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Deep space navigation, particularly the Orbit Determination (OD) operations of Cassini at Saturn, cannot easily be automated due to the complex dynamical environment in which the spacecraft flies; however several sub-processes are automated. The Cassini OD operations are often faced with unique challenges that require more than routine procedures. The OD Team is staffed appropriately to meet the demanding schedules and allow some level of flexibility. This paper will discuss how the OD processes are developed and the seven-member OD team is scheduled to support efficient and accurate Cassini navigation operations. Also discussed will be the requirements of the radio-metric Doppler and range tracking data acquired via the Deep Space Network and the optical navigation images of the satellites to support the daily OD operations. Furthermore, the reliability of the OD solutions, which is ensured within the framework of the OD processes, will be explained.

The launch of the Cassini/Huygens mission on October 15, 1997, began a seven year journey across the solar system that culminated in the entry of the spacecraft into Saturnian orbit on June 30, 2004. Cassini/Huygens Spacecraft Navigation is the result of a complex interplay between several teams within the Cassini Project, performed on the Ground Data System. The work of Spacecraft Navigation involves rigorous requirements for accuracy and completeness carried out often under uncompromising critical time pressures. To support the Navigation function, a fault-tolerant, high-reliability/high-availability computational environment was necessary to support data processing. Configuration Management (CM) was integrated with fault-tolerant design and security engineering, according to the cornerstone principles of Confidentiality, Integrity, and Availability (CIA). Integrated with this approach are security benchmarks and validation to meet strict confidence levels. In addition, similar approaches to CM were applied in consideration of the staffing and training of the System Administration team supporting this effort. As a result, the current configuration of this computational environment incorporates a secure, modular system that provides for almost no downtime during tour operations. NomenclatureCIA = Confidentiality, Integrity, and Availability CIS = Center for Internet Security CISscan = CIS internal host security scanner CM = Configuration Management DOS = Denial of Service attack DSN = Deep Space Network DR = Disaster Recovery ECC = Emergency Control Center GDS = Ground Data System GCC = Goldstone Communications Complex HP-UX = Hewlett-Packard (Unix System V based OS) for Hewlett-Packard computers

No abstract

On October 15, 1997, the Cassini/Huygens mission began a seven year journey across the solar system that culminated in the entry of the spacecraft into Saturnian orbit on June 30, 2004, that is projected to conclude on September 15, 2017. Cassini/Huygens Spacecraft Navigation is the result of a complex interplay between several teams within the Cassini Project, performed on the Ground Data System. The work of Spacecraft Navigation involves rigorous requirements for accuracy and completeness often carried out under uncompromising critical time pressures. There was a clear need for a secure, highreliability/high-availability computational environment to support Navigation data processing. As a part of this effort, security design (based around the cornerstone principles of Confidentiality, Integrity, and Availability) was a critical element in the system architecture. It is a mistaken, albeit popular, notion that security interferes with usability, and that secure systems should be hard to use. This design sought to find the complementary intersection between security and usability, a point where maximal usability and security converged, unhindered by obtrusive security measures while still confident their work is secure. This paper examines the process used to determine the point of maximal security and usability -a "gilded cage" to protect the system users from hostile external threat, while making their experience on the system as user friendly (in terms of unobtrusive security measures) and efficient as possible. We examined system requirements, obtained user feedback, and developed a secure model for the overall system. This secure system model was then augmented to include a model of user activity and data flows. An iterative control system approach was employed to observe user action and data flow and modify the user model accordingly. The goal was to determine what unused parts of the system could be used to compromise security and disallow access to those areas.