbit with the help of gravity boost and aero or gravitational breaking to orbits.

Burnin' for space

Scientists at NASA Glenn Research Center have created a prototype of a next-generation thruster that could be used for long-term space missions and is more efficient than current technology.

Whats so different about this engine:

The cylinder-shaped thruster is about six inches tall, five inches in diameter and weighs about six pounds.

How long before we can use it:

The NASA Glenn team must now make improvements on the thruster and test it to see if it can last for long-term use; it will take as long as five years before the thruster will be ready to use on a space mission

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#2 2005-09-13 17:12:10

VTTFSH_V
Member
From: Hawaii
Registered: 2005-09-13
Posts: 31

Re: ION Engines

The ion engine's exhaust velocity is pretty good, but its specifc impulse is horrible.  It would be wiser to use the 80-year-old technology of the rocket that is normally used today than to use an ion engine simply because it offers so much more pressure.

So one may ask what engine offers both high exhaust velocity and high specific impulse.  The answer is only engines that involve matter annihilation, like the photon rocket, nuclear-pulse rocket or the matter/antimatter-catalyzed fisson rocket.  This is because E=MC².  That is a LOT of energy!


Have a nice day.  big_smile

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#3 2005-09-13 18:50:12

John Creighton
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From: Nova Scotia, Canada
Registered: 2001-09-04
Posts: 2,401
Website

Re: ION Engines

The ion engine's exhaust velocity is pretty good, but its specifc impulse is horrible.  It would be wiser to use the 80-year-old technology of the rocket that is normally used today than to use an ion engine simply because it offers so much more pressure.

So one may ask what engine offers both high exhaust velocity and high specific impulse.  The answer is only engines that involve matter annihilation, like the photon rocket, nuclear-pulse rocket or the matter/antimatter-catalyzed fisson rocket.  This is because E=MC².  That is a LOT of energy!

I think you mean the thrust is low, not the specific impulse.

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#4 2005-09-13 18:50:16

GCNRevenger
Member
From: Earth
Registered: 2003-10-14
Posts: 6,056

Re: ION Engines

What? Are you some kind of a troll?

The exhaust velocity controls the specific impulse, a high-velocity engine typically has a high Isp. It also doesn't offer more "pressure" because there is no gas expansion in an ion engine. There is also a very, very small amount of thrust because the engine trades thrust for specific impulse.

Antimatter would be great, but we have no way to produce or store it in any quantity, so its not very useful. A beam-type photon rocket wouldn't have very good thrust either.

Nuclear pulse engines aren't even going to be very useful because of the fallout and expense of building an arsenal of nukes to push it with.

Antimatter catalyzed fusion engines are also a pretty far-out concept, and nobody has even started concieving how you would build such an engine.


"The power of accurate observation is often called cynicism by those that do not have it." - George Bernard Shaw

The glass is at 50% of capacity

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#5 2005-09-13 20:10:33

VTTFSH_V
Member
From: Hawaii
Registered: 2005-09-13
Posts: 31

Re: ION Engines

The ion engine's exhaust velocity is pretty good, but its specifc impulse is horrible.  It would be wiser to use the 80-year-old technology of the rocket that is normally used today than to use an ion engine simply because it offers so much more pressure.

So one may ask what engine offers both high exhaust velocity and high specific impulse.  The answer is only engines that involve matter annihilation, like the photon rocket, nuclear-pulse rocket or the matter/antimatter-catalyzed fisson rocket.  This is because E=MC².  That is a LOT of energy!

I think you mean the thrust is low, not the specific impulse.

"Thrust" is a general term for the propellent.  There are two factors of thrust.  One is the exhaust velocity, the other is the force, called specific impulse.

Say you are in a 50-ton vehicle.  It has a rocket, and its propellent is matter that is travelling at 5 miles per hour, but you have enough to apply 100,000 pounds of pressure.  You would accelerate pretty fast, but your speed would be limited to just under 5 miles per hour.  Now say the propellent is matter that is travelling at 50,000 miles per hour, but you only have 1 pound of pressure.  You would accelerate very slowly, but your top speed would be just under 50,000 miles per hour.  The ion engine is more like the second example.  Only matter annihilation engines can offer large quantities both factors.


Have a nice day.  big_smile

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#6 2005-09-13 21:16:22

John Creighton
Member
From: Nova Scotia, Canada
Registered: 2001-09-04
Posts: 2,401
Website

Re: ION Engines

The ion engine's exhaust velocity is pretty good, but its specifc impulse is horrible.  It would be wiser to use the 80-year-old technology of the rocket that is normally used today than to use an ion engine simply because it offers so much more pressure.

