While chemically-propelled spacecraft can reach geostationary orbit within days after deployment in GTO or supersynchronous transfer orbits (SSTO), electric orbit raising (EOR) typically takes several months. This extended transfer duration provides significant propellant savings but introduces the challenge of safely guiding the spacecraft multiple times through densely populated orbital regions where both space debris and active spacecraft pose a threat to mission safety. Detecting potential conjunctions – along with mitigating the associated collision risk – thus becomes an essential aspect of mission operations during the transfer phase. A dedicated pre-launch collision risk assessment, as well as continuous monitoring during the transfer, is therefore essential.

This paper presents COLA SPACE, a collision-risk assessment tool developed at DLR to ensure reliable and comprehensive risk analysis for EOR trajectories. It supports both mission preparation and in-flight collision risk monitoring throughout the EOR phase. The study uses a representative smallGEO platform as a reference spacecraft. The platform characteristics served as input for generating multiple EOR trajectories representing different start times distributed across a day. COLA SPACE can ingest these transfer trajectories in the form of CCSDS Orbit Ephemeris Messages (OEMs). Each trajectory spans 34 weeks. To enable screening against a Special Perturbations Catalogue (SPCAT) snapshot – typically containing approximately 28,000 objects and covering a one-week period – the trajectories were segmented into weekly snippets and their time tags were adjusted accordingly. Each snippet was treated as a primary object and screened in a many-versus-all analysis against all SPCAT secondary objects.

To perform collision risk assessment, COLA SPACE consists of three core modules: (1) a filter module that pre-eliminates object pairs incapable of close approaches due to their orbital geometry; (2) a covariance module that assigns uncertainty information to the secondary ephemeris; and (3) a screening module that computes the miss distance (MD), time of closest approach (TCA), and probability of collision (PoC). Parallel processing is applied to reduce computational time. The tool’s graphical outputs display, for each transfer week, the number of detected conjunctions and the corresponding highest PoC and minimum MD. Additionally, COLA SPACE quantifies the expected number of conjunctions above user-defined PoC thresholds, provides the cumulative collision probability, and assesses expected collision-avoidance manoeuvre statistics.

Using the smallGEO platform as a representative test case with a transfer duration of about 240 days, COLA SPACE demonstrates its capability as a reliable, high-fidelity risk assessment tool for electrically raised GEO transfer trajectories. Across all transfers, 33% of the cases included at least one conjunction with a PoC above 1e-6, with critical events predominantly associated with expected orbital regimes such as LEO-crossing objects, MEO spacecraft and GEO-proximity resident space objects. For all but one transfer, the cumulative PoC remained well below 1e-4. In the remaining case, the cumulative PoC reached 1.6e-4, driven by a single critical event with a PoC of 1.5e-4 and a miss distance of 213 m, which was the only event exceeding a PoC of 1e-4.

Beyond mission preparation, COLA SPACE also supports in-flight operations by providing continuous collision-risk monitoring throughout the mission phases, with the highest screening frequency in the first weeks of the EOR phase. In contrast to ESA’s DRAMA/ARES – which relies on the MASTER population model and provides statistically oriented long-term assessments – COLA SPACE uses an SPCAT-based, high-resolution snapshot of the actual space-object environment and its dynamics. This enables detailed, object-specific conjunction analyses and makes the tool suitable for pre-launch assessments to identify early-warning close approaches and realistic collision probabilities. As an object-specific, SPCAT-based collision-risk assessment tool, COLA SPACE supports both pre-operational analysis and in-flight monitoring, provides a fast and high-fidelity capability for collision-risk evaluation, and contributes to compliance with ESA and ECSS debris-mitigation requirements for upcoming missions.