Headlines

A Ringside Seat

After years of traveling through the lonely depths of space, the Cassini spacecraft finally reached its destination this summer, surviving a critical insertion into near-perfect orbit around Saturn on July 1. Since then, Cassini has been transmitting remarkable images of the planet's rings and principal moon, Titan. The success of this mission, managed for NASA by Caltech's Jet Propulsion Laboratory (JPL), has given scientists around the world a cause for celebration—including some at Aerospace, who provided technical support during various phases of the program.

For example, from approximately 1995 through launch in 1997, Aerospace and Lincoln Laboratory jointly conducted an external independent readiness review of the satellite for NASA. James Gilchrist, Aerospace cochair of the review, said it encompassed the spacecraft design, most of the instruments built by U.S. manufacturers, and the Huygens probe (sponsored by the European Space Agency). Aerospace also conducted the independent review of the Cassini ground operations.

The review lasted more than two years and began with an early independent assessment of the trajectory design, which included an Earth flyby. This trajectory held potential risk because the spacecraft carried about 33 kilograms of radioactive plutonium dioxide to power its thermal generators.

NASA/JPL

Formal risk assessment was required because of the presence of this nuclear power source onboard the spacecraft, said Sergio Guarro, director of Aerospace's Risk Planning and Assessment office. Guarro developed the risk assessment methodology to support the environmental assessment and launch approval process for the mission. Aerospace assisted with the risk assessment from early phases of the mission planning and development until launch approval. The importance of this work was recognized by NASA with a project award signed by the former administrator, Daniel Goldin.

William Ailor, director of the Aerospace Center for Orbital and Reentry Debris Studies, was chair of the Interagency Nuclear Safety Review Panel's Reentry Subpanel for the Cassini mission. Ailor's group focused on how well the material protecting the radioisotope would perform under reentry velocities approaching 20 kilometers per second—far beyond the reentry velocities from standard Earth orbits, which range closer to 7.5 kilometers per second.

Aerospace participated in launch readiness tests and the Titan IVB launch-vehicle processing and was instrumental in developing procedures to support the design, installation, and test of a modified Solid Rocket Motor Upgrade actuator. Aerospace supported integration of the payload, including special acoustic tests, thermal analysis, electromagnetic compatibility analysis, loads analysis, targeting, and software testing for the first Centaur launched on a Titan IVB.

In 1998 and 1999, at the request of JPL, Aerospace implemented a number of software enhancements to its Satellite Orbit Analysis Program (SOAP) to model the Cassini mission, said David Stodden, senior project engineer in the Software Assurance and Applications Department. Aerospace developed Cassini solid models and trajectories in 2002 and rendered them to help visualize maneuvers and scientific observation opportunities. JPL used SOAP for visualization and analysis of the June 11 Phoebe flyby, and Cassini is using it to visualize pointing and camera fields of view.

Aerospace also supported in October 2003 a review of the Saturn orbit insertion, the climax of Cassini's long journey and the crux of mission success. "These maneuvers were performed very efficiently, so it appears that the spacecraft may have sufficient propellant to conduct an extended mission beyond the planned four years," said David Bearden, Aerospace Systems Director, Jet Propulsion Laboratory Program Office. "Aerospace congratulates JPL on Cassini's successful seven-year journey to Saturn and insertion into orbit, and looks forward to the tremendous scientific return during the coming years," he said.

Satellite Sentries

Spurred by a need for greater "situational awareness" in space, the Air Force is moving ahead with development of the Space-Based Space Surveillance (SBSS) system. The Initial Operating Capability version of this system has been used to detect, track, identify, catalog, and observe man-made objects in space, day or night, in all weather conditions. The complete system will enable key warfighter decisions based on collection of data regarding military and commercial satellites in deep space and near-Earth orbits without the inherent limitations (e.g., weather, time of day, location) that affect ground systems.

"The SBSS system will provide the ability to find smaller objects, precisely fix and track their location, and characterize many objects in a very timely manner," said Dave Albert, Principal Director, Space Superiority Systems, and Jack Yeatts, Future System Director. During the creation of the program, Aerospace performed key mission-assurance risk assessments for the Air Force Space and Missile Systems Center (SMC). During the technical requirements development and source selection, "Aerospace's technical evaluations led to convincing risk-mitigation actions on the launch vehicle and the focal planes," said Arthur Chin, SBSS Program Lead.

A near-term operational pathfinder, which will operate in low Earth orbit, has completed source selection and is scheduled for launch in June 2007 to significantly improve the current on-orbit capability. It will be launched by a Peacekeeper space-launch vehicle that is under SMC/Aerospace mission-assurance and launch-readiness review. The follow-on constellation will begin acquisition in 2005, with initial operational capability slated for 2012.

Navigating Europe

The United States and the European Commission signed a historic agreement covering the compatibility and interoperability of their respective satellite navigation services, the Global Positioning System and Galileo.

ESA

The "Agreement on the Promotion, Provision, and Use of Galileo and GPS Satellite-Based Navigation Systems and Related Applications" calls for the establishment of a common civil signal. As a result, civilian users will eventually enjoy more precise and reliable navigation services. At the same time, the agreement ensures that signals from Galileo (which is still in development) will not harm the navigation capabilities of U.S. and NATO military forces and equipment.

Aerospace has been working in recent years to help define U.S. position with respect to Galileo—which could have evolved to rival, not complement, GPS. For example, Aerospace investigated the potential benefits of a shared signal and common reference frame and examined alternative approaches. Aerospace also identified candidate signals for Galileo that would be compatible with current GPS signals and facilitate future interoperability.

The United States and the European Union have shared technical analyses and information needed to implement the provisions of the new agreement.

Successful Launch for GPS

A GPS Block IIR satellite was successfully launched from Cape Canaveral aboard a Delta II rocket on June 23, 2004. The unit will replace an aging satellite as part of routine constellation management.

"The launch countdown for GPS IIR-12 was the smoothest one that I had ever seen," said Wayne Goodman, General Manager, Launch Vehicle Engineering and Analysis. The mission was the 37th consecutive launch success for the Air Force Space and Missile Systems Center, he said.

The launch occurred on the fourth attempt; the first three were scrubbed because of thunderstorms. "On the second launch attempt, there was a concern that the vehicle may have been damaged by high winds," said Goodman. Analyses performed by the launch contractor and reviewed by Aerospace validated that the vehicle was undamaged, he said. Visual inspections performed by the contractor and Aerospace also did not reveal any damage to the vehicle.

This was the 51st GPS satellite launched and the 40th carried on a Delta II. It marked the second of three GPS replacement missions scheduled for 2004. The next is slated for liftoff in late September.

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