Dawn spiraling to closest ever orbit of Ceres

New position will enable probe to conduct detailed study of dwarf planet's geology.
By Laurel Kornfeld | Nov 09, 2018
NASA'sDawnspacecraft is spiraling down toward its lowest and final orbit around the dwarf planet Ceres.

The probe's destination is less than 30 miles (50 km) above Ceres's surface, ten times closer than its previous closest orbit. From there, Dawn will collect gamma ray and neutron spectra that should help scientists better understand chemical changes in the surface's uppermost layer and also obtain detailed, high-resolution images.

This orbit will give scientists the opportunity to closely study specific sites of interest, such asOccator Crater, home to highly reflective salt deposits similar to those seen on Earth.

By studying the crater and the area surrounding it, which together are known as a "geological unit," researchers hope to better understand the site's complex geology.

Mission engineers hope to fly low overOccator Craterin each orbit.

Accomplishing this requires difficult maneuvers because Dawn's Gamma Ray and Neutron Detector (GRaND) will need to fly over the region 20 times to record enough of the site's faint nuclear radiation.

The new orbit, which Dawn will begin on June 7, is designated extended mission orbit seven or XMO7.

Dawn was not designed to operate at such close orbits. Its reaction wheels, which control its orientation, are no longer functioning, and as a result, Dawn will have to enter an elliptical orbit to study Ceres's surface.

Engineers have spent the last several months plotting the descent to the low orbit to come up with a plan that will provide the best opportunity for science observations. To accomplish this, they mapped out more than 45,000 possible paths to the close orbit before settling on the current one.

The orbit transfer is difficult because the spacecraft, which has been circling Ceres since March of 2015, uses ion engines for propulsion.

In hisDawn Journalblog, mission director and chief engineer Mark Rayman discussed the challenges of bringing the spacecraft into its final orbit in detail.

During XMO7, Dawn should orbit Ceres once every 27 hours and 13 minutes, which equals exactly three times the dwarf planet's rotational period. In what is known as a three-to-one resonant orbit, the probe should complete one orbit around Ceres for every three rotations the dwarf planet makes.

"The team is eagerly awaiting the detailed composition and high-resolution imaging from the new, up-close examination. These new high-resolution data allow us to test theories formulated from the previous data sets and discover new features of this fascinating dwarf planet,"said mission Principal Investigator Carol Raymond of NASA's Jet Propulsion Laboratory (JPL).



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