You know, that would make more sense, but unfortunately, the phrase used for what he suggested was jinkoueisei wo uchiageru, which is very definitely "launching a man-made satellite", whereas the only word for "time capsule" that I've ever heard (including in the Free! anime itself) is taimu capuseru. So I'm pretty sure Rin's just kind of a dreamer XD

(But I did go back and clean up his dialogue a bit in that section, so hopefully it doesn't sound quite as weird.)