creative types later. NASA categorized full-time international astronauts as payload specialists unless they received NASA mission specialist training, which some did. Bilodeau estimated that payload specialists would receive a couple of hundred hours of training over four or five weeks. International or scientific payload specialists were generally assigned a back-up who trained alongside the primary payload specialist and would replace him/her in the event of illness or other disability. Both primary and backup payload specialists received mission-specific and general training. Michael Lampton estimated that about 20% of his training was general, including firefighter school, capsule communicator duty, and use of Personal Egress Air Packs and the space toilet. He described training for Spacelab 1 as "going back to graduate school but majoring in everything"; as the first mission it tested Spacelab's versatility in "medical, metallurgical, remote sensing, astronomy, microgravity, lots more". Payload specialists operated experiments, and participated in experiments needing human subjects. Charles D. Walker recalled that Senator Jake Garn "and I were the obvious subjects" for Rhea Seddon's echocardiograph on STS-51-D. "We really didn’t have much of a choice in whether we were going to be subjects or not. 'You're a payload specialist; you’re going to be a subject.'" Besides his own electrophoresis work, Walker operated an unrelated experiment for the University of Alabama Birmingham, and helped build homemade repair tools for a satellite launched on the mission. Payload specialists were flown from 1983 (STS-9) to 2003 (STS-107). The last flown payload specialist was the first Israeli astronaut, Ilan Ramon, who was killed in the Columbia disaster on mission STS-107 with the rest of the crew. Criticism Within NASA, Johnson Space Center (JSC) controlled crewed spaceflight by selecting professional, full-time astronauts. The payload specialist program gave Marshall Space Flight Center (MSFC)—which supervised Spacelab, including a contracted European Space Agency-chosen payload specialist—control as well, causing conflicts. JSC director Chris Kraft and members of the NASA astronaut corps believed that mission specialists—many with doctoral degrees or other scientific background, and all with full-time astronaut training—could operate all experiments. Rick Chappell, chief scientist of MSFC, believed that the scientific community insisted on its own scientists being able to operate experiments in exchange for support of the Space Shuttle program. While mission specialists could operate most experiments, "Since we could take passengers, why not take at least a couple of passengers who had spent their whole careers doing the kind of research they