posted 06-21-2020 08:28 AM               

Space Cover #567: The HL-10 Lifting Body

I couldn’t decide which of these two covers to feature as the cover of the week, so here are both of them! Both are postmarked December 22, 1966 for the first flight of the HL-10 lifting body, piloted by Bruce Peterson. The top one was postmarked at Edwards, where the flight took place, the servicer added the rubber stamp cachet and hand printing, and Peterson signed the cover some years later. The lower cover was postmarked at Hawthorne, CA where the HL-10 was manufactured at the Northrop plant there (now SpaceX plant), the cachet was printed by the Northrop Stamp Club, and Peterson signed it some years later.

Back in SCOTW 558 we looked at the “potato shaped” SV-5 configuration lifting body that spawned the X-23, X-24, and X-38 vehicles. The HL-10 configuration had a flat bottom with a curved top, looking like a classic airfoil wing in cross section.

During the flight above, Peterson discovered a significant control problem, yet was able to land safely. NASA grounded the HL10 to fix the control problem and install the XLR11 rocket engine. The first reflight of the HL10 took place on October 23, 1968 with Gerry Gentry at the controls. The rocket engine did not start completely and was shut down shortly afterward.

On November 13, 1968, John Manke performed the first successful powered flight of the program. Bob Rank produced a gorgeous (but hard to find) Velvet Cachet for this flight as shown above.

The HL10 became the first crewed lifting body aircraft to fly faster than sound on May 9, 1969, and then set the fastest speed of any crewed lifting body (1.86 times the speed of sound - 1228 mph) on February 18, 1970. Next, the HL10 set the highest altitude record for a crewed lifting body, over 90,300 feet (17 miles) on February 27, 1970.

After this round of flights, the HL10's normal rocket engine was replaced with three smaller rocket engines. These smaller engines were to be used during the landing approach to investigate whether landing engines might be needed for the Space Shuttle. Two flights were performed with the landing rockets on June 11 and July 17, 1970 by Peter Hoag. Hoag concluded that the landing engines complicated the landing process to the point of negating their advantage. These tests helped cement the decision not to carry landing engines on the Space Shuttle.

The July 17, 1970 flight was the last for the HL10, nearly 50 years ago. The cover for this flight (above) is the typical rubber stamped cachet for the HL-10 applied by the local Boy Scout troop at Edwards.

All-in-all, the HL10 made 37 flights in the hands of Peterson, Gentry, John Manke, Hoag, and Bill Dana. These pilots all felt that the HL-10 was the best handling of all the lifting bodies.

In the 1990’s the HL-10 shape was resurrected into a concept called the HL-20 to ferry astronauts to and from the Space Station, however it never got beyond the mockup phase. More recently Sierra Nevada has taken the HL-20 design and is building it into a vehicle called the Dream Chaser to ferry cargo to and from the Space Station. The first full-scale landing test of an uncrewed Dream Chaser was performed on November 11, 2017 (cover above). Dream Chaser is scheduled to fly into space in 2021 onboard a Vulcan-Centaur launch vehicle.