MEMS-based Gyro-Stellar Inertial Attitude Estimate For NSPO Micro-Sat Program

After successfully completing two space programs, FORMOSAT-5 (FS-5) and PORMOSAT-7 (FS-7) (FS-5 was launched on August 24, 2017, while FS-7 is waiting for launch in fall of 2018), the National Space Organization (NSPO) of the National Applied Research Laboratories (NARL) in Taiwan recently initiated the Third Phase of Space Program for next ten years. The new space program will develop a series of microsatellites (less than 250 Kg) to support future global space missions such as regional navigation/communication, tactical reconnaissance/imaging, and space weather/situation awareness. The near term space mission calls for a constellation of three LEO satellites, each carries a remote sensing device providing 1-meter image resolution in black and white and 2-meters image resolution in color. In addition to performing the primary remote sensing/scientific missions, the developed micro-satellite will also service as a space qualification and demonstration testbed/platform for many NSPO future-built critical space components such as Fiber-Optics Gyros (FOGs), mini-star tracker, reaction control subsystem, etc. Although the Attitude and Orbit Control Subsystem (AOCS) design for the micro-sat will take a heritage from the FS-5 bus, many design challenges for the AOCS hardware and software need to be addressed to satisfy the new mission requirements such as smart agility imaging capability with minimum bus size, weight, and volume constraints. One of the major departures from the heritage design would be the use of gyro-stellar (GS) inertial attitude estimate (IAE) instead of original stellar IAE as a primary attitude solution for the AOCS. With this new design architecture we also investigate the potential incorporation of the Microelectromechanical Systems (MEMS) gyro arrays in the GS IAE design. Recent advances in the construction of MEMS devices have made it possible to manufacture small and light weight inertial sensors. These advances have widened the range of possible applications in many commercial as well as military areas. However, because of its low accuracy, the devices have limited their applications to tasks requiring high-precision. In addition to the common methods focusing on the design and fabrication of the device itself, many other methods have been explored to enhance the MEMS device's accuracy performance at the component levels. Furthermore, the current research and development works on gyro performance improvement using MEMS arrays were mainly applicable for the single-axis MEMS arrays. For the three-axis MEMS gyro arrays, the current methods rely on the precision knowledge of alignments among various MEMS arrays. The purposes of this paper are: (1) to examine the AOCS subsystem level performance (IAE accuracy) using the three-axis MEMS gyro arrays in the GS IAE design; (2) to address the subsystem level performance due to array misalignments and component temperature-dependent errors; and (3) to investigate various data fusion methods to optimize the IAE performance. This paper will describe: the preliminary AOCS design for the current Micro Satellite Program, the derivations of GS IAE and the analytical method used to assess the its performance using the MEMS gyro arrays; the lab-tested MEMS gyro's performance data from Invensense MUP6000; the simulation results of various data fusion methods using a Matlab-based IAE simulation model; and our preliminary conclusions and recommendation for the micro-sat IAE design using MEMS gyro arrays.