Stardust is a program to reviewuate incoming meteors by monitoring the VHF radio reflectivity of ionized meteor trails. Meteor trails normally form from 90 miles up down to about 70 miles or so. These trails are composed of ionized atmospheric gases. The more energy imparted to the atmosphere, either be velocity or by size, the longer the ionized trail will last. Incoming speeds are between about 40,000 and 140,000miles per hour.
Size is usually that of a sand grain.
The ionized meteor trail has an interesting property. It will cause reflection of radio signals in the 30 MHz to 150 MHz range. Mid-range frequencies are best. An FM or TV receiver that is tuned to a station far beyond the line of sight will occasionally detect a momentary reflection of the sky wave signal back down to earth. Depending on meteor activity, size and velocity of the meteor, power of the transmitting station, distance of the transmitting station, orientation and gain of the receiving antenna, sensitivity of the receiver, etc.