July 03, 2005
One hundred and seventy-one days into its 172-day journey to
comet Tempel 1, NASA's Deep Impact spacecraft successfully
released its impactor at 11:07 p.m. Saturday, Pacific Daylight
Time (2:07 a.m. Sunday, Eastern Daylight Time).
At release, the impactor was about 880,000 kilometers (547,000 miles)
away from its quarry. The separation of flyby spacecraft
and the washing-machine-sized, copper-fortified impactor
is one in a series of important mission milestones that
will cap off with a planned encounter with the comet at
10:52 p.m. Sunday, PDT (1:52 a.m. on July 4, EDT).
Six hours prior to impactor release, the Deep Impact spacecraft
successfully performed its fourth trajectory correction maneuver.
The 30-second burn changed the spacecraft's velocity by about one
kilometer per hour (less than one mile per hour). The goal of the
burn is to place the impactor as close as possible to the direct
path of onrushing comet Tempel 1.
Soon after the trajectory maneuver was completed, the impactor
engineers began the final steps that would lead to it being ready
for free flight. The plan culminated with activation of the
impactor's batteries at 10:12 p.m., PDT (1:12 a.m. Sunday, EDT).
Deep Impact's impactor has no solar cells; the vehicle's batteries
are expected to provide all the power required for its short
day-long life.
In order to release the impactor, separation pyros fired allowing
a spring to uncoil and separate the two spacecraft at a speed of
about 35 centimeters per second (0.78 mile per hour).
With Tempel 1 closing the distance between it and impactor at about
10 kilometers (6 miles) per second, there is little time for mission
controllers to admire their work. Twelve minutes after impactor release
the flyby began a 14-minute long divert burn that slowed its velocity
relative to the impactor by 102 meters per second (227 miles per hour),
moving it out of the path of the onrushing comet nucleus and setting
the stage for a ringside seat of celestial fireworks to come less
than 24 hours later.
Deep Impact mission controllers have confirmed the impactor's S-band
antenna is talking to the flyby spacecraft. All impactor data including
the expected remarkable images of its final dive into the comet's nucleus
will be transmitted to the flyby craft -- which will then downlink them
to Deep Space Network antennas that are listening 134 million kilometers
(83 million miles) away.
While all is going as expected on the Deep Impact spacecraft the
comet itself is putting on something of a show. The 14-kilometer-long
(8.7-mile-long) comet Tempel 1 displayed another cometary outburst on
July 2 at 1:34 a.m. PDT (4:34 a.m.EDT) when a massive, short-lived blast
of ice or other particles escaped from inside the comet's nucleus and
temporarily expanded the size and reflectivity of the cloud of dust and
gas (coma) that surrounds it. The July 2 outburst is the fourth observed
in the past three weeks.
Three of the outbursts appear to have originated from the same area on
the surface of the nucleus but they do not occur every time that that
area faces the Sun.
"The comet is definitely full of surprises so far and probably has a
few more in store for us," said Deep Impact Project Manager Rick Grammier
of NASA's Jet Propulsion Laboratory, Pasadena, Calif. "None of this overly
concerns us nor has it forced us to modify our nominal mission plan."
Information and images from a camera aboard Deep Impact's impactor and
flyby spacecraft can be watched in near-real time at www.nasa.gov/deepimpact.
For additional information about Deep Impact on the Internet,
visit http://deepimpact.jpl.nasa.gov.
DC Agle (818) 393-9011
Jet Propulsion Laboratory, Pasadena, Calif.
Dolores Beasley (202) 358-1753
NASA Headquarters, Washington
Lee Tune (301) 405-4679
University of Maryland, College Park
2005-108