Tag Archives: navigation

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.



About The Darkest Side of Saturn

DSOS Front Cover

The Darkest Side of Saturn is, among other things, an asteroid story—a female astronomer and a male engineer co-discover a two-mile wide asteroid that might or might not hit the Earth in 16 years. Their conundrum, besides a potential illicit affair between them (they’re both married to other people), is how to announce it without making jackasses of themselves.

How did the title come about?

I was at the Jet Propulsion Laboratory (JPL) in the early 80s watching the first pictures come in from the Voyager I spacecraft after it flew by Saturn. The planet’s gravity had grabbed Voyager and flung it northward out of the plane of the solar system, and now we looked back and down at Saturn’s night side nested inside the crescent of the day side.

From that higher perspective came a view that had never before been seen. Saturn had always, in all of history, never been more than a tiny  two-dimensional disk painted onto the celestial sphere. Now for the first time, seen from a new direction, the shadow cutting across the rings and that darkness nested into light made the planet real. It had finally become a three-dimensional sphere floating in space. The title popped into my head: The Dark Side of Saturn. (Darkest came later.) The dark side contrasted against the light made it real.

I didn’t start writing the story until a decade later, and by then I’d figured out what the title meant: the yin and yang aspect of the world. How opposites taken together from a wider viewpoint make a whole. Good and evil, science and religion, faith versus understanding, male versus female, each provides context for the other, and out of that you get something more complete than either by itself.

What’s the meaning of the book?

Normally this is where an author should be coy and say, “That’s for readers and critics to decide; I am but the humble author of a modest story; what would I know about its deeper meaning?” But no! Fools rush in . . .  A chapter named “Bridge to Nowhere” lays out a good chunk of what I intended:

There’s a beautiful, pristine bridge deep in the middle of the mountains northeast of Los Angeles made of white concrete—pure and unabused by tire marks. Right after it was built in the 1930s, a flood washed out the road leading onto it, and the bridge was never used. It arches gracefully over a deep canyon and runs smack into the side of a mountain. Nowhere!

That bridge is a monument to man’s folly, thinking he can compete with nature. But it’s also a tribute to man’s striving for the future and the beauty that it occasionally brings about. The story of man has always been struggle and despair, and yet despite that, despite the manifest hopelessness of our journey, man keeps striving toward some unknown destiny, always hoping, always seeing something worthy ahead. The book names that destiny, but now I’m skirting a spoiler, so I’ll stop here while I’m still ahead.

Question: Why did I write the book?

Answer: To satisfy myself. And that includes not writing in a genre.

If you’re looking for genre, don’t bother reading The Darkest Side of Saturn. It’s not one. I wrote it to please myself, not follow a deeply rutted road. It’s not science fiction, mystery, romance, literary, thriller, or any of those categories that have rules, conventions, and expectations. It has science, but it’s not science fiction. It has romance, but it’s not a romance. There’s sex, some of it extreme—not in the usual generic mold. It’s about science, romance, sex, world view, and metaphysical speculation all rolled into one.

Cabbages and kings! It’s for people who like to ponder imponderables with their entertainment. But it ain’t vanilla science fiction (whatever that is), so if you’re looking for quirky, unpronounceable alien names or a space opera that violates all the rules of physics, this book is not for you—it won’t meet your expectations.

Then why did I call it science fiction? Because I had a weak moment. Because the established publishing and marketing industries require that every work of fiction be labeled, marked, pigeon-holed, screwed, blued, and tattooed as a genre.

I like to think of it as a Greek drama, devoid of sound and fury, signifying something. Like some Greek dramas, it has an odyssey, and there’s even a Greek chorus of girl and boy scientists and engineers. It has sermons preached by a spacecraft navigator turned Prophet of Doom and his antagonist, a fanatical preacher. It has voices in their heads, and rants ranted by an obnoxious radio talk show host.


And lastly, it has a two-mile wide asteroid that might hit Earth. Start the countdown.



Epoch State: What’s it all about?


Epoch state is spacecraft-navigation-speak for the beginning, the thing that kicks everything off, specifically a trajectory. It’s the position and velocity that initializes the problem Where are we and where are we going? The spacecraft trajectory propagates downstream from there, subject to all the gravitational and non-gravitational accelerations acting on the spacecraft—such as the pull of gravity from the sun and all the planets as well as the firing of thrusters that maintain its attitude. There’s always a fair amount of uncertainty in the trajectory because you never know the epoch state perfectly and there are always errors in your model of the accelerations. Think of a trajectory as an animal path through the jungle: It’s a bit wide and fuzzy because you don’t know it exactly, but if you wait long enough you’ll see an animal come along, by-and-by.

