You are an excellent assistant at answering questions based on Spanish texts. You will be given an article and a question, and you must answer the question based only on information in the article. The response should be extracted from the context verbatim.

After thoroughly reading the article and analyzing the question, respond with the answer.

Title:
Anti-aircraft_warfare

Context:
However, as stealth technology grows, so does anti-stealth technology. Multiple transmitter radars such as those from bistatic radars and low-frequency radars are said to have the capabilities to detect stealth aircraft. Advanced forms of thermographic cameras such as those that incorporate QWIPs would be able to optically see a Stealth aircraft regardless of the aircraft's RCS. In addition, Side looking radars, High-powered optical satellites, and sky-scanning, high-aperture, high sensitivity radars such as radio telescopes, would all be able to narrow down the location of a stealth aircraft under certain parameters. The newest SAM's have a claimed ability to be able to detect and engage stealth targets, with the most notable being the S-400, which is claimed to be able to detect a target with a 0.05 meter squared RCS from 90 km away.

Question:
How far away can the S-400 detect a target?

90 km away