Cent. Eur. J. Eng. • 2(2) • 2012 • 156-163 DOI: 10.2478/s13531-011-0072-z Central European Journal of Engineering Lunar surface exploration using mobile robots Vision Paper Shin-Ichiro Nishida∗, Sachiko Wakabayashi Lunar and Planetary Exploration Program Group, Japan Aerospace Exploration Agency Received 24 May 2011; accepted 23 February 2012 Abstract: A lunar exploration architecture study is being carried out by space agencies. JAXA is carrying out research and development of a mobile robot (rover) to be deployed on the lunar surface for exploration and outpost construction. The main target areas for outpost construction and lunar exploration are mountainous zones. The moon’s surface is covered by regolith. Achieving a steady traversal of such irregular terrain constitutes the major technical problem for rovers. A newly developed lightweight crawler mechanism can effectively traverse such irregular terrain because of its low contact force with the ground. This fact was determined on the basis of the mass and expected payload of the rover. This paper describes a plan for Japanese lunar surface exploration using mobile robots, and presents the results of testing and analysis needed in their development. This paper also gives an overview of the lunar exploration robot to be deployed in the SELENE follow-on mission, and the composition of its mobility, navigation, and control systems. Keywords: Lunar exploration • Space Robot • Mobility • Remote Control © Versita sp. z o.o. 1. Introduction as a continuation of SELENE’s operation, are being con- sidered. The southern polar region of the moon is the leading candidate location for the construction of a lunar Recent missions (SMART-1, Kaguya, Chang’E, base because of the good sunlight conditions and the high Chandrayaan-1, LCROSS, and LRO) have been un- possibility that rocks from the far side of the moon, such dertaken for active lunar exploration. A lunar orbiter as the South Pole Aitoken Basin, are present. The mis- Kaguya (SELENE) was launched in September 2007 by sions are expected to use robotic technologies such as the Japan Aerospace Exploration Agency (JAXA). The mobile rovers. However, the lunar surface is an adverse spacecraft observed the moon for one and a half years, environment that presents many technical challenges to which yielded favorable results and a considerable amount exploration and survey activities, particularly since there of scientific data [1, 2]. are many unknowns related to the geographical features One of the goals incorporated in JAXA’s long-term vision and environment in the southern polar region. [3] is to advance the exploration of the moon’s surface; This paper introduces the strategy of the SELENE follow- thus, missions to survey and investigate the lunar surface, on mission and future lunar exploration. It presents the main technical issues faced by designers of lunar explo- ration robots, a technical roadmap of their development, ∗E-mail: [email protected] and the results of studies of a robot system configuration. 156 , are present Nine meetings of this panel were held by the end of July missions are expected to use robotic technologies such as 2010. The final conclusions of the panel were reported to mobile rovers. However, the lunar surface is an adverse the minister of space development in August 2010. The environment that presents many technical challenges to final report of the committee states that, in preparation explorationS.-I. Nishida, and S. Wakabayashi survey activities, particularly since there for a full-range robotic exploration in 2020, a lander and a are many unknowns related to the geographical features robot should be sent to the lunar surface in around and environment in the southern polar region. This paper introduces the strategy of the SELENE follow-on2. Planning mission and for future lunar lunar exploration exploration. It presents the main technical issues faced by designers of lunarIn Japan,exploration the “Basic robots, Plan a technical for Space roadmap Policy” wasof their estab- development,lished by Strategic and the Headquarters results of studies for Space of a robot Policy system in 2009. configuration.The report states: “The Government will conduct an exam- ination of the Japanese original, extensive and long-term 2.moon Planning exploration for Lunar that is Exploration intended to lead the world in • Insolving Japan, questions the “Basic concerning Plan for the originSpace andPolicy” evolution was of established by Strategic Headquarters for Space Policy in the moon and to investigate the possibility of scientific 2009. The report states: “The Government will conduct anexploitation examination of of the the moon Japanese and utilization original, extensive of its resources, and long-termfrom the moon perspective exploration of manned that activitiesis intended on theto lead moon the that worldwill enablein solving in situ questions informed concerning judgment.” the To origin plan a and lunar exploration program, “The Panel on Lunar Exploration” was organized