sci.physics.particle

Come on folks, this topic needs as many of those Google/NOVA Usenet
gold stars as you can muster.

Ion thrusting isn't even my idea, it just needs to get a whole lot
larger and having a greater cache of those spare/surplus ions to focus
and accelerate to at least 0.1'c'.

Why not a gigaVolt or even a teraVolt grid differential potential, or
that of a laser cannon pumped version of using those Rn222 ions as the
laser plasma gas?
. - Brad Guth


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).
> . - Brad Guth