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by The Unitary Technocracy of Etoile Arcture. . 121 reads.

M90 Arrowhead Improved Lightweight Attack Weapon

This page is a work in progress by its author and should not be considered final.

M90 "Arrowhead"


Type

Multi-role (anti-armor,
anti-fortification, anti-
personnel)

Place of origin

Etoile Arcture

Service history

In service

2003 - present

Used by

Etoile Arcture
Ground Forces

Royal Imbrinium
Marine Corps

Production history

Designer

Sequoia Dynamics

Designed

1996-2001

Manufacturer

Sequoia Dynamics
Armament And
Technical Products

Unit cost

US$4,000

Number built

~1 million

Variants

See below

Specifications

Weight

7 kg (without sights)
8.5 kg (with sights)

Length

900 mm


Calibre

88.9 mm

Muzzle velocity

250-270 m/s

Effective firing
range

300 m (point target)

Maximum firing
range

600 m (area target)

Sights

iron sights, clip-on
electro-optic sight

Detonation mechanism

point-initiated,
base-detonated
or programmable
smart fuse

M90A2 Arrowhead Improved Lightweight Attack Weapon in ready-to-fire configuration
with pop-up battlesights raised.

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The M90A2 "Arrowhead" Improved Lightweight Attack Weapon (ILAW) is a compact, multifunctional, individually-portable, 3½" (88.9 mm) calibre, shoulder-launched, one-shot disposable weapon system used against infantry, vehicles, structures, emplacements and fortifications. The M90A2 is designed around a fin-stabilised unguided free-flight rocket-assisted cartridge equipped with a multipurpose tandem high effect warhead. The launcher employs the Davis recoilless gun principle using a funnel-like venturi and a counter mass to significantly reduce recoil, back blast and launch signature. This allows firing at close range from confined enclosures and concealed firing positions. A reusable clip-on day/night/laser sight ensures the single-shot weapon has a high first-round hit probability against both static and moving targets. The launcher is fired from the right shoulder only.
Each M90A2 ILAW ships as a 'wooden' round, i.e. a pre-packed ready-to-fire single round of ammunition requiring minimal maintenance and simple pre-fire checks. The complete round consists of a fixed munition with warhead and rocket, expeller charge and counter mass pre-loaded into a sealed expendable composite launch tube, a simple high reliability electro-mechanical firing system with multiple safeties for launcher and warhead, a folding grip and shoulder rest to provide a stable firing platform, shoulder sling for easy portability, reusable clip-on day/night/laser sight, and emergency pop-up battlesights. Different tandem warhead configurations allows engagement of a range of battlefield targets including armoured fighting vehicles, light armoured vehicles, infantry in the open or protected behind cover, and fortified structures.

Description


The M90A2 ILAW consists of a smoothbore launch tube open at the muzzle and breach ends containing an electro-mechanical firing mechanism, a rocket-assisted cartridge and expeller charge loaded at the muzzle end, and a counter mass loaded at the breech end in front of a divergent nozzle or venturi. The cartridge is a fixed round comprising a warhead in tandem arrangement (a precursor and primary charge) initiated by programmable setback-armed fuses, folding aluminium alloy tail fins and an attached solid-propellant rocket motor. Frangible plastic discs secure all the elements inside the launcher.
The launch tube is formed as a single-piece moulding of filament-wound glass-reinforced plastic (GRP), except for a light aluminium liner around the venturi to resist the high pressures and temperatures produced by the rocket exhaust. To protect the cartridge and firing mechanism from water, oils, dust, dirt, snow and other contaminates, both ends of the launcher have fire-through plastic covers and water- and gas-tight rubber seals. Sling attachment points are moulded on to the body of the tube for easy transport, and there is a folding plastic hand grip and shoulder stop for weapon handling during firing. A mounting bracket is also provided for a reusable clip-on sight.
Form and function of the M90A2 is of a similar fashion to other disposable rocket launchers utilising both a Davis gun-type launcher and high-low propulsion system to achieve recoilless operation. The high-low system - generating high gas pressure and mass flow within the launch tube to provide propulsive force, with low pressure gas venting from a rear divergent nozzle or venturi - is coupled with a Davis gun-type counter mass equal to the remaining momentum of the launched projectile to cancel out the recoil. To allow use in confined (or enclosed) spaces the back blast is contained by the counter mass, which consists of compressed ceramic powder ballast. The powder is lightly bound to maintain its porosity and easily disintegrates under high gas pressure so that it will vent from the rear of the launcher as a high velocity cloud of fine particulates. The mass of the particles is such that they quickly slow and cool by air resistance alone, greatly attenuating the back blast so that it is harmless at a distance of only one metre from the rear of the launcher.
The firing mechanism uses a percussion activated thermal battery to supply electrical power to arm the warhead fuse and detonation circuits and to ignite the propelling charge. Multiple manual safeties protect the weapon from accidental discharge including a transport safety pin, a safety/cocking lever and safety release catch. All three block the trigger sear, spring-biased firing rod and percussion firing pin, and must be disengaged in a set sequence to cock (arm) the weapon, or re-engaged to safe the weapon.
The firing sequence begins with ignition of the propelling charge to eject the rocket-assisted cartridge from the launch tube. As soon as the cartridge clears the tube it deploys eight spring-biased switchblade stabilisation fins and initiates a sustainer rocket motor. The motor uses a composite modified nitramine double-base propellant that has a low flash and smoke signature. To ensure high accuracy with resistance to crosswinds the propellant grain is arranged in a constant burn geometry so the motor provides sustained thrust throughout the full length of flight to maintain a constant velocity and flat trajectory towards the target. Acceleration forces (setback) arms the warhead 10 metres from the muzzle. Depending on fusing the warhead detonates on impact or by delay action on contact. If the round overshoots a timer ensures the munition will safely self-destruct beyond a preset distance, which is typically 600 metres.

