NASA's Dawn Journal

Dawn Journal--February 24, 2010

25 Feb 2010 04:38:32 GMT

Dear Dawnthropoids,
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Pushing ever farther into space, deeper into the asteroid belt, Dawn is continuing to progress smoothly on its solar system journey.

The spacecraft spends most days climbing away from the Sun atop its pillar of blue-green xenon ions. A day�s thrusting is enough to change the spacecraft�s speed by a very modest 7.3 meters/second (16.3 miles/hour). While such an effect would be entirely inadequate for an interplanetary mission as ambitious as Dawn�s, the extraordinary efficiency of ion propulsion allows the probe to thrust for much more than a day. Although almost all spacecraft coast most of the time, as do planets, moons, and asteroids, this explorer usually maintains a gentle pressure on its orbit, constantly changing it so that it can rendezvous with Vesta next year, leave in 2012, and then rendezvous with Ceres in 2015.

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Dawn Journal--January 30, 2010

1 Feb 2010 18:11:19 GMT

Dear Plausible Dawniabilities,
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Patiently and reliably continuing with its interplanetary voyage, Dawn is now flying in a new configuration and, from the perspective of those readers who may be on Earth, in a new direction.

The spacecraft still spends most of its time gradually changing its orbit around the Sun by thrusting with its ion propulsion system. The probe is outfitted with 3 ion thrusters, assigned the heartwarming names thruster #1, thruster #2, and thruster #3. (The nomenclature and locations of the units were divulged in a log shortly after launch, before such information could be distorted and used unethically by others.)

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Dawn Journal--December 30, 2009

4 Jan 2010 18:00:08 GMT

Dear Dawnters and Sons,
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The Dawn mission continues to go smoothly, as Earth�s distant envoy carries out its interplanetary journey. Although the craft still devotes most of its time to the slow but efficient reshaping of its orbit around the Sun to match Vesta�s, controllers gave it some extra assignments since the last log to ensure its systems remain healthy and to prepare for its studies of Vesta.
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Dawn usually interrupts ion thrusting once a week for about 8 hours to point its main antenna to Earth. On November 30, however, instead of resuming thrusting, it dutifully followed different instructions that were stored onboard.

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Dawn Journal--November 27, 2009

15 Dec 2009 21:03:38 GMT

Dear Dawnticlimaxes,

Dawn continues to make steady progress through the solar system as it maintains a gentle pressure on its orbit around the Sun. It has spent 95% of the time since the last log thrusting with its ion propulsion system, stopping only briefly each week to communicate with the mission control team on distant Earth.

The probe is on an exciting journey to unlock secrets from the dawn of the solar system ensconced in the mysterious worlds Vesta and Ceres. And yet there is one aspect of this expedition that likely is much less exciting than some readers may expect.

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Dawn Journal--October 31, 2009

2 Nov 2009 14:58:13 GMT

Dear Dawn-o’-lanterns,

Dawn continues to make steady progress on its journey through the solar system. The spacecraft has devoted another month to thrusting with its ion propulsion system, ever with its sights set on its rendezvous with Vesta in July 2011. While it will have other assignments along the way, propelling itself to the giant protoplanet deep in the main asteroid belt remains its principal responsibility.

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Dawn Journal--September 27, 2009

28 Sep 2009 04:38:29 GMT

Dear Dawnniversaries,

Dawn is celebrating the second anniversary of leaving its home planet by engaging in the same function it has performed most of its time in space: with the utmost patience, it is using its ion propulsion system to gradually modify its orbit around the Sun.

In its interplanetary travels, the spacecraft has thrust for a total of about 389 days, or 53% of the time (and about 0.000000008% of the time since the Big Bang). While for most spacecraft, firing a thruster to change course is a special event, it is Dawn’s wont. All this thrusting has cost the craft only 103 kilograms (228 pounds) of its supply of xenon propellant, which was 425 kilograms (937 pounds) on September 27, 2007.

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Dawn Journal--August 30, 2009

3 Sep 2009 16:03:24 GMT

Dear Indawnmitables,

The Dawn mission remains on course as the spacecraft continues to thrust with its ion propulsion system, patiently, persistently, and gently changing its orbit to keep its appointment with protoplanet Vesta in two years. Meanwhile, closer to mission control and in stark contrast, brave firefighters work hard to protect JPL and the nearby homes of many of its employees and others in the community.

