Gregory started his career in the former Soviet Union, in Moscow, as an engineer designing image sensors and other semiconductor devices. In 1991 he joined what was then MIT’s Center for Space Research to work on the development of the focal plane for the Chandra X-ray Observatory. Since then he continues to work on different types of detectors mostly for X-ray astronomy. Gregory has led development of the detector subsystem for NICER (Neutron star Interior Composition ExploreR) – an instrument on-board of the International Space Station. Currently he works on studying fast low noise CCD detectors being developed by Lincoln Laboratory for future X-ray missions.