# A Balloon-Borne Very Long Baseline Interferometry Experiment in the Stratosphere: Systems Design and Developments

## TL;DR

This paper presents the design and development of a balloon-borne VLBI system aimed at high-frequency radio observations in the stratosphere, enhancing baseline coverage and reducing atmospheric interference for astrophysical research.

## Contribution

It introduces a novel balloon-borne VLBI platform with system design details, demonstrating feasibility for high-frequency radio interferometry in the stratosphere.

## Key findings

- Successful development of the balloon-borne VLBI flight model
- Potential for improved uv-coverage with balloon-based stations
- Feasibility of high-frequency interferometry in the stratosphere

## Abstract

The balloon-borne very long baseline interferometry (VLBI) experiment is a technical feasibility study for performing radio interferometry in the stratosphere. The flight model has been developed. A balloon-borne VLBI station will be launched to establish interferometric fringes with ground-based VLBI stations distributed over the Japanese islands at an observing frequency of approximately 20 GHz as the first step. This paper describes the system design and development of a series of observing instruments and bus systems. In addition to the advantages of avoiding the atmospheric effects of absorption and fluctuation in high frequency radio observation, the mobility of a station can improve the sampling coverage (`uv-coverage') by increasing the number of baselines by the number of ground-based counterparts for each observation day. This benefit cannot be obtained with conventional arrays that solely comprise ground-based stations. The balloon-borne VLBI can contribute to a future progress of research fields such as black holes by direct imaging.