The Aalto-1 is a 3U-cubesat project coordinated by Aalto University. The satellite, Aalto-1, will be mainly built by
students as project assignments and thesis works. VTT Technical Research Centre of Finland will develop the main
Earth observation payload, a miniaturized spectral imager, for the satellite. It is a novel highly miniaturized tunable filter
type spectral imager. Mass of the spectral imager will be less than 400 grams, and dimensions will be approximately
80 mm x 80 mm x 45 mm. The spectral imager is based on a tunable Fabry-Pérot interferometer (FPI) accompanied by
an RGB CMOS image sensor. The FPI consists of two highly reflective surfaces separated by a tunable air gap and it is
based either on a microelectromechanical (MEMS) or piezo-actuated structure. The MEMS FPI is a monolithic device,
i.e. it is made entirely on one substrate in a batch process, without assembling separate pieces together. The gap is
adjusted by moving the upper mirror with electrostatic force. Benefits of the MEMS FPI are low mass and small size.
However, large aperture (2-10 mm) MEMS FPIs are currently under development, thus it is not yet known if their
performance is adequate. The piezo-actuated FPI uses three piezo-actuators and is controlled in a closed capacitive
feedback loop. The drawback of the piezo-actuated FPI is its higher mass. However, it has a large aperture which enables
a shorter exposure times. Selection of the FPI type will be done after thorough evaluation. Depending on the selected FPI
type, the spectral resolution of the imager will be 5 - 10 nm at full width at half maximum and it will operate in the
visible and/or near infrared range.