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Lighter than air.

Military lighter-than-air drones may well eventuate as derivatives of commercial vehicles, which (sooner or later) will be developed as a less costly alternative to communication satellites. Military and commercial interests are probably both waiting for a free ride, hoping that the other side will bear the main cost of development.

At the upper end of the size spectrum, developments in unmanned lighter-than-air (LTA) vehicles depend on progress in high-strength fabrics, energy storage technologies, lightweight electric motors, thin-film solar arrays and 'paint-on' aerials.

In principle, an LTA vehicle is an ideal application for drone technology, since it exploits (to the fullest possible extent) freedom from human endurance limitations. However, it remains to be seen how long it will take the Federal Aviation Administration to routinely approve flights through controlled airspace by large unmanned airships

In 2006 Sanswire Networks (whose parent company is GlobeTel Communications) unveiled a 75-metre-long technology demonstrator for its Stratellite solar-powered communications platform, which was designed to cruise autonomously or as a remotely-piloted system at up to 65,000 ft, giving a radar horizon at around 300 nm. Sanswire has claimed to be the only company that is currently building a rigid, composite-framed high-altitude airship.

Another entity in the LTA drone business is a team consisting of Cyber Defense Systems (a subsidiary of Proxity), its own subsidiary Techsphere Systems International and Sierra Nevada. This last company would integrate the payload systems for government clients. The team plans three variants of Cyber Defense's Mars (Modular Airborne Reconnaissance Systems) project, which was designed for operation at altitudes of 15,000, 20,000, and 65,000 ft.

These efforts may well relate to a US Department of Homeland Security plan to demonstrate an untethered LTA platform for use in border patrol that is capable of operating at 18,000 ft for 24 hours.

The smaller Cyber Defense SA-80 airship has recently been tested with 'painton' antennas provided by Applied EM and Unitech. The antennas are described as a combination of polymer-based dielectrics and highly conductive paint.

Since 1928 the facility now known as Lockheed Martin, Akron has built more than 300 airships and several thousand ground-tethered LTAs. The company is working under Missile Defense Agency funding to produce a solar-powered, non-rigid High Altitude Airship (HAA) that will stay aloft at 60,000 ft with a 200-kg payload for a month. First flight is scheduled for 2010.

The production HAA, approximately 152 metres long, would be operated by the US Army. It would be flown at a height of 65,000 ft for up to six months at a time, with an 1800-kg radar using an array of transmitter/receiver modules wrapped around its envelope. The plan is to acquire up to twelve HAAs, which (in emergency) could self-deploy anywhere in the world from the Continental US.

In parallel with HAA efforts, Darpa is funding an Isis (Integrated Sensor Is Structure) programme to establish the technological basis for a stratospheric surveillance airship, the main purpose of which would be to track difficult airborne and ground targets, including low-flying cruise missiles. It is envisaged that the airship would have an X-band and UHF-band radar with a hull-mounted Active Electronically Scanned Array (Aesa). Northrop Grumman and Raytheon have received contracts to develop the radar technology.

Based on the results of these studies, a decision will be taken in late FY2009 on the construction of a one-third scale Isis technology demonstrator to fly at the end of FY2010, paving the way for initial operational capability of the production derivative around 2018.

As a former 'blimp' operator, the US Navy remains interested in airship developments and is currently funding American Blimp to produce an Advanced Airship Flying Laboratory (AAFL) to test such elements as bow thrusters for low-speed control, heavy fuel engines and automated flight controls. The AAFL will be around 60 metres long and will cruise with a 450-kg payload at 20,000 ft for up to 48 hours.

Yet another American LTA drone technology development programme is the Composite Hull High Altitude Powered Platform (Chhapp), a combined effort by the US Army, US Air Force, the Southwest Research Institute and Aerostar International. The first product of Chhapp was the Aerostar International Hisentinel, which in 2005 reached an altitude of 74,000 ft while carrying a 27-kg payload. The longer-term objective of Chhapp is to take payloads of up to 440 kg to 'near-space' altitudes for as long as a month.

The US appears destined to lead in the field of unmanned airships, if only because of its domestic communication demands and immense defence budget. However, other countries may well share in the global business.

For example, South Korea, with serious ambitions in the aerospace sector, has its own stratospheric airship programme. The first phase employs a sub-scale (50-metre-long) technology demonstrator in which the Korea Aerospace Research Institute is being assisted by Worldwide Aeros of California.

The Italian commercial airship manufacturer Nautilus was scheduled to fly a 16-metre-long subscale version of its 26-metre Elettra Twin Flyer in late 2006. This might be described as two conventional airships side-by-side, joined by a central structure that houses batteries, fuel cells, propulsion units and avionics.

Tethered Drones

Although less spectacular than their free-floating counterparts, tethered LTA (aerostat) drones are in widespread use and are being further developed to improve their operational utility and ease of deployment.

As with their winged counterparts, LTA drones come in all sizes. At the lower end of the scale, the Lockheed Martin/ISL-Bosch Aerospace Reap (Rapidly Elevated Aerostat Platform) is only 9.5 metres long and has a payload capacity of only 16 kg. Funded by the US Navy's Office of Naval Research and US Army Materiel Command for use in Iraq, it is normally operated at 300 ft, and carries day/night sensors that see out to 33 kin. Reap, designed for rapid (five minute) deployment from a Hummer, was first used in Iraq in late 2003. Its quick deployment from a ground vehicle is illustrated very convincingly in a video on boschaero.com.

