Synonymous Platform Names:
LEO > Low Earth Orbit > Polar Sun-Synchronous
Related Data Sets
ROCSat-2 is an NSPO (National Space Program Office) of Taiwan Earth imaging satellite with the objective to collect high-resolution panchromatic (2 m) and multispectral (8 m) imagery for a great ... variety of applications such as in land use, agriculture and forestry, environmental monitoring, natural disaster evaluation, and in support of research interests, in particular with the ISUAL instrument. Daily image coverage of Taiwan and the surrounding region is required.
Background: A contract was signed in May 1999 between NSPO and DASA/DSS (Dornier Satelliten Systeme GmbH) of Germany to build a high-resolution optical imaging satellite. However, the German government refused to give DASA/DSS an export licence for the S/C (the People's Republic of China was protesting the deal). The stalemate was resolved in Dec. 1999 when NSPO signed a new contract with MMS (now Astrium SAS of France). Quick approval of the export of ROCSat-2 was provided by the French government. The ROCSat program is part of a long-term effort in Taiwan to develop an autonomous space capability.
Note: A public naming competition took place in Taiwan in 2004 with regard to the ROCSat satellite program. At the end of this contest, the ROCSat program was given the new name of FormoSat in December 2004. Hence, ROCSat-2 became FormoSat-2.
The spacecraft bus has been built by EADS Astrium SAS (prime contractor) of Vélizy, France, based on the Leostar 500 XO family. There were also contributions from Taiwanese industry (including satellite computers, S-band antennas, and sun sensors). The S/C structure consists basically of a hexagonal body of 1.6 m side length (diameter), 2.4 m in height. The satellite is three-axis stabilized. The upper deck of the platform carries the payload (RSI and ISUAL) and also part of AOCS (Attitude and Orbit Control Subsystem), namely the star sensors and gyroscopes. The lower deck carries the four reaction wheels and the autonomous propulsion module. The pointing accuracy is < 0.7 km (0.12º); the position knowledge is < 70 m (0.02º). The fixed solar array uses GaAs cells and consists of two deployable flaps. The entire S/C architecture is designed in such a way as to provide a low roll inertia, a key factor for satellite agility and instrument line-of-sight stability. The S/C provides a body-pointing capability of ±45º in roll and pitch (45º pitch in 60 s, 10º roll in 25 s, 30º roll in 60 s, respectively). The S/C wet mass is about 746 kg with 81 kg of propellant (N2H4) mass. The design life is five years or better.
Launch: A launch of ROCSat-2 took place on May 20, 2004 (UTC) on a Taurus-XL vehicle of OSC (Orbital Sciences Corporation) from VAFB, CA (maiden flight of Taurus-XL configuration which offers greater lift capability compared to previous versions of the Taurus rocket).
Orbit: Sun-synchronous circular orbit, mean altitude = 888 km, inclination = 99.14º, period of 102.9 minutes, the LTDN (Local Time of Descending Node) is 9:26 AM (14 orbits/day). The agility of the spacecraft provides a daily revisit capability for event/disaster monitoring.
Note: Following the early-orbit checkout, the initial satellite orbit has been raised from 728 km to 888 km altitude in the period May 23 to June 2, 2004. A total of 32 burns were performed by the propulsion module with 4 burns for inclination change, to enter into the mission orbit with an altitude of 891 km and an inclination of 99.14º.
Ground segment: The basic elements of the ROCSat-2 ground segment are the MMC (Multi Mission Center) and the XAS (X-band Acquisition System) located in Hsinchu, Taiwan. MMC in turn consists of MOC (Mission Operations Center), MCC (Mission Control Center), SCC (Science Control Center), FDF (Flight Dynamics Facility), and GCN (Ground Communications Network). ROCSat-2 X-band imagery reception is also made available to third parties (international partners) with their own ground stations through cooperative agreements.
Mission status: The spacecraft and its payload are operating nominally as of 2007.
Mission operations started in June 2004 (the checkout and performance verification for satellite bus and RSI were started on May 21 and completed through June 2004; all performance requirements of FormoSat-2 had been successfully verified in orbit). Besides providing imagery for the domestic needs of Taiwan, the S/C is frequently being used to deliver high-resolution imagery for event monitoring (coverage of the Tsunami in Asia on Dec. 26, 2004 and thereafter, coverage of Hurricane Katarina in Aug. 2005, coverage of Typhoons on the Pacific, coverage of earthquake regions, etc.). The spacecraft is operating nominally as of 2006. 7) 8) 9) 10)
• NSPO has contracted to SPOT Image S.A. for the international distribution of FORMOSAT-2 images since June 2004
• On 4 July 2004, ISUAL successfully observed the first images of sprites, sprite halo, and elves.
• In April 2005, NSPO implemented a terminal in Kiruna, Sweden, to serve as an additional receiving station
• In May 2006, NSPO implemented a F2T (FormoSat-2 Terminal) in Svalbard, Norway, to extend the data acquisition capability of the mission.
SOH (State-of-Health) trending during two years of mission operations (May 2004-May 2006) on five major subsystems, including AOCS and EPS (Electric Propulsion Subsystem), and one major payload have been conducted. All parameters were well within specifications. The C&DH and the TT&C do not exhibit any SOH problems so far.
RSI (Remote Sensing Instrument), built by EADS Astrium SAS, France. RSI is made up of the camera and IPU (Instrument Processing Unit). The camera itself consists of the optical subassembly, the secondary structure, and the FPA (Focal Plane Assembly). The Korsch telescope (mirrors & structure) design and the focal plane structure are being made of SiC (Silicon Carbide). The video electronics, sequencer, DC/DC converter, and compression cards comprise the IPU.
RSI utilizes the agility of the satellite bus for stereo imaging over a specific region, continuous imaging over a slender region, and mosaic imaging over a large region. The imaging capability is 8 minutes per orbit, and the imaging areas during one cycle can be one 3000 km x 24 km continuous strip, two 100 km x 24 km stereo pairs, four 100 km x 24 km strips, or eight scenes.
ISUAL (Imager of Sprites: Upper Atmospheric Lightning). ISUAL is a joint international research program of NSPO, UCB (University of California at Berkeley), National Cheng Kung University of Taiwan, and Tohoku University, Japan. The objective is to observe the natural upward lightning discharge phenomena toward the ionosphere on top of the troposphere, referred to as TLEs (Transient Luminous Events). The requirements call for: 14)
• To determine the location and timing of luminous phenomena above thunder clouds to investigate their spatial, temporal and spectral properties
• To obtain a global survey of upper atmospheric optical flash transients (sprites, elves, blue jets, gigantic jets, etc.).
The instrument consists of four elements: a) intensified sprite imager, b) a six-channel spectrophotometer, c) a two-channel array photometer, and d) an electronics package. The imager is a staring-type frame CCD camera, taking 180 frames/s with a resolution of 512 x 80 pixels in a FOV of 20º x 3.15º. In Figure 8, the large disk of the ISUAL instrument contains six color filters, which can be rotated to select wavelength for measuring the emission spectrum of red sprites. ISUAL is operated in three modes:
• The sprite continuous mode to take images with a sample rate of 100 Hz
• The sprite burst mode with a sample rate of 1000 Hz
• The auroral mode at a constant rate of 1 sample/s.
Information obtained from http://www.eoportal.org/
Vandenberg Air Force Base, USA
National Space Program Office (NSPO), China