This odd-looking flying machine was used by astronauts to simulate the landing of a Lunar Module (LM) on the Moon. It consisted of a gimbaled jet engine mounted face down so that its thrust simulated the gravity the LM would encounter as it made its descent to the Moon. Built before the LM, the Lunar Landing Research Vehicle (LLRV) was the predecessor to the Lunar Landing Training Vehicle (LLTV). The LLTV was a modified version of the LLRV that made the vehicle more closely match the behavior and control of the LM under lunar-landing conditions. Despite NASA’s concern about the safety of the LLTV (there were three crashes), the astronauts considered LLTV flights an essential part of their training and so convinced NASA to allow them to continue using the craft.The LLRV was built by Bell Aerosystems. Development, testing, and refinement of this vehicle took place at Edwards Airforce Base in California while astronaut training flights took place at the Manned Spacecraft Center in Houston.