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In reading a question over on Physics.SE (I can't quite remember what it was about, something to do with rocket stages and launching over water) I came across a link to this picture:- enter image description here

Over on the west coast there is a shaded area dubbed 'ET Disposal Problem'.

At first guess I would say it's an area in which a jettisoned external tank would have a higher chance, than "usual", of hitting a populated area/land in general.

Am I correct? If so is there anything else notable about it?

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    $\begingroup$ I could probably make a joke about Extra-Terrestrials, but I'll spare everyone;-) $\endgroup$ – PearsonArtPhoto Jun 19 '15 at 15:57
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    $\begingroup$ I think you're right. This page from "Space Vehicle Design" says basically the same thing on a payload/altitude chart: "potential ET disposal problems exist for inclinations below 70˚" (from Vandenberg) books.google.com/… $\endgroup$ – Russell Borogove Jun 19 '15 at 15:59
  • $\begingroup$ Normally the tank would be kept for a lot longer, so I guess this is where the tank might fall if a Return To Launch Site abort was required... just a guess though. If one had ever launched from Vandenberg. $\endgroup$ – Andy Jun 19 '15 at 16:11
  • $\begingroup$ Pretty sure Andy's right -- this is specific to the return abort. $\endgroup$ – Russell Borogove Jun 19 '15 at 17:17
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This was when planning safe disposal of the External Tank on certain types of launch abort.

Source: Space Shuttle Abort Evolution page 9-10

A major design activity was conducted preparing for Shuttle launches on the West coast from Vandenberg AEB. Though not flown due to new program directions following the Challenger accident, a lot of design work and analysis was done. The launch abort environments were significantly different than those for the East coast launches and required a lot of changes for the aborts. Therefore the launch aborts for the initial WTR launch were designed to be benign with considerable margin. Instead of returning to the runway at Vandenberg AFB, the RTLS was designed to return to Edwards AFB where the lakebed offered multiple runway choices for surprises. This introduced a problem with an unacceptable ET disposal on land following MECO. A dogleg trajectory was inserted to steer the ET out in the Pacific Ocean prior to MECO to avoid disposal on a populated area. Then bank the Orbiter to glide in to EAFB.

In other words, if an engine failed early the plan for an RTLS abort was to turn around after SRB burnout, use the remaining fuel to aim the shuttle at a suitable landing field, and drop the External Tank. For Vandenburg launches, this additional step of targeting the tank safely was done.

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    $\begingroup$ Thanks for this answer. I had forgotten that WTR RTLSs ended up at EAFB. I did remember that the downrange abort (analogous to TAL) was to Easter Island. We got far enough in the simulations of 62-A to fly these aborts. $\endgroup$ – Organic Marble Jun 19 '15 at 19:31
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I believe you are right, it is the External Tank. Why does it have problems? The external tanks were deposited in either the Indian or Pacific Oceans, clear across the world. So, what would that do for a low southward inclination launch from Vandenburg? It would cut across South America, then over Africa, the Middle East, and Russia, with only a brief stay over the Atlantic and Pacific oceans. Basically, there wouldn't be any significant gaps at all in the land mass, and so de-orbiting it would be difficult.

A higher inclination allows for dropping it over the Antarctic region, or the Indian Ocean

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