Wil Mireu said:
If it's not possible to design a fighter as a spacecraft, and isn't possible to design it as a vehicle either, then IMO one set of rules or the other clearly has a gaping hole in them.
You can design a fighter as a spacecraft. Its just that the 5 ton limit required by the OP makes it rather hard. Thats half the size of the standard fighter.
With the standard 10 tons, you can get:
Size: 10 tons [MCr1]
Maneuver Drive: sF (12-G performance) [3 tons, MCr 6]
Power Plant: sG [3 tons, MCr 6]
24 hours fuel [0.15 tons]
Space for 1 weapon (missile rack, beam laser, or pulse laser) [1 ton]
Cockpit [1.5 tons, MCr 0.05]
Total of 8.65 tons used, at a cost of MCr 13.05. Add a layers of Titanium Steel requires 1 ton of space to give an armor rating of 2, which costs MCr 0.05. That brings us up to a total tonnage usage of 9.65 tons (0.35 tons cargo) and cost of MCr 13.1. Throw in a computer, a weapon (probably a pulse laser, with the High Guard changes to make is a 2d6 damage weapon), and possible some streamlining, and you got a fighter.
Or this one:
Size: 10 tons [MCr1]
Maneiver Drive: sA (2-G performance) [0.5 tons, MCr 1]
Power Plant: sA [1.2 tons, MCr 3]
24 hours fuel (0.1 tons)
1 hardpoint mounting a 5-ton railgun barbette with 20 rounds of ammo [total 6 tons MCr 4]
Cockpit [1.5 tons, MCr 0.05]
0.7 tons of railgun ammo magazine (14 additional rounds)
Cargo: 0 tons
Total Cost (without computer): MCr 9.05
Effectively a fighter with a spinal mount. No armor, and the railgun has a short range, but its 3d6 damage. Add streamlining (only costs MCr 0.1) for atmospheric use. Even with no armor, the scaling between ground-based weapons and starships will protect it from most non-starship weapons, so it can be put to good use in an atmosphere if its streamlined. (With the x50 multiplier, it only does 525 damage on average to vehicles and personnel...)