Malcolm D. Shuster (31 July 1943 – 23 February 2012) was an American physicist and aerospace engineer, whose work contributed significantly to spacecraft attitude determination.[1][2] In 1977 he joined the Attitude Systems Operation of the Computer Sciences Corporation in Silver Spring, Maryland, during which time he developed the QUaternion ESTimator (QUEST) algorithm for static attitude determination.[3] He later, with F. Landis Markley, helped to develop the standard implementation of the Kalman filter used in spacecraft attitude estimation.[2] During his career, he authored roughly fifty technical papers[4][2] on subjects in physics and spacecraft engineering, many of which have become seminal within the field of attitude estimation, and held teaching assignments at Johns Hopkins University, Howard University, Carnegie-Mellon University and Tel-Aviv University.[1] In 2000 the American Astronautical Society awarded him the Dirk Brouwer Award.[5][3] In June 2005 the American Astronautical Society held a special three-day Astronautics symposium in his honor[6]