RE: FT: FB2 Preview - Obi Wan Tuffley (Thruster pushes)

On Tue, 9 Mar 1999, Wasserman, Kurt wrote:

> <G>  How would you rationalize not having the ability to turn on the
"side
> engines" when the "back engines" are running?  I would refuse delivery
on a
> spaceship that couldn't maneuver and propel at the same time... <G>

> I am not sure about the physics of space travel.  Hell, I barely
remember my
> college physics, so bear with me... <G>

In my games, I don't allow thruster pushes at all.  The reason is that
the
main drives have to be huge to produce even 0.01g.  There's no way you
could afford the mass (or fuel) for three more "thrusters" which are
essentially main drives.  If you want to use physics to justify a rule
(and I realize not everyone does), then thruster pushes which are any
significant fraction of the main drive thrust are totally unrealistic.
"Maneuvering thrusters" (which I'm sure were the inspiration for this
rule) provide tiny course-correction bursts which are effective only
when
the ship's velocity is near zero (e.g., docking).

Of course, if your engines produce huge thrust, have a tiny mass, and
burn
no fuel, then there's no reason not to use thruster pushes, you just
can't
use real physics to justify it.  And since the vector movement is
supposed
to model (approximately) real physics, that's where I think the system
breaks down.  

There's more info on my FT engines page if anyone is interested, the URL
is http://www.erols.com/kwatt/SolarThrust.

> If one ignores gravitational effects of near masses,	isn't it true
that
> every little push on a mass contributes to its velocity and
acceleration?
> Aren't 10 engines that can exert 1 foot/pound of thrust equal to one
engine
> exerting 10 ft/lbs in zero-G?  If that is the case, then what is the
> difference when it comes to thrusters and main drives? 

That's right and that's my point exactly.  Under the vector rules as
written, every ship has an exhaust nozzle about half the size of their
main nozzle on the front, port, and starboard side.  Kind of
funny-looking.. <g> And as I said, the fuel and mass required just for
engines and thrusters would be huge.

There's no real reason to have thruster pushes, and they're unrealistic,
so my thoughts are why use them - especially when there's the problem
that's being discussed present.

Just my opinion..

Keith

kwatt@astro.umd.edu
Univ. of Maryland Astronomy