Infrasound Detection of Rocket Launches

The satellite launch industry is a multi billion-dollar international industry with over 100 commercial and military satellite launches conducted in 1999 alone. Rocket launches from both Cape Canaveral Air Force Station (CCAFS) and Vandenburg Air Force Base (VAFB) have been observed at operational infrasound stations monitored by the Prototype International Data Center (PIDC). As more IMS infrasound stations are installed worldwide, we can expect to more frequently observe rocket launches. Rocket launches may serve as useful “ground truth” data and/or Confidence Building Measures (CBM) to test and demonstrate IMS infrasound capabilities. Commercial and military launch facilities include Baykonyr in Kazakhstan, Plesetsk in Russia, Jinyu, Wuzhsi, Jiuquan, Xichang, and Taiyuan in China, Kourou in French Guinea, Alcantara in Brazil, Tanegashima in Japan, Vandenburg AFB and Cape Canaveral AFS in US, and the new Boeing ocean-going launch platform in the Pacific Ocean. “Summer season” Space Shuttle launches are seen at the experimental DLIAR (2550 km) infrasound array in New Mexico and the more recently installed infrasound array, ISM (2780 km), in Canada. These long-range observations are strongly correlated with the geometry of stratospheric winds across North America. The 1-4 Hz signals arrive within 5 degrees of the nominal azimuth. In order to take advantage of favorable West-to-East propagation, waveforms were examined for 14 VAFB launches in 1999 at SGAR (680 km) and DLIAR (1300 km). Detections were seen for a Titan IVB launched 5/22/99 and a Delta II launched 04/15/99. Interestingly, the Delta II of 02/22/99 and the Atlas IIA of 12/18/99 were not detected although these two rockets are of similar size. Upper atmospheric wind conditions should have been favorable for several of the detections, however noise levels were often high at SGAR and DLIAR. Relative amplitudes of the signals are consistent with relative thrusts (700 vs. 1700 thousand lbs). Observed arrival azimuths were within 5 degrees of nominal. Detailed analysis of DLIAR signals indicate azimuth can be tracked down-range from the launch site for two minutes. Arrival times and phase velocities are consistent with stratospheric propagation and nominal infrasound travel times to SGAR (2340 s) and DLIAR (4440 s). The signals were best observed between 0.1-2 Hz. Long-range detections of Space Shuttle, Titan IVB, and Delta II launches are very encouraging. The Space Shuttle burns about 1 KT of liquid oxygen and hydrogen per minute. Therefore the equivalent explosive yield of the extended infrasound source is between one and two orders of magnitude smaller than 1 KT. The Titan IVB and Delta II launch vehicles are an order of magnitude smaller than the Space Shuttle. OBJECTIVE This work examines rocket launches as potential ground truth events to demonstrate long-range IMS infrasound capabilities such as detection and azimuth estimation as a function of changing atmospheric conditions. REVIEW Man-made low-frequency infrasound (less than ~20 Hz) may be excited by large strip-mine blasts, atmospheric explosions, gas pipeline ruptures, rocket launches, orbital (and sub-orbital) vehicle reentry sonic booms, and aircraft sonic booms. Some sources are point like (explosions) and others are distributed along a trajectory (meteors, sonic booms and rocket launches). The literature contains several examples of infrasound from missile launches in the late 1960’s and early 1970’s. Most results were an off-shoot of infrasonic research done for long-range atmospheric nuclear test detection. Interest in the topic diminshed as nuclear powers shifted to underground testing. Publications by Fehr (1967), Donn et al (1968), Kaschak (1969), Kaschak et al. (1970), Donn et al. (1971), Cotton and Donn (1971), Balachandran et al. (1971a), Balachandran et al. (1971b), and Posmentier (1971) provided an analysis of the frequent and large rocket launches of the early manned space program.