Marc Rayman
Marc Rayman
Chief Engineer/ Mission Director, JPL
Dawn Journal | September 27

by Marc Rayman


Dear Dawnniversaries,

On the seventh anniversary of embarking upon its extraordinary extraterrestrial expedition, the Dawn spacecraft is far from the planet where its journey began. While Earth has completed its repetitive loops around the sun seven times, its ambassador to the cosmos has had a much more varied itinerary. On most of its anniversaries, including this one, it reshapes its orbit around the sun, aiming for some of the last uncharted worlds in the inner solar system. (It also zipped past the oft-visited Mars, robbing the red planet of some of its orbital energy to help fling the spacecraft on to the more distant main asteroid belt.) It spent its fourth anniversary exploring the giant protoplanet Vesta, the second most massive object in the asteroid belt, revealing a fascinating, complex, alien place more akin to Earth and the other terrestrial planets than to typical asteroids. This anniversary is the last it will spend sailing on the celestial seas. By its eighth, it will be at its new, permanent home, dwarf planet Ceres.

The mysterious world of rock and ice is the first dwarf planet discovered (129 years before Pluto) and the largest body between the sun and Pluto that a spacecraft has not yet visited. Dawn will take up residence there so it can conduct a detailed investigation, recording pictures and other data not only for scientists but for everyone who has ever gazed up at the night sky in wonder, everyone who is curious about the nature of the universe, everyone who feels the burning passion for adventure and the insatiable hunger for knowledge and everyone who longs to know the cosmos.

Artist depiction of landmarks on Dawn's voyage.

Landmarks on Dawn’s voyage. After leaving Earth, Dawn flew past Mars to the giant protoplanet Vesta, where it spent 14 months in orbit. Now it is on its way to orbit dwarf planet Ceres. Credit: NASA/JPL

Dawn is the only spacecraft ever to orbit a resident of the asteroid belt. It is also the only ship ever targeted to orbit two deep-space destinations. This unique mission would be quite impossible without its advanced ion propulsion system, giving it capabilities well beyond what conventional chemical propulsion provides. That is one of the keys to how such a voyage can be undertaken.

For those who would like to track the probe’s progress in the same terms used on previous (and, we boldly predict, subsequent) anniversaries, we present here the seventh annual summary, reusing text from last year with updates where appropriate. Readers who wish to reflect upon Dawn’s ambitious journey may find it helpful to compare this material with the logs from its first, second, third, fourth, fifth and sixth anniversaries. On this anniversary, as we will see below, the moon will participate in the celebration.

In its seven years of interplanetary travels, the spacecraft has thrust for a total of 1,737 days, or 68 percent of the time (and about 0.000000034 percent of the time since the Big Bang). While for most spacecraft, firing a thruster to change course is a special event, it is Dawn’s wont. All this thrusting has cost the craft only 808 pounds (366 kilograms) of its supply of xenon propellant, which was 937 pounds (425 kilograms) on Sep. 27, 2007.

Dawn launch, JSC, Sept. 27. 2007

Dawn launched at dawn (7:34 a.m. EDT) from Cape Canaveral Air Force Station, Sep. 27, 2007. Its mission is to learn about the dawn of the solar system by studying Vesta and Ceres. Credit: KSC/NASA

The thrusting so far in the mission has achieved the equivalent of accelerating the probe by 22,800 mph (10.2 kilometers per second). As previous logs have described (see here for one of the more extensive discussions), because of the principles of motion for orbital flight, whether around the sun or any other gravitating body, Dawn is not actually traveling this much faster than when it launched. But the effective change in speed remains a useful measure of the effect of any spacecraft’s propulsive work. Having accomplished about seven-eighths of the thrust time planned for its entire mission, Dawn has already far exceeded the velocity change achieved by any other spacecraft under its own power. (For a comparison with probes that enter orbit around Mars, refer to this earlier log.)

Since launch, our readers who have remained on or near Earth have completed seven revolutions around the sun, covering 44.0 AU (4.1 billion miles, or 6.6 billion kilometers). Orbiting farther from the sun, and thus moving at a more leisurely pace, Dawn has traveled 31.4 AU (2.9 billion miles, or 4.7 billion kilometers). As it climbed away from the sun to match its orbit to that of Vesta, it continued to slow down to Vesta’s speed. It has been slowing down still more to rendezvous with Ceres. Since Dawn’s launch, Vesta has traveled only 28.5 AU (2.6 billion miles, or 4.3 billion kilometers), and the even more sedate Ceres has gone 26.8 AU (2.5 billion miles, or 4.0 billion kilometers). (To develop a feeling for the relative speeds, you might reread this paragraph by paying attention to only one set of units, whether you choose AU, miles, or kilometers. Ignore the other two scales so you can focus on the differences in distance among Earth, Dawn, Vesta and Ceres over the seven years. You will see that as the strength of the sun’s gravitational grip weakens at greater distance, the corresponding orbital speed decreases.)

