How much younger did Group Captain Shubhanshu Shukla become after his sojourn in Space?

 

Some of you may have read my book 'Yo-yoing in Time'. The construct of the stories in the book(available in Amazon India ; in Amazon US  ; in Amazon Europe ) is based on the following 'de-aging' (for want of a better word) paradigm , and Simultaneity of Relativity.

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How much has Group Captain Shubhanshu Shukla 'de‑aged' during his 18‑day Axiom‑4 mission aboard the ISS?

Here is a calculation:

Mission Duration & Orbit

Launch: 25 June 2025

Docked: June 26

Return (undock/splashdown): July 14–15

Total time in orbit: 18 days

Time Dilation Effects in Lower Earth Orbit(LEO)

a. Special Relativity (due to orbital speed)

ISS orbital speed ≈ 7.66 km/s

Daily loss ≈ 28.1 μs/day

(μs represents microseconds, a unit of time equal to one millionth of a second.)

Over 18 days:

28.1 μs/day × 18 ≈ 505.8 μs (≈ 0.5058 ms)

b. General Relativity (due to weaker gravity)

Clocks tick slightly faster in weaker gravity — about +5 μs/day 

Over 18 days:

5 μs/day × 18 ≈ 90 μs (0.09 ms)

Net Effect:

505.8 μs (slower) – 90 μs (faster) = 415.8 μs total lost (0.4158 milliseconds)

So, Group Captain  S Shukla returned 0.0004158 seconds younger than if he’d stayed on Earth.

Group Captain Shubhanshu Shukla returned from an 18-day ISS stay about 0.0004158 seconds younger, the change imperceptible in daily life, though clearly measurable with atomic clocks.