141 research outputs found
Data for "Strength Evolution of Ice Plume Deposit Analogs of Enceladus and Europa"
No full textThis Excel spreadsheet contains all data necessary to reproduce the work and figures presented in Choukroun et al. GRL 2020 article:
- First tab contains all tabulated Cone Penetration Tests data (Figures 1, 2-a, 3)
- Second tab contains graduated cylinder density data (Table S2)
- Third tab contains the parameters of linear fits of strengthening as function of time at each temperature (from Figure 2-a, used in Figure 2-b)
- Fourth tab contains the parameters of the best fit Arrhenius relationship from the strengthening rate as function of temperature (derived from Figure 2-b, used to extrapolate to Enceladus and Europa conditions in Figure 4
A new sampling system tailored to experimentally-derived mechanical properties of icy analogs for evolved Enceladus surface plume deposits
No full textEnceladus is unique amongst Ocean Worlds in our Solar System: the contents of its internal ocean are continuously emitted to space by its present-day activity, and some of these materials are redeposited on the surface. This tiny moon of Saturn thus presents an opportunity to directly measure the composition of the ocean and seek evidence for habitability (including past or extant life), either by collecting and analyzing plume particles as previously proposed by Discovery and New Frontiers mission concepts, or via more ambitious mission concepts that involve landing, surface sampling and analysis, and potential deployment of subsurface probes to reach the ocean itself (Hofgartner et al., this meeting). However, the low surface gravity (1% of Earth’s) and extreme cryogenic conditions in the South Pole regions (~ 50 K, away from the Tiger Stripes) raises questions: how to best sample the upper ~ 1 cm of the surface around a lander, made of most freshly deposited plume materials? What are the expected properties of these materials, i.e. how fast does sintering proceed and how strong would these materials be as function of their exposure age? We provide answers to these questions via a two-pronged approach. First, we surveyed experimentally the time evolution of mechanical strength of large samples of ice spherules at several temperatures. A custom sample preparation system has been developed to synthesize ice spheres with a grain size distribution of mean ~ 12 microns. The samples are subsequently held at temperatures of -30, -50, and -80 C, over extended periods of time (up to 9 months at time of writing), and their strength is tested at frequent intervals using cone penetration tests. The data obtained to date suggests that the observed temperature dependence of the strength evolution is commensurate with expectations from vapor diffusion. Second, we developed a new sampling system that enables rapid sampling and transfer of surface materials into receptacles. Those receptacles can then deposit the sampled materials into the inlet of an instrument dedicated to analyzing the chemical composition of these materials and seek tracers of past or extant life. The geometry of the system and principles of operation have been established and validated by experimental tests, as well as dynamical simulations
Raman and X-Ray Diffraction Data for Acetylene Clathrate
No full textData behind figures for J. Phys. Chem. A 2019, 123, 7051-7056Related Publication:
Raman Signatures and Thermal Expansivity of Acetylene Clathrate Hydrate
Tuan H. Vu, Robert Hodyss, Morgan L. Cable, Mathieu Choukroun Caltech / JPL
The Journal of Physical Chemistry A
2019-07-16
https://doi.org/10.1021/acs.jpca.9b04426
en
Development of a Robotics-based Satellites Docking Simulator
No full textThe European Proximity Operation Simulator (EPOS) is a hardware-in-the-loop (HIL) system aiming, among other objectives, at emulating on-orbit docking of spacecraft for verification and validation of the docking phase. This HIL docking simulator set-up essentially consists of docking interfaces, simulating the servicing satellite called chaser satellite, the serviced satellite called target satellite, a sensor of the forces and torques during contact, and two industrial robots that hold the docking interfaces, and control satellites motion relative position and attitude. Furthermore, the EPOS includes a real-time controller interface linked to a computer-based numerical simulator of satellites orbital and attitude dynamics. A key feature of this set-up is the feedback loop that is closed on the real force sensed at the docking interfaces during contact. That feedback force is used as driving input to satellites dynamics numerical simulation. This HIL docking simulation concept has the unique advantage of using the measured contact forces and torques, but it presents significant challenges. The high stiffness of the industrial robots and the docking interfaces yields a high bandwidth contact dynamics at impact and, thus, very short contact time durations. These times might be shorter than the inherent time delay of the robot controllers. This leads to physical inconsistency in the docking dynamics and measured variables. This also causes a stability issue in the force feedback HIL system during contact and may cause catastrophic damages to the robots. Additional problems that need to be addressed are the characterization of the stability domain of operation, the compensation of the non-contact forces and torques, such as the measured forces and torques due to gravity effect. Finally, this thesis addresses the task of identifying the dynamic behavior of the robot end-effectors. This thesis addresses the above mentioned challenges and problems and presents solutions towards a stable and safe docking simulation operation of the EPOS facility. First, in order to mitigate the high stiffness and time delay problem, the thesis introduces a novel idea of simulating contact based on a concept called hybrid contact dynamics model. The method, developed in this thesis, is based on a combination of a passive compliance control introduced at the end-effector of the robot and a virtual contact model. The virtual contact model allows the operator to vary the contact parameters which can