The document provides information on the Thailand Earth Observation System (THEOS) Earth observation mission. Some key details include: - THEOS was developed by EADS Astrium for Thailand's GISTDA space agency to provide optical imagery for applications like cartography, agriculture, and disaster monitoring. - The THEOS spacecraft was launched in 2008 into a sun-synchronous orbit and carries panchromatic and multispectral cameras. - GISTDA operates the spacecraft and a ground station in Thailand to control THEOS and receive its imagery. - Cooperation agreements between GISTDA and Taiwan's NSPO space agency allow them to share ground station resources and provide backup support for each other's missions

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THEOUSThailand Earth Observation System
THAICHOTE

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Introduction
THEOS (Thailand Earth Observation System)
THEOS is an Earth observation mission of Thailand, under development at EADS Astrium SAS, Toulouse, France. In July 2004, EADS
Astrium SAS signed a contract for delivery of THEOS with GISTDA (Geo-Informatics and Space Technology Development Agency) of
Bangkok, Thailand. GISTDA is Thailand's leading national organization (i.e., space agency) in the field of space activities and applications.
The Thai Ministry of Science and Technology is funding the program.
The THEOS cooperative agreement includes the production and launch of one optical imaging satellite, as well as the development of the
ground segment necessary to operate and control the satellite directly from Thailand. The contract also specifies on-the-job training of
Thai engineers as part of the EADS Astrium development team. Also as part of the THEOS program, GISTDA earned the right to receive
data from the SPOT-2, 4 and 5 spacecraft of CNES in Thailand, which have many features similar to those of THEOS. The prime objective
of THEOS is to provide Thailand with an affordable access to space (i.e., a state-of-the-art Earth observation satellite for the near future),
and to spawn through this program's operational experience the country's own capability and infrastructure an indigenous potential for
the development of future space missions.
The science objectives call for the provision of:
1) Panchromatic (2 m) and multispectral (15 m) imagery from THEOS observations, and
2) The generation of geo-referenced image products and image processing capabilities for applications in the fields of cartography, land
use, agricultural monitoring, forestry management, coastal zone monitoring and flood risk management.
The Thai government has also expressed its intention to offer THEOS data to the disaster mitigation efforts under the International
Charter.
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Spacecraft
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Spacecraft total mass; power of solar arrays 750 kg (launch mass); 840 W (EOL)
Spacecraft size 2.1 m x 2.1 m x 2.4 m
Spacecraft stabilization Three-axis agile, accurate and stable attitude control
Spacecraft body pointing capability FOR (Field of Regard) of ±45º in roll and pitch for
event monitoring
AOCS sensors:
AOCS actuators:
- Magnetometer, sun sensor, star sensor, gyroscope,
GPS receiver
- Magnetotorquers, reaction wheels, and thrusters
S/C body-pointing capability ±45º in roll and pitch; a 30º roll increases the revisit
capability enormously, allowing an image of any area
within a 1000 km swath. 90% of the Earth may be
imaged any day with less than 50º roll.
S/C pointing accuracy, knowledge 0.12º; 0.02º
Electric power of spacecraft 840 W
Onboard data storage capacity 51 Gbit
Onboard image data compression 2.8 or 3.7 compression ratio (DCT)
RF communications - S-band for TT&C operations
- X-band for imagery transmission at 120 Mbit/s
Onboard hydrazine propulsion system Orbit corrections and maneuvers, 80 kg of hydrazine
Payload PAN and MS cameras
Optics (PAN) - Full SiC (Silicon Carbide) telescope
- Resolution of 2 m (GSD)
- FOV (Field of View): 22 km
Optics (MS) - Refractive telescope
- Resolution of 15 m
- FOV of 90 km (swath)
- 4 spectral bands in the range 0.45 - 0.9 µm
Spacecraft design life > 5 years (fueled for 7 years)

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Spacecraft
Launch: The THEOS spacecraft was launched on a Dnepr vehicle from the Yasny/Dombarovsky launch center (a town in Orenburg Oblast,
Russia, 51.0º N, 58.0º E) on October 1, 2008. The launch provider was ISC Kosmotras of Moscow, a Russian-Ukrainian joint venture
company.
Orbit: Sun-synchronous near-circular orbit, altitude = 822 km, inclination = 98.7º, period = 101.4 min, local equator crossing time at 10:00
hours on a descending node, repeat cycle = 26 days (14 5/26 orbits per day). Accessibility: 2 days with 50º tilting angle, and 5 days with
30º tilting angle.
The THEOS spacecraft mission orbit has the same repetivity (14 + 5/26) as the SPOT spacecraft, i.e. the same altitude of 822 km, but a
different mean local solar time. THEOS and SPOT satellites follow the same grid on Earth.

