The ANSER (Advanced Nanosatellite System for Earth observation Research ) project is an INTA project that consists of a cluster of three nanosatellites for studying and monitoring the water quality of the reserves and reservoirs of the Iberian Peninsula by means of spectrometric techniques. The satellites follow the CubeSat philosophy using low-cost COTS components. The challenges are in formation flying and fractionated instruments. The constellation will be launched Q1 2023.

The Attitude Determination and Control System (ADCS) has a paramount importance for power generation, communications, pointing the payload and, in the case of ANSER, for satellite formation control. The satellite formation is controlled by taking advantage of the aerodynamic forces present in low orbits.

A CubeSat bundle that has reaction wheels, star tracker, solar sensors, magnetometers and magnetotorquers is used for ADCS. The CubeSat bundle has its own ADCS software but it has not enough accuracy for the ANSER requirements.

IDR (Instituto Universitario de Microgravedad Ignacio da Riva) and STRAST of UPM are in charge of developing and validating more accurate algorithms for ADCS in order to fit the ANSER requirements. These ADCS algorithms include estimators and controllers for the different operational modes of the ANSER constellation.

IDR are in charge of developing estimators and controllers and validating them by a MIL (Model In the Loop) approach by using the facilities included in Simulink. STRAST is in charge of validating them by PIL (Processor In the Loop) and HIL (Hardware In the Loop) approach by using flight hardware and environment simulators. STRAST is also in charge of integrating this alternative ADCS in the CubeSat bundle by using the facilities and restrictions provided by the CubeSat bundle manufacturer.