Back in December I looked at the vessels in Star Frontiers through the lens of Traveller ship classification, just to see how the vessels in the two game-universes compared. I recently acquired a copy of Spaceship Zero, which I first mentioned in my piece on Apocryphal Gaming. Here are some rough volumes of the vessels in the Spaceship Zero rulesbook, given in Traveller displacement tons.
GOOD GUY VESSELS
Star Skipper: not enough information given for an actual calculation, but it looks like these two-man jobbies are so small as to be less than a whole ton. In Traveller terms that's way smaller than can be simulated by the design rules.
Galactic Frigate: 76 tons
Space Hopper: 223 tons (I guestimated the diameter of the Star Hopper at 32.75 feet)
Star Cruiser: ~2,900 tons
The Spaceship Zero herself is a modified Mark V Space Hopper. That puts the default PC ship right in line with a Traveller PC ship like a Free Trader. The ship cutaway on page 158 of the book makes it clear that life on either a Space Hopper or Free Trader is very crowded. At least the Free Trader crew have their own rooms. Those sorts of luxuries have been removed on the Zero for the experimental Better-Than-Light Drive.
Scout Saucer: 6.3 tons (Small, but not shockingly so. These things are basically space winnebagos for a couple of gilled goons.)
Dreadnought: 400 tons
Slave Ship: 1,000,000 tons
Planet Smasher: 10,000,000 tons (No size is given for the Planet Smasher, but it masses 10 times as much as a Slave Ship.)
Very interesting. Half of the hydronaut vessels are small enough to be viable targets for one-on-one fights with the good guys. The other half are clearly designed to make players say "That's no moon..." The Planet Smasher class Hydronaut vessel is bigger than any canonical Traveller vessel and twice as big as the Titan class MegaMerchant mentioned in passing here. In the Traveller universe only the mythical Flying Dutchman Starship outclasses the Planet Smasher.