SPINOR: Exploring the sub-30 MHz Radio Sky in Fine Resolution for the First Time

The SPINOR (Spinning Past-Ionospheric Network for Observation of Radio) program is developing tunable, narrow-band, resonant antenna networks for observing radio frequencies below 30 MHz. This frequency range has not been studied since exploratory missions in the 1960s due to ionospheric blockage requiring large space-based missions, but it offers unprecedented scientific observations. These include capturing direct observations of exoplanet magnetospheres and their interactions with solar magnetic fields, advancing heliophysics and space weather monitoring, exploring solar system magnetospheres and lightning, and mapping the redshifted 21 cm hydrogen line from the early universe. Most existing proposals to fill this observational gap employ large constellations of satellites for interferometry due to the long wavelengths. For example, GO-LoW is an MIT Haystack Observatory proposal for an interferometric mega constellation of 3U CubeSats with vector sensors. Its electrically short sensors enable simultaneous full-sky fine spatial and spectral resolution mapping, but their low sensitivity requires a very large constellation size to observe faint sources. SPINOR consists of spinning, deployable tethers with adjustable lengths to produce high-sensitivity maps across multiple resonant frequencies. This approach enables groundbreaking observations with a smaller constellation size compared to traditional interferometric designs. By leveraging modern super-resolution algorithms and a stable rotating beam pattern, SPINOR offers repeated all-sky coverage and unbiased surveys of the radio sky. Several technologies require demonstration, including low-noise readout electronics, tether deployment, precise attitude determination during slew, and deconvolution algorithms. High-altitude balloons, sounding rockets, and LEO, GTO, and cislunar CubeSats will be used to demonstrate this program’s feasibility.