Another way to investigate the progress of the mission is to chart how Dawn’s orbit around the sun has changed. This discussion will culminate with a few more numbers than we usually include, and readers who prefer not to indulge may skip this material, leaving that much more for the grateful Numerivores. (If you prefer not to skip it, click here.) In order to make the table below comprehensible (and to fulfill our commitment of environmental responsibility), we recycle some more text here on the nature of orbits.

Orbits are ellipses (like flattened circles, or ovals in which the ends are of equal size). So as members of the solar system family follow their paths around the sun, they sometimes move closer and sometimes move farther from it.

In addition to orbits being characterized by shape, or equivalently by the amount of flattening (that is, the deviation from being a perfect circle), and by size, they may be described in part by how they are oriented in space. Using the bias of terrestrial astronomers, the plane of Earth’s orbit around the sun (known as the ecliptic) is a good reference. Other planets and interplanetary spacecraft may travel in orbits that are tipped at some angle to that. The angle between the ecliptic and the plane of another body’s orbit around the sun is the inclination of that orbit. 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 ecliptic, and part of the arduousness of the journey is changing the inclination of its orbit, an energetically expensive task.)

Now we can see how Dawn has been doing by considering the size and shape (together expressed by the minimum and maximum distances from the sun) and inclination of its orbit on each of its anniversaries. (Experts readily recognize that there is more to describing an orbit than these parameters. Our policy remains that we link to the experts’ websites when their readership extends to one more elliptical galaxy than ours does.)

The table below shows what the orbit would have been if the spacecraft had terminated ion thrusting on its anniversaries; the orbits of its destinations, Vesta and Ceres, are included for comparison. Of course, when Dawn was on the launch pad on Sep. 27, 2007, its orbit around the sun was exactly Earth’s orbit. After launch, it was in its own solar orbit.

Minimum distance from the Sun (AU) Maximum distance from the Sun (AU) Inclination
Earth’s orbit 0.98 1.02 0.0°
Dawn’s orbit on Sep. 27, 2007 (before launch) 0.98 1.02 0.0°
Dawn’s orbit on Sep. 27, 2007 (after launch) 1.00 1.62 0.6°
Dawn’s orbit on Sep. 27, 2008 1.21 1.68 1.4°
Dawn’s orbit on Sep. 27, 2009 1.42 1.87 6.2°
Dawn’s orbit on Sep. 27, 2010 1.89 2.13 6.8°
Dawn’s orbit on Sep. 27, 2011 2.15 2.57 7.1°
Vesta’s orbit 2.15 2.57 7.1°
Dawn’s orbit on Sep. 27, 2012 2.17 2.57 7.3°
Dawn’s orbit on Sep. 27, 2013 2.44 2.98 8.7°
Dawn’s orbit on Sep. 27, 2014 2.46 3.02 9.8°
Ceres’ orbit 2.56 2.98 10.6°

For readers who are not overwhelmed by the number of numbers, investing the effort to study the table may help to demonstrate how Dawn has patiently transformed its orbit during the course of its mission. Note that three years ago, the spacecraft’s path around the sun was exactly the same as Vesta’s. Achieving that perfect match was, of course, the objective of the long flight that started in the same solar orbit as Earth, and that is how Dawn managed to slip into orbit around Vesta. While simply flying by it would have been far easier, matching orbits with Vesta required the exceptional capability of the ion propulsion system. Without that technology, NASA’s Discovery Program would not have been able to afford a mission to explore it in such detail. But now, Dawn has gone even beyond that. Having discovered so many of Vesta’s secrets, the stalwart adventurer left the protoplanet behind. No other spacecraft has ever escaped from orbit around one distant solar system object to travel to and orbit still another extraterrestrial destination. A true interplanetary spaceship, Dawn is enlarging, reshaping and tilting its orbit again so that in 2015, it will be identical to Ceres’.

