The Art of Falling

With gravity in your gas tank, the shortest line between two celestial points becomes a cosmic loop-de-loop.

By Oliver Morton

On Earth, falling is a straightforward business, and gravity rather dull: You're up, then you're down. That's it.

In space, though, things are different. In space there is no rest; everything is falling. But it falls around, not down. Planets fall around stars, moons fall around planets. They keep going forever, yet they do not repeat themselves. As soon as there are more than two things falling around each other, gravity becomes complicated, new paths endlessly become available. Johannes Kepler, who put rules to the planets' movements in the 17th century, imagined them humming a ceaselessly shifting melody, the music of the spheres.

So in space, falling is a science, inscribed in Kepler's laws and Isaac Newton's equations. It's also a practical skill. A cleverly designed trajectory means that a spacecraft uses less fuel - always at a premium - and thus gets to places it otherwise could not afford to go. And in some hands, it's an art.

Take NASA's Near Earth Asteroid Rendezvous spacecraft. Having been thrown off Earth by a Delta-2 rocket on February 17, 1996, NEAR has been falling around the sun ever since. For its first year in space, NEAR fell away from Sol, and past the orbit of Mars, farther than any spacecraft reliant on solar power had ever gone before. Then, slowly at first, NEAR began to drop back in. On June 27, 1997, it flew past an asteroid called Mathilde, only the second spacecraft to visit one of these flying mountains, sending back pictures of a lump of coal the size of Hawaii's Big Island. On January 23, 1998, NEAR was back at its home planet, passing so close that Earth's gravity was able to reshape its path. The spacecraft whipped over the southern oceans and flew off in a new direction, finally ready for its rendezvous with the near-Earth asteroid Eros.

Eros is not to be a one-night stand like Mathilde; it is NEAR's final destination. If all goes as planned, the little spacecraft will swing into orbit around Eros in February and start mapping the tiny world in exquisite detail. From then on, the asteroid and the spacecraft will be inseparable, NEAR falling around Eros while Eros falls around the sun.

Why take such a long way around? Largely to save fuel and thus money. The Delta-2 rocket that lobbed NEAR up into the sky did not have enough energy to throw it straight to Eros. Although Eros comes pretty close to Earth at times, the plane in which it falls around the sun is at an angle to the plane Earth orbits in, which means it takes more oomph than you might expect to get there. Only by heading off in a completely different direction for a year and then coming back, on a course perfectly chosen to make the best use of Earth's gravity, could NEAR ever make it out to Eros.

It takes an odd scientific subtlety to see that sort of possibility. That subtlety is part of what has made NEAR's mission director - a short, dapper engineer named Bob Farquhar - one of the space program's unlikely stars. It may be the only subtle thing about him. Farquhar can be so full of himself he overflows. But he's also a master of the art of the fall in all its unearthly exuberance. Asteroids, comets, even plain old planets - he can find you an unusually cost-effective way to any of them. And recently that's been a skill much in demand.

For a long time, the overall trajectory of NASA's planetary-exploration program seemed to echo the way things fell on Earth: It went downhill, slowly but surely. Missions beyond Earth's orbit became rarer and rarer - a couple each decade or so. In the early 1990s, though, the trajectory turned, when NASA set up a new planetary-science program: the Discovery missions, designed to be scientifically impressive but cheap and small-scale, run by freestanding teams of scientists, laboratories, and companies rather than the space agency's in-house bureaucracy. NEAR was the first of these missions to be launched, Mars Pathfinder the second, Lunar Prospector the third. The fourth, Stardust, a spacecraft that will bring samples of a comet's dust plume back to Earth, set off in February '99.

By summer 1999, NASA had chosen four more missions from the dozens of applications made for funds. And on two of them, scheduled for liftoff in 2002 and 2004, Farquhar is mission director: Messenger is to voyage to Mercury, finishing off the mapping of that planet begun in 1973 and left in limbo during planetary exploration's lean years. Contour is to send a simple little spacecraft falling past a series of comets in an orbit that looks like a party streamer caught in a tornado. The latter project is Farquhar's pride and joy. "Asteroids are OK, but I like comets," says the navigational artist. "They have unique characters" - and that's an attribute he appreciates. Contour's mission to three comets, using Earth flybys to change its trajectory six times, is a minimum-fuel, maximum-panache mission no one else would have thought of.













Small space missions depend crucially on the small teams that run them. While aiming to be "faster, cheaper, better" (per NASA administrator Daniel Goldin's exhortation), they also tend to be more human, taking place on the scale of a neighborhood gang and rife with idiosyncrasies - of people, of programming, of personality. Tom Krimigis saw a place for bright, brash Farquhar on his staff: "He was the right man; this was the right place."

