Scisoft

The Airbus A380 is a double-deck, wide-body, four-engine airliner manufactured by the European corporation Airbus, an EADS subsidiary. The largest passenger airliner in the world, the A380 made its maiden flight on 27 April 2005 from Toulouse, France, and made its first commercial flight on 25 October 2007 from Singapore to Sydney with Singapore Airlines. The aircraft was known as the Airbus A3XX during much of its development phase, but the nickname Superjumbo has since become associated with it.

The A380's upper deck extends along almost the entire length of the fuselage, and its width is equivalent to that of a widebody aircraft. This allows for a cabin with 50% more floor space than the next-largest airliner, the Boeing 747-400. and provides seating for 525 people in standard three-class configuration or up to 853 people in all economy class configuration. The A380 is offered in passenger and freighter versions. The A380-800, the passenger model, is the largest passenger airliner in the world, but has a shorter fuselage than the Airbus A340-600 which is Airbus' next biggest passenger aeroplane. The A380-800F, the freighter model, is offered as one of the largest freight aircraft, with a listed payload capacity exceeded only by the Antonov An-225. The A380-800 has a design range of 15,200 kilometres (8,200 nmi), sufficient to fly from Boston, Massachusetts to Hong Kong for example, and a cruising speed of Mach 0.85 (about 900 km/h or 560 mph at cruising altitude). is the first commercial jet capable of using GTL-based fuel.

Development

Background

In the summer of 1988 a group of Airbus engineers, led by Jean Roeder, began working in secret on the development of a ultra-high-capacity airliner (UHCA), both to complete its own range of products and to break the dominance that Boeing had enjoyed in this market segment since the early 1970s with its 747. McDonnell Douglas unsuccessfully offered its smaller, double-deck MD-12 concept for sale. As each manufacturer looked to build a successor to the 747, they knew there was room for only one new aircraft to be profitable in the 600 to 800 seat market segment. Each knew the risk of splitting such a niche market, as had been demonstrated by the simultaneous debut of the Lockheed L-1011 and the McDonnell Douglas DC-10: both planes met the market’s needs, but the market could profitably sustain only one model, eventually resulting in Lockheed's departure from the civil airliner business.

Roeder was given approval for further evaluations of the UHCA after a formal presentation to the President and CEO in June 1990. The project was announced at the 1990 Farnborough Air Show, with the stated goal of 15 % lower operating costs than the 747-400. Airbus organized four teams of designers, one from each of its EADS partners (Aérospatiale, DaimlerChrysler Aerospace, British Aerospace, EADS CASA) to propose new technologies for its future aircraft designs. The designs would be presented in 1992 and the most competitive designs would be used.

In January 1993, Boeing and several companies in the Airbus consortium started a joint feasibility study of an aircraft known as the Very Large Commercial Transport (VLCT), aiming to form a partnership to share the limited market.

In June 1994, Airbus began developing its own very large airliner, designated the A3XX. Airbus considered several designs, including an odd side-by-side combination of two fuselages from the A340, which was Airbus’s largest jet at the time. The A3XX was pitted against the VLCT study and Boeing’s own New Large Aircraft successor to the 747, which evolved into the 747X, a stretched version of the 747 with the fore body "hump" extended rearwards to accommodate more passengers. The joint VLCT effort ended in April 1995, and Boeing suspended the 747X program in January 1997. From 1997 to 2000, as the East Asian financial crisis darkened the market outlook, Airbus refined its design, targeting a 15 to 20 percent reduction in operating costs over the existing Boeing 747-400. The A3XX design converged on a double-decker layout that provided more passenger volume than a traditional single-deck design.

Design phase

On 19 December 2000, the supervisory board of newly restructured Airbus voted to launch a €8.8 billion program to build the A3XX, re-christened as the A380, with 55 orders from six launch customers. The A380 designation was a break from previous Airbus families, which had progressed sequentially from A300 to A340. It was chosen because the number 8 resembles the double-deck cross section, and is a lucky number in some Asian countries where the aircraft was being marketed. The aircraft’s final configuration was frozen in early 2001, and manufacturing of the first A380 wing box component started on 23 January 2002. The development cost of the A380 had grown to €11 billion when the first aircraft was completed.

Boeing, meanwhile, studied multiple 747-400 derivative designs before finally launching the Boeing 747-8 in November 2005 (with entry into service planned for 2009). Boeing chose to develop a variant for the 400 to 500 seat market, instead of matching the A380's capacity.

Production

Major structural sections of the A380 are built in France, Germany, Spain, and the United Kingdom. Due to their size, they are brought to the assembly hall in Toulouse in France by surface transportation, rather than by the A300-600ST Beluga aircraft used for other Airbus models. Components of the A380 are provided by suppliers from around the world; the five largest contributors, by value, are Rolls-Royce, SAFRAN, United Technologies, General Electric, and Goodrich.

The front and rear sections of the fuselage are loaded on an Airbus Roll-on/roll-off (RORO) ship, Ville de Bordeaux, in Hamburg in northern Germany, from where they are shipped to the United Kingdom. The wings, which are manufactured at Filton in Bristol and Broughton in North Wales, are transported by barge to Mostyn docks, where the ship adds them to its cargo. In Saint-Nazaire in western France, the ship trades the fuselage sections from Hamburg for larger, assembled sections, some of which include the nose. The ship unloads in Bordeaux. Afterwards, the ship picks up the belly and tail sections by Construcciones Aeronáuticas SA in Cádiz in southern Spain, and delivers them to Bordeaux. From there, the A380 parts are transported by barge to Langon, and by oversize road convoys to the assembly hall in Toulouse. New wider roads, canal systems and barges were developed to deliver the A380 parts. After assembly, the aircraft are flown to Hamburg, XFW to be furnished and painted. It takes 3,600 litres (950 gallons) of paint to cover the 3,100 m² (33,000 ft²) exterior of an A380.

Airbus sized the production facilities and supply chain for a production rate of four A380s per month.

Testing

Five A380s were built for testing and demonstration purposes.

The first A380, serial number MSN001 and registration F-WWOW, was unveiled at a ceremony in Toulouse on 18 January 2005. Its maiden flight took place at 8:29 UTC (10:29 a.m. local time) 27 April 2005. This plane, equipped with Trent 900 engines, flew from Toulouse Blagnac International Airport with a flight crew of six headed by chief test pilot Jacques Rosay. After successfully landing three hours and 54 minutes later, Rosay said flying the A380 had been “like handling a bicycle” .

On 1 December 2005 the A380 achieved its maximum design speed of Mach 0.96 (versus normal cruising speed of Mach 0.85), in a shallow dive, completing the opening of the flight envelope.

On 10 January 2006 the A380 made its first transatlantic flight to Medellín in Colombia, to test engine performance at a high altitude airport. It arrived in North America on 6 February, landing in Iqaluit, Nunavut in Canada for cold-weather testing.

On 14 February 2006, during the destructive wing strength certification test on MSN5000, the test wing of the A380 failed at 145% of the limit load, short of the required 150% to meet the certification. Airbus announced modifications adding 30 kg to the wing to provide the required strength.^[20]

On 26 March 2006 the A380 underwent evacuation certification in Hamburg in Germany. With 8 of the 16 exits blocked, 853 passengers and 20 crew left the aircraft in 78 seconds, less than the 90 seconds required by certification standards.

