RP 21 Sapfir Spin Scan-A
Encyclopedia
The RP-21 Sapfir was a radar
system, developed by the Soviet Union
for use in the updated MiG-21PF fighter, and later versions of the MiG-21.
The early MiG-21 fighter variants, MiG-21F and MiG-21F-13, were clear-weather daylight-only fighters. Although they were in use with the Soviet Air Force
Frontal Aviation (VVS FA), due to their limitations they were unsuited for the interception tasks of the Soviet Air Defence Forces (PVO). The Mikoyan
OKB
started development of a more sophisticated interceptor, based on the MiG-21F-13 in the late 1950s. The MiG-21P and MiG-21PF were the first MiG-21's to be equipped with a real radar that would enable them to search, track and intercept targets by night and in foul weather: the RP 21 Sapfir ('Sapphire') radar, which was given the NATO codename
of "Spin Scan-A".
The RP 21 Sapfir replaced the Mig-21F-13's SRD-5M Kvantum ('Quantum') ranging- and gun-radar. RP 21 featured a mechanically steered and gyroscopic stabilised radar dish, and had a thermionic valve (vacuum tube) circuit. In theory, it was able to detect fighter-sized targets from a range of 20 km, and lock on to them at a range of 10 km, though in practice this got reduced to 13 km and 7 km respectively. The associated weapon was the Vympel K-13
infrared guided air-to-air missile, also known as R-3S
, object 310 or AA-2 "Atoll-A" by NATO, already in use with the older SRD-5M radar. Later on, newer versions of the aircraft (namely, MiG-21 PFS) used the further upgraded RP-21M radar (NATO codename "Spin Scan-B") which allowed the semi-active radar homing
(SARH) missile, the new R-3R
(NATO codename AA-2 "Atoll-B").
Though it was a great improvement over the older SRD-5M, the new intercepting capabilities were still limited, tough this was mostly due to an inherent design flaw of the Mig-21; the nose inlet limited the size of the small radar cone, so the radar field was limited to 20° vertically and 60° horizontally. Even in the latest Chinese F-7MG copies of the Mig-21 (equipped with more advanced Israeli and Italian radars) this is still said to be a significant limiting factor for radar use. Also, because of the vacuum tube electronics, the radar system (like most other early generation radars) had a low mean time between failures (MTBF). The radar lacked look-down/shoot-down
capabilities (though this was not at all a common feature of radar systems at the time), meaning that it couldn't intercept targets that were flying under the Mig-21 because the radar system was unable to filter out "ground clutter" return. Another downside of the new radar (and other avionics) was the weight increase in the Mig-21 PF, which reduced the baseline Mig-21's otherwise impressive flight characteristics.
In its defence, the radar was simple to use and repair and was, because of the vacuum tube technology, able to withstand even a powerful electro-magnetic pulse (EMP), a side-effect from nuclear explosion, radiation harmless to men but very damaging to modern solid state
(silicon transistor) electronics. Its capabilities, as limited as they may seem, were offset by the standard PVO doctrine: pilots were tied to a ground-controlled interception
(GCI) system, which, through ground-based radars and data links, provided interceptors more extensive and more precise information.
Over the years, the West got to know the RP 21 Sapfir a better during the Vietnam war
in Indochina and the Six-Days and Yom Kippur War
s in the Middle East. Its combat record is not impressive, mostly due to the primitive and overestimated early generation R-3R radar guided missiles. Also, the radar was rather quickly compromised because of defections, and its weaknesses were well known to the west, giving way for the creation of effective electronic countermeasures
(ECM). Western pilots learned to distinguish the RP 21's rhythmic three tone pulse.
Still, the RP 21 and its developments, like the RP 22 radar (NATO codename "Jay bird") of the later Mig-21bis series, had a long career and the latter was even used in early or for export purposes downgraded MiG-23S and MiG-23MS interceptors.
