The Indian Space Research Organisation (ISRO) has decided to launch the Chandrayaan-3 mission, the space agency’s third venture to the moon and the second to attempt a soft landing on its surface, on July 14 at 2.35 pm from the Satish Dhawan Space Centre at Sriharikota.
ISRO chairman S Somanath, who earlier said that a launch window was available between July 12 and 19 for the Chandrayaan-3 mission, said in Bengaluru on Thursday that the date and timing for the launch had been fixed at 2.35 pm on July 14 with a possible moon rendezvous on August 23 or 24.
“The launch of Chandrayaan-3 will be on July 14 at 2.30 pm. If the launch takes place on that day we will be ready for landing on the moon possibly by the last week of August. The date is decided by the sunrise on the moon. When the landing takes place, sunlight has to be there. A day on the moon is 15 Earth days. You will have sunlight for 15 days and in the next 15 days there will be no sunlight for a given location,” Somanath said on Thursday on the sidelines of the G20 meeting on the space economy.
“So if we have to land on the first (earth) day of sunshine on the moon (that is the first of the 15 earth days of sun on the moon) then we will have a life of at least 15 days for the mission. This is the date on which we are going to land and if everything goes well, the date would be August 23 and it could be August 24 also… depending on calculations it will happen. It cannot be August 25 or 26. Then what we will do is we will not land and we will wait for a month when there is going to be 15 days of sun again then the date could be September 20 or later,” Somanath explained.
The ISRO chairman said that a key factor in the second attempt by the space agency to land on the moon is that multiple learnings from the failure of the Chandrayaan-2 lander have been incorporated in the Chandrayaan-3 mission, including a provision for landing at higher speeds and new technology for assessing the speed levels as the lander approaches the landing site on the moon.
“Chandrayaan-2 was unsuccessful at the landing stage and so we collected the elementary data of the landing and carried out an analysis, simulation and studied the problems in the landing stage. Since the lander crashed onto the moon, we have not received any debris and so we have data that was recorded at the time of the crash. We have used the data to simulate the incident. We have found that there are three or four reasons that the landing was a failure,” Somanath said.
In 2019, the Chandrayaan-2 mission was launched on July 15. The manoeuvring for the landing was executed on September 7, 2019. The landing was seemingly on track before the lander ended up spinning over 410 degrees, deviating from a calibrated spin of 55 degrees, and making a hard landing on the moon.
The anomaly, which occurred during the second of four phases of the landing process, was reflected in the computer systems in the mission control room, but ISRO scientists could not intervene to correct it as the lander was in autonomous mode, using data already fed into its system before the start of the powered descent onto the surface of the moon, ISRO scientists said post-mission.
With the communication system on the failed lander supplying data on its performance right up to 400 metres before crashing on the surface of the moon, ISRO is now confident that the errors that occurred have been corrected for Chandrayaan-3.
“The first thing was to get rid of the problems. We have reviewed it and strengthened various aspects. The design of Chandrayaan-2 was for a landing at a speed of 2m/sec (7.2 km/hr) with a small margin of increase but we have now increased the speed threshold for landing. We have created energy absorbing capability,” the ISRO chairman said on Thursday.
“The second thing is that Chandrayaan-3 will have more propellant quantity. We have increased the capacity of the tank and the lander will have the capability to change the landing site if there are problems with one landing site. The extra propellant will facilitate the change of location,” he said.
ISRO has also provided multi-direction solar panels on the lander to ensure that the power supply does not get knocked off if the lander makes a landing with the solar panels facing downward. “We have located solar panels in four directions so that one or two faces of the panel absorb solar energy even if it lands in the wrong direction then it will have power transmission capability,” Somanath said.
The lander, which weighs more than the lander on the Chandrayaan-2 mission, will also have additional equipment to assess the speed of landing and initiate corrections.
“There is a new instrument called the Laser Doppler Velocimeter which will have three laser beams and when it reflects from the surface of the moon then we can assess the excess speed on the lander. The beams will measure the forward speed, lift speed and up and down speed. The speed will be fed to the control feedback to control the lander,” Somanath said.
The lander has been subjected to multiple stress tests and experiments, including dropping from helicopters. “We have created various test beds at the satellite centre to demonstrate the landing; stress tests and failure simulations have been conducted. We have done whatever we could think of in terms of probabilities in the last two years and it is with this confidence that we are moving to launch Chandrayaan-3,” the ISRO chairman said.
“Our aim is to have a soft and safe landing. No instruments will work if there is a crash. There are five experiments on the mission – three are on the lander and two on the rover. These experiments will work only with a safe and soft landing. The instruments must have a communication link with the orbiter and the communication signals between the earth and the orbiter should work well. If everything works well and our communication link fails then there is no use of the mission. All aspects must work well – landing must go well, instruments must work properly, and communication must be good,” he said.
Once the lander settles on the surface of the moon, it will release a rover that it is carrying on board to take pictures of the surface of the moon and conduct experiments with two onboard instruments.
“The rover has a life of 14 days when there is sunlight. There will be temperatures below 150 degrees when the sun is absent for 14 days and we are hoping the rover can survive the period when the battery has no means of recharging. One day the battery will die and that day we will have to say bye to the rover. The life for the lander and rover is estimated to be 15 days,” the ISRO chairman said.
The Chandrayaan-2 mission was launched on July 22, 2019. The spacecraft was inserted into the lunar orbit on August 20, 2019. The lander ‘Vikram’ separated from the orbiter on September 2, 2019. The powered descent of the lander was initiated on September 7 for a soft landing but crashed.
The Chandrayaan-1 mission in 2008 to the moon was a fly-by scientific mission which had some success in finding water traces on the moon.