Three days later, the A380 received European Aviation Safety Agency (EASA) and United States Federal Aviation Administration (FAA) approval to carry up to 853 passengers.

The maiden flight of the first A380 using GP7200 engines - serial number MSN009 and registration F-WWEA - took place on 25 August 2006.

On 4 September 2006 the first full passenger-carrying flight test took place. The aircraft flew from Toulouse with 474 Airbus employees on board, in the first of a series of flights to test passenger facilities and comfort.

In November 2006, a further series of route proving flights took place to demonstrate the aircraft's performance for 150 flight hours under typical airline operating conditions.

Airbus obtained type certificate for the A380-841 and A380-842 model from the EASA and FAA on 12 December 2006 in a joint ceremony at the company's French headquarters.A380-861 model obtained the type certificate 14 December 2007.

As of February 2008, the five A380s in the test programme had logged over 4,565 hours during 1,364 flights, including route proving and demonstration flights.

Delivery delays

Initial production of the A380 was troubled by delays attributed to the 530 km (330 miles) of wiring in each aircraft. Airbus cited as underlying causes the complexity of the cabin wiring (100,000 wires and 40,300 connectors), its concurrent design and production, the high degree of customization for each airline, and failures of configuration management and change control. Specifically, it would appear that German and Spanish Airbus facilities continued to use CATIA version 4, while British and French sites migrated to version 5. This caused overall configuration management problems, at least in part because wiring harnesses manufactured using aluminium rather than copper conductors necessitated special design rules including non-standard dimensions and bend radii: these were not easily transferred between versions of the software.

Airbus announced the first delay in June 2005 and notified airlines that delivery would slip by six months. This reduced the number of planned deliveries by the end of 2009 from about 120 to 90–100. On 13 June 2006, Airbus announced a second delay, with the delivery schedule undergoing an additional shift of six to seven months. Although the first delivery was still planned before the end of 2006, deliveries in 2007 would drop to only 9 aircraft, and deliveries by the end of 2009 would be cut to 70–80 aircraft. The announcement caused a 26% drop in the share price of Airbus's parent, EADS, and led to the departure of EADS CEO Noël Forgeard, Airbus CEO Gustav Humbert, and A380 programme manager Charles Champion. On 3 October 2006, upon completion of a review of the A380 program, the CEO of Airbus, Christian Streiff, announced a third delay, pushing the first delivery to October 2007, to be followed by 13 deliveries in 2008, 25 in 2009, and the full production rate of 45 aircraft per year in 2010. The delay also increased the earnings shortfall projected by Airbus through 2010 to €4.8 billion.

As Airbus prioritized the work on the A380-800 over the A380-800F, freighter orders were cancelled (FedEx, UPS) or converted to A380-800 (Emirates, ILFC). Airbus suspended work on the freighter version, but said it remained on offer, albeit without a service entry date. For the passenger version Airbus negotiated a revised delivery schedule and compensation with the 13 customers, all of which retained their orders with some placing subsequent orders (Emirates, Singapore Airlines Qantas, Air France, Qatar, and Korean Air).

The first A380 with redesigned wiring harnesses achieved power-on in April 2008, with a 3 1/2 month delay. On 13 May 2008 Airbus announced reduced deliveries for the years 2008 (12) and 2009 (21).

Entry into service

The first aircraft delivered, MSN003, (registered 9V-SKA) was handed over to Singapore Airlines on 15 October 2007 and entered into service on 25 October 2007 with a commercial flight between Singapore and Sydney (flight number SQ380). Two months later Singapore Airlines CEO Chew Choong Seng said that the A380 was performing better than both the airline and Airbus had anticipated, burning 20% less fuel per passenger than the airline's existing 747-400 fleet. Singapore Airlines operated its first two aircraft, in a 471-seat configuration, between Singapore and Sydney. This was then expanded to include Singapore–London from 18 March 2008 after the third aircraft was delivered. A fourth aircraft was delivered to Singapore Airlines on the 26 April 2008 which enabled it to use the type on the Singapore-Tokyo route from 20 May. On 2 August 2008 Singapore Airlines began the temporary use of the A380 to Beijing to meet increased demand for the 2008 Summer Olympics in Beijing and on 4 August made the company's 1000th commercial flight with an A380. Singapore Airlines operates six A380 aircraft as of September 2008.

Emirates Airline was the second airline to take delivery of the A380 (registered A6-EDA) on 28 July 2008 and started flights between Dubai and New York on 1 August 2008. Emirates will begin flights between Dubai and London on 1 December 2008 and Dubai to Auckland (via Sydney) on 1 February 2009.

The first aircraft for Qantas (third airline to take delivery of the A380), MSN014, (registered VH-OQA) was delivered on 19 September 2008. Qantas has announced it will use the A380, in a 450-seat configuration, on its Melbourne to Los Angeles route from 20 October 2008. Subsequent routes include Sydney to Los Angeles and London starting on the 24 October 2008.

Air France has said that its A380s will be used on its Paris to Montreal and New York routes. Lufthansa will be using the aircraft for its long-haul destinations to North America and Asia.

Design

The new Airbus is sold in two models. The A380-800 was originally designed to carry 555 passengers in a three-class configuration or 853 passengers (538 on the main deck and 315 on the upper deck) in a single-class economy configuration. In May 2007, Airbus began marketing the same aircraft to customers with 30 fewer passengers (now 525 passengers in three classes) traded for 370 km (200 nmi) more range, to better reflect trends in premium class accommodation. The design range for the -800 model is 15,200 km (8,200 nmi). The second model, the A380-800F freighter, will carry 150 tonnes of cargo 10,400 km (5,600 nmi). Future variants may include an A380-900 stretch seating about 656 passengers (or up to 960 passengers in an all economy configuration) and an extended range version with the same passenger capacity as the A380-800.

The A380's wing is sized for a Maximum Take-Off Weight (MTOW) over 650 tonnes in order to accommodate these future versions, albeit with some strengthening required. The stronger wing (and structure) is used on the A380-800F freighter. This common design approach sacrifices some fuel efficiency on the A380-800 passenger model, but Airbus estimates that the size of the aircraft, coupled with the advances in technology described below, will provide lower operating costs per passenger than all current variants of Boeing 747. The A380 also features wingtip fences similar to those found on the A310 and A320 to alleviate the effects of wake turbulence, increasing fuel efficiency and performance.

Flight deck

Airbus used similar cockpit layout, procedures and handling characteristics to those of other Airbus aircraft, to reduce crew training costs. Accordingly, the A380 features an improved glass cockpit, and fly-by-wire flight controls linked to side-sticks.^[60] The improved cockpit displays feature eight 15-by-20 cm (6-by-8-inch) liquid crystal displays, all of which are physically identical and interchangeable. These comprise two Primary Flight Displays, two navigation displays, one engine parameter display, one system display and two Multi-Function Displays. These MFDs are new with the A380, and provide an easy-to-use interface to the flight management system—replacing three multifunction control and display units. They include QWERTY keyboards and trackballs, interfacing with a graphical "point-and-click" display navigation system. or two HUD (Head Up Display) is optional.

