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High Altitude Platform
SystemsAmir Gilan Varnosfaderani
Introduction 1.1 Introduction
With an ever increasing demand for capacity for future generation multimedia applications, service providers are looking for novel ways to deliver wireless communications services. In developed countries we are familiar today with seeing mobile phone masts dotted around the countryside, but these can be expensive to deploy and continually service. This patchwork of coverage delivers cellular communications, an efficient way of delivering high-capacity density services. We use the term cellular here to describe the way in which the radio spectrum is reused in order to deliver the high-capacity densities. This concept is now being adopted with a number of technologies, including the widely known 2G and 3G mobile systems, but also new technologies such as WiMAX, and also WiFi, where in this latter case islands of coverage (hot-spots) are provided through spectrum reuse. An alternative for more rural or less developed areas is to use satellite commu- nications. Satellites today are increasingly sophisticated, and capable of delivering spot beam coverage, with minimal ground infrastructure. However, they are inca- pable of matching the high-capacity densities seen with terrestrial infrastructure. A possible third alternative way of delivering communications and other services is to use high altitude platforms (HAPs). HAPs are either airships or planes, which operate in the stratosphere, 17–22 km above the ground [1, 2]. Such platforms will have a rapid roll-out capability and the ability to serve a large number of users, using considerably less communications infrastructure than required by a terrestrial network [3]. Thus, the nearness of HAPs to the ground, while still maintaining wide area coverage, means that they exhibit the best features of terrestrial and satellite communications.
Categories The main goal of HAPs is to provide semi-permanent high data rate, high capacity-density communications provision over a wide coverage area, ideally from a fixed point in the sky. In practice due to aeronautical constraints all HAPs present compromises. It is helpful to specify the following HAP ‘vital’ statistics, and as we shall see, these may radically affect the communications system design and ultimate capabilities: . payload power, mass and volume; . station keeping and attitude control; . endurance. HAPs can be divided into four categories (as shown in Figure 1.1): 1. Manned plane, e.g. Grob G520 Egrett 2. Unmanned plane (fuel), e.g. AV Global Observer 3. Unmanned plane (solar), e.g. AV/NASA Pathfinder Plus 4. Unmanned airship (solar), e.g. Lockheed Martin HAA
History Like with the start of many new fundamental technologies it is very difficult to pin- point the inventor or the first time it appeared in print. HAPs have their origins back to 1783 when the Montgolfier brothers launched the first hot air balloon. However, it is not until the early 1960s that we start to find direct references or use of airborne craft capable of providing a semi-permanent presence to deliver communications. One example was Echo which was a balloon that was used to bounce radio signals from the Bell Laboratories facility at Crawford Hill to long distance telephone call users. At a similar time the Communications Research Laboratory of Japan published a study on the use of airships to deliver communications. To our knowledge these were not taken much further, and there are other anecdotal references to projects over the years since then. The next public reference that we have come across appears in an editorial in 1992, again proposing a similar concept. It was 1997/8 when HAPs really started generating interest. This was catalysed by SkyStation International who put forward the concept of a 200 m long solar powered airshipHAP,capableofflyingat20kmaltitudeforaperiodofyears.Theiraimwasto provide 3G and broadband communications, both in their infancy at that time. Coverage was planned to be upwards of 300 km diameter, as shown in Figure 1.2, delivered from 700 cells produced from a phased array antenna system. They had a number of credible backers including Alexander Haig former US Secretary of State, and Y.C. Lee as its Chief Technology Officer. This project was taken seriously and much of the initial work within the International Telecommunications Union – Radio communication Sector (ITU-R) was undertaken on behalf of SkyStation, with ITU-R Recommendation F.1500 based on their design. They successfully managed to get 47/48 GHz band for HAPs use at the World Radio communication Conference (WRC) in 1997, with further frequencies at subsequent WRC gatherings.
1: Grob Egrett G520 Grob Egrett was a surveillance aircraft developed in Germany in the 1980s by an international partnership. It was intended to fill a joint Luftwaffe-USAF requirement for a high-altitude, long-duration surveillance platform for treaty verification and environmental monitoring. The G520 design was finalized in 1991. In 1992, the Luftwaffe placed an order for 16 Egrett IIs, including a G 520T two-seat trainer, to be delivered by 2001. However, before much production had taken place, the whole program was cancelled when Eastern Europe ceased to be perceived as a threat, Only 6 aircraft were built and only 5 survive
Manned plane
2 : Global Observer ® The Global Observer® system is designed to work like a 12-mile-high, redeployable satellite to provide coverage over an area of up to 600 miles in diameter. Global Observer will be capable of supporting multiple high-value applications, including communications relay; intelligence, surveillance and reconnaissance (ISR) missions for defense and homeland security, storm tracking, telecommunications infrastructure; wildfire detection, maritime operations, and disaster recovery services.
