The instrument control unit of the PLATO payload: design consolidation following the preliminary design review by ESA

PLATO is an M-class mission (M3) of the European Space Agency (ESA) whose launch is scheduled in 2026. The main aim of the mission is the detection and characterization of terrestrial exoplanets orbiting around bright solar-type star. The payload consists of 26 small telescopes: 24 "normal" cameras and 2 "fast" cameras. The huge amount of data produced by the PLATO telescopes is acquired and processed on-board by the Data Processing System (DPS) made up by various processing electronic units. The DPS of the PLATO instrument comprises the Normal and Fast DPUs (Data Processing Units) and a single ICU (Instrument Control Unit), are data routed through a SpaceWire network. The topic of this paper is the description of the architecture of the ICU and its role within the DPS, the status of the Avionic Validation Model (AVM) testing at the end of the Unit Preliminary Design Review (UPDR) performed by ESA and the results of the test of the first engineering model

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

The morphology of cometary dust: Subunit size distributions down to tens of nanometres

International audienceThe Rosetta orbiter carried a dedicated analysis suite for cometary dust. One of the key instruments was MIDAS (Micro-Imaging Dust Analysis System), an atomic force microscope that scanned the surfaces of hundreds of (sub-)micrometre particles in 3D with resolutions down to nanometres. This provided the opportunity to study the morphology of the smallest cometary dust; initial investigation revealed that the particles are agglomerates of smaller subunits [1] with different structural properties [2]. To understand the (surface-) structure of the dust particles and the origin of their smallest building blocks, a number of particles were investigated in detail and the size distribution of their subunits determined [3].Here we discuss the subunit size distributions ranging from tens of nanometres to a few micrometres. The differences between the subunit size distributions for particles collected pre-perihelion, close to perihelion, and during a huge outburst are examined, as well as the dependence of subunit size on particle size. A case where a particle was fragmented in consecutive scans allows a direct comparison of fragment and subunit size distributions. Finally, the small end of the subunit size distribution is investigated: the smallest determined sizes will be reviewed in the context of other cometary missions, interplanetary dust particles believed to originate from comets, and remote observations. It will be discussed if the smallest subunits can be interpreted as fundamental building blocks of our early Solar System and if their origin was in our protoplanetary disc or the interstellar material

How MIDAS improved our understanding of micrometre- sized cometary dust

International audienceThe MIDAS atomic force microscope on the Rosetta orbiter was an instrument developed to investigate, for the first time, the morphology of nearly unaltered cometary dust. It acquired the 3D topography of about 1-50 µm sized dust particles with resolutions down to a few nanometres. These images showed the agglomerate character of the dust and confirmed that the smallest subunit sizes were less than 100 nm. MIDAS acquired the first direct proof of a fractal dust particle, opening a new approach to investigate the history of our early Solar System and of comets

How MIDAS improved our understanding of micrometre- sized cometary dust

International audienceThe MIDAS atomic force microscope on the Rosetta orbiter was an instrument developed to investigate, for the first time, the morphology of nearly unaltered cometary dust. It acquired the 3D topography of about 1-50 µm sized dust particles with resolutions down to a few nanometres. These images showed the agglomerate character of the dust and confirmed that the smallest subunit sizes were less than 100 nm. MIDAS acquired the first direct proof of a fractal dust particle, opening a new approach to investigate the history of our early Solar System and of comets

