Archive for February, 2014


28 Feb
Marc Rayman
Marc Rayman
Chief Engineer/ Mission Director, JPL

Dawn Journal | February 28, 2014

by Marc Rayman

Dear Ardawnt Readers,

Continuing its daring mission to explore some of the last uncharted worlds in the inner solar system, Dawn remains on course and on schedule for its rendezvous with dwarf planet Ceres next year. Silently and patiently streaking through the main asteroid belt between Mars and Jupiter, the ardent adventurer is gradually reshaping its orbit around the sun with its uniquely efficient ion propulsion system. Vesta, the giant protoplanet it unveiled during its spectacular expedition there in 2011-2012, grows ever more distant.

Dawn will  uses ion propulsion system to spiral to RC3 orbit

Following its gravitational capture by Ceres during the approach phase, Dawn will continue to use its ion propulsion system to spiral to RC3 orbit at an altitude of 8,400 miles (13,500 kilometers). Credit: JPL/NASA

In December and January, we saw Dawn’s plans for the “approach phase” to Ceres and how it will slip gracefully into orbit under the gentle control of its ion engine. Entering orbit, gratifying and historic though it will be, is only a means to an end. The reason for orbiting its destinations is to have all the time needed to use its suite of sophisticated sensors to scrutinize these alien worlds.

As at Vesta, Dawn will take advantage of the extraordinary capability of its ion propulsion system to maneuver extensively in orbit at Ceres. During the course of its long mission there, it will fly to four successively lower orbital altitudes, each chosen to optimize certain investigations. (The probe occupied six different orbits at Vesta, where two of them followed the lowest altitude. As the spacecraft will not leave Ceres, there is no value in ascending from its fourth and lowest orbit.) All of the plans for exploring Ceres have been developed to discover as much as possible about this mysterious dwarf planet while husbanding the precious hydrazine propellant, ensuring that Dawn will complete its ambitious mission there regardless of the health of its reaction wheels.

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25 Feb

Virtual Tour of Vesta

by Thomas Roatsch

The International Astronomical Union recently approved a new set of feature names for giant asteroid Vesta: Albia, Africana and Alypia Craters, to name a few. Among the features are dorsa (ridges), fossae (long, narrow shallow depressions), a rupes (scarp or cliff), and craters from Vesta’s mysterious north polar region. This compels us to take another close look at Vesta’s marvelous atlas.

An atlas of the asteroid Vesta, created from images taken during the Dawn mission’s low altitude mapping orbit (LAMO), is accessible for the public to explore online.  The set of maps was created from mosaics of 10,000 images from Dawn’s framing camera (FC) instrument, taken at an altitude of about 210 kilometers.  The maps are mostly at a scale of 1:200 0000 (1 centimeter = 2 kilometers), about that of regional road maps.

 Vesta's Low Altitude Mapping Orbit (LAMO) Atlas is at the scale of regional road maps: 1cm = 2 km (1 in = 3 mi).

Vesta’s Low Altitude Mapping Orbit (LAMO) Atlas is at the scale of regional road maps: 1 cm = 2 km (1 in = 3 mi)

Creating the atlas was a painstaking task – each map sheet of this series used roughly 400 images. The atlas shows how extreme the terrain is on a body the size of Vesta.  In the south pole projection alone, the Severina crater contours reach a depth of 18 kilometers; just over a hundred kilometers away the mountain peak towers 7 kilometers above the ellipsoid reference level.

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