Editing Northrop B-2 Spirit (section)

==Design==
[[File:US Air Force B-2 Spirit.jpg|thumb|left|Side view of a B-2 Spirit]]

===Overview===
The B-2 Spirit was developed to take over the USAF's vital penetration missions, allowing it to travel deep into enemy territory to deploy [[aircraft ordnance|ordnance]], which could include [[nuclear weapon]]s.<ref name= "croddy 341-2">Croddy and Wirtz 2005, pp. 341–342.</ref> The B-2 is a [[flying wing]] aircraft, meaning that it has no fuselage or tail.<ref name= "croddy 341-2"/> It has significant advantages over previous bombers due to its blend of low-observable technologies with high aerodynamic efficiency and a large payload. Low observability provides greater freedom of action at high altitudes, thus increasing both range and field of view for onboard sensors. The USAF reports its range as approximately {{convert|6000|nmi|mi km|lk=in}}.<ref name=B-2_AF_fact_sheet/><ref name=Spick_p340-1>{{harvnb|Spick|2000|pp= 340–341}}</ref> At cruising altitude, the B-2 [[aerial refueling|refuels]] every six hours, taking on up to {{convert|50|ST|kg}} of fuel at a time.<ref name="chiles201309" />

The development and construction of the B-2 required pioneering use of [[computer-aided design]] and [[computer-aided manufacturing|manufacturing]] technologies due to its complex flight characteristics and design requirements to maintain very low visibility to multiple means of detection.<ref name= "croddy 341-2"/><ref>{{harvnb|Sweetman|2005|pp=73–74}}</ref> The B-2 bears a resemblance to earlier Northrop aircraft; the [[Northrop YB-35|YB-35]] and [[Northrop YB-49|YB-49]] were both flying wing bombers that had been canceled in development in the early 1950s,<ref name= "boyne 466">{{harvnb|Boyne|2002|p=466}}</ref> allegedly for political reasons.<ref>{{harvnb|Fitzsimons|1978|p=2282}}</ref> The resemblance goes as far as B-2 and YB-49 having the same wingspan.<ref>Noland, David. "[http://www.infoplease.com/spot/northropb2.html Bombers: Northrop B-2] {{Webarchive|url=https://web.archive.org/web/20140425004938/http://www.infoplease.com/spot/northropb2.html |date=25 April 2014}}" ''Infoplease'', 2007. Retrieved 24 April 2014.</ref><ref>"[http://www.military-heat.com/42/b2-spirit-stealth-bomber/ The B-2 Spirit stealth bomber] {{Webarchive|url=https://web.archive.org/web/20140425004903/http://www.military-heat.com/42/b2-spirit-stealth-bomber/ |date=25 April 2014}}" ''Military Heat'', 2007. Retrieved 24 April 2014.</ref> The YB-49 also had a small [[radar cross-section]].<ref>{{Cite web|url=https://fas.org/nuke/guide/usa/bomber/b-49.htm|title=B-49 – United States Nuclear Forces|access-date=29 July 2018|archive-date=26 March 2019|archive-url=https://web.archive.org/web/20190326095032/https://fas.org/nuke/guide/usa/bomber/b-49.htm|url-status=live}}</ref><ref>{{Cite magazine |last=Heppenheimer |first=T. A. |date=September 1986 |title=Stalth – First glimpses of the invisible aircraft now under construction |url=https://books.google.com/books?id=NUzwukoJzGIC&q=YB-49+radar&pg=PA76 |magazine=Popular Science |page=76 |access-date=27 October 2020 |archive-date=5 February 2021 |archive-url=https://web.archive.org/web/20210205101204/https://books.google.com/books?id=NUzwukoJzGIC&q=YB-49+radar&pg=PA76 |url-status=live}}</ref>

