16, Apollo 17 carried a Lunar Roving Vehicle. In addition to being used by the astronauts for transport from station to station on the mission's three moonwalks, the LRV was used to transport the astronauts' tools, communications equipment, and the lunar samples they gathered. The Apollo 17 LRV was also used to carry some of the scientific instruments, such as the Traverse Gravimeter Experiment (TGE) and Surface Electrical Properties (SEP) experiment. The Apollo 17 LRV traveled a cumulative distance of approximately in a total drive time of about four hours and twenty-six minutes; the greatest distance Cernan and Schmitt traveled from the lunar module was about . This was the only mission to carry the TGE, which was built by Draper Laboratory at the Massachusetts Institute of Technology. As gravimeters had been useful in studying the Earth's internal structure, the objective of this experiment was to do the same on the Moon. The gravimeter was used to obtain relative gravity measurements at the landing site in the immediate vicinity of the lunar module, as well as various locations on the mission's traverse routes. Scientists would then use this data to help determine the geological substructure of the landing site and the surrounding vicinity. Measurements were taken while the TGE was mounted on the LRV, and also while the device was placed on the lunar surface. A total of 26 measurements were taken with the TGE during the mission's three moonwalks, with productive results. The SEP was also unique to Apollo 17, and included two major components: a transmitting antenna deployed near the lunar module and a receiver mounted on the LRV. At different stops during the mission's traverses, electrical signals traveled from the transmitting device, through the ground, and were received at the LRV. The electrical properties of the lunar regolith could be determined by comparison of the transmitted and received electrical signals. The results of this experiment, which are consistent with lunar rock composition, show that there is almost no water in the area of the Moon in which Apollo 17 landed, to a depth of . A long, diameter device, the Lunar Neutron Probe was inserted into one of the holes drilled into the surface to collect core samples. It was designed to measure the quantity of neutrons which penetrated to the detectors it bore along its length. This was intended to measure the rate of the "gardening"