This paper presents the design and development of a Silicon Carbide (SiC) technology-based Non-Inverting Buck-Boost (NIBB) DC-DC power conversion unit for harsh space environment application with very high temperature (HT) (>300° C) and high radiation level. This work evaluates the capability of SiC devices, comprising of LDMOSFET (Lateral Diffused MOSFET) for high temperature (>300° C) power electronics. The temperature-dependent characterization of relevant switching device parameters such as channel resistance, device junction capacitances is performed through device modeling and simulations. The selection of critical passive components of the power converter is done through rigorous characterization of their performance metrics such as capacitance, inductance, leakage current, etc. under influence of increasing operating temperature. In this work, we designed and fabricated a proof-of-concept of NIBB DC-DC converter using the fabricated SiC MOSFETs that are demonstrated to operate at 300°C ambiance. It is designed to provide a 15A output load and convert the input side battery voltage levels of 2SV, 120V, and 160V to a configurable output voltage from 30V to 48V, used as the standard for NASA space missions. Results at 300° C environment report a peak efficiency of 92.5% at 450W load and 100kHz switching frequency, which validates the developed converter architecture to be a suitable candidate for high-frequency HT power conversion.