folded into a space 5 ft by 20 in (1.5 m by 0.5 m). Unloaded, it weighed 460 lb (209 kg) and when carrying two astronauts and their equipment, 1500 lb (700 kg). Each wheel was independently driven by a horsepower (200 W) electric motor. Although it could be driven by either astronaut, the commander always drove. Travelling at speeds up to 6to 8mph (10to 12km/h), it meant that for the first time the astronauts could travel far afield from their lander and still have enough time to do some scientific experiments. The Apollo 15 rover bore a plaque, reading: "Man's First Wheels on the Moon, Delivered by Falcon, July 30, 1971". During pre-launch testing, the LRV was given additional bracing, lest it collapse if someone sat on it under Earth conditions. Particles and Fields Subsatellite The Apollo 15 Particles and Fields Subsatellite (PFS-1) was a small satellite released into lunar orbit from the SIM bay just before the mission left orbit to return to Earth. Its main objectives were to study the plasma, particle, and magnetic field environment of the Moon and map the lunar gravity field. Specifically, it measured plasma and energetic particle intensities and vector magnetic fields, and facilitated tracking of the satellite velocity to high precision. A basic requirement was that the satellite acquire fields and particle data everywhere on the orbit around the Moon. As well as measuring magnetic fields, the satellite contained sensors to study the Moon's mass concentrations, or mascons. The satellite orbited the Moon and returned data from August 4, 1971, until January 1973, when, following multiple failures of the subsatellite's electronics, ground support was terminated. It is believed to have crashed into the Moon sometime thereafter. Mission highlights Launch and outbound trip Apollo 15 was launched on July 26, 1971, at 9:34am EDT from the Kennedy Space Center at Merritt Island, Florida. The time of launch was at the very start of the two-hour, 37-minute launch window, which would allow Apollo 15 to arrive at the Moon with the proper lighting conditions at Hadley Rille; had the mission been postponed beyond another window on July 27, it could not have been rescheduled until late August. The astronauts had been awakened five and a quarter hours before launch by Slayton, and after breakfast and suiting up, had been taken to Pad 39A, launch site of all seven attempts at crewed lunar landing,