Apollo Program Apollo 8 Performs The First Successful Trans Earth Injection Tei Maneuver Sending The Crew And Spacecraft On A Trajectory Back To Earth From Lunar Orbit - December 25 in History

The Apollo program, also known as Project Apollo, was the United States human spaceflight program led by NASA, which landed the first humans on the Moon in 1969. Apollo was conceived during Project Mercury and executed after Project Gemini. It was conceived in 1960 as a three-person spacecraft during the Presidency of Dwight D. Eisenhower. Apollo was later dedicated to President John F. Kennedy's national goal for the 1960s of "landing a man on the Moon and returning him safely to the Earth" in an address to Congress on May 25, 1961.

Apollo 8 was the first crewed spacecraft to leave Earth's gravitational sphere of influence, and the first human spaceflight to reach the Moon. The crew orbited the Moon ten times without landing and then returned to Earth. The three astronauts—Frank Borman, Jim Lovell, and William Anders—were the first humans to see and photograph the far side of the Moon and an Earthrise.

A trans-Earth injection (TEI) is a propulsion maneuver used to set a spacecraft on a trajectory which will intersect the Earth's sphere of influence, usually putting the spacecraft on a free return trajectory.

Earth is the third planet from the Sun and the only astronomical object known to harbor life. This is enabled by Earth being an ocean world, the only one in the Solar System sustaining liquid surface water. Almost all of Earth's water is contained in its global ocean, covering 70.8% of Earth's crust. The remaining 29.2% of Earth's crust is land, most of which is located in the form of continental landmasses within Earth's land hemisphere. Most of Earth's land is at least somewhat humid and covered by vegetation, while large sheets of ice at Earth's polar deserts retain more water than Earth's groundwater, lakes, rivers, and atmospheric water combined. Earth's crust consists of slowly moving tectonic plates, which interact to produce mountain ranges, volcanoes, and earthquakes. Earth has a liquid outer core that generates a magnetosphere capable of deflecting most of the destructive solar winds and cosmic radiation.

In astronomy and spaceflight, a lunar orbit is an orbit by an object around Earth's Moon. In general these orbits are not circular. When farthest from the Moon a spacecraft is said to be at apolune, apocynthion, or aposelene. When closest to the Moon it is said to be at perilune, pericynthion, or periselene. These derive from names or epithets of the moon goddess.

December 25 is the 359th day of the year in the Gregorian calendar; six days remain until the end of the year.

Apollo program: Apollo 8 performs the first successful Trans-Earth injection (TEI) maneuver, sending the crew and spacecraft on a trajectory back to Earth from Lunar orbit.

Apollo program

Apollo 8

Trans-Earth injection

Earth

Lunar orbit

December 25