Impact on mission design due to collision avoidance operations based on TLE or CSM information Noelia Sánchez-Ortiz a,n , Raúl Domínguez-González a , Holger Krag b , Tim Flohrer b,1 a DEIMOS Space S.L.U., Ronda de Poniente 19, 212, Tres Cantos, Madrid 28760 Spain b ESA/ESOC, Space Debris Office, Robert-Bosch-Str.5, 64293 Darmstadt, Germany article info Article history: Received 8 June 2014 Received in revised form 10 March 2015 Accepted 25 April 2015 Available online 6 May 2015 Keywords: Space debris Collision avoidance approach TLE CSM False alarms Mission design abstract Collision avoidance manoeuvres are considered for mission design and fuel budget allocation, and may have a relevant impact in particular orbital regimes. Current operations for collision avoidance are based on Two-Line Elements (TLE) orbital data or the Conjunction Summary Message (CSM) data. This paper presents the most suitable approach for collision avoidance for several mission types when operations are based on TLE or CSM data, with a detailed analysis of the impact of the orbital accuracy of catalogue data and warning time-to-event on mission design in terms of fuel budget for collision avoidance activities and operational constraints imposed by the avoidance manoeuvres. & 2015 IAA. Published by Elsevier Ltd. All rights reserved. 1. Introduction Among the activities to be considered for mission design and fuel budget allocation, the approach for collision avoid- ance activities is addressed and may have a relevant impact on the mission service interruption and fuel budget allocation for some particular orbital regimes. Current operations for collision avoidance are based on Two-Line Elements (TLE) orbital data provided by USSPACECOM (unique public catalo- gue of orbiting objects) or the data provided by the opera- tional JSpOC service raising collision event warnings on the basis of the Conjunction Summary Message (CSM) data format, now superseded by the CCSDS-compliant Conjunction Data Messages (CDM). The most suitable approach for colli- sion avoidance for a particular mission will be different, if the operations are based on TLE or CSM/CDM data, mainly due to the knowledge of the orbital accuracy of those data sets. The uncertainty associated with the miss distance is one of the most relevant aspects in the collision risk computation. Most of the algorithms computing collision risk approach the problem by translating the uncertainty of the orbit knowledge to the uncertainty of the miss distance. This determines the probability of having a real encounter by integrating this uncertainty into the projected collision volume of the two colliding objects. Therefore, it determines the operator capa- city to identify risk events, discard false alerts and finally, avoid an eventual encounter. Manoeuvres are normally applied when the computed risk is larger than an Accepted (or Acceptable) Collision Probability Level (ACPL) for the mission. This ACPL value should be carefully defined con- sidering the capabilities to reduce the risk (derived from the accuracy of the catalogues). One of the main problems associated with the computa- tion of the collision risk derives from the lack of knowledge on the orbital data accuracy. The TLE catalogue is not very accurate, and additionally, it does not provide an estimation Contents lists available at ScienceDirect journal homepage: www.elsevier.com/locate/actaastro Acta Astronautica http://dx.doi.org/10.1016/j.actaastro.2015.04.017 0094-5765/& 2015 IAA. Published by Elsevier Ltd. All rights reserved. n Corresponding author. Tel.: þ34 918063450; fax: þ34 918063451. 1 Copyright of Deimos Space S.L.U., which is releasing the paper to the American Astronautical Society to publish the paper in all forms. Acta Astronautica 116 (2015) 368–381