Ground Surveillance Aircraft.

Ten years after Operation Desert Storm, in which fixed- and rotary-wing aircraft equipped with synthetic aperture and moving-target indication radars made their operational debuts, the World's leading nations are assessing how they can cost-effectively meet their individual ground surveillance needs.

The Lockheed U-2 first flew in 1955 and made its first Soviet overflight less than twelve months later. The current military version is the U-2S, the principal sensor of which is the Raytheon Asars-2 (Advanced Synthetic Aperture Radar System-2).

More than 30 U-2S aircraft are still operated by the US Air Force. They are currently receiving several upgrades, including improved radar with better imagery and MTI (moving target indication) features. The electro-optical sensor is also being upgraded. Improvements are forecast in geolocation accuracy, area coverage and sensor resolution at longer ranges. However, since the US Air Force hopes to replace the U-2 with the Global Hawk UAV, it is not to receive Joint Signals Intelligence Avionics Family (JSIAF) equipment.

Soviet Responses

It was only in 1982 that the Soviet Union produced an aircraft comparable to the U-2. The single-engined Myasishchev M-17 (Mystic-A) was developed initially as a balloon-interceptor, and in 1990 established a sustained altitude record of 71 785 ft for the 16- to 20-tonne class. For comparison, in 1989 the much lighter U-2C had set a record of 73 700 ft in the six-to-nine tonne class. Myasishchev next developed the twin-engined M-17RN or M-55 (civil name Geophysica) sensor platform. This first flew in 1988, but the domestic military demand ended like the Cold War, and only five were built.

Joint Stars

As the Pentagon studied the needs of future conflicts and the availability of Sar and MTI radars, a joint US Air Force/Army requirement was developed for a much more capable aircraft that could carry not only larger all-weather sensors, but also sufficient personnel and communications to survey and manage the ground battle, and direct air power to support it.

The Northrop Grumman E-8C Joint Stars (Surveillance Target Attack Radar System) is based on a refurbished 707-300 series aircraft, and has workstations for 18 systems operators. On long missions with in-flight refuelling, the number of operators can be increased to 28, and the flight deck crew is doubled to six.

The Northrop Grumman APY-3 side-looking radar feeds a 7.3-metre antenna mounted under the front fuselage. The antenna looks to one side, scanning electronically through 120-degrees and scanning mechanically in elevation.

In early 1991, the two development E-8As (which had only ten operator stations) were deployed to Saudi Arabia for Desert Shield/Storm. They flew almost 600 hours in 49 combat sorties, and proved beyond doubt the value of airborne Sar/MTI radar.

The first production E-8C was later assigned to development testing. At the end of 1995 this aircraft and one E-8A were deployed to Germany to assist in peacekeeping operations over the former Yugoslavia. Ten US Army common ground stations (CGS) were deployed to the Balkans. This Operation Joint Endeavour involved 102 flights and 1097 hours by these aircraft of the 4500th Joint Stars Squadron. Further deployments to the region were to take place in October 1996 and February 1999.

The US Air Force has a requirement for at least 19 E-8s. The 15th E-8C has been fully funded in the FY 2001 budget, which includes long-lead funding for the 16th. The first delivery to the 93rd Air Control Wing at Robins AFB, Georgia, took place in March 1996, and initial operational capability was declared in December 1997. Procurement is running at one aircraft per year. A total of twelve production E-8Cs will have been delivered by the end of 2001.

The E-8C will undergo a series of upgrades to benefit from the latest avionics technology (see Block 20 to 40 in "Joint Stars Details").

The aircraft needs ground stations able to receive, process and display the downlinked radar imagery. Originally these were light and medium versions of the Ground Station Module (GSM), but these have given way to a Common Ground Station (CGS) mounted on a Hummer. The CGS is the subject of a series of upgrades, but these Block numbers are not linked to the similarly numbered aircraft upgrades. The Block 10 upgrade allows the CGS to communicate with the Airborne Reconnaissance Low aircraft, U-2S and RQ-1A Predator UAV. It also includes additional software tools, such as radar shadow mapping, video query and multi-mode enhanced target tracking. The Block 20 upgrade replaces the older Commander's Tactical Terminal with a Joint Tactical Terminal, and allows the CGS to exchange data on the local area network of Tactical Operating Centers. In the longer term, much of the automated data processing equipment in the CGS will have to be modified or replaced in order to exploit the improved capabilities of the Block 40 (RTIP) upgrade of the aircraft.

