Chandrayaan 2: Final minutes of ‘terror’ when Vikram Lander fell silent

Vikram Lander Chandrayaan 2 news: There are high chances of the impact of Vikram lander on the lunar surface at a much higher than the desired velocity.

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Chandrayaan 2:The soft landing process was under operation till 0153 hours IST after which the screen at mission control suddenly froze. (Image: ISRO)

Chandrayaan 2 Vikram Lander News: The Indian Space Research Organization has started analysing the data of the frozen screen after the glitch in successfully landing the Vikram lander module of Chandrayaan 2 in the wee hours of Saturday. The screen that was depicting parameters related to the soft-landing phase of Chandrayaan 2 mission at the Mission Operations Complex in ISRO’s Telemetry Tracking and Command Centre was frozen after the connection to the Vikram lander was lost.

The data on the screen suggested that the lander failed to undergo the fine braking phase at a distance of about 5 km above the Moon’s surface. The Lander which performed the rough braking efficiently failed on the final phase of its soft landing phase. The final phase of the soft landing process was to be performed at a distance ranging from about 5 km to 400 m above the lunar surface. Earlier, ISRO described the landing process of Vikram Lander as ’15-minutes of terror’.

ISRO in its statement has said that “A normal performance of the Vikram Lander was observed up to an altitude of 2.1 km and subsequently, the communication of the ground stations to the Lander was lost.”

At mission control, the frozen screens have shown that communication was lost with the lander when it was barely 335 metres (0.335 km) above the lunar surface. A part of the screens depicts that the green dot which was representing the lander noted a deviation when its altitude was just above 2 km and continued to fall before stopping at a point that was clearly below 1 km altitude, and approximately near or below 500 m.

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It is to be noted that, until this time the vertical velocity of the lander module was recorded at 59 metres per sec which is equal to 212 km/hr and it had a horizontal velocity of 48.1 m/sec which is equal to 173 km/hr. The height of the lander when the screen froze was around 1.09 km above its designated landing spot over the lunar surface.

If we go by the plan of a soft landing, the Vikram lander should have lost most of its velocity at about 400 m above the surface of the Moon and would have hovered above the intended landing site in order to proceed for the soft vertical descent.

According to a report published in IE, a former head of an ISRO centre, who was at mission control on September 7, said that the data received at mission control suggests that the soft landing was under process as planned until the lander reached 2 km altitude above the Moon’s surface. The communication link to the lander was lost while it was just a few metres above the lunar surface.”

Early analysis suggests that the Vikram Lander of the Chandrayaan 2 began to experience a spin (Pitch rate) in the rough braking phase while performing an altitude maneuver at 7 km. The lander during this phase had to carry out the imaging process of the lunar surface to identify the most suitable landing site in the region.

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The velocity of the lander was to be reduced to Zero m/s from a very high 1,680 m/sec speed (as much as 6,048 km/hr) during the 15-minute soft landing phase. The process was under operation till the 13th minute after which the screen at mission control suddenly froze. The Navigation Guidance and Control System which was working in automatic mode performed according to the plan.

Though the rough braking phase significantly reduced the velocity of the lander. The velocity of Vikram Lander during the rough braking came down from 1,680 m/sec to 146 m/sec while it was 7.42 km above the lunar surface according to the data on the screen at mission control.

The velocity of the lander reduced to the intended 96 m/sec (346 km/hr) in the decline from 7.42 km to 5 km. The imager onboard the Vikram was switched ON at around 9.52 minutes. It was at 0153 hours IST the Lander ceased to respond to the Mission control.

Following this the ISRO Chairman, K Sivan approached PM Narendra Modi to inform about the mission after the loss of the communication link.

The breaking of the Vikram lander to reduce the velocity was being done using four onboard 800 N liquid fuel engine. Each of them had eight thrusters and the new throttleable technology of ISRO was being used.

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First published on: 12-09-2019 at 10:17 IST