Present day remote sensing satellites orbiting in low earth orbit (LEO) have increasingly sophisticated and high
resolution onboard sensors. Their frequency and area of observation is also increasing. This generates large volume of
data which needs to be communicated. However their visibility to ground station is limited. Free space optical
communication between remote sensing satellite in LEO and communication satellite in geostationary earth orbit (GEO)
can be favorable approach. Subsequently GEO satellite relays the data to ground station. To demonstrate this, a concept
model operating at data rates greater than 1 Gbps is under development at LEOS. The system consisting of laser
transmitter with 20cm diameter telescope and receiver with 30cm telescope is planned. It uses commercially available
optical and optoelectronic components. This concept model will demonstrate and verify link margins available as against
expected. Subsequent to this, it is planned to concentrate on design and other issues involved in acquisition, tracking and
pointing (ATP) due to highly narrow laser beam.
INSAT-2 series satellites are second generation, multipurpose satellites developed by Indian Space Research Organisation for telecommunication and meteorological remote sensing. INSAT-2A was launched successfully in July 1992. The solar sail mounted on the north face of the satellite balances the differential solar radiations torque on the solar panel mounted on the south face. The sail, being lightweight, during its deployment causes very little attitude disturbance on the satellite to sense the deployment. A novel utilization of an earth sensor (ES) mounted on the same face of the satellite gave a clear indication of the deployment initiation and the progress of the boom extension during this period. This paper briefly describes the observations made using the earth sensor during the sail deployment and analyzes the data received in terms of the sail extension in this period.
The Indian Remote Sensing Satellite IRS-1A, launched in March 1988, is a three-axis stabilized, polar sun synchronous satellite orbiting at an altitude of 904 km. Two types of earth sensors are used for pointing and control of the satellite. One is a pair of conical scanning sensors using a rotating germanium wedge prism. The other is a static horizon sensor operating on the principle of radiation balancing. The latter sensor used novel normalization technique for removing the effects due to radiation gradients, which is one of the main problems of this type of sensor. The in-flight performance of the sensor is quite satisfactory with very low noise behavior. However, there were certain problems noticed in the acquisition mode of operation of the sensor which were traced to the heating of the IR filter due to direct sun viewing by the sensor near the poles. Based upon this experience, the configuration for IRS-1B to be launched in 1991 was modified. This paper briefly describes the configuration, the flight performance, and the modification carried out in the future models of the sensor.