As well as sending data to the ground, the datalinks can also be used to pass target data to other aircraft. During test sorties, the E-8C demonstrated the ability to find targets in a benign environment and pass that target information via Tadil-J to F-15E fighters that were able to successfully engage these targets.

Similar tests were conducted using bombers. In August 1997, B-1B aircrews flew missions in which the E-2C was used to provide target information: time-critical targeting data could be updated while B-1Bs are en route or in real-time once B-1Bs are on station; once targets had been located, the operators on the E-8C would use secure voice satellite communications to pass data such as target co-ordinates, elevation and description to B-1B aircrews.

In January 1998, the Air Force announced that two B-52 s from Minot AFB, North Dakota had participated in a joint exercise with the E-8C. The Latter had scanned the exercise area over Fort Stewart, Georgia and repeatedly tasked the bombers to attack various targets, passing the latter real-time targeting data via a handheld terminal unit, which the B-52 crews were using for the first time.

Smaller attack aircraft can also benefit from E-8C assistance. In March 1998, the Air Force awarded a contract for the integration of a data link between the E-8C and the Army's Apache Longbow attack helicopter. This followed an earlier `proof of concept' trial in the autumn of 1997 when an E-8 and an AH-64 exchanged data using a modern prototype engineered by Northrop Grumman and Boeing.

MR-RTIP

The next stage, Block 50, will be the Multi-Platform Radar Technology Insertion Program (MP-RTIP), a fourth-generation modular, scaleable system to suit a wide range of platforms. For example, it can be reduced from the 7.3 metres used for Joint Stars to 5.5 metres for the A321, 4.5 metres for a high-flying business jet and perhaps 2.5 metres for an unmanned aircraft like the Global Hawk. The MPRTIP includes an increased capacity data-link to relay data from the E-8Cs to various ground nodes.

Northrop Grumman is prime contractor for MP-RTIP, but Raytheon will also play a major role. Scheduled for service in 2006, the new system will introduce a new AN/APY-X 2D featuring electronic scanning in both azimuth and elevation and simultaneous (rather than interleaved) Sar and MTI modes. It will also introduce additional radar modes such as spot- and swath-Sar and High Range Resolution MTI, and a very high resolution Sar.

It will retain the I/J operating band of the AN/APY-X and MTI-mode resolution is expected to rise from the current 3.66 metres to between 0.30 and 0.91 metre, while Sar mode is expected to show a tenth the resolution currently available. New operating modes will help reject ground clutter and provide greater resistance to jamming.

These improvements will make it possible to track individual vehicles in heavy traffic, and provide automatic target category recognition. Five E-8Cs will have the improved radar by FY 2013 and the type is expected to remain in service until at least 2017.

A further development in the use of Joint Stars is being studied under the Affordable Moving Surface Target Engagement trials programme, funded by the Defense Advanced Research Projects Agency. It will link the E-8C radar directly to that of a Joint Strike Fighter and to a guided air-to-surface missile provided by Lockheed Martin.

Natar and Sostar

Nato established a Staff Requirement for an Alliance Ground Surveillance capability in the mid-1990s, and in February 2000 this became the Airborne Ground Surveillance (AGS) programme. Following a US Government offer of the Advanced Radar based on the MP-RTIP, Nato established a Natar (Nato Transatlantic Advanced Radar) Project Office in Brussels to define the system. It is anticipated that at least six AGS aircraft and up to 24 ground stations will be ordered by 2003, with service entry possibly as early as 2007.

The only AGS proposal with formal Nato status appears to be the Natar solution. The proposal is backed by Belgium, Canada, Denmark, Luxembourg, Norway and the United States (these nations have contributed representatives to the Natar Project Office) while France, Germany, Italy, the Netherlands and Spain are promoting the Sostar (Stand-Off Surveillance and Target Acquisition Radar) project.

