Tag Archives: NASA

P–30 days: Navigating Pluto

 

Goldstone_DSN_antenna

Goldstone 70 meter antenna / NASA / Wikipedia

2015/06/14. Sunday
The third of a series of posts about navigating to Pluto

Distance: About 36 million kilometers from Pluto at 5:30 am Arizona time as I write.
Velocity: A not-much-changing 13.8 kilometers per second toward Pluto and away from Home. Not-much-changing because the pull of Sun’s gravity isn’t very strong out here.

I think I’ll do nuts and bolts today: how do the Navigators do what they do? That means I need to talk about the DSN (Deep Space Network) and navigation data types and other technical what-not. Let’s try to keep it light and entertaining, shall we? If you’re not technically inclined, you may be excused from today’s session, but be warned you will be tested on the material in the final exam. Attendance at the next session is mandatory.

But first, News Flash! The maneuver this morning was successful as I see in an email from Alice, the mission operations leader: “Initial TCM assessments are showing a nominal burn within the expected parameters.” Chris, one of our Navigators at the Mission Operations Center at APL (Applied Physics Laboratory) in Maryland says “The Doppler residual came up right around 1.06 Hz … indicating very likely a nominal burn.” Woo-hoo! We’re walking a little under two feet per second slower toward Pluto so that we’ll get there about 83 seconds later, close to the intended arrival time.

Back to the Deep Space Network. What a romantic, adventurous, ambitious name! I can hardly believe it’s real; the term evokes wonder every time I give it a little thought. Especially since there wasn’t any Space when I was growing up, much less Deep Space. I mean, most people didn’t think we could ever go into Space, and if you thought differently you were a Space Cadet.

I was a Space Cadet. All the way up to Sputnik in 1957. Then Space became IN. I thought I’d become IN, too, from Space Cadet to Visionary in a single launch, but no, that didn’t happen. It’s hard to project the necessary gravitas at age fifteen. Since then, I’ve navigated spacecraft to every planet in the solar system. From zero to sixty in only seventy-two years! (And I’m still a Space Cadet. When does the gravitas kick in?)

Where was I? Oh yes, Deep Space: a term that never fails to evoke romance, mystery, and adventure. Are we earthlings actually tracking things in Deep Space? Yes, we are! And someday, if we’re good and don’t kill ourselves first, we may even go out there ourselves.

The Deep Space Network: There are three locations almost evenly spaced around the world where NASA operates antennas that track New Horizons. The locations ensure that we (New Horizons) will be in sight of at least one of them all the time. There are several antennas at Goldstone, California; several near Canberra, Australia; and about an equal number not far from Madrid, Spain. We call those sites Goldstone, Canberra, and Madrid for short, but more commonly we talk about the antennas themselves, like DSS-14 (Deep Space Station 14, a 70 meter wide antenna at Goldstone) and DSS-65 (one of the 35 meter antennas at Madrid.)

The DSN antennas collect four different tracking “data-types” from New Horizons and funnels them to the Navigators through various channels that aren’t important to this discussion. Here they are (bear with me, it gets a little thick for a few sentences here and there):

(1) Doppler data: A DSN station sends up a radio frequency signal. It travels 4.5 hours to the spacecraft. When the spacecraft gets that uplink, it sends back a downlink signal that’s in “harmony” with the uplink. That means that in the process of turning the signal around and retransmitting it, New Horizons accounts for the frequency of the uplink on a cycle-by-cycle basis. When it gets back to Earth 4.5 hours later, it’s compared to the frequency that went up. If it’s the same, then nothing has changed, and that’s evidence that we live in a static universe in which nothing moves! That doesn’t seem to be the case. We always see a shifted frequency, pretty firmly establishing that we live in a non-static universe!

eeEOoo

Doppler effect defined

The received signal is different from what went up. Why? Ta-da, the Doppler effect of course, named in honor of Christian, its discoverer. That’s the eee-ooo sound you hear when a train goes by, but radio waves behave the same. And when you analyze that shift, you get clues about how the spacecraft moves, and just as important, how the tracking station moves because of the earth’s rotation, and when you put all that information together over the course of a tracking pass that lasts several hours, you can figure out not only how fast New Horizons is moving away from the Earth, but also you can determine its location in the sky: the Right ascension and Declination (reverting to astronomy-speak for a moment). The Doppler data is incredibly powerful in navigation, at least in the radial direction, and a change in New Horizon’s radial velocity of only 1 millimeter per second will look like a big signal.

So there—we’re through the hardest part of the discussion I think.

But wait, there’s more!