So one may ask what engine offers both high exhaust velocity and high specific impulse.  The answer is only engines that involve matter annihilation, like the photon rocket, nuclear-pulse rocket or the matter/antimatter-catalyzed fisson rocket.  This is because E=MC².  That is a LOT of energy!

I think you mean the thrust is low, not the specific impulse.

"Thrust" is a general term for the propellent.  There are two factors of thrust.  One is the exhaust velocity, the other is the force, called specific impulse.

Say you are in a 50-ton vehicle.  It has a rocket, and its propellent is matter that is travelling at 5 miles per hour, but you have enough to apply 100,000 pounds of pressure.  You would accelerate pretty fast, but your speed would be limited to just under 5 miles per hour.  Now say the propellent is matter that is travelling at 50,000 miles per hour, but you only have 1 pound of pressure.  You would accelerate very slowly, but your top speed would be just under 50,000 miles per hour.  The ion engine is more like the second example.  Only matter annihilation engines can offer large quantities both factors.

Usually, specific impulse is defined as the length of time a pound of fell can produce a pound of thrust. An impulse in mechanics is used to describe a change in velocity. In collisions we call the forces impulsive because they are so fast it is easier mathematically to treat them as instantaneous. In rockets what determines the minimum fuel that can be used to travel between two points is the difference in velocity (DELTA V). It is natural to call the measure a pound of fuel contribution to that change of velocity the specific impulse because a change in velocity is an impulse and specific means per quantity.

So if we want a tem for the thrust per mass a better word for this would be specific thrust. Ion engines actually have a very high specific impulse because the high velocity of the exhaust means each pound of fuel contributes a greater amount to the total change of velocity of the rocket.

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#7 2005-09-13 22:14:36

VTTFSH_V
Member
From: Hawaii
Registered: 2005-09-13
Posts: 31

Re: ION Engines

What? Are you some kind of a troll?

The exhaust velocity controls the specific impulse, a high-velocity engine typically has a high Isp. It also doesn't offer more "pressure" because there is no gas expansion in an ion engine. There is also a very, very small amount of thrust because the engine trades thrust for specific impulse.

Antimatter would be great, but we have no way to produce or store it in any quantity, so its not very useful. A beam-type photon rocket wouldn't have very good thrust either.

Nuclear pulse engines aren't even going to be very useful because of the fallout and expense of building an arsenal of nukes to push it with.

Antimatter catalyzed fusion engines are also a pretty far-out concept, and nobody has even started concieving how you would build such an engine.

I think it would be wise to research something before making any assertions about it.

Antimatter is produce all of the time in particle accelerators.  They then store the antimatter (which are usually antiprotons) in electrommagnetic fields.  The photons of a photon rocket come from matter/antimatter annihilation, thus, barely any materials will be needed to produce a LOT of energy (E=MC²) that MOVES AT THE SPEED OF LIGHT (It IS light!).  High exhaust velocity and high pressure!

Antimatter-catalyzed fission engines are the MOST "NEAR-IN" concept of matter annihilation propulsion.  I couldn't help but notice that you stated that "nobody has even started concieving how you would build such an engine?"  Do your homework, my friend.  Penn State University has designed a ship called ICAN-II that uses this type of engine, and might I add, they did a pretty fine job.

P.S.  I am not a troll.  big_smile


Have a nice day.  big_smile

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#8 2005-09-14 06:51:11

GCNRevenger
Member
From: Earth
Registered: 2003-10-14
Posts: 6,056

Re: ION Engines

BUT we still can't hold those antiprotons in any great quantity for any length of time, since the traps "leak" and the particles are lost. The traps themselves are also very heavy if you were to build a large one, which defeats the purpose.

"and high pressure!"

No. There would be no pressure at all actually, since a beam type antimatter rocket doesn't use an expanding gas to produce thrust. And in beam type engines, since photons carry very little momentum, your thrust would be pretty low.

"Antimatter-catalyzed fission engines are the MOST "NEAR-IN" concept of matter annihilation propulsion"

Except that it isn't. Almost none of the propulsive energy comes from the antimatter, the majority of it comes from fusion. The antimatter is used only as an igniter to initiate fusion.

"Penn State University has designed a ship called ICAN-II that uses this type of engine"

No. They don't know how to build a trap that can hold antiprotons either, nobody does. I am also very skeptical that their huge megaship, which looks awfully heavy to me.


