On Tue, 29 Nov 2011 00:31:48 -0500, "Greg \(Strider\) Moore"
wrote:

He did by authorizing ET-122 be restored from Katrina damage and using
ET-138 on an actual flight and not held in reserve for a rescue
flight. The only remaining complete, flightworthy tank is ET-94, the
last Light Weight Tank, heavier than the Super Light Weight Tanks
(ET-96 and up, ET-95 was never built, neither was ET-7) used for Space
Station missions, and thus not really suitable for Station work.

I believe there were 3 more in the works (I'd have to wiki/google it but my
browser is acting up right now.)

Those were a long way from being usable tanks though. We're
essentially talking about restarting External Tank production to get
them done. This isn't the same as the two built-but-not-flown Saturn
Vs that Nixon left to be lawn ornaments.

And ET-94 was usable, just limited the payload. Which for post construction
flights was less of an issue.

ET-94 is also 14-ish years old and was sliced and diced by the CAIB
after STS-103. I highly doubt NASA would have trusted a manned mission
to it. That's why it is only being considered for use by SLS.

Brian