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Re: starship-design: Genuine STR question


Johnny, in a word, yes.

----- Original Message -----
From: Johnny Thunderbird <jthunderbird@nternet.com>
To: starship-design <starship-design@lists.uoregon.edu>
Sent: Monday, February 22, 1999 11:32 AM
Subject: starship-design: Genuine STR question

>I want to make sure my naive conception of
>special relativity is hunkey-dory with a more
>intensive understanding, with regard to reaction
>Your ship has a comfortable supply of reaction
>mass, and adequate energy reserves. You determine
>your reaction mass will be optimally used if it is
>fully ionized, and accelerated into the relativistic
>realm of velocities with a linear accelerator you
>have handy on board. ( The electrons are no
>problem, for they are boosted to relativistic
>velocities quite easily with electrostatics. )
>In the coordinate frame of the ship, still dawdling
>within the Newtonian velocity space, your linac
>is boosting the particles which comprise your
>reaction mass into the relativistic velocity realm.
>These particles approach the asymptotic limit C;
>as they do, the energy increment you must supply
>to produce further acceleration grows exponentially.
>Your labor is not unrewarded, for the "extra" energy
>( departure from linear Newtonian term ) you have
>placed into accelerating these stubborn particles,
>shows up as an increase of their mass. Your inertial
>transfer is a function of their new equivalent mass,
>not of their rest mass. In short, your overall reaction
>engine is boosted by the multiplier amounting to the
>relativistic increase in mass you impart to your ejecta.
>The net effect of this consideration, is to reduce the
>amount of reaction mass required for a given acceleration.
>( Strictly, you traded it for energy, but we can assume
>ample energy, for the intro paragraph says so! ) The
>big worry is whether enough reaction mass is available,
>which is in short supply in fairly empty space. There are
>tricks to come up with energy, it's fairly portable
>compared to fuel.
>Do you feel this logic holds, with respect to the inertial
>exchange of the reaction engine receiving the benefits of
>the relativistic mass boost? Conservation is preserved on
>the mass-energy product, which makes it seem likely to
>me. Is not the corollary, that a relativistic jet becomes an
>optimization of the reaction engine, and for really fast
>ships we should be thinking in terms of high flux particle
>accelerators in every case, to reduce the amount of
>reaction mass required for the jet in Newtonian mode?
>Just trying to clear my thoughts on this topic.
>Johnny Thunderbird
The real problem for relativistic starships is the energy of the reactions
powering them, and the systems handling those energies can only handle so
much... As power requirements [and jet-speed] go up, the possible thrust
goes down. Realistic fusion rockets would run at very low thrust levels,
unless they used fusion pulse drives, because of the extreme power levels
involved. A small percentage heat-loss at the thousand terawatt level would
easily vaporise the engine, hence why you don't run that high. Reactions
that involve "combustion" away from the drive, confined by fields, are the
highest thrust systems - pulse drives being the most studied.

Personally I think truly advanced spacedrives would involve beamed power or