MadSci Network: Physics
Query:

Re: Could an ionization trail be used to track an electric-launched missile?

Date: Tue Dec 27 17:53:23 2005
Posted By: Chris Peterson, Faculty, Denver Museum of Nature and Science
Area of science: Physics
ID: 1130900060.Ph
Message:

Ionization of atmospheric gases results when they are heated to high temperatures- thousands of degrees Celsius. When an object travels through the atmosphere at very high speed, frictional and compressional heating may produce ionization around it, and along its path. For instance, Perseid meteors (at 59 km/s) have been observed with plasma temperatures exceeding 4000 degrees C, and sometimes show ionization trails. Such ionization trails can glow visually, and are efficient reflectors of radio waves. Therefore, they can be detected both optically and by using radar.

Ionization trails are not persistent. The ionized particles recombine within a few hundred milliseconds, so any observation must be immediate.

Detecting a projectile such as you propose by observing its ionization trail is probably not practical. In order to survive at high speeds in the atmosphere and not lose too much speed to drag, the design would need to be highly aerodynamic. Such a projectile, traveling at 3 km/s, would either fail to reach the necessary temperatures for ionization, or would do so only along a very narrow boundary. The combination of very little ionization, short persistence, and rapid diffusion means that any trail would be weak.

Even with careful design, you could expect the temperature along the leading edge of your projectile to exceed 2000 degrees C. Although their specific details are classified, that might be hot enough for U.S. Department of Defense satellites designed to monitor covert rocket launches to detect. Such satellites do routinely detect meteors. I would consider detection of a kinetic weapon by its thermal signature a better mechanism than detection of atmospheric ionization.


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