[meteorite-list] Dawn Journal - May 31, 2013

From: Ron Baalke <baalke_at_meteoritecentral.com>
Date: Sat, 1 Jun 2013 20:46:55 -0700 (PDT)
Message-ID: <201306020346.r523ktqV026476_at_zagami.jpl.nasa.gov>

http://dawn.jpl.nasa.gov/mission/journal_05_31_13.asp

Dawn Journal
Dr. Marc Rayman
May 31, 2013

Dear Confidawnts,

Traveling from one alien world to another, Dawn is reliably powering its
way through the main asteroid belt with its ion propulsion system. Vesta,
the fascinating and complex protoplanet it explored in 2011 and 2012,
falls farther and farther behind as the spacecraft gently and patiently
reshapes its orbit around the sun, aiming for a 2015 rendezvous with dwarf
planet Ceres.

The stalwart adventurer has recently completed its longest uninterrupted
ion thrust period yet. As part of the campaign to conserve precious hydrazine
propellant, Dawn now suspends thrusting once every four weeks to point
its main antenna to Earth. (In contrast, spacecraft with conventional
chemical propulsion spend the vast majority of time coasting.) Because
of details of the mission operations schedule and the schedule for NASA's
Deep Space Network, the thrust durations can vary by a few days. As a
result, the spacecraft spent 31.2 days thrusting without a hiatus. This
exceeds Deep Space 1's longest sustained powered flight of 29.2 days.
While there currently are no plans to thrust for longer times, the unique
craft certainly is capable of doing so. The principal limitation is how
much data it can store on the performance of all subsystems (pressures,
temperatures, currents, voltages, valve positions, etc.) for subsequent
reporting to its terrestrial colleagues.

Thanks to the ship's dependability, the operations team has been able
to devote much of its energies recently to developing and refining the
complex plans for the exploration of Ceres. You might be among the privileged
readers who will get a preview when we begin describing the plans later
this year.

Controllers also have devised some special activities for the spacecraft
to perform in the near future, accounts of which are predicted to be in
the next two logs.

In addition, team members have had time to maintain their skills for when
the spacecraft needs more attention. Earlier this month, they conducted
an operational readiness test (ORT). One diabolical engineer carefully
configured the Dawn spacecraft simulator at JPL to behave as if a pebble
one-half of a centimeter (one-fifth of an inch) in diameter shooting through
the asteroid belt collided with the probe at well over twice the velocity
of a high-performance rifle bullet.

When the explorer entered this region of space, we discussed that it was
not as risky as residents of other parts of the solar system might assume.
Dawn does not require Han Solo's piloting skills to avoid most of the
dangerous rocky debris.

The robot could tolerate such a wound, but it would require some help
from operators to resume normal operations. This exercise presented the
spacecraft team with an opportunity to spend several days working through
the diagnosis and performing the steps necessary to continue the mission
(using some of the ship's backup systems). While the specific problem
is extremely unlikely to occur, the ORT provided valuable training for
new members of the project and served to keep others sharp.

One more benefit of the smooth operations is the time that it enables
your correspondent to write his third shortest log ever. (Feel free to
do the implied research.) Frequent readers can only hope he strives to
achieve such a gratifying feat again!

Dawn is 13 million kilometers (7.9 million miles) from Vesta and 54 million
kilometers (34 million miles) from Ceres. It is also 3.25 AU (486 million
kilometers or 302 million miles) from Earth, or 1,275 times as far as
the moon and 3.20 times as far as the sun today. Radio signals, traveling
at the universal limit of the speed of light, take 54 minutes to make
the round trip.
Received on Sat 01 Jun 2013 11:46:55 PM PDT