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View Full Version : Ion Engines, Inertial inducers, and other alternative thrust



Slamoid
2005-Jan-20, 08:50 PM
I really think inertial inducers would be best, simply using a counterweight as friction and finding a way of reusing the counterbalance without loosing inertia would be the main hurdle...

Just to conduct a census, what does everyone think will be the method of thrust for spacecraft of the future?

Evan
2005-Jan-20, 08:55 PM
Uh, excuse me. What is an inertial inducer?

russ_watters
2005-Jan-20, 08:56 PM
Uh, excuse me. What is an inertial inducer? Its kinda like a gravameric reflexor. :lol:

Evan
2005-Jan-20, 08:58 PM
Go on.

Manchurian Taikonaut
2005-Jan-20, 09:06 PM
Is that the Inertial flux engine or phase inducer you see in sci-fi books ? I think you don't need Science fiction, anyway that stuff is often more fiction than fact and you don't need much of it as there are already some real designs that could be Propulsions used in future missions, a Solar Sail perhaps, fission propulsion possibilities, The Ion Engine, Nuclear Fusion Propulsion System and Anti-Matter can produces its tremendous energy right now many are looking at Ion drives, the NASA ion engine used in deep space and the Smart-one ion drive that ESA built

lti
2005-Jan-20, 09:24 PM
one problem with propulsion of the future is simply the tolerance of humasn to acceleration.

No matter what cool and effective propulsion device we come up with, its only going to be used to accelerate at 1g. Now if we could accelerate continuously for the entire trip without running out of fuel, that would get quite some speed going. But the types of propulsion we use will be things like ion drives, or solar sails. Antimatter drives would only need to react tiny tiny amounts to generate such a slow acceleration.

Evan
2005-Jan-20, 10:32 PM
One g constant acceleration will get you to about 50% of light speed in around six months. Need unobtanium for fuel though.

Slamoid
2005-Jan-20, 11:02 PM
Great arguments...

Example of Inertial Inducer (http://jnaudin.free.fr/html/GITV2.htm)

So... How about the likelyhood of some sort of spacial tunnel or wormhole travel? Perhaps selective quantum entanglment for teleportation?

Evan
2005-Jan-20, 11:09 PM
Oh, so that's what an inertial inducer is. They don't work, period. My dad built one using the same principle back in the 50's and I played with it. It doesn't work as simple math can prove. Conservation of angular momentum kills it.

[edit to add]

It's a stick-slip drive. Put it in a boat and it goes nowhere.

What it really is is a Dean Drive (http://www.jerrypournelle.com/science/dean.html#deandrive)

russ_watters
2005-Jan-21, 04:05 PM
Go on.
Sorry, that was all I had.

Ummmmm.... see, you take the dilithium crystal and attach it to the flux capacitor, then....ehh, I dunno.

It so hard to come up with new material on the road, :lol:


Example of Inertial Inducer
Oh, I get it - its a type 1 perpetual motion machine. Ie, one that doesn't work because it violates the conservation of energy (or, more specifically, angular momentum, as Evan said).

What really makes it move, slamoid, is "friction walking": friction with the table provides the reaction force. This is easy enough to test by varying (or eliminating) the friction between the table and device. If the device really had a net force associated with it, lowering the friction would cause an increase in acceleration. Of course, from the video, you can see there is no net acceleration: it stops between hops and moves, overall, at a constant speed. Give the thing wheels and it'll just shake back and forth.

Sticks
2005-Jan-21, 04:32 PM
What you do is hook the logic cicuits of a Bambleweeny 57 Sub-Meason Brain to an atomic vector plotter suspended in a strong Brownian Motion producer (say a really hot cup of fresh tea) and feed in the improbability figure for an infinite improbability drive and switch on.

Then beware of rampaging mobs of respectable physicists :D

John Dlugosz
2005-Jan-21, 07:54 PM
I really think inertial inducers would be best, simply using a counterweight as friction and finding a way of reusing the counterbalance without loosing inertia would be the main hurdle...

Just to conduct a census, what does everyone think will be the method of thrust for spacecraft of the future?

Mini-magnetospheric plasma propulsion (http://en.wikipedia.org/wiki/Mini-magnetospheric_plasma_propulsion) and use of the Interplanetary Superhighway (http://en.wikipedia.org/wiki/Interplanetary_Superhighway) and other low-thrust transfers, for slow-cargo shipping including massive cargos like whole asteroids.

For passenger or express service, rockets powered by fusion. Likewise for getting off the Earth or Mars. For getting off the Moon, a big catepult.

That's nearest-term space society, extrapolating from what we are able to do now. A space elevator would be better, but much harder to build than a rocket, so would come later.

The plasma magnetic propultion is essentially free, since it needs no reaction mass and can be solar powered. It does leak a little plasma, so you have to top it off with He between missions. Using a long wire would eliminate that, but you need a long loop of (superconductive?) wire. It's better than solar sails, which have the added drawback of needing to be furaled for stowing them.

Like the beanstalk case, using large bolas or teathers to transfer cargo ships from different areas of the solar system would require building such a structure, and only is usable at the beginning and end of the route. The magneto sail is so efficient, those become unnecessary. Though that could suppliment launches later, doing for the asteroid belt what the catepult does for the moon, and reduce transit time with no additional fuel used.

