sci.physics.particle

Big time ion thrust is what'll get our future probes and eventually
ourselves to/from those distant places.

Even Pb gas ions are usable, although requiring a good amount of
energy for converting whatever Pb208(lead) into a gas of ions to start
with may be more or less counter productive, especially when Rn222
ions can be derived from the decay of Ra226 as is without the need of
introducing extra energy, and even the breeder cache of Ra226 that's
pumped along by a Th232 fueled reactor may in fact become a darn good
resource of energy, as well as offering a rather good breeder
alternative at maximizing those various decay processes.

At least Robert Clark isn't another one of those typical anti-think-
tank naysayers in charge of banishing any such bulk use of ions for
thrust, and of notions for storing enough of such ions (such as
LRn222) for creating a fairly substantial amount or volume sustained
thrust if given the necessary energy for accelerating such ions is
part of the package deal. Of course, I've had to correct a few of
those usual robo-moderated words as having been run together, so that
a normal key word search would even turn up this "Stored ionized gas
for ion drives" contribution of his, stating that such ion exhaust/
exit shouldn't have any difficulties in obtaining 10,000 km/s.
Whereas I'm thinking the 16.7e3 km/s of the natural 5.6 MeV radium
alpha/ion particle itself is perhaps not half of what a electrostatic
boosted and magnetic focused Rn222 ion could actually muster,
therefore its potential exit velocity of 34,000 km/s (that's better
than 0.1'c') seems entirely doable, and of utilizing the much greater
mass of those extremely active Rn222 ions should by rights benefit
this thrust potential without ignoring any of those laws of physics.

http://groups.google.com/group/sci.space.policy/browse_frm/thread/1097aea2c8e51f5b/c746ba78d45e7e1b?hl=en&lnk=st&q=ion+radium#c746ba78d45e7e1b
From: Robert Clark
Date: Sep 28 2007, 4:53 pm
Subject: Stored ionized gas for ion drives.
To: sci.space.policy, sci.astro, sci.physics, sci.physics.relativity,
sci.physics.fusion

On Sep 20, 4:47 pm, Robert Clark wrote:
> This page gives a formula for the exhaust speed of an ion engine in
> terms of the charge on the ions and the voltage driving the ion flow:
>
> Ion thruster.
http://en.wikipedia.org/wiki/Ion_thruster#Energy_usage
>
> The exhaust speed increases with the charge on the ions and decreases
> with their mass. You would think then that a light gas like hydrogen
> would be ideal since heavier gases even when fully ionized would still
> contain approximately equal numbers of neutrons as protons which would
> not contribute to the charge but would approximately double the mass.
>
> Yet it is the heavier gases like cesium and more recently xenon that
> are used. The explanation is that of the energy it takes to ionize the
> gas used as fuel. The figure on this page shows the energy to ionize a
> light gas such as hydrogen is relatively high compared to the heavier
> gases:
>
> Ionization Energies.
> http://hyperphysics.phy-astr.gsu.edu/hbase/chemical/ionize.html
>
> The figure gives the energy per mole which is high in itself. It is
> even worse when you consider this on a per mass basis since the mass
> amount of hydrogen would be so small compared to the amount of energy
> needed to ionize it.
>
> So could we instead store the hydrogen or some other light gas
> already in ionized form so we would not have to supply power to ionize
> the gas, only to accelerate it?
>
> If you used ionized hydrogen, so you would be accelerating protons,
> then using 6 x 10^18 protons to make one 1 Coulomb, and a mass of 1.6
> x 10^-27 kg for a proton, and V representing the voltage in volts, the
> speed on the ions (protons) would be about (10^4)sqrt(2*V) in meters/
> second.
>
> If we made the voltage be 5,000 V we would get 1,000,000 m/s speed
> much higher than any currention drive. Also, there are power supplies
> that convert low voltage high amperage power into high voltage, low
> amperage power, even up to 500,000 V. Then we could get 10,000,000
> m/s = 10,000 km/s exhaust speed.
>
> The question is could we get light weight means of storing large
> amounts of ionized gas? Note that is this for space based propulsion
> not launch from Earth. You would have a possibly large energy
> generating station that remained in low Earth orbit to supply the
> power to ionize the gas once the spacecraft was placed in orbit. The
> power generator would be left behind in orbit. Then the volume of the
> gas container could be large to keep the density of the gas low. This
> would allow very thin container walls. Note the low density would also
> allow the electrostatic repulsion of the positively charged ions to be
> more easily constrained.
>
> A possible problem though is the charged ions contacting the walls
> could lead to a loss of ionization. You might be able to use a low
> level magnetic field to prevent the ions contacting the walls. Low
> density of the gas would insure the strength of the magnetic field
> required would be low. It might even be accomplished by thin permanent
> magnets so you would not need to use extra power.
>
> Some questions: what would be the electrostatic pressure produced by
> a low density highly ionized gas? What strength magnetic field would
> you need to contain it?
>
> Note that with an exhaust speed of say 10,000 km/s, by the rocket
> equation we could get the rocket itself up to relativistic speeds with
> acceptable mass ratios.
>
> Then this would provide a means of testing relativistic effects on
> macroscopic bodies.
> Bob Clark
>
>
> There is a lot of research on containing charged particles of only
> one charge, that is, all positive or all negative, because of fusion
> research. These are called "non-neutral" plasmas.
>
> There is a limit on the number of charged particles you can contain
> in a magnetic trap based on the strength of the magnetic field called
> the "Brillouin limit."
>
> However, some researchers have argued it is possible to exceed
> this limit:
>
> Confinement Of PureIonPlasma In A Cylindrical Current Sheet.
> http://www.pppl.gov/pub_report//2000/PPPL-3403.pdf
> Bob Clark

