 Van den Berg was assigned as Payload Specialist on STS-51B Challenger (April 29 – May 6, 1985). STS-51B, the Spacelab-3 mission, was launched from the Kennedy Space Center, Florida, and returned to land at Edwards Air Force Base, California. It was the first operational Spacelab mission. The seven-man crew aboard Challenger conducted investigations into crystal growth, drop dynamics leading to containerless material processing, atmospheric trace gas spectroscopy, solar and planetary atmospheric simulation, cosmic rays, and laboratory-animal and human medical monitoring.
