Osamu Mori

Abstract Volatile and organic-rich C-type asteroids may have been one of the main sources of Earth’s water. Our best insight into their chemistry is currently provided by carbonaceous chondritic meteorites, but the meteorite record is biased: only the strongest types survive atmospheric entry and are then modified by interaction with the terrestrial environment. Here we present the results of a detailed bulk and microanalytical study of pristine Ryugu particles, brought to Earth by the Hayabusa2 spacecraft. Ryugu particles display a close compositional match with the chemically unfractionated, but aqueously altered, CI (Ivuna-type) chondrites, which are widely used as a proxy for the bulk Solar System composition. The sample shows an intricate spatial relationship between aliphatic-rich organics and phyllosilicates and indicates maximum temperatures of ~30 °C during aqueous alteration. We find that heavy hydrogen and nitrogen abundances are consistent with an outer Solar System origin. Ryugu particles are the most uncontaminated and unfractionated extraterrestrial materials studied so far, and provide the best available match to the bulk Solar System composition.

In this article, a self-reconfiguring OrigamiSat concept is presented. The reconfiguration of the proposed OrigamiSat is triggered by combining the effect of 4D material (i.e. origami’s edges) and changes in the local surface optical properties (i.e., origami’s facets) to harness the solar radiation pressure acceleration. The proposed OrigamiSat uses the principle of solar sailing to enhance the effect of the Sun radiation to generate momentum on the Aluminised Kapton (Al-Kapton) origami surface by transitioning from mirror-like to diffusely reflecting optical properties of each individual facet. Numerical simulations have demonstrated that local changes in the optical properties can trigger reconfiguration. A minimum of 1-m edge size facet is required for a thick-origami to generate enough forces from the Sun radiation. The thick-origami pattern is 3D-printed directly on a thin Al-Kapton film (the solar sail substrate which is highly reflective). An elastic filament (thermoplastic polyurethane TPU) showed best performance when printing directly on the Al-Kapton and the Acrylonitrile Butadiene Styrene with carbon fiber reinforcement (ABS/cc) is added to augment the origami mechanical properties. The 4D material (shape memory polymer) is integrated only at specific edges to achieve self-deployment by applying heat. Two different folding mechanisms were studied: 1) the cartilage-like, where the hinge is made combining the TPU and the 4D material which make the mounts or valleys fully stretchable, and 2) the mechanical hinge, where simple hinges are made solely of ABS/cc. Numerical simulations have demonstrated that the cartilage-like hinge is the most suitable design for light-weight reconfigurable OrigamiSat when using the solar radiation pressure acceleration. We have used build-in electric board to heat up the 4D material and trigger the folding. We envisage embedding the heat wire within the 4D hinge in the future.

Spin-type solar sails have the advantage of being lighter compared to other deployment methods, but can exhibit complex deployment dynamics. Severe asymmetric dynamics was observed in the deployment experiment in a vacuum chamber. In this study, this deployment behavior is reproduced by numerical simulations using multi-particle techniques that take into account membrane collisions. We propose a simple method to predict whether a significant asymmetry will occur by calculating the energy change of the membrane. The conditions for realizing symmetric deployment are presented.

<p>Solar sail technique was demonstrated in the IKAROS mission. However, the membrane of IKAROS has deformed to a shape that was not flat. The whole membrane changes greatly like an umbrella shape or a saddle shape depending on the warping direction of the thin-film devices on the membrane, such as thin-film solar cells, reflectivity control devices and dust counters. Objection of this study is to clarify mechanism of influence on solar radiation pressure (SRP) torque due to warp of thin-film device and its solution method. Therefore, the shape of the overall membrane is clarified by using a simple finite element model and the SRP torque with respect to the shape is calculated, and the mechanism of the overall shape change in warpage and its influence is clarified. As a result, the influence on SRP is related to membrane stiffness and warped direction and it is found that the suitable conditions to minimize SRP torque are as follows: a) the sail is warped in the radial direction, b) the base film of the sail has low stiffness, c) the outermost part of the sail has high stiffness, and d) the length of bridges between petals is short.</p>

<p>At bipropellant chemical propulsion systems, iron in oxidizer is one of the topics to be noted and controlled. Actually, to avoid the influence of the iron ingredient, several long term mission spacecraft such as interplanetary probes flush the oxidizer piping periodically. The major influence of steel contaminated oxidizer is known to be flow decay. Still, operation data of the HAYABUSA2 spacecraft indicates possibility of other drawbacks. This paper discusses its impact to the reactivity of the hypergolic propellant, especially for the propellant combination of N₂H₄/MON3, which is the case of HAYABUSA2. A series of open cup firing tests show that the reactivity deteriorates when the oxidizer is contaminated with iron.</p>

<p>A thin-film device mounted on development type membrane structure is limited to arrangement and deployment on the plane. In this paper, we propose a three-dimensional film structure (3D film) that can stereoscopically place and deploy thin-film devices. This method can be widely applied to non-spin type or spin type developable structures having a mast structure. In this paper, in order to apply to non-spin / spin type developed structures, we evaluate extension shapes of 3D film by crease and condition of existence / nonexistence of centrifugal force, and placement and arrangement of thin-film devices.</p>