Marc Rayman
Marc Rayman
Chief Engineer/ Mission Director, JPL
Dawn Journal | October 31

by Marc Rayman


Dear Dawnomalies,

Farther from Earth and from the sun than it has ever been, Dawn is on course and on schedule for its March 2015 arrival at Ceres, an enigmatic world of rock and ice. To slip gracefully into orbit around the dwarf planet, the spacecraft has been using its uniquely capable ion propulsion system to reshape its heliocentric orbit so that it matches Ceres’ orbit. Since departing the giant protoplanet Vesta in Sep. 2012, the stalwart ship has accomplished 99.46 percent of the planned ion thrusting.

What matters most for this daring mission is its ambitious exploration of two uncharted worlds (previews  of the Ceres plan were presented from December 2013 to August 2014), but this month and next, we will consider that 0.54 percent of the thrusting Dawn did not accomplish. We begin by seeing what happened on the spacecraft and in mission control. In November we will describe the implications for the approach phase of the mission. (To skip now to some highlights of the new approach schedule, click on the word “click.”)

The story begins with radiation, which fills space. Earth’s magnetic field deflects much of it, and the atmosphere absorbs much of the rest, but there is no such protection for interplanetary spacecraft. Some particles were energized as recently as a few days earlier on the sun or uncounted millennia ago at a supernova far away in the Milky Way galaxy. Regardless of when and where it started, one particle’s cosmic journey ended on Sep. 11 at 2:27 a.m. PDT inside Earth’s robotic ambassador to the main asteroid belt. The particle penetrated one of the spacecraft panels and struck an electrical component in a unit that controls the ion propulsion system.

ion engine

Photo of ion engine thrusting in a vacuum chamber at JPL. This thrust test was on Deep Space 1, which paved the way for Dawn. Credit: NASA/JPL

At the time the burst of radiation arrived, Dawn was thrusting as usual, emitting a blue-green beam of high velocity xenon ions from engine #1. Ten times as efficient as conventional chemical propulsion, ion propulsion truly enables this unique mission to orbit two extraterrestrial destinations. With its remarkably gentle thrust, it uses xenon propellant so frugally that it takes more than three and a half days to expend just one pound (0.45 kilograms), providing acceleration with patience.

Dawn’s electronics were designed to be resistant to radiation. On this occasion, however, the particle managed to deposit its energy in such a way that it disrupted the behavior of a circuit. The control unit used that circuit to move valves in the elaborate system that transports xenon from the main tank at a pressure of 500 psi (34 times atmospheric pressure) to the ion engine, where it is regulated to around two millionths of a psi (ten million times lower than atmospheric pressure), yielding the parsimonious expenditure of propellant. The controller continued monitoring the xenon flow (along with myriad other parameters needed for the operation of the ion engine), but the valves were unable to move in response to its instructions. Thrusting continued normally for more than an hour as the xenon pressure in the engine decreased very gradually. (Everything with ion propulsion is gradual!) When it reached the minimum acceptable value, the controller executed an orderly termination of thrust and reported its status to the main spacecraft computer.

When the computer was informed that thrust had stopped, it invoked one of Dawn’s safe modes. It halted other activities, reconfigured some of the subsystems and rotated to point the main antenna to Earth.

The events to that point were virtually identical to a radiation strike that occurred more than three years earlier. Subsequent events, however, unfolded differently.

In normal circumstances, the mission control team would be able to guide the spacecraft back to normal operations in a matter of hours, as they did in 2011. Indeed, the longest part of the entire process then was simply the time between when Dawn turned to Earth and when the next scheduled tracking session with NASA’s worldwide Deep Space Network (DSN) began. Most of the time, Dawn operates on its own using instructions stored in its computer by mission controllers. The DSN is scheduled to communicate with it only at certain times.

Dawn performs a carefully choreographed 2.5-year pas de trois from Vesta to Ceres. Celestial navigators had long known that the trajectory was particularly sensitive to glitches that interfere with ion thrusting during part of 2014. To ensure a prompt response to any interruptions in thrust, therefore, the Dawn project collaborated with the DSN to devise a new method of checking in on the spacecraft more frequently (but for short periods) to verify its health. This strategy helped them detect the condition soon after it occurred.

