This excerpt from The Enduring Enigma of the UFO by Dean Radin quotes astronauts saying UFOs are real:

"Apollo 14 astronaut Edgar Mitchell repeatedly has said that high-ranking military officers have privately admitted that for many decades factions of the U.S. government have been aware that UFOs and alien technology are real. Many other astronauts have provided corroborating statements. Mercury astronaut Scott Carpenter photographed a UFO while in orbit on May 24, 1962, later saying, “At no time when the astronauts were in space were they alone. There was a constant surveillance by UFOs.” In 1985, Mercury and Gemini astronaut Gordon Cooper, in an address to the United Nations, said: “I believe that these extraterrestrial vehicles and their crews are visiting this planet from other planets . . . For many years, I have lived with a secret, in a secrecy imposed on all specialists and astronauts. I can now reveal that every day, in the United States, our radar instruments capture objects of form and composition unknown to us. And there are thousands of witness reports and a quantity of documents to prove this, but nobody wants to make them public.” Such statements are not limited to U.S. astronauts. In 1979, Russian cosmonaut Victor Afanasyev commented on a UFO he saw while en route to the Solyut 6 space station: “It followed us during half of our orbit . . . It was an engineered structure, made from some type of metal, approximately 40 meters long with inner hulls.” —DR"

Astronaut Deke Slaton described an encounter with a UFO while he was flying a military plane.

"As I closed on this thing, it looked like a weather balloon and that's what I presumed it was. I had plenty of gas and time so I decided I'd just come back around and make make a pass on it. I got around where I should have been coming back on this thing all of a sudden it didn't look like a balloon anymore. It looked like a saucer sitting on edge about a 45 degree angle. I didn't have any gun camera film on board unfortunately or I'd a shot some pictures of it. About that time I guess, whatever it was, for whatever reason, it took off climbing at about a 45 degree angle and and just accelerated and disappeared. I obviously couldn't follow it with an old piston engine fighter so I turned around went home."

High ranking government and military officials have said that UFOs are extraterrestrial craft visiting the earth.

• Paul Hellyer Minister of Defense for Canada believes four species of aliens have been visiting the earth for thousands of years.

• Admiral Hellenkoetter Director CIA: "These UFOs are interplanetary devices systematically observing the earth…"

• Lord Hill-Norton, Chief of Defense Staff, Ministry of Defense, Great Britain: "The evidence that there are objects which have been seen in our atmosphere, and even on terra firma, that cannot be accounted for either as man-made objects or as any physical force or effect known to our scientists seems to me to be overwhelming…"

• President Harry S. Truman: "I can assure you that flying saucers, given that they exist, are not constructed by any power on earth."

• Air Chief Marshal Lord Dowding, Commander-in-Chief of RAF Fighter Command: "… [UFOs] are not manufactured by any nation on earth. I can therefore see no alternative to accepting the theory that they come from some extraterrestrial source."

• Nick Pope, British Ministry of Defense: "… intelligent extraterrestrial[s] are visiting Earth."

• H. Marshall Chadwell CIA Director of Scientific Intelligence: "Sightings of unexplained objects at great altitudes and traveling at high speeds in the vicinity of major U.S. defense installations are of such nature that they are not attributable to natural phenomena or known types of aerial vehicles."

• A report in the FBI archives vault.fbi.gov reports that a US Air Force investigator stated in 1950 that three flying saucers had been recovered. They were 50 feet in diameter with raised centers and each was occupied by three human shaped bodies each approximately 3 feet tall.