RQ-3A Darkstar UAV / classified Darkstar follow-on

The Gnat 750 and Predator were the first in a series of "Tier UAVs" considered by the US Air Force. In the USAF plan, the Gnat 750 was known as "Tier 1", while the Predator was known as "Tier 2". The original expectation was that the series would then move on to a very large and powerful long-range UAV known as "Tier 3", something along the lines of a B-2 Stealth bomber, but Tier 3 proved overambitious and was cancelled.

In place of Tier 3, the USAF decided to develop a smaller "Tier 3-" UAV designated the "Darkstar", and a "Tier 2+" UAV, something like a "super Predator", the Teledyne-Ryan "Global Hawk".

The Lockheed Martin / Boeing Tier 3- Darkstar was a stealth capable design that resembled a big pumpkin seed with a long straight wing at the rear. It was designed to send real-time still images produced by either SAR or EO sensors, though it did not have the capacity to carry both sensors at the same time. Data was to be returned using a satellite communications link with a bandwidth of 1.5 megabits per second. The Darkstar was intended to penetrate protected airspace to observe high-value targets for a limited amount of time. Range and endurance were intended to be similar to that of the Predator, though the Darkstar's sensor suite could cover over twice the area, and it was harder to detect.

The Darkstar was powered by a Williams Research FJ-44-1A turbofan engine with 8.46 kN (862 kgf / 1,900 lbf) thrust, and could carry a 450 kilograms (990 pounds) payload. The UAV was to cost about US$10 million each.^[1]

The Darkstar initially was unreliable. On its second take-off in the spring of 1996, it stood up on one wing and slammed into the runway, bursting into fire and smoke. An analysis of the failure showed flight software and take-off procedures to be faulty.

The Air Force and the contractors did not give up right away, and a redesigned Darkstar, now formally designated "RQ-3A", which flew in the early summer of 1998. However, the program was still unhealthy, and the Darkstar was cancelled in early 1999. Although flight tests were generally satisfactory, the Darkstar was by no means close to being a useful operational system. Building an actual operational UAV based on the Darkstar would have required major redesign and improvement, and the costs were more than the Air Force was willing to spend.

• In the summer of 2003, in a statement confirming longstanding rumors, Air Force officials announced that Lockheed Martin's "Skunk Works" had developed several prototypes of a stealthy reconnaissance UAV similar to the DarkStar but larger, and that this machine had been used in an operational evaluation over Iraq during the American invasion of that country in the spring of 2003.

The unnamed UAV's payload was described as less than that of a Lockheed U-2, featuring a "low probability of intercept (LPI)" SAR and electro-optic sensors, along with a SATCOM datalink. Range was less than that of the Global Hawk though cost is described as several times greater. The Air Force wanted to conduct the operational evaluation to see if putting the new machine into production was worthwhile. The most likely operational base for the UAV was Al Udeid Air Base in Qatar, which has extensive and well-developed facilities, is near to Iraq, and was off-limits to reporters during the invasion of Iraq.

Sources have also leaked information about a Boeing effort to develop a stealth UAV test bed. This particular machine is said to have been flown in a wide range of configurations, with different tails, noses, and wings, to validate stealth concepts.

This UAV was declassified in 2006 as the Lockheed Martin Polecat.

Northrop Grumman RQ-4A Global Hawk/sensor craft

Northrop Grumman RQ-4A Global Hawk

With the ultimate demise of the Darkstar project, the Ryan RQ-4A Global Hawk became the Air Force's focus for a strategic UAV reconnaissance platform. With the purchase of Ryan by Northrop Grumman in July 1999, the aircraft became the Northrop Grumman Global Hawk.

The Global Hawk does not feature the same stealth capabilities, but has sophisticated long-range sensors to allow it to operate outside of hostile air defences, and can survey as much as 100,000 square kilometers (39,000 sq mi) of terrain a day. In comparison to the Predator, The Global Hawk would have a 5500 mile range, patrol the target for an additional flight time of 24 hours and observe a 370 by 370 kilometers (230 by 230 miles) grid.

