3753 Cruithne It was not until 1997 that its unusual orbit was determined by Paul Wiegert and Kimmo Innanen, working at York University in Toronto, and Seppo Mikkola, working at the University of Turku in Finland. Cruithne is approximately in diameter, and its closest approach to Earth is , approximately thirty times the separation between Earth and the Moon. From 1994 through 2015, Cruithne made its annual closest approach to Earth every November. Although Cruithne's orbit is not thought to be stable over the long term, calculations by Wiegert and Innanen showed that it has probably been synchronized with Earth's orbit for
Journey of Apollo 15 to the Moon small risk that it could cause the spacecraft to depressurize. It was possible, in an emergency for the crew to spend the cruise back to Earth in their pressurized space suits. The major event of day 4 was Lunar Orbit Insertion (LOI). Occurring behind the Moon, out of contact with the Earth, this engine burn put the spacecraft into orbit around the Moon. It was the first test of the new procedures for using both SPS during a long burn. Loss of Signal (LOS) was at 78 hours, 23 minutes and 31 seconds GET as the spacecraft went behind the