Dawn from Vesta to Ceres

Artist’s concept of Dawn traveling from the giant protoplanet Vesta (in a Dawn photo at lower right) to dwarf planet Ceres (upper left). Credit: NASA/JPL

When an antenna at the DSN complex near Madrid, Spain, received the explorer’s radio signal that morning, it was apparent that Dawn was neither in exactly the configuration to be expected if it were thrusting nor if it had entered one of its safe modes. Although they did not establish until later in the day what was happening, it turns out that not one but two anomalies occurred on the distant spacecraft, likely both triggered by particles in the radiation burst. Dawn encountered difficulty controlling its attitude with its usual exquisite precision. (Engineers use “attitude” to refer to the orientation of the craft in the zero-gravity conditions of spaceflight. In this case, the spacecraft’s orientation was not controlled with its usual precision, but the spacecraft’s outlook was as positive and its demeanor as pleasant as ever.) Instead of maintaining a tight lock of its main antenna on faraway Earth, it was drifting very slightly. The rate was 10 times slower than the hour hand on a clock, but that was enough to affect the interplanetary communication. Ultimately one of the onboard systems designed to monitor the overall health and performance of all subsystems detected the attitude discrepancy and called for another, deeper safe mode.

In this safe mode, Dawn further reconfigured some of the subsystems and used a different part of the attitude control system to aim at the solar system’s most salient landmark: the sun. It switched to one of its auxiliary antennas and transmitted a wide radio beam.

Meanwhile, the operations team began working with the DSN and other missions to arrange for more time to communicate with Dawn than had previously been scheduled. Projects often collaborate this way, making adjustments for each other in the spirit of shared interest in exploring the solar system with the limited number of DSN stations. Later in the day on Thursday, when an antenna near Goldstone, Calif., was made available to point at Dawn, it was stable in safe mode.

The team decided to aim for resuming thrusting on Monday, Sep. 15. They had already formulated a detailed four-week sequence of commands to transmit to the spacecraft then, so this would avoid the significant complexity of changing the timing, a process that in itself can be time-consuming. This plan would limit the duration of the missed thrust during this sensitive portion of the long flight from Vesta to Ceres. Time was precious.

While it was in safe mode, there were several major challenges in investigating why the spacecraft had not been able to point accurately. The weak radio signal from the auxiliary antenna allowed it to send only a trickle of data. Readers who have heard tales of life late in the 20th century can only imagine what it must have been like for our ancestors with their primitive connections to the Internet. Now imagine the Dawn team trying to diagnose a very subtle drift in attitude that had occurred on a spacecraft 3.2 AU (almost 300 million miles, or 480 million kilometers) from Earth with a connection about one thousand times slower than a dial-up modem from 20 years ago. In addition, radio signals (which all regular readers know travel at the universal limit of the speed of light) took 53 minutes to make the round trip. Therefore, every instruction transmitted from JPL required a long wait for a response. Combined with the intermittent DSN schedule, these conditions greatly limited the pace at which operations could proceed.

To improve the efficiency of the recovery, the DSN agreed to use its newest antenna, known as Deep Space Station 35 (DSS-35), near Canberra, Australia. DSS-35 was not quite ready yet for full-time operational use, and the DSN postponed some of the planned work on it to give Dawn some very valuable extra communications opportunities. It’s impressive how all elements of NASA work together to make each project successful.

DSN with cranes

Deep Space Station 35 near Canberra, Australia. This antenna, still undergoing final preparations before beginning regular operational support of interplanetary missions, is 112 feet (34 meters) in diameter. Credit: CDSCC/NASA

Engineers hypothesized that the reconfigurations upon entering safe mode might have rectified the anomaly that prevented the spacecraft from maintaining its characteristic stability. While some people continued the previously planned work of finalizing preparations for Ceres, most of the rest of the operations team split into two shifts. That way, they could progress more quickly through the many steps necessary to command the spacecraft out of safe mode to point the main antenna to Earth again so they could download the large volume of detailed data it had stored on what had occurred. By the time they were ready late on Friday night, however, there was a clear indication that the spacecraft was not ready. Telemetry revealed that the part of the attitude control software that was not used when pointing at the sun in safe mode — but that would be engaged when pointing elsewhere — was still not operating correctly.

