Topmex-9 distributed SAR mission employing nanosatellite cluster

This paper presents the strategy for the development of TOPMEX-9, an innovative concept for Earth observation based on synthetic aperture radar (SAR) and nanosatellite clusters. The concept is intended as a, as a start up project for future collaboration between the Microwaves and Radar Institute (HR) of the German Aerospace Center (DLR), the Mexican Space Agency (AEM) and the Mexican Talent Network (RDTM). The idea is based on a nanosatellite formation flying around a microsatellite using a distributed constellation in multistatic SAR mode. This is an analogy with the sun providing illumination to passive optical receivers or cameras. The microsatellite acts as a speaker (Tx) while the nanosatellites around behave as listeners (Rx). Multistatic SAR mode allows the separation of radar payloads, thus decreasing volume, weight, power and consequently the mission costs. It allows permits retrieval of multi-angle measurements, thus obtaining more information about the illuminated scene than the monostatic SAR systems. The design of each TOPMEX-9 nanosatellite is based on the CubeSat standard and includes a single receiver reflector antenna in H or V polarisation in the Ka-band (32.6-37.0 GHz). The SAR system distributed architecture (i.e. radar, TM/TC, tracking and intercommunication) has the advantage of maximizing the energy of the radar antenna, thus having a better signal-to-noise ratio. TOPMEX-9 is predicted to a great impact in future low-cost Earth observation missions. This mission is focused on applications in oceanography such as ocean wave spectra and sea surface roughness measurements, coastal area monitoring, wind speed estimation and atmosphere studies. Other applications are ice roughness in cryosphere research and ship detection. The limited lifetime of a nanosatellite is compensated by the fact that new radar cluster configurations can be launched based on lessons learned, contributions in the acceleration of technology development and proving innovative data acquisition schemes.