An astrodome is a hemispherical
transparent dome that was installed in the cabin roof of certain aircraft. Such a dome would allow a trained navigator to perform
astronavigation and thereby guide the aircraft at night without the aid of land-based visual references.
Astronavigation was a principal early method for attaining an aircraft's position during nighttime by referencing the
star
A star is a luminous spheroid of plasma (physics), plasma held together by Self-gravitation, self-gravity. The List of nearest stars and brown dwarfs, nearest star to Earth is the Sun. Many other stars are visible to the naked eye at night sk ...
s. The practice of sighting stars using a
sextant
A sextant is a doubly reflecting navigation instrument that measures the angular distance between two visible objects. The primary use of a sextant is to measure the angle between an astronomical object and the horizon for the purposes of cel ...
had been commonplace amongst navigators for hundreds of years aboard
ships
A ship is a large vessel that travels the world's oceans and other navigable waterways, carrying cargo or passengers, or in support of specialized missions, such as defense, research and fishing. Ships are generally distinguished from boats, ...
, and proved to be applicable to faster moving aircraft as well, however, the task required a 360-
degree view of the celestial
horizon
The horizon is the apparent curve that separates the surface of a celestial body from its sky when viewed from the perspective of an observer on or near the surface of the relevant body. This curve divides all viewing directions based on whethe ...
. By installing an astrodome, such a view could be readily achieved. The
Royal Air Force
The Royal Air Force (RAF) is the Air force, air and space force of the United Kingdom, British Overseas Territories and Crown Dependencies. It was formed towards the end of the World War I, First World War on 1 April 1918, on the merger of t ...
(RAF) adopted astronavigation techniques into standard navigator training during the late 1930s, both the methods used and the design of the sextant were adapted to better suit the aviation environment, while many aircraft ordered by the service would be furnished with astrodomes to enable navigators to use this technique.
During the
Second World War
World War II or the Second World War (1 September 1939 – 2 September 1945) was a World war, global conflict between two coalitions: the Allies of World War II, Allies and the Axis powers. World War II by country, Nearly all of the wo ...
, astronavigation became a critical ability used to by various nations to conduct long distance flights at night, particularly strategic bombing campaigns. The RAF's choice to mainly operate its bombers at night meant that its crews were particularly dependent on astronavigation for finding their way to and from targets. The introduction of
electronic means of
navigation
Navigation is a field of study that focuses on the process of monitoring and controlling the motion, movement of a craft or vehicle from one place to another.Bowditch, 2003:799. The field of navigation includes four general categories: land navig ...
soon competed with astronavigation, although electronic techniques had their shortcomings as well.
Use in aviation
Sporadic use of astronavigation in aviation can be found in numerous long distance flights performed during the 1920s and even amid the
First World War
World War I or the First World War (28 July 1914 – 11 November 1918), also known as the Great War, was a World war, global conflict between two coalitions: the Allies of World War I, Allies (or Entente) and the Central Powers. Fighting to ...
.
During these early days of aviation, those individual officers that chose to employ astronavigation often attempted to simplify the traditional procedures of marine navigators in this new operating context. Amid the 1930s, the
Royal Air Force
The Royal Air Force (RAF) is the Air force, air and space force of the United Kingdom, British Overseas Territories and Crown Dependencies. It was formed towards the end of the World War I, First World War on 1 April 1918, on the merger of t ...
(RAF) became seriously interested in the widespread use of astronavigation for nighttime flights.
During November 1937, astronavigation was formally endorsed to be a part of standard navigation procedure amongst general reconnaissance and twin-engine bomber pilots. Two years later, a specialised bubble sextant was designed for the service, which became a preferred tool for this form of navigation.
Typically, there would be a suspension arm mounted in the vicinity of the astrodome, upon which the sextant could be mounted via a swivel clip affixed to the top of the instrument.
During the
Second World War
World War II or the Second World War (1 September 1939 – 2 September 1945) was a World war, global conflict between two coalitions: the Allies of World War II, Allies and the Axis powers. World War II by country, Nearly all of the wo ...
, astrodomes were prominent on many RAF and
Commonwealth
A commonwealth is a traditional English term for a political community founded for the common good. The noun "commonwealth", meaning "public welfare, general good or advantage", dates from the 15th century. Originally a phrase (the common-wealth ...
