BepiColombo - Solar Electric Propulsion System Test and Qualification Approach IEPC-2019-586 Presented at the 36th International Electric Propulsion Conference University of Vienna • Vienna, Austria September 15-20, 2019 S. Clark1, P. Randall2, R. Lewis3, D. Marangone4 QinetiQ, Cody Technology Park, Farnborough, GU14 0LX, UK D. Goebel5, V. Chaplin6 Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA 91109, USA H. Gray7 Airbus Defence and Space Ltd., Portsmouth, Hants, PO3 5PU, UK K Kempkens8 Airbus Defence and Space GmbH, 88039 Friedrichshafen, Germany N. Wallace9 European Space Agency, ESTEC, Noordwijk, 2200AG, Netherlands Abstract: In support of the BepiColombo mission to Mercury, a qualification programme for the Solar Electric Propulsion Thruster (SEPT) and Solar Electric Propulsion System (SEPS) was conducted by QinetiQ at its facilities in Farnborough, UK. The paper discusses the qualification of the thruster lifetime against the mission requirements and the test approach and modelling activities that form the validation. Excellent correlation between ground test data, physical measurements and model predictions have been demonstrated during the project, in which some detail is provided. QinetiQ also undertook the qualification of the Solar Electric Propulsion System (SEPS) chain, involving a complex setup of the SEPS Units (SEPT, PPU, FCU and SEPH/P). This was a unique opportunity to test the hardware in a representative chain in full beam mode, which was not possible during System level AIV activities or final spacecraft integration. The Unit level qualification of the other SEPS units (PPU and FCU) are not addressed in this paper, but have been considered in the frame of the Coupling Test Activities. 1 BepiColombo SEPS AIV lead engineer, QinetiQ, Space UK, [email protected] 2 BepiColombo SEPS system lead engineer, QinetiQ, Space UK, [email protected] 3 BepiColombo SEPS thruster lead engineer, QinetiQ, Space UK, [email protected] 4 BepiColombo SEPS test engineer, QinetiQ, Space UK, [email protected] 5 JPL Fellow, Propulsion, Thermal, & Materials Engineering, [email protected] 6 Technologist, Electric Propulsion Group, [email protected] 7 BepiColombo EP Architect, Propulsion Department, [email protected] 8 System Engineering Manager, Department TESNG, [email protected] 9 Senior Electric Propulsion Engineer, TEC-MPE, [email protected] 1 The 36th International Electric Propulsion Conference, University of Vienna, Austria September 15-20, 2019 Nomenclature BB = Bread Board BOL = Beginning of Life CMM = Coordinate Measurement Machine DANS = Discharge, Accel and Neutraliser Supply EBS = Electron Backstreaming EGSE = Electrical Ground Support Equipment EM = Engineering Model EMC = Electromagnetic Compatibility EOL = End Of Life EOM = End Of Mission EQM = Engineering Qualification Model FCU = Flow Control Unit FGSE = Fluidic Ground Support Equipment FDIR = Failure Detection, Isolation and Recovery FCU = Flow Control Unit FM = Flight Model HPEPS = High Power Electric Propulsion System ISP = Specific Impulse JAXA = Japan Aerospace Exploration Agency LEEP = Large European Electric Propulsion MEPS = MTM Electric Propulsion System MMO = Mercury Magnetospheric Orbiter MPO = Mercury Planetary Orbiter PFM = Proto Flight Model PPU = Power Processing Unit SEPH = Solar Electric Propulsion Harness SEPP = Solar Electric Propulsion Pipework SEPS = Solar Electric Propulsion System SEPT = Solar Electric Propulsion Thruster TCF = Thrust Correction Factor Xe = Xenon I.Introduction epiColombo is an ESA cornerstone mission to Mercury executed in collaboration with its partner the Japan B Aerospace Exploration Agency (JAXA), designed to place 2 spacecraft into orbit around Mercury. Airbus Defence and Space is the overall System prime and is additionally responsible for the development and provision of the Mercury Planetary Orbiter (MPO) and the Mercury Transfer Module (MTM). JAXA is responsible for the development and provision of the Mercury Magnetospheric Orbiter (MMO). The BepiColombo spacecraft has a dedicated transfer module, which provides all the propulsion and power needed to deliver the 2 orbiters to Mercury7. This makes extensive use of electric propulsion through a number of thrust arcs. The use of electric propulsion for orbital transfer between bodies within the solar system is now well established, with its use on the Deep Space 11, Smart-12, Hayabusa Explorer3, Dawn4,5 and Hayabusa26 programmes. This follows the increasing use of electric propulsion for large telecommunications satellites. The BepiColombo mission exploits this heritage. A substantial energy reduction is needed to reach Mercury. The high specific impulses which can be provided by electric propulsion systems offer the ability to achieve this large velocity increment with significantly reduced propellant mass when compared with chemical propulsion systems. As a mission to Mercury will also inherently require flight trajectories with reducing sun-earth distances, the power available from the solar arrays will increase as Mercury is approached, ensuring adequate power for electric propulsion operations. The design, development and qualification of the BepiColombo electric propulsion system is based on previous developments and flight heritage of similar electric propulsion technologies, from a variety of applications. 