Slovenian physicist Dušan Petrač, who was a leading NASA scientist, has died aged 91. The news of the death of the long-term member of the Slovenian Democratic Party (SDS) has been announced by SDS leader Janez Janša.

Petrač was a world-renowned physicist and the first Slovenian candidate for a flight into space. Since 1973 he had been directly involved in experiments in the zero-gravity laboratory, and in experiments with rockets, space taxis and artificial satellites.

He was an internationally renowned expert in space technology, author of many scientific publications and active participant in numerous scientific symposia. He was a consultant to Stanford University, Freie Universität Berlin, the University of Tsukuba in Japan and the US company Lockheed Martin.

His most challenging tasks included the development and construction of the first infrared astronomical satellite (IRAS), which pave the way for ground-breaking discoveries. Petrač contributed a solution for controlling the infrared focal plane with 64 detectors in four infrared wavebands. He introduced a method to measure the mass of superfluid helium in zero gravity.

He was born on 28 January 1932 in Kropa as the sixth child into a working-class family. He studied physics and mathematics at the University of Ljubljana. After graduating in physics in 1956, he worked as a high school teacher in Kranj from 1957 to 1963.

A chance encounter with David Saxon, who later became the president of the University of California, during a visit to the former Nazi concentration camp Dachau, opened the door for him to do his postgraduate studies in Los Angeles, where he received his PhD in physics in 1971. His thesis dealt with phenomena in superfluid helium.

He joined the NASA Jet Propulsion Laboratory in Pasadena, California, and in 1977 became a senior science advisor at NASA. He worked at the laboratory until his retirement in 2012. He was awarded the title of solar system ambassador by NASA.

He won the Kurt Mendelssohn Medal for his contribution to the introduction of cryogenics into space, and the NASA Exceptional Service Medal. In Slovenia, he was made an honorary senator of the University of Maribor, an honorary member of the Slovenian Academy of Engineering and an honorary citizen of Kranj. He was also an honorary citizen of Los Angeles.

He always stressed that Slovenia remained his homeland. He went to the US with his wife Irena, but he often returned to the country to find that his homeland did not forget him. He worked extensively with the Slovenian Science Foundation and the VTIS association of Slovenians educated abroad.