December 31, 2015 -Dawn Busy as Year Ends

Dawn is transmitting its latest Ceres observations, orbiting the dwarf planet while pointing its main antenna to Earth. This afternoon the spacecraft will use its ion engine to perform an orbit maintenance maneuver, which will keep its orbit matched with the plan for obtaining good coverage of the world beneath it. Following that, the probe will turn again to point its instruments at Ceres and resume collecting data.

The December Dawn Journal describes the highest priority scientific observations Dawn is conducting in this fourth and final mapping orbit.

December 29, 2015 -Flight Team Preparing Small Adjustment to Orbit

Dawn remains in good health as it continues to take pictures and make other measurements of Ceres. As at Vesta, occasional small adjustments to its orbital motion will be required at this low altitude to keep it synchronized with the observing plan. The flight team is working on the detailed flight plan for the first of these "orbit maintenance maneuvers," scheduled for Dec. 31.

December 23, 2015 -Dawn Observing Ceres Again

Dawn sent its latest measurements to mission control at JPL as it completed five revolutions around Ceres, each lasting about 5.4 hours. Around 11:30 p.m. PST on Dec. 22, it once again aimed its scientific instruments at the rocky, icy surface beneath it and began collecting more data.

December 21, 2015 -New Mapping Proceeding Smoothly

Since Dec. 18, Dawn has been taking neutron spectra, infrared spectra, gamma ray spectra, and photographs of Ceres from the lowest altitude orbit. As the spacecraft revolves around the dwarf planet, it points its sensors at the ground but also switches among its auxiliary radio antennas to use whichever is pointed closest to Earth. That allows engineers and scientists to use the radio signal to measure the orbital motion very accurately to map the gravity field.

Tonight Dawn will turn to point its main antenna to Earth for more than 27 hours. Tomorrow night, after transmitting most of its pictures and other data, it will resume observing Ceres.

December 18, 2015 -Dawn Ready for More Observations of Ceres

While Dawn was taking preliminary pictures and infrared spectra on Dec. 16-17, the flight team was putting the finishing touches on commands the probe will use for further observations that start later today. After the trajectory correction maneuver that completed on Dec. 13, navigators measured Dawn's orbital parameters very precisely. Combined with their latest measurements of Ceres' gravity field, they formulated a new prediction of Dawn's orbital motion over the coming weeks. The detailed plans for observing the dwarf planet then were adjusted to account for this latest information.

December 16, 2015 -Dawn Begins Photography and Infrared Spectroscopy

Dawn is now taking pictures and infrared spectra of Ceres from its new average orbital altitude of 240 miles (385 kilometers). In this fourth and final mapping orbit, the pictures will be four times sharper than those from the previous mapping orbit. Nuclear spectroscopy and gravity measurements began last week upon arrival at this low orbit.

The JPL flight team is continuing to incorporate the latest orbital parameters into the plans for the more intensive observations that will start on Dec. 18.

On Dec. 14, mission controllers activated Dawn's two operable reaction wheels to help conserve hydrazine propellant for pointing and turning the spacecraft. The plan to keep the wheels off until now was devised in 2013 following the failure of the other two wheels in 2010 and 2012. Since then, the wheels have been powered on only for a test of the current control scheme (explained in the November 2013 Dawn Journal) and routine maintenance. They are performing well, but engineers understand that the other two gave no indications of any problems until immediately before they faltered. As long as the wheels do function, they will provide a bonus reduction in hydrazine use.

December 14, 2015 -Dawn Preparing for New Observations

Dawn thrust with its ion engine on Dec. 11-13 to fine tune its orbit. When it finished, it pointed its gamma ray and neutron detector (GRaND) at Ceres. GRaND measures the energies and numbers of these two components of nuclear radiation, from which scientists can determine the abundances of some elements on the dwarf planet.

Navigators are making precise measurements of the adjusted orbit to verify that it meets the needs for the intensive observation campaign that will begin on Dec. 18. In the meantime, the spacecraft will collect more radiation measurements as well as conduct some bonus photography and infrared spectroscopy on Dec. 16-17.

Later today mission controllers will power on two of Dawn's reaction wheels. (Two others failed in 2010 and 2012.) Engineers cannot confidently predict how long the two units will operate, but as long as they do, they will reduce the expenditure of hydrazine propellant, extending the spacecraft's lifetime in this final phase of the mission. When either one fails, Dawn will return to using only hydrazine to control its orientation. (The November Dawn Journal explains this in more detail.)

December 11, 2015 -Dawn Ion-Thrusting to Adjust Orbit

Dawn is now using its ion engine to adjust its orbit. This maneuver (explained in the November Dawn Journal.) will synchronize the spacecraft's orbital motion with Ceres' rotation around its axis to fit with the plan for the extensive observations that will begin next week.

Yesterday while the flight team was preparing Dawn's flight plan, the spacecraft tested its backup camera. Controllers occasionally run the camera through a series of tests to verify that it remains in good condition should the primary camera have a problem. (The test of the camera was performed eight years to the day after its first operation in space.) Although the results have not been analyzed in detail yet, all indications are that the backup is in excellent condition.

December 9, 2015 -Dawn at Lowest Orbital Altitude at Ceres

Dawn completed ion-thrusting on schedule on Dec. 7 and continues to be healthy and operating well in its new orbit. Over the last two days, the flight team has determined that the spacecraft did an excellent job in maneuvering to its planned orbit at an average altitude of 240 miles (385 kilometers). To match Dawn's orbital motion with the intricate plan for observing Ceres, the probe will use its ion engine to perform a small adjustment (known as a "trajectory correction maneuver") to the orbit. Long before the spiral descent began, engineers had calculated that such a maneuver was likely and already had a window planned for this purpose on Dec. 11-13. (This was described in the November Dawn Journal.) They are now developing the detailed flight plan for the spacecraft.

