Lockheed U-2
American single-jet-engined, subsonic, ultra-high-altitude reconnaissance aircraft / From Wikipedia, the free encyclopedia
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The Lockheed U-2, nicknamed "Dragon Lady", is an American single-engine, high altitude reconnaissance aircraft operated from the 1950s by the United States Air Force (USAF) and the Central Intelligence Agency (CIA). It provides day and night, high-altitude (70,000 feet, 21,300 meters), all-weather intelligence gathering.[1]
U-2 | |
---|---|
A Lockheed U-2 in flight | |
Role | High-altitude reconnaissance aircraft |
National origin | United States |
Manufacturer | Lockheed Skunk Works |
Designer | Clarence "Kelly" Johnson |
First flight | 1 August 1955; 68 years ago (1955-08-01) |
Introduction | 1956 |
Status | In service |
Primary users | United States Air Force Central Intelligence Agency (historical) NASA Republic of China Air Force (historical) |
Produced | 1955–1989 |
Number built | 104 |
Lockheed Corporation originally proposed it in 1953, it was approved in 1954, and its first test flight was in 1955. It was flown during the Cold War over the Soviet Union, China, Vietnam, and Cuba. In 1960, Gary Powers was shot down in a CIA U-2C over the Soviet Union by a surface-to-air missile (SAM). Major Rudolf Anderson Jr. was shot down in a U-2 during the Cuban Missile Crisis in 1962.
U-2s have taken part in post-Cold War conflicts in Afghanistan and Iraq, and supported several multinational NATO operations. The U-2 has also been used for electronic sensor research, satellite calibration, scientific research, and communications purposes. The U-2 is one of a handful of aircraft types to have served the USAF for over 50 years, along with the Boeing B-52, Boeing KC-135, Lockheed C-130 and Lockheed C-5. The newest models (TR-1, U-2R, U-2S) entered service in the 1980s, and the latest model, the U-2S, had a technical upgrade in 2012. The U-2 is currently operated by the USAF.
Background
After World War II, the U.S. military desired better strategic aerial reconnaissance to help determine Soviet capabilities and intentions, and to prevent being caught off-guard as it had been in the attack on Pearl Harbor. The Air Force commissioned the 'Beacon Hill Report' from Project Lincoln at the Massachusetts Institute of Technology, which was researched in 1951–1952 and delivered in 1952. The committee was led by Carl F. P. Overhage and was overseen by the Air Force's Gordon P. Saville, and included James Gilbert Baker and Edwin H. Land, who would design the specialized optics in the U-2.[2]
During the early 1950s, the best intelligence the American government had on facilities deep inside the Soviet Union were World War II German Luftwaffe photographs taken during the war of territory west of the Ural Mountains, so overflights to take aerial photographs of the Soviet Union would be necessary. The committee suggested a plane with advanced optics, flying above 70,000 feet (21,300 m).[3][4][5]
After 1950, Soviet air defenses consistently intercepted all aircraft near the country's borders—sometimes even those in Japanese airspace. Existing US reconnaissance aircraft, primarily bombers converted for reconnaissance duty such as the Boeing RB-47, were vulnerable to anti-aircraft artillery, missiles, and fighters. Richard Leghorn of the United States Air Force suggested that an aircraft that could fly at 60,000 feet (18,300 m) should be safe from the MiG-17, the Soviet Union's best interceptor aircraft, which could barely reach 45,000 feet (13,700 m). He and others believed that Soviet radar, which used American equipment provided during the war, could not track aircraft above 65,000 feet (19,800 m).[6]
At the time, the highest-flying aircraft available to the US and its allies was the English Electric Canberra, which could reach 48,000 feet (14,600 m). The British had already produced the PR3 photo-reconnaissance variant, but the USAF asked for English Electric's help to further modify the American-licensed version of the Canberra, the Martin B-57, with long, narrow wings, new engines, and a lighter airframe to reach 67,000 feet (20,400 m). The U.S. Air Research and Development Command mandated design changes that made the aircraft more durable for combat, but the resulting RB-57D aircraft of 1955 could only reach 64,000 feet (19,500 m). The Soviet Union, unlike the United States and Britain, had improved radar technology after the war, and could track aircraft above 65,000 feet (19,800 m).[7]
Lockheed proposal
