In the process of landing spacecraft on the Moon, there is a nerve-wracking 15-minute window of intense uncertainty. What exactly happens during those critical moments?
Over the past four years, four countries – India, Israel, Japan, and now Russia – have attempted to land their spacecraft on the lunar surface through both governmental and private space agencies. However, these missions have encountered difficulties during the final phase, namely the landing process, resulting in mishaps on the lunar surface.
Prior to India’s Chandrayaan-2 mission in 2019, the then-chairman of ISRO (Indian Space Research Organisation), K. Sivan, famously referred to the last 15 minutes of the landing process as the “15 minutes of terror.” This statement underscores the challenges involved in descending from the lunar orbit to the lunar surface, making this phase often considered the most challenging part of lunar missions.
On September 6, 2019, India’s ambitious lunar mission, Chandrayaan-2, lost communication with its lander Vikram merely two kilometers above the Moon’s surface. The lander was descending towards the lunar surface and lost contact at an altitude of 2.1 kilometers. Until that point, everything seemed to be progressing well, but an eerie silence gripped ISRO’s control room as the communication was lost. At that moment, ISRO’s Chairman K. Sivan labeled these moments as the “15 minutes of terror.” During these final 15 minutes, Vikram had to navigate through four crucial stages.
In the first stage, Chandrayaan-2 descended from 30 kilometers to 7.4 kilometers above the lunar surface. This process took around 10 minutes. Following this, ISRO lost contact with the lander. In the second stage, the lander continued its descent from 7.5 kilometers to 5 kilometers above the surface, requiring approximately 38 seconds. During this phase, Vikram’s four engines were ignited, reducing its velocity from 550 to 330 kilometers per hour.
Unfortunately, contact was lost with the lander during the third stage of descent, where it was supposed to descend from 5 kilometers to just 2.1 kilometers above the lunar surface. This phase was expected to take around 89 seconds, but communication was severed. After this point, no further information was received.
In the fourth stage, the lander was supposed to decelerate from 400 meters to 100 meters above the surface. This descent area included two craters: Manzinus C and Simpelius N. The distance between these two craters is approximately 1.6 kilometers. The lander was supposed to select a landing site within this region. The final descent from 100 meters to the lunar surface, over a span of 10 meters, required about 65 seconds.
Subsequently, once the lander reached an altitude of 10 meters, its fifth engine was intended to initiate, ensuring a gentle landing. This phase required a slower pace. From this point, it was expected to take about 13 seconds to reach the lunar surface. Unfortunately, due to unforeseen circumstances, this entire process was not successfully completed.