**2. Onboard satellite health monitoring**

In this section, knowledge of attitude determination of a satellite is given by modelling and analysis of an actual satellite attitude motion in detail. It is necessary to understand meaning

Telemetry Data Mining with SVM for Satellite Monitoring 97

REIMEI has a bias-momentum three-axis attitude control subsystem (ACS) to meet the requirements: the attitude control accuracy should be less than 0.5 degree, and the attitude determination accuracy should be less than 0.05 degree. These requirements are specified for one of the most important observation modes, the image/particle simultaneous observation mode, in which E/ISA detect particles to count their number as well as to measure their energy, while MAC captures aurora phenomena emerging at a magnetic line foot-point,

ACS inputs data from sensors such as the spin type sun sensor (SSAS), the two-dimensional sun sensor (NSAS), the star tracker (STT), the three-axis geomagnetic field aspect sensor (GAS), and three-axis fibre-optic gyroscopes (FOGs). On the other hand, ACS outputs data to actuators such as the small momentum wheel (WHL), which provides the satellite with bias momentum (0.5 Nms), and the three-axis magnetic torquers (MTQ). Figure 2 shows the

ACS can be divided into two function blocks: the attitude control and the attitude determination blocks. Since several papers have been published (Sakai et al., 2006a; Fukushima et al., 2006) dealing with the REIMEI attitude control block that refer to its algorithm, formulation, and flight results, here we will focus on the attitude determination block illustrated in Fig.3. The inputs for the attitude determination block are the angular increment angle data measured by FOG and the five star vectors measured by STT. The outputs are the attitude and the attitude rate of REIMEI, which are expressed in an inertial coordinate system. Attitude is expressed using quaternions in this paper and is propagated by the integration of an initial or current attitude quaternion using the attitude rate with respect to time. The attitude rate is also called the angular velocity. Note that the attitude rate is calculated from both FOG outputs and the FOG bias. The FOG bias is residual output when FOG is motionless in the inertial coordinate

Fig. 2. Flight models of three FOGs assembled on one aluminium plate.

An error correction procedure must be installed into the attitude determination block since there will be a modeling error or observation error in the a priori initial attitude, the attitude

**2.2 Attitude control requirements** 

flight models of FOG of REIMEI.

system.

where the aurora is energized by the particles observed.

and mechanism of estimation of characteristic parameters of hardware as health indicators of satellite systems throughout operations. To dealing with change in value of such parameters, a complete set of analytical process of attitude determination is shown. The telemetry data used in this chapter was obtained in an actual satellite operation.

#### **2.1 Aurora science small satellite REIMEI**

The Institute of Space and Astronautical Science, Japan Exploration Agency (ISAS/JAXA) has launched a series of scientific satellites including planetary spacecraft as well as astronomical observation satellites. Although the missions have achieved fruitful scientific results, these satellites, including our own M-V launch vehicle, have cost nearly 160 million dollars and taken over eight years to develop. As a result, the launch frequency of scientific satellites has decreased significantly in the last decade. In addition to these large and expensive missions with a long development time, an inexpensive mission with a short development time involving a small piggyback satellite has been planned. This satellite should be an effective tool for demonstrating new technology and performing scientific observations.

A small satellite named "REIMEI" was developed from 2000 and was launched to a height of 610 Km by the Dnepr Launching Vehicle from Baikonur Cosmodrome launch site in Kazakhstan on August 24, 2005 (Saito et al., 2005). Since then it has followed a near Sun synchronous orbit. The Japanese word "REIMEI" means dawn, and the satellite name was chosen to celebrate the new era of high-performance small satellites developed in Japan. REIMEI's mission objective is to observe dynamic aurora phenomena using the three spectrum imagers (MAC) and two particle analysers (E/ISA) installed onboard. Observations are carried out with the aim of studying the small-scale dynamics of terrestrial aurora, namely, their spatial distributions and time variations, and their correspondence to the spectral properties and spatial distributions of charged particles. Figure 1 shows the flight configuration of REIMEI. There are two solar-concentrated deployable paddles on the top surface that can generate a power of 150 W, three camera lens holes for MAC in the black-kapton-covered front surface, and E/ISA are installed covered by the silver-Teflonlined right surface.

Fig. 1. Flight configuration of REIMEI