Engines

The A380 can be fitted with two types of engines: A380-841, A380-842 and A380-843F with Rolls-Royce Trent 900, and the A380-861 and A380-863F with Engine Alliance GP7000 turbofans. The Trent 900 is a derivative of the Trent 800, and the GP7000 has roots from the GE90 and PW4000. The Trent 900 core is a scaled version of the Trent 500, but incorporates the swept fan technology of the stillborn Trent 8104. The GP7200 has a GE90-derived core and PW4090-derived fan and low-pressure turbo-machinery. Only two of the four engines are fitted with thrust reversers.

Noise reduction was an important requirement in the A380's design, and particularly affects engine design. Both engine types allow the aircraft to achieve QC/2 departure and QC/0.5 arrival noise limits under the Quota Count system set by London Heathrow Airport, which is expected to become a key destination for the A380.

Fuel

The A380 can run on mixed synthetic jet fuel with a natural-gas-derived component. A three hour test flight on Friday, 1 February 2008 between the Airbus company facility at Filton in the UK to the main Airbus factory in Toulouse, France, was a success. One of the A380's four engines used a mix of 60 percent standard jet kerosene and 40 percent gas to liquids (GTL) fuel supplied by Shell. The aircraft needed no modification to use the GTL fuel, which was designed to be mixed with regular jet fuel. Sebastien Remy, head of Airbus SAS's alternative fuel program, said the GTL used was no cleaner in CO₂ terms than regular fuel but it had local air quality benefits because it contains no sulphur.

Advanced materials

While most of the fuselage is aluminium, composite materials make up 25% of the A380's airframe, by weight. Carbon-fibre reinforced plastic, glass-fibre reinforced plastic and quartz-fibre reinforced plastic are used extensively in wings, fuselage sections (such as the undercarriage and rear end of fuselage), tail surfaces, and doors. The A380 is the first commercial airliner with a central wing box made of carbon fibre reinforced plastic, and it is the first to have a wing cross-section that is smoothly contoured. Other commercial airliners have wings that are partitioned span-wise in sections. The flowing, continuous cross-section allows for maximum aerodynamic efficiency. Thermoplastics are used in the leading edges of the slats. The new material GLARE (GLAss-REinforced fibre metal laminate) is used in the upper fuselage and on the stabilizers' leading edges. This aluminium-glass-fibre laminate is lighter and has better corrosion and impact resistance than conventional aluminium alloys used in aviation. Unlike earlier composite materials, it can be repaired using conventional aluminium repair techniques. Newer weldable aluminium alloys are also used. This enables the widespread use of laser beam welding manufacturing techniques — eliminating rows of rivets and resulting in a lighter, stronger structure.

Avionics architecture

The A380 employs an Integrated Modular Avionics (IMA) architecture, first used in advanced military aircraft such as the F-22 Raptor, Eurofighter Typhoon, or Dassault Rafale. It is based on a commercial off-the-shelf (COTS) design. Many previous dedicated single-purpose avionics computers are replaced by dedicated software housed in onboard processor modules and servers. This cuts the number of parts, provides increased flexibility without resorting to customised avionics, and reduces costs by using commercially available computing power.

Together with IMA, the A380 avionics are very highly networked. The data communication networks use Avionics Full-Duplex Switched Ethernet, following the ARINC 664 standard. The data networks are switched, full-duplexed, star-topology and based on 100baseTX fast-Ethernet. This reduces the amount of wiring required and minimizes latency. .

The Network Systems Server (NSS) is the heart of A380 paperless cockpit. It eliminates the bulky manuals and charts traditionally carried by the pilots. The NSS has enough inbuilt robustness to do away with onboard backup paper documents. The A380's network and server system stores data and offers electronic documentation, providing a required equipment list, navigation charts, performance calculations, and an aircraft logbook. All are accessible to the pilot from two additional 27 cm (11 inch) diagonal LCDs, each controlled by its own keyboard and control cursor device mounted in the foldable table in front of each pilot.

Systems

Power-by-wire flight control actuators are used for the first time in civil service, backing up the primary hydraulic flight control actuators. During certain maneuvers, they augment the primary actuators. They have self-contained hydraulic and electrical power supplies. They are used as electro-hydrostatic actuators (EHA) in the aileron and elevator, and as electrical backup hydrostatic actuators (EBHA) for the rudder and some spoilers

The aircraft's 350 bar (35 MPa or 5,000 psi) hydraulic system is an improvement over the typical 210 bar (21 MPa or 3,000 psi) system found in other commercial aircraft since the 1940s. First used in military aircraft, higher pressure hydraulics reduce the size of pipelines, actuators and other components for overall weight reduction. The 350 bar pressure is generated by eight de-clutchable hydraulic pumps. Pipelines are typically made from titanium and the system features both fuel and air-cooled heat exchangers. The hydraulics system architecture also differs significantly from other airliners. Self-contained electrically powered hydraulic power packs, instead of a secondary hydraulic system, are the backups for the primary systems. This saves weight and reduces maintenance.

The A380 uses four 150 kVA variable-frequency electrical generators eliminating the constant speed drives for better reliability. The A380 uses aluminium power cables instead of copper for greater weight savings due to the number of cables used for an aircraft of this size and complexity. The electrical power system is fully computerized and many contactors and breakers have been replaced by solid-state devices for better performance and increased reliability.

The A380 features a bulbless illumination system. LEDs are employed in the cabin, cockpit, cargo and other fuselage areas. The cabin lighting features programmable multi-spectral LEDs capable of creating a cabin ambience simulating daylight, night or shades in between. On the outside of the aircraft, HID lighting is used to give brighter, whiter and better quality illumination. These two technologies provide brightness and a service life superior to traditional incandescent light bulbs.

The A380 was initially planned without thrust reversers, as Airbus believed it to have ample braking capacity. The FAA disagreed, and Airbus elected to fit only the two inboard engines with them. The two outboard engines do not have reversers, reducing the amount of debris stirred up during landing. The A380 features electrically actuated thrust reversers, giving them better reliability than their pneumatic or hydraulic equivalents, in addition to saving weight.

Passenger provisions

The A380 produces 50% less cabin noise than a 747 and has higher cabin air pressure (equivalent to an altitude of 1500 metres (5000 ft) versus 2500 metres (8000 ft)); both features are expected to reduce the effects of travel fatigue.The upper and lower decks are connected by two stairways, fore and aft, wide enough to accommodate two passengers side-by-side. In a 555-passenger configuration, the A380 has 33% more seats than a 747-400 in a standard three-class configuration but 50% more cabin area and volume, resulting in more space per passenger. Its maximum certified carrying capacity is 853 passengers in an all-economy-class configuration. The two full-length decks and wide stairways allow multiple seat configurations of the Airbus A380. The announced configurations go from 450 (Qantas) up to 644 passengers (Emirates Airline two-class configuration).

Compared to a 747, the A380 has larger windows and overhead bins, and 60 cm (2 ft) of extra headroom. The wider cabin allows for up to 48 cm (19 inch) wide economy seats at a 10 abreast configuration on the main deck, while 10 abreast seating on the 747 has a seat width of only 43.7 cm (17.2 inch) (seat pitch varies by airline).