Approximately 80 pilots fly the B-2.<ref name="chiles201309" /> Each aircraft has a crew of two, a pilot in the left seat and mission commander in the right,<ref name=B-2_AF_fact_sheet/> and has provisions for a third crew member if needed.<ref>{{cite web|title=B-2 Spirit Stealth Bomber Facts|url=http://www.northropgrumman.com/Capabilities/B2SpiritBomber/Documents/pageDocuments/B2-Fact-Sheet.pdf |archive-url=https://ghostarchive.org/archive/20221009/http://www.northropgrumman.com/Capabilities/B2SpiritBomber/Documents/pageDocuments/B2-Fact-Sheet.pdf |archive-date=9 October 2022 |url-status=live|publisher=[[Northrop Grumman]]|date=14 March 2007|access-date=15 June 2016}}</ref> For comparison, the B-1B has a crew of four and the B-52 has a crew of five.<ref name=B-2_AF_fact_sheet/> The B-2 is highly automated, and one crew member can sleep in a [[camp bed]], use a toilet, or prepare a hot meal while the other monitors the aircraft, unlike most two-seat aircraft. Extensive [[sleep cycle]] and [[fatigue (safety)|fatigue]] research was conducted to improve crew performance on long sorties.<ref name="chiles201309" /><ref name="tirpak199604">{{cite journal |url=http://www.airforcemag.com/MagazineArchive/Pages/1996/April%201996/0496bomber.aspx |archive-url=https://web.archive.org/web/20131112190523/http://www.airforcemag.com/MagazineArchive/Pages/1996/April%201996/0496bomber.aspx |archive-date=12 November 2013 |title=With the First B-2 Squadron |author=Tirpak, John A. |journal=Air Force Magazine |date=April 1996 |volume=79 |issue=4}}</ref><ref>Kenagy, David N., Christopher T. Bird, Christopher M. Webber and Joseph R. Fischer. [http://www.ingentaconnect.com/content/asma/asem/2004/00000075/00000005/art00001 "Dextroamphetamine Use During B-2 Combat Mission."] {{Webarchive|url=https://web.archive.org/web/20131112181039/http://www.ingentaconnect.com/content/asma/asem/2004/00000075/00000005/art00001 |date=12 November 2013}} ''Aviation, Space, and Environmental Medicine'', Volume 75, Number 5, May 2004, pp. 381–386.</ref> Advanced training is conducted at the [[USAF Weapons School]].<ref name="isis">{{cite magazine |magazine=[[The Atlantic]] |title=An Extraordinarily Expensive Way to Fight ISIS |archive-url=https://web.archive.org/web/20180627111647/https://www.theatlantic.com/magazine/archive/2018/07/william-langewiesche-b-2-stealth-bomber/561719/ |archive-date=27 June 2018 |url=https://www.theatlantic.com/magazine/archive/2018/07/william-langewiesche-b-2-stealth-bomber/561719/ |first=William |last=Langewiesche |date=July 2018}}</ref>

===Armaments and equipment===
[[File:B-2 bomb bay 050411-F-1740G-005.jpg|thumb|right|A {{convert|2000|lb|kg|abbr=on}} BDU-56 bomb being loaded onto a bomb bay's rotary launcher, 2004]]

In the envisaged Cold War scenario, the B-2 was to perform deep-penetrating nuclear strike missions, making use of its stealthy capabilities to avoid detection and interception throughout the missions.<ref name="tucker 39">{{harvnb|Tucker|2010|p=39}}</ref> 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.<ref>{{harvnb|Moir|Seabridge|2008|p=398}}</ref><ref name="tucker 177" /> The B-2 is capable of carrying {{convert|40000|lb|kg|abbr=on}} of ordnance.<ref name=B-2_AF_fact_sheet/> Nuclear ordnance includes the [[B61 nuclear bomb|B61]] and [[B83 nuclear bomb]]s; the [[AGM-129 ACM]] cruise missile was also intended for use on the B-2 platform.<ref name="tucker 177" /><ref>{{harvnb|Richardson|2001|pp=120–121}}</ref>

