Countdown begins for moon mission, I.S.R.O. fully geared up

Bangalore, Oct 20 (PTI) The countdown began Monday for
Chandrayaan-1, India's unmanned moon mission, at Sriharikota
spaceport with Indian Space Research Organisation (I.S.R.O.)
gearing up for Wednesday's much-awaited launch.

"The countdown started at 5.20 am Monday. The 52-hour
countdown has been optimised to 49 hours", I.S.R.O.
spokesperson S Satish told PTI over telephone from Satish
Dhawan Space Centre-SHAR in Sriharikota. "Propellant filling
and management of the second stage of PSLV-C11 is in
progress".

Chandrayaan-1 spacecraft is slated to be launched onboard
India's home-grown rocket PSLV-C11 at 0620 hours on Wednesday.

The launch of Chandrayaan-1 will take place from the
second launch pad at SDSC, SHAR, Sriharikota in the Nellore
district of Andra Pradesh, about 100 km north of Chennai.

Chandrayaan-1 spacecraft begins its journey from earth
onboard PSLV-C11 and first would reach a highly elliptical
Initial Orbit (10).

In the 10, the perigee (nearest point to earth) is about
250 km and apogee (farthest point from the earth) is about
23,000 km.

After circling the Earth in its 10 for a while,
Chandrayaan-1 spacecraft is taken into two more elliptical
orbits whose apogees lie still higher at 37,00 km and 73,000
km respectively. This is done at opportune moments by firing
the spacecraft's Liquid Apogee Motor (L.A.M.) when the
spacecraft is near perigee.

Subsequently, L.A.M. is fired again to take Chandrayaan-1
spacecraft to an extremely high elliptical orbit whose apogee
lies at about 387,000 km.

In this orbit, the spacecraft makes one complete
revolution around the Earth in about 11 days. During its
second revolution around the Earth in this orbit, the
spacecraft will approach the Moon's North pole at a safe
distance of about a few hundred kilometers since the Moon
would have arrived there in its journey round the Earth.

Once the Chandrayaan-1 reaches the vicinity of the Moon,
the spacecraft is oriented in a particular way and its L.A.M.
is again fired.

This slows down the spacecraft sufficiently to enable the
gravity of the moon to capture it into an elliptical orbit.

Following this, the height of the spacecraft's orbit
around the moon is reduced in steps. After a careful and
detailed observation of perturbations in its intermediate
orbits around the moon, the height of Chandrayaan-1
spacecraft's orbit will be finally lowered to its intended 100
km height from the lunar surface, "Chandrayaan-1 is expected
to settle into this orbit of 100 km height from the lunar
surface around November eight", Satish said. PTI RS
BDS