Airbus' initial publicity stressed the comfort and space of the A380's cabin, anticipating installations such as relaxation areas, bars, duty-free shops, and beauty salons. Virgin Atlantic Airways already offers a bar as part of its "Upper Class" service on its A340 and 747 aircraft, and has announced plans to include casinos, double beds, and gymnasiums on its A380s. Singapore Airlines offers twelve fully-enclosed first-class suites on its A380, each with one full and one secondary seat, full-sized bed, desk, personal storage. Four of these suites are in the form of two "double" suites featuring a double bed. Qantas Airways has shown their product which features a long flat-bed that converts from the seat but does not have privacy doors. Emirates Airline's fourteen first-class private suites have shared access to two "shower spas". First and business class passengers have shared access to a snack bar and lounge with two sofas, in addition to a first-class-only private lounge.

Integration in the infrastructure

Ground operations

Early critics claimed that the A380 would damage taxiways and other airport surfaces. However, the pressure exerted by its wheels is lower than that of a Boeing 747 or Boeing 777 because the A380 has 22 wheels, four more than the 747, and eight more than the 777. Airbus measured pavement loads using a 540-tonne (595 short tons) ballasted test rig, designed to replicate the landing gear of the A380. The rig was towed over a section of pavement at Airbus' facilities that had been instrumented with embedded load sensors.

Based on its wingspan, the U.S. FAA classifies the A380 as a Design Group VI aircraft, and originally required a width of 60 m (200 ft) for runways and 30 m (100 ft) for taxiways, compared with 45 m (150 ft) and 23 m (75 ft) for Design Group V aircraft such as the Boeing 747.The FAA also considered limiting the taxi speed of the A380 to 25 km/h (15 mph) when operating on Group V infrastructure, but issued waivers related to the speed restriction and some of the proposed runway widening requirements. Airbus claimed from the beginning that the A380 could safely operate on Group V runways and taxiways, without the need for widening. In July 2007, the FAA and EASA agreed to let the A380 operate on 45 m runways without restrictions.

The A380 was designed to fit within an 80 × 80 m airport gate, and can land or take off on any runway that can accommodate a Boeing 747. Its large wingspan can require some taxiway and apron reconfigurations, to maintain safe separation margins when two of the aircraft pass each other. Taxiway shoulders may be required to be paved to reduce the likelihood of foreign object damage caused to (or by) the outboard engines, which overhang more than 25 m (80 ft) from the centre line of the aircraft. Any taxiway or runway bridge must be capable of supporting the A380's maximum weight. The terminal gate must be sized such that the A380's wings do not block adjacent gates, and may also provide multiple jetway bridges for simultaneous boarding on both decks. Service vehicles with lifts capable of reaching the upper deck should be obtained, as well as tractors capable of handling the A380's maximum ramp weight. The A380 test aircraft have participated in a campaign of airport compatibility testing to verify the modifications already made at several large airports, visiting a number of airports around the world.

Takeoff and landing separation

In 2005, the ICAO recommended that provisional separation criteria for the A380 on takeoff and landing be substantially greater than for the 747 because preliminary flight test data suggested a stronger wake turbulence. These criteria were in effect while the ICAO's wake vortex steering group, with representatives from the JAA, Eurocontrol, the FAA, and Airbus, refined its 3-year study of the issue with additional flight testing. In September 2006, the working group presented its first conclusions to the ICAO.

In November 2006 the ICAO issued new interim recommendations. Replacing a blanket 10 nmi separation for aircraft trailing an A380 during approach, the new distances were 6 nmi, 8 nmi and 10 nmi respectively for non-A380 "Heavy", "Medium", and "Light" ICAO aircraft categories. These compared with the 4 nmi, 5 nmi and 6 nmi spacing applicable to other "Heavy" aircraft. Another A380 following an A380 should maintain a separation of 4 nmi. On departure behind an A380, non-A380 "Heavy" aircraft are required to wait two minutes, and "Medium"/"Light" aircraft three minutes for time based operations. The ICAO also advised to use the suffix "Super" to the air traffic control to distinguish the A380 from other "Heavy" aircraft

In August 2008 the ICAO issued revised approach separations of 4 nmi for Super (another A380), 6 nmi for Heavy, 7 nmi for medium/small and 8 nmi for light.

Future variants

Airbus A380-900

Airbus top sales executive and COO John Leahy confirmed the plans for an enlarged variant, the A380-900 which is a slight stretch of the A380-800 from 73m to 79.4m in length. This version would have a seat capacity of 650 passengers in standard configuration, and around 900 passengers in economy-only configuration. The development of the A380-900 is planned to start once production of the A380-800 variant reaches 40 planes per year, expected to be in 2010. Given this timeline, the first A380-900s could be delivered to customers around 2015, about the same time as the A380-800F freighter variant. Airlines including Emirates,Virgin Atlantic, Cathay Pacific, Air France/KLM,and Lufthansa, as well as leasing company ILFC have already expressed interest in the extended model. According to an interview in Airliner World magazine's December issue, Singapore Airlines CEO Chew Choon Seng revealed at the delivery of their first A380-800 that the airline is keeping their options open with their order, by only defining their first ten A380s as -800s; the remaining nine aircraft could be switched to -900s.

Market

Parallel to the design of the A380, Airbus conducted the most extensive and thorough market analysis of commercial aviation ever undertaken. As of 2007, Airbus estimated a demand for 1,283 passenger planes in the category VLA (Very Large Aircraft, with more than 400 seats) for the next 20 years if the airport congestion remains at the current level. If the congestion increases, the demand could reach up to 1,771 VLAs. Most of this demand will be due to the urbanization and rapid economic growth in Asia.

The A380 will be used on relatively few routes, between the most saturated airports. Airbus also estimates a demand for 415 freighters in the category 120-tonne plus. Boeing, which offers the only competition in that class, the 747-8, estimates the demand for passenger VLAs at 590 and that for freighter VLAs at 370 for the period 2007-2026. In 2006 two industry analysts anticipated 400 and 880 A380 sales respectively by 2025.

As of February 2008, there were 191 orders for the A380, while there were 20 for the 747-8I (both not including VIP orders) and 81 for the 747-8F. The break-even for the A380 was initially supposed to be reached at 270 units. Due to the delays and the falling exchange rate of the US dollar, it increased to 420 units.In April 2007, Airbus CEO Louis Gallois said that break-even had risen further, but declined to give the new figure. As of April 2008, the list price of an A380 was US$ 317.2 to 337.5 million, depending on equipment installed.

Orders and deliveries

Sixteen customers have ordered the A380, including an order from aircraft lessor ILFC and one VIP order. Total orders for the A380 stand at 198 as of 24 July 2008. A total of 27 orders originally placed for the freighter version, A380-800F, were either cancelled (20) or converted to A380-800 (7), following the production delay and the subsequent suspension of the freighter program. Airbus' new schedule is to deliver 12 A380s in 2008 and 21 in 2009.

