Bruce McCandless, who has died aged 80, was the first man to make a spacewalk untethered from his craft, a feat that has only been accomplished by five other astronauts.

The photograph of him floating free in his white spacesuit with jet-powered backpack, 170 miles above the curve of the Earth, has become an icon of the space age, and one of Nasa’s most reproduced images.

In space circles it earned him the nickname “McCordless”, but the media and his Space Shuttle crew mates hailed him as a real-life embodiment of the comic-book hero Buck Rogers, a label that he accepted cheerfully.

McCandless had joined Nasa in 1966, expecting to be part of the forthcoming Moon landing expeditions of Project Apollo. But although he served as a member of the support crew for Apollo 14, his lack of test pilot experience pushed him down the rankings in the eyes of management, and the Moon program was cancelled before he could secure a flight assignment.

After 18 years at Nasa, he finally found himself in the Space Shuttle Atlantis in February 1984 with a cargo of two communications satellites and the Manned Maneuvering Unit backpack, which he had played a large part in developing.

As he unlatched the device and floated off into the void, his first words were: “Well, that may have been one small step for Neil, but it’s a heck of a big leap for me!”

When he backed out of the cargo bay to a distance of 300ft McCandless was, like the Shuttle itself, orbiting the Earth at over 17,000mph. Mission Control announced that both he and Atlantis were now designated as separate spacecraft.

He felt no vertigo as he glanced down at the entire state of Florida below his feet, but shivered violently as his body heat leaked into the vacuum through his spacesuit. President Reagan called him in-flight to congratulate him.

After a safety review of the Shuttle following the Challenger disaster in 1986, which killed seven astronauts, the untethered backpack was deemed too dangerous for regular use. But McCandless’s pioneering device was transformed into the slimline Safer unit worn by present-day spacewalkers, in case their safety line fails. 

Bruce McCandless II was born in Boston, Massachusetts, on June 8 1937. His father, also Bruce, was a highly decorated US Navy officer who received the Medal of Honour for service in the Pacific during the Second World War. 

Young Bruce’s mother, Sue Worthington Bradley, was also from a distinguished Navy family. His colourful great-great grandfather, David McCanles, was shot dead by Wild Bill Hickok in a confused raid on a Pony Express station in Nebraska in 1861.

After that incident, and the subsequent disrepute of the “McCanles Gang”, the family changed its name to McCandless and moved to Colorado, where Bruce McCandless lived in later life.

His father settled the family in Long Beach, California, and Bruce was educated at the local Woodrow Wilson high school, which he left in 1954.

He then followed his father into the US Navy, graduating from Naval Academy second in a class of 899 in 1958, behind John Poindexter, the future National Security Adviser. and ahead of John McCain. 

Settling into his chosen discipline of naval aviation, McCandless flew fighters off aircraft carriers during the Cuban Missile Crisis, and subsequently became a flight instructor. He also received a Master of Science in Electrical Engineering from Stanford University in 1965. 

McCandless flew into space again in 1990 to reach a record-setting altitude for the Shuttle of 380 miles. A problem encountered during the deployment of the Hubble space telescope led to McCandless and a crewmate suited up in the airlock ready for an emergency spacewalk, but the problem was resolved before they could exit and the excursion was deemed unnecessary.

He retired from Nasa in 1990, and pursued a wide range of interests ranging from electronics and photography to scuba diving and cross-country skiing.

McCandless was a modest man, unperturbed by the fame of the ubiquitous free-flying photograph in which his face is obscured by the gold-plated visor of his space helmet.

He would pass through the Kennedy Space Center visitor complex while hordes of children gaped at his image, unaware that the occupant of the spacesuit floating above the Earth was smiling approvingly nearby.

In 1960, while taking a course at Memphis, Tennessee, he met Bernice (Bernie) Doyle, a medical technician and they married four months later.  After her death in 2014, he married Ellen Shields, a long-time friend . She survives him with a son and a daughter from his first marriage.

Bruce McCandless, born June 8 1937, died December 21 2017