In light of the dissolution of the Soviet Union, it was decided to equip the B-2 for conventional precision attacks as well as for the strategic role of nuclear-strike.<ref name="tucker 39" /><ref>{{harvnb|Rip|Hasik|2002|p=201}}</ref> The B-2 features a sophisticated GPS-Aided Targeting System (GATS) that uses the aircraft's [[APQ-181 radar|APQ-181]] [[synthetic aperture radar]] to map out targets prior to the deployment of [[Global Positioning System|GPS]]-aided bombs ([[GBU-37|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;<ref>{{harvnb|Rip|Hasik|2002|pp=242–246}}</ref> An upgrade program in 2004 raised the maximum carrier capacity to 80 JDAMs.<ref name=POGO />

The B-2 has various conventional weapons in its arsenal, including [[Mark 82 bomb|Mark 82]] and [[Mark 84 bomb]]s, [[CBU-87 Combined Effects Munition]]s, [[GATOR mine system|GATOR mine]]s, and the [[CBU-97 Sensor Fuzed Weapon]].<ref>{{harvnb|Evans|2004|p=13}}</ref> In July 2009, Northrop Grumman reported the B-2 was compatible with the equipment necessary to deploy the {{convert|30000|lb|kg|abbr=on|adj=on}} [[Massive Ordnance Penetrator]] (MOP), which is intended to attack reinforced [[bunker]]s; up to two MOPs could be equipped in the B-2's bomb bays with one per bay,<ref>Mayer, Daryl. [http://www.defpro.com/news/details/8738/ "Northrop Grumman and USAF Verify Proper Fit of 30,000 lb Penetrator Weapon on B-2 Bomber."] {{webarchive|url=https://web.archive.org/web/20090821060646/http://www.defpro.com/news/details/8738/ |date=21 August 2009}} defpro.com, 22 July 2009. Retrieved 13 September 2009.</ref> the B-2 is the only platform compatible with the MOP as of 2012.<ref name="kelley insider" /> As of 2011, the [[AGM-158 JASSM]] [[cruise missile]] is an upcoming standoff munition to be deployed on the B-2 and other platforms.<ref>[http://www.defenseindustrydaily.com/AGM-158-JASSM-Cruise-Missiles-FY-2011-Orders-06895/ "AGM-158 JASSM Cruise Missiles: FY 2011 Orders."] {{Webarchive|url=https://web.archive.org/web/20120602080654/http://www.defenseindustrydaily.com/AGM-158-JASSM-Cruise-Missiles-FY-2011-Orders-06895/ |date=2 June 2012}} ''Defense Industry Daily'', 14 May 2011.</ref> This is to be followed by the [[Long Range Standoff Weapon]], which may give the B-2 standoff nuclear capability for the first time.<ref>{{cite web |url=http://blogs.fas.org/security/2013/04/b-2bomber/ |title=B-2 Stealth Bomber To Carry New Nuclear Cruise Missile |last1=Kristensen |first1=Hans M. |date=22 April 2013 |work=FAS Strategic Security Blog |publisher=Federation of American Scientists |access-date=22 April 2013 |url-status=dead |archive-url=https://web.archive.org/web/20140422075113/http://blogs.fas.org/security/2013/04/b-2bomber/ |archive-date=22 April 2014}}</ref>

===Avionics and systems===
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)<ref>{{cite book|last=Sweetman|first=Bill|title=Inside the Stealth Bomber|year=1999|url=https://books.google.com/books?id=Q_wyJ_pKcqoC&pg=PA55|publisher=Zenith Imprint|page=57|isbn=978-1-61060-689-9|access-date=19 October 2016|archive-date=15 February 2020|archive-url=https://web.archive.org/web/20200215143146/https://books.google.com/books?id=Q_wyJ_pKcqoC&pg=PA55|url-status=live}}</ref> and a Defensive Management System (DMS) to inform the flight crew of possible threats.<ref name= POGO/> The onboard DMS is capable of automatically assessing the detection capabilities of identified threats and indicated targets.<ref name= "sweetman 73">{{harvnb|Sweetman|2005|p=73}}</ref> 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.<ref name="military24april15">[http://www.military.com/daily-news/2015/04/24/air-force-upgrades-b2-stealth-bomber-as-air-defenses-advance.html?ESRC=todayinmil.sm Air Force Upgrades B-2 Stealth Bomber as Modern Air Defenses Advance] {{Webarchive|url=https://web.archive.org/web/20161126200312/http://www.military.com/daily-news/2015/04/24/air-force-upgrades-b2-stealth-bomber-as-air-defenses-advance.html?ESRC=todayinmil.sm |date=26 November 2016}} – Military.com, 24 April 2015</ref>

