Mark Jensenius, third from left at rear, raises his hand as he and his teammates cheer after their algorithm successfully guided a NASA spacecraft into an asteroid on Monday. Image from NASA video

When Mark Jensenius was a baby, his family lived near Reagan National Airport in Washington, D.C. His mother, Linda, would take him for walks, and he would look up at the planes passing overhead. His first word? “Plane!”

“He has been interested in flying things ever since,” said John Jensenius, Mark’s father.

On Monday, Mark Jensenius watched a NASA spacecraft intentionally fly into an asteroid. The Greely High School graduate now works as a guidance navigation and control engineer at the Johns Hopkins Applied Physics Laboratory in Maryland, and he helped write an algorithm that allowed the spacecraft to navigate autonomously toward its target.

This particular asteroid – a 525-foot moonlet called Dimorphos that is orbiting a larger asteroid called Didymos – was actually harmless to Earth, and scientists said they do not expect one to threaten the planet within the next century. But this mission was an unprecedented attempt to alter the course of any giant rock that does come our way.

“We don’t want to wait until that point,” Jensenius said in an interview Tuesday. “The 10-year process to develop this technology, what we did yesterday and what we were looking to do this whole time, was to learn everything we needed to learn so we could successfully impact an asteroid. We have the technology to do it. We know all the gotchas, and the world can rest easier that if we discover an asteroid, there’s not that learning curve.”

He said his teenage years in Maine inspired him to work in space.


“You could walk outside and look up and see all those stars,” he said. “It grabs your attention.”


Jensenius moved from Maryland to Maine in middle school. His dad worked for the National Weather Service and got a job at the station in Gray, and his mom worked as a math intervention teacher at Falmouth Elementary School. He was always interested in math and science, and his parents remember he showed an aptitude for those subjects at a young age.

Childhood photo of Mark Jensenius Photo courtesy of John and Linda Jensenius

As a toddler, he tripped while walking with his grandfather, who asked him what caused him to fall down. “Gravity,” the little boy said. When he was 6 years old, he got mad because his father would not take him shopping for materials to build a flying car. When he was 9 or 10, his mother went into his room to find him still awake, trying to calculate the number of seconds in a day in his head. He asked her to write his solution on a piece of paper, and once he was asleep, she checked his work to find it was correct. In sixth grade, his father encouraged him to write a computer program for a science fair project. It worked perfectly, but Jensenius did not win the fair because the judges thought the project was too advanced for him to have completed on his own.

“We explained it to him,” said John Jensenius, 70. “It was just a sign that he was doing better work than they thought he could do.”

Jensenius graduated from Greely High School in 2000. He went on to get a bachelor’s degree in aeronautical engineering from Rensselaer Polytechnic Institute in New York and a master’s degree in mechanical engineering from Duke University in North Carolina. He has worked at the Applied Physics Lab for 17 years and is on the air and missile defense team. His description of his work experience was simple and vague: “various projects that involved hitting things at high speed.”


This mission began 10 years ago with an idea. Jensenius was part of those initial conversations, and he was on the team that developed SMART Nav (Small-body Maneuvering Autonomous Real-Time Navigation), the algorithm that allowed the spacecraft to make decisions about navigation. The project secured funding from NASA five years ago and has grown to include more than 1,000 people.

The spacecraft that collided with the asteroid Monday was the size of a vending machine. They called it Dart (Double Asteroid Redirection Test). It launched last November and traveled nearly 7 million miles before hurtling into the side of the asteroid at 14,000 mph. On Monday, Jensenius watched Dimorphos come into view from Dart’s camera. Everything went so well, in fact, that Jensenius said it was almost boring.

“It was the good kind of boring,” he said. “We all wanted boring. … It made everybody in the missions operation center feel that we had all correctly done our homework.”

As their view of the asteroid got bigger and bigger, Jensenius and his team stood for the last two-and-a-half minutes as the spacecraft traveled its last 500 miles. The images of the Dimorphos surface got sharper and sharper – and then the last image cut off with a mostly blank screen.


The spacecraft was destroyed upon impact, but when you’re trying to figure out how to save the planet, that’s just the cost of doing business.


“We’ve joked that we should create bumper stickers that say, ‘My other vehicle is embedded in an asteroid,’” Jensenius said.

On the NASA livestream, Jensenius and his team cheered and slapped high-fives. He had seen a simulation of that moment so many times.

“It was absolutely wild to see it happen for real,” he said.

Nearby, his wife and children were watching the livestream with other team families. In Cumberland, his parents were wearing their mission T-shirts and cheering too.

“We were jumping up and down like little kids,” said Linda Jensenius, 69.

It is actually too soon to know whether the spacecraft actually impacted the asteroid’s movement. Scientists will use telescopes to verify the change over the next days and weeks. Jensenius will focus on reviewing and analyzing the data from the spacecraft.


This spring, Jensenius visited Greely High School and Greely Middle School to talk to students about the mission. The district posted a photo from his visit on its social media pages Tuesday and congratulated him on his success. Jensenius said the students asked whether he still uses the math he learned in high school, and he told them how important geometry is to his current work.

“It was an absolute joy to share it,” he said.

His parents said they are incredibly proud of his achievement, and they hope he will finally get some rest.

“I’m hoping he’ll literally or figuratively crash,” his mom joked.

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