It may surprise you that if Dawn stopped thrusting today, it would sail out farther from the sun than where it is headed, as shown in the table. We can understand that, however, by thinking carefully about how the craft reaches its target. It has been propelling itself up the solar system hill so it can fly to the vicinity of Ceres, and its own momentum now is sufficient to carry it even beyond. This is little different from driving to a destination with the recognition that near the end of your trip, you need to slow down or you will overshoot. While trajectories that use ion propulsion are much more complicated, that fundamental principle applies. Indeed, Dawn’s speed toward Ceres has been declining since December 2013. In addition to the recent and future ion thrusting that guides the ship smoothly into its new port, the gravity of Ceres itself will help tug Dawn in. We will see more about that next month when we present the revised approach plan.

Dawn mission trajectory

Dawn’s interplanetary trajectory (in blue). The dates in white show Dawn’s location every Sep. 27, starting on Earth in 2007. Note that Earth returns to the same location, taking one year to complete each revolution around the sun. As Dawn climbs farther from the sun, it orbits more slowly. Credit: NASA/JPL

On Sep. 11, as the spacecraft was engaged in routine ion thrusting, a high-energy particle of space radiation struck an electrical component onboard. That triggered a chain of events that halted thrusting and required the team of flight controllers on distant Earth to leap into action to resume normal operations. Their swift and expert response was successful, and by Sep. 15 the robot was back on duty. In the next log, we will describe what happened on the spacecraft and in mission control. We will also see how navigators take advantage of the tremendous flexibility provided by ion propulsion to devise a new path into Ceres orbit following this interruption in thrust. (As we also will see, the rest of the intricate plans for exploring the dwarf planet will be unchanged. The logs from December 2013 through last month have previews of those plans.)

As Dawn begins the eighth year of its trek through the solar system, Earthlings have a convenient opportunity today to locate the distant spacecraft thanks to the moon. That celestial orb serves as a guidepost to Dawn, which will be well over one thousand times farther away. When the moon rises in the United States later this morning, it will be leading Dawn by less than nine lunar diameters. The sun, moon, planets and stars all appear to move west as Earth rotates on its axis, but the moon itself travels eastward in its orbit quickly enough that it falls behind noticeably over the course of a day. Throughout most of the day today, our natural satellite’s progression will slowly shrink the distance to Dawn. For observes in the eastern part of the country, by the time the moon sets, it will be about one lunar diameter from the spacecraft. For those on the west coast, the moon will be less than its own width from Dawn around sunset. By the time they see the moon setting, Dawn will have passed it and will lead it down to the horizon, the pair still within two lunar diameters of each other. The details are not so important, however. For observers anywhere today, the moon allows us to get a sense of where in the vast sky our faithful explorer is.

Of course Dawn is much, much, much too far away to be seen with our humble eyes. The spacecraft is more than 1.2 million times farther from Earth than the International Space Station is. It is more remote than Mars ever is. The most powerful optical telescopes on high mountains or in orbit could not detect anything nearly as faint as Dawn in the depths of space. Yet readers have ready access to vision far more acute. We can turn our mind’s eye to that part of the sky near the moon. Out there, in that direction, is a probe from Earth, an emissary to the cosmos, silently streaking through the distant void, conducting an ambitious and exciting mission of discovery on behalf of curious and ingenious humans who yearn for new knowledge and new insight and who have an insatiable passion for grand adventures.

Dawn is 2.1 million miles (3.5 million kilometers) from Ceres. It is also 3.37 AU (313 million miles, or 504 million kilometers) from Earth, or 1,290 times as far as the moon and 3.36 times as far as the sun today. Radio signals, traveling at the universal limit of the speed of light, take 56 minutes to make the round trip.

Dr. Marc D. Rayman
4:34 a.m. PDT September 27, 2014

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25 Responses to “Dawn Journal | September 27”

  1. Williams says:

    Hey Marc,
    Great Article !! Loved Reading it.

  2. Dennis Hopkins says:

    Is it possible that a program could be in place to operate Dawn automatic whenever the solar arrays just happen to be in sunlight during the parked orbit? However brief that might last! This might be useful when Ceres might be closer to the sun later! Call home ET! LOL Thank you

    • Marc Rayman says:

      You are referring to what will happen to Dawn after it completes is bold exploration of Ceres and then exhausts its dwindling supply of hydrazine propellant, as I described in August. Your idea is attractive, but it is not as easy as you might think. When the spacecraft can no longer control its orientation in the zero-gravity conditions of orbiting Ceres, its solar arrays will indeed sometimes point at the sun, and they will generate electrical power. But even when it is powered, the craft would still be unable to control where it points. It could not collect useful data, and it could not aim its radio antenna at distant Earth. In addition, NASA’s Deep Space Network is fully occupied communicating with operating interplanetary spacecraft. There would be no spare antennas that happen to be pointing toward Ceres just on the occasional chance Dawn sends a brief radio signal. In other words, there’s no one at home to answer the call!

