[meteorite-list] Dawn Operating Normally After Safe Mode Triggered

From: Ron Baalke <baalke_at_meteoritecentral.com>
Date: Tue, 16 Sep 2014 16:26:20 -0700 (PDT)
Message-ID: <201409162326.s8GNQKcX000335_at_zagami.jpl.nasa.gov>


Dawn Operating Normally After Safe Mode Triggered
Jet Propulsion Laboratory
September 16, 2014

The Dawn spacecraft has resumed normal ion thrusting after the thrusting
unexpectedly stopped and the spacecraft entered safe mode on September
11. That anomaly occurred shortly before a planned communication with
NASA's Deep Space Network that morning. The spacecraft was not
performing any special activities at the time.

Engineers immediately began working to restore the spacecraft to its
normal operational state. The team determined the source of the
problems, corrected them, and then resumed normal ion thrusting on
Monday night, Sept. 15.

"This anomaly presented the team with an intricate and elaborate puzzle
to solve," said Robert Mase, Dawn project manager at NASA's Jet
Propulsion Laboratory in Pasadena, California.

After investigating what caused the spacecraft to enter safe mode, the
Dawn team determined that it was likely triggered by the same phenomenon
that affected Dawn three years ago on approach to the protoplanet Vesta:
An electrical component in the ion propulsion system was disabled by a
high-energy particle of radiation.

"We followed the same strategy that we implemented three years ago to
recover from a similar radiation strike -- to swap to one of the other
ion engines and a different electronic controller so we could resume
thrusting quickly," said Dawn Mission Director and Chief Engineer Marc
Rayman of JPL. "We have a plan in place to revive this disabled
component later this year."

Complicating the issue, the team discovered that the spacecraft had
experienced not just one anomaly, but also a second one that affected
the ability to point the main antenna at Earth to communicate. Because
the spacecraft could not communicate using its main antenna, the team
had to utilize the weaker signals of another antenna, slowing their
progress. In addition, Dawn is so far from Earth that radio signals take
53 minutes to make the round trip. Although they have not yet
specifically pinpointed the cause of this issue, it could also be
explained by a high-energy particle corrupting the software running in
the main computer. Ultimately the team reset the computer, which
restored the pointing performance to normal.

As a result of the change in the thrust plan, Dawn will enter into orbit
around dwarf planet Ceres in April 2015, about a month later than
previously planned. The plans for exploring Ceres once the spacecraft is
in orbit, however, are not affected.

Dawn orbited Vesta, the second most massive object in the main asteroid
belt, from July 2011 until September 2012. The spacecraft's ion
propulsion system enabled it to spiral away from Vesta and head toward
Ceres, the most massive object in that region. Thanks to the power of
ion propulsion, Dawn is the only mission ever targeted to orbit two
deep-space destinations.

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, Alabama.
The University of California at Los Angeles (UCLA) is responsible for
overall Dawn mission science. Orbital Sciences Corp. in Dulles,
Virginia, 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:


Elizabeth Landau
NASA's Jet Propulsion Laboratory, Pasadena, Calif.
Elizabeth.Landau at jpl.nasa.gov

Received on Tue 16 Sep 2014 07:26:20 PM PDT

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