scales and drives was Re: [FTFB] Not ships, exactally. . .

[time to roll the subject field, i feel]

On Sat, 13 Feb 1999, John M. Atkinson wrote:

> Keith Watt wrote:
> 
> > If you use realistic engines (specifically for this case a
> > deuterium-tritium fusion drive, which seems to work best), Thrust 1
-is-
> > 0.01g.  Of course, the distance scale then works out to be 1 MU = 40
km,
> > which is smaller than a lot of people want (even if it is
realistic).
> > Just food for thought...
> 
> I go with the reactionless drives in the background

a photon drive is within the understanding of modern physics, and pretty
much within the reach of modern engineering, too. it doesn't use extra
reaction mass at all. buzz aldrin and jonh barnes suggest in "Encounter
with Tiber" that such drives could be powered by zero-point energy
recovered through the Casimir effect (which is some freaked-up quantum
physics thing which sort of makes sense) - thus, not only would you not
need reaction mass, you'd not need fuel either.

> I strongly prefer
> to have space travel be feasible as a commercial enterprise without
> generation ships. 

well, even at 0.01g, you only need to get from the planet to the jump
point, so you wouldn't need generation ships for interstellar travel.
still, i get your point.

> I havn't worked out the exact scales I'm using, but 1
> turn is going to be fairly short.  Perhaps a minute, which would give
me
> 1 Thrust is 1G and 1MU is 1000km.

eh?

thrust 1 for 1 turn gives speed 1. if thrust 1 is 10 m/s2 and 1 turn is
60 
seconds, then final velocity is 600 m/s. 600 m/s over 60 s is 36000 m.
that's 36 km, not 1000. or have i just paid the price for forgetting to
eat today?

if the turn were 5 mins long, then 1 thrust = 10 m/s2 would get you 1 mu
= 
900 km, which is close. if the turn were 5 minutes, 15 seconds and 260 
milliseconds, i believe that we'd be bang on. or we could have 1 thrust
=
11.11 m/s2, 1 turn = 5 mins and 1 mu = 1000 km.

possibly the best option is 1 turn = 10 mins, 1 mu = 1000 km and 1
thrust
= 2.78 m/s2 (about 1/4 g), as has been suggested. thus, a standard heavy

warship accelerates at one gravity, and a fast scout at two. this is
convenient for cruising - if a ship cruises at full thrust (arguable),
the
crew have a nice natural 1g to stand up in.

note that this analysis does not use Newtonian physics, but rather the
slightly modified Tuffleyan physics, where distance travelled is equal
to
time multiplied by your final velocity, not your average velocity.
that's
how it works in cinematic movement, anyway. not sure about this
new-fangled vector stuff.

it would be nice to fix this little bug in the movement system for those
who continue to use cinematic. how about saying that half the
acceleration
is applied at the start of the turn, and half at the end? alternatively,
that acceleration is applied twice, once at the start and once at the
end
of the turn. these two are basically equivalent.

another alternative would be to PSB our way out - say that ships in the
tuffleyverse use orion-type nuclear pulse engines, and apply all their
acceleration in one go, once every turn. the attractions of 1 thrust =
0.25 g start to go away when you realise that you're actually getting
150g
for one second each turn. ouch.

Tom