The Natar for the proposed Nato Airbus A321 surveillance aircraft would have an antenna fitted into a belly-mounted `canoe', while the remainder of the radar and other electronic equipment would be installed in 18 racks in the rear fuselage. In concept, the system would be closer to the E-8 than Astor, so would need a larger crew. Twelve operator consoles are planned. The Natar would be based on RTIP technology, and would have two unique modes devised to meet Nato requirements: variable-swath Sar (typically covering widths of 15 km, 20 km or 30 km, compared with the 2 km or 4 km normally employed in Joint Stars); and maritime MTI, for blue-water operation in high sea states. The service ceiling of the basic A321 is 39 000 ft, broadly in the class of the E-3C, but well below that of the Astor aircraft.

The Sostar, for its part, is run by the German-registered Sostar GmbH, owned by Fads (28 per cent), Thales (28), Fiar (28), Indra (11 per cent) and Fokker Space (5). The Sostar is proposed for both a wide-body transport such as the A321 and a Hale (High Altitude, Long Endurance) unmanned aircraft. A variant designated Saris would have a shorter antenna for installation on a business jet, or in a pod carried by a combat aircraft. The Sostar-X technology demonstration programme will make use of a Fokker 100 with three workstations.

The background experience for Sostar includes the Thales Target MTI radar used in the French Army Horizon system and the Fiar Creso radar tested on an AB-412. The Target radar was successfully operated on a Super Puma during the Gulf War. Four Target-equipped Cougars and two ground stations have since been delivered to the French Army and were successfully employed in Kosovo. Thales is now marketing this Horizon system under the designation Battle Scan for helicopters such as the Mi-17, UH-60 and EH-101.

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UK Flying Solo

The British position is that the AGS requirement should be satisfied by its Astor system (see "Astor Details"), with the Bombardier Global Express as the platform. In late 1999, Raytheon Systems was awarded the British contract, which included five aircraft and ten ground stations. Service entry is scheduled for 2005. The Astor aircraft has three workstations, and is equipped with an improved version of the Raytheon Asars-2 used on the U-2S. Raytheon is marketing a similar system under the designation Gsars (Ground Surveillance Airborne Radar System), with changes (such as the choice of vehicle for the ground station) to suit the individual customer. For example, the Gsars was unveiled at Dubai 2000 with a ground station based on a Steyr 6 x 6, rather than Astor's Bedford truck

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Unmanned Aircraft

There are so many UAVs now involved in ground surveillance that it is possible to mention here only the leading examples (as the subject will be discussed in more detail in Armada 5/2001).

The first in this field was the piston-engined General Atomics (GA-ASI) Gnat 750, which flew in 1989 and was deployed by the CIA to Albania in 1994 for various operations over the former Yugoslavia. It has an EO/IR payload and Sar is available as an option. Unusually, the Gnat has five external hardpoints. It had now made seven deployments to combat areas. Turkey has purchased some Gnats, and it is possible that Britain has secretly bought two.

The General Atomics RQ-1 Predator is basically a more powerful, long-span Gnat. It first flew in 1994, and over 50 have been purchased by the US Air Force. Italy has ordered six. The first US Air Force unit, the llth Reconnaissance Squadron, was formed in July 1995, and the second (the 15th RS) followed in August 1997. The Predator has been deployed on six occasions to the Balkans and Gulf theatres. Recent uses include the gathering of images of battle damage produced in the attacks on Iraqi targets on February 16. It has now flown over 22 000 hours, including 8200 hours in combat areas.

Thanks to its sensor suite and sat-com data-link, the Predator is the only UAV in the American inventory capable of providing on a worldwide basis real-time video imagery day and night, in all weather conditions.

The Predator B (construction number B001) that first flew in February has a turboprop engine. The next of the series to fly will be the Predator B Altair, with an extended wingspan. This will be followed by the B002 with a Williams-Rolls FJ44 turbofan, providing a higher ceiling at the expense of endurance. The RQ-1A Predator is also able to simultaneously carry electro-optic and infrared sensors. Cruising at an altitude of up to 25 000 ft, it communicates with the Ground Control Station via a C-band line-of-sight datalink, or a Ku-band satellite-based datalink, used when flying beyond line-of-sight.

