 |
 |
||
 |
|
||
 |
 |
 |
 |
 |
 |
 |
 |
 |
 |
||||||||
 |
The Planetary Society BlogBy Emily Lakdawalla
Jan. 6, 2009 | 09:57 PST | 17:57 UTC I am totally hooked on Scott Maxwell's new Mars Exploration Rover blogScott Maxwell is one of those many guys (and gals) at the Jet Propulsion Laboratory who rarely gets his name in the news but who is absolutely indispensable to the success of a space mission. I don't know what his official title is, but whatever it is, it's not as good as the colloquial name given to his position: Rover Driver. Yes, Scott drives the Mars Exploration Rovers for a living. I'd say he looks pretty pleased with his place in life, wouldn't you? I'll quote space poet Stuart Atkinson's description of him: he is "a very lively, exuberant, always smiling, great galloping puppy of a Mars geek."
In today's entry he also talked about how the science team was trying to figure out where exactly Spirit had landed. I have a couple of snapshots from sol 2, of everyone crowding around giant printouts on the table...what a crush of scientists that was!
Jan. 5, 2009 | 09:59 PST | 17:59 UTC Astronomy Cast is broadcasting press conferences from the AAS meetingI just found out that the good people of Astronomy Cast are broadcasting the press briefings at this week's meeting of the American Astronomical Society in Long Beach via Ustream. Go here to watch the live press briefings; today's schedule is below, and you can watch the Astronomy Cast LIVE website for the schedule of press briefings later this week. The video and sound quality is quite clear enough to follow what's going on -- Astronomy Cast is getting good at this! All times are Pacific (GMT-8). 9:30 AM - Exoplanets and Exoplanetary Systems 11:00 AM - Brown Drawfs 12:30 PM - Milky Way 3:00 PM - International Year of Astronomy 2009 Begins in USA At that last press briefing will be several characters from the 365 Days of Astronomy staff, talking about our daily podcast. Today's podcast explains the causes of the seasons on Earth and other aspects of the night sky as explained by simple geometry. Jan. 5, 2009 | 09:10 PST | 17:10 UTC Dawn Journal: Conjunction junctionHere's our monthly checkup with the Dawn mission, contributed by Marc Rayman, the mission's Project System Engineer. Thanks Marc! --ESL  by Dr. Marc D. Rayman
Dear Dawncember30ths, Having fulfilled all of its assignments for 2008, the Dawn spacecraft has been unusually quiescent recently. While its operators on faraway Earth have no shortage of work, the probe patiently coasts in its orbit around the Sun, awaiting a brief encounter with Mars on February 17, which will steer it into a new orbit. On October 31, Dawn completed nearly all the ion thrusting that had been planned for 2008. On November 20, mission controllers directed the spacecraft to execute a short maneuver to fine-tune its trajectory. Its only activity since then has been the routine maintenance of the gimbal system used to point ion thruster #1. On December 3, it moved the mechanism through a range of angles to help redistribute lubricant, following the same commands that were used two months earlier. As viewed from Earth, Dawn passed through solar conjunction this month, appearing to be very close to the Sun. To visualize the geometry, suppose the Sun were at the center of a clock, with Earth at the end of the hour hand and the spacecraft at the tip of the minute hand. With the relative distances at the time of conjunction, the minute hand would be almost 1.6 times the length of the hour hand -- an elegant design indeed. (This analogy applies only for the separation as viewed from Earth under limited circumstances. As explained in an earlier log, while Dawn is indeed farther from the Sun than Earth is, the planet travels more quickly around its orbit than the spacecraft does. This would be more akin to a clock on which the hour hand is longer than the minute hand; such timepieces are back-ordered at Dawn souvenir shops.) When Earth, the Sun, and the spacecraft are on a straight line, such as at 6:00, the Sun and spacecraft would appear to overlap from the perspective of an observer on Earth, near the bottom of the clock. As we noted last month, Dawn would not pass directly behind the Sun, because it does not orbit in the same plane as Earth. Therefore, the precisely linear arrangement of hands at exactly 6:00:00 never occurs. Pushing the clock analogy beyond its limits of usefulness, the minute hand would be bent toward the clock face, so it does not circle in quite the same plane as the hour hand. We shall ignore that enhancement for now but return to this point below. In the meantime, let's consider the arrangements that have occurred. On December 12, when the angle between the Sun and the spacecraft was at its minimum, it would be analogous to the alignment of the hands about 10 seconds from the hour, or the arrangement at 6:00:10. (Remember, this clock only has hour and minute hands; your correspondent types too slowly to be able to construct a useful analogy with a clock that includes a second hand.) When most modern interplanetary craft are within about two degrees of the Sun, normal communications may be less reliable. This limitation, which lasted about two weeks for Dawn, would correspond to half a minute on either side of 6:00, or between about 5:59:30 and 6:00:30. Despite the powerful interference caused by radio signals passing through the distorting environment of the Sun on their way from the spacecraft to Earth, enough of the transmissions made it through for engineers to confirm that the spacecraft remained healthy throughout the conjunction period. Dawn was programmed to modify its radio transmissions to account for the angle between it and the Sun. Operators chose to accept a reduced return of information from the ship's systems in exchange for boosting the quality of the signals used for navigation because of the upcoming flight by Mars. Some usable navigation data were obtained every day, but, as expected, most of the data, particularly during the four days when the spacecraft was nearest the Sun, were too degraded to be useful in refining the parameters of Dawn's orbit.
