We propose a university-class micro-satellite "Hu-ring" to localize
and study gamma-ray bursts. The primary mission of "Hu-ring" is to
localize gamma-ray bursts with an 10 arcmin accuracy in real time, and
transmit promptly the coordinates to the ground. Although many of its
mission concepts are modeled after HETE-2, use of avalanche
photodiodes (APDs), innovative photon detector device, make it
possible to further reduce the size and the mass of the satellite. We
designed "Hu-ring" within a size of 50 cm cube and a weight limit of 50 kg, so that it can be launched as a piggy-back payload of the Japanese H-IIA Launch Vehicle. The satellite is spin-stabilized, and has a half-sky field of view centered on the anti-sun direction. A set of scintillation counters equipped with rotation modulation collimators are employed for localization of GRBs. We also measure the soft/medium X-ray spectra of GRBs using APDs as a direct X-ray photon detectors. These two kinds of instruments cover the 0.5--200 keV energy range. The satellite bus is designed mostly with commercially available components in order to reduce the cost and the lead time. Following the HETE-2 model, in order to receive the prompt burst alerts it is designed to rely on a global network of receive-only low-cost ground stations, which may be hosted at research instutions with a small footprint. We performed analyses in many aspects: mechanical and thermal design of the satellite bus, attitude control simulations, power budget, ground contact schedule and downlink capacity, etc. We verified that the mission goal can be achieved with this proposed design philosophy.