[[File:B-2 Spirit 050413-F-1740G-001a.jpg|thumb|upright=1.35|left|A maintenance crew servicing a B-2 at [[Andersen Air Force Base|Andersen AFB]], [[Guam]], 2004]]
For safety and fault-detection purposes, an on-board test system is linked 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.<ref>{{harvnb|Siuru|1993|p=118}}</ref> In 2008, many of the 136<ref>{{cite book|title=Air Warfare|url=https://books.google.com/books?id=FW_50wm8VnMC&pg=PA466|publisher=ABC-CLIO|isbn=978-1-57607-345-2|page=466|year=2002|access-date=19 October 2016|archive-date=5 February 2021|archive-url=https://web.archive.org/web/20210205101206/https://books.google.com/books?id=FW_50wm8VnMC&pg=PA466|url-status=live}}</ref> standalone distributed computers on board the B-2, including the primary flight management computer, were being replaced by a single integrated system.<ref>Page, Lewis. [https://www.theregister.co.uk/2008/07/11/stealth_bomber_upgrades/ "Upgrade drags Stealth Bomber IT systems into the 90s."] {{Webarchive|url=https://web.archive.org/web/20170810141519/https://www.theregister.co.uk/2008/07/11/stealth_bomber_upgrades/ |date=10 August 2017}} ''The Register'', 11 July 2008.</ref> The avionics are controlled by 13 [[Electromagnetic pulse|EMP]]-resistant [[MIL-STD-1750A]] computers, which are interconnected through 26 [[MIL-STD-1553]]B-[[bus (computing)|busses]]; other system elements are connected via [[optical fiber]].<ref name="janes" />

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 to avoid interference with other operators' equipment.<ref name= POGO/> The arrays of the upgraded radar features were entirely replaced to make the AN/APQ-181 into an [[active electronically scanned array]] (AESA) radar.<ref>[http://www.raytheon.com/capabilities/products/apq181/ "AN/APQ-181 Radar System."] {{webarchive|url=https://web.archive.org/web/20120824004350/http://www.raytheon.com/capabilities/products/apq181/ |date=24 August 2012}} ''Raytheon''. Retrieved 11 August 2012.</ref> Due to the B-2's composite structure, it is required to stay {{convert|40|mi|km|abbr=out|sigfig=|sp=us}} away from [[thunderstorms]], to avoid [[static discharge]] and [[lightning strike]]s.<ref name="isis"/>

===Flight controls===
[[File:Vice President Dick Cheney talking inside cockpit at a rally for the B-2 Bomber Forces.jpg|thumb|Vice President [[Dick Cheney]] inside a B-2 cockpit with pilot Capt. Luke Jayne during a visit to [[Whiteman AFB]], 2006]]

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 to maintain aircraft stability.<ref>{{harvnb|Moir|Seabridge|2008|p=397}}</ref> The flight computer receives information on external conditions such as the aircraft's current air speed and angle of attack via [[pitot tube|pitot]]-static sensing plates, as opposed to traditional [[pitot tube]]s which would impair the aircraft's stealth capabilities.<ref>{{harvnb|Moir|Seabridge|2008|pp=256–258}}</ref> 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.<ref>[http://www.moog.com/markets/aircraft/military-aircraft/special-mission/flight-control-actuation-system-integrator-for-the-b-2-spirit/ "Flight Control Actuation System Integrator for the B-2 Spirit."] {{Webarchive|url=https://web.archive.org/web/20120922075806/http://www.moog.com/markets/aircraft/military-aircraft/special-mission/flight-control-actuation-system-integrator-for-the-b-2-spirit/ |date=22 September 2012}} ''Moog''. Retrieved 11 August 2012.</ref>

Northrop had investigated several means of applying directional control that would infringe on the aircraft's radar profile as little as possible, eventually settling on a combination of split brake-rudders and differential thrust.<ref name= "sweetman 73"/> 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.<ref>{{harvnb|Chudoba|2001|p=76}}</ref> 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.<ref name= "chudoba 201-2">{{harvnb|Chudoba|2001|pp=201–202}}</ref> 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.<ref name= "chudoba 201-2"/>

===Stealth===
[[File:B2 Spirit closeup.JPEG|thumb|The B-2's engines are buried within its wing to conceal the engines' fans and minimize their exhaust signature.]]