Farquhar describes his mission-manager role at APL as being like an architect's. Given an objective, such as getting to an asteroid, he takes account of the requirements, the technical possibilities, the politics, and the opportunities for chutzpah, and comes up with a plan that balances all the forces - budgetary, scientific, and gravitational. His plans have the elegance of form following function, and they also have decorative detailing - quirky, clever, sometimes self-indulgent. There are various flourishes on the NEAR flight path, for instance, that are pure showmanship, and one - getting the mission's first data from the Mathilde flyby just before JPL's Pathfinder landed on the face of Mars - that looks nicely political.

Like many architects, Farquhar is a mathematician, a politician, a show-off - and a romantic. He's the man with the ideas, and the Discovery program has an eager appetite for them.

Sometimes, though, spacecraft have ideas of their own. Take the afternoon of Sunday, December 20, 1998. Farquhar was watching the 49ers on a little portable in his office, killing time before overseeing a critical fine-tuning of NEAR's fall toward Eros. When his boys finally lost he headed off down APL's seemingly endless corridors to the mission operations room, where the NEAR team was getting ready for a crucial shove from the spacecraft's main engine that would slow the craft down just enough for it to go into orbit around the asteroid 21 days later.

In the mission operations center Farquhar's place was at the head of a largish table around which the project's other top brass were gathered. Next door, the operations crew huddled around computer workstations. Various people shuttled between the rooms, notably Mark Holdridge. Farquhar is the overall mission manager, but he isn't one for the details of actually running a spacecraft. That's Holdridge's job; you could tell he was the point man from the fact that it was his name on all the empty pizza boxes neatly stacked in the corner.

There were only about 15 people in each room, but even so there was not, in truth, much for most of the managers to do. The instructions telling the spacecraft how and when to start its engine had been sent up long before. The people around the table were for the most part spectators, not players - but spectators with a deep investment and immense expertise. Everyone there knew that Mars Observer, a near-billion-dollar JPL project, was lost in 1993 while the lab attempted a maneuver much like the one NEAR was about to undertake. But unlike Mars Observer, NEAR had already used its main engines, and they had given it no trouble at all. The biggest practical concern anyone had was the weather in California. There were strong winds at the site of the antenna listening to NEAR's faint, reassuring signals, and if there were any more gusts over 50 mph, the antenna would be shut down.

At the appointed time, the spacecraft announced that it had started the course correction by firing its hydrazine thrusters - miniature engines turned on to settle the fuel in the tanks before the main rocket switched on. Then, at the point when the main engine was meant to ignite that fuel, contact with NEAR was lost. The group reassured itself that this was not inauspicious. While the spacecraft was maneuvering, the antenna may well have lost track of its signal, the frequency of which shifts as the probe's velocity changes. Besides, to relieve tension, you could always tease Farquhar. "If you didn't have any friends or relations, we could have been there two years ago," someone quipped.

To get the joke you have to know that the entire mission was carefully timed: It was no coincidence Farquhar had visited his first wife's grave that morning; December 20 was Bonnie Farquhar's birthday. January 10, 1999, the day the spacecraft was due at Eros, was the fifth anniversary of his civil marriage to his second wife, Irina. The mission's nominal completion date, February 6, 2000, was the anniversary of his church weddings to both Irina and Bonnie.

Farquhar fine-tuned the mission's design to get NEAR to Eros a little earlier than it would otherwise have done, in order to commemorate the loves of his life.

The fact that he was able to do this gives him great sentimental pleasure; letting it be known that he's done it gives him a stunt to brag about. Some people say such self-indulgence costs Farquhar credibility. Others find it almost as amusing as he does.

Amusing, but never without risk. Perhaps because falling - even when done in the highest-tech way possible - is always nerve-racking, ex-paratrooper Farquhar is a great believer in contingency plans. One navigational error - in the case of JPL's ill-fated Mars Climate Orbiter, mistaking English measurements for metric ones - can result in the loss of an entire mission. So while Isaac Newton's doing the driving, as Apollo 8 astronaut Bill Anders once put it, Farquhar's in the backseat keeping a very careful eye on what's coming up. Throughout the NEAR mission he'd had his colleague David Dunham calculating all sorts of trajectories that could be put to use if things went wrong.

Ten minutes into NEAR's December 20 silence, Dunham walked into the managers' part of the operations center, his document case of contingency calculations held to his chest in both hands like a little shield.

Dunham is Farquhar's closest partner and his almost perfect complement. Where Farquhar is short and expansive, Dunham is tall and shy. Farquhar chatters, Dunham mumbles. Farquhar starts with sharp insights and follows through with broad brush strokes. Dunham works out details with deliberate, exacting precision. Farquhar cheerfully collects the accolades for the both of them; Dunham doesn't seem to mind.

"The architects are the dreamers, and the engineers are the doers," says Holdridge, remembering a summer spent working as an inspector on the Baltimore subway. "And that's very much the way I look at the relationship that Bob has with Dave and me. Bob puts the splash and one-upmanship into the equation, and we figure out how to get it done. Then he takes the credit." Indeed, Farquhar will tell you exactly the same thing; he takes pride in it. "And that almost makes it bearable," says Holdridge, with a grin. "At least he's honest."