Perhaps if those pesky MIB allow, others might care to ponder and
subsequently offer their best swag(scientific wild ass guess) as to
our getting the most out of accomplishing large scale ion thrust, not
that Ra226->Rn222 need be the one and only ion alternative. However,
with that nearby and gamma saturated moon of ours might actually
suggest there's a good amount of lunar Thorium and Radium to behold
(by night there should be LRn222 available), and you'd think Radium at
becoming worth $1M/gram seems entirely worthy of our going after,
perhaps even more so worthy than whatever 3He. (why the hell not
accomplish extracting Th232, Ra226, LRn222 and 3He, as well as
collecting Sodium and making local O2 in the process?)

BTW, for some odd reason this topic has had contributions by 6 authors
(including myself), but oddly none of those other than mine seems to
have be retained by the all-knowing command of those in charge of this
supposed public Usenet.
. - Brad Guth


On Feb 7, 10:40 am, BradGuth wrote:
> What if instead of our going with whatever's small, extremely cheap,
> fast and rad-hard robotic, what if going with larger is nearly always
> better?
>
> Perhaps this new and improved topic of "Building Spaceships" for
> accommodating us frail humans on interstellar treks, and of those
> multi generation habitat spacecraft being extensively ion thrusted,
> along with the wizardly help of William Mook and those few of us
> unafraid of whatever's out there, as such may be a little easier said
> than done, not to mention folks having to deal with my dyslexic
> encryption and frequent typos that can't always manage to keep those
> numbers or terminology half straight.
>
> Perhaps such a large scale ion thrusted spacecraft isn't quite as
> insurmountable as we've been told, and it's not that a pair or quad
> worth of substantial LRBs would not have to help get this rather
> substantial package off the pad (in modules if need be, and assembled
> at the moon's L1). However, upon launch and of once reaching the cool
> upper most atmosphere is where the potential of ion thrusting could
> start to contribute w/o Radon saturating Earth in the process, and
> obviously from whatever LEO point onward is where the real potential
> of ion thrust becomes impressive, especially since this method of
> electro-rocket thrust can be sustained for as long as the given cache
> of ions and electrical energy holds out. (with radium->radon there's a
> failsafe worth of 1600+ years before reaching half-life, so there's
> never a total lack of those Rn222 alpha/ions, and there's even some
> electron energy derived from the Radium->Rn breeder reactor)
>
> Given a sufficient cache of hefty ions and a sufficient onboard supply
> of electron energy for artificially accelerating and redirecting those
> ions into a narrow exit trajectory, and if this thrust is the direct
> result of a given ion flow rate or mass of whatever ion particles per
> second times the exit velocity squared, as then where's the
> insurmountable problem, other than your not standing anywhere behind
> those ion thrusters.
>
> Radon just so happens to make for a very good cache of substantially
> massive ions that are already quite active/reactive and supposedly
> going places as is, at roughly 1.63e7 m/sec. Liquid Radon or LRn222
> represents a nifty fluid cache of a easily stored concentration of
> Radon gas (though because of its short half-life it's still very much
> one of those use it or lose it substances, with possibly an extended
> life within a near solid 0 K storage), of which I believe this cache
> of Rn222 can be electrically induced or excited into exiting this ion
> thruster at a velocity as great as 0.1'c' (perhaps an exit velocity of
