Re: starship-design: Genuine STR question

[Johnny Thunderbird <jthunderbird@nternet.com>]

Hmm,

I got quite a range of responses. I guess the thing
to do is speak to the hardest, that it isn't
beneficial to accelerate exhaust particles to
relativistic velocity. The implication is that
efficiency is lost in the effort to ionize and boost
the jet particles. Since efficiency is a thermodynamic
term, the only possible meaning for a loss in efficiency
of an accelerative heat engine is a hotter spaceship.

To keep cool you have to radiate the difference
coming from a loss in engine efficiency, radially,
as photons. Radiating to the rear is out of the question,
it's bright and hot back there, and you'd have to find
a way to tunnel the photons into your own jet to cheat
thermodynamics, by avoiding the penalty for your
inefficiency.

I won't advocate inefficiency, certainly. The thermal
efficiency of accelerator designs is no boasting matter.
I believe it may be possible to drastically alter this
picture by a design approach which conceives the
accelerator as prime mover for the mass complex making
up the starship. With such incentive, particle
accelerators could become paragons of thermal efficiency.


The bulk, which is the spatial extension,
from the residence quarters, of the inertial framework
of the starship, I would expect to be a very low density
structure, composed largely of fields and dynamic plasmas.
In other words the rigid, massive element of the starship
structure will be very small compared to the volume of
the field structures.

When you take into account that a closed toroidal magnetic
field can become massive, in all the ways that count, as
you feed it the juice, total mass of the vessel has become
an adjustable quantity. That one's too hard to see. Let's
pack the magnetic field with plasma, or simpler, with just
homopolar particles and make it a storage ring. There, you
can see that the inertial mass of the ring increases, as
you speed up the circling particles so their speed difference
from C becomes small. ( Yeah, I know heaviness is not
what we want when we accelerate our ship, we like
lightness. Just hold on. )

I wanted to show the inertial mass of the ship complex can
be adjusted. When you start an interstellar journey, you are
deep in a gravity well, but you have the energy advantage
of being close to the system's primary, namely the Sun. For
those who want to scale up to use it, that's an arbitrary
amount of power available. If the mass of your ship is
adjustable, as I just showed for the case of the storage
ring which gains weight, it stands to reason you would want
it to be heaviest at the beginning of your journey, where
you could put impressive concentrations of energy into
getting that rascal to move.

So you take off with a vehicle complex that's really heavy.
In the course of acceleration, you make use of some of the
energy stored within this cycling of particles. Your total
vehicle mass decreases; since most of this inertial mass
was conjured up artificially by you before you left the
home system, the relative importance of the actual ship
mass decreases, so you can take a lot of luggage. Or an
iceburg, as some of us like.

Now the progressive decrease in the intertial mass of the
ship complex as the journey continues, makes whatever
kind of oars you're using to accelerate the ship become
more effective at a later time than an earlier time. As
we get lighter, we're easier to push. That makes me
propose that the storage ring mechanism, in conjunction
with whatever type of stardrive you are using, is acting
as a transducer converting rotational energy to linear
acceleration. It's a fairly efficient way to store an
arbitrary amount of energy, one of a family of energy
storage devices using magnetic fields which are all
fiendishly efficient.

That's why I wasn't overly concerned with the thermal
efficiency of the particle accelerator type main mover,
when compared to the crucial need to minimize the amount
of reaction mass required per delta-V. I knew that
reaction energy could be supplemented by stored energy,
that there are ways to wind up a ship before you let it
go.

There may be imprecision in considering relativistic
particles as manifesting an actual increase in mass,
yet an increase in the resistance of the particles to
acceleration is saying exactly the same thing. When you
pour energy into a box and get work out, it's a machine;
whatever amount of energy you put into making your jet
fly faster astern, will be reflected into the coordinate
system of your ship as an accelerative force.

I would argue in general that a relativistic jet is
optimal for transport, and that this is true whether
or not the relativistic bonus is paid, which I was
counting on to reduce the amount of reaction mass to
take with the ship. I suppose someone may take issue,
similarly, with the concept that the synchrotron or
storage ring, in this posting, results in an overall
increase of inertial mass, as the particles reach
relativistic speeds. Fine, still you'll have fun
trying to think up a more useful battery for use on
a large scale.

When I was a kid, I grew up thinking in terms of
relativistic mass increase; now I find this image
is out of fashion, but I have a hard time accepting
you can do work to speed up your jet, and not have
it directly reflected as accelerative force on your
ship.

Meditatively,
Johnny Thunderbird
http://impact-enterprises.hypermart.net/lowercase