Bosch Aerospace is now marketing the BA-R5300 version of Reap, with almost double the volume and payload capacity. The company also has a futuristic-looking, free-flying BA-71K project designed to carry a 180-kg payload at over 10,000 ft for days at a time.

The next tethered LTA system in increasing order of size is the Raytheon/ Tcom Raid (Rapid Aerostat Initial Deployment). The Tcom aerostat is 17 metres long and has a payload capacity of 90 kg. The Raid was acquired by the US Army specifically for use in Afghanistan, where it is providing operational experience for the joint-service Jlens (Joint Land Attack Elevated Netted Sensor) programme, which will employ much larger aerostats.

The Lockheed Martin PTDS (Persistent Threat Detection Systems) aerostat has about six times the capacity of the Raid. Following an initial delivery in 2004, in November 2006 a contract was awarded by the US Army for the PTDS with multi-mission sensors to support coalition forces in Iraq and Afghanistan.

The Raytheon Jlens is intended primarily to protect overseas-deployed US forces against cruise missile attack, but it will also be able to track ground targets and tactical ballistic missiles in their boost phase. It will be interoperable with the US Army's Raytheon Patriot and the Navy's Standard Missile. In 2005 Raytheon was awarded a $1.4 billion US Army contract to develop and demonstrate the Jlens.

The Jlens system will consist of two aerostats, one with a surveillance radar and the other with a precision track illumination radar. The Tcom aerostat is 71 metres long and will carry a 2270 kg payload. It will operate at 10 to 15,000 ft and have an endurance of 30 days. System testing is to begin in 2010 and be completed in 2012.

Recent figures from the US Naval Sea Systems Command compare the hourly operating cost of various surveillance systems, with a 71-metre land-based aerostat estimated at $ 610, a Northrop Grumman E-2C Hawkeye at $ 18 000, that company's Global Hawk at $ 26,500, a General Atomics Predator at $ 5000 and a helicopter platform (unspecified) at the $ 3500 mark.

The US Navy plans to develop a sea-based, weather-hardened 38-metre aerostat capable of carrying a 230-kg payload. This will pave the way for a barge-tethered 71-metre derivative that will operate at 15,000 ft.

The US Marine Corps Marts (Marine Airborne Re-Transmission System) is a communication relay vehicle 32 metres long with a 230-kg transponder payload. The contractors are Saic and Tcom. The Marts is designed for operation in winds up to 90 km/hr and to survive lightning strikes and small arms punctures.

Although operated by the US Air Force, the Lockheed Martin Tars (Tethered Aerostat Radar System) was developed primarily to provide low-level radar support for US federal agencies in interdicting drug supplies from the south. The aerostat is 63 metres long and carries a 545-kg payload in the form of Northrop Grumman's TPS-63 or the Enhanced--Low Altitude Surveillance System (E-Lass) radar at a height of 12 to 15,000 ft. Endurance is up to 30 days.

To minimise problems in operating tethered aerostats in high winds, Allsopp Helikites in Britain has developed the Helikite, which is a combination of balloon and kite. Proposed as a communication relay or sensor platform optionally armed with two Navair Spike missiles, the Helikite forms the basis of Carolina Unmanned Vehicles' Lightweight Aerostat System.

In terms of export sales of radar-equipped aerostat drones the clear leader appears to be Tcom, with its 71-metre design which has been sold to India, Israel, Kuwait and the UAE. Tcom's small 32-metre aerostat has been purchased by Italy for the South Adriatic Aerostat Coastal Surveillance programme.

China has reportedly bought the Augur/RosAeroSystems Au-21 Puma aerostat with NIIS/Leninets Novella/Sea Dragon radar for surveillance of the Taiwan Strait. The Puma can carry a payload of 2250 kg (compared to 1600 kg for the Tcom 71M) and remain in the air for 25 days at up to 16,400 ft.

IAI Elta Systems--Latest

The current trend towards the use aerostats as bearers of surveillance radars is enhanced by Elta System's recent announcement that it markets three families of aerostat-based surveillance systems:

* Extended Air-defense Aerostat. This aerostat carries only the ELM-2083 phased-array radar to provide long-range early warning of attacks by low-flying aircraft. In 2005 Elta announced that the EL/M-2083 radar had been incorporated into the Israel Air Force Extended Air Defense Aerostat system.

* Homeland Security Aerostat for Border Protection, based on the EL/I-3330 radar with movement-detection facility and a day/night electro-optical sensor. Unveiled at the 2005 Paris Air Show, this is a relatively short-range system, employed to watch movements of personnel and vehicles that would otherwise be obscured by walls, buildings, etc. On the Elta website this is referred to as the Multi-Payload Aerostat System (Mpas), based on a Tcom 32M aerostat.

* Sigint Aerostat, equipped with long-range Elint and Comint sensors. As in the above cases, the size of the aerostat is determined by the application and operational considerations.
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Title Annotation:Complete Guide
Publication:Armada International
Date:Jun 1, 2007
Words:1835
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