THERMAL SIGHTS MIGRATE TO UNCOOLED IMAGERS
By David Maxwell
Combat troops may be out of Iraq and commencing draw-down in Afghanistan but that does not mean ‘conflict’ has ceased. It continues in many places around the world and brings together many players, world powers, smaller nations and those ‘fighting for freedom’ (whatever that means!). Regular soldiers, reservists and irregulars continue to fight and when night falls, the fighting will continue.
As many engagements are taking place is areas of minimal ambient light, the thermal weapon sight (TWS) is often preferred over the image-intensified (II) sight. This feature offers a reprise and update on the TWS, highlighting several new products and indicating the way forward with more and more products using uncooled microbolometer technology in an attempt to reduce the size, weight and power (SWaP) of the genre.
As has been noted in these pages before, perhaps the most numerous thermal sight in service today is the US Army’s AN/PAS-13 Thermal Weapon Sight (TWS) family, which has been produced in three major versions:
* AN/PAS-13(V)1 Light TWS (LTWS), for weapons such as the 5.56mm M16 rifle and the M4 Carbine;
* AN/PAS-13(V)2 Medium TWS (MTWS), for weapons such as the M60 7.62mm machine gun; and
* AN/PAS-13(V)3 Heavy TWS (HTWS), for long-range weapons such as the M2/M3 0.5 in heavy machine gun, 40mm Mk 19 automatic grenade launcher and various sniper rifles.
The original TWS, today referred to as TWS I which entered service in 2001-03 used an uncooled, long-wave infrared (LWIR = 8-12/14 microns), Barium Strontium Titanate (BST) staring focal plane array (FPA) with a 320×240 pixel format for the LTWS, with the MTWS and LTWS using cooled, mid-wave infrared (MWIR = 3-5 microns), scanning Mercury Cadmium Telluride (MCT) FPA with a 40×16 pixel format.
By 2003, however, TWS was rebid as the US Army wished to expand its capabilities, reduce its weight and improve its logistics (the MTWS and HTWS used specialised batteries). As a result, BAE Systems and DRS Technologies beat the incumbent Raytheon, with the US Army awarding what is now known as the TWS II programme almost equally between BAE Systems and DRS Technolgies in 2004.
As uncooled detector technology had matured further, both companies’ bids used uncooled LWIR Vanadium Oxide (VOx) microbolometer detectors; a 320×240 pixel format for the LTWS II and having a 640×480 pixel format for the MTWS II and HTWS II. Raytheon fought back and in 2007 won a USD63.4 million contract to supply about 5,000 AN/PAS-13 units in AN/PAS-13E TWS II configuration, having also adopted uncooled LWIR VOx microbolometer solution.
All three manufacturers continue to look at further increasing the resolution of their detectors which originally featured a 25-micron pixel pitch (the space between pixels on the FPA) by reducing this spacing to 17-microns, with the aim of increasing resolution and reducing weight.
Although the AN/PAS-13 family is fast becoming ubiquitous, there are other thermal sights available and in use. In 2009, FLIR Systems Inc. Government Systems (FSI-GS) joined forces with Trijicon to develop two clip-on TWS models customised for use with Trijcon’s ACOG model TA31 sight. The first offering, known as the Advanced Combat Thermal Sight (ACTS) is based on the 320×240 pixel FPA version of FSI-GS’s uncooled LWIR VOx microbolometer, while the other – the Advanced Thermal Weapon Sight (ATWS) – uses the 640×480 pixel FPA. Two earlier thermal sights – the High-performance, In-line Sniper Sight (HISS) and the SnipIR models, both featuring cooled MWIR Indium Antimonide detectors, with 320×240 and 256×256 pixel FPAs, respectively – remain in service.
As the AN/PAS-13 detector technology has become more available, other manufacturers have thermal sights to the market, as instanced by the ThOR-320 from the American Technologies Network (ATN) Corporation being offered to military forces (domestic and international)