The Global Hawk costs about US$130 million each in full production,^[2] is powered by an Allison Rolls-Royce AE3007H turbofan engine with 31.4 (3,200 kgf / 7,050 lbf) thrust, and carries a payload of 900 kilograms (2,000 pounds). The fuselage is mostly of conventional aluminum airframe construction, while the wings are made of carbon composite.

The Global Hawk carries the "Hughes Integrated Surveillance & Reconnaissance (HISAR)" sensor system. HISAR is a lower-cost derivative of the ASARS-2 package that Hughes developed for the Lockheed U-2. HISAR is also fitted in the US Army's RC-7B Airborne Reconnaissance Low Multifunction (ARLM) manned surveillance aircraft, and is being sold on the international market. HISAR integrates a SAR-MTI system, along with an optical and an infrared imager. All three sensors are controlled and their outputs filtered by a common processor. The digital sensor data can be transmitted at up to 50 Mbit/s to a ground station in real time, either directly or through a communications satellite link.

The SAR-MTI system operates in the X-band and provides a number of operational modes:

• The wide-area MTI mode can detect moving targets within a radius of 200 kilometers (120 mi).
• The combined SAR-MTI strip mode provides 6 meters (20 feet) resolution over a swath 37 kilometers (23 mi) wide at ranges from 20 to 110 kilometers (12 to 68 miles).
• The SAR spot mode can provide 1.8 meters (5.9 feet) resolution over ten square kilometers (3.8 square miles), as well as provide a sea-surveillance function.

The visible and infrared imagers share the same gimballed sensor package, and use common optics, providing a telescopic close-up capability. The Global Hawk is also fitted with a "self-protection" countermeasures suite to help it frustrate adversary air defenses, and can be optionally fitted with an auxiliary SIGINT package.

The first flight of the Global Hawk was on 28 February 1998. Five prototypes were built, and put through a thorough flight test program. Beginning in the spring of 1999, the Global Hawk performed a series of operational evaluation flights, some of which were remarkable demonstrations of the aircraft's capability. One of the prototypes flew from Eglin Air Force Base in Florida to Alaska and back again, nonstop, in just under 25 hours.^[3]

In May 2000, a prototype flew up the Atlantic coast of the US from Eglin AFB, transmitting radar images to a US Army ground station at Fort Bragg, North Carolina, and the aircraft carrier USS George Washington, at dock at Norfolk, Virginia. The RQ-4A then proceeded across the Atlantic, monitoring shipping movements, and reached its final target, an amphibious landing exercise near Setubal, Portugal. Once done, the Global Hawk retraced its route and landed at Eglin, 28 hours after its departure.

The program has suffered some setbacks. On 29 March 1999, the second prototype fell out of the sky over the US Navy China Lake military training area in California and was destroyed. The third prototype was badly damaged during a landing incident on 6 December 1999 when a software bug told the aircraft to taxi at 290 km/h (180 mph), leading to the grounding of the survivors for three months.

The Global Hawk was scheduled to reach operational service in late 2001, and this timeframe coincided with the US intervention in Afghanistan. Four Global Hawks were available at the time, though only three were regarded as suitable for operations. These three UAVs were operated in the war, though specific details of their missions are unclear. One crashed on 30 December 2001 due to a malfunction.

Global Hawks also served in the invasion of Iraq in the spring of 2003. Although details of their service there are largely classified for the moment, reportedly their SAR payload came in very handy for pinning down targets during intense sandstorms. Ironically, despite the service of the Global Hawks in these conflicts, none of them that flew these operations were actually regarded as production machines. The first production RQ-4A, the eighth Global Hawk built, was finally rolled out in the summer of 2003.

• The Global Hawk is a very high priority program for the Air Force. The service expects to obtain two Block 5 aircraft each year, and then move on to Block 10 aircraft when the system has been proven. The Block 10 aircraft will feature an improved sensor and self-protection suite, and more electrical power.

The improved self-protection suite includes an AN/ALE-50 towed decoy, an AN/ALR-89 radar-warning receiver, and a new self-defense jammer being designed by Raytheon. The UAV will autonomously act on the information from the self-protection system, deciding whether to abort the mission, take evasive action, or continue with the towed jammer deployed. The remote operator can override whatever decision is taken.

