 In 1989, a similar concept was studied by the U.S. Navy and NASA in Project Longshot.Both of these concepts require significant advances in fusion technology, and therefore cannot be built at present, unlike Orion.From 1998 to the present, the nuclear engineering department at Pennsylvania State University has been developing two improved versions of project Orion known as Project ICAN and Project AIMStar using compact antimatter catalyzed nuclear pulse propulsion units, rather than the large inertial confinement fusion ignition systems proposed in Project Daedalus and Longshot.