      Once Dawn has consumed all of its hydrazine, the wisest use of NASA’s limited resources will be to retire it with honor and gratitude. It will have introduced Earth to two unique alien worlds on a daring and richly productive adventure, and I think that is a very worthwhile legacy.

      • Dennis Hopkins says:

        Thank you for your reply! I will just be glad that every solar system object listed on the poster in 2nd grade science class in 1965, finally in 2015 I was able to see! From Mercury to Pluto and everything in between, plus many bonus objects! Its wonderful, Thank God for the many dedicated people who have worked so hard to bring this to mankind!

        • Marc Rayman says:

          It is amazing how our knowledge of the solar system has advanced in the last 50 years, as well as in the years before. Had you been in science class 50 years earlier that you were, Pluto would not have been listed. Had you been in science class 150 years earlier than you were, Neptune would not have been included, but Ceres could have been shown as a planet. The tremendous progress in understanding the large-scale structure of the universe, the finest details of fundamental particles, and myriad other topics have been even more significant during those years.

          It is always profoundly exciting to see how science improves our picture of the cosmos, from the smallest pieces to the largest and everything in between. I hope you will continue to follow along as we discover more of nature’s fascinating secrets.

  3. Dragos says:

    This might be a little off topic, but how far away from the Sun would a probe like Dawn be able to operate a similar kind of ion propulsion system? Would it be feasible at Jupiter’s distance from the Sun, around 5 AU, where the spacecraft would receive only about 1/4 the solar power at Ceres?

    Has Dawn, with its innovative propulsion method, enlarged the available engineering landscape for future missions using ion engines?

    • Marc Rayman says:

      The ion propulsion system is power-hungry. So the limitation in how far from the sun it can operate is how much power the spacecraft can devote to it. As I have explained (see, for example, July 2013), Dawn’s large solar arrays are needed to meet the needs not only of that hungry system but all the other spacecraft systems as well. If it were going much farther from the sun than 3 AU (three times the distance between Earth and the sun), then it would need still more powerful solar arrays.

      Let’s look at this a little more carefully. At its minimum throttle setting, our ion propulsion system consumes more than 500 watts. While that’s much less than a microwave oven uses, it’s a lot for an interplanetary spacecraft. Because its solar arrays are so powerful, Dawn will never have to throttle down to that lowest setting.

      Using solar arrays at 5 AU requires very large arrays even to provide minimal power. I wrote about both Dawn’s and Rosetta’s solar arrays in this JPL blog. Rosetta had to hibernate when it was more than about 4.5 AU from the sun because its arrays could not produce enough power to keep the craft operating so far from the brilliant star. Juno, currently on its way to Jupiter, carries three massive solar arrays, and the total power they will yield at Jupiter is less than the minimum needed to turn on Dawn’s ion thrust. All spacecraft are designed to use power efficiently, and Rosetta’s and Juno’s designers devoted special creative effort to that.

      A challenge for ion propulsion is that larger solar arrays are more massive, requiring a bigger (and hence more expensive) rocket. In addition, the ion engine has to push those arrays around the solar system, and the more massive they are, the less effective the thrust is. Using ion propulsion effectively far beyond Ceres would require advances in solar arrays (making them more efficient and lower mass) or an alternate power system.

      You might think that the power systems used by Voyager, Cassini, and other missions that go very far from the sun would be a good solution. These systems, known as radioisotope thermoelectric generators (RTGs), transform the heat from the radioactive decay of plutonium into electrical power. (They are often mistakenly thought to be nuclear reactors; they are not.) Thanks to RTGs, NASA has been able to undertake some truly fantastic missions to the outer solar system. RTGs have also powered the experiments left on the moon by five Apollo missions, the two Viking Mars landers, the Curiosity rover, and other missions that haven’t ventured so far from the sun. Nevertheless, they would not be good choices for an ion propulsion system like Dawn’s. Most of the heat is not converted to electrical power, so a modern RTG yields only about 100 watts. Dawn would need at least five units just to activate the ion thrust and still more of them to power the rest of the spacecraft. RTGs are relatively expensive, and NASA did not have the resources for that. In addition, one RTG weighs almost as much as one of Dawn’s two solar array wings. Even at 3 AU, the solar arrays provide a great deal more power than an RTG, so ion thrusting with RTGs as power systems would be less effective in the inner solar system where the mission has to get started.

