Northrop Grumman B-2 Spirit

B-2 Spirit
A U.S. Air Force B-2 Spirit flying over the Pacific Ocean in May 2006
Role	Strategic stealth bomber
National origin	United States
Manufacturer	Northrop Corporation Northrop Grumman
First flight	17 July 1989
Introduction	April 1997
Status	In service
Primary user	United States Air Force
Produced	1987–2000
Number built	21[1][2]
Program cost	US$44.75 billion (through 2004)[3]
Unit cost	$737 million (1997 approx. flyaway cost)[3]

The Northrop (later Northrop Grumman) B-2 Spirit, also known as the Stealth Bomber, is an American heavy penetration strategic bomber, featuring low observable stealth technology designed for penetrating dense anti-aircraft defenses; it is a flying wing design with a crew of two.^[1][4] The bomber can deploy both conventional and thermonuclear weapons, such as eighty 500 lb (230 kg)-class (Mk 82) JDAM Global Positioning System-guided bombs, or sixteen 2,400 lb (1,100 kg) B83 nuclear bombs. The B-2 is the only acknowledged aircraft that can carry large air-to-surface standoff weapons in a stealth configuration.

Development originally started under the "Advanced Technology Bomber" (ATB) project during the Carter administration, and its expected performance was one of his reasons for the cancellation of the supersonic B-1A bomber. ATB continued during the Reagan administration, but worries about delays in its introduction led to the reinstatement of the B-1 program as well. Program costs rose throughout development. Designed and manufactured by Northrop, later Northrop Grumman, the cost of each aircraft averaged US$737 million (in 1997 dollars).^[3] Total procurement costs averaged $929 million per aircraft, which includes spare parts, equipment, retrofitting, and software support.^[3] The total program cost including development, engineering and testing, averaged $2.1 billion per aircraft in 1997.^[3]

Because of its considerable capital and operating costs, the project was controversial in the U.S. Congress and among the Joint Chiefs of Staff. The winding-down of the Cold War in the latter portion of the 1980s dramatically reduced the need for the aircraft, which was designed with the intention of penetrating Soviet airspace and attacking high-value targets. During the late 1980s and 1990s, Congress slashed plans to purchase 132 bombers to 21. In 2008, a B-2 was destroyed in a crash shortly after takeoff, though the crew ejected safely.^[5] A total of 20 B-2s remain in service with the United States Air Force, which plans to operate the B-2 until 2058.^[6]

The B-2 is capable of all-altitude attack missions up to 50,000 feet (15,000 m), with a range of more than 6,000 nautical miles (11,000 km) on internal fuel and over 10,000 nautical miles (19,000 km) with one midair refueling. It entered service in 1997 as the second aircraft designed to have advanced stealth technology after the Lockheed F-117 Nighthawk attack aircraft. Though originally designed primarily as a nuclear bomber, the B-2 was first used in combat dropping conventional ordnance in the Kosovo War in 1999 and saw further service in Iraq and Afghanistan.^[7]

Development

Origins

By the mid-1970s, it was becoming clear that there was a different way to avoid missiles and interceptors, known today as "stealth". The concept was to build an aircraft with an airframe that deflected or absorbed radar signals so that little was reflected back to the radar unit. An aircraft having stealth characteristics would be able to fly nearly undetected and could be attacked only by weapons and systems not relying on radar. Although such possibilities existed, such as human observation, their relatively short detection range allowed most aircraft to fly undetected by defenses, especially at night.^[8]

In 1974, DARPA requested information from U.S. aviation firms about the largest radar cross-section of an aircraft that would remain effectively invisible to radars.^[9] Initially, Northrop and McDonnell Douglas were selected for further development. Lockheed had experience in this field due to developing the Lockheed A-12 and SR-71, which included a number of stealthy features, notably its canted vertical stabilizers, the use of composite materials in key locations, and the overall surface finish in radar-absorbing paint. A key improvement was the introduction of computer models used to predict the radar reflections from flat surfaces where collected data drove the design of a "faceted" aircraft. Development of the first such designs started in 1975 with "the hopeless diamond", a model Lockheed built to test the concept.^[10]

Plans were well advanced by the summer of 1975, when DARPA started the Experimental Survivability Testbed (XST) project. Northrop and Lockheed were awarded contracts in the first round of testing. Lockheed received the sole award for the second test round in April 1976 leading to the Have Blue program and eventually the F-117 stealth attack aircraft.^[11]

ATB program

By 1976, these programs progressed to where a long-range strategic stealth bomber appeared viable. President Carter was aware of these developments during 1977, and it appears to have been one of the major reasons the B-1 was canceled.^[12] Further studies were ordered in early 1978, by which point the Have Blue platform had flown and proven the concepts. During the 1980 presidential election campaign in 1979, Ronald Reagan repeatedly stated that Carter was weak on defense, and used the B-1 as a prime example. In return, on 22 August 1980, the Carter administration publicly disclosed that the United States Department of Defense (DoD) was working to develop stealth aircraft, including a bomber.^[13]

The Advanced Technology Bomber (ATB) program began in 1979.^[14] Full development of the black project followed, and was funded under the code name "Aurora".^[15] After the evaluations of the companies' proposals, the ATB competition was narrowed to the Northrop/Boeing and Lockheed/Rockwell teams with each receiving a study contract for further work.^[14] Both teams used flying wing designs.^[15] The Northrop proposal was code named "Senior Ice" and the Lockheed proposal code named "Senior Peg".^[16] Northrop had prior experience developing the YB-35 and YB-49 flying wing aircraft.^[17] The Northrop design was larger while the Lockheed design included a small tail.^[15] In 1979, designer Hal Markarian produced a sketch of the aircraft, that bore considerable similarities to the final design.^[18] The Air Force originally planned to procure 165 of the ATB bomber.^[1]

