The RP-21 ''Sapfir'' (
NATO codename: ''Spin Scan)'' was a
radar
Radar is a detection system that uses radio waves to determine the distance (''ranging''), angle, and radial velocity of objects relative to the site. It can be used to detect aircraft, ships, spacecraft, guided missiles, motor vehicles, w ...
system, developed by the
Soviet Union
The Soviet Union,. officially the Union of Soviet Socialist Republics. (USSR),. was a transcontinental country that spanned much of Eurasia from 1922 to 1991. A flagship communist state, it was nominally a federal union of fifteen national ...
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
The Soviet Air Forces ( rus, Военно-воздушные силы, r=Voyenno-vozdushnyye sily, VVS; literally "Military Air Forces") were one of the air forces of the Soviet Union. The other was the Soviet Air Defence Forces. The Air Forces ...
Frontal Aviation (VVS FA), due to their limitations they were unsuited for the interception tasks of the
Soviet Air Defence Forces
The Soviet Air Defence Forces (russian: войска ПВО, ''voyska protivovozdushnoy oborony'', ''voyska PVO'', ''V-PVO'', lit. ''Anti-Air Defence Troops''; and formerly ''protivovozdushnaya oborona strany'', ''PVO strany'', lit. ''Anti-Air De ...
(PVO). The
Mikoyan
Russian Aircraft Corporation "MiG" (russian: Российская самолётостроительная корпорация „МиГ“, Rossiyskaya samolyotostroitel'naya korporatsiya "MiG"), commonly known as Mikoyan and MiG, was a Russi ...
OKB
OKB is a transliteration of the Russian initials of "" – , meaning 'experiment and design bureau'. During the Soviet era, OKBs were closed institutions working on design and prototyping of advanced technology, usually for military applications. ...
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
A vacuum tube, electron tube, valve (British usage), or tube (North America), is a device that controls electric current flow in a high vacuum between electrodes to which an electric potential difference has been applied.
The type known as a ...
(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
The Vympel K-13 ( NATO reporting name: AA-2 "Atoll") is a short-range, infrared homing air-to-air missile developed by the Soviet Union. It is similar in appearance and function to the American AIM-9B Sidewinder from which it was reverse-engine ...
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
Semi-active radar homing (SARH) is a common type of missile guidance system, perhaps the most common type for longer-range Air-to-air missile, air-to-air and surface-to-air missile systems. The name refers to the fact that the missile itself is ...
(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, 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
Mean time between failures (MTBF) is the predicted elapsed time between inherent failures of a mechanical or electronic system during normal system operation. MTBF can be calculated as the arithmetic mean (average) time between failures of a system ...
(MTBF). The radar lacked
look-down/shoot-down A radar system has look-down/shoot-down capability if it can detect, track and guide a weapon to an air target that (as seen by the radar) is silhouetted against the ground.
Problem and naming
Airborne intercept radar relying exclusively on time ...
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
Clutter
is a term used for unwanted echoes in electronic systems, particularly in reference to radars. Such echoes are typically returned from ground, sea, rain, animals/insects, chaff and atmospheric turbulences, and can cause serious performanc ...
" return. Another disadvantage 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.
The radar was simple to use and repair and, because of vacuum tube technology, was able to withstand a powerful
electro-magnetic pulse (EMP), a side-effect from nuclear explosion, radiation harmless to humans 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 Ground-controlled interception (GCI) is an air defence tactic whereby one or more radar stations or other observational stations are linked to a command communications centre which guides interceptor aircraft to an airborne target. This tactic was p ...
(GCI) system, which, through ground-based radars and data links, provided interceptors more extensive and more precise information.
Over the years, the West became more acquainted the RP-21 Sapfir during the
Vietnam war
The Vietnam War (also known by #Names, other names) was a conflict in Vietnam, Laos, and Cambodia from 1 November 1955 to the fall of Saigon on 30 April 1975. It was the second of the Indochina Wars and was officially fought between North Vie ...
in
Indochina
Mainland Southeast Asia, also known as the Indochinese Peninsula or Indochina, is the continental portion of Southeast Asia. It lies east of the Indian subcontinent and south of Mainland China and is bordered by the Indian Ocean to the west an ...
, during the
Six-Day and the
Yom Kippur War
The Yom Kippur War, also known as the Ramadan War, the October War, the 1973 Arab–Israeli War, or the Fourth Arab–Israeli War, was an armed conflict fought from October 6 to 25, 1973 between Israel and a coalition of Arab states led by Egy ...
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
An electronic countermeasure (ECM) is an electrical or electronic device designed to trick or deceive radar, sonar, or other detection systems, like infrared (IR) or lasers. It may be used both offensively and defensively to deny targeting info ...
(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 for export purposes in downgraded
MiG-23S and MiG-23MS interceptors.
Sources
*
:fr: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{{Webarchive, url=https://web.archive.org/web/20070321192415/http://www.phazotron.com/en/index.html , date=2007-03-21
RP-21 Sapfir radarat the museum of the
Phazotron
JSC Phazotron-NIIR (Phazotron-NIIR, russian: ОАО «Корпорация «Фазотрон-НИИР»), is Russia's largest developer of military radars and avionics. Named after one of its major projects, the first cosmotron in the former-USS ...
company
Aircraft radars
Russian and Soviet military radars
Phazotron products
*R-2L RADAR MANUAL ENGLISH TRANSLATION
https://www.cia.gov/readingroom/docs/CIA-RDP82-00038R001800190001-3.pdf
*R-2L RADAR SOVIET MANUAL
https://www.cia.gov/readingroom/docs/CIA-RDP82-00038R001800180001-4.pdf
RP-21MA Service manuals