Johndale Solem origin of the shape of rubble-pile asteroids. His analytic theory of the breakup of comets by planetary tidal forces resulted in his calculation of the diameter and density of the parent comet of Shoemaker-Levy 9 as it was before breaking up in the tidal field of Jupiter in 1994 (1994a). Solem's research on interplanetary travel culminated in his MEDUSA concept, a nuclear explosive propelled spacecraft for interplanetary space travel (1994b). Gregory Matloff said this was "a surprising [propulsion] concept which might greatly reduce spacecraft mass." The concept inspired research and elaboration by the aerospace community. At the behest of NASA's
Erich Meyer Erich Meyer Erich Meyer (born August 6, 1951) is an Austrian engineer, amateur astronomer and discoverer of asteroids. Between 1996 and 1999, using the private observatory Meyer/Obermair in Davidschlag (municipality Kirchschlag bei Linz, Austria), he discovered a total of 21 asteroids. Seven of these asteroids were discovered together with his colleague Erwin Obermair and one together with Herbert Raab. Furthermore, he was involved in six other discoveries of asteroids between 1996 and 2005, which were assigned as site discoveries to the observatory Davidschlag by the International Astronomical Union. Meyer's most important observations include precisie astrometry of the comet Shoemaker–Levy 9,