[meteorite-list] Cassini Set to Ring Saturn Today

From: Ron Baalke <baalke_at_meteoritecentral.com>
Date: Wed Jun 30 16:39:28 2004
Message-ID: <200406302039.NAA13145_at_zagami.jpl.nasa.gov>

MEDIA RELATIONS OFFICE
JET PROPULSION LABORATORY
CALIFORNIA INSTITUTE OF TECHNOLOGY
NATIONAL AERONAUTICS AND SPACE ADMINISTRATION
PASADENA, CALIFORNIA 91109. TELEPHONE (818) 354-5011
http://jpl.convio.net/site/R?i=h8gLqhEOIJ5O-3BCLCXxIg..

Donald Savage (202) 358-1727
NASA Headquarters, Washington

Carolina Martinez (818) 354-9382
Jet Propulsion Laboratory, Pasadena, Calif.

NEWS RELEASE: 2004-167 June 30, 2004

Cassini Set to Ring Saturn Today

After nearly seven years of asking, "Are we there yet?" the
Cassini-Huygens mission is poised to enter Saturn's orbit
this evening.

"Getting into orbit means we have a mission. If we don't
get into orbit then we have a flyby and that's not what we
are here to do," said Dr. Dennis Matson, project scientist
for the Cassini-Huygens mission at NASA's Jet Propulsion
Laboratory, Pasadena, Calif. "We are confident that the
Cassini team will get us there."

Although everything on the spacecraft is performing well,
mission managers caution that this is not a slam-dunk by
any means. There are risks as with any mission. One of
those risks is the ring plane crossing. Although this
area has been mapped extensively and is believed to be safe,
there is still a risk of an impact to the spacecraft.

"There are three hold-your-breath moments for the mission,"
said Robert T. Mitchell, program manager for the
Cassini-Huygens mission at JPL. "The first is when we see
the signal coming back after we cross the ring plane in the
ascending direction. The second is an indication that the
burn has begun at 7:36 p.m. Pacific time (10:36 p.m. EDT).
And finally, the signal showing the burn completion at the
right time."

Another concern is weather that may affect the reception of
the signal on Earth. Weather on Earth will not change the
outcome of the mission but it will impact whether or not
mission controllers will receive a signal during the orbit
insertion. Current weather predictions at the Canberra,
Australia, station of the Deep Space Network show possible
high winds that could effect this evening's operation of
that antenna.
  
This evening at 7:11 p.m. PDT (10:11 p.m. EDT), Cassini
will cross the ring plane between Saturn's F and G rings.
Its antenna will be oriented forward and act as a shield
against small particles. At 7:36 p.m. PDT (10:36 p.m. EDT),
the spacecraft will begin a critical 96-minute main engine
burn. Once the burn is complete the spacecraft will turn
and send a signal back to Earth to report how it is doing.
Then it will point its cameras and other instruments at the
rings.

"Orbit insertion is sort of like applying your brakes while
driving your car downhill," said Mitchell. "Although
you've got your foot on the brakes, you still pick up
speed as a steep gravity pulls you in."

During the burn, the spacecraft will change its velocity
by 626 meters per second (1,400 miles per hour). Relative
to Saturn, at burn start the spacecraft speed is 24.26
kilometers per second (54,270 miles per hour) and at the
end of the burn the speed is 30.53 kilometers per second
(68,293 miles per hour). Mission managers expect
periodic interruptions of the Doppler signal as Cassini
passes behind the rings.

The team that got the spacecraft to Saturn may be one of
the most seasoned teams to work on a large mission like
Cassini, mostly due to the fact they have flown the
spacecraft for seven years. "We've had nearly seven
years to iron out the wrinkles," said Julie Webster,
spacecraft team chief at JPL. "We are ready. In many
ways, the most exciting part of the journey is about to
begin because we don't know what lies ahead."

"We've been driving this bus for nearly 3.5 billion
kilometers (2.2 billion miles)," said Dr. Jeremy Jones,
navigation team chief of the Cassini-Huygens mission at
JPL. "The trip has sort of been like a long car drive,
and we can't wait to get out there and explore the sites.
In a sense the tour is just beginning."

The arrival period provides a unique opportunity for
scientists to observe Saturn's rings and the planet
itself. The spacecraft's closest approach to Saturn
during the entire mission is at 9:03 p.m. PDT. Its
distance from the center of Saturn will be 80,230
kilometers (49,850 miles) and 19,980 kilometers
(12,400 miles) from the cloud tops.

The Cassini-Huygens mission is a cooperative project
of NASA, the European Space Agency and the Italian Space
Agency. The Jet Propulsion Laboratory, a division of the
California Institute of Technology in Pasadena, manages
the Cassini-Huygens mission for NASA's Office of Space
Science, Washington, D.C. JPL designed, developed and
assembled the Cassini orbiter.

For the latest images and more information about the
Cassini-Huygens mission, visit

http://saturn.jpl.nasa.gov

and

http://www.nasa.gov/cassini .

-end-
Received on Wed 30 Jun 2004 04:39:09 PM PDT