December 7, 2015 -Dawn to Stop Ion-Thrusting Today in Low Altitude Orbit

Dawn is scheduled to conclude ion-thrusting for its spiral descent shortly before noon today. At that time, it will be orbiting about 240 miles (385 kilometers) above Ceres, closer than the International Space Station is to Earth. After it turns to point its main antenna to Earth, navigators will begin to measure its orbital parameters very accurately. During the next two days, they will analyze the orbit carefully and decide on Dec. 9 whether to make an adjustment at the end of the week. (It is likely such a trajectory correction maneuver will be needed.) The November Dawn Journal explains this in more details.

December 4, 2015 -Dawn Closing in on Final Mapping Orbit

Dawn has now reduced its orbital altitude to 270 miles (435 kilometers). The probe is continuing to make excellent progress to its fourth and final mapping orbit.

November 30, 2015 -Dawn Continuing to Thrust to Lowest Ceres Orbit

Dawn is now less than 300 miles (480 kilometers) from the alien world of ice and rock. This last major ion-thrusting period of the mission has been going very smoothly, and the spacecraft will reach its targeted altitude of 240 miles (385 kilometers) next week.

This month's Dawn Journal includes an overview of the plans for when Dawn arrives in its lowest altitude orbit around Ceres.

November 25, 2015 -Dawn Making Good Progress to Lower Altitude

During this spiral descent from the third mapping orbit to the final one, Dawn has paused ion thrusting on Thursdays so JPL mission controllers can transmit an updated flight plan. To give the flight team time off for Thanksgiving, the operations schedule has an update today instead of tomorrow. So this afternoon Dawn will stop thrusting and rotate to point its main antenna to Earth.

The tireless explorer will not take the holiday off. It will spend Thanksgiving using its ion propulsion system to reduce its orbital altitude. It will be thankful that on Nov. 26, its average altitude will be 335 miles (537 kilometers), so it will only have to lower its orbit by about 100 miles (160 kilometers) more.

November 23, 2015 -Dawn's Maneuvering Proceeding Well

As Dawn continues to lower its orbit, today its average altitude is about 355 miles (570 kilometers). At this height, each revolution around Ceres takes about 7.5 hours.

November 20, 2015 -Dawn Reaching Ever Closer to Ceres

Dawn's average altitude today is about 395 miles (635 kilometers). The spaceship is orbiting Ceres at 530 mph (855 kilometers per hour).

Once a week during its spiral descent, Dawn stops ion thrusting so it can point its main antenna at Earth. When it did so on Nov. 19, the JPL flight team transmitted the latest flight plan, which incorporated updates using the navigation data collected one week earlier. (See the Nov. 13 status update.)

November 16, 2015 -Spiral Descent Continuing Smoothly

Dawn's ion engine is continuing to push it to lower orbits. Today the spacecraft's average altitude is about 445 miles (715 kilometers).

All of Dawn's ion thrusting throughout its interplanetary journey of more than eight years has now provided the equivalent of 24,500 mph (39,400 kilometers per hour), far more than any spacecraft has achieved with its own propulsion system. 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. See here for an explanation of this curious phenomenon.

As Earth and Ceres (carrying its sole companion, Dawn) travel on their own independent orbits around the sun, the distance between them is constantly changing. This morning they were pi astronomical units (292.0 million miles, or 469.9 million kilometers) apart. They are separating at almost 52,000 mph (83,000 kilometers per hour).

November 13, 2015 -Dawn Progressing to Lower Altitude

Today Dawn's average altitude is about 490 miles (790 kilometers).

Following its weekly pattern, Dawn stopped ion thrusting yesterday afternoon to aim its main antenna at distant Earth. The flight team at JPL transmitted an updated flight plan for the descent spiral, and Dawn sent a detailed report on its activities and health during the previous week. In addition, accurate tracking of the radio signal as the spacecraft flew around Ceres provided navigators with new data to calculate the orbit. They will incorporate the results into next week's update.

The only probe from Earth ever to take up permanent residence in the main asteroid belt between Mars and Jupiter, Dawn has now been in that part of the solar system for six years.

November 9, 2015 -Dawn Lowering its Orbit

More than three times as far from Earth as the Sun is, Dawn is using its ion propulsion system to maneuver to its final orbit around Ceres. The spacecraft's average altitude above the alien world today is about 550 miles (885 kilometers).

As Dawn descends, the time to complete one revolution gets shorter, both because the velocity increases and because the distance around an orbit decreases. Today it is 11 hours. In the third mapping orbit, each revolution required 19 hours.

November 5, 2015 -Dawn Descending on Course and on Schedule

As Dawn spirals to lower orbits, its average altitude today is about 620 miles (1000 kilometers). Each week, controllers update the complex flight plan for ion thrusting, so Dawn will pause thrusting this afternoon, turn to point its main antenna to Earth to receive its new instructions, and resume thrusting tonight. Tomorrow the spacecraft will reach to below 600 miles (966 kilometers).

November 2, 2015 -Ion Thrusting to Lower Orbit Continues

Dawn has reduced its average altitude today to about 680 miles (1100 kilometers) as it maneuvers to its final orbit. Because lower orbits require higher velocity (to balance the stronger gravitational pull), the spacecraft is now orbiting the dwarf planet at about 450 mph (725 kilometers per hour). (Orbital velocity in the third mapping orbit, which concluded on Oct. 23, was about 400 mph, or 645 kilometers per hour.)

