707 NASA "Vomit Comet"Boeing 707 NASA Vomit Comet airplane model. At NASA's Johnson Space Center, there is a microgravity research aircraft, a KC 135 Low G Flight Research aircraft (a predecessor of the Boeing 707) which is typically used for refueling military aircraft. The four engine turbojet has been modified to meet NASA's needs to train astronaut and conduct microgravity research. The biggest difference (in addition to removal of the fueling probe), is the way that