A hard landing on the surface of the moon may have disabled the communication system on ISRO’s Vikram lander, former scientists from the space organisation have started to believe, with no contact being established with the lander more than a week after the attempted soft landing on the lunar surface.
ISRO has been attempting to communicate with the lander since contact was lost 335 metres from the surface of the moon — barely seconds before touchdown — while the lander was noted to be travelling at a vertical velocity of 59 m/sec or 212 km/hr and a horizontal velocity of 48.1 m/sec or 173 km/hr, which is much higher than the optimal landing velocity of nearly zero m/sec.
Window of communication narrows
The mission life of the lander is one lunar day (14 earth days) since solar panels mounted on the body of the lander are the primary source of power for various systems including communications. Technically, the systems on the lander will have no source of power from September 21, when the lunar day ends, making it difficult for ISRO to make any contact with the lander subsequently.
According to M Annadurai, former ISRO scientist and project director for Chandrayaan 1 moon mission, the factors contributing to the loss of contact with the lander could be the terrain where Vikram touched down and the lander’s touchdown position and velocity.
“A combination of different terrain than targetted along with non nominal lander orientation can lead to loss of ‘proper’ data in the last stretch beyond 335 metres. However, if one sees the full data closely to the last bit received at the ground, we will be able to explain the scene better. I hope ISRO will definitely do it for understanding,” the former director of the U R Rao Space Centre said.
“The time lag between the moon and earth is only 1.25 seconds. There is loss of communication permanently, which means hard landing of the lander disabling communication both with orbiter as well as earth,” P S Veeraraghavan, former director of ISRO’s Vikram Sarabhai Space Centre, said.
On Tuesday, ISRO stated that “Vikram lander has been located by the orbiter of Chandrayaan-2, but no communication with it yet. All possible efforts are being made to establish communication with lander,” suggesting that efforts were still on to establish contact with the lander.
On Thursday, former ISRO chairman A S Kiran Kumar said that there were no signals from the Vikram lander for ISRO to track. He also indicated that the communication break with the lander occurred just ahead of touchdown.
The lander was equipped with communication linkage to the Chandrayaan-2 orbiter, which remains in its orbit around the moon, and to earth stations. The telemetry, tracking and command network between the lander and the Indian Deep Space Network ground station was in the S-band.
“The Vikram lander followed the planned descent trajectory from its orbit of 35 km to just below 2 km above the surface. All the systems and sensors of the lander functioned excellently until this point and proved many new technologies such as variable thrust propulsion technology used in the lander,” ISRO has stated.