Electronic control system for the Lunar Landing Training vehicle

The Lunar Landing Training Vehicle (LLTV) was developed for NASA by Bell Aerosystems, Inc. which had engineering facilities located in Niagara Falls, New York. The LLTV was a second generation vehicle used by NASA Apollo Program astronauts to develop piloting skills. The LLTV provided Apollo program commanders the opportunity to experience the flight characteristics associated with the 1/6th gravity conditions on the moon. The first LLTV vehicle was assembled at Ellington Airforce Base in Houston, Texas in 1967. A total of 3 LLTV vehicles were eventually delivered to Ellington AFB. The last remaining of the three LLTV vehicles is on display at the Johnson Spacecraft Center in Houston, Texas.

The electronic control system for the LLTV was designed with redundant channels that used 2 of 2 logic. The outputs of each primary channel was compared on a continuous basis. If a fault was detected in the primary control system, then control was automatically switched to an identical backup channel and the pilot immediately took measures to bring the vehicle to the ground. All the controls were analog circuits utilizing Burr-Brown transistor amplifier modules and other analog components. Unlike modern digital control circuits used on NASA systems on the Shuttle program the technology available in 1967 was limited to discrete transistors.

Built of aluminum alloy trusses and shaped like a giant four-legged bedstead, the LLTV was built to simulate the dynamics of the actual Apollo Lunar Landing Module (LM). The LLTV had a General Electric CF-700-2V turbofan engine (with 4,200 pounds of thrust) that was mounted vertically in a gimbal. The turbofan engine provided the necessary lift to place the vehicle at the test altitude. Once at altitude the engine was then throttled back to support five-sixths of the vehicle's weight, simulating the reduced gravity of the moon. Two hydrogen peroxide lift rockets with thrust that varied from 100 to 500 pounds provided the balance of the vertical lift control. Sixteen smaller hydrogen peroxide rockets, mounted in pairs, provided control in pitch, yaw and roll. The LLTV electronic control system provided independent analog circuit channels for each of the pitch, yaw and roll hydrogen peroxide attitude rockets.

Note: The actual Lunar Landing Module (LM) used on the Apollo program was manufactured by Grumman Aerospace Corporation, Bethpage, New York.

The content for this article has been provided by Alan R. Kronenwetter, avionics electrical engineer, employed by Bell Aerosystems, Inc. at the Wheatfield plant in Niagara Falls, New York from January 1967 through January 1969. The author was responsible for breadboard development of the LLTV electronic control system in Niagara Falls, New York through December 1967. Beginning January 1968 the author was assigned to Ellington Airforce Base, Houston, Texas. Ellington Airforce Base was adjacent to the Manned Spacecraft Center (now Johnson Spaceflight Center) and provided facilities in several hangars on the base that were dedicated to the development, assembly and testing of the LLTV. The author was responsible for preflight electronics testing, modifications and documentation for the LLTV control system modules and electronic circuit boards while employed at Ellington AFB.

Major Apollo program events for 1968:

October 11 - Apollo program: NASA launched Apollo 7, the first manned Apollo mission, with astronauts Wally Schirra, Don Fulton Eisele and R. Walter Cunningham aboard. Goals for the mission included the first live television broadcast from orbit and testing the lunar module docking maneuver.

December 24 - Apollo 8 enters Moon orbit. Frank Borman, Jim Lovell and William A. Anders were the first humans to see the far side of the Moon and planet Earth as a whole.

Near Fatalities:

1968 December 8: LLTV No. 1 crashed at Ellington AFB, Texas. MSC test pilot Joseph Algranti ejected safely.

1971 January 29: An LLTV crashed at Ellington AFB, Texas. NASA test pilot Stuart Present ejected safely.

See also http://en.wikipedia.org/wiki/Space_disaster

See also http://grin.hq.nasa.gov/ABSTRACTS/GPN-2000-001901.html

See also http://www.hq.nasa.gov/alsj/LLTV-952.html