Attitude Determinant Subsystem

Last Update: 2003/June/24

What's ADS?

  Attitude Determination Subsystem conducts analyses of a direction and a motion of CUTE-I on orbit.Various missions, such as an astronomical observation, a meteorological observation and a satellite communication, are required the following functions:
   - One function determines a satellite's attitude using sensors ( = Attitude Determination) .
   - Another function stabilizes and orients a satellite in desired directions using actuator ( = Attitude Control ).
  In this project, we aim at acquiring the attitude determination techniques of CUTE-I.

Objectives

  The subsystem develops the following issues to measure motions of CUTE-I on orbit.
   - Selection of attitude determination sensors
   - Circuit design
   - Environment test (thermal-vacuum test, vibration test, and so on)
   - Sensor calibration
   - Operation and analysis
  The system measures and estimates the motion and attitude of CUTE-I through the development.

Sensor Configuration

CUTE-I has three kinds of sensors for determining the attitude.

Piezoelectric Vibrating Gyroscope

The sensors measure angular velocity vector of CUTE-I. CUTE-I has four gyroscope for redundancy. The following table indicates the specification of gyroscope.


Input Voltage	2.7-5.5V
Current Comsumption	5mA
Range	+-300 deg/s
Sensitivity	0.67mV/(deg/s)
Drift	+-20%
Sampling	50Hz
Operating Temp.	-5deg - +75deg
Dimension	15.5×8.0×4.3mm
Weight	1.0g
OutputData	Analog

Dual Axis Accelerometer

The accelerometers measure the centrifugal acceleration generated by rotation of CUTE-I. This data is used for comparing with the gyroscope's data. There are also four accelerometers for redundancy.The following table indicates the specification of accelerometer.


Input Voltage	3.0-5.25VV
Current Comsumption	0.6mA
Range	+-2.0G
Sensitivity	312mV/g
Drift	+-0.5%
Sampling	5kHz
Operating Temp.	-40deg - +85deg
OutputData	Analog

CMOS Sun sensor (LSS Original)

  The subsystem developed LSS original sun sensor using commercial CMOS camera.
  The sun sensor takes a picture of sun and calculates a pixel-based position of sun light on CMOS image. The sensor outputs the position data and other support data to On-Board Computer of CUTE-I.
  CUTE-I cannot transmit the image taken by CMOS Camera.
  We will describe the sun sensor more detail in sun sensor description page (under construction).

Sensor Circuit

The subsystem designed and made three kinds of circuit boards. The boards are indicated by the following images.

Sensor Board 1 (W80mm×L90mm×t10mm)

Sensor Board 1 has two gyroscopes and one dual axis accelerometer. Moreover the board has three multiplexers because it is in charge of a data relay station for thermistors which attaches various places into CUTE-I and current/voltage data of EPS.


Front		Back

Sensor Board 2 (W80mm×L60mm×t10mm)

Sensor Board 2 consists of only two gyroscopes and one dual axis accelerometer.


Front		Back

Sun Sensor Board (W70mm×L100mm×t10mm)

Sun sensor is divided into CMOS camera board and data processing board. On CMOS camera board, there is CMOS image sensor which takes a picture. The data processing circuit calculates a pixel-based position of sun light on CMOS image taken by CMOS image sensor and outputs the calculation results.
The following picture indicates a monochrome taken the CMOS camera. This picture shows a desktop PC.


Sun Sensor Board		CMOS Camera Board

CMOS Camera Image

Attitude Determination Method

We will explain a method of attitude determination of CUTE-I (under construction).

Development History

The following picture shows out development history. The system has developed since 4th quarter of 2000 and complete to develop FM board at the beginning of 2003. We transported the FM board to Russia in order to launch by Russian Rocket and are waiting for launch.

Future Plan

Future plan of the subsystem are the sophistication of the attitude determination technology and the development of attitude control technology based on experiences in the project.