Communications RelayProviding broad and persistent communications when mission operators need it most.A squad is patrolling an area far from base that is known for enemy activity. Ambushed! Pinned down by deadly enemy fire. Line-of-sight communications blocked by mountains. No reception and no means of contacting friendly forces. Life-saving help is needed.Global Observer® carrying a communications relay payload can link the squad to distant base. Includes satellite-like capabilities to enable affordable, persistent and seamless communications relay capabilities where mission operators need it most. Global Observer can provide more bandwidth to interconnect and route data. Teams separated by topographical barriers and using legacy radio equipment with disparate radio frequencies and signal formats can use communications relay to communicate with each other and to distant command centers in real time.
Disaster ReliefProviding real-time imagery and backup communications when lives are at stake.A Category 5 hurricane is expected to make landfall soon. Millions of lives at stake. Need to know when and where the hurricane will reach land.Global Observer® can provide real-time remote imagery, storm data and backup communications to assist with life-saving measures. Provides hurricane/storm tracking, weather monitoring and sustained support for evacuation planning, relief operations and first response coordination. With a communications payload, Global Observer can provide communications relay if terrestrial communications assets such as cell towers, microwave relays and satellite downlinks are damaged.
Maritime OperationsProviding continuous surveillance of critical shipping lanes and vital coastlines.A massive coastline plagued by transport of illegal goods. Existing manned and unmanned reconnaissance assets are unable to provide the broad coverage needed.Global Observer® at 65,000 feet in altitude can provide coverage of about 600 miles in diameter. Global Observer using an intelligence, surveillance and reconnaissance (ISR) payload can provide long-term surveillance for analysts to observe suspicious activity, determine patterns of behavior and identify threats to enable rapid and effective countermeasures/actions.In addition, Global Observer can provide:Dedicated Communications Support to other UAVsGlobal positioning systems (GPS) services including GPS Augmentation for High Power Anti-Jam/Jammer TrackingBroadband communications relay for military, government and commercial applicationsDetection and Location of Electromagnetic Interference (DCS)Tactical On-station Weather Monitoring and DataEnhancement of Freedom to Commit NSS to Higher Threat Areas/PrioritiesDynamic Tasking to Theater CommandersProvision of Limited Reconstitution CapabilityPersistent, Actionable Intelligence (Optical, IR, GMTI)Battlespace Awareness (Airspace Collision Avoidance)For high-value missions requiring persistent coverage, Global Observer provides a solution that makes sense.
Pathfinder Pathfinder Solar Powered Aircraft
Just imagine... An aircraft that could stay aloft all day, powered only by sunlight.An aircraft that is no more than a flying wing, able to maneuver without rudders, ailerons, tails or other control surfaces typical of conventional aircraft.An aircraft that flies without an onboard human pilot, but instead is controlled remotely from a ground station. At the NASA Dryden Flight Research Center at Edwards, Calif., imagination has become reality, and that reality is the Pathfinder solar powered, remotely piloted aircraft.
ERAST programPathfinder is one of several remotely piloted aircraft being evaluated under NASA's Environmental Research Aircraft and Sensor Technology (ERAST) program. The ERAST program is one of NASA's initiatives designed to develop the new technologies needed to continue America's leadership in the highly competitive aerospace industry. Additional technologies considered by the joint NASA industry ERASTAlliance include lightweight materials, avionics, sensor technology,aerodynamics and other forms of propulsion suitable for extreme altitudesand duration. The most extreme mission envisioned for solar poweredaircraft such as Pathfinder's successor, the Helios, would reach altitudes ofup to 100,000 feet for science and commercial applications, as well as fly for weeks or months at a time on extended duration missions with the assistance of a fuel cell based supplemental energy system for nighttime flight. The ERAST program is sponsored by the Office of Aerospace Technology at NASA Headquarters, and is managed the NASA Dryden Flight Research Center.
Aircraft Description The Pathfinder is a lightweight, solar powered, remotely piloted flying wing aircraft that is demonstrating the techno of applying solar power for long duration, high-altitude flight. It is literally the pathfinder for a future fleet of solar po aircraft that could stay airborne for weeks or months on scientific sampling and imaging missions.
Solar arrays covering most of the upper wing surface provide power for the aircraft's electric motors, avionics, communications and other electronic systems. Pathfinder also has a backup battery system that can provide power between two and five hours to allow limited duration flight after dark.
Pathfinder flies at an airspeed of only 15 to 25 mph. Although pitch control is maintained by the use of tiny elevons the trailing edge of the wing, turns and yaw control are accomplished by slowing down or speeding up the motors o outboard sections of the wing.
Pathfinder was designed, built and is operated by AeroVironment, Inc., of Monrovia, Calif., the firm that developed t pioneering Gossamer Penguin and Solar Challenger solar powered aircraft in the late 1970's and early 1980's.
