Radio Science

A new design for a very low frequency spaceborne radio interferometer



[1] The nontransparency and severe propagation effects of the terrestrial ionosphere make it impossible for Earth-based instruments to study the universe at low radio frequencies. An exploration of the low-frequency radio window with the resolution and sensitivity essential to meet the scientific objectives will necessarily require a dedicated satellite-based interferometer operating at these frequencies. Such missions have been proposed in the literature for about the past 15 years. Today, the steady and impressive advances in technology and computing resources have brought us to the brink of a quantum jump in the performance and capabilities of such missions, increasing their scientific desirability manyfold. This paper presents the concept design which emerged from a study to investigate the feasibility of a low-frequency satellite-based interferometer operating in the frequency range 0.1–40 MHz titled Preparation for Radio Interferometry in Space. In place of trying to stretch and adapt the existing solutions to the requirements of very low frequency interferometry, this study attempts to tailor a design to meet its specific needs. The salient features of the design are an onboard correlator to reduce the data volumes to be transmitted to the Earth by about 2 orders of magnitude, use of three orthogonal dipoles in place of two to achieve better polarization characteristics, direct digitization of the entire radio frequency band of interest allowing broadband observations, an overlap in the observing frequency range with upcoming ground-based instruments to aid in imaging and calibration, and an all-sky imaging capability. The most constraining bottleneck for the present design is the large intraconstellation telemetry requirement. It is expected that technological solutions to meet this requirement will be found in the near future as other formation-flying missions which share this requirement emerge.