The Northrop team's ATB design was selected over the Lockheed/Rockwell design on 20 October 1981.^[14][19] The Northrop design received the designation B-2 and the name "Spirit". The bomber's design was changed in the mid-1980s when the mission profile was changed from high-altitude to low-altitude, terrain-following. The redesign delayed the B-2's first flight by two years and added about US$1 billion to the program's cost.^[13] An estimated US$23 billion was secretly spent for research and development on the B-2 by 1989.^[20] MIT engineers and scientists helped assess the mission effectiveness of the aircraft under a five-year classified contract during the 1980s.^[21]

Secrecy and espionage

During its design and development, the Northrop B-2 program was a Gray Project before its reveal to the public.^[22] Unlike the Lockheed F-117 program, which was a Black project, the type of military project of which very few people knew even existed while it was being designed and developed, more people within the United States federal government knew about the B-2 and more information about the project was available. Both during development and in service, there has been considerable importance placed to the security of the B-2 and its technologies. Staff working on the B-2 in most, if not all, capacities have to achieve a level of special-access clearance, and undergo extensive background checks carried out by a special branch of the Air Force.^[23]

For the manufacturing, a former Ford automobile assembly plant in Pico Rivera, California, was acquired and heavily rebuilt; the plant's employees were sworn to complete secrecy regarding their work. To avoid the possibility of suspicion, components were typically purchased through front companies, military officials would visit out of uniform, and staff members were routinely subjected to polygraph examinations. The secrecy extended so far that access to nearly all information on the program by both Government Accountability Office (GAO) and virtually all members of Congress itself was severely limited until the mid-1980s.^[24] Northrop (now Northrop Grumman) was the B-2's prime contractor; major subcontractors included Boeing, Hughes Aircraft (now Raytheon), GE, and Vought Aircraft.^[7]

In 1984, a Northrop employee, Thomas Cavanaugh was arrested for attempting to sell classified information to the Soviet Union; the information was taken from Northrop's Pico Rivera, California factory.^[25] Cavanaugh was eventually sentenced to life in prison and released on parole in 2001.

The B-2 was first publicly displayed on 22 November 1988 at United States Air Force Plant 42 in Palmdale, California, where it was assembled. This viewing was heavily restricted, and guests were not allowed to see the rear of the B-2. However, Aviation Week editors found that there were no airspace restrictions above the presentation area and took photographs of the aircraft's then-secret rear section with suppressed engine exhausts from the air, to the USAF's disappointment. The B-2's (s/n 82-1066 / AV-1) first public flight was on 17 July 1989 from Palmdale to Edwards AFB.^[26]

In October 2005, Noshir Gowadia, a design engineer who worked on the B-2's propulsion system, was arrested for selling B-2 related classified information to foreign countries.^[27] On 9 August 2010, Gowadia was convicted in the United States District Court for the District of Hawaii on 14 of 17 charges against him.^[28] On 24 January 2011, Gowadia was sentenced to 32 years in prison.^[29]

Program costs and procurement

A procurement of 132 aircraft was planned in the mid-1980s, but was later reduced to 75.^[30] By the early 1990s, the Soviet Union dissolved, effectively eliminating the Spirit's primary Cold War mission. Under budgetary pressures and Congressional opposition, in his 1992 State of the Union Address, President George H.W. Bush announced B-2 production would be limited to 20 aircraft.^[31] In 1996, however, the Clinton administration, though originally committed to ending production of the bombers at 20 aircraft, authorized the conversion of a 21st bomber, a prototype test model, to Block 30 fully operational status at a cost of nearly $500 million.^[32]

In 1995, Northrop made a proposal to the USAF to build 20 additional aircraft with a flyaway cost of $566 million each.^[33]

The program was the subject of public controversy for its cost to American taxpayers. In 1996, the General Accounting Office (GAO) disclosed that the USAF's B-2 bombers "will be, by far, the most costly bombers to operate on a per aircraft basis", costing over three times as much as the B-1B (US$9.6 million annually) and over four times as much as the B-52H (US$6.8 million annually). In September 1997, each hour of B-2 flight necessitated 119 hours of maintenance in turn. Comparable maintenance needs for the B-52 and the B-1B are 53 and 60 hours respectively for each hour of flight. A key reason for this cost is the provision of air-conditioned hangars large enough for the bomber's 172 ft (52.4 m) wingspan, which are needed to maintain the aircraft's stealthy properties, particularly its "low-observable" stealthy skins.^[34][35] Maintenance costs are about $3.4 million a month for each aircraft.^[36]

The total "military construction" cost related to the program was projected to be US$553.6 million in 1997 dollars. The cost to procure each B-2 was US$737 million in 1997 dollars, based only on a fleet cost of US$15.48 billion.^[3] The procurement cost per aircraft as detailed in GAO reports, which include spare parts and software support, was $929 million per aircraft in 1997 dollars.^[3]

The total program cost projected through 2004 was US$44.75 billion in 1997 dollars. This includes development, procurement, facilities, construction, and spare parts. The total program cost averaged US$2.13 billion per aircraft.^[3] The B-2 may cost up to $135,000 per flight hour to operate in 2010, which is about twice that of the B-52 and B-1.^[37][38]

Opposition

In its consideration of the fiscal year 1990 defense budget, the House Armed Services Committee trimmed $800 million from the B-2 research and development budget, while at the same time staving off a motion to end the project. Opposition in committee and in Congress was mostly broad and bipartisan, with Congressmen Ron Dellums (D-CA), John Kasich (R-OH), and John G. Rowland (R-CT) authorizing the motion to end the project—as well as others in the Senate, including Jim Exon (D-NE) and John McCain (R-AZ) also opposing the project.^[39]