The only reason for Dawn to travel to the vicinity of Mars is for the help to reach its targets in the asteroid belt. Nevertheless, as the probe races by, the team will take advantage of the opportunity to accomplish some bonus goals. Some of the plans will be covered in an upcoming log. In the meantime, as the thrill of conjunction begins to fade, our vast staff has yet to sort through all the data on how many terrestrial readers used this convenient alignment to guide their mental eye toward the spacecraft. The Dawn project sincerely hopes all observers reaped the maximum possible inspiration and joy from solar conjunction, as the mission will not offer another like it. Our destinations, Vesta and Ceres, do not orbit the Sun in the same plane that Earth does, and Dawn must match its orbit to that of its targets. (The major planets orbit closer to the plane of Earth's orbit, and no spacecraft has ventured as far out of that plane to orbit another body as Dawn will.) While the probe is already in a slightly different plane from Earth's orbit now, the gravity of Mars and subsequent ion thrusting will propel it to still a greater angle. As a result, when Dawn and Earth find themselves on opposite sides of the Sun in the future, the alignment will not be as close as it was this month. Dawn's next apparent encounter with the Sun will be in November 2010, but it will appear to pass far enough north of the Sun that communications should not be significantly compromised. Following that, there will be three more times before the primary mission ends in 2015 that Earth and the spacecraft will be on opposite sides of the Sun, but in each case Dawn's path through Earth's skies will take it farther north or south of the brilliant landmark than in the 2008 conjunction. Nevertheless, each will be close enough that it may provide a visual reference once again to stir meditation upon the magnificence of a journey far away in the depths of space. Dawn is 11 million kilometers (7 million miles) from Mars. It is 372 million kilometers (231 million miles) from Earth, or 930 times as far as the moon and 2.53 times as far as the Sun. Radio signals, traveling at the universal limit of the speed of light, take 41 minutes to make the round trip. Dr. Marc D. Rayman 6:01:45 pm PST December 30, 2008 Jan. 2, 2009 | 20:15 PST | Jan. 3 04:15 UTC Five Years of Spirit on MarsOn January 3, 2004, the Mars Exploration Rover Spirit landed on Mars, and I was with the science team at JPL when it happened! I can't believe it's been five years since the successful landing. I chose the anniversary as the topic of my first podcast for 365 Days of Astronomy (follow that link to download it). Below is a transcript of my podcast -- enjoy! If you'd like to learn more about the rovers and what they've been doing for the last five years, check out our page on the Mars Exploration Rover mission, and the absolutely uniquely detailed monthly mission reports that A. J. S. Rayl has written for us for five years now. And if you'd like to contribute to 365 Days of Astronomy, you can learn more about it here. Hi, I'm Emily Lakdawalla, from The Planetary Society. Five years ago today, I waited nervously in a room with a hundred scientists at the Jet Propulsion Laboratory, for the first signals that would tell us that the Spirit rover had landed successfully on Mars. We jumped up and down when we heard Mission Control say "we have six signs of bouncing on the surface." Then the signal vanished for sixteen very tense minutes before we again heard loud and clear from Spirit that she had landed safely. That's when mission control's celebrations started, but the science team didn't really start shouting until two hours later, when the Mars Odyssey orbiter relayed Spirit's first images back to Earth, showing the rock-strewn landscape of the flat floor of Gusev crater.
