TASK DEFINITION: Generate the answer for a given question. The question requires common knowledge of English. Make sure that the answer is in detail, long, consistent with the context, and requires general knowledge of English. To be less repetitive, please vary your language for each question. Give a proper explanation to answer, and if necessary, provide the definition of various terms. And conclude your answer if it's long. If you have used other resources (e.g., Merriam Webster's.) to answer the question, include citations in your answer. You don't need to paraphrase the context of your resources, but make sure that your answer is consistent and complete.
PROBLEM: What's the difference in meaning between 'register' and 'registry'? Can both be used interchangeably when talking about an official (public) list of items, records?.

SOLUTION: The online oxford dict says: Register noun official list or record, for example of births, marriages, and deaths, of shipping, or of historic places. a book or record of attendance, for example of students in a class or school or guests in a hotel. Registry: noun (plural registries) a place or office where registers or records are kept. But yeah, it also says that a registry too can mean a list. And I think 'Registry' is used more in the former context than the later. Even while talking in context of computers we say things like 'Windows Registry'. For me, the word register brings along a sense of being finite but registry does not. like when I think of a register of records, I usually get a quantified picture of the records list comes to my mind, like a page, or a notebook. but 'registry' brings along a picture of non quantifiable !! or its just weird with me. Anyone have other thoughts on this?

PROBLEM: This very well may just be outside our lexicon at the moment, due to the fact that space travel is extremely limited, but I am looking for the proper terminology to refer to a space vessel that had been rendered a wreck or a derelict, and was repaired and refitted into a workable vessel. In naval terms, a sunk vessel would be refloated, but that term is awkward to use in space. Something like reatmosphered fits the context, but it is awkward and not in the lexicon (though its form makes its intent clear, and could be readily used). Any ideas?.

SOLUTION: Consider recommission, which is defined (somewhat obviously) by oxforddictionaries.com as 'commission again'. This sense of 'commission', in turn, is defined by oxforddictionaries.com as Bring (something newly produced) into working condition

PROBLEM: I am looking for a word or phrase which can be used in the sentence: It is a rather old, but _________________ technology. The word or phrase should address a technology that is totally investigated, researched in detail, and thoroughly optimised, so there is nothing more to find out or improve.

SOLUTION:
Most common term I have seen repeatedly and would thus use is, well established. It is rather old, but well-established technology Note as correctly point out by @Chappo below in this case grammar dictates a hyphen is required since it is a compound adjective preceding a noun. 'science can be leading edge or well established' Wiki Technology