In a special mission in March, the Indian space agency will launch an electronic intelligence satellite Emisat for the DRDO, 28 third party satellites and also demonstrate its new technologies like three different orbits with a new variant of Polar Satellite Launch Vehicle (PSLV) rocket, said a top official.

The exact date has not been specified yet.

"It is a special mission for us. We will be using a PSLV rocket with four strap-on motors. Further, for the first time we will be trying to orbit the rocket at three different altitudes," K Sivan, Chairman, Indian Space Research Organisation (ISRO) told IANS.

"The main passenger for the PSLV rocket will be the defence intelligence satellite Emisat belonging to Defence Research and Development Organisation (DRDO).

"The satellite weighs about 420 kg. The 28 satellites belonging to our customers would cumulatively weigh about 250 kg," Sivan said.

The DRDO's Emisat is an electronic intelligence satellite, he added.

The ISRO will also be launching two more defence satellites sometime in July/August with its new rocket Small Satellite Launch Vehicle (SSLV).

In January, the space agency launched a defence imaging satellite Microsat R for the DRDO.

Sivan said, after launching Emisat at an altitude of 763 km, the rocket will be brought down to put into orbit the 28 satellites at an altitude of 504 km.

"Following that the rocket will be brought down further to 485 km where the fourth stage will turn into a payload platform carrying three experimental payloads -- one developed by the students of Indian Institute of Space Science and Tecnology, besides ISRO's own technology demonstrator and a Hamsat," Sivan said.

The PSLV is a four-stage engine expendable rocket with alternating solid and liquid fuel.

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

On January 24, the ISRO flew a PSLV with two strap-on motors while in March it will have four strap-on motors.

The Indian space agency also has two more PSLV variants viz Core Alone (without any strap-on motors) and PSLV-XL a larger rocket.

The ISRO selects the kind of rocket to be used based on the weight of satellites it carries.