Planetary Radio: Space Exploration, Astronomy and Science - A Cassini at Saturn Progress Report with Linda and Tom Spilker

Episode Date: February 18, 2008

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Linda and Tom Spilker with an update from Saturn this week on Planetary Radio. Hi everyone, welcome to Public Radio's travel show that takes you to the final frontier. I'm Matt Kaplan. It's time for another Cassini update from Deputy Mission Scientist Linda Spilker, but this time with a twist. Linda is joined by her husband, Tom Spilker, also of JPL, in the

first of two conversations. We are packed tighter than spam in a can this week with a brand new Q&A from Emily Lakdawalla and a What's Up segment with Bruce Betts that goes to unheard of lengths to give away a Planetary Radio t-shirt. And I mean that literally.

Let's get started with Bill Nye, the science and planetary guy, as Bill marks one of the biggest anniversaries and discoveries in space exploration history. Hey, hey, Bill Nye, the planetary guy here. I'd like to talk to you about the 50th anniversary of Explorer 1. Explorer 1 was a spacecraft launched by the United States in response to Sputnik. In the meantime, we tried to launch Vanguard, but it blew up. So Explorer 1 was the first successful orbiting U.S. spacecraft, January 31, 1958. And this, you could say, is a piece of trivia, a footnote. No, no, my friends.

Explorer 1 discovered what are now called the Van Allen belts. Now, the Van Allen belts. These are belts. These are regions above the earth where fantastically energetic particles streaming from the sun are trapped, are held in space by nothing but the invisible earth's magnetic field. Quite remarkable. No one had much thought about this. No one had much thought about what happens to particles that might come off of a star headed our way. They're held above, kept away from the Earth's surface by magnetism. And without magnetism, we would be totally different. What would we be? We would be reptiles.

We would be amphibians. We would be humobots. Who's to say what we would be? And this discovery was made, if I may, by accident in a Cold War effort just to keep up with the other superpower, literally, on the other side of the Earth. It's another example, my friends. We do space exploration, and we make remarkable, unexpected, astonishing discoveries. Explorer 1 stayed in orbit until 1970, 12 years.

Not bad for a first shot. Who knows what we will discover with our further explorations with more energetic, more powerful spacecraft as we go to the inner and outer solar systems. Thanks for listening next time you're walking down the street looking at the sky think about the tremendous

effort it took to put Explorer 1 in orbit and the remarkable safety we enjoy thanks to the Van Allen belts. Bill Nye, the Planetary Guy, talk to you next time on Planetary Radio. Linda Spilker is Deputy Project Scientist for Cassini at Saturn. She joins us a couple of times each year for an update on that incredibly successful mission. This time she has company, and he's no stranger. Tom Spilker is a principal member of

the Jet Propulsion Lab's engineering staff, where he often serves as a so-called mission architect. He's also Linda's husband. We're going to talk with them about Cassini today, but they'll both be back next week to look at other topics, including a proposed mission to Neptune and how they have balanced work at JPL with raising a family. Lynn and Tom, this is a first for Planetary Radio. You are the first couple of guests we've had who are tied at the hip as well as the brain, I guess, because both of you are here at JPL. Tom, we're going to include you in this conversation, focus on Cassini.

But next week, we're going to come back and talk more about the stuff that you're up to, particularly this field that you are part of called mission architecture. But I hope that you will also jump in now and then as we do one of these updates we've done a few times with Linda and hear about what's happening with that mission, which is still so successfully flying around the Saturnian system. Absolutely. You are now at about, what, nearly three and a half years? No, I guess more than three and a half years in since orbital insertion. So basically, you know nearly everything there

is to know about the Saturnian system, right? Oh, no, not even close. In fact, what we're learning is there are a lot more puzzles about Saturn and its moons and the magnetosphere than we ever thought possible when we first arrived. So that three and a half years has just, in a sense, whet our appetites for what else might be out there that we can learn about the Saturn system. be out there that we can learn about the Saturn system. Now if this program airs when I think it's going to air, people will start to hear it just a few days before yet another flyby of Titan. Yes, we have flybys of Titan that happen regularly and we do all sorts of activities at Titan. We take radar swaths. In fact, just recently we got our first pass over the south pole of Titan and lo and behold we discovered that the south polar region also has lakes lakes of liquid hydrocarbons very similar to the north just not quite as many