A similar mixed suite of EO, IR and Sar sensors is being developed for the RQ-4A Global Hawk. This Integrated Sensor Suite (ISS) allows the EO or the IR sensors to operate simultaneously with the Sar. Each of the sensors provides wide area search imagery and a high-resolution spot mode, while the Sar also has a ground moving target indicator (GMTI) mode.

Such a sophisticated sensor suite could in theory swamp the ground stations with data, but the ISS has been designed to carry out data processing, which should produce a more `user-friendly' output. Sar and EO/IR imagery are processed onboard the aircraft, then transmitted to the Mission Control Element (MCE) -- the ground station -- as individual frames which the MCE can mosaic into images before passing them on to users. The GMTI mode will be used to generate information on moving targets that can be transmitted as text information listing target location and radial velocity.

Given its long range, the Global Hawk will operate autonomously, using a UHF or Ku-band satellite data link to pass sensor data to the MCE. If it is flying within line of sight of users equipped with compatible ground stations, the aeroplane will be able to send imagery directly to them.

The technology used in the Global Hawk mission package has suffered some teething problems. During a 28hr sortie flown last year, a Global Hawk flew across the Atlantic in an attempt to demonstrate the imaging of littoral areas near Portugal. During the initial part of the flight, Sar imagery was transmitted from the MCE to Fort Bragg, but attempts to direct down link to the aircraft carrier George Washington were unsuccessful. A Sar transmitter failure prevented the collection of imagery.

Ground Surveillance Aircraft Characteristics

Aircraft               Thrust/Power      MTOW     Span    Ceiling
Powerplant                [kN/kW]        [kg]      [m]      [ft]

Lockheed U-2S
GE F118                   75.6 kN      18 144     31.90   70 000
Myasishchev M-55
2 x Perm D-30           2 x 44.1 kN    24 000     37.46   68 900
Scaled Halo-Proteus
2 x Williams FJ44-2     2 x 10.2 kN      7167     28.00   51 000+
Northrop Grumman E-8
4 x PW JT3D              4 x 80 kN    152 300     44.42   35 000
Eurocopter Cougar
2 x Turbomeca Makila    2 x 1565 kW    11 200     n/a     14 000
Raytheon ASTOR
2 x R-R BR710           2 x 65.6 kN    42 412     28.65   51 000
GA-ASI GNAT-75
Rotax 582                 48.5 kW         703     12.80   25 000
GA-ASI RQ-1 Predator
Rotax 912                 78.3 kW        1035     14.84   25 000
GA-ASI Predator B
GE TPE331-10T             522 kW         3200     19.50   45 000+
NG Ryan Global Hawk
R-R AE3007H               37.0 kN      11 610     35.40   60 000+

Aircraft                     Flight    Cruise
Powerplant                    [hr]     [km/hr]

Lockheed U-2S
GE F118                        14        765
Myasishchev M-55
2 x Perm D-30                6.50        750
Scaled Halo-Proteus
2 x Williams FJ44-2           12+        480
Northrop Grumman E-8
4 x PW JT3D                    11        725
Eurocopter Cougar
2 x Turbomeca Makila            6        270/180(*)
Raytheon ASTOR
2 x R-R BR710                  14       900
GA-ASI GNAT-75
Rotax 582                    40+        220
GA-ASI RQ-1 Predator
Rotax 912                    40+        220
GA-ASI Predator B
GE TPE331-10T                  25       390
NG Ryan Global Hawk
R-R AE3007H                    36       635

(*) Cruise/Observation radar deployed

The transatlantic phase of the second sortie was not attempted due to problems in communicating with the UHF satellite, but Sar imagery was collected along the US East Coast, and three scenes were transmitted via direct down link to the George Washington.

The Ryan Aeronautical Center is now part of Northrop Grumman, and its RQ-4A Global Hawk is potentially the world's most important surveillance unmanned aircraft. However, (unlike the stealthy DarkStar -- terminated in 1999) it is intended to operate in only low/medium threat areas. Powered by a Rolls-Royce AE3007H turbofan, it was designed to provide 24 hours on station at over 60 000 ft at 6500 km radius.