(2) Ranging data: If you time the signal (and the DSN has extraordinarily good timers, accurate to a gnat’s ass (another technical term), and know the speed of light (which we do) you can get the distance to the spacecraft to an accuracy of much less than a kilometer out of 4.7 billion of them. Now there’s a truly astounding accuracy). There are a lot of complications, of course, but that pretty well sums up the big picture for ranging data.

But wait, there’s more!

(3) DDOR data: Sometimes we use two of the DSN stations simultaneously, like Goldstone and Canberra and—over the course of about an hour—alternately track the spacecraft and then a quasar near it in the sky. Quasars are conveniently loud at radio frequencies, and they’re so far away that they don’t budge over the course of many, many years,

Delta-DOR defined

Delta-DOR defined

so they provide a very nice fixed reference system (thanks, Mother Nature!) for figuring out the direction of the spacecraft to jaw-dropping accuracy, about one-millionth of a degree. This data type has the gawky-gangling name of Delta-Differential One-Way-Range, which we usually shorten by calling it Delta-DOR, or writing it “DDOR”.

But wait … (oh, never mind). There’s one more.

The three types above—Doppler, ranging, and DDOR—are so-called radiometric data types. They’re all “centered” at Earth, so-to-speak, so the farther away New Horizons gets, the less accurate they are. To add to the uncertainty, we don’t know the distance from Earth to Pluto very well yet, so even though we might know the distance from Earth to New Horizons to that gnat’s ass, we don’t know New Horizon’s distance to Pluto to better than, very roughly, 1000 kilometers. That leads us into:

(4) OpNav data: The 4th data type, optical navigation data, or OpNav in the vernacular, is based on pictures taken from New Horizons of the things out in front of it, namely Pluto and his retinue of satellites, downlinked to the DSN and thence to Navigation. The OpNav team, a subset of the larger Navigation team, is led by Coralie. She and her team pick the locations of the tiny blobs of Pluto, Charon, Nix, and Hydra out of the noise of the images (a very difficult and tedious process with all kinds of complications) and compare them to locations of stars in the same images. This “pins” the spacecraft down against the stellar background, and since the locations of the stars in the sky are well know, so is the location of New Horizons. (The remaining two known satellites, Styx and Kerberos, aren’t used for the OpNav process because they’re too small and hard to see.) The location of the stars, Pluto, and satellites in the images constitute the data passed to the Orbit Determination team led by Fred.

So, that’s the end of the data descriptions. Not so bad, eh, if you’re still with me.

Since the OpNav data is spacecraft “centered”, it gets more powerful as we get closer to Pluto, until finally there comes a time when it overwhelms the accuracy of the radiometric data and tells us where we’re located relative to Pluto rather than Earth. From then on, OpNav data is the prima donna of the navigation show except for complications (always complications!) like when the spacecraft gets really close to Pluto and the Doppler data begins to “feel” the gravity. This doesn’t happen until the last day in the flyby because Pluto is so NOT massive (at least as compared to the planets).

It’s the job of Fred and his minions (of which I may be one), to boil all of this big slurry of data down (remember that big black witches’ pot in the first post?), scads and scads of it (another technical term), until there’s nothing left but a tarry black residue. That’s what we call the solution. It tells us where we are and where we’re going.

But wait … It’s not cut and dried with just one solution. There are a lot of unknown parameters that go into the witches’ brew, and the Navigators have to make assumptions about their values and how much they trust those assumptions. There are also a host of other variables, too much to go into, so just call them toad tongues and minced-spiced bat wings. They all affect the solutions to varying degrees.

The Navigators boil down many, many pots of witches’ brew, stirring vigorously, tasting occasionally and adding different amounts of toad tongues and bat wings to suit, so there are finally a lot of those tarry residues at the end of the process of orbit determination, each with a different taste (read trajectory). It’s the Navigators’ job to assess the flavors of all these and decide which one meets the reality of a successful Plutonian encounter, then deliver that nugget of information—a predicted trajectory—to the other teams of the mission so they can act on it.

So there it is in a nutshell.

There is no more. Today.

 

Mercury Minus Ten, Pluto Minus Eighty-five

messenger

Image credit: NASA–NSSDC/MESSENGER

As of 2015/04/20 there are 10 days until the MESSENGER spacecraft goes splat somewhere in Mercury’s northern regions, and just under three months until the-little-spacecraft-that-could, New Horizons, flies by our last commonly accepted outpost, planetoid Pluto.

new_horizons

Image credit: NASA–NSSDC/New Horizons

 

These two missions bookend our solar system, innermost and outermost, if you disregard the billions of tiny bodies stretching farther out in the Kuiper belt and Ort cloud, farther than the eye can see and with more Pluto-sized bodies than the schoolchildren can memorize (which is probably one practical reason Pluto was demoted from planethood in the first place).

