Cassini Gets Software Upgrade To Study Jupiter On Way To Saturn

Engineers had been preparing and testing the software upgrades since shortly after Cassini's launch in October 1997. The plan from the start was to transmit upgrades to onboard computers before Cassini reaches Saturn in 2004, said Dr. Earl Maize, manager of the mission's spacecraft operations office at NASA's Jet Propulsion Laboratory, Pasadena, Calif. That plan allowed better use of time for software development without delaying the start of the long trip.

"We get the right stuff done at the right time," Maize said.

Mission leaders and scientists decided last year to add studies of Jupiter to Cassini's schedule. Cassini will be passing within about 10 million kilometers (about 6 million miles) of Jupiter in December to get a gravitational kick for reaching Saturn. By turning cameras and other instruments toward Jupiter and retrieving data from them, the mission is grabbing an opportunity for a pre-Saturn checkout of systems and operations. Science learned about Jupiter will be a bonus.

In March and April of this year, mission controllers transmitted software upgrades for the attitude and articulation control subsystem computer. Among other benefits, those changes allow extremely stable positioning of the spacecraft with gyroscope-like reaction wheels, instead of just short bursts by thruster engines. That makes sharper imaging possible.

A second batch of software upgrades was transmitted to Cassini July 28. This week, engineers are testing that software as it is loaded onto the command and data subsystem computer. It will allow simultaneous use of Cassini's two solid-state data recorders, plus other efficiencies in handling and transmitting scientific pictures and information.

Using the recent upgrades during the Jupiter flyby will provide an additional checkout of the software in advance of the Saturn tour. The studies of Jupiter are also putting mission scientists and engineers through the process of planning and

executing complex sequences of operations to share the craft's data-handling capabilities among the various instruments. The plans will be finished by Aug. 20, said Brian Paczkowski, Cassini science planning manager. Observations of Jupiter will begin in early October and last into March.

The images will be the first full-planet views of Jupiter returned from a nearby spacecraft since those taken in 1979 by two NASA Voyager missions, and Cassini has a higher-resolution imager than the Voyagers'. NASA's Galileo spacecraft, which has been orbiting Jupiter since late 1995, is too close to the planet for its camera to get a full-planet view.

"There should be some spectacular images of Jupiter, with all its rings and bands and zones and storms," said Cassini Program Manager Bob Mitchell.

Mission scientists are especially excited about the prospect for learning about interactions between the solar wind of ionized particles streaming away from the Sun and the magnetic field surrounding Jupiter. Cassini will be able to examine the solar wind approaching Jupiter while Galileo simultaneously measures changes from within the magnetic field. A few weeks later, Cassini will pass inside Jupiter's magnetic field while Galileo moves outside of it.

The Cassini spacecraft remains in excellent health after earlier flybys of Venus and Earth, and passage through the asteroid belt. It is on course to begin orbiting Saturn on July 1, 2004. That will begin four years of studying the planet, its dramatic rings, its moons, and its magnetic and radiation environment. Cassini will also deliver the European Space Agency's Huygens probe to parachute to the surface of Saturn's moon Titan on Nov. 27, 2004.

The mission is a joint endeavor of NASA, the European Space Agency and the Italian Space Agency, which provided the main antenna and some other hardware components. It is managed by the Jet Propulsion Laboratory, which is operated for NASA by the California Institute of Technology.