Orwell Astronomical Society (Ipswich)

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Chandrayaan-3, 26 July 2023

Chandrayaan-3 is a mission to the Moon launched by India on 14 July 2023. It did not journey directly to the Moon but instead has been orbiting the Earth in a series of highly elliptical orbits. Initially the orbits had an apogee of some 41,000 km, but a burn on 25 July raised this to 127,000 km.

The sky was clear during the early hours of 26 July so I took the opportunity to image the craft en route to the Moon (even though it is still in Earth orbit).

Predictions from JPL Horizons showed that the craft would be some 115,000 km distant and moving at some 40-50 arcseconds per minute, limiting exposures to just a few seconds before the image becomes visibly smeared. I chose to take frames of 10 s duration then, using the predictions, shift and stack them to try to reveal the probe.

The still image is an example of what I could record. This is a stack of 20 frames, clearly showing the probe as an elongated dot, with the stars as streaks. The elongation of the dot is due to motion during the exposure and not the inherent shape of the probe.

The first section of the movie is formed from a sequence of 20-frame stacks. It holds the probe stationary while the stars move behind it. At the end of the movie is a short clip constructed from single frames, showing what they reveal. ASTAP, the Astrometric STAcking Program, gives a magnitude estimate of 15.8 for the craft, close to the limit of a 10 s exposure.




Nigel Evans