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

From: Ron Baalke <baalke_at_meteoritecentral.com>
Date: Fri Apr 7 00:21:08 2006
Message-ID: <200604070059.k370xko28705_at_zagami.jpl.nasa.gov>

D A W N ' S E A R L Y L I G H T April 2006
- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -

The ninth 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.

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

http://www-ssc.igpp.ucla.edu/dawn/newsletter/html/20060405/dawnintegration.html

Dawn Proceeds to Launch
Christopher T. Russell
Dawn Principal Investigator, UCLA

On March 27, NASA Associate Administrator Rex Geveden reinstated
the Dawn mission, after it had been cancelled on March 2nd. The
Dawn team is very grateful that NASA recognized the work that the
project has accomplished to reduce technical, schedule and cost
risk, and committed the funds needed to complete the mission.
The project team has been directed to resume integration and
testing activities, and develop a detailed project schedule and
cost profile to support a launch between June and August of 2007.
The project estimates it will need <$54M in additional funds.

All of us on the Dawn project are grateful for the tremendous
outpouring of support from the community during the stand down
and following cancellation. Special thanks go to the European
Space Agency and to the Italian Space Agency for offers of
support during the operational phase of the mission and the
strong backing and commitment from Orbital Sciences Corporation
and the Jet Propulsion Laboratory to give Dawn high priority in
obtaining the resources and personnel needed to proceed smoothly
to launch. The support of the German Space Agency, DLR, is also
much appreciated.

Over the next two months, Dawn will be staffing up and returning
to the level of effort necessary to proceed to the mid-2007
launch. Due to the use of a Mars Gravity Assist in 2009, which
fixes the timing of subsequent events, the launch delay does not
affect the timing of the arrivals and departures at Vesta and
Ceres, nor the science operations. However, if we were not able
to launch by the end of October 2007, then the dual asteroid
mission would not be possible for another 15 years. Thus, it is
very fortunate that this mission was approved to go forward at
this time.

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

http://www-ssc.igpp.ucla.edu/dawn/newsletter/html/20060405/dawnstatus.html

Dawn Status Report
Carol A. Raymond
Dawn Deputy Principal Investigator, JPL

Dawn emerges from the five-month stand down period with
positive closure on several technical issues, and some new
team members.

Keyur Patel has been named the new Project Manager at JPL.
Keyur's recent experience was as Deputy Project Manager on
Deep Impact through its successful encounter with Tempel 1.
Ann Grandfield has been promoted to Project Manager (from
Deputy) at Orbital Sciences Corporation.

There is good news regarding the ion propulsion system
components, namely the xenon tank and the power processing
units, which raised concerns of NASA managers and
contributed to their decision to direct the project to stand
down. The Dawn flight xenon tank has been an item of concern
since a qualification tank and a flight spare tank ruptured
at lower-than-expected pressures during testing. The tank
is a composite overwrapped pressure vessel (COPV) with a
titanium liner. While the actual flight tank had been
tested and performed at pressures well above the expected
flight and ground pressures, there was lingering concern
that the cause of the qual and spare tank failures needed
to be understood to fully qualify the flight tank. An
Independent Review Team (IRT) team was formed to review
the issues.

The project decided to reduce the xenon load from 450 to
425 kg to add an extra margin of safety (with no impact
on planned science operations). The IRT team concluded
that the tank was flightworthy in Sept 2005, and was
succeeded by an Independent Technical Authority (ITA)
review. After extensive materials testing, the cause of
the qual/spare tank failures was determined to be due to
manufacturing anomalies that had no bearing on the
integrity of the flight tank. The ITA issued their
draft report on March 17th, concluding that the Dawn
flight xenon tank was flightworthy.

Figure 1. Dawn flight COPV tank. The tank, which was
integrated last fall, has a safety factor >2 for a
xenon load of 425 kg.

Several test failures of the Power Processing Units
(PPUs) of the ion propulsion system also were a cause
of concern that contributed to the mission stand down.
The PPUs had experienced parts failures and unplanned
shutdowns during testing. A PPU tiger team was formed
to assess the PPU design and provide independent
assessment of the cause of the testing anomalies. The
team concluded that the design was sound, devised
methods to test for defects in parts similar to the
ones that failed, and explained the shutdowns as
indicating the possible need to adjust an internal
parameter value. The tiger team recommended an extended
"run-in" test of the two identical units, in vacuum for
500-1000 hours, to validate parts quality and
operational stability. The run-in testing procedures
have been written and tested and the actual testing
is due to start immediately.

The Dawn PPU design was inherited from the Deep Space 1
(DS1) mission. The PPU flown on DS1 operated flawlessly
for 16265 hours, while the two Dawn PPUs together are
expected to operate for about 48000 hours. A minor
change was made to the DS1 PPU design to improve the
response to a serious grid short.

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

http://www-ssc.igpp.ucla.edu/dawn/newsletter/html/20060405/dawnintegration.html

Dawn Spacecraft Nearing Final Integration

Carol A. Raymond
Dawn Deputy Principal Investigator, JPL

During the stand down the team has been working on
developing and vetting test procedures and dry-running
them on the testbed. The team is anxious to integrate
the instruments, which have been stored at Orbital
since November, and begin comprehensive spacecraft
testing. Final delivery of the second (re-worked)
Attitude Control Electronics Unit, the PPUs, and
re-worked Digital Control Interface Units are pending.
The ion thrusters are the last items to be integrated.

Figure 2. State of the Dawn spacecraft as of last
October (same as current state). Reaction wheels and
coarse sun sensors are visible on the upper (+Z) deck,
and an ion thruster mounting sleeve at bottom.
Spacecraft assembly is about 90% complete.

Figure 3. View of spacecraft showing harness and
subsystem boxes in the high bay at Orbital. Boxes
are integrated to flight panels that are laid flat
for testing.

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Received on Thu 06 Apr 2006 08:59:46 PM PDT