[meteorite-list] EPOXI Mission in Final Day Before Comet Meetup

From: Ron Baalke <baalke_at_meteoritecentral.com>
Date: Wed, 3 Nov 2010 17:27:13 -0700 (PDT)
Message-ID: <201011040027.oA40REXw014066_at_zagami.jpl.nasa.gov>

http://www.jpl.nasa.gov/news/news.cfm?release=2010-370

NASA Mission in Final Day Before Comet Meetup
Jet Propulsion Laboratory
November 03, 2010

PASADENA, CALIF. - Mission controllers at NASA's Jet Propulsion
Laboratory in Pasadena, Calif., have relayed final instructions to their
comet-bound spacecraft today, Nov. 3. The new programming will guide
NASA's EPOXI mission through its close approach with comet Hartley 2,
scheduled for tomorrow, Nov. 4, at about 7 a.m. PDT (10 a.m. EDT).

"The last 1 million kilometers are always the hardest," said Tim Larson,
EPOXI project manager from JPL. "But we've prepared thoroughly for this
day and are confident that come tomorrow morning, we'll be getting the
kind of data and imagery that will keep our scientists busy for months
to come."

Today at 7 a.m. PDT (10 a.m. EDT), NASA's EPOXI mission was about
1,064,900 kilometers (661,700 miles) from Hartley 2 and closing at a
rate of 12.3 kilometers (7.6 miles) per second. Tomorrow at the same
time, the spacecraft will be at its closest approach distance to the
comet -- approximately 700 kilometers (435 miles) away from its nucleus.
All the while, the spacecraft's two imagers and one infrared instrument
will be acquiring data.

"We are really looking forward to this because the comet has shown so
many surprises, both in the data from EPOXI and the data from our many
collaborators, over the last several months," said EPOXI principal
investigator Mike A'Hearn from the University of Maryland, College Park."

When the EPOXI mission spacecraft is 18 hours and 798 thousand
kilometers (496 thousand miles) away, it will lock its instruments on
the comet and begin its encounter phase data collection. As the
distances between man-made machine and mysterious space dirtball closes,
the frequency of image-taking will increase, reaching a crescendo in the
minutes surrounding approach. All data collected during encounter phase
will be loaded into spacecraft memory for later playback.

If all goes as planned, about 50 minutes before closest approach, the
spacecraft's onboard autopilot - AutoNav Mode - is expected to go
active. When in AutoNav Mode, the spacecraft receives attitude
(pointing) instructions from its computer to help keep the comet's
nucleus centered in spacecraft's imagers.

"We're using AutoNav Mode because our mission control is 23 million
miles away from the spacecraft at time of encounter," said Larson. "Any
command we would send to the spacecraft would take 75 seconds to get
there. Not the kind of thing you want to do when you're talking about
hurtling past a 2.2 kilometer-wide object [1.36 miles] at 27,500 miles
per hour [about 44,256 kilometers per hour]."

AutoNav Mode works by having the spacecraft's Medium-Resolution Imager
look for the brightest light source in the sky (excluding the sun). It
then assumes that the bright light source must be the comet's nucleus
and adjusts the spacecraft's attitude accordingly to keep its imagers
centered.

"This spacecraft's AutoNav worked great during its prime mission in 2005
at comet Tempel 1," said Larson. "While that comet's shape provided one
central light source, new data from Arecibo indicate that comet Hartley
2 is more elongated and could have two unique bright spots on the ends.
If that is the case, we expect Auto Nav to make a decision on which of
the two is brightest and focus on that spot."

The EPOXI team expects to begin receiving imagery from the spacecraft
starting about 30 minutes after closest approach. The first images
received will be those that were taken when the spacecraft was 18 hours
out from its target. They will depict the comet nucleus as little more
than a point of light, with the fuzzy coma surrounding it. A few of the
close-approach images should be received on the ground one hour after
the event occurs.

"Those early images may not be the 'money shot,' but we on the science
team will prize them just as well, as they will help us further
understand the nature of comets," said A'Hearn. "And when we first see
those images surrounding closest approach, we are looking forward to yet
another type of nucleus compared to any we have seen up close thus far."

EPOXI is an extended mission that uses the already "in-flight" Deep
Impact spacecraft to explore distinct celestial targets of opportunity.
The name EPOXI itself is a combination of the names for the two extended
mission components: the extrasolar planet observations, called
Extrasolar Planet Observations and Characterization (EPOCh), and the
flyby of comet Hartley 2, called the Deep Impact Extended Investigation
(DIXI). The spacecraft has retained the name "Deep Impact."

NASA's Jet Propulsion Laboratory, Pasadena, Calif., a division of the
California Institute of Technology, manages the EPOXI mission for NASA's
Science Mission Directorate, Washington. The University of Maryland,
College Park, is home to the mission's principal investigator, Michael
A'Hearn. Drake Deming of NASA's Goddard Space Flight Center, Greenbelt,
Md., is the science lead for the mission's extrasolar planet
observations. The spacecraft was built for NASA by Ball Aerospace &
Technologies Corp., Boulder, Colo.

For more information about EPOXI visit http://www.nasa.gov/epoxi and
http://epoxi.umd.edu/.

Dwayne Brown 202-358-1726
NASA Headquarters, Washington
dwayne.c.brown at nasa.gov

DC Agle 818-393-9011
Jet Propulsion Laboratory, Pasadena, Calif.
agle at jpl.nasa.gov

Lee Tune 301-405-4679
University of Maryland, College Park
ltune at umd.edu

2010-370
Received on Wed 03 Nov 2010 08:27:13 PM PDT