in July 2009. The purpose of this panel Figure 1: Artist concept of a lunar base in south pole (Committee) is to study the following issues: withFigure an 1.intelligentArtist concept robot of a lunar base in south pole with an intelli- gent robot. • Lunar exploration by 2020: – the objectives of robotic exploration; 3. Environment of lunar polar zones – research roadmaps; – technical issues; The moon’s surface is an adverse environment for machines, – the spin-off effect on the business market. and designing mechanisms that can operate under such conditions is technically challenging. • Lunar exploration in the long term: In the polar regions of the moon, high areas such as crater – the objectives of robotic and human explo- rims may be permanently sunlit while the bottoms of craters ration; may be permanently shaded, especially in the southern – issues to be faced; polar region. It is assumed that a lunar base would be – international cooperation. sited at a perpetually sunlit location. However, since these locations are in mountainous areas, there are many surface Nine meetings of this panel were held by the end of July undulations and the surface inclination is expected to range 2010. The final conclusions of the panel were reported to from level to up to 30° (the rest angle of regolith), with an the minister of space development in August 2010. The average slope of about 15°. The inner walls of craters are final report of the committee states that, in preparation for even steeper. Moreover, since the incident sunlight shines a full-range robotic exploration in 2020, a lander and a almost horizontally, slight surface undulations produce robot should be sent to the lunar surface in around 2015 large shadowed domains. [4]. This corresponds to the SELENE follow-on mission, For these reasons, the south polar region contains the which includes a highly accurate unmanned automatic soft most areas where the surface receives minimum sunlight. landing on the lunar surface. A rover-type robot will then Therefore, it is expected that, even if a low vehicle such be used to select a suitable site and install observation as a rover chooses and traverses a path, it cannot receive instruments, including a seismometer. full sunlight. Moreover, there are wide local temperature The report also says that we should aim to achieve in 2020 variations, ranging between −30° and −50°C in sunlit the following outcomes that will lead the world: areas down to −230°C in shadow regions. • lunar base construction and robotic exploration con- stituting a total travel distance of more than 100 km in several months; 4. Missions and means for their re- • Long-term energy supply by the world’s first lunar alization renewable energy system; The major objectives of the deployment of robotics in the • Japan’s first round-trip to a celestial body that has SELENE follow-on lunar exploration missions have been gravity (bringing back samples). set as: An artist’s concept of the lunar base in 2020 is shown in • survey for the purpose of lunar exploitation; Fig. 1 and a road map for lunar exploration is shown in Fig. 2. • scientific exploration; 157 inner walls of craters are even steeper. Moreover, since Other options are being studied, and their inclusion the incident sunlight shines almost horizontally, slight will be determined after the international exploration surface undulations produce large shadowed domains. strategy has been clarified. For these reasons, the south polar region contains the To realize eachLunar of surface the explorationobjectives using mentioned mobile robots above, a most areas where the surface receives minimum sunlight. number of task elements can be identified, as shown in Therefore, it is expected that, even if a low vehicle such Figure 2: A road map for human lunar exploration (JAXA’s vision; not authorized) Figure 2. A road map for human lunar exploration (JAXA’s vision; not authorized). • demonstration of robot technology in outpost con- Table 1. Task elements of lunar rover. struction and operation; Elements Objects • international collaboration. Traversal the target Mapping terrain Astronomical observation from the moon is also being con- Measurement environment and position sidered as a scientific objective. Abrasion rocks The investigation of soil and bedrock characteristics will Observation rocks and soils be important for outpost construction. Validation of rover Pick-up rocks and soils Coring rocks and soils technology and trials of position measurement technolo- Installation mission equipments gies to detect surface movement are also possible mission objectives. These will appear in the late 2010s, in view of Japan’s The following methods can be considered for the analysis foreseen participation in human lunar activity. SELENE-X of the soil and rock samples collected by a rover. may perform demonstrations of any of the following: Functions required for the SELENE follow-on robot and • technology for use in outposts, such as the au- future lunar robots are listed in Table 2.