The Global Hawk first flew in 1998, and four are currently being tested (one having crashed). The sixth and seventh are due for delivery next year. The US Air Force has authorised Northrop Grumman to proceed with the engineering and manufacturing development phase, which could cost around $1.6 billion. The service hopes to have 40 to 45 Global Hawks operational by 2010 and 78 by 2020. It is looking at ways to avoid a gap in the programme and accelerate Global Hawk production, rather than adopt an expensive upgrade of the U-2.

In short

* "High altitude and a powerful radar aperture are essential for long stand-off distance"

* "The European trend is toward converted small airliners and business jets with a limited number of workstations"

* "Unmanned aerial vehicles (UAVs) are playing an increasing role in ground surveillance"

* "Some aircraft have airborne command facilities, while others are basically sensor platforms."

RELATED ARTICLE: Joint Stars Details

The most common sensor used by surveillance aircraft is synthetic-aperture radar (Sar). The best-known radar of this type used by the aircraft described in this article is the Norden AN/APY-3 carried by the E-8. This operates in I-band, and has three main operating modes. The basic mode is a Wide Area Surveillance and Moving Target Indicator mode designed to detect, locate and identify slow-moving targets, Moving Target Indicator/Sector Search mode is used to examine smaller terrain areas using an increased-resolution display. This high-resolution imagery is used to identify moving targets and provide the detailed information needed for attack planning. By analysing the Doppler shifts in the returned signals, the AN/APY-3 can discriminate between wheeled and tracked vehicles. The Synthetic Aperture Radar/Fixed Target Indicator (Sar/FTI) mode produces a photographic-like image of selected geographic regions, showing the position of non-moving features such as buildings, bridges, airports, harbours or stopped vehicles. The FTI submode is used to locate and identify fixed targets within the Sar image.

A series of planned upgrades is intended to maintain the effectiveness of the E-8C. This involves four standards of aircraft -- Blocks 10, 20, 30 and 40. Block 10 aircraft have the Tactical Digital Information Link, (Tadil-J) upgrade. This allows the aircraft to transmit ground surveillance information to other Tadil-J equipped command and control and weapons platforms. The main change introduced by the Block 20 aircraft was the Computer Replacement Program (CRP), which replaces the current five-computer system with two cots computers. On the original version of the aircraft, three processors were used, with a further two acting as `hot spares'. In the revised system, one processor is used, while the other acts as the `hot spare'. Since the new processors are cots, future upgrades to increase processing power should be relatively easy. In another modification ordered around the same time as the CRP, the aircraft's troublesome radar processor was replaced by a new unit that is far more reliable and requires less maintenance. The existing workstation network copper wiring gave way to a high-capacity switch and fibre-optic cables. Block 30 includes the integration of a satellite communications terminal. Block 40 is a major upgrade drawing on technology from the Radar Technology Insertion Program. This is intended to replace the current radar with a new sensor which will provide almost order-of-magnitude improvements in resolution and area coverage rates for all radar modes.

Astor Details

The radar system of the Astor will have a new antenna developed by BAE Systems, and will use technology drawn from the Asars improvement programme and the Hisar ground-surveillance radar. At a later stage, it will probably take advantage of technology developed under the RTIP programme seen above.

The antenna is about 4.8 metres long, significantly smaller than the 7.3-metre unit on the E-8, and uses passive rather than active technology, with a single transmitter powering all of the individual elements. It is electronically scanned in azimuth, and mechanically scanned in elevation. The Astor radar has two modes of operation -- Moving Target Indication (MTI) and a Synthetic Aperture (Sar) mode with Swath and spotlight sub-modes.

Unlike the E-8C, the Astor will have no command functions; its crew are tasked only with controlling the radar and with carrying out some data processing before the data is passed to the ground stations via an Ultra Electronics/Cubic Defense Systems secure datalink. These tasks can be handled by a smaller crew, allowing the system to be carried in a large business jet rather than an airliner. While the E-8C cruises at around 34 000 to 42 000 ft, the Bombardier BD-700 Global Express which will carry the Astor radar has a maximum certified altitude of 51 000 ft. From this altitude, the radar is expected to have a stand-off range of more than 300 km (160 nm).