Unmanned Vehicle To Gather Valuable Data
NASA has set Saturday, March 27, for the flight of its
experimental X-43A hypersonic research aircraft. The unmanned
12-foot-long vehicle, part aircraft and part spacecraft, will be
dropped from the wing of a modified B-52 aircraft, boosted to
nearly 100,000 feet altitude by a booster rocket and released over
the Pacific Ocean to briefly fly under its own power at seven times
the speed of sound, almost 5,000 mph. The flight is part of the
Hyper-X program, a research effort designed to demonstrate
alternate propulsion technologies for access to space and
high-speed flight within the atmosphere. It will provide unique
"first time" free flight data on hypersonic air-breathing engine
technologies that have large potential pay-offs.
Hyper-X is inherently a high-risk program. No vehicle has ever
flown at hypersonic speeds powered by an air-breathing scramjet
engine. In addition, the rocket boost and subsequent separation
from the rocket to get to the scramjet test condition have complex
elements that must work properly for the mission to be
successful.
The $250 million program began with conceptual design and
scramjet engine wind tunnel work in 1996. In a scramjet
(supersonic-combustion ramjet), the flow of air through the engine
remains supersonic, or greater than the speed of sound, for optimum
engine efficiency and vehicle speed. A scramjet operates by
supersonic combustion of fuel in a stream of air compressed by the
high forward speed of the aircraft, as opposed to a normal jet
engine, in which the compressor blades compress the air. Scramjets
start operation at about Mach 6, or six times the speed of
sound.
There are few or no moving parts in a scramjet engine, but
achieving proper ignition and combustion in a matter of
milliseconds proved to be an engineering challenge of the highest
order. After a series of successful wind tunnel tests, however,
NASA is ready to prove that air-breathing scramjets work in flight.
This will mark the first time a non-rocket, air-breathing scramjet
engine has powered a vehicle in flight at hypersonic speeds,
defined as speeds above Mach 5 or five times the speed of
sound.
Researchers believe these technologies may someday offer more
airplane-like operations and other benefits compared to traditional
rocket systems. Rockets provide limited throttle control and must
carry heavy tanks filled with liquid oxygen, necessary for
combustion of fuel. An air-breathing engine, like that on the
X-43A, scoops oxygen from the air as it flies. The weight savings
could be used to increase payload capacity, increase range or
reduce vehicle size for the same payload.
The X-43A will fly in the Naval Air Warfare Center Weapons
Division Sea Range over the Pacific Ocean off the coast of Southern
California. After booster burnout, the 2,800-pound, wedge-shaped
research craft will separate and fly on its own to perform a
preprogrammed set of tasks. After an approximate 10-second test
firing of the engine, the X-43A will glide through the atmosphere
conducting a series of aerodynamic maneuvers for up to six minutes
on its way to splashdown.
This will be the second flight in the X-43A project. On June 2,
2001, the first X-43A vehicle was lost moments after release from
the wing of the B-52. Following booster ignition, the combined
booster and X-43A vehicle deviated from its flight path and was
deliberately destroyed. Investigation into the mishap showed that
there was no single contributing factor, but the root cause of the
problem was identified as the control system of the booster.
For this flight, the B-52 will carry the booster with the
attached X-43A to at least 40,000 feet before its release, versus
the 24,000 feet of the first attempt. This will help reduce
atmospheric loads on the booster's control surfaces. The booster
will carry the X-43A research vehicle to approximately the same
test conditions -- altitude and speed -- as planned for the first
flight.