[meteorite-list] Dawn's Early Light - October 2006

From: Ron Baalke <baalke_at_meteoritecentral.com>
Date: Thu Oct 12 12:06:52 2006
Message-ID: <200610121606.JAA08912_at_zagami.jpl.nasa.gov>

D A W N ' S E A R L Y L I G H T October 2006
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The tenth issue of the Dawn team newsletter, Dawn's Early Light,
has been posted on the Dawn website. Follow the links below to
view individual articles, or obtain the formatted pdf version.
We look forward to obtaining your feedback.

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http://www-ssc.igpp.ucla.edu/dawn/newsletter/html/20061010/testing.html

Environmental testing of Dawn spacecraft begins
Carol A. Raymond
Dawn Deputy Principal Investigator, JPL

The Dawn project is deep into the testing phase of ATLO (Assembly, Test,
and Launch Operations) with completion of all the Comprehensive
Performance Tests demonstrating subsystem functionality, the successful
completion of the Environmental Test Readiness Review held September
6-7, and the first major environmental test (Electromagnetic
Interference/Compatibility) due to begin next week. After EMI/EMC, the
spacecraft undergoes acoustics and dynamics testing, then is shipped to
the Naval Research Lab in Washington, DC for one month of testing (late
Dec-Jan) in a large thermal-vacuum chamber. This chamber is large enough
to allow a test-firing of the ion thrusters. After thermo-vac testing,
the spacecraft ships directly to Cape Canaveral for launch, in a 20-day
window that opens June 20, 2007.

The spacecraft is fully assembled except for the two outboard thrusters
of the ion propulsion system (IPS), to be installed after dynamics
testing and before thermo-vac (TVAC), to avoid damage to these critical
appendages. The center thruster has been installed in the spacecraft
core, as well as the large high-gain antenna. The solar panels are
currently being installed.

The Power Processing Units (PPUs) of the IPS system, that had been an
item of concern a year ago, each underwent 500 hours of run-in testing
before delivery to the spacecraft to certify their robustness against
workmanship defects and early parts failures. After integration, the
PPUs were exercised during IPS comprehensive performance testing and
have operated trouble-free. There are no outstanding issues with the
flight hardware, and the flight software needed for environmental
testing has been delivered.

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http://www-ssc.igpp.ucla.edu/dawn/newsletter/html/20061010/integration.html

Dawn Instrument Integration Completed
Betina Pavri
Dawn Payload Engineer, JPL

Ed Miller
Dawn Payload Manager, JPL

The Dawn payload integration to the spacecraft was completed during
September, and all of the science instruments have now been tested for
functionality on both primary and redundant interfaces. Integration went
smoothly and all instruments checked out perfectly. As part of the
comprehensive performance testing of the instrument systems, science
data were transmitted from the spacecraft through the Dawn Science
Center at UCLA to the instrument teams' home institutions.

The spacecraft is fully assembled except for the two outboard thrusters
of the ion propulsion system (IPS), to be installed after dynamics
testing and before thermo-vac (TVAC), to avoid damage to these critical
appendages. The center thruster has been installed in the spacecraft
core, as well as the large high-gain antenna. The solar panels are
currently being installed. The Power Processing Units (PPUs) of the IPS
system, that had been an item of concern a year ago, each underwent 500
hours of run-in testing before delivery to the spacecraft to certify
their robustness against workmanship defects and early parts failures.
After integration, the PPUs were exercised during IPS comprehensive
performance testing and have operated trouble-free. There are no
outstanding issues with the flight hardware, and the flight software
needed for environmental testing has been delivered.

In the months leading up to the final integration, the Framing Cameras
had been returned to MPS in Germany for investigation and rework of an
anomaly in their cover operations. The MPS team worked diligently to
isolate the issues and rework the system. The covers now operate
flawlessly and the cameras were integrated on schedule.

The Visible InfraRed Mapping Spectrometer (VIR) instrument consists of
two parts: the Optics Module (OM) and the Main Electronics (ME). The VIR
ME was delivered and integrated last summer, since it is located inside
the spacecraft. Before the OM integration to the spacecraft, the OM
mounting panel was redesigned by engineers at Orbital Sciences, the
spacecraft contractor, to resolve a thermal expansion mismatch issue.
The OM was then integrated to the newly redesigned panel. This delicate
integration, including the electronics, cryocooler, the OM itself, and
all blanketing and cabling to the VIR panel took 6 days to complete! The
panel is now attached to the spacecraft and the OM is connected to the
Main Electronics.

The Gamma Ray and Neutron Detector (GRaND) instrument was integrated in
August to a special radiator that will keep the instrument cool in the
vacuum of space. For ground testing, a special cooler has been
temporarily installed to keep the instrument in its operational
temperature range. All of the Dawn science instruments will now
participate in a series of increasingly realistic tests to ensure that
both they and the mission operations team are flight-ready.

[Image]
Figure 1. Top view of of the spacecraft (+Z deck), showing instruments,
coarse sun sensors (CSS), star trackers (ST) and reaction wheel
assemblys (RWA).

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http://www-ssc.igpp.ucla.edu/dawn/newsletter/html/20061010/dwarfplanet.html

International Astronomical Union Declares Ceres a 'Dwarf Planet'
Christopher T. Russell
Dawn Principal Investigator, UCLA

While the Dawn team has always considered both of its intended targets
as protoplanets, the IAU has officially recognized Ceres as belonging to
a class of planetary objects called "dwarf planets" that includes Pluto,
its previously-ascribed moon Charon, and Eris, a large object recently
discovered in the Kuiper belt. While the new label draws welcome
attention to the many intriguing attributes of Ceres, Vesta also
exhibits many characteristics of planets, such as a differentiated
interior in which iron migrated to the core and lighter basaltic magma
rose to the surface. Vesta's differentiation likely occurred as a result
of formation of a magma ocean driven by decay of abundant short-lived
radionuclides. The greater apparent water retention by Ceres may have
resulted from an insufficient supply of heat-producing material,
possibly because it formed later, after these elements had decayed. The
large size of both Vesta and Ceres has helped preserve the information
contained in the surfaces and interior of the bodies since their
formation. The extraordinary ability of the Dawn spacecraft to orbit
both of these intriguing objects and shed light on the processes and
conditions that caused the observed variation within our solar system
will inform the debate on what makes a planet, a debate expected to
endure long into the future.

This subject is expounded upon in the latest blog by mission engineer
Marc Rayman. His journals can be found at
http://dawn.jpl.nasa.gov/mission/journal.asp.

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http://www-ssc.igpp.ucla.edu/dawn/newsletter/html/20061010/************

Sign up to go to the Asteroid Belt!

November 4th is the last day to sign up to have your name sent to the
asteroid belt onboard the Dawn spacecraft! The names will be carried
onboard encoded on a computer microchip. To date, over 171,000 names
have been submitted through the Dawn website. Go to
http://dawn.jpl.nasa.gov and click on "Send Your Name to the Asteroid
Belt." The "onboard verification" can be printed as a certificate
suitable for framing.

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The Dawn mission has been selected as NASA's ninth Discovery
mission to be launched in June 2007 to orbit both Vesta and Ceres.
This list has been established to keep members of the scientific
community informed about the Dawn mission.

Dawn's Early Light is published on an occasional basis and
distributed electronically. To contribute material or query the
team, email us at dawnnews_at_igpp.ucla.edu.

Editor: Carol A. Raymond, Jet Propulsion Laboratory
Received on Thu 12 Oct 2006 12:06:46 PM PDT