Here's a closer view of what I believe is the mobile service tower at SLC-17B. SLC-17 was originally built to support the Douglas PGM-17 Thor missile, which evolved into the Delta expendable launch vehicle. Pad A is now mothballed, and Pad B is awaiting the final Delta 2 launch, NASA's GRAIL satellite.
Copyright 2011, Garrett Wollman. All rights reserved. Photograph taken 2011-02-26.