Chennai: The 50-hour countdown for the launch on September 28 of an Indian rocket carrying seven satellites, including the ASTROSAT – the country’s first dedicated multi-wavelength space observatory that will help in understanding the universe – began on Saturday, the Indian space agency said.

India will cross the half-century milestone on Monday once it successfully injects the six foreign satellites into their intended orbit.

India has so far launched 45 foreign satellites for a fee.

According to Indian Space Research Organisation (ISRO), the Saturday countdown for the launch of the polar satellite launch vehicle (PSLV) began as scheduled at 8.00 a.m.

The rocket with seven satellites will blast off on Monday at 10.00 a.m. from the first launch pad of the rocket port at Sriharikota in Andhra Pradesh.

In 2008, ISRO had launched 10 satellites in one go including India’s Cartosate-2A satellite.

Now, ISRO will be launching seven satellites for the third time in its history.

On Thursday ISRO’s Mission Readiness Review (MRR) committee and Launch Authorisation Board (LAB) cleared the 50-hour countdown.

The 44.4 metre tall 320 tonne PSLV-XL version is a four-stage rocket with six strap-on motors for additional thrust during the initial phase of the flight.

The first and third stages are powered by solid fuel while the second and fourth stages are powered by liquid fuel which will be filled during the countdown.

Apart from fuelling up the engines, all the systems would be checked and rechecked during the countdown.

On Monday morning the rocket will launch India’s ASTROSAT weighing 1,513 kg, apart from four from the US and one each from Indonesia and Canada.

The PSLV will carry a total payload of 1,631 kg during this mission.

Just over 22 minutes into the flight, the rocket will eject ASTROSAT at an altitude of 650 kms above the earth.

Soon after, six other satellites will be put into orbit and the whole mission will come to an end in just over 25 minutes.

ASTROSAT, with a life span of five years, will observe the universe through optical, ultraviolet, low and high energy X-ray components of the electromagnetic spectrum, whereas most other scientific satellites are capable of observing through a narrow wavelength band, the agency said.

The Indonesian 76 kg LAPAN-A2 is a micro-satellite from the National Institute of Aeronautics and Space, meant for providing maritime surveillance using automatic identification system (AIS), supporting Indonesian radio amateur communities for disaster mitigation and carrying out earth surveillance using video and digital camera.

The 14-kg NLS-14 (Ev9) of Space Flight Laboratory, University of Toronto Institute for Advanced Studies, is also a maritime monitoring Canadian nano satellite using the next generation AIS.

The remaining four LEMUR nano satellites from Spire Global Inc., San Francisco, US, are non-visual remote sensing satellites, focusing primarily on global maritime intelligence through vessel tracking via AIS and high fidelity weather forecasting using GPS radio occultation technology, the ISRO said.