67th International Astronautical Congress (IAC), Guadalajara, Mexico, 26-30 September 2016. Copyright 2016 by DLR-SART. Published by the IAF, with permission and released to the IAF to publish in all forms. IAC-16- D2.3.11 Suitability of Reusability for a Lunar Re-Supply System Etienne Dumont Department of Space Launcher Systems Analysis (SART), Institute of Space Systems, DLR, Robert Hooke Straße 7, 28359 Bremen, Germany, [email protected] Abstract Moon landers built in the past were designed and optimized for specific missions, with a limited consideration of follow-on missions. They were expendable and based on storable hypergolic propellants. In order to enable a sustainable presence on the Moon for research but also other activities, a new type of transportation architecture is needed. Technical developments since the 1960s open a large range of new solutions which could be beneficial for a lunar transportation. The ROBEX (Robotic Exploration under Extreme Conditions) project, in particular, is focusing on new types of lunar architectures, for which modularity, re-configurability and flexibility should play a central role to guarantee the sustainability of the design. In this framework a reusable lunar single stage to orbit vehicle called RLRV (Reusable Lunar Resupply Vehicle) has been designed. It is able to land payloads on the Moon and to launch payloads from the lunar surface in anticipation of their return back to Earth. The RLRV is characterized by a design relying on the combination of cryogenic propulsion, in-situ propellant production and reusability. Important technologies that are enabling such a design have been identified to refine the RLRV design. The flexibility of the vehicle has been demonstrated with the assessment of its performance for a whole range of missions. The comparison of the RLRV with a classic lander such as the descent module of the Apollo Lunar Lander demonstrates that a large reduction of the payload to be injected by an Earth launch vehicle and an Earth departure stage can be achieved with the proposed design. Keywords: Moon mission, Reusability, ISPP, Cryogenic propellant, ROBEX Nomenclature NTO Nitrogen Tetroxide RCS Reaction Control System Isp Vacuum Specific Impulse s RLRV Reusable Lunar Resupply Vehicle MR Engine Mixture Ratio - SSTO Single Stage To Orbit Pcc Combustion Chamber Pressure bar UDMH Unsymmetrical Dimethylhydrazine T Thrust kN W (Earth) Weight N or kN 1. Introduction ΔV Velocity Increment m/s or km/s In the past, several missions managed to land safely on the Moon and were big scientific successes such as Acronyms/Abbreviations the Surveyor and Luna robotic programs or more recently China’s Chang’e 3 mission. These missions API Advanced Porous Injector together with the Apollo program helped to understand APU Auxiliary Power Unit better our natural satellite. However none of these EML1 Earth Moon Lagrange Point 1 programs succeeded to allow a long term presence and ESAS Exploration Systems Architecture Study study of the Moon. Such a goal is however currently GH2 Gaseous Hydrogen increasing in interest in particular under the impulse of GOx Gaseous Oxygen the “Moon Village” initiative launched by ESA’s ISPP In-Situ Propellant Production general director J. Wörner. IVF Integrated Vehicle Fluids Key assets which would greatly help to increase the LEO Low Earth Orbit sustainability of a new Moon program are modularity LH2 Liquid Hydrogen and reusability. Indeed landers built until now were LLH2 Lunar (produced) Liquid Hydrogen designed and optimized for very specific missions, with LLO Low Lunar Orbit a limited consideration of follow-on missions. They LLOx Lunar (produced) Liquid Oxygen were expendable and based on storable hypergolic LM Lunar Module of the Apollo programme propellants. While storable propellants are particularly LOx Liquid Oxygen adapted to several day long missions and the hypergolic LSAM Constellation Lunar Surface Access Module property increases the reliability of the mission, it NPSP Net Positive Suction Pressure implies the fueling of the vehicle with relatively large IAC-16-D2.3.11 Page 1 of 14 67th International Astronautical Congress (IAC), Guadalajara, Mexico, 26-30 September 2016. Copyright 2016 by DLR-SART. Published by the IAF, with permission and released to the IAF to publish in all forms. mass of propellant coming from the Earth. More recent those described in [3] but also to launch payload back to studies and plans to come back to the Moon such as the Earth. This characteristic naturally influences the choice ESA Lunar lander or the ESA Cargo Lander also used of the architecture and design of the transportation storable and hypergolic propellants. While these system, which should also be flexible. A lunar lander vehicles were already considering a certain modularity able, for its reference missions, to land payload masses and adaptability since they could transport various of 10 metric tons and