sci.physics.particle

Using a Th232 breeder reactor of U233, and a good amount of Ra226
that'll subsequently breed those Rn222 ions, should make those
continuously available ions of Rn222 rather interesting, as offering
an extremely fast exit velocity of such hefty radon ions that can be
focused and/or pumped into a tight beam, much like a laser cannon.

Achieving an ion exit velocity of 0.2'c' or slightly better seems
doable, even though our firing tubes may seem rather long for our
interstellar craft that'll demand all the exit velocity that can be
forced upon those ions. Of course, once getting ourselves past the
interstellar L1 is when we'd have to start thinking of ion
retrothrust, unless overshooting the mark isn't worrisome.
. - 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 oninterstellartreks, 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'sL1). 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 intointerstellarspace, and especially upon getting
> this craft past our nearestinterstellarL1, 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).
> . - Brad Guth