--John
--John

Kesh
2005-Jan-21, 10:07 PM
Ion engines, on the other hand, are real... but not terribly effective. Even getting a small probe from orbit to the moon took several months and a lot of orbital finagling to make it work. (See this BBC animation (http://news.bbc.co.uk/2/hi/science/nature/4015227.stm).)

Evan
2005-Jan-21, 10:50 PM
Ion engines don't make sense for short trips like the moon. But, for a trip to Pluto it is a different matter. Thrusting at 0.01 g for four months takes you to .33% of light speed and would take a craft 34 AU in that time. Given a nuclear reactor and multiple engines this isn't impossible.

V-GER
2005-Jan-22, 01:42 AM
Would an orbital launch make sense since the probe would already have a speed of some 20000kph on orbit?
then use a combination of sun sail and ion engine.

About the sun sail: I've seen conflicting information on how it's supposed to work, some say it's propelled by the
particles from the sun and others that it accelerates by pressure created by sun light. Which is it?

Andreas
2005-Jan-22, 02:30 AM
Would an orbital launch make sense since the probe would already have a speed of some 20000kph on orbit?
then use a combination of sun sail and ion engine.
It would definitely make sense, as it's the only possible way. :wink: Ion engines can produce only a tiny fraction of the thrust required to launch from earth.

Evan
2005-Jan-22, 06:20 AM
Although photons have no rest mass they do have momentum. A solar sail gains momentum when it reflects a photon. In exchange the photon loses a bit of energy (momentum) and is then lower in frequency, very, very slightly.

eburacum45
2005-Jan-22, 03:33 PM
The illustration I have just made show a particle beam powered interstellar ship;
these are efficient because they don't have to accelerate their own fuel for leaving the solar system (they do need enough fuel to decelerate, unless there is a particle beam cannon at the destination system)
(edit: particle beams are also more efficient than lasers because the particles have mass, and therefore impart more momentum than photons)

The picture;
http://tinypic.com/1eudyv

links
http://www.transorbital.net/Library/D001_AxA.html#top
http://www.moonminer.com/Details.html
http://www.orionsarm.com/civ/Beamrider_Network.html

V-GER
2005-Jan-22, 09:14 PM
The illustration I have just made show a particle beam powered interstellar ship;
these are efficient because they don't have to accelerate their own fuel for leaving the solar system (they do need enough fuel to decelerate, unless there is a particle beam cannon at the destination system)
(edit: particle beams are also more efficient than lasers because the particles have mass, and therefore impart more momentum than photons)

Thanks!

John Dlugosz
2005-Jan-24, 08:52 PM
(edit: particle beams are also more efficient than lasers because the particles have mass, and therefore impart more momentum than photons)


Mass or no mass, a photon with momentum m will have just as much momentum as a particle with momentum m.

Photons are more "efficient" than massive particles because the specific impulse is higher.

What does efficient mean to your application? A solar-powered beam generator would have to take on mass in order to fire particles, but it would need only sunlight if firing photons.

eburacum45
2005-Jan-25, 08:57 AM
The efficiency which advocates of the particle beam method claim appears to be mostly due to spreading in a light beam.
High powered light beams are subject to spread over large distances, while particle beams are less prone to spreading.
This phenomenon in light is caused by diffraction, and is dependent on wavelength; a particle beam spreads as well, but significantly less so -(of course the extreme example, a single massive particle would not spread at all- but I wouldn't suggest attempting to propel a spacecraft by throwing a rock at it).

Quoted from the paper by Robert Forward (referenced above)

By using pellets, the fundamental physical limitation of the spread of an electromagnetic beam with increasing distance can be overcome by using a particle beam rather than a photon beam for the momentum transfer.

Another possibility is that the massive pellets could consist of fuel rather than mere propellant; a stream of frozen deuterium might be induced to produce fusion behind the beamrider.

Evan
2005-Jan-25, 04:42 PM
The problem with laser beam spread may be overcome by a phenomenon called "Relativistic self-focusing". It causes a laser beam in the terawatt level or higher to collimate to parallel rays by simply passing the beam through an "underdense plasma" such as hydrogen. What emerges is a perfectly collimated beam. Using this method it is also possible to generate a combined laser/ion beam with protons with energies as high as 56mev.

See here (http://www.osa-opn.org/view_file.cfm?doc=%24)%3C%23.J%40%20%20%0A&id=%24* %3C%3B)K%20%20%20%0A)

Eta C
2005-Jan-25, 06:19 PM
Not to nit (OK, it's a nit) but I think you mean MeV as in mega-electron volts (x10^6) as opposed to meV as in milli-electron volts (x10^-3). Nine orders of magnitude makes a small difference.

Evan
2005-Jan-25, 07:03 PM
Yep, classic nitpick:)

eburacum45
2005-Jan-25, 07:21 PM
Nicely collimated lasers would be useful, not only for propelling Starwhisps but for interstellar communications in general- just the sort of thing the Optical SETI people suggest we look for.

tofu
2005-Jan-25, 08:14 PM
One g constant acceleration will get you to about 50% of light speed in around six months. Need unobtanium for fuel though.

You're in luck, unobtanium goes for about $4.50US on ebay.

http://search.ebay.com/unobtanium

A bigger problem is using paypal.

John Dlugosz
2005-Jan-26, 06:25 AM
So, if using a particle stream or even a photon beam, how do you have more than one space craft enroute at the same time?

Evan
2005-Jan-26, 06:29 AM
More than one beam?