2 The 36th International Electric Propulsion Conference, University of Vienna, Austria September 15-20, 2019 II.The BepiColombo Mission A. Mission Objectives Mercury is an extreme of our planetary system. Since its formation, it has been subjected to the highest temperature and has experienced the largest diurnal temperature variation of any object in the solar system. It is the closest planet to the Sun and has the highest uncompressed density of all planets. Solar tides have influenced its rotational state. Its surface has been altered during the initial cooling phase and its chemical composition may have been modified by bombardment in its early history. Mercury therefore plays an important role in constraining and testing dynamical and compositional theories of planetary system formation. To date, only the American probes Mariner 10 and Messenger have returned significant data from Mercury. Although these data have been fully exploited, a lot of gross features remain unexplained. Many conclusions are still speculative and have evoked a great number of new questions. The main scientific objectives of the BepiColombo mission are: Investigation of the origin and evolution of a planet close to its parent star Investigation of Mercury’s figure, interior structure, and composition Investigation of the interior dynamics and origin of its magnetic field Investigation of the exogenic and endogenic surface modifications, cratering, tectonics, and volcanism Investigation of the composition, origin and dynamics of Mercury’s exosphere and polar deposits Investigation of the structure and dynamics of Mercury’s magnetosphere Test of Einstein’s theory of general relativity The mission will achieve these objectives by delivering 2 separate spacecraft into orbit around Mercury, namely the Mercury Magnetospheric Orbiter (MMO) and the Mercury Planetary Orbiter (MPO). These 2 spacecraft will be placed into different orbits around Mercury. The MPO has an initial polar elliptic orbit, with an altitude of between 400 and 1508 km; the MMO also has an initial polar elliptic orbit, with an altitude of between 400 and 11824 km. B. Mission Analysis and Propulsion System Usage The spacecraft was launched by Ariane 5 from Kourou at 03:45 CEST on 20th October 2018; Mercury arrival and orbit insertion will be in December 2025, giving an overall transfer duration of 7.2 years. Both chemical and electric propulsion systems are required to achieve the mission requirements. The selected mission profile uses the launcher for direct injection into an interplanetary trajectory. The electric propulsion system is then used over a number of thrust arcs, with intermediate coast phases and planetary fly-bys. A gravitational capture, via the Mercury-Sun Lagrange point, is finally used to place the spacecraft into a weakly bound Mercury orbit. A bipropellant chemical propulsion system on the transfer module is used for attitude and orbit control during the transfer, where higher thrust levels are required. A dual mode chemical propulsion on the MPO is used in bipropellant mode for lowering into the final operational orbits; this is then used in monopropellant mode for orbit and attitude control of the MPO during the operational phase of the mission. T6 thrusters and C. MTM Structure pointing mechanisms High pressure The MTM structure design is driven by the following main Flow control regulator requirements: units Spacecraft stiffness to avoid coupling with low frequency excitations from the launch vehicle Propellant and Xenon tanks and two solar arrays (SA) constrain the structure height Centre of mass constraints Compatibility with thermal environment temperature range of -30°C to +90°C Compatibility with the launch vehicle adaptor interface Power Loads resulting from launch environment and processing units lifting / handling / transportation cases Tanks Mass minimisation Figure 1. MEPS Layout. The MTM structure consists of a central cone connected to four shear panels and to two main tank floor panels. Three radiator panels are connected to the tank floor, shear panels 3 The 36th International Electric