Orders and deliveries by year

		2001	2002	2003	2004	2005	2006	2007	2008	Total
Orders	A380-800	78	0	34	10	10	24	33	9	198
	A380-800F	7	10	0	0	10	-17	-10	0	0
Deliveries	A380-800	0	0	0	0	0	0	1	7	8

Specifications

Measurement	A380-800	A380-800F
Cockpit crew	Two
Seating capacity	525 (3-class) 644 (2-class) 853 (1-class)	12 couriers
Length	73 m (239 ft 6 in)
Span	79.8 m (261 ft 10 in)
Height	24.1 m (79 ft 1 in)
Wheelbase	30.4 m (99 ft 8 in)
Outside fuselage width	7.14 m (23 ft 6 in)
Cabin width, main deck	6.58 m (21 ft 7 in)
Cabin width, upper deck	5.92 m (19 ft 5 in)
Wing area	845 m² (9,100 sq ft)
Operating empty weight	276,800 kg (610,200 lb)	252,200 kg (556,000 lb)
Maximum take-off weight	560,000 kg (1,235,000 lb)	590,000 kg (1,300,000 lb)
Maximum payload	90,800 kg (200,000 lb)	152,400 kg (336,000 lb)
Cruising speed	Mach 0.85 (647 mph, 1,041 km/h, 562 knots)
Maximum cruising speed	Mach 0.89 (677 mph, 1,090 km/h, 588 knots)
Maximum speed	Mach 0.96 (731 mph, 1,176 km/h, 635 knots)
Take off run at MTOW	2,750 m (9,020 ft)	2,900 m (9,510 ft)
Range at design load	15,200 km (8,200 nmi)	10,400 km (5,600 nmi)
Service ceiling	13,115 m (43,000 ft)
Maximum fuel capacity	310,000 L (81,890 US gal)	310,000 L (81,890 US gal), 356,000 L (94,000 US gal) option
Engines (4 x)	GP7270 (A380-861) Trent 970/B (A380-841) Trent 972/B (A380-842)	GP7277 (A380-863F) Trent 977/B (A380-843F)
Thrust (4 x)	311 kN (70,000 lbf)

King Tutankhamun's Tomb

Howard Carter (May 9, 1874 - March 2, 1939) was an English archaeologist and Egyptologist. He is most famous as the discoverer of KV62, the tomb of Tutankhamun in the Valley of the Kings, Luxor, Egypt. Howard Carter was born in 1874 in Kensington, London, the youngest son of eight children. His father, Samuel Carter, was an artist. His mother was Martha Joyce (Sands) Carter. Carter grew up in Swaffham, in northern Norfolk, and had no formal education. His father trained him in the fundamentals of drawing and painting. Carter began work in 1891, at the age of 17, copying inscriptions and paintings in Egypt. He worked on the excavation of Beni Hasan, the gravesite of the princes of Middle Egypt, c. 2000 BC. Later he came under the tutelage of William Flinders Petrie.He is also famous for finding the remains of Queen Hatshepsut tomb in Deir el Babri. In 1899, at the age of 25, Carter was offered a position working for the Egyptian Antiquities Service, from which he resigned as a result of a dispute between Egyptian site guards and a group of drunken French tourists in 1905.

Carter and Carnarvon

After several hard years, Carter was introduced, in 1907, to Lord Carnarvon, an eager amateur who was prepared to supply the funds necessary for Carter's work to continue. Soon, Carter was supervising all of Lord Carnarvon's excavations. Lord Carnarvon financed Carter's search for the tomb of a previously unknown Pharaoh, Tutankhamun, whose existence Carter had discovered. After a few months of fruitless searching, Carnarvon was becoming dissatisfied with the lack of return from his investment and, in 1922, he gave Carter one more season of funding to find the tomb.

On November 22, 1922 Carter found Tutankhamen's tomb (subsequently designated KV62), by far the best preserved and most intact pharaonic tomb ever found in the Valley of the Kings. He wired Lord Carnarvon to come at once.

On February 16, 1923, Carter opened the burial chamber and first saw the sarcophagus of Tutankhamun.

While unwrapping the linens of the mummy, presumably looking for treasure, the skull of the ancient king fell away from the body. The impact from its fall out of the tomb made a dent in the skull. Ancient Egyptians believed a king could only be immortal if the body rested undisturbed, so some believe the name of the king must still be spoken today as a remembrance.

After cataloguing the extensive finds, Carter retired from archaeology and became a collector. He visited the United States in 1924, and gave a series of illustrated lectures in New York City which were attended by very large and enthusiastic audiences.

He died in England in 1939 at the age of 64. The archaeologist's death at this advanced age is the most common piece of evidence put forward by skeptics to refute the idea of a curse (the "Curse of the Pharaohs") plaguing the party that violated Tutankhamun's tomb. Howard Carter is buried in Putney Vale Cemetery in West London.

Excavating the Tomb

Outside the tomb before it was opened.

It took only three days before the top of a staircase was unearthed. On November 4th, 1922 Carter's workmen discovered a step cut into the rock. Then they found fifteen more leading to an ancient doorway that appeared to be still sealed.

The rumor of an ancient curse didn't stop this archaeologist from opening the tomb of King Tut. Death Shall Come on Swift Wings To Him Who Disturbs the Peace of the King was allegedly engraved on the exterior of King Tutankhamen's Tomb.

On the doorway was the name Tutankhamen. Almost three weeks later the staircase was entirely excavated and the full side of the plaster block was visible.

By November 26, the first plaster block was removed, the chip filling the corridor was emptied, and the second plaster was ready to be taken apart.

At about 4 P.M. that day, Carter broke through the second plaster block and made one of the discoveries of the century, the tomb of King Tutankhamun.

The Curse of the Mummy

When Carter arrived home that night his servant met him at the door. In his hand he clutched a few yellow feathers. His eyes large with fear, he reported that the canary had been killed by a cobra. Carter, a practical man, told the servant to make sure the snake was out of the house.

The man grabbed Carter by the sleeve. "The pharaoh's serpent ate the bird because it led us to the hidden tomb! You must not disturb the tomb!"

Scoffing at such superstitious nonsense, Carter sent the man home.

Carter immediately sent a telegram to Carnarvon and waited anxiously for his arrival. Carnarvon made it to Egypt by November 26th and watched as Carter made a hole in the door. Carter leaned in, holding a candle, to take a look. Behind him Lord Carnarvon asked, "Can you see anything?"

Carter answered, "Yes, wonderful things."

The tomb was intact and contained an amazing collection of treasures including a stone sarcophagus. The sarcophagus contained three gold coffins nested within each other (right). Inside the final one was the mummy of the boy-king, Pharaoh Tutankhamen. The day the tomb was opened was one of joy and celebration for all those involved. Nobody seemed to be concerned about a curse.

A few months later tragedy struck.

Lord Carnarvon, 57, was taken ill and rushed to Cairo. He died a few days later. The exact cause of death was not known, but it seemed to be from an infection started by an insect bite. Legend has it that when he died there was a short power failure and all the lights throughout Cairo went out. On his estate back in England his favorite dog howled and dropped dead.

Even more strange, when the mummy of Tutankhamun was unwrapped in 1925, it was found to have a wound on the left cheek in the same exact position as the insect bite on Carnarvon that lead to his death.

