12 April 2016
By Bilal Khan
Precision-guided bombs (PGB) are becoming a common sight on the global arms market. Thrown into popularity through the introduction of the American Joint Direct Attack Munition (JDAM), PGBs furthered the ability of air arms to attack fixed targets of value, especially at stand-off range – away from the threat of enemy resistance (in the form of surface-to-air missiles, for example).
Countries all over the world have the option to pick up PGB kits from the West, the East, and even Africa. The guidance systems of these munitions involve inertial navigation systems (INS) and satellite navigation aids (e.g. GPS, GNSS, BeiDou, and Galileo). The INS is used to guide the munition from A to B, but satellite coverage is used to correct for the INS’ errors (which accumulate as the munition is on course).
As one might imagine, satellite navigation systems such as GPS are crucial to ensuring that the PGBs reach their target, but this advantage is vulnerable to interdiction by the enemy. Of course, many countries may not benefit from assured satellite coverage, but coverage may not always be available, even for users in possession of satellite assets. It is for that reason that the U.S. is seeking to enhance INS technology by greatly improving microelectromechanical systems (MEMS).
MEMS are the miniature gyroscopes and accelerometers, and are a common feature in many consumer devices, particularly smartphones. But these MEMS have very high rates of ‘bias error’ – i.e. the rate at which the INS accumulates errors in the course of its travel. The U.S.’ Defense Advanced Research Projects Agency (DARPA) awarded Northrop Grumman (subscription required) to develop MEMS hardware with very low bias error for use on PGBs.
The motivation is to have a back-up guidance system for use on weapon systems such as JDAM in case of satellite navigation failure, which could theoretically occur via signals jamming by an enemy. However, many countries will be interested in seeing INS improve, at least to the extent where the loss of satellite-aided guidance is not an insurmountable challenge to overcome. It is almost certain that others, such as France, China and Russia, will follow suit with their own improvements to INS, especially in the context of pushing the appeal of their defence exports.
At the end of the day, users of PGBs will also need to know exactly where their targets are located, which in turn requires a range of other intelligence assets (such as reconnaissance satellites). Better INS has its utility, but maybe not so much in terms of long-range strikes, especially at the scale of cruise missiles.
That said, at the tactical level, especially where targeting pods are used to identify fixed targets at up to 20km or so, INS-only PGBs could be really interesting. A fighter equipped with dual-guidance munitions (i.e. those equipped with INS/GPS and laser) could potentially engage different fixed targets in an area in quick succession. This technology would basically be a significant boost for “fire-and-forget” munitions. One should not forget the improvement this will bring to beyond-visual-range air-to-air missiles as well.
Overall, one should not let this relatively low-key program out of this sight, at a few levels, it could result in genuine changes on the battlefield.