It was thought that an aircraft that could fly at 70,000 feet (21,300 m) would be beyond the reach of Soviet fighters, missiles, and radar.[8] Another Air Force officer, John Seaberg, wrote a request for proposal in 1953 for an aircraft that could reach 70,000 feet (21,300 m) over a target with 1,500 nmi (1,700 mi; 2,800 km) of operational radius. The USAF decided to solicit designs only from smaller aircraft companies that could give the project more attention.[9] Under the code name "Bald Eagle", it gave contracts[10] to Bell Aircraft, Martin Aircraft, and Fairchild Engine and Airplane to develop proposals for the new reconnaissance aircraft. Officials at Lockheed Aircraft Corporation heard about the project and decided to submit an unsolicited proposal. To save weight and increase altitude, Lockheed executive John Carter suggested that the design eliminate landing gear and not attempt to meet combat load factors for the airframe. The company asked Clarence "Kelly" Johnson to come up with such a design. Johnson was Lockheed's best aeronautical engineer,[11] responsible for the P-38 and the P-80. He was also known for completing projects ahead of schedule, working in a separate division of the company, informally called the "Skunk Works".[12]
Johnson's design, named CL-282, was based on the Lockheed XF-104 with long, slender wings and a shortened fuselage. The design was powered by the General Electric J73 engine and took off from a special cart and landed on its belly. It could reach an altitude of 73,000 feet (22,300 m) and had a 1,600 mi (1,400 nmi; 2,600 km) radius.[13] The reconnaissance aircraft was essentially a jet-powered glider. In June 1954, the USAF rejected the design in favor of the Bell X-16 and the modified B-57. Reasons included the lack of landing gear, use of the J73 engine instead of the more proven Pratt & Whitney J57 used by the competing designs, and not using multiple engines, which the USAF believed to be more reliable. General Curtis LeMay of Strategic Air Command (SAC) walked out during a CL-282 presentation, saying that he was not interested in an airplane without wheels or guns.[14]
Approval
Civilian officials including Trevor Gardner, an aide to Secretary of the Air Force Harold E. Talbott, were more positive about the CL-282 because of its higher potential altitude and smaller radar cross-section, and recommended the design to the Central Intelligence Agency's Office of Scientific Intelligence. At that time, the CIA depended on the military for overflights, and Director of Central Intelligence Allen Dulles favored human over technical intelligence-gathering methods. However, the Intelligence Systems Panel, a civilian group advising the USAF and CIA on aerial reconnaissance, had recognized by 1954 that the RB-57D would not meet the 70,000 feet (21,300 m) requirement that panel member Allen F. Donovan of Cornell Aeronautical Laboratory believed was necessary for safety. The CIA told the panel about the CL-282. The design elements that the USAF considered to be flaws (the single-engine and light load factor) appealed to Donovan. He was a sailplane enthusiast who believed that a sailplane was the type of high-altitude aircraft the panel was seeking.[15]
Edwin Land, the developer of instant photography and another member of the panel, proposed to Dulles through Dulles' aide, Richard M. Bissell Jr., that his agency should fund and operate this aircraft. Land believed that if the military, rather than the CIA, operated the CL-282 during peacetime, such action could provoke a war. Although Dulles remained reluctant to have the CIA conduct its own overflights, Land and James Killian of MIT told President Eisenhower about the aircraft; Eisenhower agreed that the CIA should be the operator. Dulles finally agreed, but some USAF officers opposed the project because they feared it would endanger the RB-57D and X-16.
The USAF's Seaberg helped persuade his own agency to support the CL-282, albeit with the higher-performance J57 engine, and final approval for a joint USAF-CIA project (the first time the CIA dealt with sophisticated technology) came in November 1954. Lockheed had meanwhile become busy with other projects and had to be persuaded to accept the CL-282 contract after its approval.[16]
Manufacture
Bissell became head of the project, which used covert funding; under the Central Intelligence Agency Act of 1949, the CIA's director is the only federal government employee who can spend "unvouchered" government money. Lockheed received a $22.5 million contract (equivalent to $245.8 million today) in March 1955 for the first 20 aircraft, with the first $1.26 million ($13.76 million today) mailed to Johnson's home in February 1955 to keep work going during negotiations. The company agreed to deliver the first aircraft by July of that year and the last by November 1956. It did so, and for $3.5 million ($37.7 million today) under budget.[17] The Flight Test Engineer in charge was Joseph F. Ware Jr.[18]
Initial design and manufacturing was done at Lockheed's Skunk Works factory in Burbank, California, with engineers embedded in the manufacturing area to address problems quickly. Procurement of the aircraft's components occurred secretly. When Johnson ordered altimeters calibrated to 80,000 feet (24,400 m) from a company whose instruments only went to 45,000 feet (13,700 m), the CIA set up a cover story involving experimental rocket aircraft. Shell Oil developed a new low-volatility, low vapor pressure jet fuel that would not evaporate at high altitudes; the fuel became known as JP-7. Manufacturing several hundred thousand gallons for the aircraft in 1955 caused a nationwide shortage of Esso's FLIT insecticide.[19]