By 1929 eleven people connected with the discovery of the Tomb had died early and of unnatural causes. This included two of Carnarvon's relatives, Carter's personal secretary, Richard Bethell, and Bethell's father, Lord Westbury. Westbury killed himself by jumping from a building. He left a note that read, "I really cannot stand any more horrors and hardly see what good I am going to do here, so I am making my exit."

The press followed the deaths carefully attributing each new one to the "Mummy's Curse."

By 1935 they had credited 21 victims to King Tut. Was there really a curse? Or was it all just the ravings of a sensational press? Perhaps, the power of a curse is in the mind of the person who believes in it. Howard Carter, the man who actually opened the tomb, never believed in the curse and lived to a reasonably old age of 66 before dying of entirely natural causes.

Inside The Tomb

Though small and unimpressive, Tutankhamun's Tomb is probably the most famous, due to its late discovery. Howard Carter's description upon opening the tomb in 1922 was, "At first I could see nothing, the hot air escaping from the chamber causing the candle flames to flicker, but presently, as my eyes grew accustomed to the light, details of the room within emerged slowly from the mist, strange animals, statues and gold - everywhere the glint of gold.

For the moment - an eternity it must have seemed to the others standing by - I was dumb with amazement, and when Lord Carnarvon, unable to stand the suspense any longer, inquired anxiously, 'Can you see anything?' it was all I could do to get out the words, "Yes, wonderful things."'

The royal seal on the door was found intact. The first three chambers were unadorned, with evidence of early entrance through one of the outside walls. The next chamber contained most of the funerary objects.

Found in Antechamber

The sarcophagus was four guilded wooden shrines, one inside the other, within which lay the stone sarcophagus, three mummiform coffins, the inner one being solid gold, and then the mummy. Haste can be seen in the reliefs and the sarcophagus, due to the fact that Tutankhamun died at only 19 years of age following a brief reign. Though extremely impressive to the modern world, the treasures of Tutankhamun must have paled when compared to the tombs of the great Pharaohs that ruled for many years during Egypt's golden age.

The tomb is much smaller than, any of the other kings tombs, with plain walls, until you reach the burial chamber. It took almost a decade of meticulous and painstaking work to empty the tomb of Tutankhamen. Around 3500 individual items were recovered.

Tutankhamen is the only pharaoh, in the valley of the kings, still to have his mummy in its original burial location.

Discovered resting on a sled dressed in silver in, the antechamber of the tomb of Tutankhamun, this wooden shrine is covered in gold leaf applied to a layer of stucco. Its form, with the roof sloping down from front to rear and the projecting cornice at the top of the walls, recalls the ancient chapels of Upper Egypt.

A double door opens on one of the short sides and is closed with two ebony latches running through gold rings. A cord would once have passed through another two and been fastened with a clay seal. Inside the shrine there is a gilded wooden support for a statue, which was probably in solid gold and removed by grave robbers. The base still carries the marks of the feet while the name of Tutankhamun is inscribed on the dorsal pillar. On the floor lay the remains of a pectoral of which fragments have been found scattered elsewhere in the tomb.

The roof of the shrine is decorated with a winged solar disc at the front and twelve images of the vulture goddess Nekhbet with outspread wings protecting the cartouches of the sovereign and his wife. Two winged serpents with long, sinuous bodies are depicted on the sides of the roof and hold in front of them the shen hieroglyph, symbolizing eternity. The lintel of the door also features a winged solar disc while the cornice above is incised with a continuous series of vertical lines.

The external walls and the doors are subdivided into panels framed by hieroglyphic inscriptions with scenes showing Tutankhamun and his wife in various aspects of married life, a theme that recalls the scenes of the Amarna Period. However, it is not only the contents of the various scenes that recall the art of Akhenaten, but also their style characterized by the fineness, grace, and sophistication of the modeling.

The couple, adorned with jewels and dressed in finely pleated, adherent clothing, appear in various poses that reveal their reciprocal affection and a sense of absolute peace and serenity. The left wall is divided into four panels. In the bottom left Ankhesenamun is crouching before the seated Tutankhamun and is receiving a liquid poured by her husband into her hands from a small ampoule.

In the other scenes Tutankhamun, always sitting on his throne, is portrayed receiving various from his wife. On the right-hand wall, divided into two registers, Tutankhamun is seen hunting in a swamp, again in the company of the queen. The rear wall and the doors, both inside and out, are decorated with scenes in which Ankhesenamun is making offerings in the presence of her husband.

The entire decorative scheme of the shrine has strong symbolic connotations associated with the religious and political spheres. The intimate ties between the pharaoh and his bride represent the serene relationship between god and man. For this reason it is almost always the queen who is the active figure, embodying the concept of humanity paying homage to the celestial being personified by Tutankhamun. The hunting scene is to be interpreted as a symbolic episode referring to the pharaoh's role in the maintenance of the cosmic order and his constant fight against chaos (symbolized by the birds in the swamp).

Thanks to the images of the king identified as a god, the sovereign¹s shrine thus becomes a reproduction of a shrine dedicated to the cult of a divinity.

These two statues were discovered in the antechamber of the royal tomb, facing each other on either side of the sealed entrance to the burial chamber. At the time of their discovery traces of the linen bandages in which they had been wrapped were found, along with two bundles of olive and persea branches placed as offerings, one on the floor, the other still propped against the wall.

The statues, of refined craftsmanship and striking in both their life-size dimensions and the black finish of the skin, are testimony to the skill of the artist who has succeeded in investing their features with a sense of the almost supernatural power they wielded as guardians of the burial chamber. Rather than being designed to frighten eventual intruders, the black skin tone was a reference to the earth and thus, given that these are ka images of the sovereign, emphasizes indestructibility of the creative nature of the king, evoking the aspects of rebirth and cyclical resurrection of Osiris.

The two statues differ only in the type of head covering they are wearing (one a khat head-cloth, the other a nemes) and the inscriptions on their skirts. The king is portrayed in a striding pose, a mace gripped in his right hand and a long staff with a papyrus stem in his left hand. A gilded bronze asp adorns his forehead while the eyes are inlaid and outlined with gilded bronze, as are the eyebrows. A gilded usekh necklace and a pectoral are worn on the chest. The pleated skirt is fastened on the hips with a belt inscribed at the rear and on the buckle with the coronation name of the king Nebkbeperura.

The protruding frontal section of the skirt of the statue with the khat head-cloth carries the vertical inscription "The perfect god, rich in glory, a sovereign to be proud of, the regal ka of Horakhty, the Osiris, and Lord of the Two Lands, Nebkbeperura, made just." The inscription on the statue wearing the nemes records the birth name of the pharaoh, "Tutankhamun, living forever as Ra each day". Both statues are wearing anklets and bracelets of gilded bronze. Although made some years after the end of the Amarna Period, these sculptures clearly show the influence of the art of Akhenaten with their prominent bellies, slim legs and pierced ears.

Thirty-four wooden statues were found in the tomb of Tutankhamun, seven portraying the pharaoh and the other twenty-seven depicting various divinities from the Egyptian pantheon. The majority of the statues had been placed in the treasure chamber inside black wooden cabinets mounted on sleds and set along the south wall. Two of these pieces, placed together in the same cabinet, are identical and depict the pharaoh stepping on the back of a panther.