and some tantalizing hints that maybe there are dry lake beds in the south where it's near its summer and perhaps as the seasons change we might see those lakes fill up and the lakes in the north might go down so we're watching and waiting to see that happen. That's pretty exciting in itself if we discover yet another world in our solar system. I mean, we know we have seasons. We know Mars has seasons. And now this world, Titan, that everybody has been saying is in so many ways like ours, even though it's an awfully cold place. Right, in very many ways. In fact, the major difference, it's so cold at Titan that

water's frozen. And so instead of having a water cycle, we have a methane cycle. Methane can be frozen, it can be a vapor, it can rain down on the surface. We see channels that look like river channels and stream beds that are probably created by this methane weather, and perhaps even the source of what's in the lakes, now primarily at the North Pole of Titan. You'll be able to tell, as usual, that I spent some time last night knowing we'd be talking, looking at some of the latest on the website. And another thing that was featured there is more about this wonderful moon, Enceladus, which just becomes more and more exciting.

There was a great image that actually showed these individual ice geysers shooting off of the surface of this little moon. Yeah, those ice geysers are very, very interesting. And, in fact, as we go move from our prime mission, which ends on June 30th of this year, and go into the extended mission, we're going to have more closer looks at this very fascinating moon. In fact, on March 12th, we're going to come within 50 kilometers of the surface of Enceladus, and it won't be real close to the plumes. We're going to be flying through that plume region and doing some sampling right there and measuring what the composition might be of the particles that are coming out of the plumes,

both with the ionine neutral mass spectrometer and with the cosmic dust analyzer. Now, those instruments, were they designed to work with stuff that was surrounding the spacecraft? Weren't they supposed to work at a distance? I mean, it's called remote sensing, right? Right. Well, in the case of the two instruments I talked about, those are really in situ or measuring what's around the spacecraft. So the two instruments I talked about, those are really in situ or measuring what's around the spacecraft. But the INMS, ion and neutral mass spectrometer, was made to sense the atmosphere of Titan. And the cosmic dust analyzer was made to sample the meteoroids that come through and look for micrometeoroid particles maybe coming off the rings or off the moon.

So they weren't intended to measure the plumes at Enceladus in part because we didn't know they were there before Cassini discovered them. Can you tell us about this discovery also, I guess, that the A-ring is a pretty good sponge, that it's soaking up some of this stuff that comes off of Enceladus? Right. It looks like by studying the trajectories of the particles that we can get from the cosmic dust analyzer that a lot of those tiny E-ring particles end up at the outermost region of the A ring. And we knew from pictures that the colors were a little bit different and that this region appeared different than the remainder of the A ring. So it does indeed appear that's one sink for these plume particles

that come out from Enceladus, form the E ring, this giant ring that fills a lot of the Saturnian system, and then some of those particles end up as part of Saturn's main rings, as part of the A ring. What can you tell us recent findings about the big planet down below all of this? Well, Saturn is a very interesting place. Right now, one of the more recent discoveries is that the poles, both the north and south poles, you have two tiny hot spots. You go northward or southward about 88 degrees latitude, those regions are very hot. We think there's downwelling into the atmosphere at that region. The atmosphere goes down, heats up, and

creates these hot spots, one at each pole. Weather. Weather, in a sense. And you've got a hurricane at the south pole, a circular-shaped hurricane, and a hexagonal hurricane at the south pole a circular shaped hurricane and a hexagonal vortex at the north pole so a very interesting place and when you say hot we're speaking in relative terms relative right relative to hot for a penguin which is not bad that that far out so we're far from over there's much more to look forward to here i saw on the timeline that in May there's another Titan flyby, but it's another one of these that's going to come very close to the top of the atmosphere. Right, and give us a chance to sample the atmosphere of Titan.

Another discovery is that there are very large chains of molecules high up in the atmosphere, maybe even 10,000 proton equivalents in length. So these huge molecules, probably hydrocarbons, maybe some nitrogen. And the question is, what kind of chemistry allows you to grow particles that are 10,000 atomic mass units in size? That's a big polymer, right? Wouldn't that be the right term for this? That's right.

And maybe that's some of the material that sort of drifts down to the surface and forms some of the dunes that we've seen on Titan, but totally unexpected. In fact, we saw these as negatively charged ions, and it was in the electron detector of the plasma instrument that we found these large negative ions. See, I did not notice this on the website. That seems very exciting because you get molecules that big. You're talking potentially, at least, enormous complexity. Right, right.

