[dave1010uk]

This is a really cool idea using fundamental properties of physics but I don't think it works.

If the spacecraft is trusted by the person with the secret, it's much simpler to instruct the spacecraft to only disclose the secret after a set date. You don't seem to gain anything from the carded complexity.

If the spacecraft isn't trusted, there's nothing it stopping it disclosing all the key pairs at once.

I think the best bet at the moment is something like Rivest-Shamir-Wagner time lock puzzles, which requires a fixed number of sequential computations to perform.