The B-2's low-observable, or "[[stealth technology|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 signature|acoustic]], [[Infrared signature|infrared]], [[Aircraft camouflage|visual]] and [[Radar cross-section|radar signature]]s ([[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 countermeasure]]s, making the bomber a "[[force multiplier]]". {{As of|2013|09}}, there have been no instances of a missile being launched at a B-2.<ref name="chiles201309" />

To reduce optical visibility during daylight flights, the B-2 is painted in an [[aircraft camouflage|anti-reflective paint]].<ref name= "tucker 177">{{harvnb|Tucker|2010|p=177}}</ref> The undersides are dark because it flies at high altitudes ({{convert|50000|ft|m|abbr=on|disp=}}), and at that altitude a dark grey painting blends well into the sky. It is speculated to have an upward-facing [[Photodetector|light sensor]] which alerts the pilot to increase or reduce altitude to match the changing illuminance of the sky.<ref>{{cite book|last=Sweetman|first=Bill|title=Inside the Stealth Bomber|year=1999|url=https://books.google.com/books?id=Q_wyJ_pKcqoC&pg=PA55|publisher=Zenith Imprint|page=55|isbn=978-1-61060-689-9|access-date=19 October 2016|archive-date=15 February 2020|archive-url=https://web.archive.org/web/20200215143146/https://books.google.com/books?id=Q_wyJ_pKcqoC&pg=PA55|url-status=live}}</ref> 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.<ref>Gosnell, Mariana. [http://www.airspacemag.com/flight-today/Flight_Lines.html "Why contrails hang around."] {{Webarchive|url=https://web.archive.org/web/20131112175852/http://www.airspacemag.com/flight-today/Flight_Lines.html |date=12 November 2013}} ''Air & Space magazine'', 1 July 2007. Retrieved 13 September 2009.</ref> The B-2 is vulnerable to visual interception at ranges of {{convert|20|nmi|mi km|abbr=on}} or less.<ref name="chiles201309" /> The B-2 is stored in a $5&nbsp;million specialized air-conditioned hangar to maintain its stealth coating. Every seven years, this coating is carefully washed away with crystallized wheat starch so that the B-2's surfaces can be inspected for any dents or scratches.<ref name=NI_Only_20_B-2s_Stealth_Bombers>{{Cite web|url=https://nationalinterest.org/blog/buzz/why-air-force-only-has-20-b-2-spirit-stealth-bombers-35802|title=Why the Air Force Only Has 20 B-2 Spirit Stealth Bombers|author=Sebastien Roblin|date=11 November 2018|website=National Interest|access-date=5 November 2020|archive-date=18 September 2020|archive-url=https://web.archive.org/web/20200918112631/https://nationalinterest.org/blog/buzz/why-air-force-only-has-20-b-2-spirit-stealth-bombers-35802|url-status=live}}</ref>