And we're not sure if they're actually polymers, linear kinds of molecules, or polycyclic aromatic hydrocarbons, combinations of benzene rings put together in a more planar rather than linear kind of fashion. We don't know which. But it's just very interesting that they're there and that they're so big. We'll continue our conversation with Linda and Tom Spilker about the Cassini mission in just a minute. This is Planetary Radio. Hey, Bill Nye the Science Guy here. I hope you're enjoying Planetary Radio. We put a lot of work into the show and all our other great Planetary Society projects.

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Welcome back to Planetary Radio. I'm Matt Kaplan. We're talking about Cassini, that magnificent bus-sized spacecraft that continues to reveal the secrets of Saturn and its big family of rings and moons. Linda Spilker is the project's deputy scientist. Her colleague and more is Tom Spilker, a principal member of JPL's engineering staff. We'll hear more from Tom about his work as a mission architect next week, but there's much more to see about Cassini's immediate and more distant future. There is much more to look forward

to. I saw also that we're not too far away from what will, I guess, be only the second of two flybys of Tethys. Am I pronouncing that correctly? Right. In the main mission, anyway. Right, right. We have some relatively close flybys of these moons. Tethys is an interesting place. It's not one of the bigger moons, but we're sort of basically putting a family portrait together of each of these moons. How are they alike, and how are they different? And, in fact, just last September, we had a very close flyby of a very interesting moon, Iapetus. Iapetus has one dark and one bright side.

And in this case, with our close flyby, it was only 1,600 kilometers away. We got to see the bright side and look for the structures there and to try and see, is the dark material coating the bright material or is the bright material coating the dark material? And what we found in a lot of the craters is that there were like, look like little pools of dark material that the dark particles had settled down into the bottoms of these craters. And so it looks like maybe the dark material is coating Iapetus. But we still don't really know what it is. I mean, this is probably, you could make a case for this being one of the top ten mysteries of the solar system, I'd say.

Right, right. We think it might be perhaps some kind of hydrocarbons, but there might be other things involved as well. be perhaps some kind of hydrocarbons, but there might be other things involved as well. You already mentioned that your main mission, four years worth, is over this coming summer. You've got a spacecraft that, according to the reports that I see every week, is in good health. I saw that just recently, I guess, there was another test of these reaction wheels that are used to help steer the spacecraft, mechanical parts, nothing lasts forever. How long might we expect to see Cassini returning good science from Saturn? Well, that's a very good question.

We have a proposal on the table for a two-year extended mission in which we'd have seven additional flybys of Enceladus, including getting very close, flying right through that plume, like flying through a car wash, if you will. A lot more Titan flybys, a chance to look at the system again at a variety of different inclinations around it. And so that's on the table as a proposal. As soon as that gets approved by NASA, we'll go ahead with it. And then after that, there's a possibility that perhaps we could last, you know, perhaps another half a dozen years even after that. It'd be very interesting to get to the solstice or the equivalent of like would be summer or winter on the earth and look for those seasonal changes, especially on Titan. So do those lakes indeed migrate as we have one idea from the north to the south as the seasons change?

We could hang around and study the material coming out of Enceladus. Do those geysers turn on and off? Are there times when they're going like a fire hose and other times when there's less activity going on? So there's potential with the healthy spacecraft that we could go perhaps out until 2016, 2017 even. Tom, where would you be watching as a spacecraft gets a little older and a little crankier? I mean, what would you be most concerned about just as things age there up in the hard vacuum? Well, I think you put your finger on the main problem, and that is mechanical systems, moving parts that wear down, they lose lubricants and so on. So anything with moving parts such as

reaction wheels, things that point different parts of the spacecraft, if anything needs pointing, I know there are some of the instruments that have what they call articulation, moving parts that will point them differently. Those might start to wear out and not be able to move anymore. We're really certain, fairly certain, in engineering terms that usually means really certain, just how long our electric power is going to last, and that's going to be for a long time. We'll have electric power long after mechanical systems are failing. Well, I think of the Voyagers, which are so many years out and still delivering science back to Earth. And then the one other thing that we do need to watch is how much propellant rocket fuel we have on board.

