"HL" stands for horizontal landing, and "10" refers to the tenth design studied by engineers at NASA's Langley Research Center, Hampton, Virginia.

Although the XLR-11 rocket engine (same type used in the Bell X-1) was installed, the first 11 drops from the B-52 launch aircraft were unpowered glide flights to assess handling qualities, stability, and control.

Nine days later, NASA pilot William H. "Bill" Dana flew the vehicle to 90,030 feet (27,440 m), which became the highest altitude reached in the program.

[1] During a typical lifting body flight, the B-52—with the research vehicle attached to the pylon mount on the right wing between the fuselage and inboard engine pod—flew to a height of about 45,000 feet (14,000 m) and a launch speed of about 450 mph (720 km/h).

[1] Following engine shutdown, the pilot maneuvered the vehicle through a simulated return-from-space corridor into a pre-planned approach for a landing on one of the lakebed runways on Rogers Dry Lake at Edwards.

During the early phases of the Space Shuttle development program, lifting bodies patterned on the HL-10 shape were one of three major types of proposals.

These were later rejected as it proved difficult to fit cylindrical fuel tanks into the always-curving fuselage, and from then on most designs focused on more conventional delta wing craft.

Once in Earth orbit, it was planned that a robotic extraction arm would remove the HL-10 from the rocket's third stage and place it adjacent to the crewed Apollo CSM spacecraft.

[2] Launching a Saturn V to low Earth orbit with a light payload would not be an efficient use of capability, and the Apollo program was ended mainly on cost grounds.