| The High Altitude, Long
Endurance mission profile was never meant to be used with manned
platform, but is perfectly suited for unmanned systems. Only
few manned aircraft are prepared to fly and operate at these
altitudes. The thin air at the Tropopause limits the use of
conventional engines, but opens new horizons for surveillance,
communications and electronic eavesdropping activities. After
overcoming the technical obstacles, mission planners could benefit
from unobstructed operations at altitudes well above civilian
or military air traffic. At these altitudes, the atmosphere
is calm, the thin air causes reduced drag, resulting in less
energy required to maintain higher ground speed. Aircraft flying
at these lofty altitudes are well above the jet stream and other
high velocity currents, averaging 40 – 80 knots in speed,
with peaks of up to 160 knots. These currents encountered at
the high troposphere, at altitudes between 20,000 to 35,000
ft., usually affect the performance of aircraft operating at
medium altitudes. (more...) |
|
Until the early 2000s, only few manned platforms could soar
to such heights. One of the first to explore these altitude
was the Lockheed U-2 strategic reconnaissance aircraft, designed
in the late 1950s. A decade later, the SR-71A strategic reconnaissance
aircraft, unofficially known as the "Blackbird," was
used as long-range, advanced, strategic reconnaissance aircraft.
The first flight took place on Dec. 22, 1964. Then the 'Blackbird'
served for 22 years providing strategic reconnaissance missions
and was retired in 1990 only to return five years later to fill
a critical recce gap. Throughout its nearly 24-year career,
the SR-71 remained the world's fastest and highest-flying operational
aircraft. The SR-71 flew at more than three times the speed
of sound (Mach 3) at altitudes in excess of 80,000 feet (approximately
15 miles high).
The successor of the U-2, the U-2R 'Dragon Lady' is still
operational today. Designed for high-altitude intelligence and
reconnaissance missions, this aircraft can fly above 70,000
feet and carry some o the most advanced long-range reconnaissance
gear available today. Its mission payloads include highest resolution
SAR radar in service today, as well as sophisticated SIGINT
systems. Providing near-real-time imagery and signals intelligence
to warfighters and national authorities, the 'Dragon Lady' was
used extensively during operation Iraqi Freedom in 2003 and
provided important damage assessment information after Hurricane
Katrina struck the Gulf of Mexico in 2005.
With the arrival of the RQ-4A
Global Hawk, the missions of U-2R were reduced to those
specific services which could not be supported yet by the unmanned
platform. These missions will be transferred to the Global hawk
fleet in the next decade, as the RQ-4B
(Block 20, 30 and 40) aircraft are fielded, capable of carrying
heavier payloads, including SIGINT and advanced SAR payloads.
 Global
Hawk may be dominating the high altitudes today, but in the
near future, it will have to share those heights with more unmanned
platforms. One such system is the Integrated
Sensor Is Structure (ISIS) developed by Lockheed Martin
Aeronautics. ISIS will provide a new model for persistent, autonomous
ISR platform. Utilizing a stationary stratospheric airship,
ISIS will establish a position on the 'high ground' at an altitude
of 70,000 ft. This airship will be deployed for long missions,
staying in position for one, five or even ten years. It will
provide a persistent early warning sensor able to detect cruise
missiles at distances of 600 kilometers or dismounted enemy
combatants at a range of 300 km.
Smaller but but not less effective for its proposed mission
is the Global
Observer high altitude UAV system developed by Aerovironment.
This aircraft was designed to provide long dwelling stratospheric
capability with global range and no latitude restrictions. Operating
at these heights, the platforms provides 'near space' capability
comparable to satellites, providing services such as persistent
ISR and communications relay, including dedicated communications
support and satellite link redundancy for other UAVs.
 Another
system under development by Aurora Flight Science and Boeing
is the the Orion, High Altitude,
Long Loiter (HALL) Unmanned Aerial System. This stratospheric
platform will be able to cruise at an altitude of 65,000 ft
for about 100 hours, powered by reciprocating engines consuming
liquid hydrogen fuel. With a gross takeoff weight of 7,000 lbs
(3.175 tons) HALL will be able to carry payloads weighing about
400 lbs (181kg). The U.S. Army/SMDC is supporting a team lead
by Aurora and Boeing as a strategic partner, developing two
Orion HALL platforms, to demonstrate the new technology. First
flight is expected by 2009. Aurora and Boeing have also teamed
since 2004 on a Boeing-led concept definition study of a twin-engine,
larger unmanned platform designed for missions over a week long,
carrying multi-sensor payloads weighing up to 2,000 lbs.
 Flying
at the edge of space in the high stratosphere, a future unmanned
aircraft could one day carry weapons or other payloads anywhere
in the world within few hours, or deploy cargo to lower space
orbit, responding within minutes to urgent mission requirements.
These high flyers will be designed to carry our fast strikes
deep into enemy territory, anywhere in the world. Such a project
known as FALCON is
pursued by DARPA and the US Air Force. Lockheed Marin, the system's
developer is planning to fly the first FALCON demonstrator by
the end of 2018, and is preparing to have such platform operational
in about 10 years.
A similar platform expected to be demonstrated around that
time is the X-51 WaveRider, developed by Boeing. This vehicle
will demonstrate capabilities similar to the FALCON, as Boeing
aims to compete with Lockheed Martin to fulfill the future USAF
requirement for global strike with the hypersonic atmospheric
vehicles. The waveRider will integrate a scramjet engine developed
by Pratt & Whitney, a boost rocket motor derived from an
ATACMS missile matched with an airframe built by Boeing. It
will demonstrate acceleration from boost (Mach 4.5+) to Mach
6 -7 cruise.
Topics covered in this review:
|
>