October 30, 2015 -Dawn's Spiral Descent Proceeding Well

Dawn is continuing to use its ion propulsion system for the gradual descent from the third mapping orbit to the fourth and final mapping orbit. Today the spacecraft's average altitude is about 750 miles (1205 kilometers).

The October Dawn Journal summarizes some of the accomplishments in Dawn's extremely productive third mapping orbit, which concluded last week.

October 26, 2015 - Dawn Maneuvering to Lower Orbit

On Oct. 23, when Dawn was orbiting at an altitude of 915 miles (1,470 kilometers), it started more than seven weeks of ion thrusting to lower its orbit to less than 235 miles (380 kilometers). Today the spacecraft's average altitude is 835 miles (1,345 kilometers).

October 23, 2015 - Dawn To Begin Final Spiral Descent

Dawn has finished transmitting its extensive observations of Ceres to Earth.

About 3:30 p.m. PDT today, the spacecraft will fire up ion engine #2 to start maneuvering to its final orbital altitude. It will take more than seven weeks to spiral down from 915 miles (1,470 kilometers) to less than 235 miles (380 kilometers).

The August 2014 Dawn Journal provided an overview of the plans for the explorer's final mapping orbit at Ceres.

October 21, 2015 - Dawn Completes Topographical Mapping

This morning Dawn conducted its final observations from its current orbital altitude of 915 miles (1,470 kilometers). Following the 12th flight over Ceres' sunlit hemisphere in its sixth mapping cycle in this orbit, the spacecraft rotated to aim its main antenna to Earth. It is now beaming its pictures and spectra to NASA's Deep Space Network.

Next week's Dawn Journal will include a summary of this extremely productive third mapping campaign, which began on Aug. 17.

Ion thrusting to spiral down to the fourth and final orbital altitude will begin on Oct. 23.

October 19, 2015 - Final Mapping Cycle Continuing Smoothly

Dawn is flying over the lit hemisphere of Ceres for the 10th time in the final mapping cycle, taking pictures and measuring spectra. After it completes the 12th revolution on Oct. 21, it will turn to point its main antenna to transmit the data to Earth.

October 16, 2015 - Dawn Halfway Through Sixth Mapping Cycle

This morning Dawn completed observations during its sixth transit over the dayside of Ceres in mapping cycle #6. The spacecraft is continuing to operate extremely well.

The flight team is now developing the detailed flight profile and the associated instructions the probe will follow for its spiral descent from this third mapping orbit to the fourth and final orbit, which it will reach in December. Ion thrusting is scheduled to begin on Oct. 23.

October 12, 2015 - Final Mapping Cycle Underway

Dawn transmitted the last of its measurements from mapping cycle #5 yesterday and started its sixth mapping cycle today at 1:40 a.m. PDT. Mapping cycle #6 will consist of 12 flights over the sunlit terrain, during which the explorer will aim its sensors at the scenery farther behind than in the third mapping cycle but not as far to the right. The pictures will add to scientists' determination of the topography of this alien world. This will be the last set of observations made at the current altitude of 915 miles (1,470 kilometers).

October 9, 2015 - Fifth Mapping Cycle Wrapping Up

Dawn will start its 12th and final passage in mapping cycle #5 over the dayside of Ceres this afternoon. After completing these observations at 1:31 a.m. PDT tomorrow, the spacecraft will aim its main antenna to Earth. It will take about two days to radio all of its photos and other data to NASA's Deep Space Network. Dawn will orbit Ceres 2.5 times while it is transmitting its findings.

The final mapping cycle in this phase of the mission will begin on Oct. 12.

October 5, 2015 - Fifth Mapping Cycle Half Complete

Dawn conducted its sixth observing session in mapping cycle #5 today, spending more than nine hours photographing Ceres and collecting more spectra.

Since entering orbit in March, Dawn has completed more than 100 revolutions around the dwarf planet, with 62 of those occurring since the start of this third mapping phase on Aug. 17.

October 1, 2015 - Dawn Begins Fifth Mapping Cycle

After sending the last of its data from the fourth mapping cycle to Earth, Dawn started its fifth mapping cycle on Sep. 30 at 11:40 p.m. PDT. During this 11-day period, the tireless explorer will aim its sensors toward the terrain immediately ahead as it orbits the alien world at an altitude of 915 miles (1,470 kilometers). This new angle will provide scientists with another stereo view to use in developing 3-D perspectives.

This morning Dawn completed the first transit in this cycle over the side of Ceres facing the sun. The dwarf planet turns on its axis in nine hours, and the spacecraft revolves around it in 19 hours, spending half that time over the sunlit landscape and half over the ground hidden in the dark of night. With 12 orbital loops, Dawn's camera can see all of the terrain.

September 28, 2015 - Fourth Mapping Cycle Nearly Complete

This afternoon Dawn will begin the 12th and final observation session in its fourth mapping cycle. Upon completing this last flight over the illuminated hemisphere, the spacecraft will point its main antenna at Earth for two days to transmit the many pictures and spectra it has acquired.

On Sep. 27, Dawn celebrated its eighth anniversary of being in space. This month's Dawn Journal looks at the spaceship's progress on its interplanetary travels.

September 25, 2015 - Dawn Conducting Fourth Mapping Cycle

Dawn has completed more than half of its fourth mapping cycle, acquiring more stereo pictures as well as spectra in infrared and visible wavelengths. Today the ship will make its eighth transit over the hemisphere of Ceres lit by the sun.