> 0.5'c' is technically doable if we're talking about a radon pumped
> laser cannon).
>
> Similar to: http://en.wikipedia.org/wiki/Ion_engines,http://eprints.soton.ac.uk/47966/01/paperColettiMPD.pdf
> Our lord all-knowing (aka World FactBook) Mook says; "Check it out"
> Here is how much thrust a rocket engine produces;
> F = mdot * Ve
> where mdot = mass flow rate, as kg/sec
> Ve = exhaust speed m/sec
> F = force (newtons) kg m/sec/sec
>
> Here is how much power a rocket engine's jet produces
> P = 1/2 * mdot * Ve^2
> That is, the rate at which energy must be added to the exhaust jet is
> the kinetic energy of the parts.
> - - - -
>
> Of course this is not about any Mook passive alpha particle directing
> application, instead taking efficiency of the overall electrical and
> ion tossing system into account (such as thermal energy losses) adds
> to this existing amount of ion worth via applied electrical and
> magnetic energy that'll focus and accelerate those ions. So, it is not
> nearly as simple to express as one as Mook might suggest.
>
> However, at the notion of our getting rid of this initial tonne worth
> of our liquid cache of LRn222, at the ion mass flow rate of 1 kg/s,
> whereas the kinetic power or energy worth of thrust supposedly
> becomes:
>
> If the 1 kg/s flow of Rn ions and the exit Ve were made as great as
> 10%'c' = 3e7 m/s
>
> P = .5 * 9e14 = 4.5e14 kgf
>
> At utilizing this ion exit velocity of 0.1'c' (3e7 m/s)
> A metric tonne of LRn that'll essentially become just plain old Rn gas
> of pure Rn222 ions, at using up one kg/s = 1000 seconds worth of
> creating 4.5e14 kgf, of which this substance would push a 4.5e12 kg
> (4.5 gigatonne) spacecraft at 100 gee in relationship to the gravity
> at the surface of Earth.
>
> At the more realistic ion exit velocity of 1% light speed is
> 0.01'c' (3e6 m/s)
> A metric tonne of LRn that'll essentially become just plain old Rn gas
> of pure Rn222 ions, at using one kg/s = 1000 seconds worth of 4.5e12
> kgf, of which would push a 4.5e10 kg (45 megatonne) spacecraft at 100
> gee in relationship to gravity at the surface of Earth.
>
> Of course the 45 megatonne spacecraft isn't hardly any more likely
> than human DNA or whatever spacecraft structurally surviving 100 gee.
>
> So, to start off with we'd likely have ourselves a whole lot smaller
> than 45 megatonne spacecraft, such as perhaps only as great as 4.5
> megatonnes that'll exit away from Earth at perhaps as great as 10 gee,
> then once 10r (63,730 km and just 1% Earth gravity) is reached,
> whereas this is when the ion exit velocity could be safely punched up
> from 0.001'c' to 0.01'c', and eventually the maximum of 0.1'c' could
> be applied to as little as using a gram of Rn222 per second, because
> at 0.1'c' or better exit velocity is where you really do not require
> all that much mass flow per second.
>
> 0.1% light speed is 0.001'c' = 3e5 m/s
>
> 1 kg/sec at 3e5 m/s = .5 * 9e10 = 4.5e10 kgf
>
> 4.5e10 kgf would push a 4.5e6 tonne spacecraft along at 10 gee
>
> Using a gram/sec:
> 4.5e7 kgf would push a 4.5e6 tonne spacecraft along at 0.1 gee
>
> I believe that 1000 seconds of 10 gee acceleration is worth 78.4 km/s,
> though of course we'd be past the 10r of Earth within the first 600
> seconds, and thereby able to ion whiz past that 78.4 km/s mark like it
> was standing still.
>
> This next part is often where my math takes yet another nose dive, but
> since I do not have the fly-by-rocket software and none others that
> claim as always being all-knowing are seldom willing to share, is why
> I'll just have to make do, especially since even the warm and fuzzy
> likes of Mook always takes the lowest road possible in order diminish
> and/or disqualify whatever isn't of his idea to start off with,
