NASA was formed in 1958 and from the very start a number of it's astronauts and test pilots testified to sighting UFOs or craft of undetermined origin.
Initially Joseph Walker was the first to announce a sighting -- he told the National Conference on the Peaceful Uses of Space Research in 1962 that he had an aerial encounter with two disc-shaped objects the previous month. He had actually filmed the encounter.
In April 1962, NASA pilot, Joseph Walker, filmed five cylindrical and disc-shaped objects from his X-15 aircraft.
Another test pilot reported an incident involving a formation of UFOs whilst flying at 314,000 feet.
NASA refused to reveal any evidence that might substantiate the pilots' claims -- photographs or films were never released.
In April 1964, two radar technicians watched UFOs following an unmanned Gemini capsule.
In 1965, the FBI received information from a confidential source that an informant at NASA was secretly divulging information on UFOs to two UFO researchers in Pittsburgh. According to FBI files:
"The source believes that the informant may be classified and had actually seen a film showing a missile separating and a UFO appearing on the screen. "The informant advised prior to the flight of Gemini 4 - watch out for something interesting because the spaceship had devices aboard to detect UFOs."
The FBI files infer that NASA was (is) withholding filmed evidence of UFOs, to which the general public is being denied access and the remarks about Gemini 4 is of special interest because James McDivitt, a pilot with Gemini 4, confirmed that during the mission he did see an "unidentified object."
On 4th December 1965, astronauts Borman and Lovell of the Gemini 7 mission were involved in this communication with Mission Control:
Gemini 7: Bogey at 10 o' clock high.
Mission Control: This is Houston, say again seven.
Gemini 7: We have bogey at 10 o' clock high.
Mission Control: Gemini 7 is that the booster or is that an actual sighting?
Gemini 7: We have several, looks like debris up here. Actual sighting.
Mission Control: Estimate distance or size?
Gemini 7: We also have booster in sight.
On 12 September 1966, Gemini astronauts, Richard Gordon and Charles Conrad reported to Mission Control that their craft was being observed by a UFO estimated at being about six miles away.
Unexplained sighting - Gemini 11
On 13th September 1966, astronauts Charles Conrad and Richards Gordon observed an object that remains unidentified to this day. The object, which they managed to capture on film, traveled so close to Gemini 11 that it would normally be very easy to identify but despite claims that it was, in fact, the Proton 3 satellite or parts thereof (claimed by NORAD) , the object still remains anomalous.
Following the Gemini missions the Apollo Space Program took effect, and on 20th July 1969 the astronauts of Apollo 11 took their first steps on the surface of the Moon. Although it was claimed that nothing unusual was seen by the astronauts, rumors that the crew were "never alone" whilst on the moon began to circulate. The following conversation is alleged to have taken place between Mission Control and the crew of Apollo 11:-
Apollo 11: What was it? What the hell was it? That's all I want to know. These babies were huge, sir... Oh God, you wouldn't believe it...
NASA : What... what the hell's going on?
Apollo 11: They are here, under the surface.
NASA : What's there? Mission Control calling Apollo 11.
Apollo 11: Roger, we're here, all three of us. But we have found some visitors... They've been here for quite a while judging by the installations... I'm telling you, there are other spacecraft out there. They're lined up in ranks on the far side of the crater's edge...
However, the evidence for the truth of this event is very doubtful, Otto Binder, a former NASA employee, claimed it was overheard by amateur radio enthusiasts who could access a confidential channel.
Neil Armstrong - the first man to set foot on the Moon - denies it. At approximately 6:30 AM on 17th March 1990, a radio ham from Baltimore, Donald Ratsch, was listening to transmissions from Discovery when he heard the following: "Houston, this is Discovery, we have a problem. We have a fire."
Shortly after, Ratsch claims he heard "Houston this is Discovery, we still have the Alien spacecraft under observance."
A former mission specialist with NASA , Bob Oeschler conducted an intense investigation into these events and concluded that the message had in fact been broadcast from the vicinity of Fort Meade in Maryland, an area where the US National Security Agency had its base.
The NSA has long been interested in UFOs, and Oeschler was of the opinion that the transmission was a deliberately set-up hoax for some intelligence purpose.
Further evidence later came to light, however, when a senior NASA source informed Oeschler that Discovery was involved in a UFO incident which lasted for eight hours. Also, apparently the electrical system on board Discovery experienced substantial problems during the encounter.
Excerpt from Presentation by Thomas P. Stafford, NASA Channel---Gallery/History Hour Dec. 20, 2002 1:00 - 2:00 PM, EST.
Amid an informative hour-long presentation today about the NASA Gemini Apollo, and Apollo-Soyuz programs, accompanied by some stock visuals, Stafford made several stone-faced quips throughout his presentation - among them: [at about 1:52pm EST]
"Then on to a place you know about... Area 51. That's where we had the dead aliens buried. We used to have them down at Roswell, but that got too much publicity, so we moved them there."
The reaction from the crowd was the expected laugh, while Stafford never flinched during the remarks. It could be stated that he appeared sincere, but the crowd took it as a joke, obviously, and he moved on without a pause and continued to talk about the F-16, the B-1, and B-2 and other aircraft tested at Area 51.
"People have been digging through the files and investigating for years now. The files are quite convincing. The only thing that's lacking is the official stamp," Edgar Mitchell, Apollo 14 astronaut.