Abstract: A spacecraft for various missions such as moon landing, space station or asteroid rendezvous, or payload delivery. The spacecraft comprises a main propellant tank, preferably toroidal in shape, that also serves as the primary structural component of the spacecraft. The spacecraft's secondary structures such as a second propellant tank, pressurant tanks, engines, and payload deck are attached directly to the main propellant tank. The spacecraft has a substantially circularly symmetric weight distribution about its centerline, The spacecraft can be configured to be monopropellant; alternatively, in a bipropellant configuration the spacecraft includes a second propellant tank, which can carry a fuel such as kerosene or ethanol and if toroidal preferably nests together with the main propellant tank. In some configurations the propulsion system can switch between monopropellant operation and bipropellant operation, and automatically switches to monopropellant operation once one of the propellants is deleted.