He Brought Space Telescope Images into Focus

Professor Emeritus Bob Gonsalves, E56, who created algorithms that help the Hubble and Webb telescopes take sharper images, continues to inspire his former students

When the Hubble Space Telescope launched in April 1990, it was a miracle of engineering, the best telescope ever built, stationed 332 miles in space above Earth. But soon astronomers at NASA realized there was a problem: The focus was off because the main mirror had been ground just a hair too fine—about 1/50th of the width of a human hair too fine, in fact.

NASA announced this on July 2, 1990. The same day, Bob Gonsalves, E56, then a professor of electrical and computer engineering at Tufts, got a call from the space agency. It was convening a panel of experts to find a fix and wanted him to join.

“I was on vacation at Hilton Head Island in South Carolina but cut it short to make the July 5 meeting in Washington,” says Gonsalves, now retired after teaching for more than 30 years at Tufts.

NASA had called the right engineer. Back in 1976, he had published a paper on what’s called phase retrieval, about how a specific algorithm could be used to correct distorted images. “Phase retrieval is the very last step to make sure that everything is tuned up sharp as can be. It’s sort of like autofocus on a camera,” Gonsalves says. Fast forward to 1990, and “it gave a prescription to fix what was wrong in the telescope.”

Gonsalves also came up with an algorithm dealing with what’s called phase diversity, for further image refinement. Pairing the two algorithms, he helped solve the problem of out-of-focus images on Hubble. “Without these corrective improvements, images would always be blurred,” he says.

A fuzzy image of a galaxy next to a sharper one with clearer outlines.

Before and after: Hubble images of Galaxy M51, before and after the fix. Image: Courtesy of Bob Gonsalves

Along with colleagues and students, Gonsalves helped with the design of the Corrective Optics Space Telescope Axial Replacement for Hubble, “a 3' by 3' by 8' miracle of optical engineering to insert the correcting lens,” he says. In 1993, astronauts made the repairs to the Hubble Space Telescope—essentially adding a lens to cover the camera—and all of a sudden, shots of stars and nebula that had been fuzzy and distorted became crisp and clear.

“Analyzing the problem and developing an optical correction was a masterpiece of optical engineering,” according to a history of Hubble by the European Space Agency.

But Gonsalves’ accomplishment didn’t end with Hubble. His technology for corrective optics is now employed in the James Webb Space Telescope, which launched in late December 2021. Webb is now stationed a million miles from Earth. Its first images were released in July 2022 to worldwide acclaim and its scientific work has been breaking new ground ever since.

That’s something that Gonsalves is especially proud of. “I have a personal connection to that telescope,” he says. Beginning in 2008 he was invited to a series of meetings at Ball Aerospace, which was designing and then building the advanced optical technology and mirror system going in Webb.

“The NASA-funded team was studying phase retrieval and phase diversity as the last steps in commissioning the 18 hexagonal elements of the mirror,” he reports. He helped the scientists write algorithms and prepare reports for NASA on this extraordinarily complex multi-decade project.

In other words, any time you see the astounding images from far outer space these days, you can thank Gonsalves in part for their clarity.

Applying Lessons in the Classroom

Having a hand in these space telescopes has been a highlight of Gonsalves’ career, but he’s equally proud of having taught for some 50 years—about 10,000 students, he reckons.

Ethan Danahy and Robert Gonsalves sitting together at a restaurant.

“I find myself inspired by and taking so many lessons from my time learning from and working with Bob, and applying all of that to my own teaching,” says Ethan Danahy, left, of his time with Robert Gonsalves, right.


After graduating from Tufts on an NROTC scholarship, Gonsalves served in the Navy, then worked in industry. But he returned to school and earned a Ph.D. from Northeastern University, where he taught engineering for 20 years. Then he received the offer he really wanted: to come back to teach at Tufts. “My goal was always to go back to Tufts,” he says.

He taught at Tufts for some three decades. He served as department chair for two years before officially retiring, and continued to teach courses at the university even after formally stepping down. While still on the faculty, he also founded and ran a digital imaging company, Lexitek.

He also had an active research career—he published 170 papers, and one paper about telescope imaging has averaged 40 references per year for the past 10 years, pretty good for research from 1982.

Gonsalves inspired many students, among them one who went on to become a professor of engineering  at Tufts. “He was my first engineering professor during my first undergraduate semester,” says Ethan Danahy, E00, EG02, and EG07, a research associate professor in the School of Engineering.

“To think, as an 18-year-old starting out, I was taking an image processing course from the person who did the actual image processing that helped solve the Hubble telescope’s problems,” he says. “It was inspiring to know that what we were learning in the theoretical classroom was so applicable to actual problems.”

Last year, Gonsalves was interviewed on the NPR program On Point, mostly about his work on the space telescopes. He said, “My whole life I’ve been helping people and I love it. I had 10,000 students and I’m still in touch with a lot of them.”

One is Danahy. Some three decades after first taking that course with Gonsalves, he too works with incoming engineering students. “I find myself inspired by and taking so many lessons from my time learning from and working with Bob, and applying all of that to my own teaching: how do I engage my students, inspire them, and excite them about the content much like he did for me.”

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