[meteorite-list] Probe Built to Visit Asteroids Killed in Budget Snarl (Dawn)

From: Ron Baalke <baalke_at_meteoritecentral.com>
Date: Sun Mar 5 23:37:04 2006
Message-ID: <200603060435.k264ZJW00503_at_zagami.jpl.nasa.gov>

http://www.spaceflightnow.com/news/n0603/03dawn/

Probe built to visit asteroids killed in budget snarl
BY STEPHEN CLARK
SPACEFLIGHT NOW
March 3, 2006

A robotic mission to study two of the solar system's largest asteroids
has been killed by NASA after months of uncertainty while extensive
reviews probed the mission's funding and technical credentials.

The cancellation of Dawn comes amid other proposed cuts in the agency's
science budget in an effort to fulfill the Vision for Space Exploration,
which calls for completing the assembly of the space station, retiring
the space shuttle fleet, and developing the next-generation Crew
Exploration Vehicle.

However, Dawn's cancellation is a rarity. Most missions under
consideration for termination or deferment are relatively early in the
development and design phases, but Dawn's spacecraft is currently
sitting at a contractor facility at Orbital Sciences where it was
undergoing final assembly last year.

Missions such as Triana - a politically charged Earth observation
satellite - have also found their way onto the chopping block as
construction neared completion. In 1998, a NASA remote sensing satellite
named Clark also fell victim to budget concerns and launch delays.

NASA has tried in the past to re-use parts and instruments from
abandoned spacecraft on other missions. The future of the Dawn hardware
is currently unclear.

Managers of the Dawn mission were first warned of trouble last October,
when NASA officials ordered a halt to operations as final testing was
getting underway before shipment of the craft to its Florida launch site
in advance of a then-planned June 2006 blastoff. NASA simultaneously
launched a thorough review of the cost overruns and technical problems
facing the mission.

At that point, workers were bolting on the last boxes and testing the
assembled spacecraft. After the stand down, the vehicle was "safed" and
attention was focused on paperwork items and answering questions from
the independent assessment team, Dawn Principal Investigator Christopher
Russell told Spaceflight Now.

"My first reaction to the news of the stand down was shock and a feeling
that there must have been a better way to accomplish the confidence
building that NASA obviously needed," Russell said.

"It is emotionally very hard to stop a race when you see the finish line
in sight. And it is very hard on those people who were laid off when the
stand down took place. A stand down is a very big hammer. It is not for
finishing nails."

Dawn was to have been the ninth mission of the Discovery program, which
attempts to fly a higher number of missions that are lower in cost and
smaller in scope than earlier NASA programs. It was selected for
implementation in 2001.

Plans originally called for Dawn to rocket into space aboard a Delta 2
booster as early as this June to begin its circuitous trek through the
solar system that would have included a fly-by of Mars in February 2009.
Dawn would have then arrived at asteroid Vesta in late 2011, where a
stay of at least six months was anticipated. After departing Vesta,
Dawn's ion engines would have navigated the probe toward asteroid Ceres,
where it would have entered orbit in August 2015 and stayed until the
end of the mission.

The stand down initially made the June launch impossible, and
postponements to November 2006 and early 2007 followed. Officials say
Dawn had until October 2007 to launch and still reach Mars for a
critical gravity assist maneuver.

Dawn's science payload consisted of a framing camera provided by German
scientists at the Max Planck Institute and the German Aerospace Center,
DLR. The Italian Space Agency was responsible for the visible and
infrared mapping spectrometer. The Los Alamos National Laboratory in New
Mexico built a gamma ray and neutron detector.

The two asteroids targeted by Dawn are believed to have remained intact
since their formation in the very early stages of the solar system.
Scientists expected to learn the chemical composition of both asteroids,
search for water-bearing minerals and a metallic core, and determine
their precise mass, shape, volume, rotation rate, and gravity.

The Discovery program had capped the costs of Dawn at $371 million, but
project officials saw the first indication of going over-budget in early
2005, according to Russell. A new cost analysis system alerted
management of a potential $7 million deficit.

"We then did a grass roots estimate of what it would take to launch
successfully," Russell said in January. "So everyone on the project was
asked to look carefully at the work to go and provide their best
estimate of the cost. This number was higher, $17 million, as one might
expect when (giving) people a chance to re-estimate."

"Then we called in a committee of experts who just took a top level look
at the costs and schedule and recommended that we add more cost and
schedule reserve and fund it. This number was $40 million. It was a
worst-case number but it was the number that NASA used to decide that
Dawn needed to be stopped for a while so that an assessment of readiness
for launch could be made."

In the period leading up to the stand down, worries also spread
concerning several key spacecraft issues. Relying on a solar electric
ion propulsion system, Dawn was to have carried a tank for the xenon gas
propellant required by the three cutting edge engines. The xenon tank -
composed of a titanium liner covered with composite wrapping - is
located deep inside the spacecraft bus, and other pieces were added
around it during the manufacturing process.

The flight tank inside Dawn passed pre-flight tests that included taking
it to pressures far above those necessary for ground or space
operations. Yet when similar tanks were put through more stringent
tests, they ruptured at pressures lower than the expected design limits.
By finding that the tank was not as strong as first thought, engineers
were forced to compensate the weakness by forming a new strategy that
included not filling the tank to its full capacity.

Trouble with the Power Processing Units was also plaguing the project.
Built by L3 Communications, the units provide the electrical power to
the thrusters in the ion propulsion system. Officials say the delivery
of at least one PPU was delayed and that there may have been workmanship
problems.

Another concern with the stress on the craft's materials during the
"bakeout" procedure was also raised shortly before the work stoppage was
ordered.

"It was not any one problem with the spacecraft, but the problems
continued to occur as the mission development continued," Russell said
before the cancellation. "I would say this is the normal course of
events in this business. Those holding the purse strings did not have my
confidence. I do not believe any one problem such as a blown fuse, or
over-heating of a part, or some contamination on a connector was the
trigger. It was that we reported every problem as it occurred, so there
was a series of problems."

Despite these issues, scientists close to the project felt that Dawn's
problems were not all that different from those encountered during in
preparation for the launch of any deep space probe.

"I have always felt that Dawn was in better shape than previous missions
with which I was involved," Russell said earlier. "At a minimum, we are
'in family' with the other missions in terms of open paperwork, schedule
delays, and technical issues."

As recently as four weeks ago, Russell still held out hope that Dawn
would be cleared to proceed toward launch.

The Discovery program is currently accepting new proposals for a new
mission that must launch by 2013 with costs under $425 million. Next in
line for the program is the Kepler mission that will seek Earth-size
planets around nearby stars in the Milky Way galaxy. Its launch is
scheduled for June 2008.
Received on Sun 05 Mar 2006 11:35:17 PM PST