"The power of accurate observation is often called cynicism by those that do not have it." - George Bernard Shaw

The glass is at 50% of capacity

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#9 2005-09-14 21:05:24

VTTFSH_T
Member
From: Hawaii
Registered: 2005-09-13
Posts: 19

Re: ION Engines

There is a way to trap antiprotons.  It's called a penning trap!  It traps atoms in electric and magnetic fields.
http://livefromcern.web.cern.ch/livefro … r/FAQ.html
http://livefromcern.web.cern.ch/livefro … .html#trap


ggkthnx big_smile

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#10 2005-09-15 02:35:26

VTTFSH_V
Member
From: Hawaii
Registered: 2005-09-13
Posts: 31

Re: ION Engines

Thank You!  But nothing can shut this guy up.  He'll start arguing with CERN now.  BWAH HAH HAH!


Have a nice day.  big_smile

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#11 2005-09-15 06:08:15

GCNRevenger
Member
From: Earth
Registered: 2003-10-14
Posts: 6,056

Re: ION Engines

But a Penning trap doesn't work very well. They can't hold many anti-protons for very long, and the device itself is too heavy/large. They are too "leaky" to use for a space ship. Nobody knows how to build a trap that doesn't leak.


"The power of accurate observation is often called cynicism by those that do not have it." - George Bernard Shaw

The glass is at 50% of capacity

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#12 2005-09-15 10:10:01

VTTFSH_T
Member
From: Hawaii
Registered: 2005-09-13
Posts: 19

Re: ION Engines

But it is a trap that exists and it works!


ggkthnx big_smile

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#13 2005-09-15 11:21:27

GCNRevenger
Member
From: Earth
Registered: 2003-10-14
Posts: 6,056

Re: ION Engines

You need to store anti-protons enough for long enough to last you until you can get a recharged trap. A round-trip to Mars will take easily six months even with a "super" engine, and nobody knows how to build a trap that will last that long... plus, if the trap were to ever fail enroute, the crew would be doomed, since you could not slow down at your destination.

Since the trap is one of the heaviest items on the ship, if you carry multiple traps, then your ship is too heavy to enjoy the bennefits of this propulsion method. I am also a bit dubious about the arrangement of the "nozzle" which does not look very reliable to me.


"The power of accurate observation is often called cynicism by those that do not have it." - George Bernard Shaw

The glass is at 50% of capacity

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#14 2005-09-15 12:47:28

RobS
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From: South Bend, IN
Registered: 2002-01-15
Posts: 1,701
Website

Re: ION Engines

A trap that "leaks" really doesn't "work." A very tiny amount of leaked antimatter will destroy the trap, the ship, and anything near the ship. And the bigger the amount of antimatter you want to store, the more reliable the trap has to be. Right now the traps are storing micrograms (or picograms? not much!) of antimatter.

                 -- RobS

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#15 2005-09-15 13:41:16

GCNRevenger
Member
From: Earth
Registered: 2003-10-14
Posts: 6,056

Re: ION Engines

The amonut of antimatter being considerd here is too small to cause the obliteration of the ship, but that is an interesting point about what would happen if the trap were to leak excessively or catastrophically fail... Say that there is a fluctuation in the containment ring and a portion of the antiprotons were to impact the wall? The walls are superconducting electromagnets, which operate only at extremely low temperatures. They also tend to fail in a big way if their temperature exceeds the critical temperature over a signifigant portion of the ring... So, a hot-spot would be created, which would disrupt the magnetic field, and possibly cause all the antiprotons to immediatly leak out. Which leaves your ship dead in the water, as it were, and if this were to happen after leaving Earth/Mars/Moon orbit or during orbital capture, you would just be plain dead.


"The power of accurate observation is often called cynicism by those that do not have it." - George Bernard Shaw

The glass is at 50% of capacity

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#16 2005-09-19 17:24:42

VTTFSH_V
Member
From: Hawaii
Registered: 2005-09-13
Posts: 31

Re: ION Engines

BUT we still can't hold those antiprotons in any great quantity for any length of time, since the traps "leak" and the particles are lost. The traps themselves are also very heavy if you were to build a large one, which defeats the purpose.

"and high pressure!"

No. There would be no pressure at all actually, since a beam type antimatter rocket doesn't use an expanding gas to produce thrust. And in beam type engines, since photons carry very little momentum, your thrust would be pretty low.

"Antimatter-catalyzed fission engines are the MOST "NEAR-IN" concept of matter annihilation propulsion"

Except that it isn't. Almost none of the propulsive energy comes from the antimatter, the majority of it comes from fusion. The antimatter is used only as an igniter to initiate fusion.

"Penn State University has designed a ship called ICAN-II that uses this type of engine"

No. They don't know how to build a trap that can hold antiprotons either, nobody does. I am also very skeptical that their huge megaship, which looks awfully heavy to me.