Radar
Radar is an object-detection system which uses radio waves to determine the range, altitude, direction, or speed of objects. It can be used to detect aircraft, ships, spacecraft, guided missiles, motor vehicles, weather formations, and terrain. The radar dish or antenna transmits pulses of radio...
system, developed by the Soviet Union
Soviet Union
The Soviet Union , officially the Union of Soviet Socialist Republics , was a constitutionally socialist state that existed in Eurasia between 1922 and 1991....
for use in the updated MiG-21PF fighter, and later versions of the MiG-21.
The early MiG-21 fighter variants, MiG-21F and MiG-21F-13, were clear-weather daylight-only fighters. Although they were in use with the Soviet Air Force
Soviet Air Force
The Soviet Air Force, officially known in Russian as Военно-воздушные силы or Voenno-Vozdushnye Sily and often abbreviated VVS was the official designation of one of the air forces of the Soviet Union. The other was the Soviet Air Defence Forces...
Frontal Aviation (VVS FA), due to their limitations they were unsuited for the interception tasks of the Soviet Air Defence Forces (PVO). The Mikoyan
Mikoyan
Russian Aircraft Corporation MiG , or RSK MiG, is a Russian joint stock company. Formerly Mikoyan-and-Gurevich Design Bureau , then simply Mikoyan, it is a military aircraft design bureau, primarily designing fighter aircraft...
OKB
OKB
OKB is a transliteration of the Russian acronym for "Опытное конструкторское бюро" - Opytnoe Konstructorskoe Byuro, meaning Experimental Design Bureau...
started development of a more sophisticated interceptor, based on the MiG-21F-13 in the late 1950s. The MiG-21P and MiG-21PF were the first MiG-21's to be equipped with a real radar that would enable them to search, track and intercept targets by night and in foul weather: the RP 21 Sapfir ('Sapphire') radar, which was given the NATO codename
NATO reporting name
NATO reporting names are classified code names for military equipment of the Eastern Bloc...
of "Spin Scan-A".
The RP 21 Sapfir replaced the Mig-21F-13's SRD-5M Kvantum ('Quantum') ranging- and gun-radar. RP 21 featured a mechanically steered and gyroscopic stabilised radar dish, and had a thermionic valve (vacuum tube) circuit. In theory, it was able to detect fighter-sized targets from a range of 20 km, and lock on to them at a range of 10 km, though in practice this got reduced to 13 km and 7 km respectively. The associated weapon was the Vympel K-13
Vympel K-13
The K-13 is an short-range, infrared homing air-to-air missile developed by the Soviet Union. It is similar in appearance and function to the American AIM-9 Sidewinder from which it was reverse-engineered...
infrared guided air-to-air missile, also known as R-3S
Vympel K-13
The K-13 is an short-range, infrared homing air-to-air missile developed by the Soviet Union. It is similar in appearance and function to the American AIM-9 Sidewinder from which it was reverse-engineered...
, object 310 or AA-2 "Atoll-A" by NATO, already in use with the older SRD-5M radar. Later on, newer versions of the aircraft (namely, MiG-21 PFS) used the further upgraded RP-21M radar (NATO codename "Spin Scan-B") which allowed the semi-active radar homing
Semi-active radar homing
Semi-active radar homing, or SARH, is a common type of missile guidance system, perhaps the most common type for longer-range air-to-air and surface-to-air missile systems. The name refers to the fact that the missile itself is only a passive detector of a radar signal – provided by an external ...
(SARH) missile, the new R-3R
Vympel K-13
The K-13 is an short-range, infrared homing air-to-air missile developed by the Soviet Union. It is similar in appearance and function to the American AIM-9 Sidewinder from which it was reverse-engineered...
(NATO codename AA-2 "Atoll-B").
