BENGALURU: India’s much-anticipated Chandrayaan-2 Moon mission will have to be launched, latest by July 20, and not later, if the mission has to run successfully without risks of compromise or even failure.
The mission was scheduled for launch in the wee hours on Monday, but was called off due to a ‘technical snag’.
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A veteran space scientist, who has the experience of Chandrayaan-1 behind him, said this urgency is because the lunar transfer trajectory (LTT) (the movement of the spacecraft from the Earth’s orbit towards the Moon’s orbit) has to be completed on August 1, which is referred to as T+17, or 17 days after the initially calculated launch at 2.51 am on July 15.
The reason for the odd timing of 2.51 am and the date (July 15) was to ensure precision entry into the lunar orbit.
This would also help the lander Vikram to accurately land at the planned spot on the high plain between two lunar craters, Manzinus C and Simpelius N, on September 6.
“No matter what, the LTT has to be done by T+17, to enter the polar orbit around the Moon, because this is the time when the Moon is ready for capture,” the veteran space scientist, who did not want to be identified, said.
This would not only ensure calculated fuel efficiency of the orbiter, but would also make the mission successful, he added.
The scientist said delaying the launch beyond July 20 will mean making a rendezvous with the Moon at a different time and location, which could delay the lander’s separation, besides requiring more fuel. This, in turn, could reduce the life of the orbiter.
The lander and the robotic rover have a mission life of just 14 days, or one lunar day, he said.
He said longer lunar orbital insertion or delays would also prevent the lander from separating. He explained that delays in orbit could affect the orbiter’s pyro-circuit, whose objective is to generate energy to light up the lander’s thrusters to separate from the orbiter and begin its descent towards the lunar surface.
“The pyro-circuit is temperature-sensitive, and the longer it takes for the separation, the higher the chance that the circuit will not kick in.
"If it does not work, the lander will not separate. And if the lander -- which carries the robotic rover — does not separate, we will not have any soft-landing. This means the entire mission will be compromised with only the orbiter stuck with the lander and rover orbiting until it crashes into the lunar surface after its one-year mission,” he said.
He emphasised the need to launch not later than July 20, or wait and launch the mission in the next launch period.