The SC
ELITE MEMBER
- Joined
- Feb 13, 2012
- Messages
- 32,233
- Reaction score
- 21
- Country
- Location
It says:
"By the 1980s the first GPS receivers were
being integrated into US cruise missiles. GPS
was attractive since it allowed the missile to
continuously correct its inertial error, regardless of
terrain and weather conditions, and worked as well
over water as land.
These advantages were offset by problems with
vulnerability to jamming, as the GPS signal is
inherently very faint, susceptibility to ‘multipath’
effects where GPS signals are reflected from terrain
or buildings, and accuracy variations resulting from
how many satellites are visible at any given time,
and how they are spread across the sky.
All US cruise missiles are now equipped with a GPS
and inertial guidance package, with mechanical
inertial technology replaced by cheaper and more
accurate Ring Laser Gyro technology during the
late 1980s and 1990s.
Problems with the basic accuracy of GPS have
been progressively addressed by the introduction
of Wide Area Differential GPS techniques, where
correction signals valid for a given geographical
are broadcast by a radio link to the GPS receiver, in
the instance of US missiles using the WAGE (Wide
Area GPS Enhancement), this being embedded
in encrypted pages within the GPS navigation
message broadcast by later model satellites. The
most accurate technology of this kind developed
in the US during the 1990s can correct GPS
errors down to several inches in three dimensions
– accurate enough to put a weapon into the open
hatch of an armoured vehicle.
Problems with susceptibility to jamming and
multipath have proven more difficult to deal with.
They have resulted in the introduction of smart
antenna technology, typically based on ‘digital
beam-forming’ in software. The idea behind this
technology is again simple in concept but complex
in detail. The most basic GPS antenna will see the
whole hemisphere above the missile, and thus
collects signals from GPS satellites, as well as
hostile jammers. So called Controlled Reception
Pattern Antennas (CRPA) will synthesise in software
narrow beams which are pointed in space in
the direction where the GPS almanac predicts a
satellite will be, making the antenna effectively
blind in all other directions. The most sophisticated
designs of this type will produce so called ‘nulls’ in
the antenna pattern which are pointed at jammers
to further suppress their effect.
Much of the widely publicised problems in early
production AGM-158 JASSM cruise missiles were
a result of software problems in this kind of GPS
receiver, causing the missile to lose track of GPS
satellites and lose its way.
Advanced GPS receivers provide precision levels
of accuracy, and good resistance to surface based
GPS jammers. They are less effective against
sophisticated opponents who might deploy GPS
jammers on satellites, UAVs or balloons.
The latest generation of US cruise missiles uses
GPS/inertial guidance, but supplements it with a
nose mounted digital thermal imaging device, the
intent being to provide a DSMAC-like capability
against fixed targets – and with suitable software,
and automatic recognition capability against a
mobile target like a radar or missile battery.
Datalinks, typically derived from the JTIDS/Link-
16 technology, are being introduced to provide a
capability to retarget the weapon if a mobile target
has moved while the missile is enroute – this
facility depending critically on the user having
the reconnaissance and surveillance capability to
detect such movements.
The longer term trends in cruise missile guidance
will be more intelligence, more autonomy, more
diversity in sensors, better reliability and lower
costs."
www.defencenews.com.au