to re-supply a Moon base has been payloads, they had an additional limitation as their pre-designed. This vehicle should also have the design is constrained by the capabilities of existing capability to launch payloads from lunar surface in launchers available: such as Soyuz or Ariane 5 [1]. anticipation of their return back to Earth. For these NASA with its Constellation program considered the reasons, we pre-designed a reusable lunar SSTO (Single design a bit differently, as from the very beginning the Stage To Orbit) vehicle called RLRV (Reusable Lunar payloads to be launched and the corresponding lander Resupply Vehicle). This vehicle, which should work as (Altair) were designed with limited constraints on the a shuttle between the Moon orbit and the Moon surface, capabilities of the launcher. As a matter of fact for this should have the capability to be refueled both in Moon program a new launch vehicle, Ares V, in the class of orbit and on the Moon surface. It has been chosen to Saturn V was planned to be built. However, with such consider liquid oxygen and liquid hydrogen as architecture, regular missions to the Moon imply the propellant for the RLRV. production and the launch of huge and expensive launch After elaborating on how newly developed vehicles. It cannot be sustained easily by any space technologies and researches allow considering the agency in the world. combination of LOx/LH2 propulsion, ISPP and A way to increase the sustainability of a Moon reusability to design an efficient and flexible program would be to take advantage of the many new transportation system, an overview of the architecture, technological developments which have been achieved focusing on trajectories, staging and the origin of LH2 is in the past years. These developments are indeed proposed. A preliminary sizing of the RLRV including allowing considering as reasonably feasible, designs, for instance the design of the structure and of the feed which for instance in the 1960s were considered as far and propulsion systems will be presented. Missions and too risky. This is the case for instance of cryogenic performance are following. In order to assess the propulsion for which experience has been gathered for advantages of the reusability of the RLRV, it is already many decades [2]. In-Situ Propellant Production compared to the Apollo Lunar Module, a classic (ISPP) has not been tested yet on the Moon, but expendable vehicle. For that purpose, different mission numerous studies on the topic have been performed and scenarios amongst which the establishment of the lunar several solutions to produce LOx from Moon regolith base with habitat, pre-sized previously in the frame of exist [3], [4] and [5], and some of them have been tested ROBEX [3] are considered. on Earth [6]. A source of propellant directly on the Moon would allow reducing strongly the mass to be 2. Design rationale launched from the Earth. Recent studies [7] also With the exception of China’s Chang’e 3, all soft indicate that water ice is present on the Moon; this landings on the Moon occurred between 1966 and 1976. would allow producing not only LOx but also LH2. These 19 missions took place in the frame of the Space While these two technologies are expected to improve Race between the Soviet Union and the United States of the performance of transportation between the Earth and America. The main design driver was at that time to be the Moon, their combination with reusability seems the first one on the Moon while sustainability or cost of particularly beneficial. It is indeed expected that a a design was only a secondary aspect. From this period further reduction of the size of the transportation system a lot of experience has been gathered and still strongly as well as an increase of the mission flexibility can be influences the design of vehicles for future missions. obtained. Actually, reusability is expected to be Basically, these designs can be summarized as being beneficial for the different sections of the transportation based on pressure-fed engines running on terrestrial system: the Earth launch vehicle, the Earth-Moon based storable propellants, often relying on Low Lunar transfer vehicle and the Lunar Lander. Orbit (LLO) for rendezvous or at least as a parking orbit In the frame of the ROBEX (Robotic Exploration and being expendable. Several studies performed in the under Extreme Conditions) project, a new transportation past years came out with ideas, which could bring a cost system for lunar missions is being studied. An important reduction in comparison with Apollo-type designs, aspect of the ROBEX project is the consideration of qualified by Zubrin as “brute-force means” [5]. But as modularity, flexibility and re-configurability for the regretted by Zubrin, these ideas such as In-Situ design of the ground infrastructure in order to increase Propellant Production (ISPP) are often applied to classic its sustainability.