ICAN-II was a proposed manned interplanetary spacecraft that used the Antimatter Catalyzed Micro-Fission (ACMF) engine as its main form of propulsion. The spacecraft was designed at Penn State University in the 1990s as a way to accomplish a manned mission to Mars. The proposed ACMF engine would require only 140 nanograms of antiprotons in conjunction with traditional fissionable fuel sources to allow a one-way transit time to Mars of 30 days. This is a considerable improvement over many other forms of propulsion that can be used for interplanetary missions, due to the high thrust-to-weight ratio and specific impulse of nuclear fuels. Some downsides to the design include the radiation hazards inherent to nuclear pulse propulsion as well as the limited availability of the antiprotons used to initialize the nuclear fission reaction. Even the small amount required by the ACMF engine is equal to the total antimatter production at the facilities CERN and Fermilab over many years, although these create antimatter only as a byproduct of physics experiments, not as a goal. Also, even though the record, as of 2011, for antimatter storage is just over 1000 seconds, that time was proposital to the needs of CERN scientists, who could have trapped it potentially much longer but needed to turn off the magnetic field to verify the antimatter's existence. ICAN-II is similar to the Project Orion design put forth by Stanislaw Ulam in the late 1950s. The Orion was intended to be used to send humans to Mars and Venus by 1968. It was to utilize a large number of nuclear bombs that would be set off one after the other, behind the ship to push it forward. It would, of course, require large shock-absorbers and ablative shielding for its pusher-plate. The ICAN-II also, in a sense, utilizes nuclear "bombs" for thrust. However, instead of regular fission bombs like the Orion would utilize, ICAN-II uses what are, essentially, a large number of very small hydrogen bombs. Set off, of course, by a stream of anti-protons. Ecological concerns would probably require that ICAN-II be assembled in space. Of course, a precedent for such large scale orbit-based assembly is already being set by the construction of the International Space Station.
The radiation from ICAN-II's ACMF engine would be intercepted by a 4 meter radius silicon carbide shell. Additionally, 1.2 meters of lithium hydride will shield the fuel rings from high-energy neutrons that are ejected from the nuclear explosions, and 2.2 meters of shielding will protect the crew modules. The spacecraft would have a total mass of 625 metric tons, with 82 additional metric tons available for payload. This is more than sufficient to carry a Mars Lander and exploration vehicles.