 The same craft could visit Saturn's moons in a seven-month mission (compared to chemically powered missions of about nine years).A number of engineering problems were found and solved over the course of the project, notably related to crew shielding and pusher-plate lifetime.The system appeared to be entirely workable when the project was shut down in 1965, the main reason being given that the Partial Test Ban Treaty made it illegal (however, before the treaty, the US and Soviet Union had already detonated at least nine nuclear bombs, including thermonuclear bombs, in space, i.e., at altitudes over 100 km