Assessing the impact risk of orbital debris on space tethers

Tethers are being proposed for a growing number of space applications. However, they may be particularly vulnerable to orbital debris and meteoroid impacts. In order to provide useful reference data for tether systems design, detailed analytical and numerical computations were carried out to assess the average impact rate of artificial debris and meteoroids. The specific geometric properties of tethers as debris targets, when compared to typical satellites, are discussed, and the results obtained are presented in tabular form, as a function of debris size and tether diameter. The computations were carried out for six circular orbits, spanning three altitudes (600, 800 and 1000 km) and two inclinations (30 and 50). Tether diameters in between 1mmand 2 cmand debris larger than 0.1mm were considered in the analysis. The collision risk of tethers with spacecraft and upper stages in orbit was estimated as well. In the debris interval and orbital regimes considered, artificial debris represent the dominant contributor to the impact rate. At 600 km and in the 0.1-10mm size range, the meteoroid and orbital debris impact rates are still comparable; however, at higher altitudes and in the 1-10 cm size range, meteoroids contribute 20-30 times less to the collision probability. The results obtained confirm that for single-strand tethers in low Earth orbit the probability to be severed by orbital debris and meteoroid impacts is quite significant, making necessary the adoption of innovative designs for long duration missions.