Ultralow Frequency Waves Generated by the Saturn F-1 Engine

Abstract

The source characteristics of the Saturn F-1 engine in the infrasonic frequency range of 0.1–20 Hz and the seismic and magnetic fluctuations from 4 to 16 Hz have been ascertained. The acoustic signals have shown a characteristic ignition and cutoff pulse. The ignition signal shows a typical explosion signature (N-type wave), while the cutoff signal produces a bubble pulse-type effect, which might have resulted from an implosion structure. The engine run produces a steady state signal. However, its acoustic energy peak in the ultralow frequency range is a function of the engine-run duration. The power spectrum shows energy distribution in two regions, with a maxima at 4–8 Hz and at approximately 1.4 Hz, with energy extending to about 0.1 Hz. The lower frequency peak becomes more significant with the increase in the engine-run duration. The magnetic signals have shown a narrow-band signal between 8 and 12 Hz during the engine run and a high-intensity cutoff signal of a wider band. The cutoff signal resembles a pulse. The downward exhaust of the static running of a rocket motor is a source for ultralow frequency acoustic and magnetic waves. Similar conclusions are drawn for the behavior of an Atlas rocket during the first few kilometers of flight.