49th International Conference on Environmental Systems ICES-2019-97 7-11 July 2019, Boston, Massachusetts The Thermal Commissioning of BepiColombo MPO Andrea Ferrero 1, Domenico Battaglia 2 and Tiziano Malosti 3 Thales Alenia Space, I-10146 Torino, Italy Daniele Stramaccioni 4 European Space Agency (ESA-ESTEC), NL-2200AG Noordwijk, the Netherlands and Jürgen Schilke 5 EADS Astrium, D-88039 Friedrichshafen, Germany BepiColombo was launched aboard an Ariane 5 rocket on 20 October 2018 at 01:45 UTC, with arrival on Mercury planned for December 2025, after a flyby of Earth, two flybys of Venus, and six flybys of Mercury. It is the first European mission to Mercury and will place in orbit around the planet two separate spacecraft: Mercury Magnetosphaeric Orbiter (MMO), provided by the Japanese Space Agency (JAXA), and Mercury Planetary Orbiter (MPO), provided by the European Space Agency (ESA). The cruise from Earth to Mercury is being ensured by a dedicated module, Mercury Transport Module (MTM). MPO, the subject of this paper, is the European scientific contribution to the BepiColombo mission. Upon cruise completion, when orbiting Mercury, it will be 3-axis stabilized, planet oriented, with a planned lifetime of 1 year, and a possible 1- year extension. The mission will perform a comprehensive study on Mercury, by means of several instruments, including a laser altimeter, different types of spectrometers, a magnetometer and radio science experiments. This paper describes the activity performed on MPO during pre-launch, launch and commissioning, besides it evaluates the first in orbit thermal results and where possible compares them with the behaviour expected from the analyses and from the results of the environmental thermal test program, in order to provide a first assessment of the spacecraft thermal design and performance. Nomenclature AOCS = Attitude and Orbital Control System RCS = Reaction Control System AU = Astronomical Unit (= 149.60×10 6 km) RSA = Ruag Space Austria GmbH CPS = Chemical Propulsion System S/C = SpaceCraft ESA = European Space Agency STM = Structural Thermal Model GFRP = Glass Fiber Reinforced Polymer TAS-I = Thales Alenia Space Italia HGA = Hi gh Gain Antenna TB = Thermal Balance JAXA = Japan Aerospace Exploration Agency TCS = Thermal Control System LEOP = Launch and Early Orbit phase TLL = Temperature Lower Limit MCS = Mercury Composite Spacecraft (stack of TMM = Thermal Mathematical Model MOSIF, MMO, MPO and MTM) TUL = Temperature Upper Limit MGA = Medium Gain Antenna TV = Thermal Vacuum MMO = Mercury Magnetosphere Orbiter UTC = Coordinated Universal Time MOSIF = Magnetospheric Orbiter Sunshade and Interface UV = UltraViolet MPO = Mercury Planetary Orbiter VDA = Vapor Deposited Aluminum 1 Thermal Verification Specialist, B.L. Space Infrastructures and Transportation, Strada Antica di Collegno 253 10146 Torino. 2 Passive Thermal Design Specialist, B.L. Optical Observation & Science, Strada Antica di Collegno 253 10146 Torino. 3 Senior Thermal Analyst, B.L. Space Infrastructures and Transportation, Strada Antica di Collegno 253 10146 Torino. 4 MPO Module Manager, BepiColombo Project, ESTEC, Keplerlaan 1, 2200AG Noordwijk, The Netherlands 5 Thermal Architect, AET42, D-88039 Friedrichshafen Copyright © 2019 Thales Alenia Space MTM = Mercury Transfer Module VUV = Vacuum UltraViolet NECP = Near Earth Commissioning Phase αS = Solar Absorptance PFM = Proto-Flight Model εIR = Infrared Emissivity I. Introduction EPICOLOMBO is the ESA’s cornerstone Z Bmission to Mercury in collaboration with JAXA MMO and will enable a better understanding of the planet history, geology, composition, atmosphere and Y X MOSIF magnetosphere. The mission is named after Italian mathematician and engineer Giuseppe “Bepi” Colombo (1920–1984), who suggested that the MPO Mariner-10 probe could perform three fly-bys of planet Mercury, thus extending significantly the coverage of the planet. It is the first European MTM mission in orbit around Mercury, the second overall after NASA’s MESSENGER (Mariner 10 actually orbited the Sun), and the first to send two spacecraft to make complementary measurements of the planet and its dynamic environment at the same time. With reference to Figure 1, Bepi Colombo Figure 1. Mercury Composite Spacecraft composed of consists of a spinning satellite, Mercury MTM, MPO and MMO inside its sunshade MOSIF . Magnetospheric Orbiter (MMO), provided by JAXA, a shield designed to protect the MMO by the intense Sun radiation during the cruise to Mercury 6 (MOSIF) and a 3-axis stabilized orbiter (MPO), both provided by ESA. Finally, the propulsion module (MTM), also provided by ESA, completes the Mercury Composite Spacecraft (MCS) that is currently cruising from Earth to Mercury. The MTM houses the solar