Dr. Suvit Vibulsresth, Waraporn Suchaichit
The National Research Council of Thailand (NRCT)
196 Phaholyothin Road, Chatuchak
Bangkok 10900, Thailand
Tel. 662-5790116 Fax. 662-5613035
In October 1994, the Ministry of Science, Technology and Environment (MOSTE) concluded a Memorandum of Understanding (MOU) with the Canadian Space Agency for cooperation in space technology and applications. An earth observation small sat mission, as the first cooperative mission under the MOU recently received the Thai Government approval. MOSTE, through its technical authority in the National Research Council of Thailand (NRCT) will own and operate the satellite system. This will be the first satellite to operate in an orbit dedicated to the equatorial regions. The first operational mission will extend the information available to both scientific and operational users and will augment data currently available from the Landsat series of spacecraft. This paper will present an overall system concept for the Smallsat Program, which will operate over its 5 years lift span.
1. System Overview
The purpose of the system is the provision of regularly updated multispectral image I data on an operational basis. Output from the system will take the form of image data products which can be distributed to users who will apply the data, either directly or after further processing, to the management of resources.
2. System Architecture
The essentilal elements of the Thai Remote Sensing Satellite System are : I. the Ground Segment .2. the Space Segment
- the Launch Segment
- the Space Segment
- the Launch Segment
2.1 System Description and Performance
2.1.1 Overall System Description
The performance parameters of the Thai Remote Sensing Satellite System are summarized in the following tables.
Table 2.1.1-1 Mission Performance
|Mission Life||5 years|
|Orbit Type||73 orbits/5 days Multi -sun-syschronous|
|Orbital Period||97 minutes|
|Orbit Inclination||28 degrees|
|Orbital Altitude||600 km|
|Coverage Repeat||Every 5 days|
|Illumination Repeat||49 days|
|Command Up link||S-Band: 2 kbps|
|Telemetry Downlink||S-Band: Direct 2/4 kbps Playback 32/128 kbps|
|Data Downlink||X-Band: < 85 Mbps|
TABLE 2.1.1-2 Temporal Performance
|Revisit Time||Twice every 5 days|
|Accessibility Region||29.60N to 29.60S|
|Maximum Imaging Capability||10 minutes/orbits|
|Useable opportunities per year||63|
Table 2.1.1-3 Spatial Performance
|Swath Width||185 km imaged swath which is selectable within a 275 km accessibility region.|
|Across Track Resolution||30 m (nadir)|
|Along Track Resolution||30 m (madir)|
|Geometric Distortion||< 1/2 pixel Band to|
|Band Registration||< 1 pixel|
|Image Locations||< 5 km|
TABLE 2.1.1-4 Spectral Performance
|Blue||0.45 to 0.52 mm+01|
|Green||0.52 to 0.60 mm+01|
|Red||0.63 to 0.69 mm+01|
|NIR||0.76 to 0.90 mm+01|
2.2 Ground Segment
The Ground Segment comprises two main system:
- the Mission Control Center (MCC) :
The role of the Mission Control Center (MCC) is to accept request for image data, plan the operations of the satellite, control, coordinate and execute the planed operations, tack end-to-end operations and monitor data quality. The MCC has the authority required for day-to-day mission operations and control, and the responsibility for ensuring that the mission objectives are satisfied. The MCC undertakes and coordinates implementation of the overall mission by monitoring, directing and controlling all mission aspects and resources.
- the Data Processing Facility (DPF)
The system is capable of processing raw satellite data, received by the X-Band Data Reception station, into high quality image products in either film or CCT formats. The products produced are geocoded and georeferenced and presented in the form of 185 km x 185 km images.
2.3 Space Segment
The Space Segment comprises a Spacecraft bus and an instrument.
- The Spacecraft Bus
The Spacecraft structure is a modular configuration comprises Bus and Propulsion modules. The Spacecraft protects against “credible” single point failures by using full redundancy, space qualified hardware, cross-strapping, and backup modes. The propulsion subsystem uses monopropellant hydrazine. The Telemetry, Tracking & Control subsystem includes a Digital Storage Unit, which may be hosted in the Integrated Avionics Processor for storage of housekeeping data and S-Band transponders for command uplink and housekeeping data downlink. The power subsystem implementation consists of a deployable, non-articulated solar ., array for primary power operating in conjunction with a nickel hydrogen (NiH2) battery for energy storage with a redundant cell. The thermal subsystem combines both passive and active elements to maintain the spacecraft temperatures within acceptance limits during normal operation, and within survival limits during emergency modes. The Attitude Determination and Control Subsystem is a zero net momentum implementation using magnetorquers and reaction wheels as actuators, and sun sensors, horizon scanners, and magnetometers as sensors. The thrusters are used to control orbit maneuvers.
The instrument mounted on the Spacecraft Bus, contains a Visible and Near Infrared (VIS/NIR) pushbroom camera. A data formatter configures the image data for relay to the ground station via the X-Band downlink
2.4 Launch Segment
The launch segment comprises the launch element, the Low Earth Orbit Phase network, and launch services.
The launch element comprises a Pegasus XL launch vehicle, an on- board monopropellant system, and the required propellant. The necessary launch support equipment for integration, handling, shipping and launch operations is also part of the element. The selected launch element meets all of the specified requirements and is consistent with the standard proven procedures of the Pegasus launch system and the Eastern Test Range.
Thai Remote Sensing Satellite System will be launched in the next few years, which will not only benefit Thailand but would also provide new opportunity for international collaboration.