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Mission Status
The THEOS spacecraft and its payload are operating nominally in 2012.
• In Dec. 2011, Orbit Logic Inc. of Greenbelt, MD, USA signed a contract with GISTDA of Thailand for the delivery of a collection feasibility
solution for the THEOS imaging satellite. Under the terms of the contract Orbit Logic will host the off-the-shelf, web-based CFT
(Collection Feasibility Tool) configured for the THEOS satellite on an Orbit Logic server for exclusive use by GISTDA. An enhanced version
of CFT will be delivered to GISTDA in early 2012 for hosting on a GISTDA server for operational use by GISTDA and THEOS imagery
customers.
• The THEOS spacecraft and its payload are operating nominally in 2011.
• On December 15, 2010, an emergency orbital maneuver was conducted to avoid a close approach of space debris.
• In the period September to December 2010, THEOS provided monitoring/coverage for the 2010 Thailand Floods.
• The THEOS spacecraft and its payload are operating nominally in 2010.
The THEOS satellite project represents a significant milestone in Thailand’s space activities; it brought about a major progress in terms of
facility, infrastructure and human resources developments for the country. Developments for future THEOS global online data service
provision are underway.
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On June 1, 2009, official announcement of THEOS data service opening to domestic users. This occurred after successful in-orbit tests,
further calibration-validation for about 3 months and preparation for operational data service.
• By the end of 2008, all space segment and ground segment functions were verified. In January 2009, there was a successful in-orbit
review and the system was declared “operational”.
• The IOT (In Orbit Test) phase started on Oct. 17, 2008 consisting of two cycles of 26 days each. All specified system performances of the
spacecraft and its payload were tested, validated and calibrated in this period. In parallel, imagery of certain regions was acquired for
image calibration and validation.
• In the period Oct. 4-14, 2008, a series of orbit transfer maneuvers was conducted to raise the orbit from 680 km to the final nominal
orbit of 822 km.
• On Oct. 3, 2008, THEOS took the first set of images over Bangkok, Phuket Island and some regions outside Thailand.
• LEOP (Launch and Early Operations Phase): After the satellite was separated from the launcher and placed into the initial orbit at an
altitude of 680 km, the communications system was activated and the spacecraft came into first contact with the Kiruna ground station
of SSC (Swedish Space Corporation) in Sweden. A series of checks was conducted followed by the switch-on of several subsystems. Then
the spacecraft was commanded into normal mode; the first mission plan was uploaded on the next day, Oct. 2, 2008.

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Sensor complement
The optical instruments are composed of a panchromatic and a multispectral camera. Both instruments employ an electronic unit in
support of the following functions: gathering of video data, numerical conversion, compression, formatting, etc. Both cameras are of the
pushbroom imaging type using linear CCD arrays in the focal plane. The primary mirror and the focal plane are made of silicon carbide
(SiC) to ensure light weight and good thermo-elastic stability (alignment).
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Sensor complement
PAN Camera (Panchromatic Camera):
This instrument is providing a spectral range of 0.45 to 0.90 µm. The spatial resolution is 2 m on a swath width of 22 km.
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Sensor complement
Stereo observation scenario (image
credit: GISTDA, EADS Astrium)
Event monitoring scenario of various
targets (image credit: GISTDA, EADS
Astrium)

