A comma splice is a flaw in punctuation, but not a grammar mistake. If two complete sentences are joined with a comma we call it a comma splice.
The first one is a headline, it consists of three noun phrases "Space", "what it is" and "what it isn't". There isn't a complete sentence here, so it can't be a comma splice. A comma is fine, a semicolon is fine too if you prefer.
The second also doesn't join two complete sentences: "his infectious smile" can't be a sentence. What you have is basically a list of thing that are remembered, and lists are usually separated by commas
The third does have two complete sentences, and so it is a comma splice. These look to me like complete sentences. I would use a full stop:
I won't win it. I just want to get through it.