Radar-based Re-Entry Predictions with very limited tracking capabilities: the GOCE case study

Abstract

The problem of the re-entry predictions of GOCE has been deeply investigated in the literature, due to the large amount of data, mainly radar and GPS, available until re-entry. The accurate GPS and attitude measurements are used to compute a precise reference orbit for the three weeks of decay, and to extrapolate the ballistic coefficient evolution of the object. In previous works, the capabilities of radar-based solutions for the re-entry predictions of GOCE and of similar objects were investigated, focusing on the german TIRA radar. In this work we have performed additional analysis, focusing on the northern european radar EISCAT-UHF, located in Troms\o, Norway. This sensor, conceived for atmospheric studies, has recently been considered for space debris applications. Due to its limited tracking capabilities, we are interested in testing its effectiveness in supporting re-entry predictions. We have simulated reliable re-entry prediction scenarios, with different availability of data from EISCAT and TIRA. The main conclusion is that, provided a suitable amount of observations, EISCAT-based re-entry predictions are comparable to TIRA-based, but also to GPS and TLE-based, corresponding ones. In general, EISCAT is not able to determine an orbit with the same accuracy of TIRA, but the results are equivalent in terms of re-entry predictions, if we consider the relevant parameters involved and their effects on the re-entry time. What is very important is the difficulty in predicting atmospheric and attitude significant variations in between the current epoch and the actual re-entry. Thus, it is not easy to keep the accuracy of predictions much lower than 10% of the residual lifetime, apart from cases with constant area to mass ratio, and low atmospheric variations with respect to the models. An experiment with real data is presented for the object 2012-006K, with consistent results.