The escalating cost of the B-2 program and evidence of flaws in the aircraft's ability to elude detection by radar,^[39] were among factors that drove opposition to continue the program. At the peak production period specified in 1989, the schedule called for spending US$7 billion to $8 billion per year in 1989 dollars, something Committee Chair Les Aspin (D-WI) said "won't fly financially."^[40] In 1990, the Department of Defense accused Northrop of using faulty components in the flight control system; the threat posed by bird ingestion potentially damaging engine fan blades also required redesigning.^[41]

In time, a number of prominent members of Congress began to oppose the program's expansion, including later Democratic presidential nominee John Kerry, who cast votes against the B-2 in 1989, 1991 and 1992 while a U.S. Senator, representing Massachusetts. By 1992, Republican President George H.W. Bush called for the cancellation of the B-2 and promised to cut military spending by 30% in the wake of the collapse of the Soviet Union.^[42] In October 1995, former Chief of Staff of the United States Air Force, General Mike Ryan, and former Chairman of the Joint Chiefs of Staff, General John Shalikashvili, strongly recommended against Congressional action to fund the purchase of any additional B-2s, arguing that to do so would require unacceptable cuts in existing conventional and nuclear-capable aircraft,^[43] and that the military had greater priorities in spending a limited budget.^[44]

Some B-2 advocates argued that procuring twenty additional aircraft would save money because B-2s would be able to deeply penetrate anti-aircraft defenses and use low-cost, short-range attack weapons rather than expensive standoff weapons. However, in 1995, the Congressional Budget Office (CBO), and its Director of National Security Analysis, found that additional B-2s would reduce the cost of expended munitions by less than US$2 billion in 1995 dollars during the first two weeks of a conflict, in which the Air Force predicted bombers would make their greatest contribution; a small fraction of the US$26.8 billion (in 1995 dollars) life cycle cost that the CBO projected an additional 20 B-2s would cost.^[45]

In 1997, as Ranking Member of the House Armed Services Committee and National Security Committee, Congressman Ron Dellums (D-CA), a long-time opponent of the bomber, cited five independent studies and offered an amendment to that year's defense authorization bill to cap production of the bombers to the existing 21 aircraft; the amendment was narrowly defeated.^[46] Nonetheless, Congress did not approve funding for the purchase of any additional B-2 bombers.

Further developments

A number of upgrade packages have been applied to the B-2. In July 2008, the B-2's onboard computing architecture was extensively redesigned; it now incorporates a new integrated processing unit (IPU) that communicates with systems throughout the aircraft via a newly installed fiber optic network; a new version of the operational flight program software was also developed, with legacy code converted from the JOVIAL programming language used beforehand to standard C.^[47][48] Updates were also made to the weapon control systems to enable strikes upon non-static targets, such as moving ground vehicles.^[49]

On 29 December 2008, Air Force officials awarded a US$468 million contract to Northrop Grumman to modernize the B-2 fleet's radars.^[50] Changing the radar's frequency was required as the U.S. Department of Commerce has sold that radio spectrum to another operator.^[51] In July 2009, it was reported that the B-2 had successfully passed a major USAF audit.^[52] In 2010, it was made public that the Air Force Research Laboratory had developed a new material to be used on the part of the wing trailing edge subject to engine exhaust, replacing existing material that quickly degraded.^[53]

In 2013 the USAF contracted for the Defensive Management System Modernization program to replace the antenna system and other electronics to increase the B-2's frequency awareness.^[54] The Common Very Low Frequency Receiver upgrade will allow the B-2s to use the same very low frequency transmissions as the Ohio-class submarines so as to continue in the nuclear mission until the Mobile User Objective System is fielded.^[55]

In July 2010, political analyst Rebecca Grant speculated that when the B-2 becomes unable to reliably penetrate enemy defenses, the Lockheed Martin F-35 Lightning II may take on its strike/interdiction mission, carrying B61 nuclear bombs as a tactical bomber.^[56] However, in March 2012, the Pentagon announced that a $2 billion, 10-year-long modernization of the B-2 fleet was to begin. The main area of improvement would be replacement of outdated avionics and equipment.^[57]

It was reported in 2011 that the Pentagon was evaluating an unmanned stealth bomber, characterized as a "mini-B-2", as a potential replacement in the near future.^[58] In 2012, Air Force Chief of Staff General Norton Schwartz stated the B-2's 1980s-era stealth would make it less survivable in future contested airspaces, so the USAF is to proceed with the Next-Generation Bomber despite overall budget cuts.^[59] The Next-Generation Bomber was estimated, in 2012, to have a projected overall cost of $55 billion.^[60]

In 2014 the USAF outlined a series of upgrades including nuclear war fighting, a new integrated processing unit, the ability to carry cruise missiles, and threat warning improvements.^[61]

Design

Overview

The B-2 Spirit was developed to take over the USAF's vital penetration missions, able to travel deep into enemy territory to deploy their ordnance, which could include nuclear weapons.^[62] The B-2 is a flying wing aircraft, meaning it has no fuselage or tail.^[62] The blending of low-observable technologies with high aerodynamic efficiency and large payload gives the B-2 significant advantages over previous bombers. Low observability provides a greater freedom of action at high altitudes, thus increasing both range and field of view for onboard sensors. The U.S. Air Force reports its range as approximately 6,000 nautical miles (6,900 mi; 11,000 km).^[7][63] At cruising altitude the B-2 refuels every six hours, taking on up to 50 short tons (45 t) of fuel at a time.^[64]