Pathfinder Plus During 1998, the Pathfinder was modified into the longer-winged Pathfinder-Plus configuration. On Aug. 6, 1998, the modified aircraft was flown to a record altitude of 80,201 feet for propeller-driven aircraft on the third of a series of developmental test flights from PMRF on Kaua'i. The goal of the flights was to validate new solar, aerodynamic, propulsion and systems technology developed for the Pathfinder's successor, the Centurion/Helios Prototype, which was designed to reach and sustain altitudes in the 100,000-foot range.Essentially a transitional vehicle between the Pathfinder and the follow-on solar wings, thePathfinder-Plus is a hybrid of the technology that was employed on Pathfinder and developed for Centurion/Helios.The most noticeable change is the installation of a new 44-foot-long center wing section that incorporates a high-altitude airfoil designed for Centurion/Helios. The new section is twice as long as the original Pathfinder center section and increases the overall wingspan of the craft from 98.4 feet to 121 feet. The new center section is topped by more-efficient silicon solar cells developed by SunPower Corp., Sunnyvale, Calif., that can convert almost 19 percent of the solar energy they receive to useful electrical energy to power the craft's motors, avionics and communication systems.,That compares with about 14 percent efficiency for the older solar arrays that cover most of the surface of the mid- and outer wing panels from the original Pathfinder. Maximum potential power was boosted from about 7,500 watts on Pathfinder to about 12,500 watts on Pathfinder-Plus.In addition, the Pathfinder-Plus is powered by eight electric motors, two more than powered the previous version of Pathfinder. Designed for the Centurion/Helios Prototype follow-on solar wings, the motors are slightly more efficient than the original Pathfinder motors. The Pathfinder-Plus also validated a new flight control system for the Centurion/Helios Prototype, although only the Pathfinder's own system actually controlled the motors and control surfaces.
Aircraft Specifications Aircraft Specifications
Wingspan: Pathfinder 98.4 feet (29.5 meters); Pathfinder Plus 121 feet (36.3 meters) Length: 12 feet (3.6 meters)Wing chord: 8 feet (2.4 meters)Wing Aspect Ratio: Pathfinder 12 to 1; Pathfinder Plus 15 to 1 Gross weight: Pathfinder about 560 pounds (252 kg.); Pathfinder Plus about 700 pounds (315 kg.). Payload: Pathfinder—up to 100 pounds (45 kg.); Pathfinder Plus up to 150 pounds (67.5 kg.)Airspeed: Approx. 17 20 mph cruise.Power: Arrays of solar cells, maximum output: Pathfinder—about 7,500 watts; Pathfinder Plus—about 12,500 Motors: Pathfinder, six electric motors; Pathfinder Plus, eight electric motors, 1.5 kW maximum each. Endurance: About 14 to 15 hours, daylight limited with two to five hours on backup batteries. Glide ratio (power off): Pathfinder—18 to 1; Pathfinder Plus—21 to 1. Manufacturer: AeroVironment, Inc., Monrovia, Calif.Primary materials: Carbon fiber, Nomex, Kevlar, plastic sheeting and plastic foam.
High Altitude Airship (HAA™) The Lockheed Martin High Altitude Airship (HAA™) – and its sub-scale demonstrator, the High Altitude Long Endurance-Demonstrator (HALE-D) – is an un-tethered, unmanned lighter-than-air vehicle that will operate above the jet stream in a geostationary position to deliver persistent station keeping as a surveillance platform, telecommunications relay, or a weather observer. The HAA also provides the Warfighter affordable, ever-present Intelligence, Surveillance and Reconnaissance and rapid communications connectivity over the entire battle space. The technology is available now and ready for integration and flight test.This updated concept of a proven technology takes lighter-than-air vehicles into a realm that gives users capabilities on par with satellites at a fraction of the cost (1 to 2 orders of magnitude less). The HAA will also integrate reconfigurable, multi-mission payload suites. HAA is significantly less costly to deploy and operate than other airborne platforms, and supports critical missions for defense, homeland security, and other civil applications. Its operational persistence eliminates the need for in-theater logistic support. In position, an airship would survey a 600-mile diameter area and millions of cubic miles of airspace.
High Altitude Airship Lockheed Martin and the U.S. Army launched the first-of-its-kinds HALE-D on July 27, 2011, demonstrating key technologies critical to the development of unmanned airships. We demonstrated a variety of advanced technologies, including launch and control of the airship, communications links, unique propulsion system, solar array electricity generation, remote piloting communications and control capability, and in-flight operations. High altitude airships can improve the military’s ability to communicate in remote areas such as those in Afghanistan, where mountainous terrain frequently interferes with communications signals. High-strength fabrics to minimize hull weight, thin-film solar arrays for the regenerative power supply, and lightweight propulsion units are key technologies ready to make a high-flying airship a reality. The combination of photovoltaic and advanced energy storage systems delivers the necessary power to perform the airship functions. Propulsion units will maintain the airship's geostationary position above the jet stream, propel it aloft and guide its takeoff and landing during ascent and descent. Lighter-than-air vehicles, operating at altitudes above controlled airspace under the control of a manned ground station, give users the flexibility to change payload equipment when the airship returns to its operational base to perform different tasks.