Realizing the plane could not be tested and flown out of Burbank Airport, they selected what would become Area 51. It was acquired and a paved runway constructed for the project. The planes were dismantled, loaded onto cargo planes, and flown to the facility for testing. The aircraft was renamed the U-2 in July 1955, the same month the first aircraft, Article 341, was delivered to Groom Lake. The "U" referred to the deliberately vague designation "utility" instead of "R" for "reconnaissance", and the U-1 and U-3 aircraft already existed.[19] The CIA assigned the cryptonym AQUATONE to the project, with the USAF using the name OILSTONE for their support to the CIA.[20]
James Baker developed the optics for a large-format camera to be used in the U-2 while working for Perkin-Elmer. The new camera had a resolution of 2.5 feet (76 cm) from an altitude of 60,000 feet (18,000 m).[21] The aircraft was so crowded that when Baker asked Johnson for six more inches (15 cm) of space for a lens with a 240-inch (610 cm) focal length, Johnson replied "I'd sell my grandmother for six more inches!"; Baker instead used a 180-inch (460 cm) f/13.85 lens in a 13 in × 13 in (33 cm × 33 cm) format for his final design.[22]
Fuel
The U-2 has used Jet Propellant Thermally Stable (JPTS) since the aircraft's development in the 1950s. JPTS is a high thermal stability, high altitude fuel, created specifically for the U-2. JPTS has a lower freeze point, higher viscosity, and higher thermal stability than standard USAF fuels. In 1999, the Air Force spent approximately $11.3 million (equivalent to $20.58 million in 2023 dollars) on fuel for the U-2 aircraft and was looking for a lower-cost alternative. JPTS is a specialty fuel and as such has limited worldwide availability and costs over three times the unit volume price of USAF's primary jet fuel, JP-8. Research was carried out to find a cheaper and easier alternative involving additives to generally used jet fuels. A JP-8 based alternative, JP-8+100LT, was being considered in 2001. JP-8+100 has increased thermal stability by 100 °F (56 °C) over stock JP-8, and is only 0.5 cents per gallon more expensive; low-temperature additives can be blended to this stock to achieve desired cold performance.[23]
The small landing gear made a perfect balance in the fuel tanks essential for a safe landing. Similarly to sailplanes, the U-2 had a yaw string on the canopy to detect slip or skid during the approach. A skid during flight with no bank was the hint of an imbalance around the longitudinal axis which could be resolved by moving the fuel to the left or right wing tank.[24]
Radar cross-section reduction
When the first overflights of the Soviet Union were tracked by radar, the CIA initiated Project Rainbow to reduce the U-2's radar cross-section. This effort ultimately proved unsuccessful, and work began on a follow-on aircraft, which resulted in the Lockheed A-12 Oxcart.[25]
Possible successor
In August 2015, the 60th anniversary of the U-2 program, Lockheed Martin's Skunk Works revealed they were internally developing a successor to the U-2, referred to as the UQ-2 or RQ-X, combining features from both the manned U-2 and unmanned Northrop Grumman RQ-4 Global Hawk and improving upon them. Disclosed details say the design is essentially an improved U-2 airframe with the same engine, service ceiling, sensors, and cockpit, with the main differences being an optional manning capability (something Lockheed has proposed for the U-2 to USAF several times, but has never gained traction) and low-observable characteristics. USAF has no requirement or schedule for a next-generation High-Altitude Long Endurance (HALE) platform, but Lockheed sees a future need and wants something in development early. The company's last attempt to create a stealth unmanned aircraft was the RQ-3 DarkStar, which never made it past flight testing and was canceled.[26] Plans for a U-2 replacement would not conflict with the development of the SR-72, another project by the company to create a hypersonic unmanned surveillance plane, as it would be suited for missions that require greater speed for time-sensitive targets.[27]
The company released a notional artist's impression of the TR-X aircraft at an Air Force Association conference in Washington on 14 September 2015. Its name was changed to mean "tactical reconnaissance" to reflect its purpose as an affordable peace and wartime intelligence, surveillance and reconnaissance (ISR) aircraft, distinguishing it from strategic, penetrating SR-71-class platforms; TR is a reference to the short-lived rebranding of the U-2 as the TR-1 in the 1980s. Size, and thus cost, is kept down by having less endurance than the Global Hawk at around 20 hours, which is still about the same time as a normal RQ-4 sortie even though it is capable of flying for 34 hours. The TR-X concept is aimed squarely at USAF needs and is not currently being marketed to the CIA or other government agencies. It would have increased power and cooling to accommodate new sensors, communication equipment, electronic warfare suites, and perhaps offensive or defensive laser weapons. TR-X could be ready for service in the 2025 timeframe, with a fleet of 25–30 aircraft proposed to replace the nearly 40-aircraft mix of U-2s and RQ-4s.[28][29][30]
