Between 1996 and 1998, a C-141A was used as a towing aircraft in the Eclipse project to demonstrate the possibility of using aerotow systems to bring towed winged vehicles to sufficient altitude to launch small satellites, the ultimate goal was to lower the cost of space launches. Six successful tests were flown with a modified Convair F-106 Delta Dart, the QF-106 variant, in tow. A similar system can be seen in SpaceShipTwo, whereby atmospheric engines carry a rocket-engined "second stage" to high altitude for launch.