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Ground Segment
Ground segment:
GISTDA is the operating agency of the THEOS spacecraft. The ground segment consists of a control center at Sriracha (Chonburi Province,
Thailand), along with an S/X-band station to control and monitor the satellite from Thailand and to receive the payload imagery within its
range of coverage. The Sriracha complex is located about 100 km from Bangkok featuring two 4.5 m antennas for S-band and a 13 m
antenna for X-band data acquisition
In addition, there is a payload processing center to acquire, process, archive, and exploit the imagery. The THEOS image acquisition is
performed on user requests. The THEOS Image Ground Segment is installed at the Thailand Ground Station Compound in Lad Krabang,
Bangkok.
The THEOS ground segment consists of two parts:
• CGS (Control Ground Segment)
• IGS (Image Ground Segment)
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Ground Segment
The CGS (Control Ground Segment) consists of 4 main subsystems which are:
• MCP (Mission Planning Center)
• FDS (Flight Dynamics System)
• SCC (Satellite Control Center)
• S-band station
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Ground Segment

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Framework of cooperation
The failure of the S-band antenna due to lightning strike brought about the initiative for the Inter-operability project. For several weeks
continually, GISTDA’s engineers had to interface with SSC’s (Swedish Space Corporation) S-band system in Kiruna in order to
communicate with the THEOS spacecraft. This incident instigated a discussion to optimize the system to reduce the probability of failure
of the system. The conclusion that was arrived at was that other agencies must also be facing similar problems and that brought about
the quest to find global partners for inter-agency cooperation that would cut costs and increase resources.
On account of this incident, GISTDA got into ground segment cooperation discussions with NSPO (National Space Organization) of
Taiwan. NSPO is currently operating the FormoSat-2 mission and is in the process of developing FormoSat-5.
After the initial discussion in Taiwan in June 2010, GISTDA and NSPO started to work hand-in-hand to improve the inter-operability of
their ground stations in order to create a common pool of resources under the banner of the mutual coordination project called ICE
(Inter-Operability, Cooperation and Engineering). It turns out there are quite a few commonalities and characteristics between both
projects. By sharing the resources, both parties aim to learn from each other and increase the knowledge pool of its employees.
In the fall of 2010, an agreement for long-standing cooperative relations between GISTDA and NSPO, was signed. It covers cross-support
in the following areas:
• Satellite system health review
• Ground station support including Bi-directional TT&C services
• Satellite performance enhancement
• Satellite system life extension
• Mission operations and Ground Data Systems services.
The agreement means GISTDA and NSPO can provide each other network support and space operations services more quickly; this is
considered as very significant. The sharing of resources is a sensible and efficient way to achieve enhanced space science value in an era
of tight budgets; particularly, the bi-directional sharing of TT&C services will enhance effectiveness and reduce risk for both agencies.
This cooperation will benefit both parties by providing back-up in case a mission's ground station is not available due to maintenance,
weather or disasters, by ensuring additional station support during critical mission phases and by expanding station resources.
The real-time network communications is provided through secure communication channel via VPN (Virtual Private Network) that links
the SCC (Satellite Control Center) of GISTDA to the RTS (Remote Terminal System) of NSPO and the SOCC (Satellite Operation and Control
Center) of NSPO to the SBS (S-band Subsystem) of GISTDA
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Framework of cooperation
The satellite control systems and antenna systems support end-to-end data security when using the communications services. Security
implementation includes IP address authentication, confidentiality of socket port numbers, IPSec encryption, tunnel encryption and
physical access control to the mission systems. Communication via the VPN may take place in real-time or non real-time.
On February 9, 2011, the GISTDA operations team completed the first successful operation of the FormoSat-2 satellite through the
GISTDA antenna subsystem. Just one day later, on February 10, 2011, the first successful test of operation of the THEOS spacecraft was
conducted by the NSPO operations team.
From the first successful test onwards, the aim of the project moved from just the success of each pass to reducing possible human
errors and removing system limitations. Automation processes were implemented and efforts were implemented to make the operation
through the secondary antenna station just like nominal operations support.
Future plans: The ICE project holds a considerable potential for expansion. With the success of the ICE project, GISTDA aims to extend
this project to more partners and finally, start a consortium. This cooperation sets in motion a possibility for new small Earth observation
and small scientific satellite operators to participate and gain from a group similar to the Landsat International Ground Station network.

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Reference
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