September 21, 2015 - Dawn Conducting Fourth Mapping Cycle

Dawn began its fourth mapping cycle on Sept. 19 at 10:13 p.m. PDT. The probe has now completed two of the 12 revolutions needed to photograph the dwarf planet's entire surface.

For this mapping cycle, the spacecraft points its camera and spectrometers at the scenery ahead and to the left as it orbits at an altitude of 915 miles (1,470 kilometers). Together with the pictures from the other mapping cycles, the different views will allow scientists to develop topographical maps. The visible and infrared mapping spectrometers, which observe a smaller area than the camera, are continuing to study previously unobserved regions with each new mapping cycle.

September 18, 2015 - Observations for Third Mapping Cycle Complete

Dawn completed the observations for the last of its 12 flights over the dayside of Ceres at 12:32 a.m. PDT. It then rotated to point its main antenna to Earth and is now beaming its pictures and infrared and visible spectra to Earth.

The fourth mapping cycle will begin on Sept. 19.

September 14, 2015 - Third Mapping Cycle More Than Half Complete

On Sept. 13, during the seventh transit over the dayside of Ceres in the third mapping cycle, the computer in the camera detected an unexpected condition in the camera and turned off. Engineers observed the situation not long afterwards when Dawn was over the night side of Ceres. In preparation for the next dayside observations, they returned the camera to its normal configuration and confirmed it is healthy.

Today Dawn will observe terrain in the illuminated hemisphere of Ceres for the eighth time. The spacecraft revolves around the dwarf planet every 19 hours, so the twelfth and final dayside pass for this cycle will conclude on Sept. 18.

September 11, 2015 - Dawn Continuing to Map Ceres

Dawn is making good progress on photographing Ceres for its third map. It is also acquiring a wealth of spectra at infrared and visible wavelengths. Today the explorer is making its fourth passage over the lit hemisphere.

September 8, 2015 - Third Mapping Cycle Commences Tonight

Dawn is completing transmission to Earth of the pictures and spectra it acquired during its second mapping cycle while orbiting Ceres at an altitude of 915 miles (1,470 kilometers).

The robotic explorer will begin its third mapping cycle at 12:12 a.m. PDT on Sept. 9. During each of its 12 flights over the dayside of Ceres, it will point its camera and spectrometers behind and to its right, providing a third perspective on the landscape for use in developing topographic maps.

September 4, 2015 - Second Mapping Cycle Going Smoothly

Today Dawn is making its ninth transit over the illuminated hemisphere of Ceres in its second mapping cycle. Throughout this cycle, it is taking pictures and making spectral measurements of the terrain behind and to its left as it orbits the dwarf planet.

The spacecraft will complete its observations for this second map shortly before 1:00 a.m. PDT on Sept. 7. It will then spend almost two days (about 2.5 revolutions around Ceres) transmitting its results to NASA's Deep Space Network.

August 31, 2015 - Dawn's Second Mapping Cycle Underway

Orbiting Ceres at an average altitude of 915 miles (1,470 kilometers), Dawn is photographing the dwarf planet for a new map. Each map requires observations during 12 flights over the dayside of Ceres (plus two more while it transmits the pictures and spectra to Earth). The team calls this one "cycle." (See the August Dawn Journal for more on how the mapping works.)

Today the spacecraft is making its fourth flight over the dayside of Ceres in the second mapping cycle.

August 27, 2015 - Dawn Completes First Mapping Observations

Shortly before midnight last night, Dawn completed its twelfth revolution over the sunlit side of Ceres in this mapping phase. That concluded the observations required to make the first map.

The spacecraft is now pointing its main antenna to Earth and transmitting its precious results. It will continue sending pictures and other data until tomorrow night.

Dawn will begin its second mapping cycle at this altitude around 11:00 PM PDT on August 28. As explained in the Dawn Journal, throughout the second mapping observations, it will point its camera a little back and to the left, rather than straight down, providing provide stereo views from which scientists can construct 3-D views of the alien terrain.

August 24, 2015 - Mapping Proceeding Extremely Well

Today Dawn is making its ninth orbital passage over the illuminated side of Ceres since beginning its new mapping phase. The explorer needs 12 dayside passes (each lasting 9.5 hours, or half an orbit) to see all of Ceres. (This is explained further in the latest Dawn Journal.)

August 21, 2015 - Dawn's New Mapping Phase Off to a Smooth Start

Dawn is performing flawlessly as it takes pictures and collects other data in its new orbit. The spacecraft's view is now three times as sharp as in its previous mapping orbit, which concluded in June.

At this orbital altitude, it takes Dawn 11 days to photograph all of Ceres and transmit the data to Earth. The probe is scheduled to map Ceres six times over the next two months. The latest Dawn Journal includes a description of the plans for this phase of the exploration of Ceres.

August 17, 2015 - Third Mapping Campaign to Begin Tonight

The mission control team has now provided Dawn with accurate knowledge of its orbit parameters. They have also completed transmitting all of the other information it needs and confirmed that the explorer is ready for its new Ceres mapping campaign.

Dawn has been pointing its main antenna to Earth since Aug. 13. Shortly after 9:00 pm PDT today it will start rotating to point its camera and other sensors at the landscape below and will begin taking pictures over the north pole less than an hour later.

August 13, 2015 - Dawn Arrives in Third Mapping Orbit

Dawn completed the maneuvering to reach its third mapping orbit and stopped ion-thrusting this afternoon. This was a little ahead of schedule because the spiral descent went so well that some of the allocated thrusting time was not needed. Since July 14, the spacecraft has reduced its orbital altitude from 2,700 miles (4,400 kilometers) to approximately 915 miles (1,470 kilometers). The orbit period has correspondingly decreased from 3.1 days to 19 hours.

