After spending ten months as a NASA representative to the Harvard/MIT Smart Medical Systems Team of the National Space Biomedical Research Institute in Boston, Massachusetts, he worked as the lead Flight Surgeon for Expedition 7 to the ISS in 2003, supporting from Russia, Kazakhstan and Houston. Until he was selected as an astronaut candidate, Marshburn served as Medical Operations Lead for the ISS. His activities included development of the biomedical training program for flight surgeons and astronaut crew medical officers, and managing the ISS Health Maintenance System.