Imrpove? The thing's already a masterpiece! a 500km orbit might require a bigger craft, most probably those mk3-sized crafts. EDIT : Your White Lightning has the old Mk2 fuselage, containing only 270-330 and 135-225 gallons of fuel. The updated version contains 360-440 and 360-440 gallons, might want to check it out! Simply swap the mk2 fuselage with the new one and you'll have more fuel