Aircraft Dynamics And Payload Interaction – SOFIA Telescope

Abstract

The Stratospheric Observatory for Infrared Astronomy (SOFIA) is now in operation out of NASA Dryden Flight Research Center and is providing astronomical science observations not possible from other Earth- and spaceborne observatories. A 2.7 meter telescope which weighs 34,000 pounds has been installed in the aft fuselage of a Boeing 747SP aircraft. This required significant structural changes to the airframe. Further, the telescope is installed on an isolation system with a dynamic control system for properly positioning and controlling the pointing of the telescope. The major structural modifications of the aircraft and the dynamic interaction of the telescope with the aircraft are important issues related to the aircraft flight stability. Ground vibration testing (GVT) was performed to recharacterize the dynamic properties of the aircraft with the telescope installed. This testing was performed prior to delivery to NASA DFRC, where the flight test program was conducted. In addition to standard GVT measurement parameters, the testing involved evaluation of the acoustic cavity where the telescope is installed. Dynamic testing was also performed to investigate the structural coupling interaction that occurs when the telescope control system is activated.