New Delhi, Oct. 19: The countdown for the launch of India’s first lunar orbiter is expected to start early on Monday, Indian Space Research Organisation (Isro) scientists said tonight after a full simulated dress rehearsal.

Isro officials, including members of the launch authorisation board, met at the Satish Dhawan Space Centre, Sriharikota, to review the status of the mission and decide on the initiation of the countdown — expected to start about 50 hours before the scheduled launch at 6.22am on Wednesday, October 22.

Chandrayaan-1, to be ferried into space by an upgraded version of Isro’s workhorse rocket, the Polar Satellite Launch Vehicle, will carry 11 scientific instruments for a two-year mission of observing the moon from 100km above the lunar surface.

“We’re watching the weather, but everything else looks fine,” a senior Isro engineer told The Telegraph from Sriharikota. But the engineer said the start of the countdown could only be confirmed later tonight by members of the launch authorisation board.

Isro chairman Madhavan Nair, Chandrayaan-1 project director Mylaswamy Annadurai, director of telemetry, tracking and command network S.K. Shivkumar, and director of the Sriharikota centre Chandra Dattan, who is also head of the launch authorisation board, were among officials at the review meeting today.

At the dress rehearsal that began early Sunday morning, Isro engineers simulated the full sequence of the launch with spacecraft tracking centres in India, Indonesia, the US and Spain.

“Data simulating the full launch sequence and spacecraft tracking in the early hours after the launch streamed into computers during this rehearsal,” said Lakshminarayan Srinivasan, general manager at Isro’s tracking, telemetry and command network in Bangalore.

Isro’s own deep space tracking station near Bangalore is expected to get the first signals from Chandrayaan-1 only about six hours after the launch, Srinivasan said.

After PSLV releases Chandrayaan-1 about 20 minutes after lift-off, a station in Indonesia will pick up signals from the spacecraft and relay them to Isro’s mission control centre in Bangalore. “After that, tracking stations in Australia, the US and Spain will relay its signals before we can directly get data,” Srinivasan said.

When the countdown begins, Isro engineers will initiate a series of checks and actions on the launch vehicle and on the spacecraft to prepare for lift-off.

They will fill liquid fuel in the PSLV and arm the devices that will help separate each stage of the rocket after it has completed its role in the launch mission.

Isro scientists had said last week that a thunderstorm, a depression or a cyclone might force them to reschedule the launch.