[1] Its stated goals were to achieve low operational costs, improved flight safety, and a possibility of landing on conventional runways.

With increasing national interest in obtaining routine access to space, a number of Earth-to-orbit transportation systems were studied in the mid-1980s.

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 "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.

Deceleration loading during entry would be limited to about 1.5 G.[4] This is important when returning sick, injured, or deconditioned Space Station crew members to Earth.

[3] Other requirements had focused on minimizing life-cycle costs of the system by ensuring simple operations, low-cost manufacturing, and high utilization potential.

The selection and design of these subsystems would emphasize simplicity and reduce maintenance requirements: for example, hydraulic systems would be replaced by all-electric controls.

These design changes and subsystem simplifications, along with the adoption of aircraft maintenance philosophies, could reduce the HL-20 preparation man-hours to less than 10 percent of the Space Shuttle Orbiter's requirement.

Its interior layout with a ladder and hatch arrangement was designed to permit rapid egress of passengers and crew for emergencies on the launch pad.

Upon splashdown, inflatable flotation devices would ensure that at least one of the PLS's two hatches is above the water and available for emergency crew egress.

A key finding of this study was the realization that while design and technological factors could reduce costs of a new crewed space transportation system, further significant savings would be possible only if a new operations philosophy were adopted which treated PLS in a manner similar to an operational airliner rather than a research and development space vehicle.

Their objectives were to assess technical attributes, determine flight qualification requirements, and develop cost and schedule estimates.