Experts at JPL, along with a colleague at Orbital Sciences Corporation in Dulles, VA, scrutinized what telemetry they could receive, performed tests with the spacecraft simulator, and conducted other investigations. The team devised possible explanations, and one by one they tested and eliminated them. Their intensive efforts were powered not only by their skill and their collective experience on Dawn and other missions but also by plenty of pizza and fancy cupcakes. (The cupcakes were delivered in a box lovingly decorated with a big heart, ostensibly by the young daughter of the team member who provided them, but this writer suspects it might have been the team member himself. Regardless, embedded in the action, your correspondent established that the cupcakes were not only a yummy dessert after a pizza lunch but also that they made a terrific dinner. What a versatile and delectable comestible!)

Despite having all the expertise and creativity that could be brought to bear, by Saturday afternoon nothing they had tried had proven effective, including restarting the part of the software that seemed to be implicated in the pointing misbehavior. Confronting such an unyielding situation was not typical for such an experienced flight team. Whenever Dawn had entered one of its safe modes in the preceding seven years of flight, they had usually established the cause within a very few hours and knew precisely how to return to normal operations quickly. This time was different.

The team had still more ideas for systematically trying to fix the uncooperative pointing, but with the clock ticking, the mission director/chief engineer, with a conviction that can only come from cupcakes, decided to pursue a more dramatic course. It would put the spacecraft into an even deeper safe mode, and hence would guarantee a longer time to restore it to its normal operational configuration, but it also seemed a more likely solution. It thus appeared to offer the best possibility of being ready to start thrusting on schedule on Monday, avoiding the difficulty of modifying the four-week sequence of commands and minimizing the period of lost thrust. The idea sounds simple: reboot the main computer.

Rebooting the computer on a ship in deep space is a little bigger deal than rebooting your laptop. Indeed, the last time controllers commanded Dawn to restart its computer was in April 2011, when they installed a new version of software. Such a procedure is very delicate and is not undertaken lightly, given that the computer controls all of the robot’s functions in the unforgiving depths of space. Nevertheless, the team made all the preparations that afternoon and evening, and the computer rebooted as commanded two minutes after midnight.

Thrusting with Engine 1

Dawn thrusting with ion engine #1, which was in use when the radiation strike occurred. Credit: NASA/JPL

Thrusting with Engine #2

Dawn thrusting with ion engine #2, which controllers switched to at the end of the recovery operations. The spacecraft rotates to aim the active ion engine in the required direction while keeping the solar arrays pointed at the sun. Credit: NASA/JPL

Thrusting with engine 3

Dawn thrusting with ion engine #3. This illustrates how the spacecraft would be oriented if it were using that engine instead of #1 or #2. Credit: NASA/JPL

Engineers immediately set about the intricate tasks of verifying that the probe correctly reloaded all of its complex software and was still healthy. It took another 12 hours of reconfiguring the spacecraft and watching the driblet of data before they could confirm around noon on Sunday that the attitude control software was back to its usual excellent performance. Whatever had afflicted it since the radiation burst was now cured. After a brief pause for the tired team members on shift in Dawn mission control to shout things like “Yes!” “Hurray!” and “Time for more cupcakes!” they continued with the complex commanding to point the main antenna to Earth, read out the diagnostic logs, and return each subsystem to its intended state. By Monday afternoon, they had confirmed that hundreds upon hundreds of measurements from the spacecraft were exactly what they needed to be. Dawn was ready to resume ion thrusting, heading for an exciting, extended exploration of the first dwarf planet discovered.

Throughout the contingency operations, even as some people on the team delved into diagnosing and recovering the spacecraft and others continued preparing for Ceres, still others investigated how the few days of unplanned coasting would affect the trajectory. For a mission using ion propulsion, thrusting at any time is affected by thrusting at all other times, in both the past and the future. The new thrust profiles (specifically, both the throttle level and the direction to point the ion engine every second) for the remainder of the cruise phase and the approach phase (concluding with entering the first observation orbit, known as RC3) would have to compensate for the coasting that occurred when thrusting had been scheduled. The flight plans are very complicated, and developing them requires experts who apply very sophisticated software and a touch of artistry. As soon as the interruption in thrust was detected on Thursday, the team began formulating new designs. Initially most of the work assumed thrusting would start on Monday. After the first few attempts to correct the attitude anomaly were unsuccessful, however, they began looking more carefully into later dates. Thanks to the tremendous flexibility of ion propulsion, there was never doubt about ultimately getting into orbit around Ceres, but the thrust profiles and the nature and timeline of the approach phase could change quite a bit.

