It’s a demonstrative, but it doesn’t necessarily mean the speaker is pointing to the lab or it’s nearby. Sometimes, we replace the indefinite article with ‘this’ in a story for emphasis (and to signal that we’re about to provide an anecdote or tell a story). I have a friend who is obsessed with Taylor Swift —> I have this friend who is obsessed with Taylor Swift and she ….

Demonstrative adjective: It modifies the noun, science lab, and indicates which one is being referred to. Deictic word: It points to a specific, nearby location or object, implying proximity or immediacy. In this context, this means, the one we're currently talking about or referring to and the one that's nearby or present. The English significance of the word this, is that it helps to clarify which noun is being referred to and provides spatial or contextual information can be used to contrast with other nouns (e.g. this vs that). In the sentence, "this" points to the amazing science lab that the speaker is excited about, implying that it's a notable or impressive facility, much like a mini NASA. I trust that this explanation will help you. Kind regards...

An article is necessary. Both ‘this’ and ‘an’ are possible and similar. ‘This’ is more colloquial and makes the lab sound closer and more important. It moves the focus of the sentence towards the lab.

The word it means NASA