Toward Optimisation of a Sub-Terahertz Spaceborne VLBI Mission

Very Long Baseline Interferometry (VLBI) provides the finest angular resolution of all astronomical observation techniques. However, observations with Earth-based instruments are approaching fundamental limits on angular resolution. These can only be overcome by placing at least one interferometric element in space. In this paper, several concepts of spaceborne VLBI systems are discussed, including TeraHertz Exploration and Zooming-in for Astrophysics (THEZA) and the Black Hole Explorer (BHEX). Spaceborne VLBI telescopes have some of the most demanding requirements of any space science mission. The VLBI system as a whole includes globally distributed elements, each with their own functional constraints, limiting when observations can be performed. This necessitates optimisation of the system parameters in order to maximise the scientific return of the mission. Presented is an investigation into how the impact of the functional constraints of a spaceborne VLBI telescope affect the overall system performance. A preliminary analysis of how these constraints can be minimised through optimisation of the spacecraft configuration and operation is also provided. A space-based VLBI simulation tool (spacevlbi) has been developed to model such missions and its capabilities are demonstrated throughout the paper. It is imperative that the functional constraints are considered early in the design of the future space-based VLBI systems in order to generate feasible mission concepts and to identify the key technology developments required to mitigate these limitations.