P–38 days: Navigating Pluto

Pluto and Charon artists impression

Pluto and Charon: Xanthine/Wikipedia

Pluto. A cold distant place we’ve never needed to think much about. Until now. Pluto and Charon (his ferryman of the dead): bodies at the outskirts of our traditional solar system which will soon have names of dead astronomers, poets, goddesses, writers, characters from literature, and other hoi polloi plastered all over their surfaces; names for everybody and every thing, real or fictitious, except for the very thing taking us there: New Horizons.

New Horizons. The spacecraft I helped launch nine years ago. New Horizons: the mission led by Alan Stern and guided by a host of dedicated engineers and scientists, navigated by Bobby Williams and his team, augmented by an independent Navigation team at JPL (the Jet Propulsion Laboratory).

Pluto moons and orbits

Pluto Satellites, NASA / Wikipedia

Unfortunately, New Horizons will not have its name on a single feature that it discovers on the surface of Pluto, Charon, Styx, Nix, Kerberos, Hydra, or any of the likely more-to-be-discovered satellites. So says the IAU (International Astronomical Union), the self-appointed official namer of names for all things astronomical. What a shame! Let’s have a waiver. Name something big on Pluto—a major crater, chasm, scarp, plain, mountain, sea, valley, whatever—for the spacecraft what brung us. It would be an insult not to do so.

I’m proud to be associated with the mission, and honored for an invitation to help out on the KinetX Navigation team at the Applied Physics Lab in Maryland next month in whatever small way possible to usher the spacecraft through its brief fling with the Plutonian system. This post and any others following it, if there’s time and wherewithal, are dedicated to Navigation and the process of getting there, true to the spirit of “The journey is more than half the fun.”

The journey is the important thing; the destination … not so much!

Project scientists will quibble with that. Many have expended a good fraction of a career to seeing what’s at the end of this particular tunnel, and that’s a perfectly good reason for them to celebrate an arrival. It’s just not the Navigators’ thing. The Navigators get us there, so their concern is Where are we? Where are we going?

Let me rework the statement above: We almost always get you there! is an unofficial and seldom mentioned motto of this particular Navigation team, because there is an example or two in history, like the Mars Climate Observer’s unanticipated and unwelcome arrival at the surface of that planet, to remind us that there is some justification for the modifier “almost.” (An almost that was barely avoided by the JPL Navigators for the Mars Polar Lander that augered in a few months later. Through a lot of effort they barely avoided missing the Martian reentry aim point only to see an onboard software failure late in the descent smear the spacecraft over the south polar region. See Embracing the Future.)

Will New Horizons accidently smack into Pluto? No. The flyby is too far away to make that kind of error. The more likely bad karma for Navigation would be to incorrectly estimate the position near the closest approach time and cause the cameras to point the wrong direction and snap pictures of empty space. Or to miss the dual occultations of the Sun and Earth when the spacecraft passes behind Pluto and Charon. To quote a character from literature (a likely candidate for a name on Pluto) Harris Mitchel in The Darkest Side of Saturn says, of the possibility of blowing a similar encounter at Neptune, “You’re totally humiliated because you said you could do this and you didn’t. As a consequence, you lose all your credibility and live the rest of your life in shame and degradation…. [And] you get pelted by the scientists. They throw outdated textbooks at your head because you lost a science opportunity, probably the only [one] in our lifetime.”

So, the pressure is on the Navigation team, as it always is for encounters like this, to get us there safely, surely, and without error. Well, at least not any major error, because there is never any surety in human activity, and the best we can do is keep the inevitable and ineradicably small errors from turning into big ones.

Here’s the Navigation process, also described in the literary masterpiece mentioned above, paraphrased to befit the occasion: Dump the tracking data into a large black cast-iron pot, metaphorically speaking—actually the pot is a computer—along with other ingredients such as data calibrations and satellite and planet ephemerides. Stir vigorously. Incant technobabble and taste frequently, adding spices, a priori covariances, and toad tongues now and again until the brew is complete and the answer apparent: we know where New Horizons is and where it’s going. The encounter will be a success.

Sorry to trouble you with the technical description above. In future posts I’ll try to put things into more down-to-earth easily-understood terms such as the interpretation of dynamic events from signatures in the Doppler tracking data, the use of Very Long Baseline Interferometry data—spacecraft versus quasars—to nail down the trajectory in heliocentric space, and the number of pixels that can dance in the frame of an Optical Navigation image to determine the solution in Plutonian-centric space. By-and-by it will all become clear as a bell.

The Navigation Team, led by Bobby Williams (the first to navigate a spacecraft, NEAR, to a landing on an asteroid), determines the spacecraft trajectory and the orbits of the satellites circling the Plutonian system, designs maneuvers to redirect the spacecraft to whatever target the mission desires, and provides the rest of the numerous New Horizons project folk—engineers and scientists—with last minute updates on positions so that the cameras and other instruments will point the right direction at closest approach, and not click pictures or take data of empty space.

One last topic to end this ever-rambling post:

Pluto the Dog

Photo: Leo Reynolds (modified)/ CC BY-NC-SA

Is Pluto a planet?

Used to be, but not any more. Why is that? Well, besides a few technical things like how it was formed, and that it doesn’t clear its orbit of debris like all the other prim and proper planets do, I think there is a much more down-to-earth reason. It resides with the schoolchildren of our planet. Since there are probably scads and scads—hundreds and thousands or more—of new Pluto-sized bodies in the Kuiper Belt and Oort Cloud far outside the traditional bounds of our solar system, don’t you think it would be cruel to commit our school kidlets to the memorization of hundreds and thousands of dubious planetary bodies when it’s already difficult enough to name the eight already out there, even using the awkwardly unusable mnemonic “Men Very Easily Make Jugs Serve Useful Needs”?

I’d propose granting Pluto, for reasons of history and tradition, the status of “Honorary Planet.” It’s the least we could do to ease the pain of Pluto-is-a-planet advocates such as Alan Stern, the New Horizons leader (who has spoken quite nicely of Navigation in one of his own blog posts.) That way, with this mission we could then say that we’ve finally explored the last planetary outpost of our traditional solar system.

Where are we going? Pluto! That faint blob in our telescopic sky, that last place of mystery and darkness, the place we go to die, crossing the river Styx, and yet also the place we go in these last 38 days to come alive and understand ourselves and our universe a bit more.

But Pluto is only another milestone in a longer trip that the human race will ultimately celebrate in the far future if we don’t kill ourselves first. Let the journey continue.



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