It's OK, but I would consider putting a comma after "launches". This kind of pattern really stems from conversation, in the case when you realise after the first sentence that your audience might not know what "them" refers to, so you say "Rocket launches that is" to clarify. Obviously in writing you have the opportunity to go back and actually change "them" to "rocket launches", but if you are trying to achieve a chatty or conversational style then you might deliberately keep it as an afterthought.
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