Fractal cometary dust – a window into the early Solar System

The ESLAB 50 Symposium - spacecraft at comets from 1P/Halley to 67P/Churyumov-GerasimenkoInternational audienceThe properties of dust in the protoplanetary disk are key to understanding the formation of planets in our Solar System. Many models of dust growth predict the development of fractal structures that evolve into non-fractal, porous dust pebbles representing the main component for planetesimal accretion. In order to understand comets and their origins, the Rosetta orbiter followed comet 67P/Churyumov-Gerasimenko for over two years and carried a dedicated instrument suite for dust analysis. One of these instruments, the MIDAS atomic force microscope, recorded the 3D topography of micro- to nanometre sized dust. All particles analysed to date have been found to be hierarchical agglomerates. Most show compact packing, however, one is extremely porous. This paper contains a structural description of a compact aggregate and the outstanding porous one. Both particles are tens of micrometres in size and show rather narrow subunit size distributions with noticeably similar mean values of 1.48+0.13−0.59 μm for the porous particle and 1.36+0.15−0.59 μm for the compact. ompact. The porous particle allows a fractal analysis, where a density-density correlation function yields a fractal dimension of Df = 1.70 ± 0.1. GIADA, another dust analysis instrument on-board Rosetta, confirms the existence of a dust population with a similar fractal dimension. The fractal particles are interpreted as pristine agglomerates built in the protoplanetary disk and preserved in the comet. The similar subunits of both fractal and compact dust indicate a common origin which is, given the properties of the fractal, dominated by slow agglomeration of equally sized aggregates known as cluster-cluster agglomeration

Cometary dust: structure at the nanometre scale

International audienceThe Rosetta orbiter carried three dedicated dust analysis instruments to investigate the properties of the comet andits dust at smallest scales. The images with the highest resolutions were obtained by the MIDAS (Micro-ImagingDust Analysis System) atomic force microscope [1,2]. It collected dust particles of one to tens of micrometresin size and imaged their surface in 3D. Nominal images had approximately hundreds of nanometres resolutionand were used to study the particle morphology at the micrometre scale. It was shown that the majority ofcollected particles were fragile agglomerates [3] with a moderate packing density of subunits at the surface [4].Exceptions were one extremely porous particle with a fractal structure that is suggested to be pristinely preservedfrom early agglomeration processes in our Solar System [4], and the particles of about one micrometre size thatshow less fragility. To study these smallest detected particles a special scanning mode, called ‘reverse imagingmode‘, was developed that reached resolutions down to eight nanometres [5]. In the reverse imaging mode dustparticles were picked up with the tip and imaged with the help of a sharp spike on a calibration sample. Theresulting images opened the possibility to identify the agglomerate structure of the dust down to the nanometrescale and to determine smallest features with mean sizes of about 100 nanometres. Whether these smallestfeatures are surface related or true subunits comprising the dust will be discussed on the basis of comparisons tosmallest subunit sizes identified by indirect Rosetta measurements and by investigations of other cometary material.References:[1] W. Riedler, K. Torkar, H. Jeszenszky, et al., MIDAS – The Micro-Imaging Dust Analysis System for theRosetta Mission. Space Science Reviews 128, 2007.[2] M.S. Bentley, H. Arends, B. Butler, et al., MIDAS: Lessons learned from the first spaceborne atomic forcemicroscope. Acta Astronautica 125, 2016.[3] M.S. Bentley, R. Schmied, T. Mannel et al., Aggregate dust particles at comet 67P/Chruyumov-Gerasimenko,Nature, 537, 2016.[4] T. Mannel, M.S. Bentley, R. Schmied et al., Fractal cometary dust – a window into the early Solar system,MNRAS, 462, 2016.[5] T. Mannel, M.S. Bentley, P.D. Boakes, et al., MIDAS results: classification and extension to the nanometrescale, submitted to Astronomy & Astrophysics, Rosetta special issue, 2018