Once controllers observed that the reboot had resolved the problem, they put the finishing touches on the Monday plan. The team combined the new thrust profile with the pre-existing four-week set of commands already scheduled to be radioed to the spacecraft during a DSN session on Monday. They had already made another change as well. When the radiation burst struck the probe, it had been using ion engine #1, ion engine controller #1, and power unit #1. Although they were confident that simply turning the controller off and then on again would clear the glitch, just as it had in 2011 (and as detailed analysis of the electrical circuitry had indicated), they had decided a few days earlier that there likely would not be time to verify it, so prudence dictated that near-term thrusting not rely on it. Therefore, following the same strategy used three years earlier, the new thrust profile was based on controller #2, which meant it needed to use ion engine #2 and power unit #2. (For those of you keeping score, engine #3 can work with either controller and either power unit, but the standard combination so far has been to use the #1 devices with engine #3.) Each engine, controller, and power unit has been used extensively in the mission, and the expedition now could be completed with only one of each component if need be.

By the time Dawn was once again perched atop its blue-green pillar of xenon ions on Monday, it had missed about 95 hours of thrusting. That has surprising and interesting consequences for the approach to Ceres early next year, and it provides a fascinating illustration of the creativity of trajectory designers and the powerful capability of ion propulsion. Given how long this log is already, however, we will present the details of the new approach phase next month and explain then how it differs from what we described last December. For those readers whose 2015 social calendars are already filling up, however, we summarize here some of the highlights.

Throughout this year, the flight team has made incremental improvements in the thrust plan, and gradually the Ceres arrival date has shifted earlier by several weeks from what had been anticipated a year ago. Today Dawn is on course for easing into Ceres’ gravitational embrace on March 6. The principal effect of the missed thrust is to make the initial orbit larger, so the spaceship will need more time to gently adjust its orbit to RC3 at 8,400 miles (13,500 kilometers). It will reach that altitude on about April 22 which, as it turns out, differs by less than a week from the schedule last year.

Hubble images of Ceres

Four views of Ceres as it rotates, as seen with Hubble Space Telescope, are the best we have. The brightest feature has been exaggerated here. Dawn’s pictures by the end of January will be better than these, and the view will continue to improve after that. Credit: NASA, ESA, J. Parker (Southwest Research Institute), P. Thomas (Cornell University), and L. McFadden (University of Maryland, College Park)

During the approach phase, the spacecraft will interrupt thrusting occasionally to take pictures of Ceres against the background stars, principally to aid in navigating the ship to the uncharted shore ahead. Because arrival has advanced from what we presented 10 months ago, the schedule for imaging has advanced as well. The first “optical navigation” photos will be taken on about Jan. 13. (As we will see next month, Dawn will glimpse Ceres once even sooner than that, but not for navigation purposes.) The onboard camera, designed for mapping Vesta and Ceres from orbit, will show a fuzzy orb about 25 pixels across. Although the pictures will not yet display details quite as fine as those already discerned by Hubble Space Telescope, the different perspective will be intriguing and may contain surprises. The pictures from the second approach imaging session on Jan. 26 will be slightly better than Hubble’s, and when the third set is acquired on Feb. 4, they should be about twice as good as what we have today. By the time of the second “rotation characterization” on about Feb. 20 (nearly a month earlier than was planned last year), the pictures will be seven times better than Hubble’s.

