Speaker
Description
Very Long Baseline Interferometry (VLBI) combines radio telescopes across vast distances to image astrophysical objects with exceptional angular resolution. Ground-based VLBI is inherently limited by the Earth's diameter and suffers from increased atmospheric opacity and phase fluctuations at higher frequencies. Balloon-borne stations, which operate above more than 99% of the atmosphere, offer an innovative intermediate step between ground-based observatories and costly space missions, facilitating observations at higher frequencies. Additionally, since balloon-borne VLBI stations move, they provide superior uv coverage by sampling regions of the uv plane that would otherwise remain empty due to the fixed positions of ground-based telescopes.
The Balloon-borne VLBI Experiment (BVEX), scheduled for launch from Timmins, Ontario in August 2025, aims to address these limitations by demonstrating a viable VLBI station operating at the K-band frequency range (21-23 GHz). BVEX incorporates a state-of-the-art Radio Frequency System-on-Chip (RFSoC) backend, developed using the CASPER toolflow, which includes a high-resolution spectrometer and a low-power 100 GbE data storage system, crucial for handling the demanding data rates of VLBI.
A significant technical challenge for balloon-borne VLBI lies in ensuring precise position and attitude tracking at millimeter accuracy while operating under the extreme environmental conditions of the stratosphere. To address synchronization and phase stability, BVEX employs an ultra-stable Oven-Controlled Crystal Oscillator (OCXO) as its primary timing reference, housed within a temperature-controlled pressure vessel to maintain optimal operating conditions.
This talk will outline BVEX's instrumental design, including a single-sideband heterodyne receiver with a particular focus on the RFSoC-based backend system. I will also detail the specific engineering challenges encountered and solutions devised for high-altitude operations, timing synchronization, and position tracking. BVEX serves as a critical proof-of-concept for balloon-borne VLBI, demonstrating the feasibility of stratospheric radio astronomy and paving the path for high resolution and uv coverage capabilities in future VLBI arrays such as ngEHT or the GMVA(Global mm-VLBI Array).
