Periodic Reporting for period 2 - ESBO DS (European Stratospheric Balloon Observatory Design Study) Reporting period: 2019-09-01 to 2021-07-31 Summary of the context and overall objectives of the project Without the protection by the Earth’s atmosphere, there would be no life on Earth – for most astronomical measurements, however, the atmosphere is an obstacle. Observers thus started early to move their instrument as high above the perturbing atmospheric layers as possible. Spacecraft provide access to optimal observing conditions in this endeavour. However, they are not very accessible after launch and comparably expensive. For some astronomical applications, though, particularly in the far infrared wavelength region and in some parts of the ultraviolet, it is sufficient to take a smaller step up – into the stratosphere.The ESBO DS (European Stratospheric Balloon Observatory – Design Study) project took a first step towards making the excellent observing conditions at an altitude of 30 to 40 km available to a broad scientific community. The explicit goal of the endeavour is to create a European research infrastructure featuring regular flights, exchangeable instruments, and open access to observation time. If successful, ESBO DS will eventually reduce the cost of cutting-edge astronomical observations considerably and enable new insights into the formation of stars, planetary systems, and life. In practice, the work on the 3-year pilot project was focused on two immediate objectives:1. On the development and construction of a prototype gondola and telescope, which shall perform technology tests as well as deliver first scientific results during its maiden flight with a newly developed UV-instrument.2. On the development of a strategy for the long-term establishment and operation of the observatory – including the study of the technical feasibility of balloon flights with larger telescopes, particularly of the 5 m aperture class for far infrared observations. Work performed from the beginning of the project to the end of the period covered by the report and main results achieved so far ESBO DS followed a two-tier approach throughout the entire project: on the one side, the development and construction of a prototype astronomical balloon gondola, including a 50 cm-aperture telescope with a newly-developed UV instrument; and on the other side, the conceptual design of a long-term, balloon-based research infrastructure, prominently including a flight system suitable for carrying a next-generation, 5-m aperture class telescope for far infrared observations. On these two tiers, the following work was performed:Work performed on the infrastructure concept study:- Science needs for the mid- and long-term to be addressed by the infrastructure were reviewed and defined;- The feasibility and benefit of innovative infrastructure technologies, including super pressure balloons, novel flight trajectories, and soft landing systems were studied for the infrastructure;- Particularly for the balloon gondola / bus, subsystems that could be scaled & built in a modular fashion were studied;- A conceptual technical design was carried out for three different flight platforms and associated ground systems (including a 0.5 m aperture telescope for UV observations, a 1.5 m aperture telescope for near infrared applications, and a 5 m aperture telescope for far infrared applications);- Different operations and governance options for a long-term astronomical balloon observatory infrastructure were studied.Work performed on the prototype development:- Detailed requirements for the prototype were derived from both the technology demonstration perspective as well as the perspective of a later scientific exploitation of the prototype (primarily for studying variable hot compact stars in the galactic plane);- Performance simulators for several of the prototype components were developed, including the newly-developed UV-instrument, the secondary visible light instrument (as part of the image stabilization system), the star tracker for guiding, and the Image Stabilization System;- A thermal simulation model for the prototype at float altitude (~40 km ) was developed to support the design of the thermal control system;- Test procedures for environmental qualification tests of components for stratospheric balloons were developed;- A highly precise Image Stabilization System for stratospheric balloons was developed and built;- A modular and scalable balloon gondola and service subsystems, including payload support systems, were developed and built.Results achieved:- Conceptual design for a regularly operating balloon-borne astronomical observatory finished;- Prototype balloon gondola for astronomical observations in the UV, including a 50 cm aperture telescope, a new-generation UV microchannel plate detector, and a highly precise gondola pointing and image stabilization system manufactured.Exploitation and dissemination activities carried out:- Presentation of project results at five conferences;- (Co-)organization of workshops on balloon- and air-borne astronomy;- Presentation of results in an Executive Summary and a Development Roadmap;- Dissemination of results through direct contact with European funding and political bodies.Further planned exploitation and dissemination activities:- Test flight of the prototype gondola and telescope preferably in 2022;- Prototype platform and telescope available for science flights with the microchannel plate detector or other instruments thereafter;- Preparation of a White Paper;- Further development of the infrastructure based on the prepared development roadmap. Progress beyond the state of the art and expected potential impact (including the socio-economic impact and the wider societal implications of the project so far) ESBO DS aims at developing and establishing a dedicated, regularly flying and community-accessible astronomical observatory based on stratospheric balloons, which currently does not exist. If this effort succeeds, it will make space-like observation conditions available to a much larger part of the astronomical community than currently possible, at a significantly lower cost and on significantly shorter timeframes than what comparable space missions would require. In particular, the far infrared astronomy community would benefit from the envisioned next-generation platform with an unprecedented telescope size for this wavelength range, which would make it possible to look into processes of star formation and molecular evolution in our universe in more detail. Having such a unique facility in Europe will foster innovation in scientific findings, methods, and instrumentation and make the European research area more efficient and competitive. The required technological developments for this infrastructure, particularly with regard to high-performance balloons, astronomical balloon gondolas, optical stabilisation systems, and large, light-weight telescopes will strengthen European industry in the respective fields. CAD model of the current balloon gondola design for the ESBO DS prototype mission "STUDIO" The ESBO DS project team during the Kick-Off meeting on 21/22 March 2018 in Stuttgart, Germany.