electric propulsion system that is needed to propel the MCS during its cruise. During the 7-year cruise, the MCS stack is 3-axis stabilized and Sun-oriented to ensure sufficient electric power from the MTM solar arrays for the electric propulsion and protection from the Sun. Once BepiColombo reaches its destination, the mission will last for one year, with the possibility of extending its measurements for another year. The Mission is led by Airbus Deutschland Friedrichshafen (ASD), with Thales Alenia Space Italia Turin (TAS-I) responsible for the MPO and MOSIF thermal design. Ruag Space Austria GmbH (RSA) developed and provided the MLI. The MPO carries eleven payloads (P/L) for Mercury Figure 2. BepiColombo liftoff. Credits: ESA/ planet observation and remote sensing. It will provide a CNES/Arianespace/Optique vidéo du CSG – JM Guillon complete mapping of the entire planet surface with unprecedented resolution and will perform also other experiments of radioscience and fundamental physics 7. The specific challenges of the thermal design of this mission and, in particular, of the Mercury orbiter (MPO) stem clearly from the demanding thermal environment in combination with the chosen orbit and with the nadir pointing attitude of the spacecraft will be explained in paragraph II. 6 The MMO cannot withstand the Sun irradiation when it is not spinning. Hence, the MOSIF is designed to keep it in shadow during the cruise to Mercury. 7 For a description of the scientific mission, see ref. 7. 2 International Conference on Environmental Systems II. Mission Overview During its journey to Mercury, BepiColombo will need to make several braking manoeuvres to adjust its orbit and counteract the gravitational pull of the Sun in order to slow down enough to be captured by the gravity of Mercury. The cruise will total around 8.5 billion kilometres – the equivalent of travelling from the Earth to Neptune and back again, or 38 times the maximum distance between the Earth and Mercury. The BepiColombo mission will go through the following phases, with considerable changes of composite spacecraft configuration and thermal environment: • Launch and Early Orbit Phase (MCS); • Near-Earth Commissioning Phase, lasting 3-4 months and including commissioning (MCS). • Interplanetary Cruise Phase (MCS), with min/max distances from Sun 0.298/1.16 AU, and including Earth, Venus, Mercury fly-by’s. The solar irradiance will correspondently range from 1,020 to 15,400 W/m 2. • Mercury approach Phase: o Mercury capture (jettisoning of MTM); o Mercury Orbit Insertion; o MMO Orbit Acquisition, potentially including a Mercury Aphelion passage in nominal MMO orbit (jettisoning of MMO in its final orbit followed by jettisoning of MOSIF); o MPO Orbit Acquisition (MPO alone). • Mercury Orbit Phase (MPO). III. Launch and early LEOP Figure 3. BepiColombo mission profile. BepiColombo was launched aboard Ariane 5 from the Credits: Loren Roberts for The Planetary Society , European Spaceport in Kourou at 01:45:28 UTC on 20 October CC BY-SA 3.0 2018. Booster separation came just two minutes later, as the two solid rocket boosters of Ariane 5 detached themselves from the core stage; later, BepiColombo began its solo flight upon separation from the Ariane upper stage at around 2:12 UTC. At 2:20 UTC, the ESA deep space tracking station at New Norcia, Western Australia, picked up the first signals from the spacecraft, confirming that the launch was successful. Then BepiColombo started communicating bundles of engineering telemetry, as well as spectacular images from three low-resolution monitoring cameras located on the Mercury Transfer Module, that allowed flight controllers to visually verify the correct deployment of solar arrays and high and medium gain antennas. MPO is also equipped with a high- resolution scientific camera, which however is located on the side of the spacecraft fixed to the MTM during cruise, and therefore able to take pictures only after separation upon arrival at Mercury. The launch and early orbit phase was completed on October 22 with the deployment of solar arrays, confirming that the spacecraft and all systems were healthy and functioning. After separation and initialization of attitude control sensors, the sun was on the -X/-Y side and illuminated the radiator. As the sun was slightly above the XY plane, it was trapped between the fins. Figure 4. First image of BepiColombo from At 02:26 the attitude was recovered, with on on +Y (anti- space. Credits: ESA / BepiColombo / MTM, CC radiator side). As usual, the attitude control was switched off BY -SA 3.0 IGO 3 International Conference on Environmental Systems during the deployment of the solar arrays. The S/C movements during the deployments can be clearly seen. The reaction wheels were switched