In this work a new single anode spherical tissue-equivalent proportional counter (TEPC) was developed for mixed field radiation dosimetry. The approach used was to divide the cathode into several rings with different thicknesses and adjust the potential difference between each ring and the anode to produce an electric field that is nearly constant along the length of the anode. A-150 tissue-equivalent plastic is used for the detector walls, the insulator material between the cathode rings is low-density polyethylene, and the gas inside the detector is propane. The detector, along with the charge sensitive preamplifier, is encased in a stainless steel vacuum chamber. This 1.8-cm-diam TEPC provides low electronic noise, a gas gain of 550 at 782 V, good spectral resolution (26 keV/m), and a full-width at half-maximum value of 17%. This spherical TEPC detector system will improve the accuracy of dosimetry in space and as a result improve radiation safety for astronauts.