Dawn is scheduled to begin its new observations on the evening of Aug. 17 (PDT) and continue for more than two months. First, however, the mission control team will measure the actual orbit parameters accurately and transmit them to the spacecraft.

August 10, 2015 - Dawn Resumes Ion-Thrusting After a Day of Planned Coasting

Dawn is now below 1,050 miles (1,690 kilometers) in orbital altitude and using its ion engine to descend further.

Mission controllers formulate the flight plan for the spirals with extra maneuvering time in case it's needed to stay exactly on course. The descent has been going so well that they instructed the spacecraft to coast for almost 23 hours on Aug. 9 and 10. Observations in the next mapping phase cannot begin early for several technical reasons, including the complexity of advancing the carefully timed computer instructions already prepared and the schedule for the Deep Space Network. Therefore, mission planners are keeping the ship close to the originally planned trajectory rather than getting ahead.

August 7, 2015 - Dawn Continuing On Course and On Schedule

Dawn is continuing to use its ion engine to maneuver to a lower orbit. Today it is just above 1,100 miles (1,800 kilometers). It has now reduced its orbital period to about 24 hours. In its targeted mapping orbit at an altitude of 915 miles (1,470 kilometers), the spacecraft will circle Ceres every 19 hours.

August 3, 2015 - Dawn Completes More than Half of Descent

Dawn has completed more than half of the maneuvering to reach its next mapping orbit. The coils in its descent spiral are getting tighter and tighter as it goes. Over the course of the day today, the spacecraft reduces its orbital altitude from 1,300 miles (2,100 kilometers) to 1,250 miles (2,000 kilometers).

July 31, 2015 - Dawn Descent Proceeding Well

Dawn has lowered its altitude to 1,400 miles (2,300 kilometers). Closer to Ceres, where it feels the dwarf planet's stronger gravitational pull, the spacecraft must travel faster in its orbit. It is now circling Ceres at 340 mph (550 kilometers per hour). At this lower altitude and higher speed, Dawn's orbit period is 1.3 days.

Once a week during the descent from the second mapping orbit to the third, the probe pauses ion-thrusting and points its main antenna to Earth. Controllers transmit an updated flight plan during these communications sessions. (This process was explained here.) The communications session yesterday confirmed that Dawn remains healthy and is continuing to perform all of its tasks very well.

The July Dawn Journal includes an updated illustration of the spiral path Dawn is following and presents other details of the adventurer's recent and upcoming activities.

July 27, 2015 - Dawn Orbiting Closer to Ceres

Today the spacecraft is orbiting 1,600 miles (2,600 kilometers) above the ground. As with all of Dawn's complex maneuvers from each mapping orbit to the next, the spacecraft is not taking a perfect spiral path for technical reasons. The altitude does not change as much over the course of the day today as it does some other days. Nevertheless, the probe is accurately following its carefully designed course.

July 23, 2015 - Dawn Maneuvering to Lower Orbit

As Dawn maneuvers closer to Ceres, today it is reducing its altitude from 1,900 miles (3,100 kilometers) to 1,800 miles (2,900 kilometers).

In lower orbits, the spacecraft circles Ceres more quickly, not only because the distance around the orbit is shorter but also because it travels faster in the dwarf planet's tighter gravitational grip. (For more on this, see this Dawn Journal explanation.) In the previous mapping orbit (at 2,700 miles, or 4,400 kilometers), it took slightly more than three days to complete one revolution. Now the orbital period is a little less than two days. When Dawn is in its next mapping orbit (at 900 miles, or less than 1,500 kilometers), each loop will take about 19 hours.

July 22, 2015 - Dawn, Ceres and Earth Closest To Each Other

As Ceres (with its new permanent resident, Dawn) and Earth follow their own independent orbits around the sun, today they are at their closest since June 2014. The dwarf planet and Dawn today are 180 million miles (290 million kilometers) from our home. (For more details and a diagram, see the June Dawn Journal.)

Meanwhile, Dawn is continuing to thrust with its ion propulsion system to shrink its orbit. Today it will descend from 2,000 miles (3,200 kilometers) to 1,900 miles (3,100 kilometers).

July 20, 2015 - Dawn's Spiral Descent Continuing Smoothly

Dawn is continuing to lower its orbital altitude. Today the spacecraft will descend from 2,200 miles (3,500 kilometers) to 2,100 miles (3,400 kilometers).

In its previous mapping orbit, the explorer was 2,700 miles (4,400 kilometers) above the alien world. When it completes its spiral to the third orbit, it will be about 900 miles (less than 1,500 kilometers) high.

July 17, 2015 - Dawn Maneuvering to Third Science Orbit

NASA's Dawn spacecraft is using its ion propulsion system to descend to its third mapping orbit at Ceres, and all systems are operating well. The spiral maneuvering over the next five weeks will take the spacecraft to an altitude of about 900 miles (less than 1,500 kilometers) above the dwarf planet.

The spacecraft experienced a discrepancy in its expected orientation on June 30, triggering a safe mode. Engineers traced this anomaly to the mechanical gimbal system that swivels ion engine #3 to help control the spacecraft's orientation during ion-thrusting. Dawn has three ion engines and uses only one at a time.

Dawn's engineering team switched to ion engine #2, which is mounted on a different gimbal, and conducted tests with it from July 14 to 16. They have confirmed that the spacecraft is ready to continue with the exploration of Ceres.

