Apollo 13s Booster Impact
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Apollo 13's Booster Impact

November 28, 2012
In April, the Apollo 13 Saturn V blasted off towards the moon. The Saturn rocket consisted of a 3-stage launching system. While the first and second stage of the launch vehicle dropped back to Earth after launch, the third stage (S-IVB) was used to propel the docked Apollo Command Module and Lunar Module from Earth orbit into a lunar trajectory. The spent rocket booster then separated from the Command Module and later impacted the moon. From the tracking of the radio signals of the rocket, the impact locations on the moon and the impact times were fairly well known. The impacts by the S-IVB stages represented unique calibration signals for the Apollo seismic station network, which operated on the lunar surface from 1969 - 1977. Since the rocket impacts occurred at known times and places, the seismic wave velocities, in particular those within the upper lunar crust could be measured directly. At the time of the Apollo 13 mission, only the seismometer at Apollo 12 was available, which had been deployed 5 months earlier. The S-IVB impact occurred at a distance of 135 km from that seismic station. Analysis by the LROC team now have identified the craters associated with most of the rocket impacts in their predicted areas. Taking advantage of the precise LRO orbit and LROC pointing knowledge, it is now possible to determine the impact coordinates of rockets and their distances from the seismic stations more accurately to within a few hundred meters, over time as the orbit calculations are improved these estimates will in turn become more accurate. The precise impact coordinates may warrant a reanalysis of the seismic calibration data for improved models of seismic wave propagation within the moon and the Lunar interior structure. The seismograph network recorded more than 13,000 seismic events and delivered some of the most important scientific results of the Apollo missions. This image shows A Saturn 5 third stage (S-IVB) being prepped for integration. Credit: NASA

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