What is the emission of your stealthiest ship? At what range would you like to detect it? If you have encountered alien life forms that are hostile to you what is the emmision rating of their ships? Where would you like to detect them?
Based on the answers to those questions you have your answer.
Your detection ability is currently for a thermal signature of 100:
14000 DSTS strength*100 IR signature = 1 400 000 K km or 1.4 billion km (around the orbit of saturn). You would pick up a missile at >14 million km from Earth.
You would detect a typical active search sensor at a minimum of 20 times that far (30 billion km)...which is pretty much in interstellar space.
