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KALPANA-1 SpaceCraft

The MetSat-1 spacecraft was developed by ISAC (ISRO Satellite Center), Bangalore. MetSat has been designed using a new spacecraft bus (I-1000 bus) employing lightweight structural elements like CFRP (Carbon Fibre Reinforced Plastic). A central structural thrust cylinder provides mounting interfaces propellant tanks, pressurant tank, equipment panels, payload, solar array assembly, and with the launch vehicle.

Structural brackets are provided to mount momentum wheels, reaction wheel, RCS (Reaction Control System) thrusters, earth sensors, sun sensors, LAM (Liquid Apogee Motor), and propulsion components.

MetSat-1 is three-axis stabilized (momentum biased control subsystem). However, unlike its INSAT predecessors, the MetSat-1 spacecraft does not feature a sail/boom design. The attitude is sensed by suite of sensors (gyros, Earth sensors, digital sun sensor, coarse analog sun sensors, and solar panel sun sensor). Magnetic torquers serve as actuators to unload the momentum of the wheels. In addition, active thrusters are used (one 440N LAM for orbit raising maneuvers and eight 22 N thrusters for orbit and attitude control).

The propulsion system employed is a unified bi-propellant with mono-methyl hydrazine (MMH) as fuel and mixed oxides of nitrogen (MON3) as oxidizer. The S/C employs passive thermal control system by utilizing multi-layer insulation blankets, optical solar reflectors, heat sinks, paints, thermal grease, thermal shields etc. The temperature of individual subsystems spread over the satellite is maintained by a bank of 112 heaters.

EPS (Electrical Power Subsystem): Electrical power of 550 W is generated by a single panel solar array of 2.15 m x 1.85 m using GaAS solar cells. The solar panel features a drive mechanism to point it into the sun. A single NiCd battery (18 Ah capacity) provides power for eclipse phases. The SADA (Solar Array Driver Assembly) slip rings and drive mechanism are modified to meet the power transfer and drive requirements, it is mass-optimized.

The spacecraft has a launch mass of 1055 kg including 560 kg of propellant (495 kg S/C dry mass). MetSat-1 has a design life of 7 years with an operational goal of 10 years.