Photograph of Lockheed L-300, a civilian version of the Lockheed C-141 Starlifter.
Source: http://www.codeonemagazine.com/article.html?item_id=34
This is the Lockheed Model 300 (L-300), the only civil-registered C-141 StarLifter transport to be be built. A number of air cargo operators -- notably Flying Tiger Lines -- placed orders for the L-300, but all of the contracts were eventually cancelled. This aircraft, registered N4141A, was later transferred to NASA and was modified to become the Kuiper Airborne Observatory at was based at Moffett Field, California. The aircraft was fitted with a thirty-six inch infrared telescope.
Source: http://www.codeonemagazine.com/article.html?item_id=34