 An AN/MSQ-77 atLima Site 85 | |
| Country of origin | United States |
|---|---|
| Manufacturer | Reeves Instrument Corporation |
| Type | Site area |
| Frequency | 8500 to 9600 MHz (X band) |
| PRF | 600 pulses/second or 300 pulses/second[citation needed] |
| Pulsewidth | .25 microsecond |
| RPM | 30 cycles/second feedhorn rotation →20 pulses/cycle conical scan signal |
| Range | 200 nmi (370 km; 230 mi) beacon track[2] 135 nmi (250 km; 155 mi) skin track 130 nmi (150 mi) UHF radio reliability[3] |
| Diameter | 8 ft (2.4 m)Cassegrain antenna |
| Precision | tbd in range tbd degrees (radar track) tbd degrees (computer track w/ joystick alignment on CCTV image) GDB ACCURACY <680 ft CEP @ 200 nmi (specification)[4] 486 ft CEP @ 44 nmi (1965 testing)[5] 300-350 ft ave @ ≤100 nmi (1967 ops)[2] |
TheReeves AN/MSQ-77 Bomb Directing Central, Radar[6] (nickname "Miscue 77") was aUnited States Air Force automatic tracking radar/computer system forcommand guidance of aircraft. It was often used duringVietnam War bomb runs at nighttime and during bad weather. Developed from theReeves AN/MSQ-35,[citation needed] the AN/MSQ-77 reversed the process ofRadar Bomb Scoring by continually estimating the bomb impact point before bomb release[7] with a vacuum tube ballistic computer. Unlike "Course Directing Central" systems which guided aircraft to a predetermined release point, the AN/MSQ-77 algorithm continuously predicted bombimpact points during the radar track while the AN/MSQ-77's control commands adjusted the aircraft course. Aclose air support regulation prohibited AN/MSQ-77Combat Skyspot bombing within 1,000 yd (910 m) of friendly forces unless authorized by aForward Air Controller,[8]: 135 and "on several occasions" strikes were as close as 273 yd (250 m).[5]
Post-war the MSQ-77 was used on US and other training ranges forRadar Bomb Scoring (RBS). The AN/MSQ-77 was also periodically used for post-Vietnamcommanding of bombers during simulated ground directed bombing to maintain aircrew and radar crew GDB proficiency (RBS could be used to score the simulated GDB mission). Most AN/MSQ-77s were replaced by solid-state equipment near the end of theCold War.
Ground radar systems for automated guidance of aircraft to a predetermined point (e.g., for bomb release using abombsight or avionics radar) included the July 1951AN/MPQ-14 Radar Course Directing Central. By 1954, the MARC (Matador Airborne Radio Control) used the AN/MSQ-1A for missile guidance to the terminal dive point,[9] andSAGEGCI provided computer-controlled guidance of aircraft to continuously computed interception points (1958AN/FSQ-7Bomarc missile guidance and the laterGround to Air Data Link Subsystem for fighters). Despite the availability ofsolid-state military guidance computers in 1961, planning for a USAF vacuum-tube trajectory computer/radar system began in early 1965.[10] In October 1965,F-100s tested the AN/MSQ-77 atMatagorda Island General Bombing and Gunnery Range on theTexas Gulf Coast.[10]
In March 1966,[2] AN/MSQ-77 operations using the "reverse MSQ method"[7] began and continued through August 1973[2] for guiding B-52s and tactical fighters and bombers[11] ("chiefly flown byF-100's").[7] By March 1967, 15,000 Skyspot sorties had been flown, and raids controlled by AN/MSQ-77s included those ofOperation Menu fromBien Hoa Air Base,Operation Niagara,[12] andOperation Arc Light. Additional AN/MSQ-77 missions included those withMC-130 Commando Vault aircraft to clear landing zones and at least 1 helicopter evacuation of wounded on August 13, 1966.[13]
Additional casualties of AN/MSQ-77 personnel included 1 killed in an enemy rocket attack[3] and 6 Skyspot personnel killed in a 1966 ambush on a survey mission.[13] Following -77 modifications in 1968,[specify][14]: 45 subsequent changes included a solid-state digital printer for RBS ("Digital Data System")[15] and implementation of aUSAF suggestion for RBS to use a late-1970sprogrammable calculator to supersede the Bomb Trajectory Group, eliminating alignment procedures for its amplifiers. In 1989, remains of an F-4C Weapon System Officer shot down during a November 10, 1967, AN/MSQ-77 bomb run were recovered in Southeast Asia.[16]
Developed from the AN/MSQ-77 and also used in Vietnam was themonopulseIndia-band[verification needed]Reeves AN/TSQ-96 Bomb Directing Central[4] with a solid stateUnivac 1219B ballistic computer[17] (Mark 152 fire control computer),[5] and the AN/MSQ-77/96 systems for GDB were replacedc. 1990 by theUS Dynamics AN/TPQ-43 Radar Bomb Scoring Set ("Seek Score").[18] There were 5 MSQ-77s atNellis Air Force Base in 1994,[6] and the "MSQ-77 or equivalent" was still listed in 2005 as support equipment for airdrops from Ground Radar Aerial Delivery System (GRADS) aircraft.[7][dead link] The AN/MSQ-77 antenna at the "Combat Skyspot Memorial" onAndersen Air Force Base was destroyed by a typhoonc. 2007.[8]Archived 2015-11-07 at theWayback Machine
Initial AN/MSQ-77 sites were the production plantReeves-Ely had built in 1958 atRoosevelt Field[19] onEast Gate Blvd inGarden City, New York; and theMatagorda Island test site also used for "Busy Skyspot" training of Vietnam crews[9] (moved toBergstrom AFB in 1970). Deployment sites were the Vietnam War operating locations, the wartime site at theNellis Range, and post-war CONUS RBS and overseas sites (e.g., Korea). The last AN/MSQ-77 locations (e.g., at museums afterc. 2000 retirements)[10] included theEllsworth Air Force Base Museum[20] (near the Antelope Butte, Belle Fourche, Conner, & Horman RBS sites) and:
