A17

「サンセンサと太陽電池出力による太陽角の推定 
 Sun angle determination by sun sensors and solar panels

Dmytro FAIZULLIN (Kyutech), Koju HIRAKI (Kyutech)


HORYU-IV is a nanosatellite of Kyushu Institute of Technology (KIT), which was successfully launched on February 17, 2016. Two of ten missions of the satellite, such as a camera (CAM) and a photo-electrons current measurement (PEC), required an attitude and orbit determination system (AODS). For the CAM mission AODS should give information about lightening conditions, pointing a camera to the Earth, latitude, longitude and time. For PEC mission AODS should send a logical signal when a sun sensor from the same panel as PEC elements detects the Sun within a field of view (FOV) ±15o. To do so, HORYU-IV is equipped with 6 pinhole sun sensors (one on each panel), 1 GPS receiver with 2 antennas, 2 gyro sensors. The satellite has a passive stabilization with a help of permanent magnets and a hysteresis dumper. It gives a stabilization of a satellite along of magnetic field lines. A sun vector is used as a second vector for defining satellite attitude. For this purpose sun sensors and solar panels are used. Fine sun   nsors were designed by KIT. They use COTS quadrant Si PIN photodiodes, which consist of four small photodiodes arranged very close to each other. Incident light, focused through a pinhole, produces a spot on the four diodes. Each diode’s output is a current proportional to the amount of light. Methods for calculation of a sun vector use just analog outputs from this type of sensors. This work proposes improving the mathematical model by taking into account dead spaces on the sensor between photodiodes. The FOV of the sensor is small. That is why a sun vector should be also calculated with the use of bus solar cells. But measured currents obtained by solar panels depend on satellite’s power consumptions. Their direct processing gives a low accuracy of a sun vector. In most cases it determines only panels which are lighted by the Sun. The satellite uses 2 MEMS gyros to detect attitude motions. Three parameters are used to adjust the sensor: gain, offset and temperature coefficient. Comparison between on ground  est and space downlink data showed that the sets of parameters are different. In this case the sensor needs to be onboard calibrated. This work will demonstrate 1) overview of HORYU-IV AODS subsystem, 2) design and mathematical model of a sun sensor, 3) determination of a sun vector with the use of outputs of quadrant sun sensors with a low field of view, solar panels during various power consumptions of a satellite and an uncalibrated gyro.