Thursday, April 27, 2006

Land Me On The Moon ... Softly: Apollo's LLRV.

How do you train astronauts flying in Earth's full gravity to land on the Moon, with its 1/6th gravity?

Dr. Christian Gelzer spoke tonight at the San Diego Air and Space Museum about NASA's Lunar Lander Research Vehicle (LLRV), developed by Dryden Flight Research Center for the Apollo program, to train astronauts to land on the Moon.

The genius of the LLRV, and later the LLTV (Lunar Lander Training Vehicle), was the use of a jet engine vertical thruster to provide 5/6 of the lift needed to lift the vehicl. The remaining thrust was provided by two hydrogen-peroxide thrusters. Control was provided by 16 other hydrogen peroxide thrusters.

Five vehicles were produced and three survived the training program. The training vehicle was an ungainly contraption susceptible to the wind and Neil Armstrong was first to crash one in a crosswind.

Yet, according to Gelzer, Armstrong later attributed his successful landing on the Moon to his training with the landers on Earth. He said that training with the landers made him feel comfortable and at home flying in Lunar gravity. Astronaut William Anders, who was in the audience, seconded that. He said without training on the LLRV, with its ability to mimic 1/6 gravity, astronauts landing on the Moon would have tended to dramatically overshoot their landing targets.

The training vehicle was dangerous to fly and NASA administrators wanted to stop using it in favor of simulators. But the astronauts kept the vehicles flying because it gave them real-life experience flying compared to simulator training. According to Gelzer, as astronaut Gene Cernan put it, flying the LLRV/LLTV "put your tail on the line." Although dangerous, it was apparently fun to fly. Astronaut Anders spoke fondly of the enjoyment he got out of flying the LLRV/LLTV.

Gelzer spoke of the legacy of the LLRV/LLTV. Its first legacy is obvious; it trained the Apollo astronauts to land on the Moon. Its second legacy is a broader one for aviation; its use of fly-by-wire controls with three onboard computers marked the advent of fly-by-wire technology. (Although see here for the sad story of Canada's Avro Arrow jet fighter.)

Gelzer told of a fitting twist that brought the legacy of the LLRV's fly-by-wire technology full circle. In the early 1970s when engineers from Dryden submitted a proposal to NASA to test the technology in a jet fighter, they admitted they had no computer to run it. NASA provided an off the shelf computer from the Apollo program, and the system was later flown in an F8 in 1972.

Two LLTVs remain. One is hanging from the ceiling at Johnson Space Center out of public view. The other is in a hanger at NASA's Dryden Flight Research Center, where it can be viewed by visitors. Dr. Gelzer serves as Deputy Historian at Dryden.

Read more about the LLRV/LLTV here and about NASA's fly-by-wire F8 here. Visit the San Diego Air and Space Museum website here.


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