Due to the aircraft's complex flight characteristics and design requirements to maintain very-low visibility to multiple means of detection, both the development and construction of the B-2 required pioneering use of computer-aided design and manufacturing technologies.^[62][65] The B-2 bears a resemblance to earlier Northrop aircraft: the YB-35 and YB-49 were both flying wing bombers that had been canceled in development in the early 1950s,^[66] allegedly for political reasons.^[67] The resemblance goes as far as B-2 and YB-49 having the same wingspan.^[68][69]

As of September 2013 about 80 pilots fly the B-2.^[64] Each aircraft has a crew of two, a pilot in the left seat and mission commander in the right,^[7] and has provisions for a third crew member if needed.^[70] For comparison, the B-1B has a crew of four and the B-52 has a crew of five.^[7] The B-2 is highly automated and, unlike most two-seat aircraft, one crew member can sleep in a camp bed, use a toilet, or prepare a hot meal while the other monitors the aircraft; extensive sleep cycle and fatigue research was conducted to improve crew performance on long sorties.^[71][72][64]

Armaments and equipment

The B-2, in the envisaged Cold War scenario, was to perform deep-penetrating nuclear strike missions, making use of its stealthy capabilities to avoid detection and interception throughout missions.^[73] There are two internal bomb bays in which munitions are stored either on a rotary launcher or two bomb-racks; the carriage of the weapons loadouts internally results in less radar visibility than external mounting of munitions.^[74][75] The B-2 is capable of carrying 40,000 pounds of ordnance.^[7][76] Nuclear ordnance includes the B61 and B83 nuclear bombs; the AGM-129 ACM cruise missile was also intended for use on the B-2 platform.^[75][77]

It was decided, in light of the dissolution of the Soviet Union, to equip the B-2 for conventional precision attacks as well as for the strategic role of nuclear-strike.^[73][78] The B-2 features a sophisticated GPS-Aided Targeting System (GATS) that uses the aircraft's APQ-181 synthetic aperture radar to map out targets prior to deployment of GPS-aided bombs (GAMs), later superseded by the Joint Direct Attack Munition (JDAM). In the B-2's original configuration, up to 16 GAMs or JDAMs could be deployed;^[79] an upgrade program in 2004 raised the maximum carriable capacity to 80 JDAMs.^[80]

The B-2 has various conventional weapons in its arsenal, able to equip Mark 82 and Mark 84 bombs, CBU-87 Combined Effects Munitions, GATOR mines, and the CBU-97 Sensor Fuzed Weapon.^[81] In July 2009, Northrop Grumman reported the B-2 was compatible with the equipment necessary to deploy the 30,000 lb (14,000 kg) Massive Ordnance Penetrator (MOP), which is intended to attack reinforced bunkers; up to two MOPs could be equipped in the B-2's bomb bays,^[82] the B-2 is the only platform compatible with the MOP as of 2012.^[57] As of 2011, the AGM-158 JASSM cruise missile is an upcoming standoff munition to be deployed on the B-2 and other platforms.^[83] This is to be followed by the Long Range Standoff Weapon which may give the B-2 a standoff nuclear capability for the first time.^[84]

Avionics and systems

In order to make the B-2 more effective than previous bombers, many advanced and modern avionics systems were integrated into its design, these have been modified and improved following a switch to conventional warfare missions. One system is the low probability of intercept AN/APQ-181 multi-mode radar, a fully digital navigation system that is integrated with terrain-following radar and Global Positioning System (GPS) guidance, NAS-26 astro-inertial navigation system (first such system tested on the Northrop SM-62 Snark cruise missile)^[85] and a Defensive Management System (DMS) to inform the flight crew of possible threats.^[80] The onboard DMS is capable of automatically assessing the detection capabilities of identified threats and indicated targets.^[86] The DMS will be upgraded by 2021 to detect radar emissions from air defenses to allow changes to the auto-router's mission planning information while in-flight so it can receive new data quickly to plan a route that minimizes exposure to dangers.^[6]

For safety and fault-detection purposes, an on-board test system is interlinked with the majority of avionics on the B-2 to continuously monitor the performance and status of thousands of components and consumables; it also provides post-mission servicing instructions for ground crews.^[87] In 2008, many of the 136^[88] standalone distributed computers on board the B-2, including the primary flight management computer, were being replaced by a single integrated system.^[89] The avionics are controlled by 13 EMP-resistant MIL-STD-1750A computers, which are interconnected through 26 MIL-STD-1553B-busses; other system elements are connected via optical fiber.^[90]

In addition to periodic software upgrades and the introduction of new radar-absorbent materials across the fleet, the B-2 has had several major upgrades to its avionics and combat systems. For battlefield communications, both Link-16 and a high frequency satellite link have been installed, compatibility with various new munitions has been undertaken, and the AN/APQ-181 radar's operational frequency was shifted in order to avoid interference with other operator's equipment.^[80] The arrays of the upgraded radar features were entirely replaced to make the AN/APQ-181 into an active electronically scanned array (AESA) radar.^[91]

Flight controls

In order to address the inherent flight instability of a flying wing aircraft, the B-2 uses a complex quadruplex computer-controlled fly-by-wire flight control system, that can automatically manipulate flight surfaces and settings without direct pilot inputs in order to maintain aircraft stability.^[92] The flight computer receives information on external conditions such as the aircraft's current air speed and angle of attack via pitot-static sensing plates, as opposed to traditional pitot tubes which would negatively affect the aircraft's stealth capabilities.^[93] The flight actuation system incorporates both hydraulic and electrical servoactuated components, and it was designed with a high level of redundancy and fault-diagnostic capabilities.^[94]

