In this article, we present the main results of the feasibility study we have carried out about autonomous decision making on board an Earth-observing agile satellite, equipped with a cloud detection instrument. We explain the requirements in terms of autonomy. Then, we describe the online decision-making problem to manage on board, the reactive/deliberative architecture we used, the decision rules used by the reactive part, and the iterated stochastic greedy search used by the deliberative part. At each step, we try to justify the design choices we made by comparing them with other possible choices. Finally, we present results of experiments performed on offline and online realistic scenarios.