-operated multi-engined aircraft and on foreign aircraft ordered by them for their use, such as the
Liberator and
Dakota. Furthermore, numerous aircraft would be retrofitted with astrodomes to better facilitate operational use. For the RAF, it was particularly important for specific aircraft to possess astrodomes as the service had opted to perform the majority of its
offensive operations over the continent under the cover of night, hindering conventional navigation by landmarks. On numerous aircraft, such as the
Short Stirling four-engined heavy bomber, the astrodome was angled so that it could provide generous external views, including of ground positions, not only those relevant to the task of astronavigation, thus the facility was sometimes used for observation (unrelated to navigation).
Several
Avro Lancaster
The Avro Lancaster, commonly known as the Lancaster Bomber, is a British World War II, Second World War heavy bomber. It was designed and manufactured by Avro as a contemporary of the Handley Page Halifax, both bombers having been developed to ...
s were outfitted with a pair of astrodomes.
Similar hemispherical-shaped domes were also installed on some Second World War era heavy bombers for the purpose of sighting of their defensive
gun turret
A gun turret (or simply turret) is a mounting platform from which weapons can be fired that affords protection, visibility and ability to turn and aim. A modern gun turret is generally a rotatable weapon mount that houses the crew or mechanis ...
s, particularly those that were remotely operated. Examples of such installations include the German
Heinkel He 177
The Heinkel He 177 ''Greif'' (Griffin) was a long-range heavy bomber flown by the ''Luftwaffe'' during World War II. The introduction of the He 177 to combat operations was significantly delayed by problems both with the development of its ...
A, which had a single forward dorsal dome to aim its remotely operated FDL 131 twin
MG 131 dorsal turret, and the American
Boeing B-29 Superfortress
The Boeing B-29 Superfortress is a retired American four-engined propeller-driven heavy bomber, designed by Boeing and flown primarily by the United States during World War II and the Korean War. Named in allusion to its predecessor, the Bo ...
heavy bomber, which had used a dome in its complex sighting system for its
quartet of remote gun turrets. On the B-29, the bonding of the astrodome was designed so that it would generate only minimal radio interference via static electric discharges.
Several RAF bombers, such as the Stirling, were equipped with an astrograph; this device, installed above the navigator's table, projected lines of equal altitude for two stars at any one time.
The navigator only needed to observe
Polaris
Polaris is a star in the northern circumpolar constellation of Ursa Minor. It is designated α Ursae Minoris (Latinisation of names, Latinized to ''Alpha Ursae Minoris'') and is commonly called the North Star or Pole Star. With an ...
from this point to achieve a three-star fix. While deemed to be useful in astronavigation, by this time
inertial guidance system
An inertial navigation system (INS; also inertial guidance system, inertial instrument) is a navigation device that uses motion sensors (accelerometers), rotation sensors ( gyroscopes) and a computer to continuously calculate by dead reckoning ...
s were becoming increasingly available; these devices would eventually displace the use of astronavigation and thus aircraft would increasingly be built without astrodomes or other accommodations for this means of navigation.
Astrodomes added drag and could fail under pressurization (called a blowout) which has occurred in several instances often with fatal consequences for the navigator. Efforts were made to reduce this danger such as retractable periscopic sextants.
Early
jet-powered bombers, such as the
English Electric Canberra
The English Electric Canberra is a British first-generation, jet-powered medium bomber. It was developed by English Electric during the mid- to late 1940s in response to a 1944 Air Ministry requirement for a successor to the wartime de Havilla ...
and the
V bomber
The "V bombers" were the Royal Air Force (RAF) aircraft during the 1950s and 1960s that comprised the Nuclear weapons and the United Kingdom, United Kingdom's strategic nuclear strike force known officially as the V force or Bomber Command Mai ...
s, while furnished with internal navigation systems, would often still be navigable by astronavigation.
During the early 1960s, astrodomes were still being employed in the USMC Lockheed Hercules GV-1 (later designated as
C-130
The Lockheed C-130 Hercules is an American four-engine turboprop military transport aircraft designed and built by Lockheed Corporation, Lockheed (now Lockheed Martin). Capable of using unprepared runways for takeoffs and landings, the C-130 w ...