Was that the wind or did I say "gas pressure?"  It was the wind!

Definition of "pressure:"  The act of pressing.  It has nothing to do with gas!  Simply put, the exhaust's "act of pressing" against the vacuum of space will cause an equal and opposite reaction, propelling the ship!

These are all basics of propulsion!  Why am I even explaining this?


Have a nice day.  big_smile

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#17 2005-09-19 17:25:21

VTTFSH_V
Member
From: Hawaii
Registered: 2005-09-13
Posts: 31

Re: ION Engines

BUT we still can't hold those antiprotons in any great quantity for any length of time, since the traps "leak" and the particles are lost. The traps themselves are also very heavy if you were to build a large one, which defeats the purpose.

"and high pressure!"

No. There would be no pressure at all actually, since a beam type antimatter rocket doesn't use an expanding gas to produce thrust. And in beam type engines, since photons carry very little momentum, your thrust would be pretty low.

"Antimatter-catalyzed fission engines are the MOST "NEAR-IN" concept of matter annihilation propulsion"

Except that it isn't. Almost none of the propulsive energy comes from the antimatter, the majority of it comes from fusion. The antimatter is used only as an igniter to initiate fusion.

"Penn State University has designed a ship called ICAN-II that uses this type of engine"

No. They don't know how to build a trap that can hold antiprotons either, nobody does. I am also very skeptical that their huge megaship, which looks awfully heavy to me.

Was that the wind or did I say "gas pressure?"  It was the wind!

Definition of "pressure:"  "The act of pressing."  It has nothing to do with gas!  Simply put, the exhaust's "act of pressing" against the vacuum of space will cause an equal and opposite reaction, propelling the ship!

These are all basics of propulsion!  Why am I even explaining this?


Have a nice day.  big_smile

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#18 2005-09-19 17:52:57

John Creighton
Member
From: Nova Scotia, Canada
Registered: 2001-09-04
Posts: 2,401
Website

Re: ION Engines

Was that the wind or did I say "gas pressure?" It was the wind!

Definition of "pressure:" The act of pressing. It has nothing to do with gas! Simply put, the exhaust's "act of pressing" against the vacuum of space will cause an equal and opposite reaction, propelling the ship!

These are all basics of propulsion! Why am I even explaining this?

You are explaining this because you didn't read what he said correctly. He said the pressure would be low (practically zero) not zero of course. Also you are wrong when you say pushing against the vacuum of space. There is nothing to push on in a vacuum. It is the momentum transfer that acts like pressure pushing against the ship.

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#19 2005-09-19 17:53:37

GCNRevenger
Member
From: Earth
Registered: 2003-10-14
Posts: 6,056

Re: ION Engines

I'm not sure which dictionary you are using VTTFSH, but outside of Websters "pressure" usually refers to the force generated by the expansion or the potential to expand of a fluid.


"The power of accurate observation is often called cynicism by those that do not have it." - George Bernard Shaw

The glass is at 50% of capacity

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#20 2005-09-20 12:53:45

ftlwright
Member
Registered: 2004-11-17
Posts: 61

Re: ION Engines

Was that the wind or did I say "gas pressure?"  It was the wind!

Definition of "pressure:"  "The act of pressing."  It has nothing to do with gas!  Simply put, the exhaust's "act of pressing" against the vacuum of space will cause an equal and opposite reaction, propelling the ship!

These are all basics of propulsion!  Why am I even explaining this?

No, pressure is the force exerted on a unit surface and is a function of temperature, density and specific gas constant (represented by p = rho*R*T).  Isp is a measure of efficiency or the amount of energy within the reactive mass.

You really need to go back and balance your forces.  You cannot "press" against vacuum as there is nothing for you to transfer momentum to.  Simply put you have two pieces of information, mass and velocity.  Your propellant has a certain mass and velocity as does your spacecraft.  At the end of the day, the total momentum of the system is going to be zero, i.e. the sum of the momentum from the propellent is going to equal to the momentum imparted to the spacecraft.  There are a number of text you can get that will expand upon this for you; if you live near a college town you should be able to find an older edition of "Rocket Propulsion Elements - Sutton" for around $15 bucks.

To the topic at hand, what's particularly nice about this ion thruster is that it will play pretty nicely in a clustering configuration.  For a while, Glenn was simply increasing the diameter of there ion thrusters to gain performance, with little thought to the consequences.  This is not entirely a bad thing as they have been able to ratchet up performance without much of a hit to the lifetime of the acceleration grid.

