This paper studies the requirements for a small constellation of satellites to perform measurements of the magnetic field of the Earth and a payload and boom design for such a mission is discussed. After studying communication, power and mass requirements it is found that it is feasible to develop a 10 x 10 x 30 cm(3) satellite with a mass of about 2.5 kg, which can fulfill such a mission. We also study the feasibility of controlling a constellation of such small satellites by means of air drag by extracting one or more flaps. It is found that it is indeed possible, but for best performance it is limited to altitudes around 450 to 550 km, depending on the time of launch with regard to the solar sunspot cycle.