Northrop had investigated several means of applying directional control that would least infringe on the aircraft's radar profile, eventually settling on a combination of split brake-rudders and differential thrust.^[86] Engine thrust became a key element of the B-2's aerodynamic design process early on; thrust not only affects drag and lift but pitching and rolling motions as well.^[95] Four pairs of control surfaces are located along the wing's trailing edge; while most surfaces are used throughout the aircraft's flight envelope, the inner elevons are normally only in use at slow speeds, such as landing.^[96] To avoid potential contact damage during takeoff and to provide a nose-down pitching attitude, all of the elevons remain drooped during takeoff until a high enough airspeed has been attained.^[96]

Stealth

The B-2's low-observable, or "stealth", characteristics enable the undetected penetration of sophisticated anti-aircraft defenses and to attack even heavily defended targets. This stealth comes from a combination of reduced acoustic, infrared, visual and radar signatures (multi-spectral camouflage) to evade the various detection systems that could be used to detect and be used to direct attacks against an aircraft. The B-2's stealth enables the reduction of supporting aircraft that are required to provide air cover, Suppression of Enemy Air Defenses and electronic countermeasures, making the bomber a "force multiplier". As of September 2013, there have been no instances of a missile being launched at a B-2.^[64]

To reduce optical visibility during daylight flights, the B-2 is painted in an anti-reflective paint.^[75] The undersides are dark because it flies at high altitudes (50,000 feet), and at that altitude a dark grey painting blends well into the sky. It is speculated to have an upward-facing light sensor which alerts the pilot to increase or reduce altitude to match the changing illuminance of the sky.^[97] The original design had tanks for a contrail-inhibiting chemical, but this was replaced in production aircraft by a contrail sensor that alerts the crew when they should change altitude.^[98] The B-2 is vulnerable to visual interception at ranges of 20 nmi (37 km) or less.^[64]

Radar

Reportedly, the B-2 has a radar cross-section of about 0.1 m² (1.1 sq ft).^[99] The bomber does not always fly stealthily; when nearing air defenses pilots "stealth up" the B-2, the details of which are secret. The aircraft is not seen by radar, except briefly when the bomb bay opens. The B-2's clean, low-drag flying wing configuration not only provides exceptional range but is also beneficial to reducing its radar profile.^[62][100] The flying wing design most closely resembles a so-called infinite flat plate (as vertical control surfaces dramatically increase RCS), the perfect stealth shape, as it would lack angles to reflect back radar waves (initially, the shape of the Northrop ATB concept was flatter; it gradually increased in volume according to specific military requirements).^[101]

RCS reduction as a result of shape had already been observed on the Royal Air Force's Avro Vulcan strategic bomber,^[102] and the USAF's F-117 Nighthawk. The F-117 used flat surfaces (faceting technique) for controlling radar returns as during its development (see Lockheed Have Blue) in the early 1970s, technology only allowed for the simulation of radar reflections on simple, flat surfaces; computing advances in the 1980s made it possible to simulate radar returns on more complex curved surfaces.^[103] The B-2 is composed of many curved and rounded surfaces across its exposed airframe to deflect radar beams. This technique, known as continuous curvature, was made possible by advances in computational fluid dynamics, and first tested on the Northrop Tacit Blue.^[104][105]

The leading edges of the wing converge at the nose of the aircraft, which prevents radar reflections in the direction of flight; the W-shaped rear of the aircraft is for similar reasons. The engine air intakes are placed on top of the fuselage to minimize reflection to ground-based radar. To avoid detection by look-down radars, engines are buried within the B-2's wing (S-duct) to conceal the engines' fans. The B-2 also carries all ordnance internally.

Infrared

Some analysts claim infra-red search and track systems (IRSTs) can be deployed against stealth aircraft, because any aircraft surface heats up due to air friction and with a two channel IRST is a CO2 (4.3 µm absorption maxima) detection possible, through difference comparing between the low and high channel.^[106][107]

Burying engines deep inside the fuselage also minimizes the thermal visibility or infrared signature of the exhaust.^[75][108] At the engine intake, cold air from the boundary layer below the main inlet enters the fuselage (boundary layer suction, first tested on the Northrop X-21) and is mixed with hot exhaust air just before the nozzles (similar to the Ryan AQM-91 Firefly). According to the Stefan–Boltzmann law, this results in less energy (thermal radiation in infrared spectrum) being released and thus a reduced heat signature. The resulting cooler air is conducted over a surface composed of heat resistant carbon-fiber-reinforced polymer and titanium alloy elements, which disperse the air laterally, in order to accelerate its cooling.^[90] The B-2 lacks afterburners as the hot exhaust would increase the infrared footprint; breaking the sound barrier would produce an obvious sonic boom as well as aerodynamic heating of the aircraft skin which would also increase the infrared footprint.

Materials

According to the Huygens–Fresnel principle, even a very flat plate would still reflect radar waves, though much less than when a signal is bouncing at a right angle. Additional reduction in its radar signature was achieved by the use of various radar-absorbent materials (RAM) to absorb and neutralize radar beams. The majority of the B-2 is made out of a carbon-graphite composite material that is stronger than steel and lighter than aluminum. Perhaps most crucially, a beneficial characteristic of this composite material is the absorption of significant amounts of radar energy.^[66]

The B-2 is assembled with unusually tight engineering tolerances to avoid leaks as they could increase its radar signature.^[71] Innovations such as alternate high frequency material (AHFM) and automated material application methods were also incorporated into the aircraft to enhance its radar-absorbent properties and lower maintenance requirements.^[75][109] In early 2004, Northrop Grumman began applying a newly developed AHFM to operational B-2s.^[110] In order to protect the operational integrity of its sophisticated radar absorbent material and coatings, each B-2 is kept inside a climate-controlled hangar (Extra Large Deployable Aircraft Hangar System) large enough to accommodate its 172-foot (52 m) wingspan.^[111]

