Vikram - last contact @ 335-m NOT 2.1-km
13th September, 14.00 hrs IST
As per the Indian Express report (12th Sept), the last signal received from Vikram appears to be from as low altitude as 335-m.
Lets see what could have happened during the 2-phases of breaking in the height range of 18-km to 400-m.
Tapan Mishra, Ex-SAC (Space Application Center) and PRL (Physical Research Laboratory) director, Ahmedabad; distinguished scientist @ ISRO-HQ; has written in his facebook account the details of Vikram landing of 15-minutes. In his smooth flow of words; he has thrown light on what exactly would happen when Vikram switched from Rough breaking (18-7.4 km) to Fine breaking (7.4-km to 400-m). Apparently, it was a switch-over from 4-cornered retro engines to 2-diagonally opposite engines for the fine breaking phase from 7.4-km to down below upto 400-m. Without mentioning the actual cause of the Vikram incident; he did warn that during the fine breaking the operation of 2-diagonally opposite engines is a pretty involved and tricky procedure. Considering the fact that a less filled fuel tank would "slosh" leading to the exhaust of fuel to these engines and hence would lead to un-even burn. Hence, it will be very difficult to provide a "uniform centrally directed breaking force"; this is what clearly emerges from that discussion.
Taking a cue from the above explanation; it can be conjectured that:
1. Though the switch-over to 2-engines from 7.4-km and downwards would have occurred.
2. The signal loss at 2.1 km could be due to a tumble; taking the direction of communication (antenna) away and hence the signal loss
3. Best part is: Vikram did sail through 2.1-km to 335-m. If one recalls; it had 3-more milestones below 400-m to accomplish: a. @400-m: hover and activate Hazard Detection and Avoidance sensor b. @100-m: select one of the 2-targeted locations c. @10-m: stop and hover to ensure the point of landing
4. Since, the above 3-milestones are AI-based. There is a very high probability of Vikram making it safely to lunar surface and hence a good news, which could emerge in these couple of days....
Wishing ISRO-team again a very best of luck.
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