Scanning the Earth's Limb from a High-Altitude Balloon: The Development and Flight of a New Balloon-Based Pointing System

The development and first flight of a new balloon-borne pointing system is discussed. The system is capable of pointing a platform of optical instruments at an inertial target from a pendulating platform suspended below a high-altitude balloon. It operates in both a traditional occultation-scan mode, to observe solar absorption, and a limb-scan mode, to make measurements of Earth's limb. The system employs integrated sensors and high-level icon-based software (Labview). A microprocessor controller derives real-time estimates of gondola attitude, employing an extended Kalman filter to combine gyro, magnetometer, tilt-sensor, and shaft-encoder information. These estimates are used to develop control demands that point a platform of instruments in elevation and azimuth. The system's first flight was from Vanscoy, Saskatchewan, Canada, on 29 August 2000. Results of the system's performance during this mission are presented. In flight, the system demonstrated a pointing accuracy better than 0.1° (1σ) in elevation and 3° (1σ) in azimuth.