NEW DELHI — India has begun assembling the Polar Satellite Launch Vehicle (PSLV) that will launch the country’s first Mars orbiter later this year, according to a senior scientist responsible of the mission.

Assembly of the four-stage rocket is underway at the Sriharikota spaceport in south India, the scientist at the Indian Space Research Organization (ISRO) tells Aviation Week. “The launch window is between Oct. 31 and Nov. 7,” the official says.

ISRO’s PSLV-C25 mission with the Mars orbiter will mark the 25th PSLV flight. It will be the fifth flight of the XL variant, which is the most powerful in the PSLV stable and the same variant used to launch the Chandrayaan-1 mission to the Moon.

The orbiter, including the Liquid Apogee Motor that will propel it to Mars and the rocket motor that will slow it down for Mars orbit insertion, will together weigh 1.35 tons.

“Work has to commence right from the launch pedestal,” the ISRO scientist says. “Next, the mission will undergo various environmental tests before it is launched to ensure it is qualified to face various levels of vibration and temperature it might encounter as it travels into space and is finally inserted into the Martian orbit.”

The orbiter with the five payloads will undergo “various rigorous environmental tests this month” before being moved to Sriharikota by September for integration with the rocket, he says.

The schedule calls for insertion into Mars orbit in September 2014. The unmanned satellite, dubbed “Maangalyaan,” will study the thin Martian atmosphere to determine the existence and sustainability of life and focus on the planet’s climate, geology, origin and evolution.

So far, the process to integrate the five scientific payloads with the Mars orbiter has “almost been completed” at the satellite center in the south Indian city of Bengaluru, the ISRO scientist says.

Among the payloads for the mission is the Exospheric Neutral Composition Analyzer, which would study the Martian atmosphere, and a methane sensor to look for the gas, considered a signature for life. The mission will try to determine whether the source of methane is thermogenic or biogenic.

NASA will be providing the deep space navigation and tracking support for this mission when communications are not possible with the Indian Deep Space Network.

If the ISRO fails to launch the Mars mission this year, the next launch opportunities occur in January-April 2016 and April-May 2018. The mission is estimated to cost 4.5 billion rupees ($83 million).