The Cassini-Huygens Program is an international science mission to the Saturnian system. Three space agencies and seventeen nations contributed to building the Cassini spacecraft and Huygens probe. The Cassini orbiter is managed and operated by NASA's Jet Propulsion Laboratory. The Huygens probe was built and operated by the European Space Agency. The mission design for Cassini-Huygens calls for a four-year orbital survey of Saturn, its rings, magnetosphere, and satellites, and the descent into Titan's atmosphere of the Huygens probe. The Cassini orbiter tour consists of 76 orbits around Saturn with 45 close Titan flybys and 8 targeted icy satellite flybys. The Cassini orbiter spacecraft carries twelve scientific instruments that are performing a wide range of observations on a multitude of designated targets. The Huygens probe carried six additional instruments that provided in-situ sampling of the atmosphere and surface of Titan. The multinational nature of this mission poses significant challenges in the area of flight operations. This paper will provide an overview of the mission, spacecraft, organization and flight operations environment used for the Cassini-Huygens Mission. It will address the operational complexities of the spacecraft and the science instruments and the approach used by Cassini-Huygens to address these issues. I. The Mission Saturn has fascinated observers for over 300 years. The only planet whose rings were visible from Earth with primitive telescopes, it was not until the age of robotic spacecraft that questions about the Saturnian system's composition could be answered. Previous robotic spacecraft encounters with Saturn were the flybys of Pioneer 11 in 1979, Voyager 1 in 1980, and Voyager 2 in 1981. Plans for a dedicated Saturn orbiter were begun in 1982 and became the Cassini-Huygens mission. Launched from Cape Canveral on October 15, 1997, the Cassini-Huygens spacecraft reached the Saturnian region in July 2004. After a seven-year, 2-billion mile voyage that included four gravity-assist planetary flybys, the Cassini orbiter entered Saturn's domain and began a four-year mission featuring 76 orbits around the ringed planet and its moons and deployment of the Huygens probe into Titan's atmosphere. The main scientific goals include measuring Saturn's huge magnetosphere, analyzing, from up close, the stunning ring system, studying Saturn's composition and atmosphere, as well as detailed, targeted observation campaigns of Titan and the other large satellites. The design of the Cassini primary mission involved trades between competing objectives. Science objectives at Saturn include investigations into atmospheric properties and composition, internal structure and rotation, and the ionosphere. The rings of Saturn are being observed for structure and composition, dynamical processes, interrelation between the rings and satellites, and the dust/micrometeoroid environment. The magnetosphere of Saturn is to be investigated for its dynamical configuration, particle composition, sources, and inter...

The Cassini Solstice Mission (CSM) is the second extended mission phase of the highly successful Cassini/Huygens mission to Saturn. Conducted at a much-reduced funding level, operations for the CSM have been streamlined and simplified significantly. Integration of the science timeline, which involves allocating observation time in a balanced manner to each of the five different science disciplines (with representatives from the twelve different science instruments), has long been a labor-intensive endeavor. Lessons learned from the prime mission (2004-2008) and first extended mission (Equinox mission, 2008-2010) were utilized to design a new process involving PIEs (Pre-Integrated Events) to ensure the highest priority observations for each discipline could be accomplished despite reduced work force and overall simplification of processes. Discipline-level PIE lists were managed by the Science Planning team and graphically mapped to aid timeline deconfliction meetings prior to assigning discrete segments of time to the various disciplines. Periapse segments are generally discipline-focused, with the exception of a handful of PIEs. In addition to all PIEs being documented in a spreadsheet, allocated out-of-discipline PIEs were entered into the Cassini Information Management System (CIMS) well in advance of timeline integration. The disciplines were then free to work the rest of the timeline internally, without the need for frequent interaction, debate, and negotiation with representatives from other disciplines. As a result, the number of integration meetings has been cut back extensively, freeing up workforce. The sequence implementation process was streamlined as well, combining two previous processes (and teams) into one. The new Sequence Implementation Process (SIP) schedules 22 weeks to build each 10-week-long sequence, and only 3 sequence processes overlap. This differs significantly from prime mission during which 5-week-long sequences were built in 24 weeks, with 6 overlapping processes.

No abstract

After a 14-year odyssey, the historic Galileo mission to Jupiter ended on September 21, 2003 when the spacecraft entered the atmosphere of the giant planet it had studied for almost seven and a half years. The planned destruction of the orbiter was necessary to satisfy planetary protection concerns about Europa, a prime target in the search for extraterrestrial life. Almost 11 months earlier, on November 5 , 2002, the spacecraft flew to within 71,500 km of Jupiter's cloud-tops, sampling the inner magnetosphere and the Gossamer ring. The trajectory allowed Galileo to obtain the first density estimate of Amalthea, a small inner moon. This encounter presented challenges both in preparing for this risky flyby and in recovering from this traverse deep within the radiation belts. By limiting the observations to two primary experiments, radio science and fields and particles, the flight team was able to simplify sequence design and facilitate a robust strategy to continue data acquisition in the event of an anomaly. Based on previous experience, changes were made to onboard fault protection routines to either facilitate recovery or keep Galileo from entering safe mode (and subsequently canceling the science command sequence). Not unexpectedly, two new types of hardware problems were manifested during this perijove passage. About 16 minutes after Amalthea closest approach, the extreme radiation levels caused erratic behavior in the Command and Data Subsystem phase lock loops. This resulted in multiple swaps of the timing chains and entry into spacecraft safe mode. An autonomous science recovery sequence designed to continue recording fields and particles data was initiated but did not run to completion because of the specific type of hardware anomaly. This problem was resolved as Galileo moved outside the region of highest radiation levels. The second problem occurred when high-energy protons were encountered with sufficient flux to case significant displacement damage in optical electronic circuits responsible for control of the tape recorder drive mechanism. The resolution of this anomaly is discussed in Section 3.2. Designed to withstand 150 krad inside a 2.2 g/cm2 shell, the spacecraft is remarkably healthy after sustaining over 650 krad but is showing the effects of both age and radiation. Radiation effects include damage to electronic parts in the attitude control subsystem, the computer memory, the tape recorder and some science instruments. Software patches and modified operating strategies were implemented to work around most of the radiation effects. A summary of spacecraft performance in the harsh jovian environment and a report of final subsystem and instrument status are provided.

The Cassini orbiter is an international science mission to the Saturnian system with 12 science instruments onboard. The Cassini spacecraft lacks a scan platform, which means the entire spacecraft must be rotated to control pointing of any one instrument's boresight. The resulting complex sequences of commands are built beginning many months before execution onboard. Late ephemeris updates from improved navigation data (i.e. after an orbital trim maneuver) often result in pointing commands in the sequence no longer being accurate enough to obtain the desired science observation. This paper will provide an overview of how Cassini uses live updates to address this potential loss of data, including the software developed for this process.