Let a spacecraft in permanent orbit around the earth be used for delivering payloads from leo to geostationary (gso) orbit. before each flight from leo the spacecraft is refueled with propellant which it uses up in its round trip to gso and back. the outbound leg requires four times as much propellant as the inbound return leg. the delta-v for hohmann transfer from leo to gso is 4.22 km/s. the specific impulse of the propulsion system is 430 s. if the payload mass is to be 3500 kg, calculate the mass of the empty vehicle.