By Marc Rayman

NASA’s Dawn spacecraft is less than two months away from getting into orbit around its first target, the giant asteroid Vesta. Each month, Marc Rayman, Dawn’s chief engineer, shares an update on the mission’s progress.

Artist’s concept of the Dawn spacecraft using its ion propulsion system during the approach to Vesta. Image credit: NASA/JPL-Caltech

Dear Dependawnble Readers,

Dawn remains healthy and on course as it continues to approach Vesta. Thrusting with its ion propulsion system, as it has for most of its interplanetary journey so far, the spacecraft is gradually matching its solar orbit to that of the protoplanet just ahead.

As these two residents of the asteroid belt, one very new and one quite ancient, travel around the sun, they draw ever closer. Vesta follows its own familiar path, repeating it over and over, just as Earth and many other solar system bodies do. Dawn has been taking a spiral route, climbing away from the sun atop a blue-green pillar of xenon ions. With an accumulated total in excess of two and a half years of ion thrusting, providing an effective change in velocity of more than 6.5 kilometers per second (14,500 mph), the probe is close to the end of the first leg of its interplanetary trek. On July 16, Vesta’s gravity will capture the ship as it smoothly transitions from spiraling around the sun to spiraling around Vesta, aiming for survey orbit in August. For several reasons, the date for the beginning of the intensive observations there has not yet been set exactly.

Astronomers have estimated Vesta’s mass, principally by measuring how it occasionally perturbs the orbits of some of its neighbors in the asteroid belt and even the orbit of Mars, but this method yields only an approximate value. Because the mass is not well known, there is some uncertainty in the precise time that Dawn will become gravitationally bound to the colossal asteroid. As we have seen before, entry into orbit is quite unlike the highly suspenseful and stressful event of missions that rely on conventional chemical propulsion. Dawn simply will be thrusting, just as it has for 70 percent of its time in space. Orbit entry will be much like a typical day of quiet cruise. That Vesta will take hold at some point will matter only to the many Dawnophiles throughout the cosmos following the mission. The ship will continue to sail along a gently curving arc to survey orbit.

› Continue reading Marc Rayman’s May 27, 2011 Dawn Journal

By John Callas

Mars Exploration Rover Project Manager John Callas sent this letter to his team shortly after the final command was sent to the Mars rover Sprit, which operated on the surface of Mars for more than six years and made numerous scientific discoveries.

Artist’s concept of NASA’s Mars Exploration Rover. Image credit: NASA/JPL-Caltech

Dear Team,

Last night, just after midnight, the last recovery command was sent to Spirit. It would be an understatement to say that this was a significant moment. Since the last communication from Spirit on March 22, 2010 (Sol 2210), as she entered her fourth Martian winter, nothing has been heard from her. There is a continued silence from the Gusev site on Mars.

We must remember that we are at this point because we did what we said we would do, to wear the rovers out exploring. For Spirit, we have done that, and then some.

Spirit was designed as a 3-month mission with a kilometer of traverse capability. The rover lasted over 6 years and drove over 7.7 kilometers [4.8 miles] and returned over 124,000 images. Importantly, it is not how long the rover lasted, but how much exploration and discovery Spirit has done.

This is a rover that faced continuous challenges and had to fight for every discovery. Nothing came easy for Spirit. When she landed, she had the Sol 18 flash memory anomaly that threatened her survival. Scientifically, Mars threw a curveball. What was to be a site for lakebed sediments at Gusev, turned out to be a plain of volcanic material as far as the rover eye could see. So Spirit dashed across the plains in an attempt to reach the distant Columbia Hills, believed to be more ancient than the plains.

Exceeding her prime mission duration and odometry, Spirit scrambled up the Columbia Hills, performing Martian mountaineering, something she was never designed to do. There Spirit found her first evidence of water-altered rocks, and later, carbonates.

The environment for Spirit was always harsher than for Opportunity. The winters are deeper and darker. And Gusev is much dustier than Meridiani. Spirit had an ever-increasing accumulation of dust on her arrays. Each winter became harder than the last.

It was after her second Earth year on Mars when Spirit descended down the other side of the Columbia Hills that she experienced the first major failure of the mission, her right-front wheel failed. Spirit had to re-learn to drive with just five wheels, driving mostly backwards dragging her failed wheel. It is out of this failure that Spirit made one of the most significant discoveries of the mission. Out of lemons, Spirit made lemonade.

Each winter was hard for Spirit. But with ever-accumulating dust and the failed wheel that limited the maximum achievable slope, Spirit had no options for surviving the looming fourth winter. So we made a hard push toward some high-value science to the south. But the first path there, up onto Home Plate, was not passable. So we went for Plan B, around to the northeast of Home Plate. That too was not passable and the clock was ticking. We were left with our last choice, the longest and most risky, to head around Home Plate to the west.

