December 31, 2010 - Dawn Swaps Ion Thrusters
As it has each month this year, Dawn thrust for most of December, continuing to make excellent progress to Vesta.
Earlier this month, after using ion thruster #2 since January, mission controllers commanded the spacecraft to use thruster #3. After not being operated in two and a half years, #3 resumed thrusting smoothly and efficiently. All thrusters remain healthy.
Meanwhile, the operations team has been working on the sequences to be used in the third science phase at Vesta, known as the low altitude mapping orbit (LAMO). Dawn will spend two months in LAMO at an altitude of about 180 kilometers (110 miles).
November 30, 2010 - Upgrades Allow Reduced Hydrazine Consumption
Dawn devoted most of the month to continuing to thrust with its ion propulsion system.
Mission controllers radioed new parameters to the spacecraft to allow it to use less of its hydrazine propellant. Hydrazine is fired through the small reaction control jets to help the spacecraft hold stable or rotate in the zero-gravity of spaceflight. Even before powering off the reaction wheels in August, at which point the reaction control system took over, engineers began working on methods to use the hydrazine more efficiently. The successful operation with the new parameters this month was the culmination of that work.
October 31, 2010 - Dawn Thrusting to Vesta on the Far Side of the Sun
Dawn devoted most of October to thrusting on its interplanetary trajectory to Vesta. The spacecraft is on the opposite side of the sun from Earth and will reach its maximum distance from our planet on November 13.
September 28, 2010 - Dawn Completes Third Year of Flight
Dawn passed its third anniversary of being in space on September 27. It spent most of the month continuing to thrust with its ion propulsion system.
It has expended about 189 kilograms (417 pounds) of xenon in its 715 days of thrusting since launch. The effective change in speed so far is more than 5.0 kilometers per second (11,000 miles per hour). The Dawn team is developing the sequences the spacecraft will follow in its second Vesta science orbit, known as the high altitude mapping orbit (HAMO).
It will take about a month to spiral down from survey orbit to HAMO at an altitude of about 660 kilometers (410 miles). Dawn will spend a month in HAMO making more detailed observations of the surface.
August 31, 2010 - Dawn Motors Onward To Vesta
The spacecraft spent most of the month thrusting with its ion propulsion system. It is now so far from the Sun that the electrical power from the solar arrays is limited. The engineering team has implemented several of the power conservation measures that it had planned well in advance, including operating the ion propulsion system at a reduced throttle level.
The team also powered off the reaction wheels, switching control of the spacecraft's orientation to the reaction control system.
July 30, 2010 - Spacecraft and Its Instruments Continue to Operate Well
The spacecraft has now accomplished so much thrusting that it has accelerated by more than 10,000 mph over the course of the mission. As it continues to recede from the sun, it has passed 2.0 astronomical units, or twice Earth's average distance from the sun.
The week of July 19 was designated for coasting. Mission controllers used this time to operate each of the science instruments and proved all of them are in excellent health. A minor bug was corrected in the software in the cameras. Engineers also stored two copies of the new version of the software for the spacecraft's main computer in the spacecraft's backup computer.
The operations team successfully tested the procedures they will use for refining sequences of commands when Dawn is completing its approach to the first science orbit around Vesta in August 2011.
June 30, 2010 - New Software Installed in Main Computer
Dawn spent most of the month continuing to thrust to Vesta. On June 5, it surpassed the record set by Deep Space 1 (the first interplanetary ion propulsion mission) for the greatest velocity change by a spacecraft¹s propulsion system. It has now exceeded 4.4 kilometers per second (9,800 mph).
A coasting period from June 15 to June 24 was planned to allow the operations team to install new software in the spacecraft's main computer. They used the same procedure followed the last time (in April 2009), and it went smoothly. This latest version of software principally contains enhancements to aid in the acquisition of science data at Vesta and Ceres.
On June 17, spacecraft software detected an increase in the friction in one of the reaction wheels used for controlling the orientation. The spacecraft responded correctly by turning it off. Dawn normally uses only three of its four wheels, so it is continuing with that wheel powered off.
May 30, 2010 - Operations Team Continues Development of Survey Orbit Sequences
The Dawn team continued developing the sequences the spacecraft will use in survey orbit. That 17-day phase of the mission will allow extensive mapping with the science camera and the visible and infrared mapping spectrometer.
Meanwhile, the spacecraft completed another month of ion thrusting, remaining on course and schedule for its rendezvous with Vesta.
April 30, 2010 - Engineers Conclude Approach Phase Commands and Begin Survey Orbit
The development of approach phase commands concluded. They will be updated and refined next year before being radioed to the spacecraft. The team is now working on the commands that will be used in the first science orbit, which will be in August 2011. At an altitude of about 2700 kilometers (1700 miles), this will be the beginning of the intensive scientific observations of Vesta.
The spacecraft devoted most of the month to thrusting, and it continues to be in good health. An improved version of the December measurement of the relative alignment of the visible and infrared mapping spectrometer and the science camera was executed successfully.
March 31, 2010 - Engineers Continue Developing Approach Phase Commands
The team began running some of the commands the spacecraft will follow during the approach phase through the Dawn spacecraft simulator at JPL. Meanwhile, Dawn thrust with its ion propulsion system for most of the month, remaining on target for Vesta. The spacecraft is now farther from Earth than the Sun ever is, and it will never come as close as the Sun again.
February 28, 2010 - Dawn Now Farther than the Sun as It Continues to Vesta
Dawn made steady progress toward Vesta as it thrust for most of February.
This month, Dawn controllers began formulating the specific instructions the spacecraft will use for operating at Vesta. They are beginning with the "approach phase," which commences in May 2011 and concludes in August 2011, when Dawn has thrust to the first science orbit from which it will conduct intensive science observations. By the time Dawn actually begins the approach phase, most of the instructions for its year at Vesta will have been prepared.
Hubble Space Telescope observed Vesta on February 25 and 28 to collect data that will help refine plans for Dawn's mission.
On February 28, the spacecraft was as far from Earth as the Sun is, and it will never again be this close to the planet from which it began its mission.
January 31, 2010 - Dawn Swaps Ion Thrusters and Begins Receding from Earth
Dawn continued thrusting with its ion propulsion system for most of January, but mission controllers instructed it to stop using thruster #1 and start using thruster #2. All three thrusters are in excellent condition. This change is part of the plan to balance the use of the thrusters during the mission.
On January 18, Dawn and Earth reached their smallest separation since March 2008, although still more than 74 million miles from each other. Now, their separate orbits are taking them farther apart again.