Why did space shuttle Columbia's last mission use a light weight external tank instead of the super light weight external tank?

The super light weight tank was first used in June 1998 on STS-91, so just wondering why STS-107 used a older light weight tank instead of the newer super light weight tank?

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  • 6 years ago
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    The Super Lightweight Tank (SLWT) was first flown in 1998 on STS-91 and was used for all subsequent missions with two exceptions (STS-99 and STS-107).[8] The SLWT had basically the same design as the LWT except that it used an aluminum/lithium alloy (Al 2195) for a large part of the tank structure. This alloy provided a significant reduction in tank weight (~3,175 kg/7,000 lb) over the LWT. Although all ETs produced after the introduction of the SLWT were of this configuration, one LWT remained in inventory to be used if requested until the end of the shuttle era. The SLWT provided 50% of the performance increase required for the shuttle to reach the International Space Station.[9] The reduction in weight allowed the Orbiter to carry more payload to the ISS' highly inclined Orbit.

    As Columbia on STS 107 was not going to the ISS' orbit, it had no need of the capabilities of the SLWET.

  • The newer version was lightweight but the engineers who created it didn't take into consideration the nonlinear nature of time when they created it, which would have made for catastrophic failures on exiting the atmosphere.

    This was a lesson NASA had learned with the Challenger being destroyed, that 'lowest bidder and/or 'best' materials aren't t necessarily the best way to go. Publicly, they blamed this on the O-Ring to simplify the public discussion, but privately, it was a cascading failure which caused the Challenger destruction, in part due to the government's flawed 'low bidder' and 'top quality' technology models.

    New technology isn't necessarily always new. Nor always the most reliable, which in mission critical situations like this where lives and public image is at stake, can you blame them for being cautious?

    On that note: The catastrophic failure of the commercial rocket in the Mojave demonstrates the VERY same problem NASA had successfully avoided.

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