Cometary dust analogues for physics experiments

The CoPhyLab (Cometary Physics Laboratory) project is designed to study the physics of comets through a series of earth-based experiments. For these experiments, a dust analogue was created with physical properties comparable to those of the non-volatile dust found on comets. This "CoPhyLab dust" is planned to be mixed with water and CO$_2$ ice and placed under cometary conditions in vacuum chambers to study the physical processes taking place on the nuclei of comets. In order to develop this dust analogue, we mixed two components representative for the non-volatile materials present in cometary nuclei. We chose silica dust as representative for the mineral phase and charcoal for the organic phase, which also acts as a darkening agent. In this paper, we provide an overview of known cometary analogues before presenting measurements of eight physical properties of different mixtures of the two materials and a comparison of these measurements with known cometary values. The physical properties of interest are: particle size, density, gas permeability, spectrophotometry, mechanical, thermal and electrical properties. We found that the analogue dust that matches the highest number of physical properties of cometary materials consists of a mixture of either 60\%/40\% or 70\%/30\% of silica dust/charcoal by mass. These best-fit dust analogue will be used in future CoPhyLab experiments

Spacecraft Proximity Navigation and Autonomous Assembly based on Augmented State Estimation: Analysis and Experiments

This paper presents a spacecraft relative navigation scheme based on a tracking technique. The augmented state estimation technique is a variable-dimension filtering approach, originally introduced by Bar-Shalom and Birmiwal[1]. In this technique, the state model for a target spacecraft is augmented by introducing, as extra state components, the target's control inputs. The maneuver, modeled as accelerations, is estimated recursively along with the other states associated with position and velocity, while a target maneuvers. By using the proposed navigation method, a chaser spacecraft can estimate the relative position, the attitude and the control inputs of a target spacecraft, flying in its proximity. It is assumed that the chaser spacecraft is equipped with on-board sensors able to measure the relative position and relative attitude of the target spacecraft. The available sensors would provide a measurement update sample time of the order of one second and be subject to random measurement interruption longer than one second. As preliminary analysis, this work introduces the technique applied to the planar, three-degree-of- freedom, spacecraft relative motion. The proposed approach is validated via hardware-in-the-loop experimentation, using four autonomous three-degree-of- freedom robotic spacecraft simulators, floating on a flat floor. The proposed navigation method is proved to be more robust than a standard Kalman Filter estimating relative position and attitude only

The CoPhyLab comet-simulation chamber

The Comet Physics Laboratory (CoPhyLab) is an international research program to study the physical properties of cometary analog materials under simulated space conditions. The project is dedicated to studying, with the help of multiple instruments and the different expertise and background from the different partners, the physics of comets, including the processes inside cometary nuclei, the activity leading to the ejection of dust and gas, and the sub-surface and surface evolution of cometary nuclei when exposed to solar illumination. CoPhyLab will provide essential information on the formation and evolution of comets and insights into the origins of primitive Solar System bodies. To this end, we constructed a new laboratory that hosts several small-scale experiments and a large-scale comet-simulation chamber (L-Chamber). This chamber has been designed and constructed to host ice–dust samples with a diameter of up to 250 mm and a variable height between 100 and 300 mm. The cometary-analog samples will be kept at temperatures below 120 K and pressures around 10−6 mbar to ensure cometary-like conditions. In total, 14 different scientific instruments are attached to the L-Chamber to study the temporal evolution of the physical properties of the sample under different insolation conditions. Due to the implementation of a scale inside the L-Chamber that can measure weight changes of the samples with high precision, the cooling system is mechanically decoupled from the sample holder and cooling of the samples occurs by radiation only. The constructed chamber allows us to conduct uninterrupted experiments at low temperatures and pressures up to several weeks