> excluding just enough of the good stuff in order to foil any further
> thought process.
>
> The required energy for a given thousand seconds worth of accelerating
> those Rn222 ions up to 3e5 m/s isn't exactly insignificant, demanding
> perhaps at least 245.2 GW.h (8.826 e14 J) for accommodating all 16.7
> minutes worth of ion thrust. However, due to the overall efficiency
> of this energy transfer into accelerating those Rn ions is why it'll
> more than likely demand somewhat greater energy for accomplishing this
> task of tossing out the entire tonne worth those Rn222 alpha ions at
> the rate of one kg/s, even if that's initially accomplished at this
> minimal 0.001"c". However, since the existing Rn alpha particle
> velocity is already self motivated at 1.6e7 m/s(.054'c'), perhaps
> along with given another 5.6 MeV boost is where the required energy
> can be limited as to whatever's necessary for accomplishing a good
> exit focus or creating that laser cannon like beam, in which case the
> required ion thruster energy could become relatively minimal for
> accomplishing an impressive exit ion velocity of 3.26e7 m/s.
>
> At times this spacecraft is going to require a hole lot more
> electrical energy than any cache of Radium to Radon reactor could
> manage at 32 kw/Ra tonne, or even 320 kw/breeder Ra tonne. However,
> at a gross spacecraft mass of 4.5e6 tonnes, there's no problem with
> incorporating an h2o2/aluminum fuel cell of 100 GW.h capacity, or
> accommodating whatever Lithium nanotube ion battery storage, nuclear
> reactors or fusion alternatives.
>
> Once trekking off into interstellar space, and especially upon getting
> this craft past our nearest interstellar L1, and of the other gravity
> pulling us towards the likes of the relatively massive Sirius star/
> solar system that we're already in blueshift as headed towards Sirius,
> as this is when as little as a mdot microgram/sec of Rn222 at the exit
> velocity of 0.2'c' would be more than sufficient ion thrust for
> continually accelerating this 4.5e6 tonne spacecraft towards the
> gravity pull of Sirius.
>
> For a one microgram/sec of Rn222 mdot at 0.2'c' example:
> P = .5e-9 * 3.6e15 = 1.5e6 kgf (1,500 tonnes/s of thrust, or in this
> case 0.000333 gee)
>
> The next problem gets down to the business of continually building up
> another cache of LRn from the Ra->Rn breeder reactor while on the fly,
> on behalf of that pesky matter of our having to ion retrothrust long
> before overshooting the intended target. At 4.5e9 kg, stopping this
> sucker that's by now going like a bat out of hell (possibly having
> reached 0.1'c') is going to take some doings. Of course, there would
> be generations of new and improved minds onboard in order to figure
> most of this out before arriving into the Sirius star/solar system,
> not to mention whatever could have been transmitted from Earth over
> the past century.
>
> BTW, at this point of topic argument sake, this mission to Sirius is a
> one way ticket to ride, with absolutely no travel package guaranties
> or ticket refunds allowed, because we may not be able to sufficiently
> retrothrust in order to save any of those brave souls, and a purely
> gravity-well trajectory turn-around or that of sufficiently
> aerobraking is at best iffy, although a substantial solar wind
> parachute as brake might eventually work. Also, recall the sheer size
> of these required ion thrust nacelles, as being somewhat Star Trek
> Enterprise like, and for all we know in need of those lithium crystals
> or perhaps lithium nanotubes as part of their function (after all, any
> good science fiction uses the regular laws of physics and the best
> available science, and for all we know lithium could still be part of
> it).
> . -BradGuth