The HL-20 Personnel Launch System was a NASA spaceplane concept for crewed orbital missions studied by NASA's Langley Research Center around 1990. It was envisaged as a lifting body re-entry vehicle similar to the Soviet BOR-4 spaceplane design. Its stated goals were to achieve low operational costs, improved flight safety, and a possibility of landing on conventional runways. No flight hardware was built.
PLS concept 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 29-foot (9 m) long engineering research model was used at Langley to define the full-scale external and internal definition of the HL-20 for utilization studies. The PLS mission was to transport people and small amounts of cargo to and from low Earth orbit, i.e., a small space taxi system. Although never approved for development, the PLS concept spaceplane was designed as a complement to the Space Shuttle and was being considered an addition to the crewed launch capability of the United States for three main reasons:
Assured crewed access to space. In the era of Space Station Freedom and subsequent missions of the Space Exploration Initiative, it is imperative that the United States have an alternate means of getting people and valuable small cargo to low Earth orbit and back, should the Space Shuttle be unavailable. Enhanced crew safety. Unlike the Space Shuttle, the PLS would not have main propulsion engines or large payload bay. By removing large payload-carrying requirements from personnel-delivery missions, the PLS would be a small, compact vehicle. It is then more feasible to design an abort capability to safely recover the crew during critical phases of the launch and return from orbit. Affordable costs. As a small vehicle designed with available technologies, the PLS is forecast to have a low development cost. Subsystem simplification and an aircraft approach to PLS ground and flight operations can also greatly lower the costs of operating PLS. Two designs that were considered for PLS differed in their aerodynamic characteristics and mission capabilities:
the Johnson Space Center's approach used a blunt cone shape (similar to the various Moon-mission return vehicles), incorporating a parachute system for coming to rest; the Langley Research Center proposed a lifting body that could make a conventional runway landing on return from orbit.
Lifting-body development
Predating and influencing the design of the Space Shuttle, several lifting-body craft, including M2-F2, M2-F3, HL-10, and the X-24 A and X-24B, were flown by test pilots from 1966 through 1975. The M2-F2 and the HL-10 were proposed in the 1960s to carry 12 people to a space station following launch on a Saturn IB. The HL-20 PLS concept was evolved from these early shapes, being further influenced by the Soviet MiG-105 and especially BOR-4. The "HL" designation stands for horizontal lander, and "20" reflects Langley's long-term involvement with the lifting-body concept, which included the Northrop HL-10. A lifting-body spacecraft would have several advantages over other shapes. With higher lift characteristics during flight through the atmosphere while returning from orbit, the spacecraft can reach more land area, and the number of available landing opportunities to specific sites would be increased. Deceleration loading during entry would be limited to about 1.5 G. This is important when returning sick, injured, or deconditioned Space Station crew members to Earth. Wheeled runway landings would be possible, permitting simple, precision recovery at many sites around the world, including the Kennedy Space Center launch site.
Proposed missions
Originally, delivery of passengers to Space Station Freedom would have been the primary mission of a PLS. For the baseline space station mission, depending on design, the crew size would be either 8 or 10 crew members. A typical HL-20 mission operation would commence at the Kennedy Space Center with the HL-20 being processed horizontally in a vehicle-processing facility, while an expendable launch vehicle is processed vertically in a separate facility. The launch vehicle and HL-20 would be mated at the launch pad, and the launch sequence initiated as the space station passes over the launch site. Following launch, the HL-20 would initially enter a low 100-nautical-mile (200 km) orbit to chase after the space station and then transfer up to the space-station orbit altitude of 220 nautical miles (410 km). After rendezvous and docking at Space Station Freedom, crews would be exchanged, and the HL-20 would decelerate for return to Earth. The HL-20 would land horizontally on a runway similar to the return of the Space Shuttle. Total mission duration could be as low as 72 hours. Other potential missions defined for a PLS included the orbital rescue of stranded astronauts, priority delivery and observation missions, and missions to perform satellite servicing. For these other missions, the basic HL-20 design would be unchanged, but interior subsystems and arrangements would be modified according to crew accommodations, duration, and equipment required for the particular mission.
Design features
… excerpt ends here. Continue reading the full article.
