Seung-Wu Rhee

Optical Design of A Compact Imaging Spectrometer for STSAT3

A compact imaging spectrometer (COMIS) for use in the STSAT3 microsatellite is currently under development. It is scheduled to be launched into a low Sun-synchronous Earth orbit (

Time optimal attitude maneuver strategies for the agile spacecraft with reaction wheels and thrusters

{\sim}700km

KOMPSAT-2 AOCS Control Mode & Power Safe Mode Design

) by the end of 2010. COMIS was inspired by the success of CHRIS, which is a small hyperspectral imager developed for the ESA microsatellite PROBA. COMIS is designed to achieve nearly equivalent imaging capabilities of CHRIS in a smaller (65 mm diameter and 4.3 kg mass) and mechanically superior (in terms of alignment and robustness) package. Its main operational goal will be the imaging of Earths surface and atmosphere with ground sampling distances of

Slowly varying bias of magnetometer based on orbit geometry

{\sim}30m

Design Criteria and Cluster Configuration Improvement of Single Gimbal Control Moment Gyros for Satellite

at the

Development of 0.6Nm Small CMG Hardware and Performance Test

18{\sim}62

Experiments of singularity avoidance steering control laws for redundant single-gimbal control moment gyros

spectral bands (

A compact imaging spectrometer (COMIS) for the microsatellite STSAT3

4.0{\sim}1.05{\mu}m

On-orbit magnetic field correction of magnetometers and geometry-based attitude determination for small satellites

). This imaging will be used for environmental monitoring, such as the in-land water quality monitoring of Paldang Lake, which is located next to Seoul, South Korea. The optics of COMIS consists of two parts: imaging telescope and dispersing relay optics. The imaging telescope, which operates at an f-ratio of 4.6, forms an image (of Earths surface or atmosphere) onto an intermediate image plane. The dispersion relay optics disperses the image and relay it onto a CCD plane. All COMIS lenses and mirrors are spherical and are made from used silica exclusively. In addition, the optics is designed such that the optical axis of the dispersed image is parallel to the optical axis of the telescope. Previous efforts focused on manufacturing ease, alignment, assembly, testing, and improved robustness in space environments.

Radial Type Satellite Attitude Controller Design using LMI Method and Robustness Analysis

Reaction wheels and thrusters are commonly used for the satellite attitude control. Since satellites frequently need fast maneuvers, the minimum time maneuvers have been extensively studied. When the speed of attitude maneuver is restricted due to the wheel torque capacity of low level, the combinational use of wheel and thruster is considered. In this paper, minimum time optimal control performances with reaction wheels and thrusters are studied. We first identify the features of the maneuvers of the satellite with reaction wheels only. It is shown that the time-optimal maneuver for the satellite with four reaction wheels in a pyramid configuration occurs on the fashion of single axis rotation. Pseudo control logic for reaction wheels is successfully adopted for smooth and chattering-free time-optimal maneuvers. Secondly, two different thrusting logics for satellite time-optimal attitude maneuver are compared with each other: constant time-sharing thrusting logic and varying time-sharing thrusting logic. The newly suggested varying time-sharing thrusting logic is found to reduce the maneuvering time dramatically. Finally, the hybrid control with reaction wheels and thrusters are considered. The simulation results show that the simultaneous actuation of reaction wheels and thrusters with varying time-sharing logic reduces the maneuvering time enormously. Spacecraft model is KOrea Multi-Purpose SATellite (KOMPSAT) -2 which is being developed in Korea as an agile maneuvering satellite.