A newly designed Tissue Equivalent Proportional Counter (TEPC) has been developed for the CubeSat mission, SIGMA (Scientific cubesat with Instruments for Global Magnetic field and rAdiation) to investigate space radiation. In order to test the performance of the TEPC, we have performed heavy ion beam experiments with the Heavy Ion Medical Accelerator in Chiba (HIMAC), Japan. In space, human cells can be exposed to complex radiation sources, such as X-ray, Gamma ray, energetic electrons, protons, neutrons and heavy charged particles in a huge range of energies. These generate much a larger range of Linear Energy Transfer (LET) than on the ground and cause unexpected effects on human cells. In order to measure a large range of LET, from 0.3 to 1,000 keV/μm, we developed a compact TEPC which measures ionized particles produced by collisions between radiation sources and tissue equivalent materials in the detector. By measuring LET spectra, we can easily derive the equivalent dose from the complicated space radiation field. In this HIMAC experiment, we successfully obtained the linearity response for the TEPC with Fe 500 MeV/u and C 290 MeV/u beams and demonstrated the performance of the active radiation detector.