• One high-profile update for the Global Hawk is now being pursued under the "Multi-Platform Radar Technology Insertion Program (MP-RTIP)", which will give the UAV an advanced "active electronically scanned array (AESA)" multifunction radar.

MP-RTIP originally started out as an upgrade program for the "E-8 Joint-STARS" manned battlefield reconnaissance aircraft, which is based on the Boeing 707-320 jetliner, but the scope of the program expanded to envision the development of an AESA that could be adapted for use on a range of platforms.

An Active Electronically Scanned Array (AESA) is akin to a radio-frequency (RF) array processor, comprising a network of interlinked transmit-receive modules. Each module in this grid is equipped with its own RF, processing, and control electronics. These modules collectively perform a broad range of functions by working in unison. The modular nature of the AESA makes it scalable, allowing for the adjustment of the number of modules in accordance with the size constraints of the platform, with its capabilities being directly proportional to its size. The AESA system is versatile in its functions, capable of handling communication, jamming, and sensing operations simultaneously by efficiently managing the usage of its modules. Current developments in the Global Hawk's AESA technology are increasingly focusing on enhancing its airborne search capabilities. This enhancement aims to augment the UAV's functionality, enabling it to serve as an "airborne early warning (AEW)" platform.

Raytheon and Northrop Grumman were awarded a contract for the MP-RTIP system in late 2000, with Raytheon to build the AESA and the Northrop Grumman to perform systems integration. The Global Hawk was selected as the initial target system for MP-RTIP, with initial flight tests in 2005.

• Yet another high-priority update that is being considered for the Global Hawk is to fit it with a SIGINT payload. This option was being considered as a long-term program until the spring of 2001, when a Chinese F-8 fighter trying to "spook" a US Navy EP-3 Aries SIGINT aircraft cruising off the Chinese coast collided with it instead. The F-8 and its pilot were lost, and the EP-3 was forced to make an emergency landing on Hainan Island. The result was a protracted diplomatic quarrel, with the Chinese holding the aircraft and the crew and demanding that the US end surveillance of Chinese territory. The crew was returned unharmed, but the Chinese refused to let the EP-3 fly out, forcing the Americans to retrieve with a leased Antonov transport.

In the wake of the 1969 downing of an EC-121 SIGINT aircraft by North Korea, the U.S. military developed the "Combat Dawn" Firefly variant, a response aimed at preventing a recurrence of such incidents. This approach was revisited following an event in 2001, underscoring the need for a similar strategy. Although the Global Hawk UAV lacks the payload capacity of larger SIGINT aircraft such as the EP-3, it has been identified as a potential interim solution. Consequently, enhancing the SIGINT capabilities of the Global Hawk has become a high priority.

Further enhancements to the Global Hawk are under consideration. These include an expedited initiative to equip the UAV with stores pylons for additional payloads. Such payloads may encompass advanced electro-optic/infrared and multispectral sensors, as well as jamming pods. There has been contemplation of a Global Hawk configuration capable of carrying either two 225-kilogram (496-pound) or four 112-kilogram (247-pound) GPS-guided bombs. However, senior Air Force officials have expressed reservations about arming the UAV. Their concern is that weaponizing the Global Hawk could complicate its use in peacekeeping missions or in obtaining overflight permissions from allied nations.

Another possible role is for "information warfare (IW)", picking up and penetrating enemy voice, video, and data communications, but currently no miniaturized IW payload suitable for the Global Hawk is available. Northrop Grumman is promoting schemes where several Global Hawks with different but complementary payloads could be used to perform a single mission.

According to the United States Air Force's (USAF) projections, as of 2010, between 40 and 45 Global Hawks were expected to be in service, with this number increasing to 78 by 2020. Out of these, 40 would be equipped with electro-optic payloads, while the remaining 38 would carry SIGINT payloads. The USAF was planning to phase out the U-2 reconnaissance aircraft by 2011 at the latest, with the Global Hawk being a potential replacement, although this decision was met with some hesitation. Concurrently, Lockheed Martin was advocating for a UAV version of the U-3, named the "U-2U," as an alternative to the Global Hawk, but this proposal had not gained significant traction against the Air Force's existing commitments to the Global Hawk program.

