Bangalore, Nov 27 (IANS): India's maiden interplanetary spacecraft Orbiter, headed to Mars, entered the final orbit around earth early Wednesday to prepare for its trans-injection into the sun's orbit early Sunday (Dec 1).

Its voyage to the red planet, as Mars is called, will take nine months (280 days).

"Orbiter has passed its penultimate perigee (closest to equator) and its final orbit around earth began at 7:10 a.m.. It will spin around the earth over the next four days to leave for Mars early Sunday at 00:49 a.m., a senior official of the state-run Indian Space Research Organisation (ISRO) said here.

The 1,337 kg Orbiter has already completed the six orbit raising manoeuvres between Nov 7-16, and crossed an apogee (farthest from equator) of 192,915 km.

"To put into the trans-Mars injection, the 440 Newton liquid engine will be fired for around 23 minutes to give incremental velocity (speed) of 648 metres per second to the Orbiter with a fuel consumption of 190 kg," ISRO scientific secretary V. Koteshwara Rao told reporters at the space agency's telemetry, tracking and command network (Istrac) in the city where the Orbiter's geo-centric phase is being operated.

All going well, the Orbiter will be slung into the heliocentric (sun) orbit towards Mars for a 680-million mile interplanetary voyage.

"The slingshot for the trans-injection will be a complex combination of navigation and propulsion technologies, governed by the gravity of sun and Mars. The Orbiter's trajectory will be achieved using the attitude and orbit control thrusters during the correction manoeuvres planned enroute," Rao said at a briefing on the Rs.450-crore mission's next phase.

Orbiter was launched Nov 5 from Sriharikota spaceport off the Bay of Bengal, about 80 km northeast of Chennai, onboard a 350-tonne rocket -- an extended version of the space agency's workhorse -- the polar satellite launch vehicle (PSLV-C25) with five scientific experiments to detect methane in the Martian atmosphere, measure thermal emission and capture images of the red planet from its orbit at a distance of 500 km.

As the fourth planet from the sun, and behind earth, Mars is the second smallest celestial body in the solar system. Named after the Roman god of war, it is also known as the red planet due to the presence of iron oxide in abundance, giving it a reddish appearance.

Though earth and Mars have equal period of revolution around their axis, the red planet takes 24 hours and 37 minutes to complete a revolution.

Earth takes around 365 days to orbit the sun and Mars 687 days.

"The spacecraft (Orbiter) will be injected into the outer space in a trajectory by precisely computing 280 days in advance the position it would achieve near Mars Sep 14, 2014, which will be 500 km above its surface at that time," Rao pointed out.