====Radar====
The B-2's clean, low-drag [[flying wing]] configuration not only provides exceptional range but is also beneficial to reducing its radar profile.<ref name="croddy 341-2" /><ref>{{harvnb|Siuru|1993|pages=114–115}}</ref> Reportedly, the B-2 has a [[radar cross-section]] (RCS) of about {{convert|0.1|m2|ft2|abbr=on}}.<ref>{{harvnb|Richardson|2001|p=57}}</ref> The bomber does not always fly stealthily; when nearing air defenses pilots "stealth up" the B-2, a maneuver whose details are secret. The aircraft is stealthy, except briefly when the bomb bay opens. 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).<ref name="SpiritofInnovation">{{cite web |url=https://www.northropgrumman.com/wp-content/uploads/B-2-Spirit-of-Innovation.pdf |title=B-2: The Spirit of Innovation |website=Northrop Grumman Corporation |access-date=15 October 2023 |archive-date=8 April 2023 |archive-url=https://web.archive.org/web/20230408033411/https://www.northropgrumman.com/wp-content/uploads/B-2-Spirit-of-Innovation.pdf |url-status=live}}</ref> Without vertical surfaces to reflect radar laterally, side aspect radar cross section is also reduced.<ref>{{cite web|url=https://nationalinterest.org/blog/buzz/americas-new-b-21-stealth-bomber-vs-russias-s-300-or-s-400-who-wins-36137|title=America's New B-21 Stealth Bomber vs. Russia's S-300 or S-400: Who Wins?|first=Kris|last=Osborn|date=15 November 2018|website=nationalinterest.org|access-date=16 November 2018|archive-date=15 November 2018|archive-url=https://web.archive.org/web/20181115195225/https://nationalinterest.org/blog/buzz/americas-new-b-21-stealth-bomber-vs-russias-s-300-or-s-400-who-wins-36137|url-status=live}}</ref> Radars operating at a lower frequency band (S or L band) are able to detect and track certain stealth aircraft that have multiple control surfaces, like canards or vertical stabilizers, where the frequency wavelength can exceed a certain threshold and cause a resonant effect.<ref>{{cite web|url=https://nationalinterest.org/blog/buzz/how-russia-could-someday-shootdown-f-22-f-35-or-b-2-stealth-bomber-35512|title=How Russia Could Someday Shootdown an F-22, F-35 or B-2 Stealth Bomber|first=Dave|last=Majumdar|date=8 November 2018|website=nationalinterest.org|access-date=21 November 2018|archive-date=20 November 2018|archive-url=https://web.archive.org/web/20181120221212/https://nationalinterest.org/blog/buzz/how-russia-could-someday-shootdown-f-22-f-35-or-b-2-stealth-bomber-35512|url-status=live}}</ref>

[[File:B-2 radar reflection.jpg|thumb|left|upright=1.35|Illustration of the B-2's basic radar reflection angles]]
RCS reduction as a result of shape had already been observed on the [[Royal Air Force]]'s [[Avro Vulcan]] strategic bomber,<ref>Dawson 1957, p. 3.</ref> and the USAF's [[Lockheed F-117 Nighthawk|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.<ref name="rich4">{{harvnb|Rich|1994|p=21}}</ref> 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]].<ref>{{cite book|author=Christopher Lavers|title=Reeds Vol 14: Stealth Warship Technology|url=https://books.google.com/books?id=wMB3Pg3vtbsC&pg=PA13|year=2012|publisher=Bloomsbury Publishing|isbn=978-1-4081-7553-8|page=13|access-date=19 October 2016|archive-date=5 February 2021|archive-url=https://web.archive.org/web/20210205102939/https://books.google.com/books?id=wMB3Pg3vtbsC&pg=PA13|url-status=live}}</ref><ref name="SpiritofInnovation"/>

====Infrared====
[[File:B-2 inlet.jpg|thumb|The gap below the air intake has the purpose of keeping the [[boundary layer]] out of the jet engine.]]

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&nbsp;μm absorption maxima) detection possible, through difference comparing between the low and high channel.<ref>{{cite web |last=Radar |first=Cordless |url=http://www.flightglobal.com/blogs/the-dewline/2008/10/infamous-jsf-report-precedes-a.html |title=RAND Report Page 37 |work=Flight International |access-date=16 December 2010 |archive-date=10 May 2013 |archive-url=https://web.archive.org/web/20130510192736/http://www.flightglobal.com/blogs/the-dewline/2008/10/infamous-jsf-report-precedes-a.html |url-status=live}}</ref><ref name="fas_stealth">{{Cite web |title=VI – STEALTH AIRCRAFT: EAGLES AMONG SPARROWS? |publisher=Federation of American Scientist |url=https://fas.org/spp/aircraft/part06.htm |access-date=21 February 2008 |journal= |archive-date=13 February 2008 |archive-url=https://web.archive.org/web/20080213001551/http://www.fas.org/spp/aircraft/part06.htm |url-status=dead}}</ref>

