Integration and Testing of the Lunar Reconnaissance Orbiter Attitude Control System

Prior to the successful launch of the Lunar Reconnaissance Orbiter (LRO) on June 18, 2009, the Attitude Control System (ACS) team completed numerous Integration and Testing (I&T) tests on each hardware component in ever more flight like environments. The ACS utilizes a select group of attitude sensors and actuators. This paper will chronicle the evolutionary steps taken to verify each component was constantly ready for flight as well as providing invaluable trending experience with the actual hardware. The paper will include a discussion of each ACS hardware component, lessons learned of the various stages of I&T, a discussion of the challenges that are unique to the LRO project, as well as a discussion of work for future missions to consider as part of their I&T plan. LRO ACS sensors and actuators were carefully installed, tested, and maintained over the 18 month I&T and prelaunch timeline. The use of new Coarse Sun Sensors (CSS) stimulators provided the means of testing each CSS sensor independently, in ambient and vacuum conditions as well as over a wide range of temperatures. Optical ground support equipment was designed and used often to check the performance of the star trackers throughout I&T in ambient and thermal/vacuum conditions. This paper will review how each time the spacecraft was at a new location and orientation, the gyro was checked for data output validity. A review of reaction wheel testing is discussed. The paper also includes further discussion on the testing of the Propulsion Deployment Electronics (PDE). The PDE controls the use of Non Explosive Actuators (NEA) as well as NASA Standard Initiators (NSI) to open thruster isolation valves, deployment of Solar Array (SA), and High Gain Antenna (HGA). These series of tasks were successfully concluded with the ACS Phasing verification tests. Environment testing of the LRO spacecraft provided the ACS team valuable performance data, long-term trending data, and operational proficiency training with the LRO ground system. The paper describes the testing from the ACS point of view of the nominal spacecraft environmental tests. The vibration, electromagnetic interference (EMI), acoustic, shock, and thermal/vacuum testing allowed the ACS team to understand how the hardware would behave under various conditions and how their interaction with the software could be more fully understood. The environment testing also gave the ACS team time to improve the skills of using the ground system telemetry pages, hone our trouble shooting skills, and sharpen off-line analysis tools needed to provide immediate and accurate spacecraft operations during all mission phases. The paper also discusses early mission rehearsals performed during I&T. The experience taught the ACS team how to work problems together, create better off-line analysis tools, understand the key time critical events, and improve operational proficiency. Lessons learned about the overall testing philosophy and implementation are discussed in the paper. The LRO mission was given a generous amount of resources but very limited time to successfully execute the project objectives. Therefore what testing and when the tests were run (and rerun) became a contentious topic.