Though it was a great improvement over the older SRD-5M, the new intercepting capabilities were still limited, tough this was mostly due to an inherent design flaw of the Mig-21; the nose inlet limited the size of the small radar cone, so the radar field was limited to 20° vertically and 60° horizontally. Even in the latest Chinese F-7MG copies of the Mig-21 (equipped with more advanced Israeli and Italian radars) this is still said to be a significant limiting factor for radar use. Also, because of the vacuum tube electronics, the radar system (like most other early generation radars) had a low mean time between failures (MTBF). The radar lacked look-down/shoot-down
Look-down/shoot-down
Look-down/shoot-down is a capability a radar system is said to possess if it is able to detect, track and put a weapon onto an air target moving below the horizon as seen by the radar...
capabilities (though this was not at all a common feature of radar systems at the time), meaning that it couldn't intercept targets that were flying under the Mig-21 because the radar system was unable to filter out "ground clutter" return. Another downside of the new radar (and other avionics) was the weight increase in the Mig-21 PF, which reduced the baseline Mig-21's otherwise impressive flight characteristics.
In its defence, the radar was simple to use and repair and was, because of the vacuum tube technology, able to withstand even a powerful electro-magnetic pulse (EMP), a side-effect from nuclear explosion, radiation harmless to men but very damaging to modern solid state
Solid state (electronics)
Solid-state electronics are those circuits or devices built entirely from solid materials and in which the electrons, or other charge carriers, are confined entirely within the solid material...
(silicon transistor) electronics. Its capabilities, as limited as they may seem, were offset by the standard PVO doctrine: pilots were tied to a ground-controlled interception
Ground-controlled interception
Ground-controlled interception an air defense tactic whereby one or more radar stations are linked to a command communications centre which guides interceptor aircraft to an airborne target. This tactic was pioneered during World War II by the Royal Air Force with the Luftwaffe to follow closely...
(GCI) system, which, through ground-based radars and data links, provided interceptors more extensive and more precise information.
Over the years, the West got to know the RP 21 Sapfir a better during the Vietnam war
Vietnam War
The Vietnam War was a Cold War-era military conflict that occurred in Vietnam, Laos, and Cambodia from 1 November 1955 to the fall of Saigon on 30 April 1975. This war followed the First Indochina War and was fought between North Vietnam, supported by its communist allies, and the government of...
in Indochina and the Six-Days and Yom Kippur War
Yom Kippur War
The Yom Kippur War, Ramadan War or October War , also known as the 1973 Arab-Israeli War and the Fourth Arab-Israeli War, was fought from October 6 to 25, 1973, between Israel and a coalition of Arab states led by Egypt and Syria...
s in the Middle East. Its combat record is not impressive, mostly due to the primitive and overestimated early generation R-3R radar guided missiles. Also, the radar was rather quickly compromised because of defections, and its weaknesses were well known to the west, giving way for the creation of effective electronic countermeasures
Electronic countermeasures
An electronic countermeasure is an electrical or electronic device designed to trick or deceive radar, sonar or other detection systems, like infrared or lasers. It may be used both offensively and defensively to deny targeting information to an enemy...
(ECM). Western pilots learned to distinguish the RP 21's rhythmic three tone pulse.
Still, the RP 21 and its developments, like the RP 22 radar (NATO codename "Jay bird") of the later Mig-21bis series, had a long career and the latter was even used in early or for export purposes downgraded MiG-23S and MiG-23MS interceptors.
Sources
- http://fr.wikipedia.org/wiki/MiG-21
- http://www.vectorsite.net/avmig21_1.html#m3
- Various written sources regarding radar technology, e.g., combat aircraft
External links
- Phazotron - NIIR Corporation, the developer of the RP-21 Sapfir radar
- RP-21 Sapfir radar at the museum of the PhazotronPhazotronJSC Phazotron , is Russia's largest developer of military radars and avionics. Named after one of the major projects and the most important one it was involved in, the first cosmotron in the former-USSR, it was first formed in 1917 to produce aviation instruments...
company
