Some information I read on the lightwave group
The, "Serenity" is a Firefly Class interplanetary ship. Originally conceived and built as a medium range cargo ship.
Dimensions and Weights:
She is comparable to that of Boeing 747. She is 63 meters long, 40 meters wide and 18 meters tall. Her gross empty weight is 575,000 lbs and her maximum takeoff weight is 945,000 lbs.
Performance and Powerplants:
Primarily powered by 2 wing mounted Smith & Davis SD-2595 (95,000 lb) turbofan and solar induction engines, she can achieve a maximum airspeed of mach 2 (1484 mph) at 1000 Meters EBSL (Earth Based Sea Level,) and mach 30 (22270 mph) at 100,000 Meters (62 miles) EBSL. During the transitional phase from atmospheric to orbital flight the fan blades rotate to collect photons emitted by a solar source to feed the engines keeping the relative thrust ratio comparable to it's atmospheric rating.
The "Firefly" engine, a Smith & Davis SD-4631 photon reaction drive, was developed on the same principles that drive fusion in a star, (4 1H + 2 e --> 4He + 2 neutrinos + 6 photons.) The reaction produces enough thrust to propel the ship to 643,738 kph (400,000 mph) taking it approximately 16 days to travel 1 AU. (The Astronomical Unit is the distance from the Earth to the Sun, 149,597,871 kilometers.) Although very reliable, this reaction produces large volumes of plasma as hot as the surface of a star. Thermal panels on the outside of the engine dissipate the plasma and heat that builds up during the process typically glowing in a yellowish hue as they cool down.
The maneuvering of the ship is handled in two different ways. In atmosphere she has flaps and ailerons that in conjunction with the pitch of the side engines control her direction. In space she uses an RCS, (Reaction Control System,) consisting of Hydrazine fueled thrusters that work in a countered measure. For example if she were to turn nose up, thrusters on the back rear of the ship would fire upwards and thrusters of the front nose would fire downwards pushing the tail down and the nose up. Variations on this, tied into the side engines pitch, produce all her movement in space.
For landing her side engines rotate vertical and vents on the front of the engine open to allow the engine the "breathe" as she hovers.
The Firefly class ships gravity comes from a rotating ring just aft of the ships midsection. It produces a gravity field using the "Peristere Principal," that also acts as an momentum dampener to allow passengers more freedom of movement during all aspects of flight.
SO now it puts the ship at 63m or 206.69ft instead of the 190ft I have been using. This will make the scale of my model 1:190.79 or 1:191. A very odd number. I am sure I will get flak for that if I produce a kit. Ask me if I care.