I have a feeling Mongoose-V (32-bit MIPS) is manufactured in a 0.18um process node. I'm not 100% sure but it would coincide with the time of the release. HR5000 (64-bit MIPS) might be manufactured in a more recent SOI process node.
I don't think these are normal CPUs. I'm not an expert on this by any means, but is a radiation-hardened CPU (as is needed in space) manufactured with a different process than chips designed to operate within the Earth's atmosphere?
Yes but process node characteristics such as the gate length and/or the silicon film thickness should be relatively similar.