Not to labour a theme, but a little known application for the venerable Boeing 707 is in low gravity research. The US military have been using a few of their KC-135 aircraft, which is the military version of the B-707, for years to perform low-G tests by performing parabolic flight patterns. Imagine an aircraft viewed from the side swooping up from about 10,000' to nearly 40,000' and then down again, forming a parabola. At the top of the arc the occupants experience very low gravity for a short period (it's rather like going over a hump-back bridge in a car). Compared with sending up space ships, this provides a low-cost way to experience low gravity.
Unfortunately for the occupants, who are often scientists with little extreme flight experience, the effect of performing these manouvers repeatedly for several hours can cause some queasiness. That's why the aircraft used to fly these missions is known as 'The Vomit Comet'. It is reputed that one machine's interior had been exposed to so much stomach acid that it had begun to corrode the rivets holding the fuselage together and had to go in for major maintenance. Hope you're enjoying your breakfast.