      NASA is interested in developing nuclear power systems that are more efficient than RTGs (that is, systems that would generate more electrical power for the same amount of plutonium) and new ion propulsion systems that are optimized to work with them. When resources allow, the development of such technology would enable a wide range of outer solar system missions.

      In the meantime, using your own wording, yes indeed the available engineering landscape is enlarged thanks to Dawn’s use of ion propulsion. Indeed, taking it a step earlier, NASA’s Deep Space 1 mission was the first interplanetary probe to use ion propulsion. That was where we really learned how to design a spacecraft that incorporates it and how to take advantage of its extraordinary capabilities in flying the mission. DS1’s success paved the way for more ambitious missions like Dawn. Now that Dawn has taken ion propulsion even further, NASA will consider other missions that propose to use it. Ion propulsion is a powerful tool in the toolbox of mission designers as we continue to advance our knowledge of the cosmos.

      I hope this answers your questions.

  4. Hi Marc.
    1. Why dawn will have orbits more’ “tall” around Ceres, compared with dawn orbit around Vesta? we can get close-up pictures(fantastic)as the crater Marcia or Cornelia on Vesta?

    2. You show designed Ceres as a globe of ice, long fissures and strange colors (yellow-light brown,ochre) like a small Europa moon. Why is this?
    You think that Cerere is so really? is little cratered-
    respect Vesta or the Moon? and why this color?
    Many Thanks,

    • Hi there.

      1. The orbits are higher because Ceres is larger than Vesta and its gravity is stronger.

      2. In some ways, Ceres may be similar to the icy moons of the giant planets, so that is a reasonable basis for an artist. The blue is used to suggest the presence of water ice. Marc Rayman will write in December more about Ceres itself (as he has promised in three of four Dawn Journals since February).

      Dawn E/PO (Education and Public Outreach)

  5. Certainly Raiman! I do not doubt this fantastic journey that I look for years, with impatiencee! more every day !
    I’m sure it will be ‘a journey of discovery and great,
    regardless of how far Ceres is from the sun.
    Maybe we fans have exaggerated, imagining steam jets, similar to those observed on Enceladus moon or over the cometa 67/P? ? (when Ceres more ‘close to the Sun)
    Ceres is more ‘away from Vesta, but can’ have maximum temperatures equal or more ‘higher being more’ big and having its surface more ‘dark (albedo)?
    I thank you for the quick answers that you give me:
    Thanks, Daniele!

    • Marc Rayman says:

      Daniele, I am confident Ceres is nothing like comet 67P/Churyumov-Gerasimenko. The comet is only a few miles (kilometers) across. Ceres is more than 590 miles (950 kilometers) in diameter. Active comets release far more water molecules than Ceres. Saturn’s moon Enceladus also probably gives a misleading impression. Although around half the diameter of Ceres, it too produces much more water vapor than the dwarf planet. Ceres is its own world, with its own characteristics, and we are going there to find out what they are!

  6. Kamal Lodaya says:

    I like your table. Wikipedia says that one reason Dawn cannot target Pallas after Ceres is that the inclination of Pallas’s orbit is quite a lot. But it seems the inclination of Ceres’s orbit is quite a bit too. Can you give an idea about this?

    I would have liked to see the orbital velocities of all these bodies also. I understand Earth’s orbital velocity is about 30 kmps, Mars is about 24, Vesta is about 19 and Ceres is about 18. Would it be accurate to say that Dawn has been all the time trying to slow down its orbital velocity?

    • Marc Rayman says:

      I’m glad you found the table helpful.

      As I wrote in my blog above, changing the inclination, or the plane, of a spacecraft’s orbit is energetically very expensive. I can’t explain it in detail here, but in brief, you can think of changing the plane as being like changing the direction you are driving. If you are traveling at high speed and want to to turn, you have to put on the brakes, turn the steering wheel, and then reaccelerate. As Dawn travels around the sun, it would have to do the equivalent of all that with its propulsion system. Thanks to the spacecraft’s extraordinary ion propulsion system, it is capable of reaching Ceres’ inclination of 10.6 degrees. But Pallas is almost 35 degrees, and by the end of its mission at Ceres, that will be far, far beyond even Dawn’s unique capability. With no bodies in the vicinity massive enough to provide a significant gravitational bending of its orbit around the sun, even Dawn could not accomplish such a large plane change. (I wrote in January 2009 about how Dawn used Mars to help change its orbital inclination. It had no such help in going from Vesta to Ceres. It is far beyond Mars now.)

