The overarching theme of the Orbiting Astronomical Satellite for Investigating Stellar Systems (OASIS), an Astrophysics MIDEX-class mission concept, is Following water from galaxies, through protostellar systems, to Earth's oceans. The OASIS science objectives address fundamental questions raised in "Pathways to Discovery in Astronomy and Astrophysics for the 2020s (National Academies of Sciences and Medicine, Pathways to Discovery in Astronomy and Astrophysics for the 2020s, 2021, https://doi.org/ 10.17226/26141, https://www.nap.edu/catalog/26141/pathways-to-discovery-in-astronomyand-astrophysics-for-the-2020s)" and in "Enduring Quests and Daring Visions" (Kouveliotou et al. in Enduring quests-daring visions (NASA astrophysics in the next three decades), 2014, arXiv:1401.3741), in the areas of: 1) the Interstellar Medium and Planet Formation, 2) Exoplanets, Astrobiology, and the Solar System, and 3) Galaxies. The OASIS science objectives require space-borne observations of galaxies, molecular clouds, protoplanetary disks, and solar system objects utilizing a telescope with a collecting area that is only achievable by large apertures coupled with cryogenic heterodyne receivers. OASIS will deploy an innovative 14-meter inflatable reflector that enables >16× the sensitivity and >4× the angular resolution of Herschel, and complements the short wavelength capabilities of James Webb Space Telescope. The OASIS state-of-the-art cryogenic heterodyne receivers will enable high spectral resolution (resolving power > 10 6) observations at terahertz (THz) frequencies. These frequencies encompass far-IR transitions of water and its isotopologues, HD, and other molecular species, from 660 to 63 µm that are otherwise obscured by Earth's atmosphere. From observations of the ground state HD line, OASIS will directly measure gas mass in a wide variety of astrophysical objects. Over its one-year baseline mission, OASIS will find water sources as close as the Moon, to galaxies ∼4 billion light years away. This paper reviews the solar system science achievable and planned with OASIS.Read less <