By the end of the day on July 17, Dawn will have descended to an altitude of about 2,400 miles (3,900 kilometers). After arrival at its next mapping orbit -- called the High-Altitude Mapping Orbit, or HAMO -- in August, Dawn will begin taking images and other data at unprecedented resolution.

July 15, 2015 - Dawn Performing System Checkout in Ceres Orbit

As part of their investigation of the anomaly on June 30, engineers have performed some further configuration changes on the spacecraft, and they are now conducting a test to confirm that all systems are operating well and ready to continue with the exploration of dwarf planet Ceres.

July 13, 2015 - Dawn Healthy as it Orbits Ceres

Dawn remains healthy and functioning normally in its second mapping orbit at Ceres. Engineers are continuing their investigation into the anomaly that caused a discrepancy in the orientation on June 30.

July 6, 2015 - Dawn Holding in Second Mapping Orbit

NASA's Dawn spacecraft is healthy and stable, after experiencing an anomaly in the system that controls its orientation. It is still in its second mapping orbit 2,700 miles (4,400 kilometers) above dwarf planet Ceres.

On June 30, shortly after turning on its ion engine to begin the gradual spiral down to the next mapping orbit, its protective software detected the anomaly. Dawn responded as designed by stopping all activities (including thrusting), reconfiguring its systems to safe mode and transmitting a radio signal to request further instructions. On July 1 and 2, engineers made configuration changes needed to return the spacecraft to its normal operating mode. The spacecraft is out of safe mode, using the main antenna to communicate with Earth.

Dawn will remain at its current orbital altitude until the operations team has completed an analysis of what occurred and has updated the flight plan.

Because of the versatility of Dawn's ion propulsion system and the flexibility of the mission's plan for exploring Ceres, there is no special "window" for starting or completing the spiral to the third mapping orbit. The plans for the third and fourth mapping orbits can be shifted to new dates without significant changes in objectives or productivity.

June 30, 2015 - Dawn Successfully Completes Second Ceres Mapping Orbit

Dawn is over the nightside of Ceres and nearing the end of the eighth and final revolution in its survey orbit phase.

During the observations on June 27, the camera's internal computer reset and about three hours later the computer in the visible and infrared mapping spectrometer reset. The operations team observed both events in telemetry transmitted through one of the spacecraft's auxiliary antennas and concluded no prompt response was necessary. Dawn continued to perform all of its other functions smoothly. (More details are here.)

The second mapping orbit has now concluded successfully. See the June 29 Dawn Journal for a summary of the accomplishments in this mission phase at an altitude of 2,700 miles (4,400 kilometers).

Tonight Dawn will power on its ion propulsion system to begin a spiral descent to the third mapping orbit. It will take about five weeks to complete the maneuvering to an altitude of about 900 miles (less than 1,500 kilometers).

June 25, 2015 - Dawn Performing Penultimate Survey Orbit Observations

Early in the morning on June 24, the spacecraft began its seventh arc over the lit side of Ceres. It has been acquiring spectra and photographs since then. It will cross from the day side to the night side over the south pole later today and will begin transmitting its data shortly after that.

Dawn's final set of observations at this altitude will start on June 27.

June 22, 2015 - Mapping of Ceres Continuing Smoothly

On June 20, Dawn completed transmitting the results of its fifth set of observations. After 10:00 PM PDT that day, it traveled once again 2,700 miles (4,400 kilometers) over the terminator from the night side to the day side of Ceres. The probe is now collecting more pictures and spectra in infrared and visible. After its orbit takes it to the dark side later today, it will turn to point its main antenna to Earth to relay its latest results.

June 18, 2015 - Dawn Now in Second Half of Second Mapping Phase

Dawn is now on its fifth flight over the sunlit side of Ceres in this phase of the mission. It is operating well as it takes more pictures and spectral measurements. The explorer will continue its observations until tomorrow morning when it will pass over the south pole. Then when it flies once again over the unilluminated side, it will send the data to Earth.

During the fourth observing period on June 15, the visible and infrared mapping spectrometer’s internal computer detected an unexpected condition and stopped collecting data. The main spacecraft computer then powered the device off. The same events occurred in 2011 as Dawn was approaching Vesta. This time, as was the case four years ago, engineers and scientists concluded that the most likely cause was a cosmic ray strike. When it was powered back on for the fifth observing cycle, the spectrometer resumed normal operation.

Navigators are continuing to refine their measurements of Ceres’ gravity as they track Dawn’s orbital motion, and they are now using the results to design the next spiral maneuvers with the ion propulsion system. The spacecraft is scheduled to begin lowering its orbital altitude at the end of this month following the conclusion of its eighth revolution.

June 15, 2015 - Dawn Conducting Fourth Set of Survey Observations

On June 13 and 14 Dawn transmitted to distant Earth all of the data from its third dayside observations of Ceres. Yesterday the spacecraft began its fourth trip over the illuminated side of the dwarf planet at this altitude (2,700 miles, or 4,400 kilometers). As Dawn flies south, it will observe the alien world until looping back to the night side again tomorrow morning, when it will start transmitting the results to distant Earth.

June 12, 2015 - Dawn Performing More Ceres Measurements

Dawn is orbiting over the side of Ceres lit by the sun, and it is taking more photos and making other observations. It will travel to the night side again on Saturday and will then turn to point its main antenna to Earth to report its findings.

The veteran explorer remains healthy, and all systems are operating well.

June 10, 2015 - Dawn Completes a Second Round of Observations

Dawn acquired more pictures and other measurements of Ceres in its second arc over the dayside of the dwarf planet. It is now on the night side, sending its precious data to NASA’s Deep Space Network.

