Micrometeoroid Impact Risk Assessment for Interplanetary Missions J. Rodmann(1), A. Miller(1), M. Traud(1), K.D. Bunte(1), and M. Millinger(2) (1) etamax space GmbH, Lilienthalplatz 1, 38108 Braunschweig, E-mail: [email protected] (2) ESA/ESTEC, Keplerlaan 1, 2201 AZ Noordwijk, The Netherlands, E-mail: [email protected] ABSTRACT called meteoroid models have to make strong assumptions on the particle properties, often fixing the For Earth-orbiting manned and unmanned space bulk density. The expected damage on a spacecraft systems the analysis of the risk due to hyper- surface as a result of meteoroid impacts can be assessed velocity impacts by space debris and/or through empirically derived design equations providing micrometeoroids is an integral part of the crater depths, crater diameters, or penetration spacecraft design. As more challenging missions probabilities as function of the particle properties (e.g. beyond low-Earth orbit and into the impact velocity, impact angle) and specifics of the target interplanetary space are devised, planned, and (e.g. thickness of outer shielding wall). designed, meteoroid impact risk assessment Due to the high complexity of the risk and damage become a necessity for ensuring subsystem, analyses on a three-dimensional spacecraft geometrical mission or crew safety using the least amount of model, considering shadowing effects as well as impacts micrometeoroid/orbital debris (MMOD) of so-called secondary ejecta, and allowing the shielding possible to save mass. This paper application of various environment models and provides a concise overview of the ongoing particle/wall interaction models, sophisticated software software development activities towards tools are needed to perform these kind of analyse. extending ESABASE2/Debris, ESA’s standard ESABASE2/Debris is the standard software for MMOD tool for analysing the effects of space debris and impact risks assessments and is used by ESA, various meteoroid impacts on spacecraft, for European satellites manufacturers, as well as in interplanetary missions. academia. 1 INTRODUCTION In view of upcoming interplanetary missions, and extension of the ESABASE2's Debris analysis Meteoroids are solid particles of interplanetary or capabilities is required to be able to assess the risk of interstellar origin. Hypervelocity impacts of meteoroid impacts during the entire mission. The micrometeoroids (with typical velocities of tens of km/s) capabilities of the ESABASE2/Debris software tool need pose a significant environmental hazard to spacecraft to be enhanced to implement existing interplanetary and/or astronauts conducting EVAs. The damage caused meteoroid models, like IMEM, IMEM2, MEMR2, and by impacts of meteoroids depends on the size, density, MEM 3. Furthermore, the software shall be able to ingest porosity, speed, and direction of the impacting particles and process trajectory files in various common formats, on the outer surface element of a spacecraft. Repeated e.g. SPICE or CCSDS/OEM, and allow user-defined impacts of micron-sized to sub-mm particles or lead to spacecraft attitudes. the gradual degradation of spacecraft surfaces and materials by erosion/cratering, affecting for example In Chapter 2 of this paper, we provide a brief overview mirrors, lenses and sensors. Larger particles can perforate of the existing ESABASE2/Debris tool, explain the GUI insulation layers and optical baffles. A micrometeoroid layout and the general workflow for going from with sufficient kinetic energy can puncture pressurized spacecraft model to impact fluxes and risk figures. vessels (manned habitats, propulsion tanks), batteries, Chapter 3 introduces the meteoroid models IMEM, coolant lines or spacesuits, as well as sever cables, tethers IMEM2, MEMR2, and MEM 3 that are being and springs. Millimetre-sized grains are able to cause implemented. Chapter 4 summarises the main software structural damage by penetration or spallation, leading to development activities, with emphasis on new features the potential failure of components or subsystems up to and functionalities. Also in this chapter, the approach for the complete destruction of the spacecraft or loss of crew software validation and testing will be outlined and test in the worst case. cases listed. The paper concludes with an outlook on possible future extensions and enhancements of the Statistical environmental models have been developed ESABASE2/Debris interplanetary tool. that describe the expected flux (i.e. the number of particles per unit area and unit time), speed, and sometimes also directionality of meteoroids. The so- LProc.eave 8th foo Europeanter em pConferencety – The on C onSpacefer eDebrisnce f (virtual),ooter w Darmstadt,ill be add Germany,ed to th 20–23e firs tApril page 