Space Flight Gold Plating / Soldering

Hello all,
I'm new to this finishing website, any insight and advice will be greatly appreciated. Thank you in advance.

My current situation revolves around my involvement with a space project that has been revived from approximately 15 years ago. Several tin plated steel components in the previous design were mated together by way of soldering (Sn63). As a new requirement (due to tin whisker concern) we have been exploring alternative plating methods that contain less than 97% tin content. After some preliminary testing we have found that a gold over nickel plate soldered with Sn63 looks to be a viable option. We are looking for any heritage space applications that may have used a similar method in order to ease our customers hesitancy towards a design change. Does anyone have experience with this?

Additionally, are there longevity concerns when dealing with such a soldered connection? Is it possible that this connection could become brittle over time?

Regards,

For my nickel, if you have any Sn63 on the surface, you will have a similar if not identical tin whisker potential problem.
EN under plate with a silver overplate might be a solution and using silver solder, possibly the lower temp version.