Well, that’s a little bit like what this initial post is supposed to do: kick off a trajectory of blogs subject to the forces of reality and non-reality (i.e., imagination) as they impinge on my consciousness, as well as dollops of whimsy bubbling up from the subconscious and elsewhere (e.g., from you). And like errors in a spacecraft trajectory that grow and grow after you depart the epoch state, I expect these blogs to also wander considerably. They’ll start off oriented towards my last novel, The Darkest Side of Saturn, but after a while you can expect to see them drift farther and farther from that fuzzy animal path.


Embracing the Future

My Op-Ed piece on the Mars Polar Lander ran in the Pasadena Star-News on 2000/01/20.
I was one of the NAG (Navigation Advisory Group) folks providing advice and help to the Mars Polar Lander Navigation Team after the crash of the Mars Climate Observer a few months earlier. We were chagrined to learn that the entry target region at Mars was incredibly small, and maybe not even attainable by the Navigation Team. Promises had been made which should not have been made. Unless the team was beefed up and new methods were implemented, the second failure in a row at Mars was itching to happen. After a lot of effort and worry, the day of the landing arrived. The Navigators and NAGs rejoiced because we had delivered the spacecraft to where it should be. Alas, the Navigation was right but the landing software was wrong …


Mars: NASA / Foter /

Dearly beloved, we gather to celebrate an arrival, not mourn a departure. Let us give thanks for the future and bury the past.

Conversation dies and silence gathers as the minutes tick-tick-tick toward 12:39 in the afternoon of a Southern California day at the Jet Propulsion Laboratory. I’m jammed cheek-by-jowl with fifty other people in a narrow hallway running half around a glass-enclosed operations room. Another thirty people wedge into that small room. Dan Goldin, NASA Administrator, is there — a gray eminence watching quietly and lethally. There’s Richard Cook, Project Manager, and bird-like Ed Stone, JPL Director. There’s John McNamee, Project Developer, looking intensely haunted and somber. Where are we? Where are we going?

“Take more risks,” Goldin said. “Don’t be afraid of failure,” he pronounced at the dawn of Faster, Better, Cheaper. More recently he added a stern codicil: “But don’t fail.”

We’ve been at risk for eleven months since our dearly departed little brother, Mars Polar Lander, became irretrievable at launch. Today, December 3rd, 1999, a cloud of uncertainty begins to precipitate into reality as we listen for the first available peep from little brother. We won’t know for several minutes yet, thirteen, twelve, eleven …

You have to roll dice in the space biz, there’s no getting around it. Everyone in that room and hallway has something on the line. For the mission engineers and scientists it’s a few years of their lives and careers. For others like myself—one of the navigators trying to figure out where we are going—only a few weeks of commitment are at stake. Only a few weeks? Wrong! It has been an agony of weekends, long nights and Thanksgiving holidays sacrificed to the demanding God of Exploration.

The God of Exploration! He has been benevolent to Viking and Voyager and Galileo and Pathfinder—and He has been cruel to Mars Observer and Mars Climate Observer. You have to sacrifice time, money, talent and ingenuity; he doesn’t provide safe passage to Mars for peanuts, you have to bleed and sacrifice a virgin or two.

… eight, seven, six …

Where are we and where are we going? All conversation ceases! All eyes lock onto the display of the spectrum analyzer. A green fuzzy-flat line lies horizontally across the range of radio frequencies expected from our departed kin.

… three, two, one …

Collective intake of breath. In moments we will shout joyfully to see a tiny needle-sharp peak of signal rise from that fuzzy-flat line to tell us that our dearly departed is dearly arrived, yet …

Yet now the possibility of failure congeals. Until NOW it was abstract and empty—was simply the dark underside of a probability cloud drifting far away.

Now! A nugget of information has propagated over fourteen minutes of light-travel-time from Mars to Earth, to the Deep Space Network, to this control room, to this display, to these eyes. Now. The probability cloud roils overhead, leaden black underbelly churning malevolently. A lightning stroke, abrupt and powerful, strikes nearby. Reality arrives.

The flat line remains flat-line. The nugget of information is the null bit, the absence of a needle-sharp peak, the lack of signal where signal is wanted.

Wait! Maybe the timing is off, maybe the receivers need tweaking, maybe the antenna is mis-pointed, maybe …

Silence. A downpour of cold wet reality begins, soaking the mind, depressing the soul. Dan Goldin’s face darkens; Ed Stone stares at the spectrum display. John McNamee gazes into space.

… five, six, seven …

Speculation begins in whispers. Maybe it’s in safing mode, maybe earth is temporarily out of sight, maybe …

There are a hundred possibilities. Over the next few days I will watch Richard Cook’s face filling TV screens, always optimistic, upbeat. There’s always one more thing to try—but I feel in my heart from that first moment, as do most of us assembled here, dearly beloved, that the roll of the dice has come up snake eyes. Our dearly departed has truly departed, smeared all over the landscape, or perhaps rolled into a ball at the foot of a steep slope, or perhaps …

There are many possibilities but only one actuality, which we may learn when the first human explorers eventually reach the forbidding southern climes of Mars. Meanwhile, we deal with failure—with breast-beating, investigation boards, program restructuring, launch cancellations …

And growth, and lessons learned, and a chance to do it better, because we WILL do it better, again and again, because we melt in the crucible of failure and mold to something better, but more fundamentally because we, as human beings, worship the God of Exploration and will sacrifice for the future.