The image of the sovereign is sculpted with great realism in a very hard wood, stuccoed and covered with a thin layer of gold leaf. Tutankhamun is gripping a long staff in one hand and the flail symbolizing his power in the other. He is wearing the crown of Upper Egypt, adorned with the royal asp on the forehead. The body of the snake is painted black.

The modeling of the head and body reflects the influence of Amarna-era art in the emphasis and exaggeration of certain physical details such as the long, forward-tilted neck, the protruding breasts, the swollen belly, and the low waist. It is therefore legitimate to suggest that the statue may have been made for Akhenaten, a hypothesis supported by the fact that when it was discovered it was wrapped in linen cloths that carried inscriptions datable to the third year of this pharaoh's reign.

With its serene, youthful expression, the face features eyes inlaid with obsidian, bronze, and glass. The sovereign is bare chested but is wearing a large collar that covers his breast and shoulders and terminates with a droplet motif. The pharaoh's clothing consists of a long, tightly-fitting loincloth, knotted at the front and lined with thin incisions imitating the folds in the cloth, and sandals on his feet.

The statue stands on a black-painted, rectangular pedestal fixed to the arching back of a panther, also black. The animal is portrayed with great realism, pacing slowly and furtively. Its body has a sinuous, elegant profile and the head, with gilded ears and muzzle, is slightly dipped. A second black-painted pedestal constitutes the base for the entire sculptural group.

The composition is not intended to evoke a hunting scene, since the sovereign is not bearing arms, but rather it has a symbolic value. The panther might constitute an allegorical image of the sky, which in the Predynastic era was depicted as a feline that swallowed the sun in the evening before regenerating it in rejuvenated form the following morning. With the extensive gilding of his body the sovereign could represent the sun god. According to another interpretation supported by a pictorial scene in the tomb of Sety I, the sovereign whose gilding identifies him as the sun god, is located in the under world. The panther is in fact painted black like all the inhabitants of the under world.

The Treasure Chamber in the tomb of Tutankhamun contained twenty-two black-painted wooden caskets, each of which contained one or more wooden statues portraying the pharaoh or a number of deities from the Egyptian pantheon. All of the figures contained in the black tabernacles are fixed to a rectangular base and at the moment of their discovery were wrapped in a linen cloth datable to the third year of the reign of Akhenaten.

Two twin statues in gilded wood depict Tutankhamun standing upright on a papyrus raft and engaged in a mythical hunt for the hippopotamus symbolizing evil. The pharaoh is represented as the incarnation of Horus, the god that according to the legend fought in the swamps against the evil Seth who was transformed into a hippopotamus and was finally defeated.

Tutankhamun, like the victorious god, has the task of fighting against evil and preserving the universal order of which he is the sole guarantor. The sovereign, seen in a striding pose taking a long, solemn step appears realistically to be concentrating on launching a long spear against his enemy. He is wearing the crown of Lower Egypt decorated at the front with a representation of the royal cobra above his youthful, refined facial features.

His eyes are inlaid. An usekh necklace is depicted around his neck, incised into the wood in imitation of the rows of beads of which it is composed. The soft modeling of the naked torso with the slightly protruding pectoral muscles, the swollen belly and the low hips are clear indications of the influence that was still exercised over the art of this era by the Amarna Period.

The arms are separate from the body and emphasize the dynamism of the hunting pharaoh: in his right hand he is gripping the long spear whilst in his left he is holding a rope in rolled bronze with which to capture the defeated animal. Tutankhamun is wearing a pleated skirt, knotted at the front from where the cloth falls to various levels and opens in a fan-like fashion.

The striding pose of the statue means that the narrow pleats of the cloth adhere tightly to the thighs, allowing the underlying musculature to appear. The pharaoh is wearing precious thong sandals that were part of the his official costume. The front foot is flat on the ground while the rear is poised on the tips of the toes in realistic imitation of the pose of one taking aim prior to throwing a spear.

The slim vessel on which the sovereign is floating is typical of the simple "Its made of papyrus used by the Ancient Egyptians. It is painted in green, with the prow and the stern taking the form of sophisticated images of papyrus flowers with gilded petals. The raft is attached to a rectangular pedestal painted in black that supports the entire sculptural composition.

This elegant and precious game table composed of interlocking pieces is the largest of the four discovered in the annex of the tomb of Tutankhamun. The piece takes-the form of a box resting on a base supported by four leonine legs, partially covered with gold leaf and fixed to a sled. The upper surface is veneered with ivory and is subdivided by means of strips of wood into thirty squares, five of which carry inscriptions. The game of senet was played on this board. There are the same number of squares in ivory on the lower surface of the box, three of which are inscribed. This side was used for the game tjau.

On one of the short sides there is an aperture in which a drawer (discovered empty elsewhere in the tomb) would have been inserted. This would once have contained the pieces used for the games which were probably taken away by thieves as they would have been made of precious materials.

The four sides of the box feature yellow hieroglyphic inscriptions with augural phrases in favor of Tutankhamun, to whom the board belonged. The pharaoh's names and complete titles are recorded. The rules of the two games played on this board are unknown, but it is probable that the two competing players had to move their pieces after throwing a stick or a form of die.

Senet was very popular in Egypt from the remotest times. Boards were frequently placed in tombs to allow the deceased to continue playing after their deaths. It had magical-religious values and in the tomb paintings and in the Book of the Dead the deceased appears seated alone, intent on playing an imaginary adversary in a scene symbolizing his successful passage to the spiritual world.

Tut Chalice Lamp

Taken to the Cairo Museum

Statue of Ptah

Casket

Numerous caskets and chairs were piled hazardly as a result of the violations of the tomb in the western corner of the antechamber. The containers were almost all rectangular in shape, with lids that were flat, featured triangular pediments, or were vaulted. With the exception of certain examples in alabaster and cane, the majority were made of wood, with precious inlays in ivory, gold leaf, turquoise, or vitreous paste.

Frequently a hieratic or hieroglyphic inscription indicated their function, followed by the name of the sovereign and the ritual verse in which the sovereign was augured "life, strength and health." This casket takes the form of a rectangular parallelepiped, supported on simple square feet and closed with a vaulted lid in imitation of the primitive shrines of Upper Egypt.

The two large button-like knobs in blue faience were used to fasten the casket by means of ties and are placed on the curved part of the lid and in the center of the upper part of the front side.

The decoration is of a sophisticated elegance, thanks above all to the prevalent two-tone color scheme, interrupted only by the checkered frame around the panels, which create an attractive contrast with the elegant turquoise faience inlays on the gilded surfaces.

On the long side panels there are a series of five royal cartouches set between asps surmounted by the solar disc; the birth name of the sovereign, Tutankhamun, alternates with his coronation name Nebhheperura. The two cartouches are also found on the front and rear short sides, placed centrally and flanked by the protective figures of the genii of the millions of years arranged symmetrically either side.

Tutankhamun's Throne

This throne was produced in the early years of the reign of Tutankhamun, prior to the religious counter reformation that marked the definitive end of the Amarna Period.

