This is my interpretation.
The whole album OK Computer, from which this song is from, is a concept album about how machines are gaining more importance in our lives, and how they'll dominate us soon. So in that context, "airbag" is literally about an airbag saving a man's life in a car crash, and after saving the man's life, it realises that it has the power to save lives, and so it says "i'm back to save the universe". And the "interstellar burst" can be compared to a sudden car crash's impact, kinda like a burst.
This is my interpretation. The whole album OK Computer, from which this song is from, is a concept album about how machines are gaining more importance in our lives, and how they'll dominate us soon. So in that context, "airbag" is literally about an airbag saving a man's life in a car crash, and after saving the man's life, it realises that it has the power to save lives, and so it says "i'm back to save the universe". And the "interstellar burst" can be compared to a sudden car crash's impact, kinda like a burst.