Air strikes – how precise are they?
As the UK RAF joins the coalition bombing campaign against Daesh in Syria a lot has been made of the precision capabilities of its missiles and the ability to avoid civilian casualties.
In its first strike on 3 December against an oil field in Omar, eastern Syria, the RAF dropped six Paveway IV precision-guided bombs from three Tornado GR4 fighter-bombers and further strikes have taken place with Paveway launched from both Tornado and MQ-9 Reaper drones since in both Iraq and Syria. The RAF also has its Dual Mode Brimstone (DMB) missile.
But how precise are we talking? How does a bomb or missile become precision-guided?
In the case of the Paveway IV bomb, built by Raytheon, it has two modes: GPS-guidance and laser-guidance. The good thing about GPS guidance is that it can be used in any weather. The bomb can be dropped and it will guide itself towards the GPS coordinates to hit the target. Laser-guidance is affected by the weather and can’t be used in heavy cloud cover or bad conditions as it disrupts the signals.
But GPS guidance relies on getting target information in advance. This is gathered from satellites or surveillance aircraft and drones and includes GPS coordinates and imagery data. This is used to create a targeting data pack with all the information needed to carry out an air strike. The data pack is then sent to headquarters where a mission planning unit will create a full plan for an aircraft to carry out.
Because GPS targeting relies on a pre-programmed data package put on the bomb it means that it can’t hit moving targets. But Paveway IV is usually used for static targets like buildings and facilities or formations that are not expected to move and have fixed GPS coordinates.
The Tornado aircraft will take the bomb over the target area and drop it. Inside, the bomb has an Inertial Navigation System (INS) that includes an accelerometer and laser gyrometer to measure angular velocities and accelerations and a radar altimeter for measuring altitude. This allows the bomb or missile to know its location.
In Paveway IV, the GPS-assisted INS is called GAINS. There are two GPS antenna on the front, allowing the bomb to know its longitude and latitude and the target’s GPS coordinates. Once it is dropped from the Tornado, the bomb’s command and control system directs it towards the target by moving the fins on the side and front.
Using Paveway IV means the RAF can drop the bomb from higher altitudes and the aircraft is safer from small arms as well as providing the all-weather capability unavailable to laser-only guidance systems.
But the addition of the laser guidance option gives some flexibility to Paveway IV. For this the aircraft needs to have a direct line of sight to the target so that it can point the laser onto it.
When a target has a laser pointed at it the laser energy bounces off – this is called a splash or a painted target. It is this radiated laser energy that a missile or bomb will lock on to using a seeker on the front. It is also why the weather needs to be good, if the signal pointing at the target is disrupted or the seeker on the bomb or missile cannot pick up the radiated energy from the target it won’t be able to find it.
But laser guidance means that when a pilot reaches the site of the target and finds it may have moved slightly, the bomb can still be launched. The laser designator, which is in a pod fitted on the underside of the Tornado, can point at where the target is and direct the bomb to the alternative location. In some circumstances laser guidance means the missile can hit a very slow moving target, but this is difficult as laser guidance alone is not accurate enough for moving targets (see below).
Paveway IV has a smaller warhead of 500lb, which still creates a big explosion but is smaller than previous versions. This means the blast is more concentrated on the target area with less likelihood of civilians getting caught up.
But precision technology is not cheap, each Paveway IV missile costs about £62,500. It is not perfect either, as guidance using GPS coordinates still relies on advanced planning and the missile itself can’t tell if civilians are on the site. However, the alternative of using unguided bombs, although much cheaper would result in many more civilian casualties as they are less likely to hit their targets.
Paveway IV has been used on Tornado since 2009 and in Libya about 900 were dropped (£56 million). In the latest raids in Syria the RAF’s Typhoon aircraft have dropped their first Paveway IV and the missile is being further developed so it can hit moving targets.
Paveway IV also has two Radio Frequency (RF) antenna to detect the missile’s distance from the ground. This gives it an airburst capability.
Missiles with RF seekers are usually cone-shaped at the front, whilst other missiles with electro-optic sensors are usually rounded.
But if the target is not in a fixed location and is moving – like armoured vehicles or military trucks – then a different system is needed.
GPS coordinates cannot be used because the target will move away from them. So the RAF uses the Dual Mode Brimstone (DMB) missile, built by MBDA, for this role.
Although the missile does not have GPS, Brimstone is called ‘dual-mode’ because it has been fitted with a semi-active laser (SAL) alongside a millimetre wave (mmW) radio frequency radar. The reason it is called ‘semi-active’ is because the laser on the aircraft will point at the target and the missile uses its seeker to pick up the laser energy reflections and head towards it when launched. A purely ‘active’ system is different as there would be a laser designator emitting a signal on the missile itself.
The problem with laser targeting is that there is some natural jittery movement as the laser points at the target and the splash signal covers an area larger than the target itself. If the target is static and the bomb is large this is less of an issue but it becomes much harder to hit when moving.
Therefore Brimstone uses the mmW radar for accuracy in the final phase. The missile is already heading towards the target courtesy of the laser but now it will start to emit a mmW radio frequency signal and receive returning reflections, giving it the range, angular position and closing speed and this is how it homes in. This is an active system as the missile itself emits the signal and it is not affected by the weather.
This is the classified bit as the mmW radar is already programmed to identify certain radio frequency signals that enable it to find specific moving targets at close range that look like military vehicles and complete the strike.
The addition of the SAL means that moving targets can be hit from higher up, whereas before this was not possible with only the mmW. This means the Tornado would have fly in low under the enemy radar and when it gets close to a group of moving vehicles or tanks, it would fire a salvo of Brimstone missiles which would then autonomously find and hit the targets using its RF seeker.
But operational circumstances have changed. An enemy like Daesh does not have sophisticated surface-to-air radar and missile systems so the aircraft can fly higher and avoid small arms fire from the ground. The DMB technology means that the Tornado can launch the missile from higher altitudes and get the same effect.
However the mmW radar only works well when the target is big enough to reflect radio frequency signals for the seeker to pick up. Vehicles give large returns, but individual soldiers for example would give little in the way of return signals.
But this additional precision technology is expensive. Each missile is estimated at about £105,000.
The DMB was first fired in combat in June 2009 in Afghanistan. It is fitted to the Tornado GR4 and was used in Libya in 2011 where 120 were fired. More recently has been used in operations against ISIL in Iraq in Sept-Nov 2014. It will be on Typhoon by 2018 (although this may be accelerated) and has been successfully fired from MQ-9 Reaper drones.
A five-year project called the SPEAR Capability 2 programme plans to extend the range of the DMB to beyond the horizon so the aircraft are further away and can still hit moving targets. It has meant a re-design of the whole missile and will replace DMB. This version was due to be in-service in November 2015.
Dual Mode Brimstone is a unique capability that the UK does possess that will offer something that neither the US or France has. The US has the Hellfire, which is either guided by semi-active laser or mmW radar. It is not dual mode and can only be launched from an attack helicopter or unmanned aerial vehicle, but not from fixed wing fighter or bomber aircraft. The US is attempting to catch up with its Joint Air-to-Ground Missile (JAGM) programme to give Hellfire a dual mode capability.