Astronaut Steven Nagel, who flew on four space shuttle missions in the 1980s and 90s, including two as mission commander, has died after a long battle with cancer, NASA confirms.Nagel, an Air Force pilot who had logged many hours in fighter jets and as a test pilot, joined the NASA astronaut corps in 1978 in the first crop of trainees selected for the space shuttle program.Although trained as a shuttle pilot, Nagel's first mission, aboard STS-51G (Discovery) in June 1985, was as a mission specialist."I really wanted to fly as a pilot, so at the time — because there was no explanation that went with it — I wondered, 'Are they telling me I'm not good enough to fly as a pilot?'" Nagel told a NASA interviewer about his 1985 assignment to the shuttle Discovery's STS-51G crew, according to Space.com. "Nothing against mission specialists. I would trade my pilot's slot to go be a mission specialist and do a [spacewalk], certainly, but it's just that 'What are they trying to tell me here?'""But I think what it really was, our class was very large, and they're getting down to the point where I think [they] probably wanted to get us all flown, and this was a way to do it a little quicker," Nagel recalled.According to his official NASA bio, Nagel went on to pilot Challenger (STS-61A) four months later. Among other things, the flight still stands as the only time eight people launched into space at the same time on the same vehicle. It was also the last successful Challenger mission — the orbiter exploded shortly after launch on its next mission, on January 27, 1986. All seven astronauts aboard were killed and the shuttle program was put on hold for two years.Following the Challenger disaster, Nagel represented the Astronaut Office in efforts to develop a crew escape system."This was my best time at NASA, actually," Nagel stated. "Nothing I ever did was more fulfilling than that two years, to be honest, even flying.""This was better, because everybody was so focused on getting the shuttle flying again," he remarked, Space.com says.Nagel later commanded Atlantis (STS-37) in 1991, deploying the Compton Gamma Ray Observatory (GRO) and Columbia (STS-55) in 1993 on the second German-led Spacelab flight.Space.com writes that on Nagel's final flight nitrogen leak disabled the system used to flush waste water from the orbiter's toilet:
