ESA UNCLASSIFIED – Releasable to the Public Session 7: Science and engineering lessons from the de- orbiting and re-entry phase C. Pardini (1), H. Krag (2) (2) Institute of Information Science and Technologies, National Research Council of Italy (2) European Space Agency, Space Debris Office

ESA UNCLASSIFIED – Releasable to the Public GOCE and Re-entry Science Ca 70% the atmospheric re-entries occur in an uncontrolled way – Roughly 100 tons per year – 20-40% of the mass of larger structures typically survives Prediction accuracy of re-entry epoch and location is poor – Rule of thumb: prediction accuracy ≈ ± 20% of remaining prediction time Future missions will have to respect limits for the on-ground risk – Very constraining requirement with potentially large system impacts – Validation by simulation (confidence in the simulation needs to be high) After the loss of drag-free mode, GOCE became a reference object for (quasi) uncontrolled re-entries

ESA UNCLASSIFIED – Releasable to the Public Predicting Uncontrolled Re-entries Atmosphere model ( km) Solar and geomagnetic activity forecasts Attitude motion evolution (and motion measurements) Drag coefficient Quality of orbit determination results using radar ranging Effect of sparse ranging data GPS and ILRS reference Attitude data Drag levels ! GOCE data

ESA UNCLASSIFIED – Releasable to the Public Understanding Atmospheric Break-Up Altitude Aerodynamically induced torques dominate Peak Heating Peak deceleration Initial Heating ≈ 200km ≈ 120km ≈ 80-45km GPS and ILRS reference Attitude torques Drag levels Payload temperature sensors ! GOCE data Initial fragmentation ≈ 95km

ESA UNCLASSIFIED – Releasable to the Public Seed Questions To which degree will an upgraded atmospheric density models between 100km and 200km improve the prediction results? What can we learn in the area of ground-based measurements of uncooperative low altitude targets? What can we learn in terms of understanding how accurate our predictions are? What can we expect to learn from recorded component temperatures? To which degree are the results obtained with GOCE transferable to other uncontrolled re-entries? – Similarity to re-entering upper stages? Which kind of future data might be of interest for a further refinement of re-entry predictions?