Lockheed Martin revealed more specifications about the TR-X concept at a 15 March 2016 media day, confirming the aircraft would be unmanned and air refuelable. Its maximum takeoff weight would be greater than either the U-2's or RQ-4's at around 54,000 lb (24,000 kg), with a 5,000-pound (2,300 kg) payload and 130-foot (40 m) wingspan. It will use the same F118-101 turbofan and generator as the U-2, but thrust could increase to 19,000 pounds (8,600 kg) and power increased to 65–75 kVA; service ceiling would increase to 77,000 ft (23,000 m) with a second engine. The TR-X is meant to be "survivable, not unnoticeable", operating outside of enemy air defense bubbles rather than penetrating into them.[31]
Avionics Tech Refresh
In 2020, the US Air Force awarded the Avionics Tech Refresh contract to Lockheed Martin for upgrading the U-2.[32] In February 2020, the flight tests and the installation of new electro-optical reconnaissance systems were completed. SYERS-2C cameras manufactured by Collins Aerospace equip the entire U-2S fleet. The contract is valued at $50 million.[33] The U-2S's ISR very high altitude mission requires changes for avionics suite for the U-2's onboard systems, a new mission computer designed to the U.S. Air Force's open mission systems standard[34] and a new and modern cockpit displays (Primary Flight Display or PFD).[35]
The avionics upgrades are scheduled to be completed by 2022. Lockheed Martin then plans to refresh the U-2's sensors and other electronic systems., to act as a node in the Advanced Battle Management System (ABMS) now under development.[36]
The design that gives the U-2 its remarkable performance also makes it a difficult aircraft to fly. Martin Knutson said that it "was the highest workload air plane I believe ever designed and built … you're wrestling with the airplane and operating the camera systems at all times", leaving no time to "worry about whether you're over Russia or you're flying over Southern California".[37] The U-2 was designed and manufactured for minimum airframe weight, which results in an aircraft with little margin for error.[21] Most aircraft were single-seat versions, with only five two-seat trainer versions known to exist.[38] Early U-2 variants were powered by Pratt & Whitney J57 turbojet engines.[39] The U-2C and TR-1A variants used the more powerful Pratt & Whitney J75 turbojet. The U-2S and TU-2S variants incorporated the more powerful General Electric F118 turbofan engine.[40]
High aspect ratio wings give the U-2 glider-like characteristics, with an engine out glide ratio of about 23:1,[41] comparable to gliders of the time. To maintain their operational ceiling of 70,000 feet (21,000 m), the early U-2A and U-2C models had to fly very near their never-exceed speed (VNE). The margin between that maximum speed and the stall speed at that altitude was only 10 knots (12 mph; 19 km/h). This narrow window is called the "coffin corner",[42][43] because breaching either limit was likely to cause airflow separation at the wings or tail.[44] For most of the time on a typical mission the U-2 was flying less than five knots (6 mph; 9 km/h) above stall speed. A stall would cause a loss of altitude, possibly leading to detection and overstress of the airframe.[21]
The U-2's flight controls are designed for high-altitude flight; the controls require light control inputs at operational altitude. However, at lower altitudes the higher air density and lack of a power-assisted control system make the aircraft very difficult to fly: control inputs must be extreme to achieve the desired response, and a great deal of physical strength is needed to operate the controls. The U-2 is very sensitive to crosswinds, which, together with its tendency to float over the runway, makes the aircraft notoriously difficult to land. As it approaches the runway, the cushion of air provided by the high-lift wings in ground effect is so pronounced that the U-2 will not land unless the wings are fully stalled. A landing U-2 is accompanied on the ground by a chase car, which is driven by a second U-2 pilot who assists the landing U-2 by reporting the aircraft's altitude and attitude.[45][46] In practice, once the aircraft has descended to an altitude of two feet (0.61 m) above the runway the pilot initiates a stall and the aircraft falls from this height. Chase cars and live calling of aircraft altitude are necessary because the landing gear is not designed to absorb the weight of the aircraft when falling from altitudes much above two feet (0.61 m).