Cometary dust: structure at the nanometre scale

International audienceThe Rosetta orbiter carried three dedicated dust analysis instruments to investigate the properties of the comet andits dust at smallest scales. The images with the highest resolutions were obtained by the MIDAS (Micro-ImagingDust Analysis System) atomic force microscope [1,2]. It collected dust particles of one to tens of micrometresin size and imaged their surface in 3D. Nominal images had approximately hundreds of nanometres resolutionand were used to study the particle morphology at the micrometre scale. It was shown that the majority ofcollected particles were fragile agglomerates [3] with a moderate packing density of subunits at the surface [4].Exceptions were one extremely porous particle with a fractal structure that is suggested to be pristinely preservedfrom early agglomeration processes in our Solar System [4], and the particles of about one micrometre size thatshow less fragility. To study these smallest detected particles a special scanning mode, called ‘reverse imagingmode‘, was developed that reached resolutions down to eight nanometres [5]. In the reverse imaging mode dustparticles were picked up with the tip and imaged with the help of a sharp spike on a calibration sample. Theresulting images opened the possibility to identify the agglomerate structure of the dust down to the nanometrescale and to determine smallest features with mean sizes of about 100 nanometres. Whether these smallestfeatures are surface related or true subunits comprising the dust will be discussed on the basis of comparisons tosmallest subunit sizes identified by indirect Rosetta measurements and by investigations of other cometary material.References:[1] W. Riedler, K. Torkar, H. Jeszenszky, et al., MIDAS – The Micro-Imaging Dust Analysis System for theRosetta Mission. Space Science Reviews 128, 2007.[2] M.S. Bentley, H. Arends, B. Butler, et al., MIDAS: Lessons learned from the first spaceborne atomic forcemicroscope. Acta Astronautica 125, 2016.[3] M.S. Bentley, R. Schmied, T. Mannel et al., Aggregate dust particles at comet 67P/Chruyumov-Gerasimenko,Nature, 537, 2016.[4] T. Mannel, M.S. Bentley, R. Schmied et al., Fractal cometary dust – a window into the early Solar system,MNRAS, 462, 2016.[5] T. Mannel, M.S. Bentley, P.D. Boakes, et al., MIDAS results: classification and extension to the nanometrescale, submitted to Astronomy & Astrophysics, Rosetta special issue, 2018

Cometary dust: structure at the nanometre scale

International audienceThe Rosetta orbiter carried three dedicated dust analysis instruments to investigate the properties of the comet andits dust at smallest scales. The images with the highest resolutions were obtained by the MIDAS (Micro-ImagingDust Analysis System) atomic force microscope [1,2]. It collected dust particles of one to tens of micrometresin size and imaged their surface in 3D. Nominal images had approximately hundreds of nanometres resolutionand were used to study the particle morphology at the micrometre scale. It was shown that the majority ofcollected particles were fragile agglomerates [3] with a moderate packing density of subunits at the surface [4].Exceptions were one extremely porous particle with a fractal structure that is suggested to be pristinely preservedfrom early agglomeration processes in our Solar System [4], and the particles of about one micrometre size thatshow less fragility. To study these smallest detected particles a special scanning mode, called ‘reverse imagingmode‘, was developed that reached resolutions down to eight nanometres [5]. In the reverse imaging mode dustparticles were picked up with the tip and imaged with the help of a sharp spike on a calibration sample. Theresulting images opened the possibility to identify the agglomerate structure of the dust down to the nanometrescale and to determine smallest features with mean sizes of about 100 nanometres. Whether these smallestfeatures are surface related or true subunits comprising the dust will be discussed on the basis of comparisons tosmallest subunit sizes identified by indirect Rosetta measurements and by investigations of other cometary material.References:[1] W. Riedler, K. Torkar, H. Jeszenszky, et al., MIDAS – The Micro-Imaging Dust Analysis System for theRosetta Mission. Space Science Reviews 128, 2007.[2] M.S. Bentley, H. Arends, B. Butler, et al., MIDAS: Lessons learned from the first spaceborne atomic forcemicroscope. Acta Astronautica 125, 2016.[3] M.S. Bentley, R. Schmied, T. Mannel et al., Aggregate dust particles at comet 67P/Chruyumov-Gerasimenko,Nature, 537, 2016.[4] T. Mannel, M.S. Bentley, R. Schmied et al., Fractal cometary dust – a window into the early Solar system,MNRAS, 462, 2016.[5] T. Mannel, M.S. Bentley, P.D. Boakes, et al., MIDAS results: classification and extension to the nanometrescale, submitted to Astronomy & Astrophysics, Rosetta special issue, 2018