A former RAF Kinloss Mountain Rescue Team leader has told how he sought evidence that a Russian satellite crashed in the Highlands 50 years ago.
David "Heavy" Whalley was intrigued by a story from the 1960s that a shepherd found the remains of a Sputnik on a moor above Ardgay in Sutherland.
An RAF Kinloss Mountain Rescue Team member sent to the scene later told Mr Whalley of finding unusual debris.
Team members involved were allegedly told to "keep quiet" about it.
After becoming Kinloss's rescue team leader in the late 1980s, Mr Whalley tried to find a record of the search in the team's logs. He believes the information was deliberately suppressed.
Sputniks were a series of satellites built and launched by the former Soviet Union.
The first was launched in 1957 and was the first man-made satellite to orbit the Earth.
The achievement has been widely credited with starting the space race between Russia and the US.
In 1962, a shepherd reported finding wreckage from a Sputnik in the hills above Ardgay.
The late Jack Baines, an experienced climber who later became an RAF Kinloss MRT leader, was among military searchers sent to investigate.
For the first time, Mr Whalley has revealed publicly that he looked for records of what they recovered.
He said: "They found various bits and pieces.
"They included a part with Russian and pictures on it explaining what to do if the satellite was found crashed, and that a reward would be given for its return.
"Jack said the team were told to keep quiet about what they found.
"When he told me the story I first thought it was an urban myth, but he convinced me and I believe they definitely found a crashed Sputnik."
Mr Whalley added: "There is no incident report, or mention in the team archives, as I checked when I became the team leader in the late 80s."
The story of the crash is recalled in a section of Frank Card's 1993 book Whensoever, which marked 50 years of RAF mountain rescue.
The book places the incident in spring 1962.
In September of that year, a chunk of Sputnik IV smashed into a street in Manitowoc, Wisconsin, after the satellite burned up in the atmosphere.
Keith Bryers, a Dingwall-based amateur historian, investigated the Ardgay incident in the 1990s.
He found mention of "problematic wreckage" among an informal RAF list of crashes.
Mr Bryers said his investigations left him 99% convinced the wreck was the remains of a crashed US high altitude spy balloon.
The balloons carried a gondola fitted with cameras and drifted over the Soviet Union on winter jet streams to photograph military airfields and bombers.
Mr Bryers said there was a cover story that the balloons were for researching weather conditions.
He said: "This was the period before spy satellites and the American U2 spy plane.
"The balloons were launched from various sites around Europe."
Mr Bryers is certain the Ardgay wreckage was of a balloon from the US 28th Weather Squadron which was based at a Royal Navy station at Evanton, in Easter Ross, from 1955 to 1966.
He said the gondolas had stickers on them with cartoons showing people what to do if they found it. It was possible there was also writing in Russian, or Asian, languages on the stickers, he added.
The Ministry of Defence said it did not hold records from that time and could not make any comment on the claims.