7.14 How come the LM simulator was so unstable that it crashed?

IN A NUTSHELL: Neil Armstrong narrowly escaped from a crash of the lunar landing simulator vehicle. But that doesn’t mean that the Lunar Module was unstable. The simulator was a completely different vehicle than the LM, and anyway the crash was caused by a rare malfunction of the vehicle, not by Armstrong’s inability to control it. The simulator had flown normally over 790 times without loss of control.

THE DETAILS: The Apollo astronauts familiarized with the unique characteristics of the lunar module by using two types of flying simulator, known as Lunar Landing Research Vehicle (LLRV) and Lunar Landing Training Vehicle (LLTV). These were essentially bare frames on which a gimbaled jet engine was mounted vertically, so that its thrust supported five sixths of the weight of the ungainly craft. The remainder (the weight it would have had on the Moon) was supported by two throttleable rocket engines (Figure 7.14-1).

Figure 7.14-1. An LLRV in flight in 1964. Detail from NASA photo ECN-506.

Like the LM, these vehicles had sixteen small thrusters for attitude control. An electronic system kept the main jet engine constantly vertical and adjusted its thrust so as to simulate the effects of the reduced vertical acceleration that occurs on the Moon. Flights lasted only a handful of minutes, but were long enough to practice landing from an altitude of approximately 1,200 meters (4,000 feet).

Two LLRVs were built first, followed by three LLTVs. Armstrong’s accident occurred on May 6, 1968, with an LLRV (Figure 7.14-2): the pressurization system of the attitude thrusters failed, a gust of wind caught the vehicle, and Armstrong had no choice but to eject, landing safely under his parachute while the LLRV crashed and burned.

Figure 7.14-2. Neil Armstrong parachutes to safety after the malfunction of his LLRV.

During the training flights, these experimental vehicles suffered two more accidents, in December 1968 and in January 1971, leading to their destruction. The pilots were unharmed.

Conspiracy theorists make it sound as if crashing was the normal conclusion of the flights of these vehicles, but in actual fact the five simulators that were built flew a total of 792 flights with successful landings. Armstrong’s LLRV had flown without mishap 281 times before the crash.*

* Unconventional, Contrary, and Ugly: The Lunar Landing Research Vehicle, by Gene J. Matranga, C. Wayne Ottinger and Calvin R. Jarvis with C. Christian Gelzer. NASA SP-2004-4535 (2005), p. 142.

For example, here is a video of a 1969 flight of the LLRV which ended with a smooth landing. Neil Armstrong was at the controls.

Figure 7.14-3. Neil Armstrong flies the LLRV without mishap in 1969. Source: NASA Armstrong Flight Research Center.