The probe has continued in “quiet cruise” since the last log. During this month, engineers did give the robot a few extra tasks to ensure it remains healthy, but these were routine. When each such assignment was conducted the first time or two that Dawn was in space, they were treated as special activities, with even greater diligence than is normally applied to the unforgiving and complex undertaking of flying a spacecraft far from Earth. Now however, the commands for these activities are stored onboard well ahead of time along with the routine commands for thrusting, communicating with Earth, and carrying out all the other functions the spacecraft normally conducts without the mission control team devoting extra attention.

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Dawn Journal--July 28, 2009

3 Aug 2009 15:21:52 GMT

July 28, 2009

Dear Indawnfatigables,
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Shhhh! Dawn is in “quiet cruise,� and we do not want to disturb it. The indefatigable spacecraft is devoting most of its time to thrusting with its ion propulsion system, applying a gentle but persistent pressure to its trajectory around the Sun. With patience, it will reshape its orbit to match those of the mysterious and intriguing protoplanets Vesta and Ceres. In order to conduct its detailed explorations of each of these exotic worlds, Dawn will accompany them around the Sun, visiting with Vesta in 2011�2012 and rendezvousing with Ceres in 2015.

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�

Dawn Journal--June 28, 2009

28 Jun 2009 15:33:23 GMT

June 28, 2009

Dear Dawnterested Readers,

Having completed the longest planned coasting period of its entire mission, Dawn is now back to its familiar routine. On June 8, the ion propulsion system was called back into action to propel the probe to its rendezvous with asteroid Vesta.

The spacecraft began its 7-month coast period on October 31, 2008. Since then, it had used its ion thrusters for a measurement of the solar array power, a small adjustment in its course to Mars (the gravitational effect of which provided a boost to its distant destination), and tests of the software remotely installed on the main computer in April. The accumulated thrusting during all of those activities added only about 10 hours to the mission�s log of 282 days when coasting commenced.

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�

Dawn Journal--May 25, 2009

28 May 2009 00:43:14 GMT

May 25, 2009

Dear Astrodawns,

Dawn�s mission continues to go very well, as the spacecraft nears the end of the longest coasting period of its astronomical journey. The deep-space member of the team has completed more special activities under the helpful guidance of the terrestrial contingent.
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The previous log described the installation of software in the spacecraft�s main computer. (Known as flight software 8.0, this name was chosen as part of Dawn�s new outreach effort to increase public awareness of the number 8. Please consider yourself aware. The outreach plan for the designation of the subsequent version of the software is expected to be 12.5% better.) The software had been tested extensively in simulators on Earth, but the ultimate test is its performance in keeping the spacecraft running smoothly. Because Dawn devotes more time in space to thrusting with its ion propulsion system than doing anything else (this does not count the time it spends in eager anticipation of the exciting rewards to be garnered at its destinations Vesta and Ceres), it was important to verify that the capability to thrust was not compromised with the new software. Despite the assiduity with which 8.0 was developed, the possibility of a subtle bug being introduced could not be discounted.

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Dawn Journal--April 26, 2009

8 May 2009 02:34:56 GMT

Dear Dawngrades, The upgraded Dawn spacecraft is now traveling in a new direction in its orbit around the Sun. The mission continues to go smoothly during this long coasting period, scheduled to conclude in June, when powered flight with the ion propulsion system will resume. Dawn has many computers in its onboard crew and one that serves as the captain of the ship. This primary computer�s software had been unchanged since February 2008. That last modification involved only a small patch, making version 7.0.3 of the software. That was preceded by a small update in January 2008 and one in December 2007. Prior to this month, Dawn had had only one complete in-flight replacement of its main software, in November 2007.

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�

Dawn Journal--February 12, 2009

14 Mar 2009 02:48:28 GMT

February 12, 2009

Dear Charles Dawnwins,

While Dawn and Mars move in their separate orbits around the Sun, they are approaching each other at the stately pace of 2.56 kilometers/second (5720 miles/hour). Gradually, the gravitational pull of the planet will grow as the distance shrinks, and the spacecraft�s path will start to change, beginning the boost we seek. By about noon PST on February 14, the tug from Mars will have grown to be the same as the famously gentle thrust from Dawn�s ion propulsion system. When Dawn is closest to Mars, speeding past it at 5.31 kilometers/second (11,900 miles/hour), the red planet will be exerting 34,000 times greater force than the blue-green xenon beam generates.

