Research Astrophysicist, NASA's Goddard Space Flight Center, January 2022 to present.
Chief of the Laboratory for Observational Cosmology, NASA's Goddard Space Flight Center, April 2006 to January 2022.
Astrophysicist, NASA's Goddard Space Flight Center, March 1999 to April 2006.
Program Scientist, NASA Headquarters, April 2004 to October 2004.
Assistant Scientist, A.U.R.A., Hubble Space Telescope STIS Project, NASA's Goddard Space Flight Center, September 1996 to February 1999.
NSF-NATO Postdoctoral Fellow/Senior Research Assistant, Department of Physics, University of Durham, October 1992 to August 1996.