[meteorite-list] Cassini Set to Ring Saturn Today

[Ron Baalke]

MEDIA RELATIONS OFFICE
JET PROPULSION LABORATORY
CALIFORNIA INSTITUTE OF TECHNOLOGY
NATIONAL AERONAUTICS AND SPACE ADMINISTRATION
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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-