The frequency transmission data for Vikram, lander of Chandrayaan-2, received by 25 meter Dwingeloo radio telescope is plotted and tweeted by Cees Bassa. Kinks in the Doppler curve are interpreted as transitions from one phase to the other, such as burning of thrusters to begin descent or moving into fine braking phase from rough braking phase.

  • How can we extract information from the Doppler curve here? Is the principal identical to the one-way Doppler effect i.e. $f_{\rm{observed}} = (1-\dfrac{v_{\rm lander}}{c})f_{\rm lander}$?

  • Only a change in the velocity results in a change in the frequency observed, which is what seems to be plotted. Is it possible to decipher the actual velocity of the lander from the plot?

  • What does the frequency in the plot refer to? Could it be the signal transmission frequency?

  • Could the wiggles at the end be a signature of landing and subsequent bouncing?

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Doppler curve kink showing rough to fine braking phase transition
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Zoomed-in version

  • $\begingroup$ Though there are many questions in a single post, I hope only the first one needs an elaborative answer and the rest are follow-up questions that could be answered in a sentence. Hope this is fine with the community. $\endgroup$ – Abhay Hegde Sep 14 '19 at 14:21
  • $\begingroup$ Also, these questions are not really related to this mission in particular, but the physics behind the Doppler curve. $\endgroup$ – Abhay Hegde Sep 14 '19 at 14:23
  • $\begingroup$ I suspect the guys at the Space Exploration SE could answer this better than we can. $\endgroup$ – John Rennie Sep 14 '19 at 14:30
  • $\begingroup$ @JohnRennie Oh yeah! Forgot about that SE. However, leaving the specific details apart, I thought this community would help me understand the physics behind this plot better. $\endgroup$ – Abhay Hegde Sep 14 '19 at 14:39

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