      I understand your interest in the orbital speeds, but I did not want to give every possible number. I hoped it would be clear from the travel distances I presented what the relative speeds are (because they are all measured for the same travel time). You are quite right that Dawn has been slowing down. That is why I describe the use of the ion propulsion system as not to speed up, but rather to climb what I call the solar system hill. You might find my explanation in February 2013 to be helpful. Still, the equivalent change in speed is a handy way to measure the effectiveness of a spacecraft’s maneuvering, and that is why I often give such statistics (and include the caveat, as I did this month, that the full story requires a more thoughtful examination of the principles of orbital motion).

      To reach the alien worlds it seeks to explore, Dawn has to change the plane of its orbit, slow down, make other changes in the shape of its orbit, and arrive at the same location along each destination’s orbit that the destination itself is. I described some of this last part of the problem in April 2013.

      As an aside, I have seen some occasional mentions in the popular press that Dawn might go to Pallas after Ceres, but we have never had such a plan nor even entertained that as a serious possibility. Orbiting and investigating both Vesta and Ceres, for lower cost than many missions that can orbit only one target, provide all of us who are enthusiastic about probing the unknown with quite a gratifying return.

  7. Thanks Marc; I hope Dawn, can ‘take data for at least ONE year and a half, (at least..).the reason ..?
    I was hoping to see THe Max temperaturE that can reached this body when he was at the maximum proximity at the Sun .. but unfortunately, Dawn, come ‘at the maximum distance from the sun, about.
    One year lasts almost 4 years .;.
    moreover, the probablY Vapour jets, probably occurred in the period in which Ceres was more ‘close to the sun .. you can’ confirm this?
    Many Thanks and Sorry for my english,Daniele

    • Marc Rayman says:

      Daniele, The observations of the water vapor (it may not be in jets — we simply do not know) were not accurate enough to reveal whether the amount of water vapor depends on the distance from the sun. Dawn’s instruments were designed and built to observe solid, airless worlds to reveal details of mineralogy and other aspects of the geology of Vesta and Ceres. The water vapor was not discovered until last year, long after Dawn had begun its interplanetary journey. As I have written before, we will look for water vapor, but given how tenuous it is, Dawn may not be able to detect it. But Dawn also will investigate the surface and even the interior of Ceres for evidence of water and interactions between water and other chemicals. Indeed, we already have many very important objectives at Ceres, and we can accomplish them regardless of how far Ceres is from the sun.

      I will describe more about the mysterious Ceres in December. But one thing I am already certain of is that whatever we find there, it will be fascinating and exciting to explore this dwarf planet!

  8. Jaheira says:

    After the disruption to thrusting last month (probably due to a cosmic ray hit), it was reported in the JPL website news that Dawn’s arrival at Ceres had been delayed one month from March to April 2015. Yet in one of your replies below, you state Dawn is due to arrive in March as was originally anticipated prior to the intervention of our high energy friend! Could you please confirm what month Dawn is currently expected to arrive at Ceres?

    Could you also give us some idea of when images of Ceres from Dawn are due to exceed the best resolution achieved by Hubble?


    • Marc Rayman says:

      Dawn is on course and on schedule to arrive at Ceres in March. As I wrote in my blog above, a particle of radiation did indeed strike an electrical component on the spacecraft on Sep. 11, and that caused it to interrupt ion thrusting (more than an hour later). Because of the subsequent four days of unplanned coasting, we have significantly changed the approach trajectory to Ceres. Although Dawn will enter orbit in early March, the maneuvers to reach the first observational orbit (RC3, which I described in February) will take about one month longer, so RC3 will start in April instead of March. (The distinction between arrival at Ceres, which I explained in January, and the start of RC3 was not appreciated in the report you refer to.)

      In December 2013, I detailed the plans for acquiring images during the approach phase. We are now just a little ahead of that schedule, so we will have a better view than Hubble early in February.

      As I so boldly predicted in this blog, my October blog will explain what happened on the spacecraft and in mission control following the radiation strike as well as the significantly new path to RC3 navigators have planned and how the approach timeline is changed. The rest of the mission will not change.

