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Today, the near‐Earth space is facing a paradigm change as the number of new spacecraft is literally skyrocketing. Increasing numbers of small satellites threaten the sustainable use of space, as without removal, space debris will eventually make certain critical orbits unusable. A central factor affecting small spacecraft health and leading to debris is the radiation environment, which is unpredictable due to an incomplete understanding of the near‐Earth radiation environment itself and its variability driven by the solar wind and outer magnetosphere. This paper presents the FORESAIL‐1 nanosatellite mission, having two scientific and one technological objectives. The first scientific objective is to measure the energy and flux of energetic particle loss to the atmosphere with a representative energy and pitch angle resolution over a wide range of magnetic local times. To pave the way to novel model‐in situ data comparisons, we also show preliminary results on precipitating electron fluxes obtained with the new global hybrid‐Vlasov simulation Vlasiator. The second scientific objective of the FORESAIL‐1 mission is to measure energetic neutral atoms of solar origin. The solar energetic neutral atom flux has the potential to contribute importantly to the knowledge of solar eruption energy budget estimations. The technological objective is to demonstrate a satellite deorbiting technology, and for the first time, make an orbit maneuver with a propellantless nanosatellite. FORESAIL‐1 will demonstrate the potential for nanosatellites to make important scientific contributions as well as promote the sustainable utilization of space by using a cost‐efficient deorbiting technology.

RADMON is a small radiation monitor designed and assembled by students of University of Turku and University of Helsinki. It is flown on-board Aalto-1, a 3-unit CubeSat in low Earth orbit at about 500 km altitude. The detector unit of the instrument consists of two detectors, a Si solid-state detector and a CsI(Tl) scintillator, and utilizes the ΔE-E technique to determine the total energy and species of each particle hitting the detector. We present the results of the on-ground and in-flight calibration campaigns of the instrument, as well as the characterization of its response through extensive simulations within the Geant4 framework. The overall energy calibration Email addresses: philipp.oleynik@utu.fi (Philipp Oleynik ), rami.vainio@utu.fi (Rami Vainio ), arjupu@utu.fi (Arttu Punkkinen), dudnik@rian.kharkov.ua (Oleksiy Dudnik), jan.gieseler@utu.fi (Jan Gieseler), hannu-pekka.hedman@utu.fi (Hannu-Pekka Hedman), heli.hietala@utu.fi (Heli Hietala), edward.haeggstrom@helsinki.fi (Edward Haeggström), petri.niemela@aalto.fi (Petri Niemelä), juhpe@utu.fi (Juhani Peltonen), jaan.praks@aalto.fi (Jaan Praks), rpunk@utu.fi (Risto Punkkinen), teansa@utu.fi (Tero Säntti), eino.valtonen@utu.fi (Eino Valtonen)margin achieved is about 5%. The full instrument response to protons and electrons is presented and the issue of proton contamination of the electron channels is quantified and discussed.

The Radiation Monitor (RADMON) on-board Aalto-1 CubeSat is an energetic particle detector that fulfills the requirements of small size, low power consumption and low budget. Aalto-1 was launched on 23 June 2017 to a sun-synchronous polar orbit with 97.