[meteorite-list] Dawn Asteroid Probe Won't Launch Until September

From: Ron Baalke <baalke_at_meteoritecentral.com>
Date: Mon, 9 Jul 2007 09:05:04 -0700 (PDT)
Message-ID: <200707091605.JAA07524_at_zagami.jpl.nasa.gov>

http://www.spaceflightnow.com/delta/d325/070707delay.html

Dawn asteroid probe won't launch until September
BY JUSTIN RAY
SPACEFLIGHT NOW
July 7, 2007

The scientist leading NASA's Dawn spacecraft on a three-billion-mile
reconnaissance mission to explore a massive asteroid and a "dwarf
planet" believed to harbor water has been designing the project for more
than a decade. Liftoff was supposed to happen this weekend, yet troubles
interfered. And officials Saturday ordered another launch delay -- all
the way to September.

Chris Russell, professor of geophysics and space physics at the UCLA,
first proposed the mission in 1994. He's been waiting a long time to see
the robotic probe, powered by exotic ion thrusters, travel into the
asteroid belt where it will orbit the rocky body Vesta, then venture out
further to the small world called Ceres and also orbit that tantilizing
object.

But getting the spacecraft built and launched has been beleaguered by
setbacks.

"The spacecraft will spend much less time in space than we put in
preparing for the mission," Russell said recently. "I want to get this
spacecraft up in space, where it belongs. I'm really confident about the
spacecraft. We've been testing and retesting."

Russell's team hoped to see the instrument-laden space probe leave Earth
in the coming days. Now, everyone must wait a bit longer.

A 12-story United Launch Alliance Delta 2-Heavy rocket with Dawn nestled
inside the vehicle's nose cone was supposed to blast off from Cape
Canaveral's pad 17B on Saturday afternoon. But stormy weather prevented
the rocket's second stage from being fueled on Thursday, forcing the
liftoff to be delayed from Saturday to Sunday.

NASA decided early Friday morning to slip the launch another 24 hours -
to Monday - because of troubles with a telemetry-relay aircraft
downrange. Then a decision was made late Friday to retarget the launch
for no earlier than Sunday, July 15.

Problems with the tracking plane and delays getting a substitute ship
into the Atlantic Ocean region has been a source of headaches for the
launch officials. Either the aircraft or the instrumented ship is
required to receive telemetry from the rocket during the second and
third stage firings off the west-central coast of Africa. Without a
mobile tracking asset in place, engineers would have no insight or data
while those critical events of the launch occur.

NASA has been racing against the calendar because Dawn's current launch
opportunity closes July 19, giving just a few days left to get the
spacecraft on the required trajectory to fly past Mars for a sling-shot
maneuver and then into the asteroid belt for its rendezvous with Vesta
and Ceres over the next eight years.

Missing this launch period forces a wait until the next window, which
opens in September and extends through late October.

With the dwindling dates left to fly and the looming August 3 launch of
the Mars lander Phoenix aboard another Delta 2 rocket from the
neighboring Cape Canaveral pad, NASA management on Saturday opted to
call an end to Dawn's liftoff chances in July.

"The decision was made Saturday to move the launch to September after
careful review by NASA's Science Mission Directorate officials, working
with Dawn mission managers, the Dawn principal investigator, and with
the concurrence of the NASA Administrator," an agency spokesman said.

"Primary reasons for the move were a combination of highly limited
launch opportunities for Dawn in July and the potential impact to launch
preparations for the upcoming Phoenix Mars Lander mission, set for early
August."

The alignment of the planets dictates a tight August 3 to August 24
window for the Phoenix liftoff to happen. If the craft doesn't launch
within those three weeks, the next shot at Mars won't come until 2009.

"A September launch for Dawn maintains all of the science mission goals
a July launch would have provided," the NASA spokesman said.

An additional complicating factor for Dawn is its launcher's second
stage. A propellant blend of nitrogen tetroxide and hydrazine fuel must
be loaded into the Delta vehicle two days prior to liftoff. But the
corrosive nature of the rocket fuel limits the amount of time the stage
remains suitable for flight -- roughly 40 days -- after the propellant
is pumped aboard. Proceeding with the fueling for a launch next weekend
and then possibly experiencing weather or technical delays that pushed
the flight past the July 19 window cutoff date would have added further
problems and cost to the Dawn mission.

The start of Dawn's adventure to examine Vesta and Ceres has experienced
a number of hurdles, including outright cancellation of the project in
March 2006. After a heated controversy, NASA restarted the mission less
than a month later.

"It has been quite an emotional roller coaster," said Russell.

"There were some days I didn't think we were going to make it. But we
never kept trying."

Recent plans called for the launch to happen June 20, but that date was
scrapped because more time was needed to prepare the Delta rocket before
on-pad assembly could start. Then a targeted June 30 launch day was
doomed when the pad's crane developed a problem last month, causing a
hiatus in attaching the solid-fuel boosters.

Those slips in the launch schedule coupled with this week's weather and
tracking aircraft problems left Dawn with little of its window left
prior to the high priority Mars lander liftoff.

Dawn's ion thrusters, derived from the engine successfully demonstrated
on NASA's Deep Space 1 technology pathfinder craft, will propel the
spacecraft during its eight-year, three-billion-mile mission, reaching
Vesta in 2011 and Ceres in 2015. The spacecraft will orbit at
increasingly lower altitudes above the objects to determine the
composition, internal structure and evolutionary history of the bodies.

"I think of Dawn as two journeys," Russell said. "One is a journey into
space. This is analogous to what ancient explorers did, who knew there
was unexplored territory and wanted to discover what was there. We're
going to explore a region for the first time to find out what the
conditions are today.

"Dawn is also a journey back in time. Ceres and Vesta have been altered
much less than other bodies. The Earth is changing all the time; the
Earth hides its history, but we believe that Ceres and Vesta, formed
more than 4.6 billion years ago, have preserved their early record.
They're revealing information that was frozen into their ancient
surfaces. By looking at the surface and how it was modified by the
bombardment of meteoroids, we will get an idea of what the early
conditions of Ceres and Vesta were and how they changed. So Dawn is a
history trip too. We're going back in time to the early solar system."

Scientists suspect that Vesta is solid rock. The oval-shaped object has
an average diameter of approximately 320 miles. On the other hand, Ceres
could have water or ice beneath its rocky crust. This "baby planet" has
an average diameter of about 600 miles.

"Why do we explore the solar system? Why did Lewis and Clark go across
the U.S. at the start of the 19th century? We're not going to expand the
human race off this planet for a long time, but discovering our origins
and how the solar system evolved is valuable in itself. Mankind has
always expanded horizons. Exploration is a human imperative."

Exactly when Dawn will blast off to begin its expedition wasn't
immediately clear Saturday. NASA officials did not announce a target
launch date for September.
Received on Mon 09 Jul 2007 12:05:04 PM PDT