 Brennecke's responsibilities included selecting materials and techniques for building the rockets, especially the cryogenic fuel tanks.Later in her career, she played a similar role in choosing materials and techniques for Spacelab and booster rockets on the Space Shuttle.Brennecke's nickname, "Hap", was chosen in part because of its gender neutrality, and as a "middle ground between the courtesy of the times and the informality" of the NASA engineering team.