Dunham's arrival at mission operations was an opportunity for more banter. After all, no one really thought the spacecraft was lost. It was just the course correction interfering with communications. Wasn't it? Sure it was, they reassured each other.

But the spacecraft was still silent. And, increasingly, so were the managers. The operations team next door, though, was making itself busy. Various ideas were being floated, the most popular of which seemed to be that the people in charge of the antenna were looking in the wrong place or at the wrong frequency. Then there was the possibility that the spacecraft had already started looking at Eros, which it had to do to check its navigation, and thus wasn't pointing its antenna at Earth.

After a couple of hours, the innocent explanations were all used up. Something was wrong. Analysis of the spacecraft's last radio transmissions showed that the rocket burn clearly hadn't happened and that something bad most likely had. Crisis meetings were called. Still the silence went on. Farquhar was convinced NEAR was gone for good. When he called Irina late on Sunday night, he asked her what it was like being married to a failure.

Tom Krimigis, though, never lost faith. "We will get it back if we just keep trying," he told everyone, apparently unflappable.

Sure enough, after 27 hours of silence, NEAR's radio was heard again. Holdridge's team eventually worked out that when the main engine had started up on the 20th, it had done so a bit roughly, and the spacecraft had immediately shut the rocket down in self-defense. This left NEAR tumbling, and for reasons that are still not entirely clear, it found getting out of the tumble difficult. In its flapping about, it went "antisun" - its solar arrays found themselves in shadow - and lost power. Worried, as its programmers had taught it to be, it shut down various systems (including the radio) and concentrated on getting power back.

After spending the day basking in the sun recharging its batteries, NEAR started scanning the sky with its radio beams again, calling for Earth. Earth heard it, and a couple of dozen earthlings let out sighs of relief.

By the early morning of December 22, Mark Holdridge's operations team had put the little ship back on an even keel. But the relative motions of spacecraft and asteroid meant that any possibility of slowing its fall in such a way as to get to Eros on the appointed date was long gone. New instructions were rushed up to the spacecraft so that the asteroid - three or four Everests jammed together into an elongated kidney shape - could be caught on camera as it tumbled past at about 2,000 mph later that day. Most spacecraft encounters are planned over the course of months; this one was hacked together in a matter of hours.

And so 15 years to the day after they skimmed ISEE-3/ICE over the dark side of the moon and outward to a comet, Bob Farquhar and David Dunham were feverishly busy again. Farquhar was not going to be satisfied with just a flyby of Eros, a mission that would go down as at best a partial success. "I'm a poor loser," he told me once, before checking himself with a grin and adding, "but I'm a poor winner, too - I rub the other guy's face in it."

Farquhar and Dunham combed the contingency plans for the best possibilities. One involved a maneuver on December 28 that would have gotten the probe into orbit around Eros on July 20, 1999. Farquhar quite liked that - it would be the 30th anniversary of the first Apollo moon landing. It would also be the 23rd anniversary of the first American robot landing on Mars - an event originally intended for July 4, 1976. (Farquhar is not the only person in the space program who has a weakness for anniversaries.)

Some of the people at NASA headquarters and APL thought a rocket burn so soon after getting the spacecraft back would be a bit too risky, however. Another orbit was produced, and on January 3, 1999, having been told not to be quite so sensitive to a bit of rocket-induced roughness, NEAR fired its main engine perfectly for what was probably the last time.

On February 2, 2000, NEAR's little maneuvering engines will apply the final touches to its new trajectory. With well over a billion miles on the odometer, the tiny spacecraft will rendezvous with Eros on February 14 - Valentine's Day. Even in extremis, Farquhar has had time to indulge himself.

In a way, that time may be running out. Next-generation planetary missions will make ever more use of ion engines, devices capable of delivering low thrust for very long periods of time. That will allow them to do things that falling alone would never permit. There will still be a place for craft and guile - fuel will always matter. But the skills involved in finding odd little pathways around the solar system will be less vital when fully motorized vehicles go where they will.

Farquhar, though, has got more than enough up in the air to satisfy him for the rest of his career. There's Messenger, there's Contour - and there's always ICE. The tiny spacecraft he threw to a comet in 1983 is slowly wending its way back to Earth. It will arrive in August 2014, and Farquhar has every intention of being around to greet the prodigal, kill a fatted calf or two - and send it straight off somewhere else.

ICE doesn't have much by way of fuel or state-of-the-art instrumentation, but it's falling toward a flyby with Earth, and that's enough for Farquhar. Maybe he'll put it back into the halo orbit from which he took it as a way of placating the solar physicists who still think he basically stole the spacecraft from them. Maybe there will be another comet worth visiting. And maybe he'll find a way to throw it off somewhere completely new, letting it fall down a path no one else ever imagined.

Oliver Morton (oliver@dial.pipex.com) writes about science and technology from the shadow of the Royal Observatory in Greenwich, England; he is working on a book about maps and Mars.

