Sensors - Wescam

Even light helicopter drones, like this Schiebel Camcopter S-100 and its side-pylon
mounted Picosar, are now able to join the ‘Sar League’ in which membership was
hitherto restricted to the larger Male and Hale drones. (Schiebel)
(Persistent Threat Detection System),
with the company’s 56K aerostat flown
at 2500 ft.
Tars: Lockheed Martin is also responsible
for the US Air Force Tars (Tethered
Aerostat Radar System), using the company’s
420K aerostat, with an envelope
made by ILC Dover. Flown at 15,000 ft, it
gives the Lockheed Martin L-88 radar a
range of 370 km.
Marts: Employed for communication
relay, the Marts (Marine Airborne Re-
Transmission System) was developed by
Darpa for use by the US Marine Corps in
Iraq. The Tcom 32M aerostat takes a 225-
kg payload to 3000 ft, giving a radius of
125 km.
Jlens: A major advance in aerostats will
be achieved by the Raytheon/Tcom Jlens
(Joint Land Attack Cruise Missile
Defense Elevated Netted Sensor System),
which – in combination with the US
Army’s IAMD (Integrated Air and Missile
Defense) – is intended to provide
deployed forces with the detection and
tracking of potential threats and targets,
including large-calibre rockets, drones
and moving surface vehicles.
The Jlens will employ the Tcom 74M
aerostat, which can carry a 1600-kg payload
to a normal operating height of 10,000
ft, with an endurance of one month. The
74M is designed to operate in 130 km/h
winds, and survive winds of 170 km/h.
Each Jlens system (or ‘orbit’), of which
14 are planned, will employ two aerostats,
one with a surveillance radar and the other
with a fire control radar for the new interceptor
missile, which will have a range of
up to 400 km. The Jlens programme was
motivated by the failure of US forces to
detect the five HY-2/C-201 Silkworm
cruise missiles fired at their positions in
Kuwait during the 2003 invasion of Iraq. It
is currently proceeding on the basis of a
$ 1.4 billion design and demonstration contract,
awarded to prime contractor
Raytheon. This contract includes the delivery
of two Jlens orbits.
The decision on Jlens low-rate initial
production is now due in FY12, and the
last orbit is to be delivered in 2019. The
programme is expected to total around
$ 6.4 billion, each orbit costing approximately
$ 360 million.
Sensors
Long gone are the days when the drone’s
primary observation weaponry consisted
of downward shooting wet-film still and
cine cameras whose precious booty had
to be laboratory processed before being
handed over to the analysts. Digital cameras
came of age in the early 1990s and
with them the means to transmit live (or
almost live) imagery down to base. Now
video cameras easily fit into a thimble
and are used in the cheapest of drones,
the body and wing of which are carved
out of polystyrene foam, which makes
them almost expendable.
After the wet film era, and together
with the inception of their electronic
counterparts, the next significant step
that was afforded by the miniaturisation
of electronics was stabilisation, which
itself led to what are commonly referred
to now as stabilised turrets, or balls.
Granted, the ‘older’ cameras could be
slewed, but hardly locked on – particularly
in space-restricted aircraft like drones,
including the larger types.
With stabilisation came a host of amenities.
First and foremost of course, are clearer
pictures, since not only is the relative
displacement of the ground target relative
to the platform compensated, but so are
the bumps, leaps and side-slips of the aircraft
in low-altitude turbulent air.
Secondly, proper stabilisation came to
the rescue of lock-on. Lock-on (which
means that, upon command from the
ground operator, the camera will keep
staring at a given spot) is obtained by an
electronic analysis of the pixels in the
cross-hairs area. If the ‘target’ is a darker
spot and the movement of the camera’s
cross-hairs slips into an area of brighter
neighbouring pixels, the processor will
send commands to the platform to drive
the camera back to its original darker spot.
If one imagines the number of electronic
commands that such a procedure requires,
say in one second, one can just as easily
understand the benefits derived from a
camera that is readily ‘kept still’, because
there is a limit (made up of contrast threshold
and judder speed) beyond which the
lock-on system will simply give up.
Finally, stabilisation allows one to
obtain a permanent and accurate reading
of the three-dimensional geographical
co-ordinates of the spot the crosshairs are
locked onto and, datalink allowing, these
and the pictures are received and read
live on the ground. Not only does this
enable target data to be forwarded to
command for an artillery intervention, or
to a bomber aircraft, it also allows the
drone to directly and steadily illuminate
the target with a laser beam (if the turret
is so equipped) to provide a spot for surface-
or air-launched laser-guided
weapons to home onto. The ultimate
refinement is what Flir, for example,
terms «Geo-lock», meaning that should
the ball be locked onto an object and that
an obstacle (a tower, chimney or tall
building) temporarily cross the aiming
path, the system will anticipate the platform’s
motion to immediately and seamlessly
re-lock onto the original target
once the obstacle is cleared.
Evidently, reaction times and the number
of sensors housed are what make the
difference between the various systems
available on the market, but also of
course, their size and cost. As usual, it is
the mission that drives the requirement,
which in turn drives the type of stabilised
platform and hence the type and size of
drone that is finally required.
The most complete stabilised turrets are
those that can simultaneously house a day
and low-light camera (CCD), an infrared
camera, a rangefinder and a laser target
designator. The leaders in the field of drone
Northrop Grumman has
completed flight testing of
its Vader, a ground target
moving indicator synthetic
aperture radar that is able
to detect slow moving small
objects such as men and
animals walking over a
wide area. (Northrop
Grumman)
34 armada Compendium Drones 2010