I doubt it's intended to be sarcasm. There is a lot of fearmongering going on regarding Brexit. Regarding this particular article, as another commenter pointed

I doubt it's intended to be sarcasm. There is a lot of fearmongering going on regarding Brexit. Regarding this particular article, as another commenter pointed out the majority of the UK's space spending goes to the ESA, which is separate from the EU. However, pesky things like "facts" shouldn't get in the way of a Brexit story. /s