Re: Time/Distance scale for FT (sort of related top safe speed, et al)

On Wed, 22 Dec 1999, Laserlight wrote:

> >I look at the canon FT universe as rather medium-tech I suppose
> (compared to
> >most popular science fiction media depictions) and therefore assume
> >relatively short weapon range, which leads to the following:
> 
> The usual assumption is T = 15min (to tie in with one Dirtside turn)
> and D = 1000km (because it's neat).

this is indeed the hallowed consensus scale, based on what feels right.

i have heard it suggested that the rules for orbits in MT can be used to
deduce a scale, but i know little about this.

> To the best of my knowledge, I was first to propose the T = 7.5 min,
> D= 1000km, which also fits 2 to 1 with DS2 and lets you assume 1
> thrust point = 1 gee.

i'm not entirely sure that's the case.

1 mu	=	1000 km
	=	1e6 m

1 tu	=	7.5 min
	=	450 s

speed 1 =	1 mu / tu 
	=	1e6 m / 450 s

dv	=	a * dt
a	=	dv / dt
	=	(1e6 / 450) / 450
	=~	5 m/s^2

under these assumptions, one thrust point is 5 m/s^2, which is about
half a gee.

unless, of course (a) you're using a more sophisticated analysis of
motion
than i am (b) i've forgotten a factor of two, which i am prone to doing.

incidentally, with 1 tu = 15 min, you get 1 th = 1.2 m/s^2; if you use 1
tu = 16 min 40 s (ie 1000s), you get 1 th = 1.0 m/s^2.

i'd add that this all assumes continuous thrust over the turn, which is
not how it works in FT, as you will tell from the fact that if you go
from
a standing start to a speed of 1 mu/tu in a turn, you cover 1 mu doing
it;
this indicates that all the acceleration happens at the very start of
the
turn. this leads to a model of thrust where the engine makes a short,
powerful burn for a few seconds, following which the ship coasts for
several minutes. if 1 turn is 16m40s, and if 1m40 (100 s, one-tenth of
the
turn) is spent burning, then 1 th = 1 gee *while the drives are on*.

> Keith Watt, whose site you should memorize if you want realistic
> numbers, says D = 80km (or 40km is you distribute acceleration over a
> turn as Real physics as opposed to Full Thrust physics) and he goes
> into all the reasons why:  www.exodusproject.com .

more precisely:

http://www.exodusproject.com/FTExodus.htm

the reasoning is based on the thrust you can get from a DT fusion
engine,
alongside fuel consumption constraints; realism, you know the deal. i
don't hold with it myself :).

tom