[meteorite-list] Dawn Engineers Assess Reaction Wheel

From: Ron Baalke <baalke_at_meteoritecentral.com>
Date: Tue, 14 Aug 2012 08:43:11 -0700 (PDT)
Message-ID: <201208141543.q7EFhBcA008939_at_zagami.jpl.nasa.gov>

http://www.jpl.nasa.gov/news/news.cfm?release=2012-242

Dawn Engineers Assess Reaction Wheel
Jet Propulsion Laboratory
August 13, 2012

Dawn Mission Status Report

PASADENA, Calif. -- Engineers working on NASA's Dawn spacecraft are
assessing the status of a reaction wheel -- part of a system that helps
the spacecraft point precisely -- after onboard software powered it off
on Aug. 8. Dawn's mission is to study the geology and geochemistry of
the giant asteroid Vesta and dwarf planet Ceres, the two most massive
objects in the main asteroid belt. Dawn is now using its thrusters to
point at Earth for communications. The rest of the spacecraft is
otherwise healthy.

During a planned communications pass on Aug. 9, the team learned that
the reaction wheel had been powered off. Telemetry data from the
spacecraft suggest the wheel developed excessive friction, similar to
the experience with another Dawn reaction wheel in June 2010. The Dawn
team demonstrated during the cruise to Vesta in 2011 that, if necessary,
they could complete the cruise to Ceres without the use of reaction wheels.

The spacecraft has been orbiting Vesta since July 15, 2011. Dawn
concluded its primary science observations of Vesta on July 25, 2012,
and has been spiraling slowly away from the giant asteroid using its ion
propulsion system. Ion thrusting was halted to accommodate the reaction
wheel investigation, which may briefly delay the escape from Vesta.

"The Vesta mission has been spectacularly successful, and we are looking
forward to the exciting Ceres mission ahead of us," said Robert Mase,
Dawn project manager, of NASA's Jet Propulsion Laboratory, Pasadena,
Calif.

JPL manages the Dawn mission for NASA's Science Mission Directorate in
Washington. Dawn is a project of the directorate's Discovery Program,
managed by NASA's Marshall Space Flight Center in Huntsville, Ala. The
University of California at Los Angeles (UCLA) is responsible for
overall Dawn mission science. Orbital Sciences Corp. in Dulles, Va.,
designed and built the spacecraft. The German Aerospace Center, the Max
Planck Institute for Solar System Research, the Italian Space Agency and
the Italian National Astrophysical Institute are international partners
on the mission team.

For more information about Dawn, visit: http://www.nasa.gov/dawn and
http://dawn.jpl.nasa.gov .

Jia-Rui C. Cook 818-354-0850
Jet Propulsion Laboratory, Pasadena, Calif.
Jia-Rui.C.Cook at jpl.nasa.gov

2012-242
Received on Tue 14 Aug 2012 11:43:11 AM PDT