MIMOSA microsatellite is sixth satellite of the Czech Republic and it is dedicated to yield new experimental data on total atmosphere density of the upper ionosphere. The complex verification of total density analytical model (TD88) is the main project objective. The only payload on board is a highly sensitive accelerometer MACEK. Moreover, designed accelerometer accuracy(10(-9) ms(-2)) enables to study a weak forces like reflected solar radiation pressure or pressure of the thermal radiation dissipated by the Earth. Presented paper describes payload properties, satellite and subsystem features, budgets and mission performance. The project is at C/D phase presently. The launch is scheduled for the second half of 2000 and expected lifetime is at least two years, (C) 2000 Elsevier Science Ltd. All rights reserved.