Oceansat-1 (IRS-P4)

India's first satellite built mainly for studying the ocean, launched by PSLV-C2 in May 1999 and operated for more than eleven years.

No longer operational, according to the public satellite catalogue.

What it did

Oceansat-1 was the first Indian satellite built mainly for ocean applications. It carried two instruments:

• The Ocean Colour Monitor (OCM), a camera with eight narrow colour bands. It measured chlorophyll, tracked blooms of phytoplankton, and recorded aerosols in the air and sediment in the water.
• The Multi-frequency Scanning Microwave Radiometer (MSMR). It worked at four microwave frequencies and measured sea surface temperature, wind speed, cloud water and water vapour over the ocean.

Spacecraft

The satellite weighed 1,050 kg at lift-off and measured 2.8 m × 1.98 m × 2.57 m, reaching 11.67 m long with everything unfolded. A 9.6 square metre solar array gave 750 watts, backed by two 21 Ah nickel-cadmium batteries. It was three-axis stabilised with reaction wheels, magnetic torquers and hydrazine thrusters.

Launch and orbit

PSLV-C2 launched Oceansat-1 from SHAR Centre, Sriharikota, on 26 May 1999, together with the small satellites KITSAT-3 and DLR-Tubsat. It flew a polar sun-synchronous orbit at 720 km, taking 99.31 minutes per orbit. It crossed the equator at noon and covered the same ground every 2 days.

Mission status

The mission ended on 8 August 2010, after 11 years and 2 months.

Sources

1. IRS-P4 (OCEANSAT-1) — satellite catalogue record (NORAD 25758) — CelesTrak
2. Oceansat (IRS-P4) — ISRO
3. IRS P4 (Oceansat 1) — Gunter's Space Page
4. List of DoS/ISRO satellites launched so far (10 April 2025) — ISRO