Dawn’s third dayside passage over Ceres at this altitude will start tomorrow afternoon and continue for a little more than a day and a half.

June 8, 2015 - Dawn Conducts First Observations in New Science Phase

Dawn photographed Ceres and measured its spectrum in infrared and visible wavelengths as it orbited over the illuminated side on June 5 and 6. All measurements were completed as planned. When its orbit took it to the night side again, the spacecraft pointed its main antenna to Earth and transmitted its findings.

Later this morning it will travel back to the day side and begin its second set of observations.

June 5, 2015 - Dawn Begins New Science Phase

As Dawn flew 2,700 miles (4,400 kilometers) over Ceres’ north pole this morning, the spacecraft passed from the night side to the day side of the dwarf planet. That marked the beginning of the new mapping phase, and Dawn began taking photos and making other measurements on schedule. Circling Ceres every 3.1 days, Dawn will make extensive scientific observations when it is over the sunlit side and will transmit its findings to Earth when it is over the side in darkness. The pictures will be three times as sharp as those from the first mapping orbit. This mapping phase is scheduled to continue for eight revolutions, providing plenty of opportunities to gather a wealth of data.

June 3, 2015 -Dawn Arrives in Second Mapping Orbit

Dawn completed the maneuvering to reach its second mapping orbit and stopped ion-thrusting on schedule this morning. Since May 9, the spacecraft has reduced its orbital altitude from 8,400 miles (13,600 kilometers) to 2,700 miles (4,400 kilometers). The orbit period has correspondingly decreased from 15.2 days to 3.1 days. Dawn is scheduled to begin its new observations on June 5, as explained in the most recent Dawn Journal. First, however, the mission control team will measure the actual orbit parameters accurately and transmit them to the spacecraft.

June 1, 2015 - Dawn Closing in on Second Mapping Orbit

Dawn spent the weekend maneuvering with its ion propulsion system and is now almost in its targeted mapping orbit. Last night it completed its final ascent in this complicated trajectory. Today it is descending from 3,000 miles (4,900 kilometers) to 2,800 miles (4,600 kilometers). It is scheduled to conclude thrusting on June 3 at an altitude of 2,700 miles (4,400 kilometers).

May 28, 2015 - Dawn Receiving Updated Flight Profile

Dawn remains in good health as it has been reshaping its orbit around Ceres. Today the spacecraft orbits from 3,100 miles (5,000 kilometers) up to 3,400 miles (5,500 kilometers) and then will start to descend again. Meanwhile, it paused ion-thrusting this afternoon to point its main antenna to Earth for a routine telecommunications session. Engineers have refined the flight profile based on analyses of the recent optical navigation pictures as well as measurements of the orbit from the radio signal and other data. Controllers are transmitting the new information to Dawn, and it will resume thrusting tomorrow.

Today's Dawn Journal includes a summary of the first mapping orbit, the maneuvering it does between mapping orbits, the second mapping orbit and a suggestion to look at this mission status update.

May 26, 2015 - Dawn Reaching to Lower Altitudes

Dawn is following the carefully plotted trajectory around Ceres, maneuvering to prepare for its second mapping campaign next month. The probe's mapping orbits are nearly circular, but during the flight from one to another, the intermediate orbits are more elliptical. Tonight Dawn's complicated route will take it temporarily below the targeted mapping orbital altitude of 2,700 miles (4,400 kilometers). It will descend to 2,500 miles (4,100 kilometers) tomorrow before beginning another ascent.

On May 22 Dawn photographed Ceres to help the navigation team maintain a tight fix on its orbital position. Controllers used the opportunity to acquire bonus visible and infrared spectra.

May 22, 2015 - Dawn's Orbital Maneuvers Progressing Well

Dawn has made good progress this week continuing to reshape its orbit around Ceres. Today the spacecraft's altitude reaches down to 3,100 miles (5,000 kilometers). Now, as earlier in the week, it will ascend slowly for a while, traveling up to 4,200 miles (6,700 kilometers) on May 24. Even as it climbs, Dawn will continue using its ion engine to maneuver to the next planned mapping orbit at 2,700 miles (4,400 kilometers).

Later today the explorer will stop ion-thrusting to take pictures of Ceres for navigation. This is the second and final photo op between mapping orbits. Dawn will resume thrusting tomorrow.

May 18, 2015 - Dawn’s Complex Maneuvering Continues Smoothly

On May 16, Dawn paused ion-thrusting to observe Ceres for two hours. Navigators use the pictures to help refine the trajectory as the spacecraft winds its way down to lower altitudes. The probe collected bonus infrared and visible spectra as well.

Dawn remains on course for its complex flight from the first mapping orbit to the second. Last week, the spacecraft descended every day. After dipping down to 4,400 miles (7,100 kilometers) on May 17 and 18, now the ship is slowly ascending as it continues to reshape its orbit around the dwarf planet. It will sail up to nearly 5,200 miles (more than 8,300 kilometers) tomorrow before descending again.

May 15, 2015 - Dawn Spiraling Lower

Dawn is using its ion engine to maneuver to its second mapping orbit, which will be 2,700 miles (4,400 kilometers) high. It will reach that altitude in early June.

During the course of the day today, Dawn’s altitude will decrease from 5,500 miles (8,900 kilometers) to 4,800 miles (7,700 kilometers).

Tomorrow the spacecraft will pause ion-thrusting to take pictures of Ceres for navigation.

May 11, 2015 - Dawn Spiraling to Lower Altitude

On May 9 Dawn began the spiral descent to its second mapping orbit. Today the spacecraft is at an altitude of about 8,000 miles (13,000 kilometers).