Dawn Journal--March 29, 2009

31 Mar 2009 15:35:15 GMT

March 29, 2009

Dear Dawntpanics,

�Dawn continues to coast quietly and calmly in its orbit around the Sun, keeping its main antenna pointed to faraway Earth. The mission control team has given the spacecraft relatively few assignments in recent weeks, providing time to prepare for a busier future. To ensure the distant craft remains healthy and safe, operators transmitted instructions for conducting routine maintenance, activities that are familiar to the probe now that it has been on its deep-space journey for more than 1.5 years. Perhaps what is most noteworthy and satisfying since the last log is not what Dawn did, but rather what it did not do.

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Dawn Journal--January 27, 2009

2 Feb 2009 21:55:12 GMT

Dear Dawncers,
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Dawn continues on course for its pas de deux with Mars on February 17. The planet�s gravity will gracefully assist the spacecraft on its way to rendezvous with its intended celestial partners Vesta and Ceres in the more distant asteroid belt. Even the extraordinary capability of its ion propulsion system would not be sufficient for Dawn to complete its celestial dance without the help of Mars.
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In the last log we saw that the mission operations team was preparing to adjust the probe�s flight path to keep it on target for next month�s flyby. Just getting to the vicinity of Mars is not sufficient, as the passage by the planet is only one short segment of a very long itinerary. Indeed, choreographing Dawn�s trajectory is a complex matter of finding the most efficient route through the solar system to travel from the moving platform on which it started (Earth) to encounter Mars in just the right way to reach Vesta at the proper time to complete its work there before it has to begin the trek to Ceres to meet it on schedule, aided during most of the journey by the ion propulsion system. Dawn must arrive at Mars on time, traveling in the correct direction and at the necessary location, for the gravitational slingshot to yield the desired effect. Flying the spacecraft through that “window� at Mars is like threading a celestial needle.

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Dawn Journal--March 8, 2009

13 Mar 2009 00:05:11 GMT

Dear Dawnlight Saving Times,

Now boosted into a new solar orbit courtesy of Mars, Dawn continues its interplanetary journey. The spacecraft is healthy and coasting, keeping its main antenna pointed to Earth, as it will for most of the next 3 months. After that, it will resume its familiar routine of devoting most of the time to gently thrusting with its ion propulsion system, with only a short period each week for communications.

Following the last log, as the probe succumbed to the gravitational pull of the red planet, its trajectory gradually began to change. Flying true to the plan, Dawn swooped close to Mars and then left it behind on a new course, having taken advantage of Mars's gravity.

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Dawn Journal--December 30, 2008

23 Jan 2009 21:29:23 GMT

Dawn continues to close in on Mars, ready for the gravitational slingshot that will help it on its expedition to the asteroid belt and its quest to gain insights into the evolution of the solar system. The ship remains on course, with the latest calculations of its trajectory being very close to those described in the last log. The spacecraft will streak about 549 kilometers (341 miles) above the planet at 4:28 p.m. PST on February 17.
�
While Dawn and Mars move in their separate orbits around the Sun, they are approaching each other at the stately pace of 2.56 kilometers/second (5720 miles/hour). Gradually, the gravitational pull of the planet will grow as the distance shrinks, and the spacecraft�s path will start to change, beginning the boost we seek. By about noon PST on February 14, the tug from Mars will have grown to be the same as the famously gentle thrust from Dawn�s ion propulsion system. When Dawn is closest to Mars, speeding past it at 5.31 kilometers/second (11,900 miles/hour), the red planet will be exerting 34,000 times greater force than the blue-green xenon beam generates.

Dawn Journal--November 26, 2008

26 Nov 2008 22:28:11 GMT

November 26, 2008

Dear Indawnviduals,

The Dawn spacecraft is healthy and on course for its flyby of Mars early next year. The planet�s gravity will help boost the probe on its way to rendezvous with Vesta. While the spacecraft has its sights set on the asteroid belt (via Mars), its path is now bringing it closer to Earth. Meanwhile, from Earth�s perspective, Dawn appears to be approaching a blindingly close encounter with the Sun. With so much happening in the solar system, all readers, whether local or not, are invited to turn their attention here.
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In the last log, we saw that Dawn was nearing the end of an extended period of thrusting with is ion propulsion system that began on December 17, 2007. When it left Earth on September 27, 2007, the Delta II rocket deposited the spacecraft into a carefully chosen orbit around the Sun. By October 31, 2008, the spacecraft had completed the thrusting it needed to change that orbit so it would encounter Mars at just the right time, location, and angle to sling it on its way to Vesta. During this interplanetary cruise phase, Dawn thrust for 270 days, or 85% of the time. Expending less than 72 kilograms (158 pounds) of xenon propellant, the spacecraft changed its speed by about 1.81 kilometers per second (4050 miles per hour).