Tuesday, July 30, 2013

Northrop Grumman B-2 Spirit

Northrop Grumman B-2 Spirit

The Northrop Grumman B-2 Spirit, also known as the Stealth Bomber, is an American strategic bomber, featuring low observable stealth technology designed for penetrating dense anti-aircraft defenses; it is able to deploy both conventional and nuclear weapons. The bomber has a crew of two and can drop up to eighty 500 lb (230 kg)-class JDAM GPS-guided bombs, or sixteen 2,400 lb (1,100 kg) B83 nuclear bombs. The B-2 is the only 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 performance was one of the reasons for his cancellation of the B-1 Lancer. 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 Grumman with assistance from Boeing, 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, and the crew ejected safely.[4] A total of 20 B-2s remain in service with the United States Air Force.
The B-2 is capable of all-altitude attack missions up to 50,000 ft, with a range of more than 6,000 nautical miles unrefuelled and over 10,000 nautical miles with one refueling. Though originally designed primarily as a nuclear bomber, it was first used in combat to drop conventional bombs on Serbia during the Kosovo War in 1999, and saw continued use during the wars in Iraq and Afghanistan.[5]

Origins

In the mid-1970s, the search for a new U.S. strategic bomber to replace the Boeing B-52 Stratofortress was underway, to no avail. First the B-70 and then the B-1A were canceled after only a few of each aircraft were built. The B-70 was intended to fly above and beyond defensive interceptor aircraft, only to find these same attributes made it especially vulnerable to surface-to-air missiles (SAMs). The B-1 attempted to avoid SAMs by flying close to the ground to use terrain to mask its radar signature, only to face a new generation of interceptors with look-down/shoot-down capabilities that could attack them from above.[6]
By the mid-1970s, it was becoming clear that there was a different way to avoid missiles and intercepts; 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.[7]
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.[8] 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.[9]
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.[10]


Program costs and procurement

A procurement of 132 aircraft was planned in the mid-1980s, but was later reduced to 75.[27] 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.[28] 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.[29]
In 1995, Northrop made a proposal to the USAF to build 20 additional aircraft with a flyaway cost of $566 million each.[30]
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$9.6 million annually) and over four times as much as the B-52H ($US6.8 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.[31][32] Maintenance costs are about $3.4 million a month for each aircraft.[33]
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.[34][35]


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 fibre 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.[44][45] Updates were also made to the weapon control systems to enable strikes upon non-static targets, such as moving ground vehicles.[46]
B-2 from below
On 29 December 2008, Air Force officials awarded a US$468 million contract to Northrop Grumman to modernize the B-2 fleet's radars.[47] Changing the radar's frequency was required as the U.S. Department of Commerce has sold that radio spectrum to another operator.[48] In July 2009, it was reported that the B-2 had successfully passed a major USAF audit.[49] 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.[50]
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.[51]
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 bomb as a tactical bomber.[52] However, in March 2012, the Pentagon announced a $2 billion, 10 year-long modernization of the B-2 fleet was to begin, these upgrades would be mainly focused on replacing outdated avionics and equipment.[53]
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.[54] 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.[55] The Next-Generation Bomber was estimated, in 2012, to have an projected overall cost of $55 billion.[56]


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.[57] The B-2 is a flying wing aircraft, meaning it has no fuselage or tail.[57] 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).[5][58]
Side view of a B-2 Spirit
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.[57][59] Northrop Grumman is the B-2's prime contractor; other contributing subcontractors include Boeing, Raytheon (formerly Hughes Aircraft), G.E. and Vought Aircraft.[5] The B-2 bears a resemblance to earlier Northrop aircraft, the YB-35 and YB-49 were both flying wing bombers that had been cancelled in development in the early 1950s;[60] allegedly for political reasons.[61]
The B-2 has a crew of two: a pilot in the left seat, and mission commander in the right;[5] the B-2 has provisions for a third crew member if needed.[62] For comparison, the B-1B has a crew of four and the B-52 has a crew of five.[5] The B-2 is highly automated and, unlike most two-seat aircraft, one crew member can sleep, 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.[63][64]

Armaments and equipment

A 2000 lb BDU-56 bomb is being loaded onto a bomb bay's rotary launcher, 2004
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.[65] 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 externally mounting of munitions.[66][67] 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.[67][68]
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.[65][69] 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;[70] an upgrade program in 2004 raised the maximum carriable capacity to 80 JDAMs.[71]
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.[72] 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,[73] the B-2 is the only platform compatible with the MOP as of 2012.[53] As of 2011, the AGM-158 JASSM cruise missile is an upcoming standoff munition to be deployed on the B-2 and other platforms.[74] 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.[75]

Avionics and systems

In order to make the B-2 more effective than any previous bomber, it has integrated many advanced and modern avionics systems into its design, these have been modified and improved in light of the switch to conventional warfare missions. The B-2 features 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, and a Defensive Management System (DMS) to inform the flight crew against possible threats.[71] The onboard DMS is capable of automatically assessing the detection capabilities of identified threats and indicated targets.[76]
A maintenance crew servicing a B-2 at Andersen AFB, Guam, 2004
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.[77] In 2008, many of the standalone distributed computers on board the B-2, including the primary flight management computer, were being replaced by a single integrated system.[78]
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.[71] The upgraded radar features entirely replaced arrays by those of a newer design, the AN/APQ-181 is now an Active Electronically Scanned Array (AESA) radar.[79]

Flight controls

Vice President Dick Cheney sits inside a B-2's cockpit with pilot Capt. Luke Jayne during a visit to Whiteman AFB in 2006.
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.[80] 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.[81] 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.[82]
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.[76] 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.[83] 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.[84] 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.[84]

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 to evade the various detection systems that could be used to detect and be used to direct attacks against an aircraft. The majority of the B-2 is made out of a carbon-graphite composite material that is stronger than steel and lighter than aluminium; perhaps most crucially, it also absorbs a significant amount of radar energy.[60] Reportedly, the B-2 Spirit has a radar signature of about 0.1 m2.[85]
The B-2's engines are buried within its wing to conceal the engines' fans and minimize their exhaust signature
In contrast to the flat surfaces of the earlier F-117 Nighthawk, the B-2 is composed of many curved and rounded surfaces across its exposed airframe to deflect radar beams. Additional reduction in its radar signature was achieved by the use of various radar-absorbent materials (RAM) to absorb and neutralize radar beams. The B-2's clean, low-drag flying wing configuration not only gives it exceptional range but is also beneficial to reducing its radar profile.[57][86]
Another design feature is the placement of the engines, which are buried within the wing to conceal the engines' fans and minimize thermal visibility of the exhaust.[67][87] 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.[88] To reduce optical visibility during daylight operations, the B-2 is painted in an anti-reflective paint.[67]
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.[67][89] In early 2004, Northrop Grumman began applying a newly-developed AHFM to operational B-2s.[90] 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 large enough to accommodate its 172-foot (52 m) wingspan.[91]


General characteristics
Performance
Armament
  • 2 internal bays for 50,000 lb (23,000 kg) of ordnance and payload[58]



 

Accidents

Main article: Andersen Air Force Base B-2 accident
Wreckage of the 2008 B-2 crash
On 23 February 2008, B-2 Spirit of Kansas, 89-0127 crashed on the runway shortly after takeoff from Andersen Air Force Base in Guam.[111] 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. It was the first crash of a B-2. 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.[112][113] 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.[114] 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.[115]
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 temporary repairs in order to enable it to fly back to the mainland for more comprehensive repairs.

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