STANFORD UNIVERSITY
EE 350 RADIOSCIENCE SEMINAR
Professor Len Tyler
Fall 2000-2001
Date: Wednesday, December 6, 2000
Time: 4:15-5:30 PM; Refreshments at 4:00 PM
Location: Building380, Room #380Y
CASSINI RADIO SCIENCE: POTENTIAL AT SATURN
Essam Marouf
San Jose State University
Abstract
Launched in October 1997, the spacecraft Cassini receives a gravitational assist from Jupiter this month (December 2000) that will send it on its way to Saturn for an encounter in July 2004. Captured in orbit around Saturn, Cassini will "tour" the Saturn system for a period of four years (2004-2008). Observations of the Saturn system during roughly 75 orbits promise to yield the first detailed investigation of Saturn, its massive rings, its magnetosphere, and many of its satellites. In addition, 44 targeted encounters with Saturn's largest moon Titan will allow a detailed scrutiny of this enigmatic planet-size satellite. Of particular interest to this talk are the Cassini Radio Science investigations conducted using three coherent wavelengths (0.9, 3.6, and 13 cm; Ka-, X-, and S-band, respectively). The investigations follow along the footsteps of the highly successful exploratory Voyager observations of the Saturn system. Performance improvements over Voyager are expected because of some hardware improvements, but especially because of the multiple observation opportunities during the four year Cassini tour. The present selected tour is the outcome of nearly four years of intensive effort to identify among more than 25 tours considered the one that maximizes the collective science return. The selection was strongly influenced by the requirements of the Cassini Radio Science observations, as we stress in this seminar. The tour implements a highly optimized set of ring occultation observations early in the mission, as well as other less optimized set of ring occultations later in the mission. Fortunately, good ring occultations also allow good occultations of Saturn's atmosphere and ionosphere that are spread in latitude. With Titan being the gravitational engine that drives a very specific tour geometry, it has proven difficult to optimize the Titan encounter geometry to yield good Titan occultations reasonably spread in latitude. Nonetheless, several good opportunities do exist. The close flyby distance of many of the 44 Titan encounters also allow detection of bistatic radio-wave scattering by Titan's surface if quasi-specular surface scattering is the responsible physical mechanism. Presently, assignment of a particular observational opportunity at Saturn or Titan to a particular investigation is still being competitively debated among the twelve Cassini instrument teams.
About the speaker
Donald Brownlee is with the Department of Astronomy at the University of Washington (Seattle) where his primary research interest is the origin of the solar system as revealed through study of meteorites, comets and cosmic dust. As part of this work, he has devised methods for collection of dust using high-altitude aircraft. These materials, drifting downward through the atmosphere after being swept up by the Earth in its regular orbital motion, are now referred to as 'Brownlee Particles.' Professor Brownlee is Principal Investigator on NASA's Discovery Program sample return mission STARDUST, currently en route to a 2004 encounter with Comet Wild 2. He is also active in the field of astrobiology and is co-author of Rare Earth, a book dealing with the relationship of Earth's history, astrobiology, and the prevalence of intelligent life in the universe. Professor Brownlee is a member of the National Academy of Sciences and is a Fellow of the American Association for the Advancement of Science, the Meteoritical Society, and the American Geophysical Union.