[krazycp]

Once it’s flipped over, how do you open it back up?

[The Ninja Scot]

Once it’s flipped over, how do you open it back up?

At the end of your turn, you may discard a card from hand to flip Spacedoor over. (Immune to cards that close doorways.)

https://www.trekcc.org/1e/index.php?id=111&cardID=2141

[eberlems]

Spacedoor is one of the double sided cards.
The way Spacedoor flips is mentioned on the card.
In place of your normal card play, you may return your empty ship docked here (and all cards played on it) to owners' hands, nullifying any Static Warp Bubble targeting you.
OR
In place of your normal card play, download Spacedock or one compatible ❖ ship to outpost.
Flip Spacedoor over after either use.

Spacedoor Back
At the end of your turn, you may discard a card from hand to flip Spacedoor over.