Astronotes Armagh Planetarium's Stellar Blog! ... After running through the mass numbers for Skylon that Reaction Engines offers, I?m left believing that they?ve got an engine that will theoretically get them to orbit in one stage, but only by them making unrealistic assumptions about the structural weight of the rest of the vehicle , total dry mass 53 tonnes , engine thrust 270 tonnes , engine T/W 14 therefore mass of engines ~19 tonnes , therefore mass of the rest of the ...