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In addition to the communication and maintenance van, other AN/MSQ-77 trailers were the 33 ft (10 m) radar van with roof-mountedCassegrain antenna, "control and plotting van, two diesel generator vans, [and] an administrative and supply van" which were emplaced as a military installation at the surveyed site.[10] The primary modification for the AN/MSQ-77 was the control equipment for aircraft guidance (ballistic computer, guidance/release circuitry, and UHF command equipment). The central also had an added beacon tracking capability used when the aircraft had a receiver/transmitter (e.g.,Motorola SST-181 X Band Beacon Transponder)[13] to increase the range, so the radar site could be located farther from the hostile region of bombing targets. Beacon track upgrades included radar circuitry to switch the heterodyne receiver to demodulate the transponder frequency, compensation for the transponder delay, and modification of the central's plotting board circuitry to allow display for increased ranges. The plots were of tracks calculated by the computer's Aircraft Coordinates and Plotting Group which converted radarspherical data to plotting board cartesian coordinates (non-inertialeast, north, up coordinate system) using sine/cosine voltages and radar-estimated range respectively from the Antenna Group (azimuth/elevation resolvers) and from the Track Range Computer. Additional A/C Coordinates amplifiers computed the velocity components (not plotted) which along with the track position components were provided as initial bomb conditions to the ballistic computer (Bomb Trajectory Group).
TheBomb Trajectory Group (BTG) was the AN/MSQ-77's analog ballistic computer using 3-dimensionaldouble-integration to continually predict the bomb impact point from an aircraft track during a bomb run. The Cartesian aircraft data were propagated by the BTG mathematical modeling which included aerodynamics for different bombs,Earth "curvature andCoriolis corrections", andvacuum tube integrating amplifiers. The integration was based on the varying aircraft position and velocity prior to the bomb release, so as with the use of theNorden bombsight analog computer inWorld War II, a nearly steady bomb run was required for the AN/MSQ-77 to provide sufficient bombing accuracy. As in the1950s Nike missile guidance system(s), electro-mechanical servos controlled sine/cosine resolvers in a feedback loop for computing the simulated bomb's horizontal velocity and along with the drop rate, the simulated bomb's airspeed and dive angle ("Pitch Servo"). Likewise, a "Z servo" allowed the Air Resistance Circuits to adjust for altitude-varying air density, and the drag aerodynamics were vectorized by a servo operating potentiometers to pick-off 3 bomb-specific deceleration voltages based on each cartesian velocity voltage.[15]
The AN/MSQ-77 radar track began after the aircraft (A/C) arrived near the Initial Point (IP) on a heading toward the target. When the computer's groundspeed and elevation rate servos had stabilized to the A/C cartesian velocity from the differentiating amplifiers, an operator placed the central into "computer track" to provide rate-aided tracking signals to the radar. With the computer track and the central having target position, A/C heading, & bomb type information; and with the Bomb Trajectory Group's servos tracking the bomb-in-aircraft course and pitch, the operator then activated the BTG integrators for thecomputer simulation to begin integrating a bomb trajectory from the A/C coordinates at that integration start point. Acceleration voltages from the BTG dynamic models were double-integrated by the 6 computer amplifiers which generated 3 voltages for the simulated bomb displacement (altitude, north, & east deltas) which were summed to the A/C position (simulated bomb release point, BRP). Use of the continually-changing current A/C position as the simulated BRP ensured a more accurate Earth Curvature Correction (ECC) was generated for the simulated bomb's horizontal range from the radar. When the simulated bomb's altitude (simulated BRP altitude - integrated altitude delta + altitude ECC) equalled the target height, the integration automatically stopped, and the integrateddisplacements wereheld as constant altitude, north, and eastdelta voltages. Subsequent summing of more current simulated bomb release points (A/C bomb run positions after the integration ended) with the integrator deltas generated a path of simulated bomb impact (SBI) points that moved relative to the A/C position throughout the remainder of the bomb run. The latest SBI was the AN/MSQ-77's best estimate of the impact position if bomb release was from the current A/C position:[15]
The AN/MSQ-77 control algorithm continually commanded the A/C so the BTG simulated bomb impact point, which was plotted separately from the A/C track,[15] would move toward the target. While the A/C was being guided, an AN/MSQ-77 bomb release algorithm used a model for thefuture path of simulated bomb impact points to predict the nearest impact to the target (a No-Go condition aborted before effecting an outlying bomb release). Instead of releasing from the A/C position corresponding to the nearest predicted impact point, the AN/MSQ-77 began the bomb release sequence just prior,[specify] which accounted for the delay in generating the radio command, in transmitting the command, and in the A/C effecting the mechanical release. The delay time was based on calibration testing of the AN/MSQ-77 with A/C bomb release circuitry (e.g., mean bomb release time for salvo drops from B-52s).
