Abstract: Abstract Aiming at the problems of aerodynamic drag and disturbance torques acting on the very low Earth orbit (ULEO) spacecraft during long-term on-orbit operation, an overall design scheme combining a slender main body configuration for drag reduction and down-swept solar arrays for stability enhancement is proposed. The test particle Monte Carlo (TPMC) method is adopted to optimize the spacecraft aerodynamic layout, which finalizes the outer shape of Qiankun-1 (Qiankun-1: QK-1), China’s first long-duration VLEO technology demonstration satellite. On-orbit verification of aerodynamic drag and attitude stability is also completed. The results show that with a constant volume of the spacecraft main body, the aerodynamic drag first decreases and then increases as the slenderness ratio rises. The minimum drag occurs at a slenderness ratio of 14.64. This optimal slenderness ratio is applicable to the gas-surface interaction (GSI) accommodation coefficient ranging from 0.8 to 1 and orbital altitudes between 180 km and 300 km. Based on the optimal slender main body configuration, down-swept solar arrays are adopted to realize self-trimming of the spacecraft under the constraints of payload arrangement, structural strength and power supply performance. The final configuration of QK-1 is determined according to thermal dissipation requirements. When the GSI follows the fully diffuse reflection model, the drag predicted by the TPMC method is in best agreement with the on-orbit measured data at orbital altitudes of 300 km and 268 km, with a relative error of approximately 12%. It is preliminarily indicated that the on-orbit GSI process is close to fully diffuse reflection. Special static stability tests of QK-1 without control at 300km demonstrate that the satellite remains stable when the sideslip angle is ± 180° and the angle of attack ranges from -48° to 64°, which verifies the effectiveness of the proposed self-trimming design. The static stability design of QK-1 is validated within the predicted attack angle stability range of -100° to 80°.