Growing up in California, Peter C. Theisinger assembled model airplanes, tinkered with electronic hobby kits and operated a ham radio set. But when it came to building anything bigger than a bread box, even as an adult, he recalled, “I was never mechanical, never tried to fix my car.”
“I’m a klutz,” he said.
Belying his modesty, though, Mr. Theisinger (pronounced THIGH-sin-ger) oversaw projects for NASA and the Jet Propulsion Laboratory in California that landed three jalopy-like robotic contraptions weighing a combined 2,700 pounds on the surface of Mars, hundreds of millions of miles from Earth.
The rovers, as they were called, searched successfully in freezing deserts and mineral deposits for geological clues to whether the planet’s environment had supported water in ancient times and was therefore potentially conducive to life. They uncovered evidence of ancient hot springs that could have provided ideal habitats for microbial life billions of years ago.
The names of the rovers were chosen in a contest by schoolchildren, but the names given to the three that Mr. Theisinger supervised — the golf-cart-size twins Spirit and Opportunity, which landed on Mars in January 2004, and the larger and heavier Curiosity, which alighted in August 2012 — might just as well have described Mr. Theisinger himself.
He died at 78 on June 26 at his home in La Crescenta, Calif. The cause was throat cancer, his wife, Dona Theisinger, said.
“Scientists and engineers come at this sort of thing somewhat differently,” Steven W. Squyres, a planetary scientist at Cornell University and the principal investigator on the Spirit and Opportunity mission, said in an oral history interview with NASA in 2017.
“The scientists, if they think about it purely from the standpoint of the science, are interested in learning what happened on Mars; I’ve always said scientists are seekers of truth,” he said. “Engineers, on the other hand, have to make it work. They’ve got to actually build something that will do a specific job and not fail.”
“Pete intuitively, instinctively realized that our mission was engineering in the cause of science,” Professor Squyres said.
Adam D. Steltzner, who worked with Mr. Theisinger at the Jet Propulsion Laboratory, called him “a titan of the Mars program.”
Mr. Theisinger’s vision went well beyond Mars. He also worked on the 1967 Mariner mission to Venus, the 1971 Mariner orbiter mission to Mars, the 1977 Voyager mission to the solar system’s outer planets, and the 1989 Galileo mission to Jupiter.
Mr. Theisinger and Richard Cook, a colleague at the Jet Propulsion Laboratory, were included in Time magazine’s 2013 list of the 100 Most Influential People in the world for their work on Curiosity. In 2017, Mr. Theisinger received a lifetime achievement award from the Smithsonian’s National Air and Space Museum.
Peter Charles Theisinger was born on Aug. 7, 1945, in Fresno, Calif., to Leslie and Patricia (Horan) Theisinger. His father was an electrical engineer who worked in the aerospace industry. His mother, who was known as Agnes, was a teacher.
Peter earned a bachelor’s degree in physics from the California Institute of Technology in 1967. “In those days, if you were at the top end of your high school class, you tended to see math and physics and chemistry as exciting topics,” he said.
While he was in college, he spent a summer working at the Jet Propulsion Laboratory, in La Cañada Flintridge, where it is managed for NASA by Caltech. He was hooked, and that sense of wonder never waned.
When astronomers unveiled the first full-color mosaic picture of Io, one of Jupiter’s moons, at a news conference in 1999, he recalled, “the entire audience just gasped — a very audible gasp.”
“And I said to myself at the time, I know why I do this,” he said. “The ‘psychic’ return is phenomenally high, and we are addicted to it.”
When he graduated from Caltech, he jumped at a job offer from the lab and went on to serve as manager of the spacecraft system engineering section and director for engineering and science. Except for three years working for a contractor, he remained there until he retired in 2017.
He married Dona Myers in 1983. In addition to her, he is survived by his two sons, Peter Jeffrey and William, both from an earlier marriage to Cathy Barber, which ended in divorce; his stepdaughters, Tracy Haywood and Kelly Neate; and a granddaughter.
Work on the Mars Exploration Rover program followed two embarrassing failed attempts to explore the planet in 1999 — glitches blamed on a “faster, better, cheaper” mantra at NASA that got stretched too far. A mix-up between metric and imperial units caused the Mars Climate Orbiter to be ripped apart in the atmosphere on Sept. 23, 1999. Just over two months later, the Mars Polar Lander vanished as it was landing. An investigation found that its engines had most likely shut off too early, causing it to plummet to its destruction.
As the project manager responsible for developing the Spirit and Opportunity rover program, Mr. Theisinger completed in 27 months a project that could easily have taken nearly five years.
In late 2003, the twin rovers were ready to descend to Mars’s forbidding terrain. Spirit’s destination was a crater that scientists believed may once have contained water. Opportunity was headed for a plain on the other side of the planet that satellite studies suggested might contain gray hematite, a mineral often associated with the presence of water.
Spirit nearly crash-landed on Jan. 3, 2004, just days after engineers on the ground discovered a potentially fatal flaw in the electronic timing mechanisms that would inflate airbags and fire rockets to cushion the landing.
Hours before touchdown, Mr. Theisinger’s team suggested switching the system on about 40 minutes earlier than planned. That was risky to attempt with so little time, but the engineers argued that it was essential to avoid what might otherwise be certain doom.
Mr. Theisinger told them that he would back them up if they were unanimous. They were, and the plan worked.
“The solution was to manually send commands from the ground in the hour before entry,” David C. Agle, a spokesman for the lab, said in an interview. “After analyzing the rovers post-landing, the consensus of the team was that if we hadn’t sent those commands, Spirit would probably have crashed.”
Mr. Theisinger summed up the lab’s ethos to Brian Muirhead and Judith and Garfield Reeves-Stevens in their 2004 book, “Going to Mars”: “They will forgive you for being unlucky, but they will not forgive you for being stupid.”
The twin rovers were supposed to explore the Martian landscape for only 90 days. They were so productive that Spirit’s mission continued until 2010. Opportunity endured until 2018, meandering nearly 30 miles instead of the third of a mile it had been expected to traverse. Along its expanded trek it provided intimate geological images, including some of layers of rock that had preserved ripples of flowing water.
The success of Mr. Theisinger and his team restored luster to NASA’s planetary exploration program.
Recalling the morning of Jan. 3, 2004, Mr. Theisinger said: “I got up that first Saturday when Spirit was to land, and as I was shaving I looked in the mirror and I said, ‘OK, when I look in this mirror tomorrow, the world will be different.’ I did not know how it will be different, but it will be different, because we will hit Mars tonight.”
Kenneth Chang contributed reporting.
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