It was along this path that Spirit, with her degraded 5-wheel driving, broke through an unseen hazard and became embedded in unconsolidated fine material that trapped the rover. Even this unfortunate event turned into another exciting scientific discovery. We conducted a very ambitious extrication effort, but the extrication on Mars ran out of time with the fourth winter and was further complicated by another wheel failure.

With no favorable tilt and more dust on the arrays, Spirit likely ran out of energy and succumbed to the cold temperatures during the fourth winter. There was a plausible expectation that the rover might survive the cold and wake up in the spring, but a lack of response from the rover after more than 1,200 recovery commands were sent to rouse her indicates that Spirit will sleep forever.

But let’s remember the adventure we have had. Spirit has climbed mountains, survived rover-killing dust storms, rode out three cold, dark winters and made some of the most spectacular discoveries on Mars. She has told us that Mars was once like Earth. There was water and hot springs, the conditions that could have supported life. She has given us a foundation to further explore the Red Planet and to understand ourselves and our place in the universe.

But in addition to all the scientific discoveries Spirit has given us in her long, productive rover life, she has also given us a great intangible. Mars is no longer a strange, distant and unknown place. Mars is now our neighborhood. And we all go to work on Mars every day. Thank you, Spirit. Well done, little rover.

And to all of you, well done, too.

Sincerely,
John

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By Julie Cooper

Each month in “Slice of History” we’ll be featuring a historical photo from the JPL Archives. See more historical photos and explore the JPL Archives at https://beacon.jpl.nasa.gov/.

Low Temperature Propellant Tests — Photograph Number 6-8

It was 1943 and JPL was at the beginning stages of rocket motor research and development.  Over the next decades, JPL would design and test rocket motors with a variety of sizes and propellants.  This small (50 pound thrust) liquid propellant jet unit was immersed in a bath of ice and salt in order to test the ignition properties of the propellants at temperatures near 0°F. 

This post was written for “Historical Photo of the Month,” a blog by Julie Cooper of JPL’s Library and Archives Group.

By Marc Rayman

NASA’s Dawn spacecraft is less than three months away from getting into orbit around its first target, the giant asteroid Vesta. Each month, Marc Rayman, Dawn’s chief engineer, shares an update on the mission’s progress.

Artist’s concept of NASA’s Dawn spacecraft. The giant asteroid Vesta, Dawn’s next destination, is on the lower left. The largest body in the asteroid belt and Dawn’s second destination, dwarf planet Ceres, is on the upper right. Image credit: NASA/JPL-Caltech

Dear Dawntalizingly Close Readers,

Dawn is on the threshold of a new world. After more than three and a half years of interplanetary travel covering in excess of 2.6 billion kilometers (1.6 billion miles), we are closing in on our first destination. Dawn is starting its approach to Vesta.

The interplanetary cruise phase of the mission ends today and the 15-month Vesta phase begins. The first three months are the “approach phase,” during which the spacecraft maneuvers to its first science orbit. Many of the activities during approach were discussed in detail in March and April last year, and now we are about to see those plans put into action.

The beginning of the phase is marked by the first images of the alien world Dawn has been pursuing since it left Earth. Vesta will appear as little more than a smudge, a small fuzzy blob in the science camera’s first pictures. But navigators will analyze where it shows up against the background stars to help pin down the location of the spacecraft relative to its target. To imagine how this works, suppose that distant trees are visible through a window in your house. If someone gave you a photo that had been taken through that window, you could determine where the photographer (Dawn) had been standing by lining up the edge of the window (Vesta) with the pattern of the background trees (stars). Because navigators know the exact position of each star, they can calculate where Dawn and Vesta are relative to each other. This process will be repeated as the craft closes in on Vesta, which ultimately will provide a window to the dawn of the solar system.

Even though the mysterious orb is still too far away to reveal new features, it will be exciting to receive these first pictures. During the approach phase, images will be released in periodic batches, with priority viewing for residents of Earth. The flow will be more frequent thereafter. For most of the two centuries that Vesta has been studied, it has been little more than a pinpoint of light. Interrupting thrusting once a week this month to glimpse its protoplanetary destination, Dawn will watch it grow from about five pixels across to 12. By June, the images should be comparable to the tantalizing views obtained by the Hubble Space Telescope. As the approach phase continues and the distance diminishes, the focus will grow still sharper and new details will appear in each subsequent set of images.

› Continue reading Marc Rayman’s May Dawn Journal