A space inertial reference unit (SIRU(tm)) produced by Northrop Grumman Corporation (NYSE:NOC) has operated continuously aboard NASA’s Cassini-Huygens spacecraft, which successfully entered orbit around Saturn on June 30, seven years after being launched from Kennedy Space Center.
The company’s Navigation and Space Sensors Division produced and delivered a primary and a backup unit to JPL/NASA in 1997. The primary unit has operated continuously since launch. The SIRU(tm) is a key element in the spacecraft and provides critical information to its attitude control system, which was important to the insertion of the spacecraft into orbit around Saturn. It will also be important for the pointing of Cassini’s instruments throughout the mission.
The SIRU(tm) utilizes Northrop Grumman’s exclusive hemispherical resonator gyros (HRG). The inherent high-reliability, high-performance, radiation tolerant features of the HRG and the dual redundant features of the SIRU(tm) make this the ideal inertial reference unit for long-term space mission applications such as Cassini-Huygens.
“Although the original specifications permitted the inertial reference unit to be powered off during portions of the mission, the high reliability of the SIRU(tm) allowed our customer to keep it operating throughout the mission,” said Alexis Livanos, vice president and general manager of the Navigation and Space Sensors Division. “The unmatched reliability of the SIRU(tm) is ideally suited to the Cassini-Huygens mission.”
NASA’s mission is twofold. Cassini will orbit Saturn and its moons for four years; the Huygens probe will descend into the atmosphere of Titan, Saturn’s largest moon, later this year and land on its surface. Through the sophisticated instruments onboard, NASA scientists hope to learn more about Saturn, its rings, its magnetosphere, its principal moon Titan, as well as its other moons.
The hemispherical resonating gyro (HRG) uses a thin-walled quartz shell that is energized by an electrical field to produce an imperceptible vibration pattern within itself. This pattern is electrically sensed and used to determine the gyro’s output parameters. The vibration is so minute that it creates virtually no internal stress and fatigue effects, leading to its unmatched reliability. Northrop Grumman is the exclusive producer of the HRGs, which to date have accumulated more than 4,500,000 hours of operation in over 50 systems in space without a mission failure.
Northrop Grumman’s Navigation and Space Sensors Division, part of Northrop Grumman’s Electronic Systems sector, supplies situational-awareness products for international and domestic defense and commercial markets and offers integrated avionics, navigation and positioning systems and sensors for space and high-value platform products, navigation-grade and tactical-grade inertial systems, fiber-optic gyro systems designed to customer unique requirements, underwater fiber-optic sensors, identification friend-or-foe transponders and interrogators, cockpit displays and computers, and logistic support products and services.
