Orbiter program launched by NASA from 1966 to 1967. Most of the coverage of the far side was provided by the final probe in the series, Lunar Orbiter 5. The far side was first seen directly by human eyes during the Apollo 8 mission in December, 1968. Astronaut William Anders described the view: It has been seen by all 24 men who flew on Apollo 8 and Apollo 10 through Apollo 17, and photographed by multiple lunar probes. Spacecraft passing behind the Moon were out of direct radio communication with the Earth, and had to wait until the orbit allowed transmission. During the Apollo missions, the main engine of the Service Module was fired when the vessel was behind the Moon, producing some tense moments in Mission Control before the craft reappeared. Geologist-astronaut Harrison Schmitt, who became the last to step onto the Moon, had aggressively lobbied for his landing site to be on the far side of the Moon, targeting the lava-filled crater Tsiolkovskiy. Schmitt's ambitious proposal included a special communications satellite based on the existing TIROS satellites to be launched into a Farquhar–Lissajous halo orbit around the L2 point so as to maintain line-of-sight contact with the astronauts during their powered descent and lunar surface operations. NASA administrators rejected these plans on the grounds of added risk and lack of funding. The idea of utilizing Earth–Moon for communications satellite covering the Moon's far side has been realized, as China National Space Administration launched Queqiao relay satellite in 2018. It has since been used for communications between the Chang'e 4 lander and Yutu 2 rover that have successfully landed in early 2019 on the lunar far side and ground stations on the Earth. And L2 is proposed to be "an ideal location" for a propellant depot as part of the proposed depot-based space transportation architecture. Soft landing The China National Space Administration's Chang'e 4 achieved humanity's first ever soft landing on the lunar far side on 3 January 2019 and deployed Yutu-2 lunar rover onto far side lunar surface. The craft included a lander equipped with a low-frequency radio spectrograph and geological research tools. The far side of the Moon provides a good environment for radio astronomy as interferences from the Earth are blocked by the Moon. In February 2020, Chinese astronomers reported, for the first time, a high-resolution image of a lunar ejecta sequence, and, as well, direct