      After more than two centuries of waiting for close-up images of Ceres, we don’t have much longer to wait!

  9. I
    Im Daniele Bianchino from Roma, italia:
    I initially had trouble writing here, but I signaled the problem and now I aM here!
    How long Ceres Dawn will remain ‘in orbit around the planet?
    How many months is for the duration around CERES?
    When it exhausts supply of hydrazine, could last longer ‘than expected or will be’ all ‘about detailing his end?
    Ceres is many important for me, I insert it in many of my maps of the Solar System.
    At The Moment is absent in many Solar-system images, but certainly, is gaining a lot of popularity ‘thanks to Dawn Mission!
    Molte Grazie
    Daniele – Italy

    • Marc Rayman says:

      I’m sorry you had trouble posting here, Daniele. There was a temporary problem with the website that prevented people from submitting comments, which is why there are none on last month’s blog.

      I appreciate your interest in Dawn. Yes, Ceres is absent from many solar system images, but such depictions are not necessarily a good reflection of how scientifically interesting or just plain cool an object is. It’s interesting to note that for nearly half a century following its 1801 discovery by Giuseppe Piazzi, many people considered Ceres to be a planet. Later it was consistently called an asteroid, but still later it was recognized to be entirely unlike typical asteroids. Hence Ceres (like Pluto) is now called a dwarf planet. As scientific knowledge advances, our vocabulary changes.

      Thank you for your questions. I covered these topics in some detail in August, but I am happy to give you brief answers here.

      Dawn will remain in orbit around Ceres indefinitely. To prevent the spacecraft from contacting Ceres even after the mission is over, we have chosen a final orbit that is stable. Of course, a spacecraft does not need propulsion to stay in orbit, just as the moon does not need propulsion to orbit Earth, and Earth does not need propulsion to orbit the sun.

      Dawn is on course to enter orbit in March 2015, and the primary mission is scheduled to conclude in June 2016. The mission may be extended beyond that time if the spacecraft is healthy, if hydrazine remains, and if NASA chooses to invest some of its limited funds in further operations. But when the hydrazine is exhausted, the mission will conclude. As I wrote in in August, the spacecraft then will become an inert celestial monument to the power of human ingenuity, creativity, and curiosity, a lasting reminder that our passion for bold adventures and our noble aspirations to know the cosmos can take us very, very far beyond the confines of our humble home.

      La ringrazio ancora per il Suo interesse. (Thank you again for your interest.)

  10. Matt W says:

    Hello Marc,

    I just wanted to comment, as others have above, that I really enjoy reading this monthly chronicle of humanity’s adventures to the asteroids. I’d hope these blog posts might be collected in printed form someday; they’re like fascinating hard science-fiction that isn’t fiction at all, complete with malfunctions and close calls, the ingenuity of human engineers and scientists, breathtaking images, cutting edge technology, and the exploration of the unknown.

    • Marc Rayman says:

      Thank you very much for your kind comment, Matt. As I’ve mentioned before, I write these in what would have been my free time, and it’s very gratifying to know they are appreciated. I understand exactly what you mean about hard science fiction that isn’t fiction. I love turning science fiction into science fact, and to me, the real thing is more exciting than fiction ever can be! As a lifelong space enthusiast, I think it is incredibly cool to experience everything that you describe, and I often take the time to step back and really think about how wonderful this all is. Sometimes I feel like just a big kid living a fantasy life! I really like that through these blogs, I can help you and others share in this real-life outer-space drama.

      I don’t know whether these will ever be collected and printed (although perhaps I can get the same deal I referred to in my first Dawn blog about late night reruns of my Deep Space 1 mission logs throughout the Virgo Supercluster of galaxies). But they will always be here on the Dawn website, and I hope you will continue to follow along with each new installment of this amazing adventure as we close in on the dwarf planet ahead, enter orbit, and then explore that alien world.

      Thank you again!

  11. Sean Deany says:

    Love this site and am keenly following DAWN as it gets that little bit closer to 1Ceres. I have been making some interpretations on what Ceres looks like as we only so far have those fuzzy Hubble pictures to relay on. My illustrations can be found on my blog site. I hope I’m right with my interpretations!

    • Marc Rayman says:

      Thank you for your message, Sean. I share your fascination with Ceres and your eagerness to know more about this dwarf planet. It has been intriguing people for more than two centuries. It will be exciting for all of us to discover what it really looks like and more about its nature. We don’t have much longer to wait! (Then you will have plenty of new information to inspire additions to your website too.)

