Sriharikota: Like children firing Diwali rockets, the Indian Space Research Organisation (ISRO) plans to launch more commercial satellites from the Satish Dhawan Space Centre this year.

According to chairman G Madhvan Nair, ISRO has planned three more launches this year out of which one will be a fully commercial flight. Curiously all of them will be historic.

For instance the geo-synchronous satellite launch vehicle (GSLV) will be used to launch the communication satellite Insat 4C. This will be the first time an Insat series satellite gets launched from the Indian soil using a domestic launch vehicle.

The other two launches will be of the Polar Satellite Launch Vehicle (PSLV). One of them will carry the cartography satellite - Cartosat 2A and six small satellites from Canada. The other PSLV will be a fully commercial one similar to the recent flight PSLV C8. (See: PSLV-C8 mission successful)

Configured as a core-alone rocket, or the PSLV minus its customary six strap-on motors in the first stage, the rocket will carry a commercial payload of a third-party satellite. The negotiations are on for that mission. The second dedicated commercial PSLV is expected to get ISRO and its commercial arm Antrix Corporation more satellite launch business.

Though the PSLV can carry a payload of 1,600kg for polar sun synchronous orbits the commercial payloads it gets are less than 500kg. The PSLV C8 launched Agile, an Italian satellite weighing 352kg in equatorial orbit.

The freight rates of a commercial satellite launch are calculated on a per kiligram or per kilogram, per km basis. However, there is no precise demand data for getting small satellites under one tonne or lower launched. It comes in fits and starts as the owners are largely educational or scientific institutions. Satellites that are used for communication weigh more than three tonnes.

"The global satellite launch market is estimated to be in the region of $1.2 - $1.5 billion. However, it is difficult to estimate the market for satellites weighing one tonne or less," says K R Sridhara Murthi, executive director, Antrix Corporation.

According to him the Italian Space Agency was charged at the rate of $29,000 per kilo to carry the 352kg Agile. Given the average launch charge that ranges between $10,000 – 15,000 per kilo, it might appear that ISRO has charged a steep premium and has a big kitty. But it is not so as PSLV''s configuration had to be changed for this equatorial launch. In addition the avionics too had to be reconfigured for this orbit.

According to ISRO officials, PSLV-C8 is more or less a new launch vehicle given the changes made in the configuration. "Aerodynamically it is a different vehicle," explains Nair.

However, the overall vehicle weight cannot be altered depending on the changes in the size of payload fairing or the top chamber inside which the satellite is housed, as it would change the entire dynamics.

Says George Koshy, associate project director, PSLV, Vikram Sarabhai Space Centre, "Originally PSLV was designed to carry an 800kg payload. Subsequently its carrying capacity was increased not by increasing the vehicle size but improving upon the design and also reducing the weight by use of composite materials."

Interestingly, the total fees of around Rs45 crore received from the Italian Space Agency do not cover the total vehicle cost estimated at around Rs68 crore. There are two reasons for ISRO undertaking this launch. First, the launch demonstrated ISRO''s capability to design satellite launchers for varied orbits and second, the latest launch also enabled ISRO the opportunity to test its own rocket avionics.