message 0153

• Speculations on spaceship (esp. Rider) drive and fuel
• On Riders: Shape and Armor

>From: Jo Jaquinta <jaymin@maths.tcd.ie>
>Subject: CherryhList -- M-drive
>Date: Mon, 31 May 93 9:55:33 BST

from: Onno Meyer
> Riderships have no vanes, according to _HB_ they are manta-shaped
> to accomodate the engines and still provide one very small cross-section
> to pass high-velocity chaff or dust.
> Another thing I can't believe, but it sounds nice.
	Actually the small amount of microscopic dust and such in normal
space "vacuum" is enough to produce drag when travelling at near
relativistic speed. Or so I've heard. I've never sat down and worked out
the calculations.

> > 	I don't think the carriers (or any of their ships) use an
> > inertial based system.
> I don't agree with this.
> - Water makes a nice starship fuel, if it is broken down into hydrogen
>   and oxygen. In _Rimrunner_, the Station was unable to aquire and
>   _process_ enough water in time (That's from memory, I might be wrong).
	Oh, I agree that water is the *fuel*.

> - "Raw" water can be heated (for example, by a fusion plant) and then
>   ejected as water vapor: a simple but efficient rocket engine.
	It doesn't corespond to what we see in the books. Assuming the
exhaust velocity of a ship's propellant was lightspeed the ship would
have to eject twice its own mass in propellant to boost it up to
lightspeed, under simple newtonian mechanics. Thus to carry out the
maneuvers in the books the ship would have to have started off with
about 98% of its mass as fuel. This doesn't match the picture of the
Norway on "The Company War" (I have this in a GIF on FTP if anyone wants
it) let alone descriptions of the ships.

> - In _Hellburner_, the craft lost an significant part of it's mass
>   in an instant because it fired and moved. The powerplant would 
>   consume it's fuel in a more steady manner.
	I'd say that was more the weight of the armament. Taking the
analogy of modern fighter/bombers their payload is a significant
proportion of their mass. Thus when they exhaust their arms they
become much more maneuverable.

> - In one of the Chanur books (I boldly assume it's the same technology)
>   a docking port is hit and someone said that if the "ugly" pipes
>   hadn't been outside, they would all be dead. this _might_ have been
>   fuel.
	This can be answered along with:
> - If the engines were hydrogen-consuming plants, why haul all the
>   unnecessary oxygen that is contained in the water.
	There was a long discussion on the Traveller Mailing List about
how the fuel for the hydrogen-burning powerplants of Traveller was stored.
It was always assumed to be liquid hydrogen (H2). All the physists came out of
the closet, though, and pointed out that water (H2O) was nearly as efficient
a way of storing hydrogen as in its liquified form. It also doesn't need
special storage. Methane (CH4) apparently wasn't that great but ammonia
(NH3) was better than water. Perhaps some of the Compact ships (more
technologically advanced) burn Ammonia rather than Water, assuming
fusion plants.
	Of course in Traveller only the *volume* of the ship is considered
when computing drive speed rather than *mass*. There is a much lower
%weight of hydrogen in water/methane/ammonia than pure hydrogen.

>   Further more, the _Legacy_ aquired speed in a gentle _burn_ due to
>   it's passenger, and that sounds like a "conventional" rocket.
	I'd propose it is more a case of Conventional Terminology being
applied to advances. (Like I "knit" chainmail or ask friends if they want
to "go down" a MegaTraveller "dungeon" :-)

> - Why introduce another "magic" technology without compelling reason?
	Well I hope my arguments for them not having a inertia based
system are convincing. All the "magic" required is some device that
converts heat energy (created by a conventially plausable fusion plant)
into inertial energy. A common device in SF.

				Jo