Although the 1967Commando Club missions againstNorth Vietnam by the7th Air Force were temporarily suspended due to successful enemy defenses on November 18, the AN/MSQ-77 variant at LS-85 had effected a direct hit (zero miss distance) as well as a 5 mi (8.0 km) miss—its Commando Club CEP through November 16 for "14 runs was 867 feet".[25] The suspension period for modifying attack tactics was used to reduce GDB errors of LS-85, since other Skyspot sites had been more accurate. AN/MSQ-77 errors included the typical automatic tracking radar errors such as the antenna lag due to the conical scan tracking, Track Range Computer error, any inaccuracy of the A/C transponder delay value used by the central, and the range offset of the A/C transponder antenna from the actual position of the bomb release point(s) on the A/C (particularly negligible when the radar was tracking from the side of the A/C). The AN/MSQ-77 compensation for antenna lag during[specify] rate-aided computer track used a telescopicCCTV system with operator's joystick[14] to aim the antenna axis toward the A/C (e.g., bomb bay section of the fuselage). AdditionalAN/MSQ-77 errors were in the bomb trajectory algorithm (e.g., different simulation rates for each of 6 integrating amplifiers)[15] and in the bomb release algorithm.
{{cite web}}: CS1 maint: archived copy as title (link)On 1 November 1967, another MSQ-77 became operational in Laos, but it was destroyed by the enemy in March 1968. DJSM-800-68 (TS ), Memo for DDR&E, CSAF, CNO, et al, 28 June 68, subj: Update of the NIGHT SONG Study
In March 1966 the first MSQ-77 arrived at Bien Hoa. … Skyspot's accuracy let heavy bombs be dropped on occasion within 250 meters of friendly positions. …many maps of South Vietnam contained distance errors of up to 300 meters. … Skyspot (S) MSQ-77 and TPQ-10 ground radars
In SEA, the MSQ-77 system is utilized by tactical fighters, tactical bombers, and B-52 bomber aircraft for controlled release of ordnance on targets during periods of darkness and adverse weather. It was used by: F-100, F-4C, F-105, A-1E, A-26, B-52, and B-57, though most frequently used by F-100s and B-52s.
{{citation}}: CS1 maint: multiple names: authors list (link) CS1 maint: numeric names: authors list (link){{cite report}}: CS1 maint: multiple names: authors list (link) CS1 maint: numeric names: authors list (link) (partial transcription at 1stCombatEvaluationGroup.com)Archived 2013-06-06 at theWayback Machineworking to find an MSQ-77[for] the 8th AF Museum… The curator … found another one…at Ellsworth AFB… given to the museum there when CEVG was decommissioned.[1]
around 1972/1973? There was a plaque in the Day room about the Day and year the site was commissioned in Guam, w/ the original crew members names. …on the very Northern tip of the Island. Not sure why it was moved[to a 2nd Guam site.] the AN/MSQ-77 was shipped direct from Vietnam to Guam.(message 23682)
Earlier in the war, OL-23 and OL-27 were co-located at OL-23 later was moved to Udorn. OL-23 was the TSQ-96 system while OL-27 was the TSQ-81NOTE: "Teepee" equipment moved from Quangtri toMukdahan in 68-69 and Mukdahan equipment was moved to NKP. (Mukdahan was a planned Skyspot site and didn't have an AN/MSQ-77.)"Combat Skyspot Overview". Archived fromthe original on 2010-11-01. Retrieved2015-01-24.