Northrop Grumman has been engaged in the development of the "Block 20" or "RQ-4B" version of the Global Hawk. This variant is characterized by several enhancements including an upgraded engine, an extended wingspan from 35.4 meters (116 feet) to 39.9 meters (131 feet), and a lengthened fuselage from 13.5 meters (44 feet) to a maximum of 14.5 meters (48 feet). The RQ-4B offers a 50% increase in electrical power compared to the RQ-4A and can carry a heavier payload, with a capacity of up to 1,360 kilograms (3,000 pounds) compared to the 910 kilograms (2,010 pounds) of the RQ-4A. Additionally, it features an enhanced communications system and an "open architecture" design, simplifying the process of future upgrades. A larger variant of the Global Hawk, designed to carry a jamming payload weighing up to 2,720 kilograms (6,000 pounds), was also under consideration.

• Following the conflict in Afghanistan, the US Navy also became interested in the Global Hawk, ordering two for delivery in 2005. The two UAVs will be used to evaluate concepts for a naval endurance UAV under the "Broad Area Maritime Surveillance (BAMS)" program. BAMS would complement manned maritime patrol aircraft, such as the P-3C Orion or its successor, the Boeing 737-based "Multi-mission Maritime Aircraft (MMA)", and the Navy would like to field BAMS by 2008.

The United States Navy's Broad Area Maritime Surveillance (BAMS) program aims to achieve an operational radius of 2,775 kilometers (1,724 miles) with a continuous on-station duration of 12 hours. The envisioned system is expected to include a comprehensive payload, comprising electro-optical/infrared (EO/IR) imaging sensors, a multifunctional radar capable of wide-area search across sea, air, and land, as well as high-resolution spot beam, Moving Target Indicator (MTI), and Synthetic Aperture Radar (SAR) imaging modes. Additionally, a Signals Intelligence (SIGINT) package will be integrated, featuring emitter identification and targeting capabilities. The payload systems are designed to be modular, though it is unlikely that a single vehicle could carry the entire suite simultaneously.

Operational flexibility is a key aspect of BAMS, with the system being primarily land-based but also capable of being controlled from airborne and maritime platforms. Navy officials have not definitively chosen the Global Hawk for this application. However, the preference is to modify an existing unmanned aerial vehicle (UAV) rather than develop a new one from the ground up, making the Global Hawk a prominent contender. In the competition for fulfilling the BAMS requirements, General Atomics and Lockheed Martin are also prominent players. They propose the "Predator B-ER (Extended Range)," also known as the "Mariner," which offers enhanced power, payload capacity, endurance, and the ability to carry an Active Electronically Scanned Array (AESA) radar, along with up to 16 air-dropped sensors or munitions. As of now, the final decision for the BAMS program remains undecided.

Northrop Grumman has been trying to sell the Global Hawk internationally, and has had European interest in a EuroHawk and Middle Eastern interest in a "GulfHawk". Japan and Australia are considering the type as well, but nobody expects international sales any time soon.

• Northrop Grumman has conducted preliminary investigations for the USAF Research Lab of a follow-on HALE vehicle, known as the "Sensor Craft", which would have greater endurance and payload. One Northrop Grumman concepts features a diamond-shaped "joined wing" airfoil, with long conventional airfoil extensions. Boeing has also produced Sensor Craft concepts, featuring a pure joined-wing airfoil.

Sensor Craft appears to be a purely experimental program, but the confrontation between the US and China over the EP-3 SIGINT aircraft in the spring of 2001 helped increase interest in a new, large surveillance UAV. Many defense officials are now promoting acquisition of a large, capable UAV designated the "U-X" with stealthy characteristics that can fly at altitudes above the ceiling of a piloted interceptor.`

The UAV would not necessarily be designed to overfly protected airspace. One or two dozen such UAVs would be bought at a minimum total price of $1.5 billion USD. Ironically, if the new UAV is built, it will bring the US full circle, back to the "Tier 3" UAV that was cancelled early in the 1990s.

References

This article contains material that originally came from the web article Unmanned Aerial Vehicles by Greg Goebel, which exists in the Public Domain.