Hang a Right at Jupiter

For space navigators, the best course to a distant object is never a straight line.

The tumbling asteroid Eros (shown here in a time sequence taken during NEAR's approach) was a challenging target for space navigators. (NASA/JHU Applied Physics Laboratory)
Air & Space Magazine

Bob Farquhar feels lucky. And that’s good, since there’s nothing he or anyone else can do now but hope for the best. His spacecraft is out there on its own, 119 million miles away, and whatever’s going to happen next has already been programmed into the onboard computers.

Farquhar, whose mild manner seems more like that of a high school teacher than a space explorer, watches and waits from an unlikely place—not the Jet Propulsion Laboratory in Pasadena, California, headquarters for almost all past U.S. interplanetary missions, but a nondescript building at Johns Hopkins University’s Applied Physics Laboratory, outside Baltimore. It could be any office park in the country, except that the room in which Farquhar sits—at the head of a long conference table—is linked to NASA’s Deep Space Network. At the moment, one of the network’s giant dish antennas is relaying signals from a boxy little spacecraft called NEAR Shoemaker in orbit around a potato-shaped asteroid known as Eros.

NEAR stands for Near Earth Asteroid Rendezvous, the first spacecraft ever to match orbits with an asteroid and hang around for an extended study of its chemical and physical makeup (“Shoemaker” was added to the name in memory of the late astrogeologist Eugene Shoemaker). While Farquhar and his team monitor the signals, NEAR orbits 62 miles above the slowly tumbling asteroid’s surface. The satellite is about to go in for a closer look, firing thrusters to cut the orbital altitude in half.

Farquhar has just learned that the engine burn, the instructions for which were long ago loaded into the spacecraft’s computers, should last 144 seconds, nudging the craft from its piddling 5 mph to a whopping 6.5 mph. “Oh, that’s great!” he exclaims, drawing quizzical looks from others watching a screen full of numbers charting NEAR’s position. “144 is 12 squared. 12 is a lucky number. I was born September 12. [My first space mission] launched 12 minutes and 12 seconds after the hour and can you guess what the date was?

“August 12.”

Farquhar’s faith in lucky numbers should not be easily dismissed, considering that he and his colleagues have sent spacecraft where no one thought possible, on less fuel and in less time than most people would have guessed. He calls himself an astrodynamicist, but he’s the unofficial king of the space navigators, a cadre of behind-the-scenes engineers who direct shiny, expensive spacecraft from here to there, with here being Earth and there being an asteroid, comet, planet, or moon.

Space navigation is like threading a needle, only a thousand times harder. With today’s space missions aiming at ever smaller targets (like asteroids), the eye of the needle gets so narrow, with so little room for error, that those threading it either succeed spectacularly, like Farquhar and his team have done so far at Eros, or they miss.

And in space, there’s no way to miss but spectacularly.

That’s what happened to the Mars Climate Orbiter, which vanished in September 1999 as it prepared to enter Mars orbit because of a now-infamous confusion between metric and English units—and more to the point, because it wasn’t where the navigators thought it was. The incident forced JPL space navigators into an unfamiliar and uncomfortable spotlight. It also proved—the hard way—that accurate navigation is every bit as vital to space exploration as raw rocket power.

In the early days of space travel, accuracy was relative. Mission planners were more than happy in the mid-1970s to put a Viking spacecraft within 25 to 30 miles of its planned orbit around Mars, recalls Myles Standish Jr., who left Yale’s astronomy department for JPL in 1972 to work on the Viking project. Tall and debonair, Standish, a distant relation to the Mayflower captain of the same name, is one of the few top JPL navigators who doesn’t belong to the “Texas Mafia,” a contingent of University of Texas astronomy and engineering graduates who seem to dominate the laboratory’s navigation and mission design section.

About Michael Milstein

Michael Milstein is a freelance writer who specializes in science. He lives in Portland, Oregon.

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