Prev: Re: [SG] large games Next: Stone Mountain Figs

# re: Thruster pushes was re: FB2 preview

From: Thomas Anderson <thomas.anderson@u...>
Date: Tue, 9 Mar 1999 20:23:35 +0000 (GMT)
Subject: re: Thruster pushes was re: FB2 preview
``````
On Tue, 9 Mar 1999, Wasserman, Kurt wrote:

> No offense but either of those are really good solutions.

i assume kurt intended to put an 'n' on the front of that 'either' ...

> A) really tears a lot of the fun out of maneuvering and B) is just
weird.
> <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>

well, if the main drive produces an exhaust which can then be vented
through any one of a number of drive ports, you'd have a justification:
if
you wanted a push, you'd need to divert thrust from the main drive.
likewise for reverse thrust. think of the reverse thrust buckets some
big
aircraft have to use for braking on landing.

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

well, there's one main drive and twenty thrusters, but the main drive is
much more than 20 times bigger than a thruster ...

<physics-n-maths>

it's fairly straightforward to figure out possible values for the size
of
a move unit, turn and thrust point based on simple mechanics - the
1000km-15min-1m/s2 combination is, i think, the most widely accepted.
it's
even possible to rationalise the slight deviation from newtonian
mechanics
which has all of a ship's thrust take effect at the start the turn in
which it was made: we say ships use a short, powerful burst type of
drive,
which only fires at the start of the turn. if the burst is 1/10th the
length of the turn (100s, 1m40s), then it works out that one thrust
point
is 10 m/s2, which is 1 g.

however, it's a bit harder to analyse rotation. if we stuck to real
physics, then the time taken for a ship to do a particular rotation is
not
proportional to the size of the rotation, but to the square root of the
size. i think.

this wouldn't be all that hard to factor in to FT, actually (i think).
if
you spend T thrust points on rotation, you can rotate up to T*T course
points.

here's a quick table:

Thrust	Change

1	1
2	4
3	9

this isn't very pretty, is it. curses. you might want to say that you
can
do (T*T)/2 or (T*T)/4 instead, though.

anyway, if we work this in, then the acceleration needed (if split into
two and applied at the ends of the ship in opposite directions, a bit
like
certain types of lawn sprinkler) to get one maneuver point is

a	=	(pi / 9) * r / t^2

where r is the length of the ship and t is the time used for turning.
let's say this is one-tenth of a turn (as i have suggested for the main
drive burn). if we assume a ship length of 100m, and a turn of 1000s
(16m40s), then a comes out as about one three-thousandth of a g. given
that a main drive point in the same scale is about 1 g, you see why
thruster pushes are not realistic.

qed, i believe ...

</physics-n-maths>

> Each propulsion
> subsystem would and should be able to act independently.  Also,
wouldn't a
> 1-G acceleration drive eventually propel a ship towards light speed,
just
> slower than a 10-G drive?

yes. any acceleration will reach any speed (pace Einstein) given long
enough.

> I find it logical (and pleasing) to imagine a ship boosting itself in
one
> direction then whipping around to fire off the mains.  It "feels"
right.
> And, since this "Thruster Effect"(tm) is common to all ships using
vector
> movement, this isn't a game unbalancing problem.

that's certainly true. many games have thruster pushes, and no-one seems
to mind very much.

Tom
``````

 Prev: Re: [SG] large games Next: Stone Mountain Figs