While the primary purpose of the approach photos is to help guide Dawn to its orbital destination, the images (and visible and infrared spectra collected simultaneously) will serve other purposes. They will provide some early characterizations of the alien world so engineers and scientists can finalize sensor parameters to be used for the many RC3 observations. They will also be used to search for moons. And the pictures surely will thrill everyone along for the ride (including you, loyal reader), as a mysterious fuzzy patch of light, observed from afar for more than two centuries and once called a planet, then an asteroid and now a dwarf planet, finally comes into sharper focus. Wonderfully exciting though they will be, the views will tantalize us, whetting our appetites for more. They will draw us onward with their promises of still more discoveries ahead, as this bold adventure into the unknown begins to reveal the treasures we have so long sought.

Dawn is 1.2 million miles (1.9 million kilometers) from Ceres. It is also 3.65 AU (339 million miles, or 546 million kilometers) from Earth, or 1,475 times as far as the moon and 3.67 times as far as the sun today. Radio signals, traveling at the universal limit of the speed of light, take one hour and one minute to make the round trip.

Dr. Marc D. Rayman
5:00 p.m. PDT October 31, 2014

P.S. While Dawn thrusts tirelessly, your correspondent is taking the evening off for Halloween. No longer able to fit in his costume from last year (and that has nothing to do with how many cupcakes he has consumed), this year he is expanding his disguise. Expressing the playful spirit of the holiday, he will be made up as a combination of one part baryonic matter and four parts nonbaryonic cold dark matter. It’s time for fun!

All Dawn Journal entries


21 Responses to “Dawn Journal | October 31”

  1. Dennis Hopkins says:

    Marc, in your blog comments you told about a sci-fi tail you wrote about DS1. [See here.] I love these kind of stories, so I went right to the link and got right into it. Wondering how DS1 saved earth! You wrote “In my final DS1 blog, I mentioned an imagined future in which it would be reawakened to save Earth!” Only to find out the story abruptly ends :( is there more to it somewhere?

    • Marc Rayman says:

      I love these kinds of stories too, Dennis. Alas, I didn’t say I had written the tale, but rather only that I had mentioned that imagined future. I still like the idea that I raised in that DS1 blog, but I haven’t written such a story (yet) and, to my knowledge, no one else has either. I look forward to someone being inspired to tell that tale (and if they do, I hope DS1 is successful in saving Earth).

  2. Robert Willie says:

    It seems ion propulsion was conceived WAY before I was ever born! Really exciting to see this become a reality in my generation with DS1 and Dawn.

    With a software engineering background, I must admit you did great planning… this is proved by your recovery of the mission despite the faulty pointing of Dawn during a system failure… safe mode?… you have EXTRA SAFE mode :)

    So thanks for a great article which documents a great mission!

    Looking forward to Ceres images in 2015,

    Robert W

    • Marc Rayman says:

      I appreciate your interest, Robert!

      On such a long mission so incredibly far from Earth in the forbidding environment of deep space, Dawn has to be able to accommodate quite a bit. Hardware and software can have problems, as you obviously appreciate, so we design missions like this to be as resilient as possible. Dawn is going to accomplish all of its original objectives despite losing two of its four reaction wheels, even though it was not designed to fly with fewer than three. In fact, we could complete the mission now even with zero operable reaction wheels. In 2000 we conducted an exceedingly ambitious rescue of Deep Space 1 following what should have been a truly fatal failure of its sole star tracker, and the mission went on to accomplish a spectacular encounter with Comet Borrelly in Sep. 2001. That rescue story has never been told in great detail, although I wrote about some of it in those years. I think it’s amazing what interplanetary missions can do under the guidance of capable flight teams.

      You’re right about the long history of ion propulsion (although I don’t know when you were born). In May 2008, I mentioned work by Dr. Ernst Stuhlinger in the 1950s, but the scientific ideas underlying ion propulsion date back a century! Many people (including me) first heard of it in science fiction, but that is not where it originated. While there had been theoretical work, laboratory tests, and even some limited uses in suborbital flights or Earth orbit, DS1 was the first mission to use ion propulsion to travel through the solar system. I agree with you that it is exciting to see it become a reality, and even more exciting is that we can now undertake missions like Dawn that would be quite impossible without ion propulsion.

      Thanks again for your interest in Dawn and for your comments.


  3. Mark Raphael says:

    Hi Marc:

    In reading about the scientic payload carried by Dawn, it seems that a magnetometer was not included. One of the things that interest me is the effects of the solar wind on a planetary magentic field, ((a dipole field (Earh) or an induced field (Venus) in or a lumpy crustal field (Mars).))