2021, of epublishedach pa pbye rthe. ESA Space Debris Office Ed. T. Flohrer, S. Lemmens & F. Schmitz, (http://conference.sdo.esoc.esa.int, May 2021) 2 IMPACT RISK ASSESSMENT TOOL analysis related input such as selection of the ESABASE2/DEBRIS environment models and their parameters, failure and damage equations, ray-tracing parameters and ESABASE2/Debris, developed, maintained and particle size range to be considered. distributed by etamax space, is ESA’s standard software • Outline: application to analyse the effects of space debris and Displays the content of an editor or the underlying meteoroid impacts on spacecraft in the near-Earth file, respectively. environment, i.e. on Earth and lunar orbits, on transfer orbits to the Moon, around the Sun-Earth Lagrangian • Properties Editor: points L1/L2, and now also for interplanetary orbits. Displays the content of an outline item and allows editing of its parameters. ESABASE2/Debris allows reading in or building 3D spacecraft models, setting damage and failure equations/laws, and incorporates the latest models of the Near-Earth space debris and meteoroid environments. 3 INTERPLANETARY METEOROID The software computes impact fluxes, distributions for MODELS mass, size and velocities of the impactors as functions of The meteoroid environment encountered by a spacecraft time and spacecraft surface area, as well as risk are specified by different statistical models. They assessments (e.g. probability-of-no-penetration values) describe the spatial distribution of meteoroids over the complete mission. A detailed description of the (interplanetary dust particles) and provide information of capabilities of ESABASE2/Debris can be found in [1]. their number (flux), impact speed, and directionality. ESABASE2 is stand-alone desktop application for Meteoroids originate from three distinct sources: Windows and Linux. It comes with a freely customisable cometary activity (ejection through outgassing, graphical user interface (GUI) and is based on the well- fragmentation of the nucleus); mutual collision of known open-source Eclipse software, see Figure 1. asteroid or rotational break-up; and particles entering from interstellar space. The main contribution to the dust cloud in the inner solar system stems from Jupiter-family comets (JFCs) with orbital period below 20 years and low to moderate inclinations against the ecliptic (i < 30 deg). Meteoroids model have been built from various types of observations and measurements, e.g. lunar microcrater number distributions [2], meteor observations by ground- based radars (e.g. AMOR, CMOR), zodiacal light/infrared sky brightness measurements (e.g. by Helios, COBE), as well as in-situ dust particle detectors (e.g. on Pioneers, Cassini, New Horizons). Reference [7] contains a good summary of the history of meteoroid models for the interplanetary space. Here we focus on those interplanetary meteoroid models that are being implemented into the ESABASE2/Debris tool as part of an ongoing ESA project, see Table 1 for an Figure 1. Layout of the ESABASE2/Debris GUI showing overview. the main window elements for project setup, orbit and model input, visualization, and user information. 3.1 IMEM The GUI consists of the following window elements: ESA developed the Interplanetary Meteoroid • Project Explorer: Environment Model (IMEM), which models the orbits of Provides access to all ESABASE2 projects in the particles from Jupiter-family comets and asteroids, and user’s workspace and the related input/output files. was fitted largely to in situ data and infrared brightness • Geometry Editor: measurements [6]. An interstellar population is Provides geometry creation, viewing and editing parametrized as mono-directional stream. capabilities. Cometary and asteroidal populations are split into • Mission Editor and Visualisation: heavier (“collision dominated”) and lighter (“Poynting- Enables the specification of the orbit, mission and its Robertson dominated”) groups. This results in a visualisation. -5 discontinuity in the mass flux at around 10 g. Modelled • Debris Editor: meteor observations were not used because they were Allows the specification of all debris and meteoroid found to be inconsistent with modelled infrared data. Leave footer empty – The Conference footer will be added to the first page of each paper. Table 1: Comparison of different interplanetary meteoroids models. Models shown in boldface are implemented into ESABASE2/Debris. Meteoroid Model range Particle radius Particle density (g/cm3) References model (au) (μm) or mass range (g) Grün model at 1 au 10‒18... 100 g 2.5 Grün et al. (1985) [2] Divine-Staubach r = 0.1…20 10‒18... 1 g 5 populations Divine (1993) [3] model Staubach (1997) [4] IMEM r = 0.05…6 10‒18... 1 g 5 populations