The National Environmental Satellite, Data, and Information Service (NESDIS) acquires and manages the Nation\u27s operational environmental satellites. NESDIS environmental satellite observations support a variety of civil and military environmental monitoring missions, including weather and climate prediction. A key input to weather forecast and climate models are atmospheric sounder observations from polar-orbiting satellites. These satellites are traditionally large, complex, and expensive, and take several years to design and build. The community must look for ways to reduce the cost and complexity of environmental satellites while meeting weather and climate sensing needs. This paper describes a new IR sounder concept that significantly reduces the size, mass, complexity, and consequent costs. This is accomplished through higher spectral resolution and the use of new large-area focal plane arrays, combined with novel dispersive optical design. In this design, one spectrometer with one FPA is required to perform both temperature and humidity sounding by imaging both bands onto the same FPA with an order sorting filter to separate the two bands. This paper details the design of the sensor and validation of sensor noise performance. Additionally, a thermal and spacecraft design are discussed to show the feasibility of a small-satellite scale instrument