further testing or to make small changes. Mechanical problems came from the fact the instruments were designed to operate in space, but had to be tested on the surface of the Earth. As such, things like the 7.5 m (24 ft) booms for the mass and gamma ray spectrometers could be tested only using equipment that tried to mimic the space environment, and, in space, the mass spectrometer boom several times did not fully retract. On the lunar module, the fuel and oxidizer tanks were enlarged on both the descent and ascent stages, and the engine bell on the descent stage was extended. Batteries and solar cells were added for increased electrical power. In all this increased the weight of the lunar module to , heavier than previous models. If Apollo 15 had flown as an H mission, it would have been with CSM-111 and LM-9. That CSM was used by the Apollo–Soyuz Test Project in 1975, but the lunar module went unused and is now at the Kennedy Space Center Visitor Complex. Endeavour is on display at the National Museum of the United States Air Force at Wright-Patterson Air Force Base in Dayton, Ohio, following its transfer of ownership from NASA to the Smithsonian in December 1974. Launch vehicle The Saturn V that launched Apollo 15 was designated SA-510, the tenth flight-ready model of the rocket. As the payload of the rocket was greater, changes were made to the rocket and to its launch trajectory. It was launched in a more southerly direction (80–100 degrees azimuth) than previous missions, and the Earth parking orbit was lowered to . These two changes meant more could be launched. The propellant reserves were reduced and the number of retrorockets on the S-IC first stage (used to separate the spent first stage from the S-II second stage) reduced from eight to four. The four outboard engines of the S-IC would be burned longer and the center engine would also burn longer. Changes were also made to the S-II to dampen pogo oscillations. Once all major systems were installed in the SaturnV, it was moved from the Vehicle Assembly Building to the launch site, Launch Complex 39A. During late June and early July 1971, the rocket and Launch Umbilical Tower (LUT) were struck by lightning at least four times. There was no damage to the vehicle, and only minor damage to ground support equipment.