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[GZG] [FT] Vectoring Kra'Vak

From: Robert N Bryett <rbryett@m...>
Date: Sat, 24 Dec 2005 17:22:16 +1100
Subject: [GZG] [FT] Vectoring Kra'Vak

 >>>> I don't like that idea. At any sort of velocities which it is  
reasonable to assume FT ships are moving, it should be much easier to  
turn a ship on its own axis than to alter its vector. <<<<

You might be confusing velocity, speed and acceleration and comparing  
apples and oranges. In physics velocity is not a synonym for speed,  
and acceleration is not a synonym for going faster. Velocity and  
acceleration are *both* vectors and imply both size and direction.  
Speeding up, slowing down, changing course *and* rotating a spaceship  
all involve velocity changes, and all involve accelerating the mass  
of the ship. At non-relativistic velocities the ship's ability to do  
this is not affected by the speed at which it happens to be moving  
when it starts to accelerate.

The mass of a spaceship must be accelerated, whether to change the  
overall velocity of the ship, or to spin the ship round its axis. In  
rotation this is complicated by the fact that the ship's Moment Of  
Inertia (MOI is the rotational analogue of mass in linear motion) is  
affected not only by the total mass, but also by the distribution of  
that mass round the rotational axis. Roughly speaking, a long  
cylindrical spaceship, or worse yet a dumbbell-shaped one, would  
require more force to rotate it round an axis normal to its long axis  
than a short stubby one of the same mass. FT doesn't model this  
(thankfully), though Attack Vector does.

Assuming a spaceship using today's physics, the time required to, for  
example, rotate 180 degrees from one steady heading to another would  
be determined by the MOI of the ship and the rotational acceleration  
imparted by the manoeuvring system, just as the ship's ability to  
accelerate in a straight line would be determined by its mass and the  
thrust of its main propulsion system. Present-day spacecraft like the  
Space Shuttle have lower thrust manoeuvring thrusters than their  
propulsion rockets, not so much because it is somehow "easier" to  
accelerate the mass of the vehicle in rotation than in a straight  
line, as because much lower accelerations are required. My physics is  
*way* too rusty to crunch the numbers, so I'll leave that exercise  
for younger minds... :)

However the Thrust Rating in FT clearly does not simply represent  
thrust, so much as ability to accelerate in one turn. After all it is  
possible to design a battlecruiser or a frigate with Thrust 6. Each  
would be able to change its velocity by the same number of MUs per  
turn, but the greater mass of the battlecruiser would presumably  
require more thrust to do it. The difficult part is deciding on the  
equivalency of a Thrust Points (TPs) used for linear or rotational  

I think the question is whether an FT player feels it is reasonable  
for a 20,000 tonne, high MOI behemoth like a Von Tegetthoff SD	
(Thrust 2 from FB1) to be able to do a 180 to port followed by a 180  
to starboard (two TPs) in one turn of game time. Or to put it another  
way, is it reasonable for for the SD to start from a steady heading,  
and spin to any new steady heading, in the same time (half a turn) it  
would take the same ship to change its overall velocity by one MU?

 >>>> I don't know what the effect on play balance of any of these  
systems is; I am thinking more from the physics of the issue. I would  
hate to see a change made for the sake of play balance which I would  
think is a big step away from realism (SF realism at least) when it  
could also be handled by ship design or points values. <<<<

My extended blather above is intended to show why I don't think  
"realistic physics" is decisive either way. The effect of the  
existing vector movement rules is that the Von Tegetthoff can rotate  
from one heading to any other in half a game turn. If the rule were  
changed to one TP per 60 degree segment, the effect would be that the  
lumbering, armoured monster would need 1.5 game turns to do it. There  
isn't really any way to say that one is more realistic than the  
other, since one could argue the time/thruster power/hull strength/ 
acceleration compensator PSB to suit.

Best regards, Robert Bryett
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