# Sino-InSpace: A Digital Simulation Platform for Virtual Space Environments
## 1 Introduction  
The astounding advances in aerospace technology are making the dream of space exploration come true. Since the launch of the first artificial satellite by the Soviet Union in 1957, human beings have been constantly exploring the vastness of the universe, which includes the near-earth space [1], the moon, Mars, and asteroids [2]. Chinese space activities started with the launch of Dong Fang Hong I in 1970; since then, a number of BeiDou navigation satellites, resource remote sensing satellites, and Fengyun meteorological satellites had been sent into operation. In addition, China's progress indeep space exploration is also noteworthy [3]. The Chang'E lunar exploration program, which involves achieving lunar orbit, soft-landing on the moon, and returning a lunar sample has now entered its third stage [4]. The first Chinese Mars exploration mission has also been formally approved, and a Mars probe is planned for launch in the second half of 2020. With the possible opportunities and new avenues that space exploration promises, especially considering the problems of environmental pollution and resource depletion, many countries have set up ambitious space programs [5; 6; 7]. For human beings, outer space is a relatively \"new world\" and difficult to reach currently. However, virtual environments, initially viewed as \"mirror worlds\", can supply computer-based digital spaces that we observe, participate in, and experience in person [8]. With the increasing scope and scale of human space activities, it is essential to construct a digital simulation platform for virtual space environments (VSEs). The traditional geographical information disciplines primarily study the Earth's surface including commercial (e.g., ArcGIS, MapInfo, and SuperMap) or open source geographic information system (GIS) platforms [9]; these platforms focus on processing, expressing, and analyzing the surface geographical data that are closely related to daily production and life. With the data acquired by deep space probes, the visualization of the planets' surface map based on GIS has been studied by some organizations such as the 'Multilingual Maps of the Terrestrial Planets and their Moons' [10], 'Lunar Web Mapping Application' [11], 'Mars Global GIS Mapping Application' [12], and Gazetteer of Planetary Nomenclature [13]; however, these maps are often relatively simple and lack effective three-dimensional (3D) visualization. Since the concept of a digital globe was proposed in 1998 by U.S. Vice President [PERSON], a large number of platforms such as Google Earth [14], World Wind [15], ArcGIS Earth [16], DEPS/CAS [17], and GeoGlobe [18] have been developed, providing a new means to understand the Earth. Furthermore, some similar digital visualization platforms such as Moonworld [19], Sino-Virtual Moon [20], Google Mars [21], JMARS [22], and ADVISER [23; 24] have been developed, which can intuitively display the images of planetary surfaces and depict information regarding their topography, geology, and landing point through virtual reality (VR) while also supporting collaborative simulation. However, these platforms are often limited to a single planet and lack the capability to simulate the entire process of complex space-based activities. Due to the specialization of space science, there are not many mature aerospace mission simulation platforms thus far. Systems Tool Kit (STK) [25], developed by AGI, is a leading commercial software used for analysis in the aerospace field, which can support space exploration simulation including design, testing, launch, operation, and task application. Recently, the company also introduced a simplified open-source, web-based version of the platform called Cesium [26]. In addition, World Wind, General Mission Analysis Tool (GMAT) [27], SaVi [28], 3 DView [29], and Cosmographia [30] can offer certain capabilities for track design, simulation, and scientific data visualization; moreover, these were made open source for the public.