Only 20% of the 12,000-odd artificial objects, including satellites, are operational in space, but unwanted "debris" are causing a lot of problem in launching new ones, former ISRO director Suresh Naik said.

There are around 12,000 satellites and other artificial objects in the space, out of which only 20% are active. Satellites have a life of 15-20 years, and then they get lost in space, he said while interacting with school students here.

"The others (artificial objects) along with some other unwanted materials, make space debris. These debris cause a lot of problems in the launching of new satellites."

About man's expected odyssey to the Mars he said, "Scientists are seeing Mars as an alternative habitat for humans. By 2035, the first human should be able to reach Mars".

Two years prior to sending a human to the planet, robots would land there, the space scientist said.

On ISRO's moon mission Chandrayaan-II in 2013, he said the lunar craft would carry two rovers for further exploration of earth's natural satellite.

Naik said Chandrayaan-III is scheduled for launch in 2015.