NEW DELHI: ISRO 's Mars Orbiter or Mission (MoM) on Monday successfully completed the fourth trajectory correction manoeuvre and test fire of the main liquid engine on the spacecraft "Main Liquid Engine test firing on Mars orbiter spacecraft successful: We had perfect burn for 4 seconds as programmed. The trajectory has been corrected. Mars Orbiter Mission will now go ahead with the normal plan for Mars Orbit Insertion," said ISRO. "#MarsOrbiter Main Liquid Engine test firing successful!," tweeted ISRO.This was one of the biggest tests of this complicated project. The test entailed switching on the engine that has been lying dormant for 10 months, and firing it for four seconds to slow down the spacecraft.Now, the ISRO will fire the engine for a longer duration two days later and ease the spacecraft into an orbit around Mars. The 440N liquid engine was last fired on December 1 to slingshot the spacecraft from an Earth orbit to the Martian trajectory. The spacecraft authorization committee earlier this month decided to carry out the four-second test to ensure that the long duration of idling hasn't affected the engine that carries corrosive fuel.India is set to make history, thanks to its maiden Mars Orbiter Mission! After being launched from ISRO's spaceport of Sriharikota on November 5 last year, the MOM had left Earth's orbit on December 1 and began its historic voyage to put India on the list of elite nations, which has sent a mission to Mars.Cruising towards its historic rendezvous with the red planet, the MoM is scheduled for Orbit Insertion on September 24.Earlier today, the MoM entered the Mars Gravitational Sphere of Influence. The Mars mission, as planned by ISRO, was a sophisticated exercise. Compared to other Mars missions, ISRO had a smaller rocket and payload. This reduced the cost significantly but increased the mission's complexity. Other Mars missions are not planned this way.