May 8, 2015 - Dawn Completes First Mapping Campaign

Yesterday Dawn successfully completed its final observations in this mapping orbit, focusing on Ceres' southern hemisphere. It is transmitting the pictures and other scientific data to Earth now.

It takes about 15 days to make one orbital revolution around Ceres at this altitude (8,400 miles, or 13,600 kilometers). Today the spacecraft completed one revolution since its arrival in this orbit on April 23. It is scheduled to start ion-thrusting tomorrow to spiral down to its second mapping orbit. (The orbital spirals were described in the April 2014 Dawn Journal.)

May 6, 2015 - Dawn Observes Ceres' Equatorial Region

The spacecraft is continuing to perform flawlessly in its first mapping orbit at Ceres. Last night Dawn completed its second set of dayside observations at this altitude. Earlier in the evening, the probe flew southward over the equator as it was taking pictures and making other measurements. It is now relaying its findings to Earth.

May 4, 2015 - Dawn Observes Ceres' Northern Hemisphere

Now orbiting over the side of Ceres illuminated by the sun, Dawn collected images and spectra of the northern hemisphere yesterday and today. It is sending its findings back to Earth today and tomorrow.

May 1, 2015 - Dawn Completes Night Side Measurements

Dawn concluded its observations from the night side of Ceres today. It is now transmitting to Earth the large volume of data it collected.

At this altitude, it takes just over 15 days to complete one revolution around Ceres. Dawn's leisurely orbit will bring it from the night side to the day side later today. The spacecraft is scheduled to observe Ceres again on May 3-4 while it flies over the northern hemisphere on the day side. For the complete schedule of observations in this first mapping orbit, see the March 31 Dawn Journal.

April 29, 2015 - Dawn Observing Ceres Again

Dawn is observing Ceres from the night side of the dwarf planet. On April 27 and 28, the spacecraft transmitted to Earth the data it had collected during its first science observations of the southern hemisphere. Its orbit is taking it north, and it passed over the equator on April 28. Although the ground directly beneath it is still in darkness, it is viewing the illuminated terrain of the northern hemisphere, much like a crescent moon.

April 27, 2015 - Update: Dawn Enters Science Orbit

Dawn began its science operations at 7:25 p.m. PDT/10:25 p.m. EDT on Friday, April 24 and performed as expected over the weekend.

April 24, 2015 - Dawn Enters Science Orbit

NASA's Dawn spacecraft entered into its first science orbit on Thursday, April 23, as scheduled. Following a delay in communicating a command sequence, the spacecraft briefly entered into safe mode and awaited further instructions, which were sent by mission controllers. As of early Friday, April 24, the spacecraft returned to normal operating mode and the mission team continues to prepare for science data collection

April 23, 2015 - Dawn Commences its First Science Oribt

Launched on September 27, 2007, the Dawn spacecraft is finally ready to embark on its prime science campaign at Ceres. On April 23rd, at around 1:00 AM PDT, Dawn completed the ion thrusting necessary to shape its first mapping orbit "RC3." Dawn is now in a circular, polar orbit about 8,400 miles (13,600 kilometers) in altitude with an orbit period of about two weeks.

The most recent Ceres pictures show the famous bright spots again (Ceres' Bright Spots Come Back Into View | NASA). These final images of the approach phase were taken from a vantage point 14,000 miles (22,000 kilometers) above the north pole as the spacecraft crossed the terminator from the dark side of the dwarf planet to the lit side.

Dawn maneuvered extensively with the ion propulsion system to reach this mapping orbit. Since entering orbit around Ceres on March 6, it has changed its velocity by 250 mph. The total velocity change accomplished since launch is 24,000 mph (nearly 39,000 kilometers per hour.) This is not the speed Dawn is traveling, however. See the February 2013 Dawn Journal for an explanation of the velocity change.)

March 31, 2015 - Dawn Closing in on Ceres

Dawn is in an elliptical orbit at an altitude of 40,000 miles (64,000 kilometers), traveling at 73 mph (117 kilometers per hour) relative to Ceres. The spacecraft passed the highest point of its elliptical orbit on March 18, where Ceres' gravitational pull was the weakest and Dawn's orbital velocity the lowest, and is closing back in on the dwarf planet, slowly picking up speed.

The spacecraft is still on the shadowed side of Ceres. It is continuing to use its ion propulsion system to reshape its orbit, targeting its first circular science orbit at an altitude of 8,400 miles (13,500 kilometers), which it is on schedule to achieve on April 23. For more information, read this month's Dawn Journal.

February 28, 2015 - Dawn Approaching the Dark Side of Ceres

Dawn is in the final stages of its approach trajectory to Ceres and will slip into orbit around the dwarf planet March 6, 2015. Dawn halted ion thrusting four times this month to take pictures of the dwarf planet for use in navigation. The spacecraft reached its closest distance to Ceres this past week. On Feb. 23 it was less than 39,000 kilometers (10% of the Earth-moon distance); Dawn will not be that close again until early April. This month's Dawn Journal and a new video: Destination Ceres: Breakfast at Dawn, explain Dawn's unique trajectory to Ceres and what we can anticipate when science orbits begin in April.

January 29, 2015 - Dawn Approaching Ceres and Seeing the Sights

Dawn devoted November to ion thrusting, and it is now about three times as far from Ceres as the moon is from Earth. As Earth and Dawn follow their separate orbits around the sun, they are moving to opposite sides of the solar system's star. To learn how to use the sun to locate Dawn early in December, see the November Dawn Journal, which also describes the new route the spacecraft will take into orbit around the dwarf planet.