The Ganymede Laser Altimeter (GALA) for the Jupiter Icy Moons Explorer (JUICE): Mission, science, and instrumentation of its receiver modules

The Jupiter Icy Moons Explorer (JUICE) is a science mission led by the European Space Agency, being developed for launch in 2023. The Ganymede Laser Altimeter (GALA) is an instrument onboard JUICE, whose main scientific goals are to understand ice tectonics based on topographic data, the subsurface structure by measuring tidal response, and small-scale roughness and albedo of the surface. In addition, from the perspective of astrobiology, it is imperative to study the subsurface ocean scientifically. The development of GALA has proceeded through an international collaboration between Germany (the lead), Japan, Switzerland, and Spain. Within this framework, the Japanese team (GALA-J) is responsible for developing three receiver modules: the Backend Optics (BEO), the Focal Plane Assembly (FPA), and the Analog Electronics Module (AEM). Like the German team, GALA-J also developed software to simulate the performance of the entire GALA system (performance model). In July 2020, the Proto-Flight Models of BEO, FPA, and AEM were delivered from Japan to Germany. This paper presents an overview of JUICE/GALA and its scientific objectives and describes the instrumentation, mainly focusing on Japan’s contribution

The Comet Interceptor Mission

Here we describe the novel, multi-point Comet Interceptor mission. It is dedicated to the exploration of a little-processed long-period comet, possibly entering the inner Solar System for the first time, or to encounter an interstellar object originating at another star. The objectives of the mission are to address the following questions: What are the surface composition, shape, morphology, and structure of the target object? What is the composition of the gas and dust in the coma, its connection to the nucleus, and the nature of its interaction with the solar wind? The mission was proposed to the European Space Agency in 2018, and formally adopted by the agency in June 2022, for launch in 2029 together with the Ariel mission. Comet Interceptor will take advantage of the opportunity presented by ESA’s F-Class call for fast, flexible, low-cost missions to which it was proposed. The call required a launch to a halo orbit around the Sun-Earth L2 point. The mission can take advantage of this placement to wait for the discovery of a suitable comet reachable with its minimum ΔV capability of 600 ms−1. Comet Interceptor will be unique in encountering and studying, at a nominal closest approach distance of 1000 km, a comet that represents a near-pristine sample of material from the formation of the Solar System. It will also add a capability that no previous cometary mission has had, which is to deploy two sub-probes – B1, provided by the Japanese space agency, JAXA, and B2 – that will follow different trajectories through the coma. While the main probe passes at a nominal 1000 km distance, probes B1 and B2 will follow different chords through the coma at distances of 850 km and 400 km, respectively. The result will be unique, simultaneous, spatially resolved information of the 3-dimensional properties of the target comet and its interaction with the space environment. We present the mission’s science background leading to these objectives, as well as an overview of the scientific instruments, mission design, and schedule

Thermal model and analysis of the BELA transmitter Stavroudis baffle in Mercury orbit

In the frame of the ESA BepiColombo mission to the planet Mercury the German Aerospace Center (DLR), in cooperation with the University of Bern, is designing the first European laser altimeter for planetary exploration (BELA). While orbiting Mercury the solar flux reaches 14 kW and strikes on the instrument at angles of > 38 deg from the instrument line of sight. The planet surface reaches 700 K while the view factor with the instrument aperture is high due to the low orbit altitude. Under these conditions a major challenge is the design of the instrument baffles, which shall avoid direct sunlight to reach the optics, minimize the heat load to the instrument and the S/C cavity and reduce stray light. We describe the thermal model of the transmitter baffle, focusing on advanced features like the approximation of ellipsoids and hyperboloids in the geometrical mathematical model, its optimization with respect to computational time and baffle efficiency, the dynamic implementation of wavelength dependant thermo- optical properties for the calculation of both absorbed planetary fluxes – as function of Mercury surface temperature – and radiative conductances (GR). The worst cases selection in the scenario of the whole Mercury orbit about the sun is also presented followed by a detailed overview of the analysis results

Implementation of temperature dependant thermo-optical properties and complex 3D geometries in ESATAN-TMS

Radiative heat transfer plays a major role in the thermal behavior of any space application compared to a typical Earth-based system. Space systems are known to operate in an environment characterized by a wide range of temperatures and heat loads, such as planetary and solar fluxes or deep space, planet and sun temperature. All these factors will critically impact upon the thermal design of spacecraft and special thermal coatings are generally used in thermal control. Many of these coatings present temperature dependent thermo-optical properties, which cannot be neglected in the design of space systems. However, in most thermal models, the temperature dependence is often reduced to the definition of two sets of properties, namely the IR and UV ranges. In addition, space systems usually present complex 3D geometries like antennas, optical devices or reflective baffles. For such components, the thermal behaviour is generally strongly coupled to their geometry, for instance the amount of rejected environmental radiation of a reflective baffle depends upon the shape of its reflective surfaces. It is therefore essential to model their surfaces with high accuracy. Unfortunately, complex shapes are often not fully implemented in thermal software. The objective of this paper is to present a general method to implement temperature dependant thermo-optical properties and to approximate complex 3D geometry using ESATAN-TMS, the European standard thermal analysis package. Practical applications for current space missions will be used to illustrate both methods and a comparison between different models will be presented to show the high inaccuracy that occurs when temperature dependencies are neglected

A Novel Spectral and Radiometric Calibration Target for the TIR Imager and the MARA Instrument on the Hayabusa2 Mission

At DLR we have developed a spectral and radiometric calibration target that will allow a cross calibration of the MARA and the TIR instrument. We use a serpentinite rock sample, which in the thermal infrared shows a strong spectral slope as well as well defined spectral feature. Obtaining measurements of this target with both instruments will greatly facilitate the correlation of orbital measurements obtained by the TIR with in-situ measurements by MARA. The calibration target is portable and highly adaptable, which will allow use for future mission

The Ganymede Laser Altimeter – Instrument design overview with radiation hard transmitter

The JUICE (Jupiter Icy Moons Ex-plorer) mission is part of ESA‘s Cosmic Vision Programme and its objective is to study Jupiter‘s plasma environment and the three icy moons Ganymede, Eu-ropa and Callisto. The JUICE spacecraft will be launched in 2022 on an Ariane 5 rocket. After its 8 year cruise it will enter an orbit around Jupiter. During the following three years the orbit will be gradually adjusted and after several fly-bys at Callisto, Europa and Ganymede the spacecraft will reach its final circular orbit around Gany-mede. One of the ten scientific instruments is the Ganymede Laser Altimeter – GALA. It will determine the topography and time dependent shape of the moon by direct laser altimetry approach. This talk presents the instrument design of GALA with the focus on the transmitter laser. In particular radiation hardness and efficiency aspects are explained

The Ganymede Laser Altimeter (GALA)

The Ganymede Laser Altimeter (GALA) is one of the instruments selected for the first ESA large class mission JUICE. The scientific goals of the GALA instrument cover a wide range of questions of geology, geophysics and geodesy. Here we will present an overview on the scientific goals as well as on the instrument baseline design concept and the current performance analysis