28-11-2012, 05:08 PM
IEEE 1st Flight Testing Conference
AIAA_1981-2512.pdf (Size: 516.57 KB / Downloads: 23)
Abstract
The Orbiter Experiments Program, referred to as
OEX, is a NASA program to provide research instru-mentation on the Shuttle Orbiter. The individual experiments currently under development are described as well as the specific research problems to be attacked. The research focuses on the entry phase of the flight. The experiments, combined with other instrumentation onboard the orbiter, will provide a wealth of benchmark flight data which is expected to make a significant impact on the design of future space transportation systems.
Introduction
One of the distinguishing marks of the 1980's for aerodynamicists ani aerothennodynamicists kill be periodic flights of the space shuttle, Nhich will provioe recurring opportunities to stbdyflight problems of a winged vehicle from hypersonic entry conditions to touchdown. In order to capi-talize on this opportunity, the National Aeronautics and Space Administration has instituted the Orbiter Experiments Program, familiarly known as OEX. The purpose of the OEX program is to pro-vide the means by which researchers may design,develop, and mount on the shuttle instrumentation for specific flight research purposes.
Ground-Based Data Limitations
The most extensive portion of this base has been ground test data. cient in modeling of several aspects of entry envi-ronment. The most serious of these deficiencies are in the failure to duplicate flow chemistry and failure to predict reliably boundary-layer transi-tion. Conventional wind tunnels are not designed to produce high flow enthalpy, and although they may be hypersonic, they are not hypervelocity.other devices, which include shock tunnels, shock tubes, arc tunnels, hot-shot tunnels, expansion tubes, and free piston compressors, have been built in attempts to mdel the high enthalpy aspects of entry. While such devices have made valuable con-tributions, each has encountered limitations which impaired its usefulness and restricted the type of prgblem to which it could contribute useful data.
Rarefied Flow Effects
For entry trajectories such as flown by the orbiter, signiftcant forces and heat transfer are sensed while the atmosphere is still quite rarefied. Figure 1 Illustrates the range of values of mean free path and viscous interaction parameter, T,encountered. The author is not aware of any experi-mental data on the orbiter which model this rarefied portion of the entry.particularly the transttional regime between con-tinuum and free-molecule flow, has increased because of possible future missions utilizing aero-assist for trajectory control. orbital transfer vehicle operating between geosyn-chronous orbit and low Earth orbit may accomplishits orbit change by a decelerating pass through the upper atmosphere. In such a maneuven the principaldeceleration and heating would occur in the transi-tional flow regime. Thus, evaluation of rarefied flow effects on the orbiter would help assess per-formance of such aero-assist vehicles.