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Miniature Synthetic Aperture Radar (Mini-SAR)
Scientific Objectives:
To detect water ice in the permanently shadowed regions on the Lunar poles, upto a depth of a few meters.
Although returned lunar samples show the Moon to be extremely dry, recent research suggest that water-ice may exist in the polar regions. Because its axis of rotation is perpendicular to the ecliptic plane, the poles of the Moon contain areas that never receive light and are permanently dark. This results in the creation of “cold traps”, zones that, because they are never illuminated by the sun, may be as cold as 50–70 ?K. Cometary debris and meteorites containing water-bearing minerals constantly bombard the Moon. Most of this water is lost to space, but, if a water molecule finds its way into a cold trap, it remains there forever – no physical process is known that can remove it. Over geological time, significant quantities of water could accumulate.
An onboard SAR at suitable incidence would allow viewing of all permanently shadowed areas on the Moon, regardless of whether sunlight is available or the angle is not satisfactory. The radar would observe these areas at incidence angle near 45 degrees, recording echoes in both orthogonal senses of received polarization, allowing ice to be optimally distinguished from dry lunar surface.
The Mini-SAR radar system can operate as an altimeter/scatterometer, radiometer, and as a synthetic aperture radar imager.
Payload Configuration Details:
The Mini-SAR system will transmit Right Circular Polarization (RCP) and receive, both Left Circular polarization (LCP) and RCP. In scatterometer mode, the system will measure the RCP and LCP response in the altimetry footprint, along the nadir ground track. In radiometer mode, the system will measure the surface RF emissivity, allowing determination of the near normal incidence Fresnel reflectivity. Meter-scale surface roughness and circular polarization ratio (CPR) will also be determined for this footprint. This allows the characterization of the radar and physical properties of the lunar surface (e.g., dielectric constant, porosity) for a network of points. When directed off nadir, the radar system will image a swath parallel to the orbital track by delay/Doppler methods (SAR mode) in both RCP and LCP.
The synthetic aperture radar system works at a frequency 2.38 GHz, with a resolution of 75 m per pixel from 100 km orbit and its mass is 8.77 kg.
Miniature Synthetic Aperture Radar (MiniSAR) is from Applied Physics Laboratory, Johns Hopkins University and Naval Air Warfare Centre, USA through NASA.
 
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Last Update
11 Nov 2008