John Casani, engineer at NASA's Jet Propulsion Lab whose craft unlocked the solar system's secrets

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John Casani, who has died aged 92, was an American spaceflight engineer who led the teams that pioneered Nasa's explorations of the planets since the dawn of the Space Age. They took the first close-up images and scientific measurements of remote planets, moons and asteroids across the length and breadth of our solar system – from burning Mercury to freezing Neptune, in space endeavours unequalled before or since.
Working at Nasa's Jet Propulsion Laboratory (JPL) in California, Casani was at the centre of the golden age of space exploration for five decades from the late 1950s. Some of his spacecraft from the 1970s are still functioning in deep space, having now outlived him.
His early spacecraft were so small that he carried them around in a briefcase – but despite their primitive design, they became the first objects to escape the Earth's gravity and measured our planet's radiation belts.
Casani was project manager for the two Nasa Voyager probes that departed Earth in 1977 for the outer planets Jupiter, Saturn, Uranus and Neptune. Despite being the fastest man-made craft to that date, Voyager 2 took 12 years to reach the final planet, Neptune. Now, having left our solar system and entered uncharted interstellar space, both Voyagers are still functioning as they approach 48 years since launch. Voyager 1 is zipping along at more than 38,000 mph, still the fastest human-built object.
The two craft carry the celebrated Voyager Golden Records, which have messages for any alien civilisations which might stumble across these earthly emissaries in some distant corner of the galaxy. Casani asked the astronomer Carl Sagan to come up with the content – recordings of natural sounds including surf, wind, and animals, greetings in 55 languages, music, pictures of Earth and drawings of two naked humans.
Casani later ran the troubled Galileo mission to Jupiter for a decade. In 1985 the completed spacecraft was being transferred to Cape Canaveral in Florida for launch when the space shuttle Challenger exploded in flight, killing seven crew. Galileo was designed for launch on another shuttle, but the fleet was grounded, and so it missed the carefully planned trajectory to its destination. Galileo languished on Earth for four more years while Casani's team came up with a complicated new pathway to Jupiter via Venus, two asteroids and two fly-bys of Earth.
With everything ready for a second launch attempt, anti-nuclear protesters threatened to disrupt the mission due to concerns about the nuclear power sources it carried. So the spacecraft was delivered to the Kennedy Space Center by a high-speed truck convoy that departed JPL in the middle of the night.
Fearing that the trucks might be hijacked by the protesters, or by terrorists seeking the plutonium, the route was kept secret from the drivers in advance. They drove across the US in one almost continual trip. Protests erupted as activists stormed the Space Center, and three were jailed, but Galileo launched without incident.
After 18 months in the vicinity of Venus and Earth, Galileo was commanded to unfurl its main antenna as it sailed deeper into space. But the mechanism had by now spent four years in unplanned storage and would not work. Without the big antenna, the stream of photos and data from distant Jupiter would be a meagre trickle. Casani and his team re-purposed two smaller antennae and salvaged most of the mission's scientific objectives.
John Richard Casani was born on September 17 1932 to Jack and Julia Casani in Philadelphia, spending his childhood in the city's suburbs. From an early age he was fascinated by mechanical devices and invented several for his parents' home – a garage door opener and automatic light switches. He graduated in electrical engineering from the University of Pennsylvania in 1955.
After brief employment at the US Air Force's Rome Air Development Center in New York, he went off on a capricious road trip to California fuelled by a lack of direction in life. But he was soon hired, almost by accident, by Nasa's then-secretive Jet Propulsion Laboratory in Pasadena, where he stayed.
In addition to the Voyagers and Galileo, Casani also worked on space probes to the Moon, Mars and Saturn. In 1994 he was appointed JPL's Chief Engineer, a position created specifically for him.
Casani co-wrote The Moons of Jupiter (2004) which described the discoveries of Nasa's Galileo probe. He also appeared in The Farthest, a 2017 documentary on the Voyager craft. He did not live to see his biography Born to Explore: John Casani's Grand Tour of the Solar System by Jay Gallentine, which is to be published in December 2025.
John Casani's wife, Lynn, née Seitz, died in 2008. The couple had five sons.
John Casani, born September 17 1932, died June 19 2025
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