Most commercial satellites are insured in case something bad happens on launch. Although the Ariane 5 is a fairly reliable rocket, a launch failure is not out of the question.
While other questions have said that if the JWST fails to deploy it's basically SOL ("Sadly Out of Luck") and I would assume uninsurable, rocket launches are regularly insured. Is the JWST insured against the failure of the Ariane 5?
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