| Popis: |
CloudSat, now in its 13th year on orbit, has employed various strategies over its lifetime to compensate for a weakened battery and the loss of a reaction wheel. The creative efforts required to keep the mission going have been documented in a number of earlier papers [1]–[4]. This paper focuses on a prospective change in on-orbit operations which will help maintain or reduce the current loads on the battery in eclipse and enhance mission longevity. Keeping the battery healthy drives many of the operational modes on the SC (spacecraft) and seasonal operational adjustments have often been required in the past. In the normal mode of operation, called DO-Op (Daylight only Operations), science data is collected only during the daylight portion of the orbit and then the spacecraft goes into a spin stabilized, low power, hibernate mode in eclipse. To implement DO-Op, the spacecraft exits umbra spinning with the +X axis pointed at the sun. Then, after capturing attitude control, the spacecraft performs an approximately 180 deg yaw around the boresight of the CPR (Cloud Profiling Radar) so that at umbra entry the +X axis is again pointed at the sun. The spin rate in eclipse is high enough to maintain the orientation of the +X axis but low enough and properly timed to simplify capture at umbra exit. The largest load in umbra is the thermostatically controlled CPR Stability Heater. As the vehicle has aged, there has been a yearly trend towards increased CPR stability heater on-time which has reduced already critical power margin. The on-time of the CPR stability heater varies during the year and in the summer season the heater, which is not manually controllable, turns on longer resulting in the minimum power margin. The concern was that, if this trend continued, coupled with loss of capacity as the battery ages, it would be necessary to suspend science data collection for longer and longer periods in the summer. Reducing loads in eclipse would, of course, maintain the science collection and ultimately increase the mission's lifetime. A new operational mode called Hip-Hop (Hi Power Amplifier Heater Operation) has been developed which accomplishes this goal. In Hip-Hop a carefully timed sequence of SC attitudes exposes the CPR -X radiator to the Sun while simultaneously maintaining uninterrupted science operation. On-orbit tests have confirmed that this mode significantly reduces the heater on time. This paper will discuss the design of Hip-Hop, illustrating the ADCS impacts, and the predicted thermal and power usage improvements. Detailed software test bench runs will be discussed, as will results from on-orbit testing. |
