A novel method for achieving synthetic aperture radar imagery by means of a micro-satellite constellation.

摘要

The current emphasis in the satellite industry is on replacing large satellite platforms with one or more smaller satellites, built at lower costs, yet able to accomplish similar mission objectives. In this context, there is increasing interest in the potential capabilities and applications of so-called "micro-satellites" -satellites of 10-100 kg. However it is recognized that such small satellites pose severe constraints on payload volume, mass and power. Thus, they would appear to be inappropriate for missions such as synthetic aperture radar (SAR) imaging, where payloads have significant size and power demands - specifically the large SAR antenna and high-power radar transmitter. The primary reason for the high transmit power requirement is that traditional SAR systems use backscatter, which is weak from most terrain types as most energy is scattered in the forward direction. Thus, if it were possible to gather this forward scattered element, then the transmit power requirements could drop significantly, potentially making it feasible for installation on a micro-satellite. This research is based on this principle of collecting to the forward scattered element -a novel method by which two micro-satellites "fly" in a specific formation to accomplish a SAR imaging mission bi-statically. The transmitting satellite will be the master, with the receiver satellite slaved off it for synchronization. The satellites view a swath of 30x30 km, at a ground resolution of 30 m, from an altitude of 700 km. The constellation geometry proposed requires minimal orbit control resources, and allows for the resolution of the left-right ambiguity. The satellite design is based on the Surrey Satellite Technology, Ltd. enhanced microsatellite, with a mass of 100 kg, and a standard volume of 1x1m base and a 0.6 m height. The satellite shape will be a truncated pyramid, allowing for increased power production by the body-mounted Gallium Arsenide solar cells and provides a larger platform base for the 2.5 m diameter parabolic dish antenna. The signal is transmitted at 2.4 GHz, as a "chirped" pulse of 34 mus duration. The receiver will collect, compress and store the data, which will later be sent to a ground station. This will require a data storage of 1 Gbit and a downlink of 2 Mbps. The main processing of the SAR data will be conducted on a ground facility, due to the complex and time required for processing.