Most in the area in electric propulsion acknowledge, however, the increased ion density in the thruster makes the ion thruster more susceptible to damage (especially for the long duration mission these large diameter thruster would be used for), nor do they have the necessary redundancy needed for a JIMO-type mission.  The more immediate issue is that the cathode emitters don't have the performance or lifetime to maintain the spacecraft's neutral charge.  If similar performance can be achieved with a cluster of ion thruster it's a definite win from a engineering and cost standpoint.

By the way, if anyone is interested in getting into electric propulsion now, the hot areas (for EP anyway) are grid optics and charge balancing.  Most of the other areas are loaded with experts in an already crowded niche of a niche market.  One of the joke we had in academia was "MPD produces more PhD than Isp."

WRT antimatter propulsion, 50-75 years off.  It takes more energy than we get out of it, reducing it to a glorified battery.  I think something along the lines of 50 mg of antimatter is produce annually (this may be wrong, but the triviality of the amount produced is not) which is not nearly enough to do anything worthwhile.  And as I said earlier it's just a battery, raw energy.  That energy needs to be imparted to some reactant mass for it to be useful (unless you plan on using some pusher-plate explosion thingy).  Point being, you will need some sort of space infrastructure to support this type of vehicle; unfortunately this is 40 years down the line.

Please remember folks, space is really, really, really hard.  It is both energy and time intensive and rarely yields something profitable.  At the end of the day, however, we do space to test the endurance of the human condition.  If we can sustain life in far away places such as the Moon, Mars and beyond; think about the things we can accomplish in those far away places right here on Earth.

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#21 2005-09-23 15:19:08

publiusr
Member
From: Alabama
Registered: 2005-02-24
Posts: 682

Re: ION Engines

Look at this chart. Look at the far right-hand side (middle right) You will see that an 80% NSWR rocket outclasses most everything. You don't need anti-matter

http://www.projectrho.com/rocket/RocketChart01Work.pdf

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#22 2005-10-03 14:19:41

redhorizons
Member
From: Oklahoma
Registered: 2005-09-27
Posts: 50

Re: ION Engines

Just a question to show off my ignorance.
Would it be possible/feasible to build a couple of Ion driven tugs that would travel between Earth and Mars.  I believe I heard at some point that the longer you "burn" an Ion engine in space the faster it will go, up to some point.  If so, then if you were to launch a couple Ion tug boats to circle Mars-Earth and use the zip around each body's gravity to help propel them you would get some craft blazing circles around the inner solar system. 
Now with those blazing tugs you fling cargo vessels or manned vessels at them to be capture as they approach Earth and have the tugs zip on to Mars where the craft would jettison into orbit.  I know my science is weak here, but it sounds cool.  What do all you brilliant people think of that?

Go ahead and laugh if needed, I have a strong ego.

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#23 2005-10-03 14:51:16

John Creighton
Member
From: Nova Scotia, Canada
Registered: 2001-09-04
Posts: 2,401
Website

Re: ION Engines

Just a question to show off my ignorance.
Would it be possible/feasible to build a couple of Ion driven tugs that would travel between Earth and Mars.  I believe I heard at some point that the longer you "burn" an Ion engine in space the faster it will go, up to some point.  If so, then if you were to launch a couple Ion tug boats to circle Mars-Earth and use the zip around each body's gravity to help propel them you would get some craft blazing circles around the inner solar system. 
Now with those blazing tugs you fling cargo vessels or manned vessels at them to be capture as they approach Earth and have the tugs zip on to Mars where the craft would jettison into orbit.  I know my science is weak here, but it sounds cool.  What do all you brilliant people think of that?

Go ahead and laugh if needed, I have a strong ego.

Sounds like you want to use ion engines to regulate the orbit of a cycler.

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#24 2005-10-03 18:35:35

GCNRevenger
Member
From: Earth
Registered: 2003-10-14
Posts: 6,056

Re: ION Engines

The trouble with such a scheme is how do you dock the faster-moving ion drive cycler and the slow-moving payload. If you put rockets on the payloads to speed them up to docking speed, then the amonut of rocket fuel you spend is just the same as using those rockets to send them to Earth/Moon

Plus, you can't make your cycler go too fast, or it won't be able to "cycle" effectively; there is an upper limit to how fast you can go on a cycling orbit.


"The power of accurate observation is often called cynicism by those that do not have it." - George Bernard Shaw

The glass is at 50% of capacity

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#25 2005-10-04 07:49:23

redhorizons
Member
From: Oklahoma
Registered: 2005-09-27
Posts: 50

Re: ION Engines

Would a Space Tether create enough velocity to zip a payload to the cycler tugs?

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