    Is there any expectation of an intrinsic magentic field existing on Ceres? Is it possible if Ceres does have a tenous atmosphere, it might have an induced field? Is it possible other scientific instruments could give indirectly indications of a magentic field?


    • Whitney says:

      Dear Mark,

      Marc Rayman is engrossed in readying for a review, but sent this quick response to your good questions.

      – The Dawn spacecraft carries instruments that provide an excellent initial close-up study of Vesta and Ceres, though we cannot make every conceivable measurement on the first mission.
      – If Ceres has an atmosphere, it is expected to be extremely tenuous. Marc’s December Dawn Journal will address some of what we can expect at Ceres, including — PERHAPS — a tiny, tiny amount of water vapor. However, Dawn’s instruments will not be able to give even an indirect indication of a magnetic field.

      Thanks so much for your interest in the mission!

      Dawn Education and Public Outreach

  4. Good Morning dawn mission staff! I have two questions;

    1. In Simulated view of Ceres, Ceres appears always as a small star, does not change:
    Ceres is at 4 lunar distance at moment. This image change in size,or present only for position Ceres?

    2. The first image of Vesta was taken about 3 lunar distances (1’200’000 km).
    Being that Ceres is twice the size of Vesta, the first image of Ceres could arrive already ‘5-6 lunar distances. Well I know that this has been avoided, because we can not waste movements Alba, important first of all get to Ceres.
    Ceres will find at the same distance of the first image of Vesta approximately around December 20 (3 moon distance).
    You explained that the first images arrive January 13, and these will not be very clear images; but on the January 13 Dawn, should stand at less that 1 Lunar Distances .. should have very clear images … what is wrong in my calculations?
    Have I done this that shows the possible visions of Ceres from Alba; I hope you like;

    Daniele Bianchino

    • Whitney says:

      Hi Daniele,

      1) Because the simulation displays a wide field of view, Ceres still looks like a star. When it is closer, the view will show the size.

      2) You are right in your calculation: on Jan. 13, Dawn will be around the same distance from Ceres that Earth is from the moon. However, as Dr. Rayman has mentioned in a number of blogs, Dawn’s camera is not like a telescope. It is designed for mapping from orbit. So even at that distance, Ceres will still not appear as large as in Hubble’s view.

      As ever, thanks for your interest!

      Dawn EPO

  5. Steve Gribble says:

    Thank-you greatly for taking the time to write such clear and detailed logs. I have been appreciating them since DS1 days.

    I had a question about the event and the reboot. I suppose that means that there could well be a gremlin still lurking in the spacecraft, because you weren’t able to find the root cause before the increasing cost of finding a solution called for stronger measures. I was wondering if you are still looking for the cause in the software and/or simulator? If the issue recurs, I was wondering if that means that a reboot would restore normal functioning, although at a cost of 24+ lost hours. Unlike most missions, I’m guessing that there is no critical period where 24 lost hours would imperil the mission or the science in an unrecoverable way. Is that true?

    • Marc Rayman says:

      Thank you for your interest, Steve!

      We are indeed continuing to investigate the underlying cause of the pointing problem. It seems very unlikely it will recur, as we have more than seven years of perfect attitude control operation in space plus a tremendous amount of testing in simulators both before launch and during the mission. That the misbehavior occurred so close to the time that radiation clearly disrupted the ion propulsion controller suggests even more strongly that it was a rare event. Nevertheless, our current plan is that if it recurs, we will reboot the computer again, although that may change depending on what our investigation reveals. I presume the plan will include more cupcakes too, although we haven’t finalized that aspect of it either.

      You are quite correct that there is no period where losing 24 hours (or even a week or more) would preclude us from accomplishing the mission. Ion propulsion gives us a tremendous flexibility, and we have the trajectory software as well as other technical capabilities and knowledge to take advantage of it. (Through our extensive testing of ion propulsion on Deep Space 1, we learned not only how to make the hardware work on the spacecraft but also how to design and operate the mission to gain the greatest benefit from its unique capability.) We can complete our ambitious objectives at Ceres regardless of when we arrive there. Ceres has waited patiently for our arrival, and we can be patient in exploring it.

