In this report, the preliminary design and sizing of a long-duration stationary Venus lander named KYTHERA is performed. In contrast with previous Venus landers, KYTHERA is designed to survive on the hellish Venusian surface for at least 200 Earth days to study long-term atmospheric and seismic phenomena. In addition to the chemical analysis of the atmosphere and seismic measurements, the lander is capable to do 20 individual chemical analyses of surface rock material, using Laser-Induced Breakdown Spectroscopy (LIBS) and Raman spectroscopy. To meet the duration goal, the lander is actively cooled, using a Stirling-generator-cooler chain to remove heat from the inside, powered by the radioactive decay of plutonium. The corrosion and heat resistant structure is sized to survive 120 Earth G-s of acceleration during entry and a landing impact speed of 8.5 m/s, as well as 93 bars of pressure difference at 460 °C. To maximize insulation efficiency, the internal structure of the lander (the coldbox) is separated from the outer shell (the hotbox) by 3.5 cm of vacuum. Although the mission is expected to fit within the required mass budget, the cost is likely to be exceeded, as the power system is more expensive than initially anticipated. The lander weighs 350 kg and is expected to cost around 300 million euros.