FF&S: Broken Daedalus Drive?

Recent Excursions Into _Fire, Fusion, & Steel_.

Ok, I take back what I said about proofreading, here's a *real*
doozy....

Recently, for whatever reason, I looked into designing a ship
capable of interstellar flight with a payload of five billion
tons, using FF&S.  (A *huge* payload.  Some of the CT referees
out there who liked FASA may know where my number is coming
from.)  So I checked out drive systems.

FTL travel works great...a ship with jump-1, and able to jump
three times without refueling, uses 32% of its internal volume
for drive systems, including fuel, as would any other large
jump-1 ship.

STL travel stinks.  And it revealed a *major* bug in the FF&S
rules.  At tech-9 and above, the best options are the fusion
rocket and the Daedalus drive.  Supposedly, the Daedalus drive
is a better choice; "the engines [have] a lower thrust-to-mass
ratio than a conventional fusion rocket, but provide fuel
efficiency about one order of magnitude higher." (p. 74)

#$**$%^@!  <This is a family mailing-list.>  :)

Per cubic meter of maneuver drive: (in metric tons)

                  THRUST       FUEL USE  ...fuel per ton of thrust
 Daedalus drive: 1.5 ton   0.00050 ton/hr.     0.000334 ton/hr
 Fusion rocket   9.0 ton   0.00035 ton/hr.     0.000039 ton/hr
 HEPlaR drive:  33.4 ton   0.02917 ton/hr.     0.000873 ton/hr

Figures are rounded.  HEPlaR figures include the required fusion
power plant in the drive's cubic meter, here assumed to be at
tech-10, are included for comparison with the tech-9 drive systems.
The advantage of a higher thrust-to-mass ratio is that your engine
is smaller.  HEPlaR fuel use doesn't improve...but the engines
get smaller.

The Daedalus drive is an order of magnitude *worse* in fuel
efficiency than the conventional fusion rocket!!!  Combined
with its' worse thrust-to-mass ratio, the engine is fairly
worthless.

Of course, maybe fuel efficiency isn't the issue...a big fusion
rocket isn't exactly a healthy thing to be around.  But that
wasn't the selling point in FF&S!  At tech-10, the smaller motor
of the HEPlaR probably outweighs the fuel efficiency advantage
of the Daedalus drive.  (It might be worthwhile at late tech-8.
The Daedalus design was originally supposed to be staged, and
that may also help its' prospects as an interstellar drive, but
not as a competitor with the fusion rocket.)  The fuel
efficiency of all of these seems to be a bit short of the kind
of performance I was looking for.  (It *is*, however, quite
realistic.)

This also brings up another interesting point.  It seems to me
that even accounting for the extra mass needed in the motor of
a fusion rocket, it is more efficient than a HEPlaR drive.  This
suggests that there may be an advantage to using fusion rocket
designs in some cases on a military vessel, perhaps as a second
drive system.

Any comments?  Am I reading this wrong?

  Steve Bonneville
  [email removed]