Radio Echoes From the Ionized Trails Generated by a Manned Satellite During Re-Entry
Abstract
Observation was made of the ionized trails produced during re-entry by the MA-6 Mercury capsule carrying Lt. Col. John Glenn in his first orbital flight on February 20, 1962. The observation was made from San Salvador Island (Bahama Island Group), approximately 370 miles uprange from the impact point. The apparatus employed was an omni-directional pulsed radar (of 30.25 Mc/sec carrier frequency) similar to those employed by radio astronomers in the study of meteor echoes. When the Mercury capsule was passing over the vicinity of the observation station at about 14 hr. 33 min. EST., five clearly separated ionized trails were observed. The most prominent trail, which may be identified with the wake of the main capsule, was visible radar for a total duration of about 20 seconds, and displayed an equivalent isotropic scattering cross-section of about 1,000,000 radio square meters at its peak. The other four trails, which were probably due to fragments of the disintegrating retro-rocket package by Col. Glenn, showed only short duration glints (of the order of one second) characteristic of the smooth, rapidly decaying trails of small meteors. While some of the fine structure of the long-duration, scintillating echo from the main capsule trail is not yet understood, the overall characteristics of the trail can be accounted for by a combination of high-light from a strongly reflecting front segment of the ionized wake, which appeared electromagnetically smooth to the 10-meter wavelength employed; and diffuse scattering from a fully developed turbulent rear segment of the wake, which appeared rough to the wavelength. This readily suggests a simple explanation for the formation of "head-echoes" by large meteors, which have been previously reported (but not explained) in the literature. The fact that the main capsule trail appeared turbulent indicates a Reynolds number of less than 10000 (based on the velocity and diameter of the MA-6 capsule, and on the ambient air density.
Document Details
- Document Type
- Technical Report
- Publication Date
- Sep 01, 1961
- Accession Number
- AD0275098
Entities
People
- R. B. Janney
- Stanley Lin
- W. P. Goldberg