In the history of Japanese Earth-observation satellites, technical improvements have made it possible to obtain images approximately 100 times finer than those of 40 years ago. This means that even geostationary orbit satellites, which are 60 times farther away than ordinary sun-synchronous low-orbit satellites, could now be capable of useful spatial resolution. With this in mind, the Japan Aerospace Exploration Agency (JAXA) seeks to achieve high temporal resolution image acquisition with

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... l spatial resolution. The new high temporal resolution satellite images are expected to be used for disasters, agriculture, coastal management, forest management, etc. For this purpose, JAXA has taken on the challenge to develop a geostationary satellite with a large segmented telescope. The main mirror will have a diameter of 3.6 m and will use the active optics technique, which will yield a ground resolution of approximately 7 m with a 100-km 2 field of view at nadir. It will be equipped with 7 bands from visible to near-infrared, plus one thermal infrared band. A one-segment mirror subsystem proto-model with actuator and sensor is under production and evaluation as the key technology for the large segmented telescope. An all-electric propulsion satellite bus system is under consideration as a means of supporting the heavy weight of the telescope. Additional factors that are also currently under study include adding to the propulsion system, quick pointing ability, pointing stability, precise pointing determination, and the establishment of a ground station to maintain a latency of 30 minutes for image acquisition and delivery.