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The obvious advantages of small spacecraft - their lower cost structure and the rapid development schedule - have enabled a large number of missions in the past. However, most of these missions have been focused on Earth observation from low Earth orbits. In 2006, the Small Spacecraft Division at the NASA Ames Research Center began the development of the Modular Common Bus, a spacecraft capable of delivering scientifically and technically useful payloads to a variety of destinations within 0.1 AU around the Earth. The core technologies used in the Common Bus design are a composite structure with body-mounted solar cells, an integrated avionics unit, and a high performance bipropellant propulsion system. Due to its modular approach, the Common Bus can be adapted to fit specific mission needs while still using a standardized and qualified set of components. Additionally a number of low cost launch vehicles are supported, resulting in overall mission costs of around $150M including the launch vehicle but excluding the science payloads. This significant reduction in cost and the shorter development time would enable NASA to conduct more frequent exploration missions within its budget and timeframe constraints, compared to the status quo. In this paper the suitability of the Common Spacecraft Bus for four different exploration scenarios is analyzed. These scenarios include a lunar orbiter, a lunar lander, a mission to a Sun-Earth Libration Point, and a rendezvous mission to a Near Earth Object. For each scenario, a preliminary design reference mission is developed and key design parameters for the spacecraft are determined.

This paper analyses the ability of small, low cost spacecraft to deliver scientifically and technically useful payloads to lunar orbit and the lunar surface, in particular precursor mapping, infrastructure and in-situ resource utilization functions, that are necessary prior to human return as part of the US Vision for Space Exploration. It is based upon a technical study of the NASA-Ames Research Center’s Small Spacecraft. Following an overview of the generalized capabilities of small spacecraft in comparison to the objectives of the robotic lunar exploration program, the paper documents the mission planning (including trajectory, launch stack and timeline), and overall spacecraft design (including mass budget, structure, propulsion, thermal, electrical power, descent guidance, navigation and control, and telecommunications) for a lunar lander mission. The study shows that spacecraft subject to the constraints laid out, in particular within a budget of < $100 Million and which can be launched on one of the next generation affordable launch vehicles such as Falcon-1 or Minotaur-V, can deliver payloads of 5-50 kg to the lunar surface or 10-200 kg payload to lunar orbit. The payloads carried would be capable of covering most of the functions of lunar missions that are needed prior to human arrival, as identified in NASA’s Lunar Robotic Architecture Study, with the exception of the bulk ISRU tasks of the ‘Lander Rover’ (In-situ Resource Utilization (ISRU)) mission. The key advantages of smaller spacecraft are reduced cost and schedule.