Dawn Journal - March 30, 2008
- From: baalke@xxxxxxxxxxxxx
- Date: Fri, 4 Apr 2008 16:57:12 -0700 (PDT)
http://dawn.jpl.nasa.gov/mission/journal_3_30_08.asp
Dawn Journal
Dr. Marc Rayman
March 30, 2008
Dear Heliodawns,
Dawn is as far from Earth as the Sun. (That seemed a better opening
sentence than the next sentence. If you, loyal reader, disagree,
please
read the next one first.) The Dawn mission is continuing very
smoothly,
with the spacecraft spending almost all of the time since the last log
thrusting with its ion propulsion system.
As the probe and Earth follow their independent orbits around the Sun,
not only has their separation grown, but the relative velocity
has as well. So, the rate at which the range
from the spacecraft to its erstwhile planetary residence increases has
itself increased since the previous report. Today the distance is
climbing by nearly 1.6 million kilometers (almost 970 thousand miles),
or more than 5 light seconds, per day.
Now, 6 months after launch, the separation between Earth and Dawn has
widened to be equal to the distance between Earth and the Sun. Most
readers, particularly those living elsewhere, recognize that the
distance between these latter two solar system bodies, about 150
million
kilometers (93 million miles) and known to astronomers as 1
astronomical
unit, is arbitrary. Still, using the Earth-Sun distance as a reference
may help put the spacecraft's travel into context, and astronomical
units are no more arbitrary than kilometers, miles, or the length
scales
in common use on over 85% of planets subscribing to these logs.
That Dawn is as far from Earth as the Sun does not reveal anything, of
course, about its direction as viewed from Earth. The Sun and Dawn are
98 degrees apart; Dawn is nearly overhead when the Sun sets. Although
the spacecraft is much much too far from Earth to be visible, even
with
the most powerful telescopes, readers who find enjoyment, if not
inspiration for rich thoughts, in celestial sights may consider gazing
in the direction of the emissary Earth dispatched to the cosmos. The
craft is in Gemini, about 8 degrees east of Mars, an easily located
ruby
among the gems of the night sky. Your correspondent (reporting on
location from Earth) plans to contemplate his view of the Sun during
the
day and the sky near Dawn in the evening.
The spacecraft's reliable performance has allowed the operations team
to
devote time to more than ensuring the spacecraft stays healthy and on
course. In addition to an occasional moment of waxing philosophical
about another of humankind's robotic marvels being so remote, the team
has been preparing for some special activities during the first part
of
April. Readers not obeying rules of causality already know the
outcome,
but the rest may look forward to learning the story in the next log.
Dawn is 150 million kilometers (93 million miles) from Earth, or 390
times as far as the moon and as far as the Sun. Radio signals,
traveling
at the universal limit of the speed of light, take almost 17 minutes
to
make the round trip.
Dr. Marc D. Rayman
8:00 am PDT March 30, 2008
P.S. This log is short, so it would qualify for entry in the highly
competitive "Best Dawn Log Fewer than 500 Words Written by a Mortal
Corporeal Entity" contest. Unfortunately, this postscript causes it to
exceed the length limit. That's particularly disappointing, as the
first
place prize is a small galaxy.
.
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