P–7 days: Navigating Pluto

As of the first instant of this morning, July 7th on the US east coast, the little spacecraft was about 8.7 million kilometers from Pluto, getting 1.2 kilometers closer each day.

We’re almost completely recovered from the hiccup that happened July 4th when New Horizons took on a little too much multitasking trying to simultaneously compress data for downlink and load up the sequence of activities for the flyby at the same time. This caused the equivalent of a brain freeze, and the spacecraft went into a defensive fetal position, spinning up to 5 rpm to provide stability for its earth-pointed dish antenna, then dropping off into a light midsummer night’s snooze. We have to wonder, when spacecraft sleep do they dream of electric sheep? (With a nod to Philip K. Dick.)

We lost some tracking and science data, but it’s not a vital loss that won’t be made up in the following days with much more powerful information on where we are and what Pluto looks like. Pluto currently spans about one percent of the field of view of our long-range camera, covering about 55 pixels. You can’t see a lot of detail in an image only 55 pixels across, you can only be taunted and tantalized by vague shapes and shadows. Those shapeless, shifty features will begin to stabilize and fill out in exquisite detail over the next few days.

Our last maneuver is behind us—several days ago—and we have delivered the spacecraft from our capable hands into those of Misters Newton and Einstein whose inviolable laws of physics will guide New Horizons the rest of the way in. Nothing more can be done about where it is and what time it gets there, but we can do a series of Knowledge Updates to better inform us on where to point the cameras and other instruments. That’s what the Navigators get into today, delayed by the little snooze, as the first new tracking data comes down from the now revived and presumably refreshed, spacecraft. Here is where the rubber meets the road in a series of tightly coordinated and time limited interactions between the Navigators and the rest of the project teams. The spacecraft may get its snoozes now and then, but the Navigators are headed into some sleepless days and nights.

 

I don’t know if I’ll be able to continue these posts while things get hectic, so for interim entertainment here’s some filler about Voyager’s encounter with Neptune in 1989 from a Navigator’s perspective. There are a lot of similarities with the current Pluto adventure, and differences too. The excerpt is from the chapter titled “Neptune” from my novel The Darkest Side of Saturn. The spacecraft is named Nomad, but don’t be fooled, it’s really Voyager. There are some fictionalized versions of real events that happened during that wondrous time, but the rest is full of lies. Your task, dear reader, is to separate the wheat from the chaff.

Navigating Neptune

The party started in the Navigation Team’s operations area an hour before midnight, two hours before the Neptune closest approach time. They fished drinks out of a metal washtub filled with ice, beer, juice, and sodas. They cut slices of brie and slabs of pâté from paper plates between the computer terminals lining long tables on both sides of the room. They spread their fare on stout crackers and delicate wafers, popped olives into their mouths, and poured wine from bottles and jugs into plastic cups.

They were very happy, all nineteen members belonging to the Navigation Team functional groups: Radiometric Data Conditioning, Maneuver and Trajectory, Optical Navigation, and Orbit Determination. Harris, the newest of the new and lowest of the low on the navigation totem pole, was perhaps happiest of all. After working nearly twenty-four hours straight, their job was finished. Nomad was nearly on course. The new camera pointing commands had been uplinked across four hours and seventeen minutes of light travel time to the spacecraft. Now the laws of physics ruled supreme. There was nothing more to do, nothing more that could be done. Eat, drink, and be merry, for in a few more hours we either bathe in glory or go splat!

They pitched darts at Neptune. On the far wall of the navigation operations area was a large bulletin board. Tacked onto the center of it was a square of graph paper three feet on each side with tick marks annotating every ten kilometers of the divisions. This was the navigation target plane for Neptune, although Neptune was not on it. At this scale, Neptune would have been represented as an enormous circle whose closest edge was a few feet down and to the right—off the chart.