); the navigator was able to employ a bubble sextant hung from a hook in the middle of the dome. The USMC operated its
Aerial Navigation School at MCAS Cherry Point, NC with graduates receiving their
designation and wings as an Aerial Navigator.
The
Lockheed SR-71 Blackbird
The Lockheed SR-71 "Blackbird" is a retired long-range, high-altitude, Mach 3+ strategic reconnaissance aircraft developed and manufactured by the American aerospace company Lockheed Corporation. Its nicknames include " Blackbird" and ...
, a high speed
aerial reconnaissance
Aerial reconnaissance is reconnaissance for a military or Strategy, strategic purpose that is conducted using reconnaissance aircraft. The role of reconnaissance can fulfil a variety of requirements including Artillery observer, artillery spott ...
aircraft, was furnished with a complex array of navigation systems, which included an
astro-inertial guidance system (ANS) to correct deviations produced by the
inertial navigation system
An inertial navigation system (INS; also inertial guidance system, inertial instrument) is a navigation device that uses motion sensors (accelerometers), rotation sensors (gyroscopes) and a computer to continuously calculate by dead reckoning th ...
via a series of
celestial observations.
[Morrison, Bill. SR-71 contributors, Feedback column, ]Aviation Week and Space Technology
''Aviation Week & Space Technology'', often abbreviated ''Aviation Week'' or ''AW&ST'', is the flagship magazine of the Aviation Week Network, a division of Informa. The weekly magazine is available in print and online, reporting on the aero ...
, 9 December 2013, p. 10. This system performed its observations of the stars above the aircraft via a circular quartz glass window set onto the upper fuselage.
[Shul and O'Grady 1994] Its "blue light" source
star tracker
A star tracker is an optical device that measures the positions of stars using photocells or a camera.
As the positions of many stars have been measured by astronomers to a high degree of accuracy, a star tracker on a satellite or spacecraft may ...
, which could see stars during both day and night, would continuously track a variety of stars as the aircraft's changing position brought them into view. The system's digital computer
ephemeris
In astronomy and celestial navigation, an ephemeris (; ; , ) is a book with tables that gives the trajectory of naturally occurring astronomical objects and artificial satellites in the sky, i.e., the position (and possibly velocity) over tim ...
contained data on
a list of stars used for celestial navigation: the list first included 56 stars, and was later expanded to 61.
["SR-71A-1 Flight Manual, Section IV, p. 3."](_blank)
''sr-71.org''. Retrieved: 13 December 2011.
Use at sea
During the
postwar
A post-war or postwar period is the interval immediately following the end of a war. The term usually refers to a varying period of time after World War II, which ended in 1945. A post-war period can become an interwar period or interbellum, ...
era, the use of the astrodome spread to other vehicles, including a number of ocean-going vessels. In particular, they found popularity on long distance racing yachts, especially those that were being used in solo racing.
Eric Tabarly, record-breaking winner of the 1964
OSTAR single-handed transatlantic race, and former French Aéronavale (Fleet air arm) pilot, had fitted his revolutionary lightweight ketch-rigged racer ''Pen Duick II'' with an astrodome scavenged from a decommissioned
Short Sunderland
The Short S.25 Sunderland is a British flying boat Maritime patrol aircraft, patrol bomber, developed and constructed by Short Brothers for the Royal Air Force (RAF). The aircraft took its service name from the town (latterly, city) and port of ...
flying boat. Not only could he use it for sextant astro-navigation, but it provided a sheltered place from which he could steer his yacht during a stormy race. This was quite useful, as his wind-vane autopilot (also derived from aeronautical technology) had broken down.
See also
*
Index of aviation articles
Aviation is the design, development, production, operation, and use of aircraft, especially heavier-than-air aircraft. Articles related to aviation include:
A
Aviation accidents and incidents
– Above Mean Sea Level (AMSL)
– ADF
– Acces ...
References
Citations
Bibliography
* Shul, Brian and Sheila Kathleen O'Grady. ''Sled Driver: Flying the World's Fastest Jet''. Marysville, California:
Gallery One, 1994. .
{{DEFAULTSORT:Astrodome (Aviation)
Air navigation
Aircraft canopies
Celestial navigation
Navigational equipment