With increasing national interest in obtaining routine access to space, a number of Earth-to-orbit transportation systems were studied in the mid-1980s. One, referred to as a "Personnel Launch System" (PLS), could utilize the HL-20 and an expendable launch system to provide crewed access complementing the Space Shuttle. A full-size engineering research model of the HL-20 was constructed in 1990 by the students and faculty of North Carolina State University and North Carolina A & T University for studying crew seating arrangements, habitability, equipment layout and crew ingress and egress. This long engineering research model was used at Langley to define the full-scale external and internal definition of the HL-20 for utilization studies.