NASA’s Deep Impact project, led by University of
Maryland Professor Michael A’Hearn, has passed another milestone on
its road toward a January 2004 launch and a July 2005 encounter with
a speeding comet.

The Deep Impact project, which will be the first mission to punch a
spectacular football field-sized crater seven stories deep into a
comet, successfully completed a three-day critical design review
last week. After examining details of the mission, three independent
review boards concluded that there are no significant flaws in the
design and that the project can proceed with building and testing
the project’s two spacecraft.

"This was a major step for us in ensuring both ourselves and NASA
that our designs are solid and reliable," said A’Hearn, who directs
the mission as principal investigator. "It is truly exciting to see
the first pieces of hardware beginning to arrive at Ball Aerospace
and to realize that we are well on our way."

Comet Science

The Deep Impact mission is the eighth mission in NASA’s Discovery
Program and the third targeted at a comet. The Stardust mission,
which is currently en route to comet Wild 2, will bring back a
sample of dust from the comet’s atmosphere to study in Earth-based
laboratories. The CONTOUR mission, which is scheduled to launch
in July of this year, will fly past at least two comets of very
different histories to understand the evolutionary differences on
their surfaces. Deep Impact will intercept comet Tempel 1 in July
of 2005. Its flyby spacecraft will release a 770-pound impactor
that will excavate a large crater in the comet’s nucleus, thus
allowing both the flyby spacecraft and Earth-based observers to
study the differences between the surface material and the interior
of the cometary nucleus and to determine key physical properties of
the outer tens of meters of the nucleus.

Comets are essentially giant dirty snowballs orbiting the sun. They
are thought to preserve, particularly in their ices, a unique record
of conditions in the early solar system when the planets were being
formed. Previous passages near the sun by Tempel 1, the target comet
for the Deep Impact mission, have led to significant evolutionary
changes in the outer layers of the comet’s nucleus. However, the
nature of this evolution is not understood. Even basic properties,
such as mass and density, have never been measured for any cometary
nucleus. Deep Impact should allow determination of the density of
the surface layers, although no currently planned mission is intended
to determine the mass and overall density of any comet until the
European Rosetta mission arrives at comet Wirtanen in 2011. Deep
Impact will provide the first data probing below the very surface of
a cometary nucleus.

Countdown to Deep Impact

The mission launches in January 2004 and orbits the sun for one year,
passing again very close to Earth in January 2005. At the Earth flyby,
the instruments are tested and calibrated and the spacecraft pair is
diverted to comet Tempel 1, arriving in July 2005. On July 3, 2005,
the impactor is released from the flyby spacecraft and takes over its
own operation, aiming for an impact at 10 kilometers/second on
July 4, 2005. Meanwhile, the flyby spacecraft slows down by 100
meters/second and diverts to watch the impact happen and fly past the
nucleus at a distance of 500 kilometers (310 miles), 14 minutes after
the impact.

The impactor, which is a fully functional spacecraft, will take
pictures of the nucleus with ever-increasing resolution as it closes
with the comet. These pictures are for scientific purposes and for
automatic navigation to ensure an impact. The camera is intended to
provide the highest resolution pictures of the cometary surface ever
taken, providing unique information about the surface that will give
clues to its formation and evolution. The flyby spacecraft has two
cameras and an infrared spectrometer to observe the formation process
of the crater and the final crater. The measurements are intended to
tell scientists about the composition of the interior and the surface
and, by observing the crater’s formation process, determine the
physical properties of the nucleus. The size of the final crater
and the length of time it takes to form are key measurements, since
these are controlled by the physical properties of the cometary
nucleus, properties that are now totally unknown.

The Deep Impact Team

A partnership among the University of Maryland, the Jet Propulsion
Laboratory (JPL), and Ball Aerospace & Technologies Corp., is
carrying out the Deep Impact mission. The university, through
Principal Investigator Michael A’Hearn, is responsible for the
entire mission and directly manages the scientific effort, the
education and outreach effort, and the development of the
instruments on the spacecraft. The science team includes a dozen
scientists from the United States and Germany working with several
additional supporting scientists. The Jet Propulsion Laboratory,
through Project Manager Brian Muirhead, provides the overall
project management, provides selected items of hardware and
portions of the software, and carries out the in-flight operations.
Ball Aerospace & Technologies Corp., under the direction of Deputy
Project Manager John Marriott, is building both the two spacecraft
and all the instruments.

The Discovery Program

NASA’s Discovery Program consists of a series of cost-capped,
competitively selected missions proposed by individual scientists
and their chosen teams. Using the results of peer reviews by both
scientists and engineers, NASA has typically selected one or two
new missions every two years. Deep Impact was selected from a
proposal submitted in 1998. The total budget for Deep Impact is
capped at $279 million in real-year dollars ($240 million in FY99
dollars before adjustment for inflation). This includes all launch
costs, communications and operations during flight, delivery of the
calibrated data to the scientific community, and education and public
outreach activities.

NASA Reviews

The Critical Design Review is, for all NASA’s missions, the point at
which NASA gives approval to the detailed design and authorizes the
project to complete the building of all the hardware and preparing
it for launch. For this mission, the CDR had three separate review
boards. The Deep Impact project has its own standing review board of
personnel from outside the project, who follow the project closely.
JPL’s System Management Office appointed a review board to ensure
that JPL management is aware of all aspects of the mission. NASA
appointed an Independent Assessment Team to provide an independent
assessment of mission readiness at this stage of development. All
three review boards found that the Deep Impact system design is
mature and the project is fully ready to start the spacecraft and
science instrument fabrication, assembly, integration and test

The next major review of the system will be in February 2003. Known
as the integration and test readiness review, it is conducted prior
to shipping the Deep Impact spacecraft to Cape Canaveral for
integration into the launch vehicle.

Note to editors: digital images of initial components of the Deep
Impact spacecraft are available on the web at or