Dawn will enter lowest ever orbit around Ceres

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June 2, 2018 4:15 am Published by
This picture is one of the first images returned by Dawn in more than a year, as Dawn moves to its lowest-ever and final orbit around Ceres. Dawn captured this view on May 16, 2018 from an altitude of about 270 miles (440 kilometers). Image Credit: NASA/JPL-Caltech/UCLA/MPS/DLR/IDA

This picture is one of the first images returned by Dawn in more than a year, as Dawn moves to its lowest-ever and final orbit around Ceres. Dawn captured this view on May 16, 2018 from an altitude of about 270 miles (440 kilometers). Image Credit: NASA/JPL-Caltech/UCLA/MPS/DLR/IDA

NASA’s Dawn spacecraft has begun maneuvers that should bring it to its lowest and final orbit around dwarf planet Ceres.

The probe’s destination is less than 30 miles (50 km) above Ceres’s surface, which is ten times closer than its previous closest orbit. From there, it is planned to have Dawn gather gamma ray and neutron spectra that should help scientists better understand chemical changes in the surface’s uppermost layer as well as obtain detailed, high-resolution images.

From this vantage point, scientists will have the opportunity to closely study specific sites of interest, such as Occator 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 over Occator Crater in 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. Because the spacecraft was not designed to operate at such close orbits and because the reaction wheels that control its orientation are no longer functioning, Dawn will have to take an elliptical orbit to study Ceres’s surface.

“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).

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 his Dawn Journal blog, 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 blue curve is Dawn’s flight path from XMO5, the outer green ellipse, to XMO6, the inner one. Image credit: NASA/JPL-Caltech

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Laurel Kornfeld is an amateur astronomer and freelance writer from Highland Park, NJ, who enjoys writing about astronomy and planetary science. She studied journalism at Douglass College, Rutgers University, and earned a Graduate Certificate of Science from Swinburne University’s Astronomy Online program. Her writings have been published online in The Atlantic, Astronomy magazine’s guest blog section, the UK Space Conference, the 2009 IAU General Assembly newspaper, The Space Reporter, and newsletters of various astronomy clubs. She is a member of the Cranford, NJ-based Amateur Astronomers, Inc. Especially interested in the outer solar system, Laurel gave a brief presentation at the 2008 Great Planet Debate held at the Johns Hopkins University Applied Physics Lab in Laurel, MD.

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