Operational history

The first operational aircraft, christened Spirit of Missouri, was delivered to Whiteman Air Force Base, Missouri, where the fleet is based, on 17 December 1993.^[112] The B-2 reached initial operational capability (IOC) on 1 January 1997.^[113] Depot maintenance for the B-2 is accomplished by U.S. Air Force contractor support and managed at Oklahoma City Air Logistics Center at Tinker Air Force Base.^[7] Originally designed to deliver nuclear weapons, modern usage has shifted towards a flexible role with conventional and nuclear capability.^[75]

The B-2's combat debut was in 1999, during the Kosovo War. It was responsible for destroying 33% of selected Serbian bombing targets in the first eight weeks of U.S. involvement in the War.^[7] During this war, six B-2s flew non-stop to Kosovo from their home base in Missouri and back, totalling 30 hours. Although the bombers accounted 50 sorties out of a total of 34,000 NATO sorties, they dropped 11 percent of all bombs.^[114] The B-2 was the first aircraft to deploy GPS satellite-guided JDAM "smart bombs" in combat use in Kosovo.^[115] The use of JDAMs and precision-guided munitions effectively replaced the controversial tactic of carpet-bombing, which had been harshly criticized due to it causing indiscriminate civilian casualties in prior conflicts, such as the 1991 Gulf War.^[116] On 7 May 1999, a B-2 dropped five JDAMs on a target building that was actually the Chinese Embassy, killing several staff.^[117] By then, the B-2 had dropped 500 bombs in Kosovo.^[118]

The B-2 saw service in Afghanistan, striking ground targets in support of Operation Enduring Freedom. With aerial refueling support, the B-2 flew one of its longest missions to date from Whiteman Air Force Base, Missouri to Afghanistan and back.^[7] B-2s would be stationed in the Middle East as a part of a US military buildup in the region from 2003.^[119]

The B-2's combat use preceded a U.S. Air Force declaration of "full operational capability" in December 2003.^[7] The Pentagon's Operational Test and Evaluation 2003 Annual Report noted that the B-2's serviceability for Fiscal Year 2003 was still inadequate, mainly due to the maintainability of the B-2's low observable coatings. The evaluation also noted that the Defensive Avionics suite had shortcomings with "pop-up threats".^[7][120]

During the Iraq War (Operation Iraqi Freedom), B-2s operated from Diego Garcia and an undisclosed "forward operating location". Other sorties in Iraq have launched from Whiteman AFB.^[7] As of September 2013 the longest combat mission has been 44.3 hours.^[64] "Forward operating locations" have been previously designated as Andersen Air Force Base in Guam and RAF Fairford in the United Kingdom, where new climate controlled hangars have been constructed. B-2s have conducted 27 sorties from Whiteman AFB and 22 sorties from a forward operating location, releasing more than 1,500,000 pounds (680,000 kg) of munitions,^[7] including 583 JDAM "smart bombs" in 2003.^[80]

In response to organizational issues and high-profile mistakes made within the Air Force,^[121][122] all of the B-2s, along with the nuclear-capable B-52s and the Air Force's intercontinental ballistic missiles (ICBMs), were transferred to the newly formed Air Force Global Strike Command on 1 February 2010.^[123][124]

In March 2011, B-2s were the first U.S. aircraft into action in Operation Odyssey Dawn, the UN mandated enforcement of the Libyan no-fly zone. Three B-2s dropped 40 bombs on a Libyan airfield in support of the UN no-fly zone.^[125] The B-2s flew directly from the U.S. mainland across the Atlantic Ocean to Libya; a B-2 was refueled by allied tanker aircraft four times during each round trip mission.^[126][127]

In August 2011, The New Yorker reported that prior to the May 2011 U.S. Special Operations raid into Abbottabad, Pakistan that resulted in the death of Osama bin Laden, U.S. officials had considered an airstrike by one or more B-2s as an alternative; an airstrike was rejected because of damage to civilian buildings in the area from using a bunker busting bomb.^[128] There were also concerns an airstrike would make it difficult to positively identify Bin Laden's remains and so concluding he was in fact dead would be problematic.^[129]

On 28 March 2013, two B-2s flew a round trip of 13,000 miles (20,800 km) from Whiteman Air Force base in Missouri to South Korea, dropping dummy ordnance on the Jik Do target range. The mission, part of the annual South Korean–United States military exercises, was the first time that B-2s overflew the Korean peninsula. Tensions between North and South Korea were high during and after the exercise, North Korea protested against the participation of the B-2s and made threats of retaliatory nuclear strikes against South Korea and the United States.^[130][131]

Operators

United States Air Force (20 aircraft in active inventory)

Global Strike Command

• 509th Bomb Wing – Whiteman Air Force Base, Missouri (currently has 19 B-2s)

13th Bomb Squadron 2005–

325th Bomb Squadron 1998–2005

393d Bomb Squadron 1993–

394th Combat Training Squadron 1996–

Air Combat Command

• 53d Wing – Eglin Air Force Base, Florida

72d Test and Evaluation Squadron (Whiteman) 1998–

• 57th Wing – Nellis AFB, Nevada

325th Weapons Squadron 2005– (Whiteman)

715th Weapons Squadron 2003–05

Air National Guard

• 131st Bomb Wing (Associate) – Whiteman Air Force Base 2009–

110th Bomb Squadron

Air Force Materiel Command

• 412th Test Wing – Edwards Air Force Base, California (has one B-2)

419th Flight Test Squadron 1997–

420th Flight Test Squadron 1992–97

Air Force Systems Command

• 6510th Test Wing – Edwards AFB 1989–92

6520th Flight Test Squadron

Accidents

On 23 February 2008, B-2 "AV-12" Spirit of Kansas crashed on the runway shortly after takeoff from Andersen Air Force Base in Guam.^[132] Spirit of Kansas had been operated by the 393rd Bomb Squadron, 509th Bomb Wing, Whiteman Air Force Base, Missouri, and had logged 5,176 flight hours. The two person crew ejected safely from the aircraft and survived the crash. The aircraft was completely destroyed, a hull loss valued at US$1.4 billion.^[133][134] After the accident, the Air Force took the B-2 fleet off operational status until clearing the fleet for flight status 53 days later on 15 April 2008.^[135] The cause of the crash was later determined to be moisture in the aircraft's Port Transducer Units during air data calibration, which distorted the information being sent to the bomber's air data system. As a result, the flight control computers calculated an inaccurate airspeed, and a negative angle of attack, causing the aircraft to pitch upward 30 degrees during takeoff.^[136] This was the first crash of a B-2 and the only loss as of 2016.

