Capella: A Space-only High-frequency Radio VLBI Network Formed by a Constellation of Small Satellites

ABSTRACT :
We present Capella, a tentative design of a space-only VLBI system. Using four small (<500 kg) satellites in two orthogonal polar low-Earth orbit planes, and single-band heterodyne receivers operating at frequencies around 690 GHz, the interferometer is able to achieve angular resolutions of approximately 7 microarcsec. Capella will be able to address a range of science cases, including: photon rings around supermassive black holes; the acceleration and collimation zones of plasma jets emitted from the vicinity of supermassive black holes; the chemical composition of accretion flows into active galactic nuclei through observations of molecular absorption lines; mapping supermassive binary black holes; the magnetic activity of stars; and nova eruptions of symbiotic binary stars. With its ability to obtain high-resolution, low-sensitivity maps of selected targets, Capella will be complementary to ALMA's ability to obtain high-sensitivity, low-resolution data.