Abstract
The breakup of Hitomi (ASTRO-H) on 26 March 2016 is analysed. Debris from the fragmentation is used to estimate the time of the event by propagating backwards and estimating the close approach with the parent object. Based on this method, the breakup event is predicted to have occurred at approximately 01:42 UTC on 26 March 2016. The Gaussian variation of parameters equations based on the instantaneous orbits at the predicted time of the event are solved to gain additional insight into the on-orbit position of Hitomi at the time of the event and to test an alternate approach of determining the event epoch and location. A conjunction analysis is carried out between Hitomi and all catalogued objects which were in orbit around the estimated time of the anomaly. Several debris objects have close approaches with Hitomi; however, there is no evidence to support the breakup was caused by a catalogued object. Debris from both of the largest fragmentation events—the Iridium 33–Cosmos 2251 conjunction in 2009 and the intentional destruction of Fengyun 1C in 2007—is involved in close approaches with Hitomi indicating the persistent threat these events have caused in subsequent space missions. To quantify the magnitude of a potential conjunction, the fragmentation resulting from a collision with the debris is modelled using the EVOLVE-4 breakup model. The debris characteristics are estimated from two-line element data. This analysis is indicative of the threat to space assets that mission planners face due to the growing debris population. The impact of the actual event to the environment is investigated based on the debris associated with Hitomi which is currently contained in the United States Strategic Command’s catalogue. A look at the active missions in the orbital vicinity of Hitomi reveals that the Hubble Space Telescope is among the spacecraft which may be immediately affected by the new debris.Graphical abstract.
Highlights
To date, over 250 objects have broken up in Earth orbit (Johnson et al 2008; Flegel et al 2011)
Several all-on-all conjunction assessments are performed for epochs [23, 24] and 25 March 2016 and [1, 2] and 3 April 2016, i.e., excluding the erroneous two-line elements (TLEs). These results identify all objects with a close approach with Hitomi, and the whole catalogue of TLEs was downloaded each day between 20 March 2016 and 4 April 2016 to run the complete all-on-all conjunction assessment
The Union of Concerned Scientists (UCS) list about 120 active spacecraft for this region. As these orbits are below the current altitude of the Hitomi fragments, a close conjunction may only occur in the future when the drag-induced decay causes the debris to pass through the orbital altitude regime of the listed intact objects
Summary
Over 250 objects have broken up in Earth orbit (Johnson et al 2008; Flegel et al 2011). Application to Hitomi The osculating orbit at the instances before and after the breakup is required for the current analysis The former is obtained by propagating the last available TLE from before the event to the estimated event epoch 26 March 01:42 UTC using the Simplified General Perturbations 4 (SGP4) method. As the uncertainties associated with Hitomi’s true anomaly have not been assessed here, a definitive statement as to the absolute accuracy of the method would be premature Such an analysis requires knowledge of the accuracy of given orbit data which is not available for TLEs. the solutions for Δv are below 10 m/s in radial and in-track and below 33 m/s in cross-track for all valid solutions.
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