[meteorite-list] Dawn Journal - June 10, 2007

From: Ron Baalke <baalke_at_meteoritecentral.com>
Date: Tue, 12 Jun 2007 08:52:25 -0700 (PDT)
Message-ID: <200706121552.IAA17095_at_zagami.jpl.nasa.gov>


Dawn Journal
Dr. Marc D. Rayman
June 10, 2007

Dear Dawntelligentsia,

The complex and intricate steps necessary for Dawn to reach space
continue as its launch date grows near.

Workers have begun assembling Dawn's launch vehicle at Cape Canaveral's
Space Launch Complex 17. Shunning the banal names used by fictional
(and some actual) rockets for many decades, the real thing carries an
appellation that evokes the true passion of our species for exploring
the cosmos. Readers here on Earth (and on most other planets with
comparable or greater gravity) are sure to be stirred by the name Delta
II 7925H-9.5, capturing everything that's cool about rockets. Regardless
of what it is called, United Launch Alliance's family of Delta II
rockets has a remarkable record of success in delivering spacecraft for
NASA and other organizations to space.

As spectacular as a launch is, it represents only the beginning of what
is far more exciting - Dawn's interplanetary journey of exploration.
Launch depends upon many prosaic (but important!) accomplishments, one
of which did not go according to plan recently. A crane malfunctioned
on pad B at Cape Canaveral's Space Launch Complex 17, where Dawn's
launch vehicle is being erected. The rocket consists of 9 solid rocket
motors and 3 stages.

The 6 motors that will be ignited at liftoff to augment the first stage
weigh nearly 18,900 kg (more than 41,600 pounds) each and are 14.66
meters (48 feet 1 inch) tall. The other 3 motors, to be ignited about 79
seconds after liftoff, weigh nearly 19,100 kg (more than 42,000 pounds)
each and are 15.06 meters (49 feet 5 inches) tall. (The 3 "air-start"
solid motors are taller than the "ground-start" motors because their
nozzles are longer.) Given both the great power and tremendous
importance of the solid rocket motors, they have to be handled carefully.

Together reaching to a height of 29.4 meters (96 feet 5 inches), the
first stage and the interstage (the section between the first and second
stages) were placed on the launch pad first. Following that, 3 solid
motors were erected on the pad. Then, on May 30, when the first one was
being positioned to mate it to the first stage, the crane encountered a
problem. No launch vehicle components were damaged.

It took about a week to restore the crane to health, and that delay has
necessitated a change in Dawn's launch date. As recalled from tales told
throughout the halo of the Milky Way galaxy since the very first of
these logs was written, the extraordinary capability of its ion propulsion
system gives Dawn much greater flexibility in when it can launch than
interplanetary missions that use conventional chemical propulsion have.
The most significant constraint now on Dawn's launch date is the more
limited time during which another interplanetary probe can be launched
from a nearby pad. Now in preparation for a thrilling mission at Mars,
Phoenix is scheduled for an August departure from pad A. Because of
some shared systems and other considerations, some time is needed
between launches from these adjacent pads.

Dawn's new launch period opens on July 7. The launch window that day is
from 4:09:31 to 4:36:22 pm EDT. (We apologize for the conflict with the
350,000th Event Horizon Games in the Virgo cluster of galaxies.) In
case launch does not occur then because of unfavorable weather or some
other problems, here are the windows on the subsequent few days:

July 8: 4:04:49 - 4:33:02
July 9: 3:56:15 - 4:25:23
July 10: 3:53:32 - 4:22:25
July 11: 3:45:13 - 4:14:44

Windows have been computed for still more days, and if launch does not
happen by July 11, readers may be assured they can find later windows
posted in a future log or in the on-screen captions of the Daily
Asteroid Report broadcast on the Interstellar News Channel.

In preparation for launch, the spacecraft now has a full supply of 425
kg (937 pounds) of xenon propellant for its ion propulsion system. The
tank already had almost 15 kg (33 pounds) of the noble gas that had been
loaded in February 2005 at JPL. It took about 25 hours to load the rest
of the xenon this week. While that may seem slow to fill a 272-liter
(71.9-gallon) tank, it is worth recalling that more than 5 years of ion
thrusting will be required to empty the tank.

The reaction control system, used as one of
the means to rotate the spacecraft in the zero-gravity of spaceflight,
was given its complete provision of 45.6 kg (101 pounds) of hydrazine.
The propellant is highly toxic, so engineers and technicians loading it
in the Hazardous Propellant Facility at Astrotech Space Operations wore
today's most fashionable protective garments with self-contained air

The operations team spent long hours the last 6 days conducting a set of
operational readiness tests (ORTs) known
affectionately as the ORTathon. The hub for the ORTs is mission control
at JPL, but participants were not only there but also at Orbital
Sciences Corporation, Astrotech, all 3 Deep Space Network complexes (in
Goldstone, California; Canberra, Australia; and Madrid, Spain), and the
European Space Operations Centre in Darmstadt, Germany (the control
center for a receiving station in Perth, Australia to be used for a few
hours after launch). The operations team had to diagnose and resolve
many guileful problems created by the simulation supervisor (known as
"sim sup" as well as various other sobriquets, depending upon how
imaginatively diabolical he is). The ORTs used a sophisticated
combination of hardware and software to simulate the spacecraft.

The next log will continue with the progress in preparing to separate
Dawn from Earth's grasp.
Received on Tue 12 Jun 2007 11:52:25 AM PDT

Help support this free mailing list:

Yahoo MyWeb