December 31, 2008 - Dawn Passes Through Solar Conjunction

Dawn was on the opposite side of the Sun from Earth this month in an arrangement known as solar conjunction. The smallest separation between the Sun and the spacecraft was on December 12, when they were only about 1/3 degree apart as viewed from Earth. (To put this in perspective, the Sun itself appears to be 1/2 degree in diameter.) Communications were limited from December 5 to December 18, as the radio waves passing near the Sun experienced interference.

Although Dawn could have carried out more complex assignments even with the limited communications, no special tasks were necessary. The spacecraft continues to coast toward its February 17 gravitational assist from Mars.

Engineers have been gathering additional navigational data to use in fine tuning Dawn's trajectory in January.


November 30, 2008 - Dawn on Course for Mars Gravity Assist

Dawn needed to thrust with its ion propulsion system for less than 2.5 hours in November. The maneuver on November 20 was designed to adjust the trajectory to put it on course for a gravity assist from Mars on February 17, 2009.

On November 4, the spacecraft successfully executed a procedure to calibrate the power of the solar arrays. The method was identical to that used in a test in September, but this time the arrays were rotated to point 60 degrees away from the Sun instead of 45 degrees. With the arrays not pointed directly at the Sun, their power output was reduced to a level the spacecraft could measure.


October 31, 2008 - Dawn Completes Its Last Month of Thrusting

After mission controllers finished routine maintenance on components of the attitude control and ion propulsion subsystems on October 3, Dawn devoted the rest of the month to thrusting. On October 31, it completed almost all of the thrusting required for 2008.


September 30, 2008 - Dawn Conducts a New Solar Array Test and Routine Maintenance

Dawn continued to operate smoothly in September. Most of the month was devoted to ion thrusting, including September 27, the first anniversary of launch.

On September 22, operators conducted a revised version of the solar array test executed in July. This new test worked well, and it provided the data required to finalize a technique for calibrating the solar array power.

The spacecraft ended the month in a period of planned coasting that began on September 29. This time is used to perform periodic maintenance routines on some components.


August 30, 2008 - Dawn Reaches Greatest Distance from the Sun for 2008

Dawn spent most of August continuing to thrust with its ion propulsion system. On August 8, it reached its greatest distance from the Sun this year of 1.68 times Earth's average distance from the Sun. For the rest of 2008, it will gradually travel closer to the Sun. The spacecraft's elliptical orbit will never bring it as close to the Sun as Earth's orbit. In 2009, it will resume moving away from the Sun.

On August 26, the primary and backup science cameras were commanded to execute standard calibration procedures. The results verify that the cameras remain in good health.


July 31, 2008 - Dawn Conducts a Solar Array Test and Updates Software

Dawn completed another month of thrusting, as it passed outside the orbit of Mars. It stopped thrusting for two days this month to perform other activities.

Controllers conducted a test on July 21 of a method to determine how much power the solar arrays could produce (the spacecraft consumes less than the arrays generate while still this close to the Sun). The test did not provide the full set of calibration data that was wanted, but it yielded enough information to guide engineers to minor modifications of the design for the backup calibration opportunity.

On July 22, operators installed an update to software in one of the auxiliary computers to further harden it against the affects of space radiation.


June 30, 2008 - Dawn Switches to Ion Thruster #1 and Continues Thrusting

Dawn devoted most of the month to continuing to thrust with its ion propulsion system.

Based on the thermal tests conducted last month, engineers determined that it was safe to switch to ion thruster #1 this month. Therefore, on June 18, when it was time to resume thrusting after pointing its main antenna to Earth, Dawn began using that thruster for the first time since October. Data returned from the spacecraft the next day verified that all temperatures were within their required ranges.


May 30, 2008 - Dawn Conducts Routine Spacecraft Maintenance and Tests for Future Thrusting

Dawn devoted most of the month to continuing to thrust with its ion propulsion system.

A planned coast period from May 12 to 14 let the operations team conduct periodic maintenance. Some computer memory locations were checked and verified to be healthy. One of the three powered reaction wheels was turned off and the fourth wheel was powered on. All gyroscopes were powered on and operated for two days.

To investigate the temperatures that would be experienced for future long-duration thrusting with thruster #1, the spacecraft spent a few hours in the orientations that would be required. The resulting temperature data will contribute to determining when to switch from thruster #3 to #1.


April 30, 2008 - Special Activities Conducted During First Part of April

The month began with a non-thrusting period, scheduled to allow special activities:

  1. The Gamma Ray and Neutron Detector (GRaND) was operated for about a week to collect data on the "noise" cosmic rays create in its detectors. By making such measurements, scientists will be able to compensate for this noise when GRaND Is operated at Vesta and Ceres.
  2. The visible and infrared mapping spectrometer (VIR) observed the star Canopus and Mars. Both are well characterized, so these observations aid in calibrating VIR's detectors.
  3. New software was transmitted to both science cameras, and tests confirmed that the software operates correctly.
  4. A software patch was loaded into the spacecraft's backup main computer, bringing it to the same version already operating in the primary computer.
  5. A test of the pointing accuracy of one of the ion thrusters was interrupted when software detected a signal that appeared incorrect.

The combined attempt to process the response from other software and commands sent by the mission operations team led to a conflict and the computer called "safe mode." After controllers returned the spacecraft to its normal configuration, ion thrusting resumed on April 14.

Meanwhile, engineers established that the software that interrupted the thrust test did so because of an unnecessary step. On April 21 they updated the software, removing that step.

The rest of the month was devoted to ion thrusting, as usual.


March 31, 2008 - Dawn Completes Another Month of Thrusting

Dawn thrust with its ion propulsion system for most of March, stopping once each week to point its main antenna to Earth. Almost 96% of the month was devoted to thrusting. By the end of March, the spacecraft was farther from Earth than the Sun.


February 29, 2008 - Thrusting Continues and Backup Framing Camera Tested

Dawn continued ion thrusting through most of February. On February 21 and 22, the backup framing camera was put through a series of tests to demonstrate its performance. The camera successfully completed all the steps, and analysis shows the instrument is healthy and operating as expected.


February 1, 2008 - Thrusting Continues and Software Updated in Main Computer

Dawn spent most of January continuing with ion propulsion thrusting. A cosmic ray that hit an electronic component on January 15 caused an interruption in thrusting for a few days. Thrusting halted on schedule on January 22 so the operations team could update the software in the main computer. The changes account for the increasing distance from Earth by lowering the speed of communications with Earth when the spacecraft enters "safe mode," the configuration called by software to resolve certain errors. Following the software changes, thrusting resumed on January 25.


January 2, 2008 - Interplanetary Cruise Continues

Dawn has continued thrusting with its ion propulsion system since December 17. Following programmed instructions, it interrupted thrusting on December 26 and on January 2 to point its main antenna to Earth to report on its status. All systems are performing well. Now that Dawn is in interplanetary cruise, these updates will occur less frequently.