Thermal Microwave Signature of Rocket Exhaust Plumes

A physics-based method for computing the passive microwave spectrum emitted by rocket engine exhaust plumes is proposed. Microwave emissions have an advantage over infrared for early detection of missile and rocket launches due to their superiority in penetrating through clouds, dust, and fog. The primary technical approach will be based on a well known model called bremsstrahlung, braking radiation, produced by the collision of free electrons with atoms, molecules, and ions in rocket exhaust plumes. This results in a continuum spectrum, in contrast to the line or band spectra of molecular species. A continuum spectrum is consistent with at least one detailed set of measured results. The Phase I program will validate aspects of the current bremsstrahlung model, include effects of the plumes index of refraction, and explore a number of absorption mechanisms.  A basic initial model will compute emission from complete plumes as a function of frequency, altitude, aspect angle, and propellant formulation. BENEFITS: The development of a physics based code to compute passive microwave emissions from rocket exhaust plumes will provide a modeling capability to those DoD and commercial entities requiring knowledge of RF signatures.  For example, the All-Weather Radio Frequency Launch Detection System (AWRFLD) being developed by the U.S. Army Space & Missile Defense Command/Army Forces Strategic Command, uses RF emissions to detect and locate missile launches in all weather conditions.  The results of this SBIR will provide a theoretical understanding of RF emission from missile plumes.