How We Saved the Deep Space 1 Spacecraft

On Sept. 22, 2001, about 50 people huddled around computer monitors in a control room at NASA's Jet Propulsion Laboratory in Pasadena, California, some more anxious than others. The Deep Space 1 (DS1) spacecraft had already suffered a near-fatal setback on its journey to Comet 19P/Borrelly, along with countless minor obstacles since launch. Would it pull through now?

This could be a moment for history books: NASA's first close look at a comet. But in this case, failure was definitely an option. A device critical to pointing the spacecraft had stopped working 15 months earlier, and with no backup plan, the team had to invent a series of workarounds to keep the mission going. If they could just see the comet, it would all be worth it.

Marc Rayman, mission director and project manager for DS1, nervously paced between computer stations, fearing his team's hard work had been for nothing. Engineers had already made thousands of decisions and sent hundreds of commands to the spacecraft, working countless stressful hours to make this comet encounter a success. But any one error along the way could now end the mission. What's more, if the spacecraft ran out of hydrazine fuel or got battered by dust – tiny grains carrying the energy of bowling balls knocking over pins – it would be over. "You would spend the rest of your life thinking, 'If only…' " Rayman remembers.

A Mission of Firsts

Launched 20 years ago, on Oct. 24, 1998, Deep Space 1 was originally designed to test 12 technologies that had never flown in space before. The team that developed this mission had the enormous challenge of both getting all the new technologies to work and making sure those technologies didn't interfere with one another. Engineers and mission planners had a lot of freedom to solve problems in new ways.

"The team was small, and everyone was doing a job that was bigger than they had done before," recalls Leslie Livesay, spacecraft manager for DS1, and now the director of JPL's Astronomy and Physics directorate. "It was a great learning experience for all of us and definitely one of the highlights of my career."

DS1's most essential technology was the ion engine, representing a brand new way to fly spacecraft. Ion propulsion's gentle force allows for graceful and fine-tuned maneuvering of a spacecraft and very high speeds over time. Another new technology DS1 tested was called Autonomous Navigation, or AutoNav, a system to let DS1 determine its own position in space and then adjust itself if its estimated course was not correct. Ion propulsion and AutoNav would be used on subsequent interplanetary missions. Learn more about DS1's technologies: 10 Things About DS1

With so many aspects of DS1 that were brand new, navigation lead Ed Riedel felt the mission had a "cowboy or cowgirl" spirit.

"You're out on your own, out there on the prairie, just you and your horse -- or you and your spacecraft -- and somehow you have to get to your destination," Riedel said.

The DS1 team was successful in thoroughly testing all 12 new technologies in space. What's more, in 1999, DS1 completed a flyby of asteroid 9969 Braille. While the photos DS1 sent back were fuzzy, observing any object at all was considered a bonus.

Having achieved its initial goals, DS1 received a new charter from NASA: take close-up images of a comet, which had never been done before, and collect other scientific data.

Rayman took this objective personally. He had wanted to work at NASA since the fourth grade. DS1 represented what he had always wanted to do: explore an uncharted destination in space where no one had gone before.

'Pop' Goes the Star Tracker

Like ancient explorers, spacecraft look out at the stars to figure out if they're pointed in the right direction. A device called a star tracker -- a camera with a built-in computer that takes images of stars -- helps the spacecraft orient itself so that its main engine can take it on the right path. DS1's star tracker was a commercially purchased product; it wasn't one of the advanced, high-risk technologies that the mission set out to test.

In the beginning, Livesay's biggest concern about the spacecraft had been its high voltage power supply, which experienced problems before launch. In space, that seemed to be doing just fine. "I wasn't as worried about the star tracker," she said.

On Nov. 11, 1999, the DS1 spacecraft went into safe mode, a minimum-activity state that signals to the mission team that something has gone wrong. The engineers ran tests and determined the star tracker had failed. That meant there was no obvious way to get the spacecraft to point its main antenna to Earth to receive instructions. Making matters worse, Rayman was battling bronchitis and laryngitis at the time, and could barely speak as he struggled to diagnose the spacecraft's essential tool. As the weeks wore on, there was serious talk at JPL and NASA that this problem could end the mission.

"Most people's reaction was: You can't do anything productive without a star tracker. The mission was already extremely successful; we should retire Deep Space 1, let it rest on its laurels, and move on to something else," Rayman said.

But one motto Rayman imparted to the team was, "If it isn't impossible, it isn't worth doing."

This would be one of the most challenging recoveries in NASA history.

An Unconventional Solution

The star tracker had a large view of the sky. The DS1 science camera saw an area 150 times smaller. It was the difference between gazing at the night sky with your naked eye and looking through a soda straw. To make matters worse, the camera generally could not see stars as faint as the ones the star tracker could, and operated 120 times more slowly. But after careful analysis it was clear: The science camera was the only hope of getting to Comet Borrelly.

In order to use the "straw" to control the spacecraft's orientation, the team would have to solve a multitude of technical problems and then write software to make the spacecraft understand how to track its orientation with the science camera. If they figured that out, they would have to operate the spacecraft in a brand new way.

"We would find one big bright star we could point at, and keep ourselves adjusted with the Sun sensor in the other direction, and thereby point the main engine," Riedel said.