Dozens of small multicolored paste-on dots sprinkled the chart—yellow, blue, green, brown, black, and red ones. A red one near the center, larger than the others, was labeled “TCM20 aimpoint.” Because of the inevitable maneuver errors, this was where Nomad certainly would not go, although it shouldn’t be far away. The smaller colored dots, representing solutions vying with each other to show where Nomad was actually headed, had meandered away from the aimpoint as new data came in after the maneuver.

They were throws of the navigator’s darts, almost literally. Each dot represented an experiment to test the sensitivity of the trajectory to the ubiquitous errors in every source of information. No two solutions were exactly the same except that they tended to cluster in places. There was a cluster of green dots for solutions that used optical data of Triton and a blue grouping about thirty kilometers away accounting for data that included optical observations of the temporarily named N1—first of the new satellites discovered by Nomad.

For the latest solution—they were loathe to call it final; there was always just one more data point to include, just one more computer run to make—they’d placed a red dot and labeled it NAV3, the name for their ultimate delivery of knowledge. Nevertheless, it was final, the last delivery that could affect the success or failure of the encounter, delivered to the sequence designers so that Nomad’s camera angles could undergo a last-minute shift and she would send back pictures of things like satellites and cloud features instead of nothings in empty space.

Knowledge and control were the two halves of the navigator’s function. Gather the data to determine Where are we and where are we going?, then use the knowledge to apply the control: Burn the engine! Change the trajectory! Finally, when it’s too late in the game to burn the engine, when it’s too late to control the trajectory, all you can do is improve the knowledge to point the instruments, whose purpose is . . . to gain more knowledge.

Job done, the party navigators pitched darts while the rest of the Nomad engineers and scientists labored away over hot computers in rooms upstairs. They watched the Lab TV news report as Nomad approached the ring plane crossing at midnight, or rather, as the downlink data containing that event approached Earth, because the event had already happened over four hours earlier. Either Nomad had already splattered against a random rock just outside the visible ring, in which case the signal would come to an abrupt halt in a few minutes, or it had not. The navigators, including Harris, were well into some serious beer drinking.

At six minutes after one o’clock in the morning, as Nomad skimmed over the top of Neptune and Carl Sagan’s face graced the TV, Harris ambled to one of the several phones scattered over the operations tables and punched a number.

“Hello?” Diana answered.

“Hi. Whatcha doin’?”

“Oh, nothing much right now.” She seemed distracted.

“Why don’t you-all come on down here to our party?”

“Why thanks, Harris. I believe I will.”

Minutes after they talked, as Harris lifted his fifth can of beer for the evening, Diana walked through the door of the navigation area trailing a TV crew carrying lights, sound equipment, and a camera. They taped her even as she walked. As one of the few female scientists on the project, and a good-looking one at that, she was in heavy media demand.

Uh oh. Harris discreetly parked the beer can on the table behind a stack of printouts as she walked straight up to him. Drinking at the Lab was forbidden; getting caught on television was certain career death. He tried not to wobble as she shook his hand.

“Congratulations,” she said formally for the camera. “Looks like it’s going to be successful.”

“Congrad . . . grajlations to you too. It’s a good encounter, huh? Good stuff, you know what I mean? I mean we’re doin’ good.”

“Loosen up,” the director said. “You’re like statues.”

At the director’s suggestion they linked elbows—beautiful young female scientist and intrepid male engineer—and faced the camera with silly grins on their faces.

“No no. Too posed. How about a toast.”

Somebody brought them plastic glasses filled with orange juice. Harris and Diana held them high and clicked them together.

“Here’s to science,” Diana toasted and smiled.

“Here’s to engineering,” Harris answered.

“Here’s to knowledge,” she said.

“And here’s to control and a dual occultation.”

“May we be so lucky.” Diana’s smile began to crack. “Here’s to wisdom.”

“And good ol’ ingenuity.”

They chugged their orange juices, the navigators clapped, and the director was mollified. A few minutes later another network TV crew stole Diana away for an interview.

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