There are two things that does for you. You can change the direction of motion of the spacecraft. So if you need to fly by a moon a little bit closer or a little further away to tune the trajectory from then on, you use the rocket engines to do that. But also, small rocket engines can control the attitude of the spacecraft. And when these reaction wheels have spun up, as we call it, they absorb torques that are from the sun, from the magnetic field, and so on, that try to twist the spacecraft. And to prevent the spacecraft from twisting, we spin up those reaction wheels to oppose the torque that's being applied to the spacecraft.

And then when they get to a certain point, you have to what we call desaturate them, spin them back down. But you can only do that when a thruster is holding the spacecraft in position so it doesn't go spinning off in a direction you don't want. So as long as we have that propellant on board, we can desaturate the reaction wheels. When we run out of propellant, we'll only be able to do that until the next time the reaction wheels saturate, and then we're at end of mission. Now, you can also control the attitude of the spacecraft directly by the thrusters instead of the reaction wheels,

but you tend to burn up a lot more fuel more quickly than you do with the reaction wheels. So that propellant will be a major concern. Well, Cassini has Titan to use basically as part of their way to change the shape of the orbit in different places that we visit. So you can think of Titan as having like an extra big fuel tank on Cassini. And so these close flybys of Titan not only give us exciting data about Titan, but also help us change the shape of and the destination of each of our orbits thereafter. An active participant in the ongoing Cassini mission. We're out of time, but we're going to come back next week and we're going to talk about another very exciting mission, which at the moment is still on the drawing boards, but you're both involved with it.

And then, Tom, I hope we'll be able to talk with you about this field that you excel at, mission architecture, and then maybe a little bit about how the two of you balance life at this little paradise on the hill here with a home life, a family that you've raised. It'll be my pleasure, Matt. We will do that when we come back in a week. Our guests are Linda Spilker, the deputy project scientist for Cassini-Huygens, and her husband, Tom Spilker, a mission architect, but his official title is principal member. He's a principal member of the engineering staff. We'll put it that way since that's how JPL puts it.

When we come back right after commentary from Emily, this week's Q&A, we'll have Bruce Betts for this week's edition of What's Up. Hi, I'm Emily Lakdawalla with questions and answers. A listener asked, I remember that observations of Mercury's orbit were used to test Einstein's theory of general relativity. Did messenger mission planners need to account for relativistic effects when they planned its orbit? Einstein's theory of general relativity predicts that spacetime will be curved near massive objects like the Sun. This curvature of spacetime affects the orbits of objects

close to the Sun. Mercury's elliptical orbit precesses around the Sun by a tiny amount, about a tenth of a degree per century, as a result of the curvature of spacetime. The software that's used to predict spacecraft motions generally does take relativistic effects into account, but if the effect is so small, do they really need to do that? To answer this question, Tony Taylor of Kinetics Incorporated, a private company that navigates MESSENGER, simulated MESSENGER's Mercury flyby with a general relativity expressions turned off. He found that failure to account for relativistic effects after MESSENGER's last deep space maneuver would have resulted in the spacecraft being 10 kilometers

high and 13 seconds late for its gravity assist flyby, a difference that's not disastrous but would have required corrections later to return MESSENGER to its proper course. Relativistic effects accelerate MESSENGER by very tiny amounts, only about one percent the magnitude of the acceleration that the spacecraft feels due to solar radiation pressure. But Taylor found that if the forces weren't accounted for, MESSENGER would be noticeably off its predicted course within days. Thus, Taylor's conclusion was that general relativity is definitely required for accurate navigation of messenger. Got a question about the universe? Send it to us at planetaryradio at planetary.org.

And now here's Matt with more Planetary Radio. Time for What's Up on Planetary Radio. Bruce Betts is out there via Skype speaking to us from his home on this holiday weekend, at least here in the U.S. He's ready to tell us about the night sky and a little bit about the diameter of Jupiter, which went in directions to lengths that nobody expected. Lengths, I get it. Amazing. I just mentioned something casually about whatever units you want, and people went wonderfully crazy with giving us units.

We'll get to that at the end of the show. In the meantime, let's talk about what's up there in the sky. If you're listening to this shortly after it's posted, then you've still got a total lunar eclipse in store, depending on where you live in the world, on the evening of February total lunar eclipse in store, depending on where you live in the world. On the evening of February 20th or 21st, depending on where you are, there will be a total lunar eclipse visible from most of the Americas, Africa, Western Europe.

