Mast Mounted Sight
On military helicopters, a mast mounted sight (MMS) is analogous to a periscope on a submarine: it is a way to provide a line-of-sight for sensors, without the rest of the vehicle being visible to enemy sensors. In this case, the "mast" is the central driveshaft for the helicopter's rotary wing (i.e., rotor).
For a MMS implementation, a hollow extension goes above the top of the driveshaft, capped with a roughly spherical sensor housing. The housing may be flattened, so it is more of a thick "flying saucer", or if more spherical, is called a "disco ball". In use, the pilot hovers the helicopter behind an barrier to observation, such as a building or hill, and then slowly rises until the sensors in the MMS have a view beyond the barrier.
Typical sensors in the ball include:
- Millimeter wave radar
- Forward-looking infrared : An older term for thermal imaging systems, typically airborne, that can "see" objects by their heat emissions and difference from background, in conditions including night and fog
- Low-light television : Night vision devices that are sensitive principally in the visible light spectrum, but at intensities below the threshold of human sight. If they have multiple image-forming elements sensitive to different visible wavelengths, they can produce color displays.
- Thermal viewer : A third-generation infrared viewing device, which creates images based on heat radiated, rather than reflected, from targets, allowing it to visualize such things as cold metal against earth, frictionally-heated aircraft/missile edges against the sky, and vehicle engines long after they have been turned off.