At first, though, Spirit's landing site was a big disappointment. From space, Gusev crater, which is 160 kilometers across, certainly has a huge riverbed entering it, and pretty much everybody agrees it was once filled with water, at least briefly. But everywhere Spirit looked, she saw nothing but a common volcanic rock called basalt, which is found everywhere that there's rock in the solar system; it's all over Mars, the Moon, Mercury, and Venus, and makes up all of Earth's ocean floors. The basalt must have come from lava flows that poured across the crater after the lake dried up, and it covered everything that scientists really wanted to see. The science team drove Spirit to a biggish crater in the floor of Gusev, called Bonneville, in the hopes that the crater might have dug to some other kind of rock, something that would tell a story of Gusev crater's early days as a lake, but no luck. The frustrated science team started calling Gusev a "basalt prison." So they hatched a daring plan: drive Spirit as fast as possible, farther than she was ever designed to drive, across the plains until she could reach a line of hills that were distantly visible on the horizon. The science team thought the hills might contain rocks that were older than the plains, but wouldn't be sure until Spirit got there. And they didn't even know if Spirit would last the trip; she was already well past her mission goal of three months and 600 meters of driving After a three-month drive, Spirit finally reached the West Spur of the Columbia hills and immediately hit pay dirt. Almost the first rock she examined was a weird-shaped one called Pot of Gold, that looked like it had been eaten from the inside out. As Spirit climbed the West Spur, her spectrometers showed rock after rock that didn't look like the plains basalt at all; the chemistry kept changing, and all of it pointed to the action of warm liquid groundwater, rich in dissolved minerals, circulating through solid rock. It wasn't the lake that geologists had been looking for, but it was signs of long-lasting liquid water within Mars' rocks.
Although she was much slower than a human geologist on Earth, Spirit was doing exactly what a geologist would do, climbing up a mountain and studying its rocks to learn about the history of the landscape. On the way up, a fortuitous blast of wind swept her solar panels clean of a year's worth of accumulated dust, doubling the amount of power that the panels could generate. Spirit completely wore out the grinding wheels on her rock scraping tool during the campaign as she bore into rock after rock. The team decided that the Columbia Hills had been partially buried by deposits of broken-up rock and dust by either the massive asteroid impacts that pockmark Mars, or by explosive volcanism. Later, the deposits cemented into rock, and were fractured; warm groundwater seeped up from depth, dissolving minerals here and redepositing them there, making the diverse array of rock types that Spirit encountered. Spirit finally summited Husband Hill at the height of the next martian summer, capturing an amazing 360-degree view of the landscape falling away on all sides, and also getting action movies of dust devils spinning across the plains below. On top of the world, with the wind wiping her solar panels clean, she generated so much power that she actually had to nap in the afternoons to keep from overheating. Then she headed down the opposite side of the hill for the Inner Basin and a curious-looking rock formation that the science team called Home Plate.
Spirit didn't move for more than 200 days, but she survived the winter. She painstakingly analyzed the rocks in front of her. She watched how the weather changed with the season. And she patiently captured the most data-rich color panorama ever returned from the surface of another planet. Even better, the science team discovered that the dead wheel had dragged with it a mound of strange bright soil scraped from just below the surface that turned out to be bizarrely rich in sulfur. It was an amazing stroke of luck – if the wheel hadn't jammed, the exotic material would never have been discovered.
Since then, Spirit has been hobbled by that dead wheel, but her explorations have continued. The next spring and summer she spent nosing around the edges of Home Plate, discovering silica soils of a type never seen anywhere else in the solar system except water-rich Earth. For her third winter she parked off the northern slope of Home Plate, where she's been for almost a whole Earth year. As of today, another spring is arriving, and Spirit has survived one thousand, seven hundred and seventy-eight Martian days, nearly twenty times her warrantied lifespan. Spirit is old now, and slow, but as long as she can still rove, and tell Earth what she finds, Earth geologists will explore Mars with her wheels and through her eyes. And during the International Year of Astronomy 2009, by looking at each new sol's fresh images on countless websites, we can all explore Mars – at least in spirit.
|
||||||||||||||||
 |
 |
||||||||||||||||
Copyright © 1993 – 2009 The Planetary Society. All rights reserved.
Privacy Policy | Contact Us | Society Updates
[ what is this? ]
[ what is this? ]