Instead of the typical tricycle landing gear, the U-2 uses a bicycle configuration with a forward set of main wheels located just behind the cockpit and a rear set of main wheels located behind the engine. The rear wheels are coupled to the rudder to provide steering during taxiing. To maintain balance while taxiing and take-off, two auxiliary wheels called "pogos" are attached under the wings. These fit into sockets underneath each wing at about mid-span and fall off at takeoff. To protect the wings during landing, each wingtip has a titanium skid. After the U-2 comes to a halt, the ground crew re-installs the pogos, then the aircraft taxis to parking.[47]
Because of the high operating altitude and the cockpit's partial pressurization, equivalent to 28,000 feet (8,500 m) pressure altitude, the pilot wears a partially pressurized space suit, which delivers the pilot's oxygen supply and provides emergency protection in case cabin pressure is lost. While pilots can drink water and eat various liquid foods in squeezable containers[48] through a self-sealing hole in the face mask, they typically lose up to 5% of their body mass on an eight-hour mission.[49] Most pilots chose not to take with them the suicide pill offered before missions. If put in the mouth and bitten, the "L-pill"—containing liquid potassium cyanide—would cause death in 10–15 seconds. After a pilot almost accidentally ingested an L-pill instead of candy during a December 1956 flight, the suicide pills were put into boxes to avoid confusion. When in 1960 the CIA realized that a pill breaking inside the cockpit would kill the pilot, it destroyed the L-pills, and as a replacement, its Technical Services Division developed a needle poisoned with a powerful shellfish toxin and hidden in a silver dollar. Only one was made because the agency decided if any pilot needed to use it the program would probably be canceled.[50] Like the suicide pill, not all pilots carried the coin, and Knutson did not know of any that intended to commit suicide; he carried it as an escape tool.[37]
To decrease the risk of developing decompression sickness, pilots breathe 100% oxygen for an hour prior to taking off to remove nitrogen from the blood. A portable oxygen supply is used during transport to the aircraft.[51] Since 2001, more than a dozen pilots have reportedly suffered the effects of decompression sickness, including permanent brain damage in nine cases; initial symptoms include disorientation and becoming unable to read. Factors increasing the risk of illness since 2001 include longer mission durations and more cockpit activity. Conventional reconnaissance missions would limit pilot duties to maintaining flight paths for camera photography. Operations over Afghanistan included more real-time activities, such as communication with ground troops, increasing their bodies' oxygen requirements and the risk of nitrogen bubble formation. U-2 pilots now exercise during oxygen pre-breathing.[52] In 2012, modifications were initiated under the Cockpit Altitude Reduction Effort (CARE), increasing the cabin pressure from 3.88 psi to 7.65 psi, a 15,000-foot (4,600 m) altitude equivalent. The urine collection device also was rebuilt to eliminate leakage.[48][53]
Sensors
Existing cameras had ground resolution down to 23 feet (7 m) from an altitude of 33,000 feet (10,000 m), and were inadequate for the 70,000 feet (21,000 m) altitude. Ground resolution of 9.8 feet (3 m) was required, at a maximum payload weight of 440 pounds (200 kg). The U-2's camera was specially designed by James G. Baker of Harvard and Richard Scott Perkin of the Perkin-Elmer Company, initially in collaboration and later separately.[54]
Initial missions were flown with the trimetrogon "A" camera, consisting of three 24-inch-focal-length (610 mm) cameras, with F/8 resolving 60 lines per mm, and the ground resolution can be inferred by calculation to be 24 inches (60 cm). This was followed by the "B" camera with a 36-inch-focal-length (910 mm) lens with F/10 and image motion compensation, resolving 100 lines per mm, and the ground resolution can be inferred by calculation to be 9.1 inches (23 cm). It was a panoramic camera which took pictures of an extremely large area of the earth's surface. The lens design consisted of a single aspheric singlet lens. Six-thousand-foot (1,800 m) reels of film were used, with the emulsion being coated on a polyester (PET) base that offered significantly improved dimensional stability over extremes of temperature and humidity compared to conventional cellulose acetate.[55][56]
In addition, the U-2 also carried a low-resolution Perkin-Elmer tracking camera using a 3-inch lens, which made continuous horizon-to-horizon photographs. This is common practice in high resolution cameras in later systems also, where the large image helps localize the small high-resolution images.
The aircraft carries a variety of sensors in the nose, Q-bay (behind the cockpit, also known as the camera bay), and wing pods. The U-2 is capable of simultaneously collecting signals, imagery intelligence and air samples. Imagery intelligence sensors include either wet film photography, electro-optic, or radar imagery—the latter from the Raytheon ASARS-2 system. It can use both line-of-sight and over-horizon data links.