Beam riding Beam - riding , also known as beam guidance , is a technique of directing a missile to its target by means of radar or a laser beam . The name refers to the way the missile flies down the guidance beam , which is aimed at the target . It is one of the simplest guidance systems and was widely used on early missile systems , however it had a number of disadvantages and is now found typically only in short - range roles . Basic concept . Beam riding is based on a signal that is pointed towards the target . The signal does not have to be powerful , as it is not necessary to use it for tracking as well . The main use of this kind of system is to destroy airplanes or tanks . First , an aiming station ( possibly mounted in a vehicle ) in the launching area directs a narrow radar or laser beam at the enemy aircraft or tank . Then , the missile is launched and at some point after launch is “ gathered ” by the radar or laser beam when it flies into it . From this stage onwards , the missile attempts to keep itself inside the beam , while the aiming station keeps the beam pointing at the target . The missile , controlled by a computer inside it , “ rides ” the beam to the target . Radar beam riding . Beam riding is one of the simplest methods of missile guidance using a radar . It was widely used for surface - to - air missile s in the post - World War II era for this reason . Early tracking radars generally use a beam a few degrees wide , which makes it easy to find the target as it moves about . These radars are normally used in conjunction with wide - scanning early warning radar systems , although in modern systems the two functions can be combined . When a target is detected , some radars had the ability to " lock on " , and track the target automatically . Beam riding systems can be easily adapted to work with such a system . By placing receiver antennas on the rear of the missile , the onboard electronics can compare the strength of the signal from different points on the missile body and use this to create a control signal to steer it back into the center of the beam . In practice , the systems used additional information from the signal , such as conical scanning , to more accurately calculate the centerline . With this simple system , the majority of the tracking problem is offloaded from the missile to the launching platform . In early examples , these were ground - based radars with all the equipment necessary for tracking . The inherent disadvantage of the radar beam riding system is that the beam spreads as it travels outward from the broadcaster . As the missile flies towards the target , it therefore becomes increasingly inaccurate . This is not a problem at short ranges , but as many early surface - to - air missile s were designed to work at long ranges , this was a major issue . For example , earlier versions of the RIM - 2 Terrier missile introduced in the 1950s were beam riders , but later variants employed semi - active radar homing to improve their effectiveness against high - performance and low - flying targets . In contrast to beam riding , semi - active guidance becomes " more " accurate as the missile approaches the target . Another issue is the guidance path of the missile is essentially a straight line to the target . This is useful for missiles with a great speed advantage over their target , or where flight times are short , but for long - range engagements against high - performance targets the missile will need to " lead " the target in order to arrive with enough energy to do terminal manoeuvres . A possible solution for this problem was to use two radars , one for tracking the target and another for guiding the missile , but this drove up implementation costs . A more common solution for long - range missiles was to guide the missile entirely independently of the radar , using command guidance , as was the case for the Nike Hercules . Pure radar beam riding was rare by 1960 . Laser beam riding . Beam riding guidance became more popular again in the 1980s and 90s with the introduction of low - cost and highly portable laser designator s . A laser beam can be made much narrower than a radar beam while not increasing the size of the broadcaster . Additionally , it is simple to encode additional information in the beam using digital means , which has a number of advantages . Missiles with small optical receivers on their tail can beam ride on lasers with similar ease as earlier radar beam systems , but will be inherently more accurate . Additionally , as the beam is very narrow by design , less power is needed than a semi - active design where the volume of space being " painted " is generally larger , in order to ensure the missile body does not block all of the signal . This makes it more difficult to be noticed by the target ' s warning receiver . Very low power signals can be used . In modern use , laser beam riding is generally limited to short - range missiles , both anti - air and anti - tank . Examples include the Starstreak , the RBS 70 , MSS - 1 . 2 and 9M119 Svir .