Dearly beloved, give thanks for the future and bury the past. Where are we and where are we going? To Mars and beyond.


Voyager at Neptune

This OpEd ran in the Sunday L. A. Times, 1989/08/06

Neptune! Almost 3 billion miles from earth. It’s a cold, impersonal place, a speck of a planet through even the largest telescope, but an enormous gas giant full of mysterious wonders when seen up close.

In a few more weeks we’re going to experience it up close, you and I. We will see it through the eyes of a solar diplomat: a traveler, explorer, adventurer, and representative of the human race; a large metal, plastic, silicon representative named Voyager.

When we arrive, what should we expect? The unexpected! That’s the lesson learned from previous visits to unexplored planets. Are there rings at Neptune like those at Jupiter, Saturn and Uranus? Possibly, but in incomplete arcs, unlike rings anywhere else. Are there other satellites, besides the already known Triton and Nereid? Yes! One has already been discovered, and there’s tantalizing evidence of more—perhaps many more, maybe even clouds of them — lurking just beneath the fuzz in the images painting the screens of video terminals at the Jet Propulsion Laboratory. In just days, now, they could rise to visibility above the electronic background noise.

Neptune has its own internal heat source, and radiates more energy than it receives from the sun. Why? Is this what drives its turbulent atmosphere, generating the large spots already found? Soon, we may know.

And Triton? We’ll find whether it has an atmosphere, and whether we can see through to the surface. Will there be pools of liquid nitrogen, or will gasses be frozen in slabs littering a desolate landscape of craters and mountains?

Among the answers to the questions we know to ask will be more questions we’ve not imagined—the unexpected!

When Voyager arrives at Neptune—on August 25th—it will be the first time since creation that anything human-made has been to that planet. We should enjoy, appreciate, and celebrate the event, since it will also likely be the last time it will happen during our lives.

That’s because a very special arrangement of the solar system, one that occurs only about every 175 years, was required to allow Voyager to make the trip in “only” twelve years. It had to go by Jupiter first, making a hard left turn in that planet’s gravity to pick up energy in a crack-the-whip fashion to go on to the next planet. That was Saturn, which turned it left again, gave it more energy, and pointed it towards Uranus. At Uranus, in 1986, it picked up still more energy and made course for Neptune. Since then it has been “cruising” at ten miles per second toward the planet. At Neptune it will skim over the north pole three thousand miles above the atmosphere, turn downward so that it’s headed south out of the solar system, and make a final encounter with Neptune’s largest satellite, Triton, before beginning a larger interstellar voyage.

The science at Neptune is important, but think also about the voyage, the adventure. Knowledge is good for the human mind, but travel is food for the psyche. And Voyager’s travels have been and will be prodigious. It has been on its way from earth since 1977, wending a crooked path through the outer solar system. Now, in a handful of days, it makes its final rendezvous, a close brush and embrace with Neptune, before flying out of the solar system to begin an odyssey through the Milky Way galaxy; an unattended, lonely voyage that may last from millions to billions of years.

Towards the beginning of that longer journey, a mere few hundred thousand years in the future, our sun will have become a faint, uninteresting star in Voyager’s eternally night sky. But no one will be with the spacecraft to appreciate that fact, and our ambassador will slowly tumble—sightless, senseless, and alone —in an immensely empty void.

A fellow engineer on the navigation team claims that the spacecraft will be on display in the Smithsonian Museum 200 years from now. He thinks that by then we’ll have both the technology and wherewithal to go out, find and catch Voyager, and bring it back. I’d like to think we would be able to do that, but if I’m still around I’ll vote to leave it alone. There’s something wonderful about the thought that a piece of ourselves is somewhere out there on a winding journey between the stars on its way to eternity. It’s like having immortal children.

So this is an adventure, and we’re all on board. The solar system is our playground, and after that—the stars! There are hazards ahead—for example, unseen ring particles orbiting Neptune could smack into us, prematurely ending Voyager’s life—but we’ll probably make it through to see the wonders of Neptune and Triton.

Then will begin the grander voyage—the one that requires us to be romantics instead of realists; dreamers rather than schemers: Even though Voyager will go blind and deaf after a few tens of years; even though it will die an electronic death, it will still have the germ of human creativity and daring incorporated into its very structure. It carries two messages—an explicit one in the form of a golden record, and an implicit one stated by its profoundly improbable existence. And both messages will say to the finder, in essence, “I am from the planet earth. I am of the human race. We are small and insignificant, but our souls are large because we have set out on a journey to know the universe.”