The 25-hour countdown for the Thursday evening launch of the Indian Polar Satellite Launch Vehicle (PSLV) rocket, carrying three Singapore satellites, began on Wednesday evening, the Indian space agency said.

The mission is codenamed PSLV-C53/DS-EO by the Indian Space Research Organisation (ISRO).

During the countdown, the rockets' engines powered by liquid fuel will be filled and all other systems will be checked.

The Indian rocket will carry three satellites -- the 365 kg DS-EO and 155 kg NeuSAR, satellites belonging to Singapore and built by the Star Initiative of South Korea.

The third satellite is a 2.8 kg Scoob-1 of Nanyang Technological University (NTU), Singapore.

If the launch is successful, the PSLV rocket would have launched 345 foreign satellites belonging to 36 countries since 1999.

According to the ISRO, the PSLV-C53 rocket is expected to blast off from the second launch pad at the Sriharikota rocket port at 6 p.m. on June 30.

The Indian space agency, ISRO will use the rocket's fourth and final stage as an orbital platform for six payloads, including two from Indian space start-ups, Digantara and Dhruva Aerospace.

The mission proposes to demonstrate the utilization of the spent upper stage of the launch vehicle as a stabilized platform for scientific payloads, after the separation of the satellites.

The four-stage expendable, 44.4 m tall PSLV-C53 has a lift-off mass of about 228 tons and the total weight of the three satellites is 522.8 kg.

The rocket's four stages will be powered by alternating solid and liquid fuel.

Thursday's flight will be the 55th mission of PSLV and the 15th mission using the PSLV-Core Alone variant.

In its normal configuration, the rocket will have six strap-on motors hugging its first stage.

In the Core Alone variant of PSLV, the six strap-on motors will not be there as the payload weight is less.

The Indian space agency has PSLV variants with two and four strap-on motors and larger PSLV-XL. (AA/IANS)