The grace of the forms combines well with the richness of the decoration and the luminosity of the colors, giving rise to a composition of exquisite craftsmanship. The scene depicts the sovereign relaxing on his throne with his feet resting on a low stool with cushions. He is wearing a short wig surmounted by a composite crown and the typical pleated robe of the era, which left the prominent stomach uncovered, another feature typical of the Amarna period.

The arms of the throne are in the form of two winged and crowned serpents holding the cartouche of Tutankhamun in front of them. The legs, which were linked at the front and rear with a heraldic motif symbolizing the union of southern and northern Egypt, terminate in leonine paws. Two lions' heads also emerge from the front section of the throne. The rear of the backrest is decorated with a frieze of asps.

source : http://www.crystalinks.com

Radio astronomy is a subfield of astronomy that studies celestial objects at radio frequencies. The field originated from the discovery that many astronomical objects emit radiation in the radio wavelengths as well as optical ones. The great advances in radio astronomy that took place after the Second World War yielded a number of important discoveries including Radio Galaxies, Pulsars, Masers and the Cosmic Microwave Background Radiation. Radio telescopes use many different methods to collect information, sometimes using techniques that are similar to those used in Optical telescopes (although radio telescopes have to be much larger due to the longer wavelengths being observed). The development of radio interferometry and aperture synthesis has allowed radio sources to be imaged with unprecedented angular resolution.

History

The idea that celestial bodies may be emitting radio waves had been suspected some time before its discovery. In the 1860's James Clerk Maxwell's equations had shown that electromagnetic radiation from stellar sources could exist with any wavelength, not just optical. Several notable scientists and experimenters such as Thomas Edison, Oliver Lodge, and Max Planck predicted that the sun should be emitting radio waves. Lodge tried to observe solar signals but was unable to detect them due to technical limitations of his apparatus.

The first identified astronomical radio source was one discovered serendipitously in the early 1930s when Karl Guthe Jansky, an engineer with Bell Telephone Laboratories, was investigating static that interfered with short wave transatlantic voice transmissions. Using a large directional antenna, Jansky noticed that his analog pen-and-paper recording system kept recording a repeating signal of unknown origin. Since the signal peaked once a day, Jansky originally suspected the source of the interference was the sun. Continued analysis showed that the source was not following the 24 hour cycle for the rising and setting of the sun but instead repeating on a cycle of 23 hours and 56 minutes, typical of an astronomical source "fixed" on the celestial sphere rotating in sync with sidereal time. By comparing his observations with optical astronomical maps, Jansky concluded that the radiation was coming from the Milky Way and was strongest in the direction of the center of the galaxy, in the constellation of Sagittarius . He announced his discovery in 1933. Jansky wanted to investigate the radio waves from the Milky Way in further detail but Bell Labs re-assigned Jansky to another project, so he did no further work in the field of astronomy.

Grote Reber helped pioneer radio astronomy when he built a large parabolic "dish" radio telescope (9m in diameter) in 1937. He was instrumental in repeating Karl Guthe Jansky's pioneering but somewhat simple work, and went on to conduct the first sky survey in the radio frequencies . On February 27, 1942, J.S. Hey, a British Army research officer, helped progress radio astronomy further, when he discovered that the sun emitted radio waves . By the early 1950s Martin Ryle and Antony Hewish at Cambridge University had used the Cambridge Interferometer to map the radio sky, producing the famous 2C and 3C surveys of radio sources.

Techniques

Radio astronomers use different types of techniques to observe objects in the radio spectrum. Instruments may simply be pointed at an energetic radio source to analyze what type of emissions it makes. To “image” a region of the sky in more detail, multiple overlapping scans can be recorded and piece together in an image ('mosaicing'). The types of instruments being used depends on the weakness of the signal and the amount of detail needed.

Radio telescopes

Radio telescopes may need to be extremely large in order to receive signals with low signal-to-noise ratio. Also since angular resolution is a function of the diameter of the "objective" in proportion to the wavelength of the electromagnetic radiation being observed, radio telescopes have to be much larger in comparison to their optical counterparts. For example a 1 meter diameter optical telescope is two million times bigger than the wavelength of light observed giving it a resolution of a few arc seconds, whereas a radio telescope "dish" many times that size may, depending on the wavelength observed, only be able to resolve an object the size of the full moon (30 minutes of arc).

Radio interferometry

The difficulty in achieving high resolutions with single radio telescopes led to radio interferometry, developed by British radio astronomer Martin Ryle and Australian-born engineer, radiophysicist, and radio astronomer Joseph Lade Pawsey in 1946. Radio interferometers consist of widely separated radio telescopes observing the same object that are connected together using coaxial cable, waveguide, optical fiber, or other type of transmission line. This not only increases the total signal collected, it can also be used in a process called Aperture synthesis to vastly increase resolution. This technique works by superposing (interfering) the signal waves from the different telescopes on the principle that waves that coincide with the same phase will add to each other while two waves that have opposite phases will cancel each other out. This creates a combined telescope that is the size of the antennas furthest apart in the array. In order to produce a high quality image, a large number of different separations between different telescopes are required (the projected separation between any two telescopes as seen from the radio source is called a baseline) - as many different baselines as possible are required in order to get a good quality image. For example the Very Large Array has 27 telescopes giving 351 independent baselines at once.

Very Long Baseline Interferometry

Since the 1970s telescopes from all over the world (and even in Earth orbit) have been combined to perform Very Long Baseline Interferometry. Data received at each antenna is paired with timing information, usually from a local atomic clock, and then stored for later analysis on magnetic tape or hard disk. At that later time, the data is correlated with data from other antennas similarly recorded, to produce the resulting image. Using this method it is possible to synthesise an antenna that is effectively the size of the Earth. The large distances between the telescopes enable very high angular resolutions to be achieved, much greater in fact than in any other field of astronomy. At the highest frequencies, synthesised beams less than 1 milliarcsecond are possible.

The pre-eminent VLBI arrays operating today are the Very Long Baseline Array (with telescopes located across the North America) and the European VLBI Network (telescopes in Europe, China, South Africa and Puerto Rico). Each array usually operates separately, but occasional projects are observed together producing increased sensitivity. This is referred to as Global VLBI. There is also a VLBI network, the Long Baseline Array, operating in Australia.

Since its inception, recording data onto hard media has been the only way to bring the data recorded at each telescope together for later correlation. However, the availability today of worldwide, high-bandwidth optical fibre networks makes it possible to do VLBI in real time. This technique (referred to as e-VLBI) has been pioneered by the EVN who now perform an increasing number of scientific e-VLBI projects per year.

Astronomical sources

Radio astronomy has led to substantial increases in astronomical knowledge, particularly with the discovery of several classes of new objects, including pulsars, quasars and radio galaxies. This is because radio astronomy allows us to see things that are not detectable in optical astronomy. Such objects represent some of the most extreme and energetic physical processes in the universe.

Radio astronomy is also partly responsible for the idea that dark matter is an important component of our universe; radio measurements of the rotation of galaxies suggest that there is much more mass in galaxies than has been directly observed. The cosmic microwave background radiation was also first detected using radio telescopes. However, radio telescopes have also been used to investigate objects much closer to home, including observations of the Sun and solar activity, and radar mapping of the planets.