But time was running out: To reach the comet, the spacecraft's engine would have to be thrusting toward Comet Borrelly by July 5, 2000. Otherwise, the comet's own orbit around the Sun would put it out of reach.

To the Rescue

For two months the team struggled to restore communication with the spacecraft, which required inventing a way to point the main antenna to Earth without the star tracker. Engineers had to execute a complex, risky rotation maneuver, then calculate exactly when DS1's main antenna would sweep past Earth so it could receive the command to stop. Because of DS1's distance, it took more than 28 minutes to get back the result of each communication. But the strength of the radio signal allowed them to discern how the spacecraft was positioned. Engineers sent commands to adjust it one or two degrees at a time until they were reasonably sure the main antenna was in the optimal position. "From farther than Earth is from the Sun, we were practically joysticking the spacecraft," Rayman said.

Tensions and anxieties mounted as the team worked long hours to design the new system, write the software and get it to the spacecraft. Each problem seemed to give way to a host of others. For the sake of the team's motivation, Rayman, whom Livesay describes as "the glue on the project," did his best to hide how worried he really was. The team developed this unprecedented software largely on the basis of engineering intuition. A major part of this software was dubbed MURKY.

Despite problems with transmission, the new software finally reached DS1 in June 2000. And on June 12, after seven months in safe mode, the spacecraft found the first star that could be used for orientation. Soon, just one week before the July 5 cutoff, DS1 was bound for Borrelly.

The Final Countdown

The Sept. 11, 2001, attacks happened just 11 days before DS1's scheduled date with its comet. Spacecraft team members called one another to deliver the grim news that shook the world. JPL shut down for the day and tightened security. But the DS1 team, having been through 15 grueling months of problem-solving since the star tracker failure, was determined to get to the comet. Engineers who happened to get to work before JPL's closure managed to complete a critical ion engine maneuver that morning.

"The team sort of pulled together and said, 'Well, let's concentrate on doing this,' " Collins said. "I remember personally thinking, 'By gosh, we're going to make this encounter work.' "

Everything hung in the balance on September 22. The DS1 team operated from one floor above JPL's large Mission Control area famous for big Mars rover landings like Curiosity. There was no live televised news event for DS1. Rayman, known for keeping track of exact numbers, estimated that thousands of things could go wrong. Collins was more optimistic: "I figured that our odds were maybe 50-50," he wrote in his journal at the time. Staff coordinator Michelle Leonard brought burritos to the adjacent conference room for the team.

With only a few minutes until the photos from Comet Borrelly were expected to come in, attitude control engineer Tony Vanelli handed out small American flags. Collins donned his search-and-rescue helmet in honor of the 9/11 rescue workers at the World Trade Center site.

The first round of applause erupted because the spacecraft was still communicating after it passed the comet's nucleus. No pictures yet, but spacecraft data indicated that its camera had gotten something in view. Team members looked at one another, shaking their heads. "Every moment we last now, we get safer and safer," Collins wrote in his journal. But the clapping was tentative -- there were still risks ahead.

A Whole New World

DS1's first Borrelly images to the JPL computers were distant and fuzzy. Collins could see a jet forming along one side of the comet. Rayman became a little less anxious with each new picture but still tempered his enthusiasm – after all, these fuzzy views might be the best DS1 could deliver.

And then -- screaming and clapping as a glorious 170-pixel-wide image -- more than three times better than they had planned -- appeared. There on the screen: A strange-looking, peanut-shaped comet nucleus, unlike any space object seen before.

Collins and Rayman cried with joy. Rayman and Riedel hugged. For a few hours after, the only words Rayman could muster were, "I just can't believe how incredibly cool this is." To this day, recalling the moment of seeing those comet photos brings tears to Rayman's eyes.

Riedel still gets tingles up his spine thinking about the comet encounter. While the European Space Agency's Giotto mission had photographed Comet Halley previously, the DS1 images of Comet Borrelly delivered much clearer views.

"From some of the first Borrelly images that splashed on the screen from DS1, the science team began to gain key insights about what makes comets tick," Riedel said. "DS1 gave us a look down into the pocks and crevasses, the smooth plains and oddly-textured fields that mysteriously give rise to the iconic cometary tail. Getting those images gave us, finally, an important idea of what these strange things called comets are."

With world events overshadowing the comet encounter, DS1 did not receive a great deal of attention in 2001. But those who worked on it miss the camaraderie of that special team. There are still occasional reunions.

"It was probably the most fun I ever had here at JPL," Riedel said.

Many DS1 team members have become distinguished leaders at JPL. Rayman is now mission director and chief engineer of NASA's Dawn spacecraft. Dawn's mission to orbit the two largest bodies in the main asteroid belt, Vesta and Ceres, was made possible because of DS1's test of ion propulsion. As successful as Dawn has been technologically and scientifically, Rayman will always consider DS1's comet flyby the most amazing moment of his career.

"We got to see something humankind had never seen before, and boy did we pay for it, with an incredibly difficult rescue of a distant, mortally wounded spacecraft and years of no solid reason to believe the comet encounter was going to work so well," Rayman remembers. "I have never had, nor do I ever need to have again, an experience as wonderful as that one. This will last me for a lifetime."

Media Relations Contact

DC Agle
Jet Propulsion Laboratory, Pasadena, Calif.
818-393-9011
agle@jpl.nasa.gov