  12. Mark says:

    Hi Marc:

    I love reading your blogs and I’m looking forward to the exciting new discoveries that Dawn will have at Ceres. It is amazing to think that the great asteroids like Ceres, Vesta and Pallas are hardly ever mentioned in basic science courses in college, let alone high school. DAWN will change that!!

    Question: While the Hollywood, cinematic version of the asteroid belt where asteroid are constantly crashing into one another and spacecraft have to dodge the resultant debris merely fiction. The truth being that one couldn’t normally eve see one asteroid from the orbit of another. Is is possible, just by sheer chance that at some point in the future, the orbit of Ceres will bring it into viewing distance of another large asteroid? In other words, when the main mission at Ceres is over, would it be technically possible to put Dawn into a parking orbit, where it can obtain enough sunlight on it’s solar arrays to keep it’s batteries charged and to view the solar systems from Ceres orbit? Or is that beyond the technical means of Dawn and in any event no object will ever approach Ceres that could not be resolved in more detail from earth based telescopes than be resolved by Dawn’s own optical equipment (in any of the electromagnetic spectrum)? I’m guessing not, but thought I would ask.


    • Marc Rayman says:

      Hi Mark,

      I appreciate your kind message and your interest in Dawn.

      You’re right that these large bodies are rarely mentioned. The prevalence of topics in popular science or even in some science courses is not necessarily a reflection of their scientific importance nor of their intrinsic appeal as targets for exploration and opportunities for exciting discoveries. As you probably know, Ceres had been considered a planet for a time and was subsequently reclassified as an asteroid and then again as a dwarf planet. Pluto had been considered a planet for a time and was subsequently reclassified as a dwarf planet. Despite that (admittedly superficial) historical similarity, Pluto’s status is widely considered by the public to be an important issue, and yet few even know about the status of Ceres.

      But that’s OK! This isn’t a popularity contest. What matters most is that we are going to learn myriad fascinating secrets that Ceres has held since the dawn of the solar system, and we are undertaking a bold expedition into the unknown. You and I and everyone else who has a thirst for knowledge and a hunger for grand adventures will share in it.

      You’re also right about the sparsity of the main asteroid belt. Space is big! Although in movies the asteroid belt looks so dense that you would you need Han Solo’s piloting skills to avoid collisions, the reality is that asteroids are generally very far apart. (I wrote about one aspect of this in November 2009.) And Dawn’s camera and other sensors were designed to study bodies from orbit. The spacecraft does not carry the kind of instruments needed to conduct a productive search for asteroids. While we have not specifically studied this, I think it is extremely unlikely that anything would come close enough to Ceres for Dawn to resolve details on it. The camera has a broad field of view for mapping; it is not a powerful telescope, because that usually yields a narrow field of view.

      To put this into perspective, let’s consider what size asteroids we can find now in the main asteroid belt (near Earth asteroids is an entirely separate topic). The actual value depends on the distance, how much sunlight the surface reflects, the telescope size, and many other factors, but a reasonable size for our purposes is about half a mile (1 kilometer). For Dawn to get even a fuzzy picture of just five pixels across, the object would have to come to within 1,300 miles (2,100 kilometers) of Ceres. That is extremely close indeed! Dawn’s first two science orbits (RC3 and survey) will be farther from Ceres than that.

      There is a more fundamental consideration however. Appealing as your idea is, Ceres itself presents the most attractive possible target for Dawn. Even at the end of its primary mission in 2016, if the spacecraft remains healthy and if NASA chooses to invest more funds into this project given the many exciting solar system missions we would like to conduct, the best use of it would be to study Ceres even more. Dawn’s lifetime will be very limited at that point, and the remaining time would be most productively devoted to ferreting out a few more of the mysteries of the alien world of rock and ice. When it exhausts is supply of hydrazine, it will not be able to be able to keep sunlight on its solar arrays and it will cease operating. I explained this in a little more detail last month.

      It would be neat if we did have a facility to look for more asteroids than can be detected or resolved from the Earth. There certainly is a great deal out there yet to investigate. Dawn’s explorations will remain focused on the two most massive residents of the main asteroid belt, Ceres and Vesta. While there will always be worthwhile new questions to ask, I think the detailed study of two exotic worlds still makes for quite a sufficient legacy for one mission, and from your enthusiastic message, it sounds like you would agree.