Not much information was released about Zond 5, but many believed it was a precursor to Soviet's manned lunar flight attempt. Zond 5 carried a biological payload (including two russian tortoises, wine flies, meal worms, plants, seeds, bacteria, and other living matter) flew around the moon and returned to Earth six days later. The success of Zond 5 added pressure on the US Apollo program to make its 1969 landing goal. There was speculation within NASA and the press that the Soviet might be preparing to launch cosmonauts on a similar circumlunar mission before the end of 1968.
On December 21, 1968, Apollo 8, the second human spaceflight mission in the United States Apollo space program, was launched and became the first manned spacecraft to leave Earth orbit, reach the Earth's Moon, orbit it and return safely to Earth.
On December 24, 1968, Frank Borman, Jim Lovell, and Bill Anders became the first humans to enter into orbit around the Moon. They orbited ten times, and transmitted one of the most watched TV broadcasts in history. A few hours later, the crew performed the first-ever Trans-Earth injection (TEI) burn, to blast the Apollo 8 spacecraft out of lunar orbit and on to a trajectory back to the Earth. Just over two days later, on December 27, Apollo 8 safely splashed down in the Pacific.