  6. Chris Lea says:

    Having followed many a NASA “Journey into space” (BBC radio shows – 1953 to 1958….and yes, and I’m even older than that!) and the blogs that accompanied them, I was delighted to find your remarkably chatty, cheerful and very informative blog….all about a mission that’s spent much of it’s time more or less doing nothing!
    Far, far better than most others. Too many scientists fill their pages with data that only they are interested in – you’ve created a very happy balance. Well done – congratulations, etc, even if the cupcakes somewhat detracted from your slimline stature, Marc!
    And here’s hoping that your blogs from 2015 will be even better as photos and a lot more data about Ceres are incorporated.
    Keep up the good work – best wishes for a magnificent New Year – New Dawn to all of you.
    Many thanks indeed,
    Taunton, Somerset, UK

    • Marc Rayman says:

      I am most grateful for your kind message, Chris. I write these blogs in what would otherwise be my free time, so it is very nice to know that they are appreciated. Thank you.

      Dawn actually is pretty busy, even if it appears to be doing nothing. But in any case, we don’t have long to wait before it is even more active, as it begins unveiling secrets Ceres has held since the dawn of the solar system.

      Thank you again for such a generous messages. I look forward to our sharing an exciting 2015 deep in the heart of the main asteroid belt!


  7. Vincent Celino says:

    Dear Sir,

    Last time I contacted you was around eight or nine years ago when I asked how my favourite mission, DS1 was faring and where she might be in the universe after the mission ended in 2001. You replied very promptly – today I’m watching the Rosetta mission avidly in the UK and can’t help but wonder where DS1 is now ! I recall reading systems were not shut down in case future generations decided to make contact with her – is this still the case ?

    All the best,


    • Marc Rayman says:

      Dear Vincent,

      The Philae landing is wonderfully exciting! Rosetta is a fabulous mission, and I’m extremely happy for my friends and colleagues who work on it as well as for all people (including myself) who are thrilled by the exploration of the cosmos.

      I appreciate your interest in Deep Space 1. DS1 obtained NASA’s first close-up images of a comet (and the first that were detailed enough to allow geological analysis). Many subsequent missions were enabled by DS1’s scientific discoveries and by its engineering accomplishments. Dawn’s unique mission would be truly impossible without ion propulsion, which was tested so successfully on DS1’s revolutionary mission.

      DS1 is in orbit around the Sun between Earth and Mars. In my final DS1 blog, I mentioned an imagined future in which it would be reawakened to save Earth. That will not happen. Shortly after we concluded the mission, DS1 exhausted its supply of hydrazine, which was necessary for controlling its orientation in space. (Note that Dawn’s mission also is very limited in hydrazine, but for quite different reasons.)

      While the spacecraft would not respond to contacts by future generations, you might enjoy this story. Even though it is to be posted 988 years in the future, you can read it now.

      Thank you for remembering this extraordinary mission.


  8. Jeremie Ferrand says:

    Dear Dr Rayman,

    As you spoke about the pictures Dawn will send us from Ceres, I was reminded of reflexions I made to myself earlier today while watching some of the lastet pictures sent by Rosetta. As incredible as these pictures are, and as equally beautifull as the vistas from Ceres will most certainly be, I can’t help but think that the instruments embarked on both spacecraft are respectively 10 and 8 years old, and when I look at cameras here on Earth I can’t help but notice a difference in the quality of pictures taken in 2005 and pictures taken in 2014.

    I understand that the devices used by Dawn (or any spacecraft for that matter) aren’t as trivial as the camera I use everyday but still, I have to wonder : if you were to magically “update” some of Dawn’s parts, would you notice any difference in the data you gather ? Isn’t it frustrating to use tools that can be outdated by the time they make it to were you want to use them, or is it a parameter that you take into account in the early steps of designing a mission ?

    Following Dawn since I met him in the vicinity of Mars has beeen and remains every month a thrilling experience thanks to the time, energy and elloquence you put into this journal. I did not think I would someday travel as far in the solar system, nor did I think that I would learn so much about space exploration.

    Thank you so much for letting us join you in this adventure !

