This is rather odd: The Ion Interstellar Spaceship, from Hell to
Sirius
"Feb 11 by BradGuth - 11 messages - 6 authors"

So, where exactly are these other 5 authors hiding out, if not posting
into any of the following groups?

sci.space.history, sci.space.policy, sci.space.shuttle, alt.astronomy,
sci.physics.particle

Are the Usenet moderator bots hard at work (removing whatever they
don't like), or what?
.. - 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