In February 2010, another serious incident involving a B-2 occurred at Andersen AFB. The aircraft involved was AV-11 Spirit of Washington. The aircraft was severely damaged by fire while on the ground and underwent 18 months of repairs in order to enable it to fly back to the mainland for more comprehensive repairs.^[137][138] Spirit of Washington was repaired and returned to service in December 2013.^[139][140] At the time of the accident the USAF had no training to deal with tailpipe fires on the B-2s.^[141]

Aircraft on display

No operational B-2s have been retired by the Air Force to be put on display. B-2s have made periodic appearances on ground display at various air shows.

B-2 test article (s/n AT-1000), the second of two built without engines or instruments for static testing, was placed on display in 2004 at the National Museum of the United States Air Force near Dayton, Ohio.^[142] The test article passed all structural testing requirements before the airframe failed.^[143] The Museum's restoration team spent over a year reassembling the fractured airframe. The display airframe is marked to resemble The Spirit of Ohio (S/N 82-1070), the B-2 used to test the design's ability to withstand extreme heat and cold.^[142] The exhibit features Spirit of Ohio's nose wheel door, with its Fire and Ice artwork, which was painted and signed by the technicians who performed the temperature testing.^[142] The restored test aircraft is on display in the museum's "Cold War Gallery".^[144]

From 1989 to 2004, the South Dakota Air and Space Museum located on the grounds of Ellsworth Air Force Base displayed the 10-short-ton (9-metric-ton) "Honda- Stealth", a 60% scale mock-up of a stealthy bomber which had been built by North American Honda in 1988 for an advertising campaign.^[145] Honda donated the model to the museum in 1989, on condition that the model be destroyed if it was ever replaced with a different example. The museum received a B-1 Lancer for display (Ellsworth being a B-1 base) in 2005 and destroyed the mock-up.^[146][147]

Specifications (B-2A Block 30)

Data from USAF Fact Sheet,^[7] Pace,^[148] Spick^[63]

General characteristics

• Crew: 2: pilot and commander (co-pilot)
• Length: 69 ft (21.0 m)
• Wingspan: 172 ft (52.4 m)
• Height: 17 ft (5.18 m)
• Wing area: 5,140 ft² (478 m²)
• Empty weight: 158,000 lb (71,700 kg)
• Loaded weight: 336,500 lb (152,200 kg)
• Max. takeoff weight: 376,000 lb (170,600 kg)
• Powerplant: 4 × General Electric F118-GE-100 non-afterburning turbofans, 17,300 lbf (77 kN) each
• Fuel Capacity: 167,000 pounds (75,750 kg)

Performance

• Maximum speed: Mach 0.95 (550 knots, 630 mph, 1,010 km/h) at 40,000 ft altitude / Mach 0.95 at sea level^[148]
• Cruise speed: Mach 0.85^[63] (487 knots, 560 mph, 900 km/h) at 40,000 ft altitude
• Range: 6,000 nmi (11,100 km (6,900 mi))
• Service ceiling: 50,000 ft (15,200 m)
• Wing loading: 67.3 lb/ft² (329 kg/m²)
• Thrust/weight: 0.205

Armament

• 2 internal bays for ordnance and payload with an official limit of 40,000 lb (18,000 kg); maximum estimated limit is 50,000 lb (23,000 kg).^[63]
  • 80× 500 lb class bombs (Mk-82, GBU-38) mounted on Bomb Rack Assembly (BRA)
  • 36× 750 lb CBU class bombs on BRA
  • 16× 2,000 lb class bombs (Mk-84, GBU-31) mounted on Rotary Launcher Assembly (RLA)
  • 16× B61 or B83 nuclear bombs on RLA (strategic mission)
  • Standoff weapon: AGM-154 Joint Standoff Weapon (JSOW) and AGM-158 Joint Air-to-Surface Standoff Missile (JASSM). ^[149][150]

