###### Abstract
In contrast to the limits on load weight, volume, and size for a satellite, i.e., the TerraSAR-X, ALOS-PALSAR, GF-3 and so on, the same limitations on MBS are able to overcome owing to unlimited deployment on Moon's surface. It is believed that in the near future, MBS can be designed using the same aperture size and power supply as on those used on Earth. Moreover, the ground-based imaging radar technology and actual observation experiments, i.e., on the Moon, obtain valuable experience and data, which in turn helps the research of MBS [11; 12]. Fourth, in contrast to a low orbit platform, the small elliptic orbit and long distance during Earth-Moon motion makes the zero-Doppler plane and valid pulse repeat frequency (PRF) no longer stable, but changes along with MBS's revolution. In existing research, the track speed of MBS in the near side is almost perpendicular to the line from MBS to Earth centroid, this is to say, there exist intersections of zero-Doppler plane on the Earth's surface for any MBS located in the near side, and Doppler centroid of MBS can be compensated for after at least two-dimensional attitude steering. According to zebra map of a valid PRF interval, the PRF can be set higher when incident angle is small, but reversely when incident angle becomes bigger [13]. Currently, the MBS is still at a theoretical analysis stage, lacking actual data for pro-cessing, but longing for extensive observation of Earth's phenomena requires this theoretical analysis in advance. Moreover, the development of ground-based imaging radar technology on Moon would also prove feasibility of MBS. During the processing of a SAR image, incorrect slant range and Doppler centroid estimates will result in high coupling feature of the azimuth and range signal, thus increasing the complexity of signal processing and sacrificing the quality of imaging formulation in frequency domain [14; 15], all of which are unfavorable for MBS. To avoid the disadvantages in decoupled range and azimuth signals in frequency domain, this paper utilizes a method in time domain, namely the BP algorithm for MBS imaging. As showed in Figure 1, a MBS can continuously monitor various Earth targets (e.g., the red solid dot of imaging area) during its synthetic aperture time in large scale. Moreover, to further reduce the computational complexity, the BP algorithm will be converted to a FBP algorithm, as will be explained later in this paper. The feasibility of ground-based imaging radar technology on Moon might indicate the mission is reasonable. The size, power, etc. of MBS can use the same scale as that used on Earth. With a primary focus on the renewed algorithm for MBS, the influence of attenuation in signal transmission, the light aberration, and also MBS's and EGT's digital elevation mode (DEM) on imaging are not considered. The remainder of this paper will prove the effectiveness of MBS from two aspects, i.e., the spatial relationship and the establishment of the algorithm model; the framework is organized as below. In Section 2, a description of the FBP algorithm, mainly regarding the division of aperture and imaging areas for MBS, is presented based on real motion between MBS and EGT. The real motion, including the range history, is calculated separately for uplink and downlink, based on ephemeris. In Section 3, a theoretical analysis of the image is provided, and the target responses are simulated for confirming the superiority of FBP. Finally, Section 4 offers a brief conclusion for the simulation.