Warheads


Three warhead options are available.

  • The M901A2 HEAA (High Explosive Anti-Armour) warhead contains a tandem high-explosive anti-tank (HEAT) armour defeat mechanism, consisting of a probe fitted with a point-initiating base-detonating (PIBD) piezoelectric fuse and 100 g shaped charge precursor to initiate explosive reactive armour (ERA) blocks at stand-off distance, and a 500 g full-calibre shaped charge to defeat composite armour and armour plate behind ERA and produce beyond-armour effects. The main shaped charge is configured with a plastic-bonded explosive (PBX) filler and hollow conical bonded bimetallic liner. The liner is deformed on detonation to focus the explosive force as a narrow high velocity jet of molten metal able to perforate 29 inches (740 mm) of homogeneous steel. Single shots are effective against the side, rear and top armour of main battle tanks, and two shots effective against the frontal arc (the first to knock out ERA and partly penetrate frontal armour, and the second to travel through the initial hole to complete the penetration.) The warhead can also be employed in an anti-materiel role against light armoured vehicles and field fortifications.

  • The M902A1 MPP (Multi-Purpose Programmable) warhead is the most common variant due to its versatility and is primarily designed for barrier penetration and neutralising troops inside buildings and bunkers, or behind reinforced concrete, brick or stone walls. It is similarly arranged in a tandem layout but with a crushable double ogive housing a PIBD fuse connected to a multifunctional electronic time (ET) fuse with dual mode impact/graze and impact-inertia-fired delay functioning powered by a setback generator on firing and programmed with range data; a high-explosive squash head (HESH) break-in charge that punches holes through walls; and a high-explosive follow-through (HEFT) grenade containing 2,000 0.1 g pre-formed forged steel ball fragments. The programmable ET fuse allows selection between three modes of operation to match different classes of targets.

    • Delay Action (DA) fuses the HESH precursor in impact mode to break through the target leaving a hole that allows the HEFT grenade to enter the structure, where it detonates on a piezoelectric delay fuse to produce behind-the-target fragmentation effects.

    • Super Quick (SQ) mode is optimised for dynamic breaching or mouse-holing. The break-in charge and follow-through grenade are fused to detonate in quick succession on contact by PIBD impact/graze fuse as if a unitary HESH charge. The enhanced blast effect is in a projected cone with a circular cutting motion that creates a man-sized "mousehole" without compromising the structural integrity of the target structure. This mode is also effective against fortifications, emplacements and light armoured vehicles.

    • Variable Time (VT) mode is used for anti-defilade defeat. A time delay is set for a particular range by the fire control system (using laser rangefinder data) so that the weapon can employ a timed air burst to produce maximum fragmentation effects against troops in open terrain, entrenchments and dense vegetation.

  • The M904E1 HIT (High Impulse Thermobaric) warhead is based on the M902 MPP pattern with the follow-through fragmentation grenade exchanged by a metal augmented charge (MAC) and a setback-armed PIBD fuse. The warhead contains a novel explosive (NE) consisting of a plastic-bonded explosive (PBX) bursting charge and slurry of reactive metal, liquid fuel and oxidant. The high sustained blast overpressure this produces is effective against personnel in both open terrain and confined spaces including entrenchments, fighting positions, and structures. The long duration blast wave generates expanding flame fronts and volume producing pressure fronts that are especially effective in defeating troops within multi-room structures.

Sights


M90A2 Arrowhead Improved Lightweight Attack Weapon in ready-to-fire configuration
with folding hand grip and shoulder stop extended and clip-on Emerson Optronics
XM743 Day/Night/Laser Sight mounted over the launch tube.

The Emerson Optronics XM743 Day/Night/Laser Sight is a reusable clip-on computerised aiming device with a rugged weather-proof Zytel ST (Super Tough) polymer housing. It is secured by a detachable mounting plate to the left side of any M90 launch tube and retains boresight between launchers. The XM743 combines a 4× day telescope with fog proof optics, Generation III+ thin film autogated image intensification tube that works in starlight or moonlight conditions to provide night vision, low-power Class IM eye-safe (1.54µ) laser rangefinder, solid-state three-axis accelerometer, digital magnetic compass for bearing, an automatic crossing speed rate sensor, full-solution digital ballistics computer and a fuse control processor.
Electrical connectors on the XM743 mate via connectors on the mounting plate with the launcher firing system to send signals to the programmable fuse on the warhead. The operator uses controls on the sight to engage the laser rangefinder, and select from one of three operating modes (DA, SQ and VT) that in turn set the impact and delay fuses on the rocket warhead. To enhance hit probability an electronically driven reticle provides the operator an aiming point with the impact point automatically corrected for launcher elevation and target position, motion (lead angle), rotational (spin) drift, rocket trajectory drop and crosswind as measured and calculated by the fire control system.
Emergency battlesights are also provided allowing snap fire at short range, and are identical in function to a back-up iron sights. The rear sight is a rotary diopter adjustable for windage and elevation, with four different apertures corresponding to firing ranges 50 m, 100 m, 200 m and 300 m. The front sight has a centre post with left and right lead posts for aiming at moving targets, and have Tritium luminous dots for night shooting. The sights are hidden behind sliding plastic covers on the launch tube and flip-up for deployment.

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Users


Etoile Arcture

  • Etoile Arcture Ground Forces

Arcturia

  • Armée de Terre

  • Corps des Marines

Imbrinium

  • Royal Imbrinium Army

  • Royal Imbrinium Marine Corps

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