Individual aircraft

Individual aircraft

Air Vehicle No.	Block No.[151]	USAF s/n	Formal name	Time in service, status
AV-1	Test/30	82-1066	Spirit of America	14 July 2000 – Active[152]
AV-2	Test/30	82-1067	Spirit of Arizona	4 December 1997 – Active
AV-3	Test/30	82-1068	Spirit of New York	10 October 1997 – Active
AV-4	Test/30	82-1069	Spirit of Indiana	22 May 1999 – Active
AV-5	Test/20	82-1070	Spirit of Ohio	18 July 1997 – Active
AV-6	Test/30	82-1071	Spirit of Mississippi	23 May 1997 – Active
AV-7	10	88-0328	Spirit of Texas	21 August 1994 – Active
AV-8	10	88-0329	Spirit of Missouri	31 March 1994 – Active
AV-9	10	88-0330	Spirit of California	17 August 1994 – Active
AV-10	10	88-0331	Spirit of South Carolina	30 December 1994 – Active
AV-11	10	88-0332	Spirit of Washington	29 October 1994 – Severely damaged by fire[137] Repaired.[139]
AV-12	10	89-0127	Spirit of Kansas	17 February 1995 – 23 February 2008, Crashed[132]
AV-13	10	89-0128	Spirit of Nebraska	28 June 1995 – Active
AV-14	10	89-0129	Spirit of Georgia	14 November 1995 – Active
AV-15	10	90-0040	Spirit of Alaska	24 January 1996 – Active
AV-16	10	90-0041	Spirit of Hawaii	10 January 1996 – Active
AV-17	20	92-0700	Spirit of Florida	3 July 1996 – Active
AV-18	20	93-1085	Spirit of Oklahoma	15 May 1996 – Active, Flight Test
AV-19	20	93-1086	Spirit of Kitty Hawk	30 August 1996 – Active
AV-20	30	93-1087	Spirit of Pennsylvania	5 August 1997 – Active
AV-21	30	93-1088	Spirit of Louisiana	10 November 1997 – Active
AV-22 through AV-165				Cancelled

Sources: B-2 Spirit (Pace),^[153] Fas.org^[154]

Notable appearances in media

See also

Related lists

• List of active United States military aircraft
• List of bomber aircraft
• List of flying wing aircraft
• List of aerospace megaprojects

References

Notes

Bibliography

Further reading

• Richardson, Doug. Northrop B-2 Spirit (Classic Warplanes). New York: Smithmark Publishers Inc., 1991. ISBN 0-8317-1404-2.
• Sweetman, Bill. Inside the Stealth Bomber. St. Paul, Minnesota: MBI Publishing, 1999. ISBN 0-7603-0627-3.
• Winchester, Jim, ed. "Northrop B-2 Spirit". Modern Military Aircraft (Aviation Factfile). Rochester, Kent, UK: Grange Books plc, 2004. ISBN 1-84013-640-5.
• The World's Great Stealth and Reconnaissance Aircraft. New York: Smithmark, 1991. ISBN 0-8317-9558-1.

External links

Wikimedia Commons has media related to B-2 Spirit.

• B-2 Spirit fact sheet and gallery on U.S. Air Force site
• B-2 Spirit page on Northrop Grumman site
• B-2 Spirit Stealth bomber on airforce-technology.com
• B-2 Stealth Bomber article on How It Works Daily
• B-2 Spirit page at GlobalSecurity.org

Northrop aircraft Manufacturer designations 'Greek' series Alpha Beta Gamma Delta 'N' series Note: Northrop company designations include a wide variety of technologies. Only aircraft, aero engines, and missiles are linked here. N-1 N-2 N-3 N-4 N-5 N-6 N-7 N-8 N-9 N-10 N-12 N-14 N-15 N-16 N-18 N-19 N-20 N-21 N-23 N-24 N-25 N-26 N-29 N-31 N-32 N-34 N-35 N-36 N-37 N-38 N-39 N-40 N-41 N-46 N-47 N-48 N-49 N-50 N-51 N-52 N-54 N-55 N-59 N-60 N-63 N-65 N-67 N-68 N-69 N-71 N-72 N-73 N-74 N-77 N-81 N-82 N-94 N-96 N-102 N-103 N-105 N-110 N-111 N-112 N-117 N-124 N-132 N-133 N-134 N-135 N-138 N-141 N-144 N-149 N-150 N-151 N-155 N-156 N-205 N-267 N-285 N-300 'P' series P530 P600 P610 By role Attack YA-13 XA-16 A-17 Nomad YA-9 Bombers YB-35 YB-49 B-62 BT B2T B-2 Drones Q-4 Fighters 3A XP-56 P-61 XP-79 F-89 XFT F2T F-5/CF-5/CF-116 YF-17 F-18L F-20 YF-23 Reconnaissance F-15 RF-61 RF-5 Trainers T-38 Transports Alpha Beta Gamma Delta C-19 C-100 YC-125 RT Experimental N-1M N-9M JB-1 MX-324 MX-334 M2-F2 M2-F3 HL-10 Tacit Blue X-4 X-21 Names Bantam Black Bullet Black Widow Chukar Nomad Pioneer Raider Reporter Scorpion Snark Talon Tigershark See also: TR-3

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USAAS/USAAC/USAAF/USAF bomber designations, Army/Air Force and Tri-Service systems Original sequences (1924-1930) Light Bomber LB-1 LB-2 LB-3 LB-4 LB-5 LB-6 LB-7 LB-8 LB-9 LB-10 LB-11 LB-12 LB-13 LB-14 Medium Bomber B-1 B-2 Heavy Bomber HB-1 HB-2 HB-3 Main sequence (1930-1962) B-1 B-2 B-3 B-4 B-5 B-6 B-7 B-8 B-9 B-10 B-11 B-12 B-13 B-14 B-15 B-16 B-17 B-18 B-19 B-20 B-21 B-22 B-23 B-24 B-25 B-26 B-27 B-28 B-29 B-30 B-31 B-32 B-33 B-34 B-35 B-36 B-37 B-38 B-39 B-40 B-41 B-42 B-43 B-44 B-45 B-46 B-47 B-48 B-49 B-50 B-51 B-52 B-53 B-54 B-55 B-56 B-57 B-58 B-59 B-60 B-61 B-62 B-63 B-64 B-65 B-66 B-67 B-68 RB-69 B-70 Long-range Bomber (1935-1936) BLR-1 BLR-2 BLR-3 Oddities Redesignated A-series B-20 B-26 'FB-' designations FB-111 FB-22 Tri-Service sequence (1962-current) B-1 B-2 See also: SR-71 (designation in bomber sequence) Next-Generation Bomber ("B-3") 2037 Bomber

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