You need to use the Babbage-Kasiski method to work out the likely length of the keyword. In this case the answer is in the headline of this article:
https://edition.cnn.com/2018/11/25/opinions/nasa-insight-mars-landing-don-lincoln/index.html
(Trying to avoid spoilers if you want to work it out for yourself!)
That tells you the repeating pattern. If the answer is n then every nth letter is encrypted using the same alphabet so you can do frequency analysis on them to see what substitutions may have been made. Since the word structure is given this might help with finding cribs.
Does that help?
Hope so.
Happy New Year,
Harry
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