Burying engines deep inside the fuselage also minimizes the thermal visibility or [[infrared signature]] of the exhaust.<ref name= "tucker 177"/><ref>Croddy and Wirtz 2005, p. 342.</ref> 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 [[nozzle]]s (similar to the [[Ryan AQM-91 Firefly]]). According to the [[Stefan–Boltzmann law]], this results in less energy ([[thermal radiation]] in the 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, to accelerate its cooling.<ref name="janes">Jane's Aircraft Upgrades 2003, p. 1711f</ref> The B-2 lacks [[afterburner]]s as the hot exhaust would increase the infrared signature; 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 signature.

====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 material]]s (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, lighter than aluminum, and absorbs a significant amount of radar energy.<ref name= "boyne 466"/>

The B-2 is assembled with unusually tight [[engineering tolerance]]s to avoid leaks as they could increase its radar signature.<ref name="tirpak199604" /> Innovations such as alternate [[high frequency]] material (AHFM) and automated material application methods were also incorporated to improve the aircraft's radar-absorbent properties and reduce maintenance requirements.<ref name= "tucker 177"/><ref>Lewis, Paul. [http://www.flightglobal.com/news/articles/b-2-to-receive-maintenance-boost-144086/ "B-2 to receive maintenance boost."] {{Webarchive |url=https://web.archive.org/web/20130516141406/http://www.flightglobal.com/news/articles/b-2-to-receive-maintenance-boost-144086/ |date=16 May 2013}} ''Flight International'', 5 March 2002.</ref> In early 2004, Northrop Grumman began applying a newly developed AHFM to operational B-2s.<ref>Hart, Jim. [http://www.irconnect.com/noc/press/pages/news_releases.html?d=56001 "Northrop Grumman Applies New Coating to Operational B-2."] {{Webarchive |url=https://web.archive.org/web/20111209000416/http://www.irconnect.com/noc/press/pages/news_releases.html?d=56001 |date=9 December 2011}} "Northrop Grumman Integrated Systems", 19 April 2004.</ref> 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 {{convert|172|ft|m|adj=on}} wingspan.<ref name=AW_20070107_Away>Fulghum, D.A. [https://archive.today/20130117150011/http://www.aviationnow.com/search/AvnowSearchResult.do?reference=xml/awst_xml/2007/01/08/AW_01_08_2007_p50-51-01.xml "First F-22 large-scale, air combat exercise wins praise and triggers surprise" (online title), "Away Game".] ''[[Aviation Week & Space Technology]]'', 8 January 2007. Retrieved 13 September 2009.</ref>

====Shelter system====
B-2s are supported by portable, environmentally-controlled hangars called B-2 Shelter Systems (B2SS).<ref name="stripes">{{cite news |url=https://www.stripes.com/news/portable-b-2-bomber-shelters-are-built-in-parts-officially-unknown-1.1054 |title=Portable B-2 bomber shelters are built ... in parts (officially) unknown |newspaper=[[Stars and Stripes (newspaper)|Stars and Stripes]] |first=Wayne |last=Specht |date=16 January 2003 |access-date=24 June 2018 |archive-date=25 June 2018 |archive-url=https://web.archive.org/web/20180625022005/https://www.stripes.com/news/portable-b-2-bomber-shelters-are-built-in-parts-officially-unknown-1.1054 |url-status=live}}</ref> The hangars are built by American Spaceframe Fabricators Inc. and cost approximately US$5&nbsp;million apiece.<ref name="stripes"/> The need for specialized hangars arose in 1998 when it was found that B-2s passing through [[Andersen Air Force Base]] did not have the climate-controlled environment maintenance operations required.<ref name="stripes"/> In 2003, the B2SS program was managed by the Combat Support System Program Office at [[Eglin Air Force Base]].<ref name="stripes" /> B2SS hangars are known to have been deployed to [[Naval Support Facility Diego Garcia]] and [[RAF Fairford]].<ref name="stripes"/>