I'm wondering when to use or not to use the definite article, when using acronyms or initialisms in a sentence. Is there a rule for this, or does it depend on the context?
For example, let's look at some example sentences
DDR = detailed design review.
NASA is planning to launch the final shuttle soon (no article)
The FBI shut down this website (article)
ESA is a full partner in the ISS (no article, article)
The project was cancelled at the DDR. (article)
What confuses me is that if NASA or ESA would be written in full, the article would be necessary.