    – jérémie

    • Marc Rayman says:

      Thank you for your very kind message, Jérémie! The pictures from Rosetta and other missions that explore the cosmos are indeed wonderful. It is quite exciting to see sights that have eluded us for so very, very long. Now no longer bound by our humble terrestrial view, we can behold what, until quite recently, was beyond even our imagination. It’s amazing, and for me personally it provides one of the great rewards of such an adventure.

      The improvements in your cameras came about from advances in software and computing, optical designs, and detectors. We can still take complete advantage of progress in software and computing, because we transmit the full pictures (in the equivalent of what terrestrial photographers call “raw”) and can do any processing we wish with the data here on Earth. More generally, Dawn was designed to accomplish its unique mission with the camera (and other sensors) it has, so truly all the parameters were taken into account, including those of the camera optics and detector, the other instruments, the spacecraft’s data storage, pointing capability, antenna size and radio transmitter power, funding and more. Everything has to work together to make the mission work, and changing one part might not help unless many of the other parts were changed too. For that matter, there were other camera designs available even at the time, but for the first orbital mission to these uncharted alien worlds, our camera (with its optics and detectors) yields quite a gratifying view. (Also, of course, the hardware has to operate reliably even after being subjected to the rigors of launch and eight years of spaceflight.) I don’t think the data would look fundamentally different if we invoked your magic, but of course incremental improvements, whether in resolution, sensitivity or other details are always possible.

      Certainly as technology improves, we take advantage of it however we can, but I think we are extremely fortunate to live in a time that we have the tools and resources — plus the will — to undertake such journeys. We have a fabulous bounty of pictures and other data from our space missions, and we continue to gather more and more. I’m glad you participated in the spectacular exploration of Vesta, and it’s good to have you onboard as we look forward to the wonders of Ceres!


  9. Matt Whealton says:

    Thank you for the insight into the process of recovering from the particle impact. The level of communication the Dawn Team provides to eager watchers is exemplary!

    A question on distances: The last couple of months I’ve checked, the Blog entry distance from Dawn to Ceres is rather less than the simulator distance on the main Dawn page. As I write on 11/3/2014, the Simulator shows the distance as 2.57 million km, versus the distance from the 10/31/2014 blog – 1.9 million km. Should we just take the Simulator numbers with big grains of salt? Or do they perhaps get reset periodically? Or is there a back of the envelope correction we can apply to lessen the roughness of those estimates?

    Thanks! Matt

    • Marc Rayman says:

      Thank you for your comment, Matt. I appreciate your interest in the mission, and I’m glad you find our communications helpful. I have been an “eager watcher” of space missions my whole life, and I know how much I would have loved to get the inside story on a real interplanetary mission when I was young. It’s my pleasure now to try to give a glimpse of that to people who aren’t lucky enough to be on the flight team. I had a little more to say about this here. I’m happy that others on the Dawn team share my desire to bring the public along on this exciting adventure.

      You’re quite right about the discrepancy between the simulator and my blog entries, and I apologize for that. The blog numbers are more accurate. The simulator requires occasional manual intervention to reflect our latest trajectory. The flexibility of ion propulsion can translate into changes in the mission timeline quite unlike what we are accustomed to in missions using conventional chemical propulsion. (Note: we could pin down the schedule if we needed to, but it turns out to be better for the mission — although more difficult for outreach — to remain flexible.) We design a new flight profile every four weeks during the interplanetary journey from Vesta to Ceres. The simulator sometimes gets a little out of date when my friend and colleague who maintains it finds himself too busy with his excellent technical work on our navigation team. He is going to update the simulator this week, and we’ll make an effort to keep it more current.

      Thank you for pointing it out, and thanks again for not only watching but riding along with us!


      • Marc Rayman says:

        Here is an update, Matt. We intend to radio a new flight plan to the spacecraft during a scheduled DSN communications session on Monday, Nov. 10, as we do (almost) every four weeks during the long trek from Vesta to Ceres. (We call the new flight plan dl078 — isn’t it cool that the names we use are just as exciting as the mission itself?!) That new profile is now loaded into the simulator. So for the next few days, it will be ahead, and then when thrusting resumes after the DSN session, the simulator will be up to date.


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