## 1 Introduction
This project was mainly developed for public engagement and outreach purpose to stimulate the public's interest in planetary and space sciences [10]. The virtual \"Thinking Journey to Mars\" program was developed using the MGS and the Mars Pathfinder data in a 3D VR system to educate the high-school students in Israel. The program helped students to visualize the abstract and alien landscapes with images, animations and simulations [11]. Other educational virtual environments to support the teaching of planetary phenomena were introduced in [12, 13]. In addition, several computer-based 3D VR simulators were developed for testing, validation and operation of planetary rovers. A detailed summary of the development of robotic exploration systems was given in [14]. VEVI (Virtual Environment Vehicle Interface, [15]) was the earliest robotic operational system developed since 1990s. Viz [14] was a visualization tool designed for the Mars Polar Lander mission based on previous experience with VEVI, MarsMap (for Mars Pathfinder mission, [16]), C-Map (the Chernobyl Mapping System, [17]), and VDI (Virtual Dashboard Interface, [18]). Viz was further customized for VIPER (Virtual Intelligent Planetary Exploration Rover, [19]). A 3D VROS (Virtual Rover Operation Simulator, [20]) and RSVE (Rover Simulation Environment [21]) were also developed recently by research groups in China. A Virtual Astronaut (VA) has been developed for scientific exploration at the Geosciences Node of NASA's Planetary Data System (PDS). Unlike the systems for the rover simulation, education, or outreach purpose as introduced above, the major objective of the VA is to develop a precise, highly-detailed, scientifically accurate 3D virtual reality environment that allows users to not only view observations made by a rover from the rover's perspective, but also allows them to view the scene and data from any perspective they want. In effect, the VA allows scientists to view a location of another planet in a manner similar to the way geologists would investigate the area if they were actually present there. The VA tool also combines images and topographic data obtained from orbital spacecraft with the rover-based observations to provide a regional context to the area being investigated by the rover. The VA is targeted at the planetary science community and is designed to run as a desktop application or within a web browser. An initial version of the VA was built for the MER Opportunity's campaign at Santa Maria Crater on Mars. Figure 1 presents a virtual view of the VA with multiple image mosaics overlaid on a digital elevation model. The functionality and features of the VA evolved during design and development based on testing and feedback from many potential science users. Other versions of the VA are planned for Opportunity's exploration of Endeavour Crater, including several areas of its rim along Cape York, and selected areas studied by the Mars Science Laboratory rover. In this paper we describe the general approach and challenges for building the VA including how user feedback helped refine its functionality. Then, the specific aspects of the Santa Maria version are detailed.