MESSENGER has been spaceborne since 2004, New Horizons, 2006. New Horizons was pretty much a straight shot to Pluto; MESSENGER was a complicated mess, the equivalent of a 6 bank shot in billiards, flying by Earth once after launch, Venus twice, and Mercury three times before dropping into the pocket—that is, going into orbit—on the fourth Mercury encounter in 2011.

Now MESSENGER is out of hydrazine and quite literally running on fumes, squirting the helium gas that used to pressurize the fuel straight out of the tanks and through the thrusters. Not as efficient as the hydrazine, but sufficient to delay the inevitable a few maneuvers and days at a time as the orbit closest approach altitude inches (kilometers!) toward an inevitable rendezvous—a kiss of death with the Mercury surface somewhere in the North-polar region, the final splatt. One more planned maneuver on April 24th should stave it off until about the 30th of April, and then it’s bye-bye MESSENGER.

New Horizons was the fastest ever spacecraft at launch, peaking at a blistering 43 kilometers per second relative to the Sun. The inexorable hand of gravity slowed it so that—even though a distant flyby of Jupiter gave it a boost—today it glides at a more leisurely pace, 14.5 kilometers per second through the deeps and darks of space. When it gets to Pluto it’ll fly by that remote outpost—more than 30 times the distance from Sun to Earth—at a tad under 14 kilometers per second.

Interestingly, the distance New Horizons has traveled all the way out to Pluto is less than MESSENGER traveled in its pinball encounters with the inner solar system planets to lose enough energy to get into orbit at Mercury. Gee, Mr. Wizard, you have to lose a lot of energy to get to Mercury.

traj_helioecl_earth2moi2_10292010

Image credit: NASA–APL

Too bad MESSENGER’s demise can’t be delayed two more months. Then the Deep-Space Navigators of both spacecraft, who work for KinetX Aerospace, would be able to say they’re navigating simultaneously to the extremes of the solar system. Nevertheless, to do them both within a few months of each other is pretty noteworthy.

Important science was done at Mercury and more knowledge comes from Pluto in July, but the purpose of this blog is to celebrate the art and science of deep-space navigation—and particularly the two KinetX Navigation Teams (both of which I was once a member)—that guided us there, for truly the journey is more than half the fun …

And we almost always get you there!

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Naming Pluto

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Image credit: NASA-JHU APL/New Horizons

Update 2015/04/14! The voting is extended to April 24th. Here’s your chance!

Pluto – 113 days and counting as of 2015/03/23. The New Horizons spacecraft flies close by Pluto this July 14th—the first encounter in history and probably the last in your lifetime.

Looking for a link to the blessed event, I ran across this site, http://www.ourpluto.org, describing itself as a public campaign to name the surface features on Pluto and Charon. “Working with the International Astronomical Union (IAU), the New Horizons team plans to assign names to the features on the maps of Pluto and its large moon Charon, once we have seen them in sharp detail this summer. At this site, you can suggest your ideas for names and vote for your favorites. The team will use your best ideas in their proposal to the IAU.”

In other words, you get to suggest names, but the IAU gets the last word, and if your proposed name doesn’t fit into its naming policy, out it goes.

Well, maybe that’s as it should be. We certainly don’t want corporate sponsors naming craters after automobiles, religious organizations naming mountains or valleys after holy names in the Quran or Bible, or politicians naming smoking fumaroles after themselves. What better way to handle it than let an international organization of astronomers fairly and impartially dictate the terms?

The only problem is that the IAU rules for naming features on solar system bodies seem to preclude naming anything for the spacecraft or mission that discovered those features in the first place.

The only exception I know is Valles Marineris (Mariner Valley) on Mars, named after the Mariner 9 Mars orbiter that discovered it. This instance seems to have irked the IAU because you’ll have a hard time finding the names of spacecraft for features on any other planets or their satellites since then. Not Viking or Voyager or Cassini or Galileo or MESSENGER, or apparently now, New Horizons. Hardly a valley, scarp, crater, hollow, chasm, knob, ridge or volcano has been named for the spacecraft or mission that found it.

There are plenty of deceased astronomer names plastered over those terrains, gods and goddesses, fictional characters, writers, and other hoi polloi, but exceedingly rarely, or maybe never, will you find the name of a spacecraft or mission or its engineers or scientists.

To qualify, if you’re a person, you have to be both famous and dead. This precludes having anything you’ve discovered being named after you at the time of discovery. Maybe you’ll get a tiny crater fifty years from now if there’s anything left over, but certainly nothing big. Perhaps this is as it should be, but this exclusion of mission names and the names of the scientists and engineers that run them violates, in spirit at least, the moral dictum “You gotta dance with the one that brung ya.”

