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NASA Dryden Past Projects: Pegasus Hypersonic Experiment (PHYSX)
August 20, 2009

Pegasus mated under wing of B-52 mothership - closeupPegasus mated under wing of B-52 mothership - closeup

The Pegasus Hypersonic experiment consisted of a smooth, information-gathering "glove" installed on the first-stage wing of a Pegasus Space Launch Vehicle, which reached a speed of Mach 8 and an altitude of 200,000 feet. The glove was bonded to the right wing and wrapped from the underside of wing, over the leading edge and onto the upperside, although it did not cover the wing completely.

The experiment gathered information about how the air flowed over the Pegasus wing. Scientists were particularly interested in the transition of air from smooth (laminar) to turbulent flow. The goal of the experiment was to discover when the airflow over the wing became turbulent and why.

Airflow has a great impact on how hot vehicles get. Turbulent air generates a lot of heat because of increased friction, which can burn through the skin of an aircraft. The hypersonic X-15 experienced such problems due to turbulence-induced friction. In addition, turbulent air creates more "drag," slowing down aircraft or making them less efficient.

Data from the Pegasus glove experiment also included temperature, heat transfer and pressure measurements, as well as reconstruction of the Pegasus flight path. This experiment provided critical information not obtained anywhere else, as wind tunnels here on the ground can't adequately simulate both the hypersonic speeds and atmospheric conditions the Pegasus booster encounters.

A secondary goal for the program was to provide engineers with valuable experience in instrumenting and testing hypersonic vehicles.

The Pegasus Hypersonic Experiment was one way that NASA continues to meet its goal of achieving revolutionary technology leaps to make aerospace programs more affordable. This goal aims to revolutionize the way in which aerospace vehicles are designed, built and operated.


Flight Scenario

The hypersonic glove experiment flew in October 1998. Pegasus' primary goal for the mission, which originated from the Cape Canaveral Air Force Station, Cape Canaveral, FL, was to launch a commercial satellite payload. Pegasus carried the glove aloft as a secondary mission that did not interfere with the launch vehicle's primary payload.

Once the first stage Pegasus booster rocket launched from its L-1011 mothership, the highly instrumented glove gathered information about flight at high speeds and altitudes. Sensors in the glove gathered information for about a minute and a half before the first-stage of the rocket burned out and was jettisoned.

All information the glove obtained was transmitted to the ground through a radio signal as the glove was not recovered. To make transmitting the data possible, engineers at the NASA Langley Research Center, Hampton, VA, developed a special data acquisition, compression and processing system. In January 1995, Dryden's F-15 aircraft tested the system during a series of flights over Edwards Air Force Base, CA.



Two Pegasus Hypersonic Experiment gloves were manufactured for the program - one that flew aboard the Pegasus booster rocket and one for thermal ground tests. Both gloves were made of nickel-plated steel.

PHYSX Glove testPHYSX Glove test

The ground-test glove was mounted on a plywood and fiberglass structure for a series of tests that concluded May 30, 1996. The glove was painted a flat black to maximize heat absorption. During the tests, engineers pre-cooled the glove and heated it in NASA Dryden's Flight Loads Laboratory, simulating the heat the glove will experience during its first-stage flight profile. The tests revealed that the glove was hardy enough to survive the intense heat it experienced while traveling at eight times the speed of sound.

The flight-test glove was mounted on balsa wood and surrounded by a drag-reducing thermal protection system structure made of Space Shuttle tile material that blended the glove into the wing. NASA Ames Research Center, Moffett Field, CA, supplied the thermal protection system, which dissipates heat. The glove was mounted to the Pegasus wing at Dryden. The Pegasus booster rocket was secured to its L-1011 launch vehicle at the Orbital Sciences Corp.'s Vehicle Assembly Building at Vandenberg Air Force Base, CA.

The glove carried traditional and high-frequency sensors capable of functioning during the flight conditions the Pegasus rocket will experience. The sensors gave engineers a variety of information like acceleration, air flow, pressure, temperature, and strain. Many of these sensors were evaluated in July 1994 aboard an earlier Pegasus mission. The mission verified that the sensors do not interfere with the airflow over the Pegasus wing and that the vibrations the sensors will experience during flight will not interfere with obtaining accurate data.


Roles and Responsibilities

Dryden provided overall management of the glove experiment, glove design and buildup. Dryden was responsible for conducting the flight tests. Langley was responsible for the design of the aerodynamic glove as well as development of sensor and instrumentation systems for the glove. Other participating NASA Centers included Ames; Goddard Space Flight Center, Greenbelt, MD; and Kennedy Space Center, FL. Orbital Sciences Corporation, Dulles, VA, was the manufacturer of the Pegasus vehicle, while Vandenberg Air Force Base, CA serves as a pre-launch assembly facility.


Pegasus Background

First flown in 1990, Orbital Sciences Corporation's Pegasus rocket supports a wide range of missions, including space technology validation, earth science and space physics experiments, hypersonic flight research, earth imaging, communications, and planetary exploration. The three-stage Pegasus launch vehicle is carried aloft by the company-owned L-1011 "Stargazer" aircraft to a point approximately 40,000 feet over open ocean areas, where it is released and then free-falls in a horizontal position for five seconds before igniting its first stage rocket motor. With the aerodynamic lift generated by its delta wing, the small rocket achieves orbit hundreds of miles above the Earth in approximately ten minutes. Pegasus is capable of carrying payloads up to 1,100 pounds.

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Page Editor: Yvonne Gibbs