Track-via-missile

From Freepedia

"Track-via-missile" (or TVM) refers to a missile guidance technique which combines many of the best features of semi-active radar homing (SARH) and radio command guidance. It is also similar to active radar homing.

Explanation

A missile using this technique carries a radar receiver like an active homing missile, but not the transmitter and so it requires less power to operate its seeker. As with semi-active homing missiles, a ground-based radar illuminates the target with radar energy which is then reflected, and similarly the missile picks up the energy being returned from the target. However, unlike an SARH missile, the missile itself does not process and act on this information. Instead, data on the radar returns is relayed back to the ground station via a data link. The ground station then processes the information and sends signals back to the missile telling it what to do in order to intercept its target, similarly to a command-guided missile.

Advantages

• Unlike an active radar homing missile, the missile does not alert the target to the fact that it is homing in on it by blasting it with radiation. Typically the target will know it is being illuminated by the SAM radar but doesn't know whether a missile is closing in. Modern phased-array radars, by virtue of their thin beams and low side lobes aren't even that easy to detect until they are illuminating the target. These combine to greatly increase the surprise factor.
• Unlike semi-active radar homing missiles, the electronics needed to calculate and follow an interception path don't need to be built into each missile, reducing their complexity, weight and cost. Because of this, it is also possible to make the missiles more accurate by using more sophisticated algorithms for calculating their flight paths. In addition, it is possible for operators to adjust the missile's flight path, even during the terminal homing phase. It also does not require a continuous-wave radar to operate.
• Unlike radio command guided missiles, because the missile's radar receiver is much closer to the target than the ground station, much more accurate tracking information can be generated. It is much more difficult to jam or spoof the tracking signal also.

It is also possible for the ground station to receive direct radar reflections from the target and combine the two sources of information to generate the interception course. This adds an extra element of ECM resistance to the system.

Disadvantages

There are some potential disadvantage but they are minor. For example, the data link could potentially be jammed, which is not possible with an active homing missile, and this technique requires the ground-based radar to be active the whole time, potentially aiding the launch of anti-radiation missiles against it, although the modern types of radars used for this kind of engagement tend to also have a low probability of intercept (LPI). Another potential disadvantage compared to active radar homing is that during the terminal phase, the missile still relies on the radar for guidance, so if the target is able to put an obstacle between itself and the radar system (e.g. a hill) or get outside of the radar's tracking envelope (e.g. get to extremely low altitude far away enough from the radar) then the missile won't get any reflected radiation from the target and will be unable to track it. Note, however, that because the missile is tracking the target and not the radar, the radar's engagement envelope will likely be significantly larger than its regular tracking envelope.

These disadvantages are avoided by the Patriot system since it uses terminal active radar homing, however this reduces some of the advantages also, especially that of missile simplicity.

Examples

Most very modern long-range SAM systems use the track-via-missile technique. This includes:

• The U.S. MIM-104 Patriot anti-aircraft and anti-cruise missile system (with some limited anti-ballistic missile capability)
• The Russian S-300PS/S-300F/S-300-PMU (NATO designation SA-10 "Grumble") anti-aircraft/anti-missile system.
• The Russian S-300V (NATO designation SA-12 "Gladiator"/"Giant") anti-missile system.