A literally down-to-earth historical precedent is seen in the many geographical features on earth named for their discoverers. Why should this not also be the case for the solar system?

Check it out. Go to http://www.ourpluto.org and nominate a name for a Pluto feature (voting closes on April 7th), but at the same time notice the categories of names that the IAU will allow, and note that you won’t find New Horizons or any of its live participants in any of the “allowed” themes. Go ahead and suggest names, but please also entertain the question of why mission names are not allowed for the features they’ve discovered. And of course if you like the idea of something big on Pluto or Charon being named for the mission that brung us, the public, along on this long distance voyage of discovery, then certainly write it in.

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Farewell to Neptune


Here’s my OpEd piece in the L.A. Times 1989/11/25 titled “Music for a Stellar Generation.”
I’m no longer as optimistic about our prospects for colonizing the solar system and the stars as I was back then, twenty-six long years ago. As I said in a recent post, we have little need to be optimistic in the short run—I think we’ll have a series of disasters and recoveries—but the future is very bright indeed over the long haul of centuries, millennia, or even millions of years. After all, we’ve only been around as a species for a couple of million years on Earth; think what we’ll be like in a couple more!

Gustav Holst began writing “The Planets” in 1914. Its first performance, five years later, was a symphonic celebration of planets Mercury through Neptune (Pluto wasn’t discovered until 1930). The music is beautiful and grand—but something is lacking. Despite its variety, there is no human adventure. The planets, in those days, were still “Gods”—remote, aloof in a separate, self-contained universe, hermetically sealed from human interaction or contamination. The solar system was a very large and inaccessible place for mortals.

Now another piece of music has played out: The last note of Voyager’s Neptune encounter fades into vacuum as the spacecraft departs our solar system, to be succeeded in the public mind by the discordance of the Bay Area earthquake and Eastern European upheavals. But we come not to bury Voyager; rather to praise. The brief encounter with Neptune was not an ending but a prelude yo a larger quest and a longer symphony.

After Voyager the Gods no longer reign. The planets belong to humankind.

The outer planets and their satellites were but tiny, pretty baubles in our skies before Voyager’s flight to Neptune and beyond. Now they are worlds in their own right, concrete and beautiful in their gargantuan presence.

Gustav Holst was born too early. How was he to know the adventure of the planets and man’s place among them? There was no way then to experience, even vicariously through the eyes of a Voyager, the pastoral solitude of interplanetary cruising; the rolling, thundering crescendo of planetary encounter.

I imagine him looking over our shoulders, following Voyager across the sky. NASA’s Goldstone antenna, a white leviathan creature in the center of an empty desert stage, glows in a fading twilight, hard bright stars overhead, the silence of the horizon dropping away into pink-gray distance. Why is it that this sight and silence seems so much like music? Gustav, are you listening? Can you hear the slow motion turning against the sky?

It’s time for a new musical genius to bring us a modern symphony of adventure among the planets, of man’s place among the Gods. Let us hear the chaos of departure from earth’s surly bonds, the basso profundo of planetary encounter. It’s time for that symphony, and I hope someone will write it because it is the beginning of a story of human drama of Wagnerian proportion. It will help to tell us where we are and where we’re going.

And where is that? “To the supermarket,” some will say. “My feet are firmly planted on Earth, and I’m going to work, I’m going home, I’m going to the hospital to visit a friend. I need to tend my garden.”

Worthy activities, but our children, or perhaps our grandchildren, are going to live in space. The urge to explore and expand is inborn. We are going, sooner or later, because we have no choice. Cast aside any debates about manned versus unmanned space exploration. They are irrelevant.

As a species, we will begin by colonizing the solar system.

We will break ourselves—bodies and spirits—on new shores, and we will regroup and plunge again, groping for dry land. Careers will be spent, lives lost in the quest. And the music will help us mend, and drive us forward again.

Many will not share our enthusiasm—will not want to assume hardships of pioneering. They are the equivalent of the Europeans who stayed behind, concerned with the problems of the Old World while explorers looked to the new.

Let them be. Very few will be able to go, anyhow. We will need their help, a large home base for support while we explore and settle, until we are independent. And what will explorers do for our homeland, our mother Earth at that time? Probably the same thing that the United States did for England in 1776. Children have no responsibility to their parents; only to the children that follow.

Voyager represents the beginning of a magic age. Its goodbye to Neptune is our hello to the solar system. The journey will begin with small steps: footprints on Mars, new ones on the moon. Every step will be hard-fought, but eventually we will inhabit most of the solar neighborhood. At that point, we’ll begin to get restless again—we’ll turn up our music and consider how to follow Voyager on her questing note, a trip to the stars.

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.”

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