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.
As a co-investigator of the Vapor Crystal Growth System (VCGS) experiment, Van den Berg was responsible for the crystal growth aspects of the VCGS experiment. He had intimate knowledge of VCGS and Fluid Experiment System (FES) hardware, and had participated in all major design and science reviews of those systems.
By the end of the mission, Van den Berg had traveled over 2.9 million miles in 110 Earth orbits, and logged over 168 hours in space.