[meteorite-list] Dawn Journal - June 2, 2007

From: Ron Baalke <baalke_at_meteoritecentral.com>
Date: Tue, 5 Jun 2007 08:43:05 -0700 (PDT)
Message-ID: <200706051543.IAA13730_at_zagami.jpl.nasa.gov>

http://dawn.jpl.nasa.gov/mission/journal_6_07.asp

Dawn Journal
Dr. Marc D. Rayman
June 2, 2007

Dear Dawngeneers,

Dawn has been greatly enjoying its stay in the Cape Canaveral area,
literally the last place on Earth it will be. Following its arrival in
April, the spacecraft and other equipment were unpacked and verified to
be in good condition after the long drive from Washington. (Note that
"long" is a relative term. Dawn's space voyage will last cover 3.8
million times greater distance and last 3900 times longer.)

The spacecraft has not visited most of the popular sites in its
vicinity, but it still has had a very successful stay in the Sunshine
State. (Ironically, it has not been exposed to any sunshine there, but
it will be see plenty of sunshine at its next destination.)

One of the major accomplishments at Astrotech Space Operations was the
successful completion of the final set of comprehensive performance
tests (CPTs). It took about two weeks to run
these tests on the hardware and software subsystems. Following that,
comparison with the results from earlier CPTs verified that the long
series of environmental tests and work on the spacecraft did not
introduce any unexpected changes that might compromise its operation in
space.

The alignment of spacecraft components was verified and finalized,
ensuring that antennas, ion thrusters, scientific instruments, and other
devices are properly oriented.

The huge solar arrays, the largest used for any NASA interplanetary
mission, were reinstalled, and the deployment system was given one final
test. The last time the two wings, each the width of a singles tennis
court, were attached to the spacecraft was December.
Each wing consists of 5 panels, and
hinges allow the system to be folded for launch, so the spacecraft can
fit comfortably in the rocket's nose cone (known to engineers and
perhaps some otorhinolaryngologists as the "payload fairing").

The next time the arrays are opened will be when Dawn is in space, where
its 11,480 solar cells will provide the spacecraft with electrical
power. A battery will power the spacecraft from liftoff until it is able
to extend the arrays and point them at the Sun. When it does, the full
length of the spacecraft from wing tip to wing tip will be 19.7 meters
(almost 65 feet), which is greater than the distance from the pitching
mound to home plate on Earth's major league baseball fields. In response
to many inquiries we have received, we should point out that it truly is
purely coincidental that Dawn's arrays span exactly the same size as the
famously profound sculpture "Tribute to Coincidence," a popular site for
visitors to the Small Magellanic Cloud.

While some team members have been preparing the spacecraft, others have
been working with equal diligence to be ready to operate it during its
mission. Many tests have been conducted both with the spacecraft and
with simulators to verify that all systems onboard and on the ground are
ready.

Mission scenario tests (MSTs) (initiated last autumn) have continued,
with the final one on the spacecraft taking place on May 20 in a
successful simulation of launch. Others have demonstrated the
capabilities needed to diagnose and recover from problems during launch
or during interplanetary flight. Some MSTs concentrated on the methods
that could be used during the mission if it were necessary to reload
software in the central computers, the computers in the scientific
instruments, or the computers in the star trackers. Installing new
software when a probe is far from Earth has proven to be a vital
ingredient in the successes of many missions.

Dawn also passed a series of radio communications tests with MIL-71, the
facility at the nearby Kennedy Space Center that mimics all of the
essential characteristics of the much larger Deep Space Network (DSN)
stations. This work verified that Dawn's systems
are fully compatible with the DSN, which, apart from happy memories and
fond thoughts, will provide its only link with distant Earth when it is
otherwise isolated in the forbidding depths of interplanetary space.

The Dawn project also has been conducting operational readiness tests.
(These are known quite unimaginatively as ORTs; and even less cleverly,
the acronym is spoken letter by letter and not pronounced as "ort" might
sound. Our readers on icy moons of gas giants certainly will recognize a
thought-provoking concept herein, although it likely will escape readers
elsewhere.) Some ORTs have used the spacecraft and others have relied on
simulators, as the focus is less on the spacecraft and more on the team
members and the processes, procedures, software, and hardware (including
the selection of snacks in mission control -- kudos to the unofficial
but vital mission control nutrition engineer!) they will use during
operations. ORTs of launch and some of the activities that will be
conducted to check out the spacecraft during its first weeks in space
have been completed, and more are planned.

On May 28, Dawn was moved to the Hazardous Propellant Facility at
Astrotech where xenon and hydrazine will be loaded. The complex
procedures of pumping these propellants into the spacecraft tanks have
not begun yet, but relocating the spacecraft allows engineers to make
preparations.

As work here on Earth has continued to ready Dawn for its flight,
scientists took advantage of a favorable opportunity in May to study the
explorer's first destination, asteroid Vesta. During portions of 7
orbits of Earth, the Hubble Space Telescope observed Vesta, the first of
Dawn's two destinations. Even this fantastically capable observatory
cannot detect the kind of detail Dawn will find after its 4 year, 3.0
billion kilometer (1.9 billion mile) voyage to Vesta, but the data from
Hubble will aid scientists as they plan for Dawn's detailed observations.

While Dawn may get as close as 200 km (about 120 miles) to Vesta,
Earth's closest distance in many years occurred on May 31, at a range of
about 171 million kilometers (106 million miles). Vesta is the only
resident of the asteroid belt that occasionally is bright enough to see
with naked eyes, although good observing conditions are required. Visit
http://dawn.jpl.nasa.gov/feature_stories/Vesta_nightsky.asp to learn
more, including how you can spot this intriguing asteroid this month.

Reports from the near future reveal that the next log will include news
about the propellant loading and related work as well as the status of
Dawn's rocket and the plans for using it to leave the Sunshine State.
Received on Tue 05 Jun 2007 11:43:05 AM PDT