Overview of challenger space shuttle tape-data recovery study

Degraded magnetic tapes recovered from the Challenger space shuttle, after being immersed in seawater for six weeks, could not be unwound without damaging the recording surface. The recording side had become cemented to the backside. During unwinding, the fragments from the recording side, mostly at tape edges, transferred to the backside, and remained firmly adherent. Magnesium hydroxide was found to be the substance adhering the recording surface to the backside. It is thought Io have precipitated due to the increased concentration of magnesium ions resulting from the corrosion of the magnesium alloy flanges of the reel assembly. In addition, we found that low-molecular weight degraded magnetic-coating binder was present on large areas of the backside of the tape. Matrix experiments showed that the presence of magnesium hydroxide was primarily responsible for the interlayer adhesion. We found that magnesium salts could be removed with a treatment of 0.5 molar nitric acid, and low-molecular weight binder could be dissolved with a methanol rinse. We devised a method to chemically treat the damaged reels. We first removed the eroded magnesium hub and placed the reel on a spring-loaded plastic ring. The reel was then treated in a wash tank. The reel was treated under partial vacuum with nitric acid and methanol. As a last step, the treated reel was relubricated to replenish it with lubricant. After treatment, the reels were carefully unwound without any damage to the recording surface. The reels had to be manually unwound in a 180° peel mode at a very slow rate of about 0.15 meters per minute. The digital data from the unwound reels were recorded in analog mode for optimizing reprocessing using a commercial drive which operates under low tape tension and speed. The copied reels were then digitized by NASA. Over 90% of the data blocks from a recorder were readable and 100% of the voice data blocks were recovered.