Archive for May, 2014


 

31 May
2014
Marc Rayman
Marc Rayman
Chief Engineer/ Mission Director, JPL

Dawn Journal | May 31

by Marc Rayman
 

Dear Dawnosaurs,

Silently streaking through the main asteroid belt, emitting a blue-green beam of xenon ions, Dawn continues its ambitious interplanetary expedition. On behalf of creatures on distant Earth who seek not only knowledge and insight but also bold adventure, the spacecraft is heading toward its appointment with Ceres. In about 10 months, it will enter orbit around the ancient survivor from the dawn of the solar system, providing humankind with its first detailed view of a dwarf planet.

This month we continue with the preview of how Dawn will explore Ceres. In December we focused on the “approach phase,” and in January we described how the craft spirals gracefully into orbit with its extraordinary ion propulsion system. The plans for the first observational orbit (with a marvelously evocative name for a first examination of an uncharted world: RC3 — is that cool, or what?), at an altitude of 8,400 miles (13,500 kilometers), were presented in FebruaryLast month, we followed Dawn on its spiral descent from each orbital altitude to the next, with progressively lower orbits providing better views than the ones before. Now we can look ahead to the second orbital phase, survey orbit.

Survey_orbit

This figure shows Dawn’s second observational orbit, “survey orbit,” at the same scale as the size of Ceres. At an altitude of 2,730 miles (4,400 kilometers), the spacecraft will make seven revolutions in about three weeks. Credit: NASA/JPL

In survey orbit, Dawn will make seven revolutions at an altitude of about 2,730 miles (4,400 kilometers). At that distance, each orbit will take three days and three hours. Mission planners chose an orbit period close to what they used for survey orbit at Vesta, allowing them to take advantage of many of the patterns in the complex choreography they had already developed. Dawn performed it so beautifully that it provides an excellent basis for the Ceres encore. Of course, there are some adjustments, mostly in the interest of husbanding precious hydrazine propellant in the wake of the loss of two of the spacecraft’s four reaction wheels. (Although such a loss could have dire consequences for some missions, the resourceful Dawn team has devised a plan that can achieve all of the original objectives regardless of the condition of the reaction wheels.)

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29 May
2014

Greetings From Berlin–Grüße aus Berlin!

by Chris Russell
 

The Dawn Team Converges at the German Aerospace Agency

The Dawn spacecraft moved back in solar system time when it cruised into the main asteroid belt, first orbiting protoplanet Vesta in 2011-12, and now on its way to dwarf planet Ceres, due in March 2015. When the Dawn team met in Berlin this month, it offered an opportunity for the mission to do a bit of its own time travel.

Dawn Team at the German Aerospace Agency, Berlin, 2014

fig 1: Dawn Team at the German Aerospace Agency, Berlin, 2014

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23 May
2014

Vesta 360

by David O'Brien
 

The Dawn mission is currently en route to dwarf planet Ceres, its second destination. It spent a productive fourteen months orbiting its first destination, giant asteroid Vesta, in 2011-12, gathering splendid sets of data. The spacecraft may have moved on, but the science team continues to explore that data, enriching our understanding of Vesta’s formation and history.

Getting the “Big Picture”

Vesta: Clementine color ratios

Clementine color ratios

Vesta is a large protoplanet with remarkably variable topography—mountains, troughs, boulders, craters, cliffs, and more. The wealth of high-resolution imaging data from the Dawn mission has given us an amazing view of its surface. However, looking through individual frames or image mosaics can make it difficult to see its surface features in a global context and get the “big picture” of Vesta. On the other hand, the images taken early on as the mission approached the protoplanet show the whole of Vesta, but with low surface resolution. To better visualize Vesta at high resolution, I used the open-source program POV-Ray[1], combining images and topography data to create striking 3-D graphics.

The program let me take a shape model of Vesta, created from Dawn’s framing camera data by Bob Gaskell at the Planetary Science Institute, and wrap an image around it. For the image, I used a global mosaic[2] developed by our framing camera team partners at the German Aerospace Center (DLR) from high altitude mapping orbit clear-filter images. This mosaic has a resolution of 60 meters (about 200 feet) per pixel. I then used POV-Ray to make ‘snapshots’ of this model of Vesta as it rotated, varying the latitude from +45 to -45 degrees. Those individual frames were combined into the movie shown below.

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Footnotes:
  1. [1] Persistence of Vision Raytracer
  2. [2] The global mosaics used here can be downloaded from this page at the Dawn Public Data website, although they are very large files. For labeled maps of smaller regions of the surface, see the Vesta Atlas.


 

2 May
2014
Marc Rayman
Marc Rayman
Chief Engineer/ Mission Director, JPL

The Hundredth Journal

by Marc Rayman
 
Colleague Keri Bean's festive (and delicious) cake

Colleague Keri Bean’s festive (and delicious) cake with some of the greetings used in the Dawn Journals.

I have been captivated by space since I was four years old, and my enthusiasm has grown stronger and stronger ever since. With a lifelong passion for the exploration and utilization of space, covering the science, the engineering and the pure thrill of a cosmic adventure, working on a mission to explore some of the last uncharted worlds in the inner solar system has been a dream come true for me. My work is indescribably exciting.

And although it literally is indescribable, I can’t help but try! As one facet of that effort, I started writing the Dawn Journal eight years ago. Now that I have written 100, I was invited to write a short blog to celebrate. (In other words, I’ve been asked to blog about blogging.)

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