TERCOM
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Terrain Contour Matching (TERCOM) navigation system uses an on-board contour map of the terrain that a cruise missile will be flying over. The system "sees" the terrain it is flying over using its radar system and matches this to the map stored in memory. A Tercom system considerably increases the accuracy of a missile compared to the older and simpler inertial navigation system (INS). A Tercom system also allows a missile to fly lower, making it harder to detect by ground radar.
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[edit] TAINS
A Tercom system is usually employed together with the inertial navigation system. The inertial navigation system provides a rough positional information. The Tercom unit uses this information to find an approximate area on the map where the missile may be. By comparing the contour map with the actual contour reading provided by the radar, the Tercom obtains a more precise estimate of the position. The corrected information is fed back to the INS. This combined system is called the TAINS system (Tercom-Aided Inertial Navigation System).
A Tercom system requires very accurate maps of the path to target (for example, at 1-meter resolution) and a radar able to obtain precise changes in elevation. When flying over water, contour maps (elevation information) are replaced by magnetic field maps.
[edit] Comparison to other navigation systems
[edit] DSMAC
Another navigation system employed by cruise missiles is the Digital Scene-Mapping Area Correlator (DSMAC). This system is usually employed on the approach to target. A DSMAC system compares a photograph of the target with the picture provided by an onboard camera, providing a further increase in accuracy. Therefore, DSMAC is complementary to TAINS.
[edit] Satellite navigation
Yet another way to navigate a cruise missile is by using a satellite positioning system, such as GPS or GLONASS. Satellite navigation systems are precise and cheap. Unfortunately, they rely on satellites. If the satellites are interfered with (e.g. destroyed) or if the satellite signal is interfered with (e.g. jammed), the satellite navigation system becomes inoperable. Therefore, the GPS-based (or GLONASS-based) navigation is useful in a conflict with a technologically unsophisticated adversary. On the other hand, to be ready for a conflict with a technologically advanced adversary, one needs missiles equipped with TAINS and DSMAC.
[edit] Missiles that employ TERCOM navigation
The cruise missiles that employ a TERCOM system include:
- Supersonic Low Altitude Missile (early version of TERCOM was used in this prototype missile)
- AGM-86B (made by the United States)
- AGM-129 ACM (made by the Unites States)
- BGM-109 Tomahawk (some versions, made by the United States)
- Kh-55 Granat NATO reporting name AS-15 Kent (made by the USSR)
- Newer Russian cruise missiles, such as Kh-101 and Kh-555 are likely to have a TERCOM navigation, but little information is available about these missiles
- C-802 or YJ-82 NATO reporting name CSS-N-8 Saccade (made by China) - it is unclear if this missile employs a TERCOM navigation
