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

[Ron Baalke]

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

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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. 

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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. 

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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.

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