HORN%HYDRA%sdi.polaroid.com@RELAY.CS.NET (01/17/90)
From: HORN%HYDRA%sdi.polaroid.com@RELAY.CS.NET In recent notes there has been some question about the need for compute cycles in the B-2. The estimate for cycles needed in electronic warfare threat assessment is 10^9 - 10^10 complex operations per second. This already assumes that non-digital means are employed where more cost effective. This is quite a contrast to the ``$250 radar detector''. To understand the difference, consider what that detector will tell you. It beeps whenever you are painted by an X-band radar. If the pulses come frequently enough, it squeals. In a radar dense air defense network you are likely to hear many beeps just from ordinary scans. If you hear a squeal, you have a few moments to figure out where the bad guy is and evade. Actually, if an X-band is locked onto a B-2 you might consider aborting your mission. It means that either a fighter or SAM has you in target track. Unless you know where they are -- and the detector won't tell you -- you are unlikely to evade and survive. A modern passive ECM system provides the following information: what radars are operating within sight, what mode they are in, where they are located (both angle and range estimate), what kind of weapons systems are associated with these radars, what threat is posed (given the weapon system and operating mode), and provides this information to the crew and the active ECM system. To do this every pulse received must be analyzed for direction, frequency, operating mode, radar code words, and similar information. Then each pulse must be correlated with the pulses from the past few minutes to associate pulses from the same source. The sources must be tracked. A dense radar environment will have thousands to millions of pulses each second. These must be correlated in real-time, analyzed into the operating mode for various weapon systems, and displayed so that the B-2 crew can evade the danger spots. In support of this is some analog processing that is equivalent of even more gigaflops. The initial requirement for frequency per pulse analysis is a monster. The goal is to listen on 0-20 GHz and analyze each pulse to within 50MHz. You need to do this in about 250 nsec to avoid losing pulses or missing some operating modes. The FFT to handle 500 MHz of bandwidth to this resolution and speed is 2x10^9 butterflies per second (10 gigaflops). This is likely to remain analog processing for some time. (Not cheap either). _Introduction to Electronic Warfare_, by D. Curtis Schleher, Artech House, is a book that I found to be good as an overview of most aspects of electronic warfare. It does not cover stealth technology much, but does address most of the goals and techniques of EW, ECM, ECCM, etc. Brookner's new Radar Technology has a good section on stealth. One important thing to remember in all stealth discussions is the basic stealth truism ``A 100% effective stealth is 100% useless'' because you must sacrifice all performance and payload to achieve it. Stealth is like wearing good camouflage at night. You are much harder to find, but findable if you get too close or make a mistake. Rob Horn Horn%hydra@polaroid.com