Check out more about that from a link on our Planetary Radio page, planetary.org slash radio. And I will mention that the middle of the eclipse is at about 730 Pacific time there on the 20th. You can also always, anytime, check out Mars in the evening sky glowing still high overhead, moving towards the west, that bright orangish looking thing. We've also got Saturn that is rising in the east shortly before sunset, so it'll already be up in the east, and you can check it out all through the night, looking kind of yellowish. But the real treat is the pre-dawn sky. We have still Venus and Jupiter,

not that far apart, both very low in the east, but two brightest planets, both brighter than the brightest star in the sky, and they are visible in the east, with Jupiter being the one that's to the upper right, and not quite as bright as Venus. So that's where our sky holds. Let's go on to this week in space history. Of course, you know, Matt, in 1473, Nicolaus Copernicus was born. I knew it was sometime around that. Yeah, yeah. We also had Pluto discovered in 1930.

And this week, John Glenn in 1962, first American to orbit the Earth. And something we're going to come back to, in 1968, discovery of the first pulsar was announced. And we'll come back to that in just a moment. In fact, let's go to our random space fact. Did you know that when pulsars were first identified by a graduate student at the time at Cambridge, Jocelyn Bell, she actually called them LGMs for a while? I was going to mention that. I thought that was probably where you were going.

LGM. Yes, little green men, because of this regular pulsing seen coming in radio wavelengths from stars in the sky. I thought they could be little green men, but it turned out to be a natural effect of a neutron star spinning really, really fast

and putting out a beam of electromagnetic radiation, almost like a lighthouse spinning, but very regular in their pulsing. Very kind of weird objects, one of the weird objects of the universe. And I just love themes, so we're going to come back to pulsars for our trivia question. Excellent. But first, let's go to the last trivia question, because I know you've got some groovy units to discuss. We asked you a seemingly simple question. What is the diameter of Jupiter? You know, rough diameter of Jupiter,

and I mentioned people could give it in kilometers or any other unit, and we got some weird units. How'd we do, Matt? Yeah, that was where you went right by saying any unit that we can actually verify. So we got almost 40 different kinds of units from the very prosaic, like our winner, who came up with the correct number in miles, 88,700 miles in diameter. That came from Ron Miller in Fairhaven, Michigan. Ron, we're going to send you a Planetary Radio t-shirt. But man, oh man, people had great fun with this. We're going to try and put the list up on the website, planetary.org slash radio, because it's just such fun. We don't have time to go through all of them, but you want to hear a few of these? I would love to. Here you go. How about

16,887,840,240 barley corns. Ah, yes. I remember having to do physics problems in those units. Almost 440,000 Eiffel Towers. It's a French unit, right? Viva la France. One-tenth of the sun's diameter. That's approximate.

0.47 light seconds. Then we got into the ones where people got really creative, like Lindsay Dawson, who went to the trouble of figuring out that it's 658 million BBs. That's bowling balls. I love it. Gosh. How about from Olivier Lassaux? 80,224,719 me's. That is him. That's based on his 178 centimeter height. Now that I never did physics problems with. 178 centimeters of pure ego, as Olivier put it. Here's a really simple one that actually a couple of people came up with. Torsten Zimmer and James A. Brown both came up with the answer of one. That's one JD, or Jupiter Diameter.

There you go. And I mean, just an amazing assortment. Qubits, of course, we had to get Qubits. But like I said, we'll try and post these because they are so entertaining and just more proof that our listeners are a bunch of wiseacres. More proof that our listeners are a bunch of wiseacres. Yes, thank you all. I kept getting these emails all week forwarded from Matt, and it was nice to have some laughs. What do you got for us next time?

Well, surprisingly enough, we're going back to pulsars. I've got a question for you. In the middle of the Crab Nebula is the Crab Pulsar. How many times a second does it spin on its axis? First of all, it's totally freaky that there's a neutron star spinning that quickly to begin with, that it's measured. This time, I'll give you the units, times per second. How many times per second does it spin?

Go to planetary.org slash radio to find out how to enter. And you're going to need to get that to us by the 25th of February, 2008, Feb 25 at 2 p.m. Pacific. All right, everybody, go out there, look up at the night sky, and think about Smokey Bear. And then maybe what the diameter of Chupar would be in Smokey Bears. Thank you, and good night.

He's Bruce Betts, the Director of Projects for the Planetary Society, and he joins us every week for What's Up. I'm not thinking Smokey, I'm thinking smooch. 84,019,273 smooch. Look it up. Planetary Radio is produced by the Planetary Society in Pasadena, California.

Have a great week. Thank you.