P–11 days: Navigating Pluto


Part of the Project Nav Team: Jeremy, Bobby, Chris, Derek, Dale, Coralie, Tony. (Photo credit: Dale Stanbridge)

As of midnight beginning the morning of July 3rd on the U. S. east coast, our intrepid New Horizons spacecraft—the long-distance eyes and ears of the human race and our ambassador to the outer reaches of the traditional solar system—cruised along at 13.5 million kilometers from Pluto, looming closer by 1.2 million kilometers every day.

The Plutonian system of satellite orbits now swells rapidly in our telescopic eye: the camera named LORRI (LOng-Range Reconnaissance Imager). If abstract orbits were visible, the outermost one—Hydra’s—is about twice as large as the one-third degree field-of-view of the camera. That means the system is only a little larger in New Horizons’ black sky than the full moon seen from your back yard.

Even the orbit of Styx, the innermost of the small satellites, overflows the image boundary by about 20 percent. Only Pluto and its large companion, Charon, still fit comfortably within a camera frame. From this point onward, the spacecraft will have to “slew” to get OpNav images of satellites from one side of the system to the other.

The day before yesterday we had a close encounter with Styx. The band! Not the satellite.

Rock stars and around a hundred-or-so space cadets mingled in close proximity, taking pictures and signing autographs. A photo-op is a photo-op, for rockers to mingle with Lords of the Solar System, and space cadets to schmooze with Lords of Rock. Who was most impressed? I’d say the space cadets.

Which raises the question: I assume the band was named for the mythological river, but was the satellite named for the river or the band? Well, ostensibly for the river of course, but was there a hard-core rock fan lurking amongst the namers of names? And I don’t mean a geologist.

The Navigators’ DTpD (Dreaded Target-plane Drift) seems to have drifted to a dead-end, coming to rest about 25 kilometers from the aim-point, that point—just outside Charon’s orbit in the big Plutonian dart board—which is most desired by scientists and engineers alike of the project. The solution and its attendant cloud of possible errors is comfortably inside the box of acceptability, a 300 x 200 kilometer region where the photo-ops are best and all the other instruments stay happy. Now, if the DTpD is really dead and stays dead, not coming zombie-like back across the river Styx, we’ll have only one more thing to worry about. (And it’s a good thing, since there are no more maneuvers planned and therefore no way to change the trajectory. We have what we have.)

That one last thing to worry about is the arrival time, which is still uncertain by a little more than a minute earlier or later. We don’t know the distance to Pluto precisely, so we’re not sure when we’ll get there. We’ll find out in the last few days by closely watching how the satellites spiral outwards as their orbits expand in LORRI’s point-of-view. When we know how far we are and when we’ll get there, we’ll tweak our already-loaded sequence of events by the right amount of seconds, and all will be well.

That will be a very intense time for the Navigators. But we’ll cross that river when we get to it.



Conspicuously missing from the KinetX Project Nav Team image are Fred, Ken and Philip. Also not shown but very appreciated are the ones who provide reality checks to keep us honest—the JPL Independent Nav Team: Paul, Shyam, Dylan, Steve, Gerhard, Bill, and Mike.

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