also be used as a control gain. The method also allows to solve the stability problem coming from the combination of time delay of the robot controller and high stiffness of the robot end-effector. For the passive compliance control, a new device is designed that has fairly known stiffness properties which are softer than the robot and docking interface stiffness. Second, the thesis presents a stability analysis of the proposed method via the adaptation of the pole location method to dead-time systems. The analysis is based on a linearized design model of the dynamics; linearization is performed around the docking geometrical configuration. This work first presents an analysis for the single dimensional case, which is then extended to two dimensions. The highlight of the stability analysis is the development of physically intuitive state-space model that easily unveil the modes of the contact dynamics. The application of the pole location method to the resulting second-order characteristics polynomial is straight forward. The contribution of this analysis is a closed-form relationship, and associated plots, among the system's parameter, i.e., the satellite's masses, the stiffness and damping coefficient of the contact parameters, the delay, and the geometry. In addition, the stability analysis is supported using the passivity method which is valid for three dimensions. Third, a model of the force-torque sensor is presented, and the classical weighted least-squares estimation technique is suggested for the identification and compensation of the non-contact forces and torques from the contact force and the torque measurement. Finally, it is proposed to utilize a LEICA laser tracker, a positioning measurement system, in order to identify the robot end-effectors dynamics behaviors such as the natural frequency and damping ratio. This hybrid contact dynamics model and the accompanying analysis is envisioned as a tool for safe and flexible EPOS operations. This tool shall allow emulation of the desired impact dynamics for any stiffness and damping characteristics within the stability region without recurring to a modification of the hardware. The experimental results of the robotics based hybrid docking simulator comply with experimental data from an air-bearing testbed that was independently performed by this author at the Space Robotics Laboratory of Tohoku University. It demonstrates the validity of the novel EPOS concept of operations and increases the confidence of using this approach for future on-orbit docking/contact algorithm validation, at the EPOS facility.Space Systems EngineeringAerospace Engineerin
Formation Kinetics of Ethane Clathrate on Titan
No full textData behind figures for "Rapid Formation of Clathrate Hydrate From Liquid Ethane and Water Ice on Titan," published in Geophysical Research Letters on Jan 29, 2020Related Publication:
Rapid Formation of Clathrate Hydrate from Liquid Ethane and Water Ice on Titan
Tuan H. Vu, Mathieu Choukroun, Christophe Sotin, Victoria Munoz-Iglesias, Helen E. Maynard-Casely
Geophysical Research Letters
2020-01-29
https://doi.org/10.1029/2019GL086265
en
Sampling tool concepts for Enceladus lander in-situ analysis
No full textA potential future in-situ lander mission to the surface of Enceladus could be the lowest cost mission to determine if life exists beyond Earth since material from the subsurface ocean, where the presence of hydrothermal activity has been strongly suggested by the Cassini mission, is available on its surface after being ejected by plumes and then settling on the surface. In addition, the low radiation environment of Enceladus would not significantly alter the chemical makeup of samples recently deposited on the surface. A study was conducted to explore various sampling devices that could be used by an in-situ lander mission to provide 1cc to 5cc volume samples to instruments. In addition to temperature and vacuum environmental conditions, the low surface gravity of Enceladus (1% of Earth gravity) represents a new challenge for surface sampling that is not met by sampling systems developed for microgravity (e.g., comets and asteroids) or higher gravity (e.g., Europa 13%g, Moon 16%g, or Mars 38%g) environments. It is desired to acquire surface plume material that has accumulated in the top 1cm to ensure acquisition of the least processed material. Several sampling devices were developed or adapted and then tested in simulated conditions that resemble the Enceladus surface properties. These devices and test results are presented in this paper
The Dual-Rasp Sampling System for an Enceladus Lander
No full textThe Dual-Rasp sampling system has been developed for the unique sampling environment of a lander mission to the surface of Saturn's moon Enceladus. Plume material from the subsurface ocean that has fallen to the surface is desired resulting in an objective to sample the topmost layer of icy material. The low gravity and potential large range of surface properties are challenges for the sampling system. The Dual-Rasp sampling system has two counter-rotating rasp cutters with teeth that remove material that is thrown up between the cutters. Two prototypes of the Dual-Rasp sampling system were built and tested, one with a carousel and one that uses pneumatics for sample transfer
Relative Navigation in Asteroid Missions: Dual Quaternion Approach
No full textAerospace EngineeringSpace EngineeringAstrodynamics & Space Mission
Thermodynamic model for water and high-pressure ices up to 2.2GPa and down to the metastable domain
No full textAttitude control system of the Delfi-n3Xt satellite
No full textThis work is concerned with the development of the attitude control algorithms that will be implemented on board of the Delfi-n3xt nanosatellite, which is to be launched in 2013. One of the mission objectives is to demonstrate Sun pointing and three axis stabilization. The attitude control modes and the associated algorithms are described. The control authority is shared between three body-mounted magnetorquers (MTQ) and three orthogonal reaction wheels. The attitude information is retrieved from Sun vector measurements, Earth magnetic field measurements, and gyro measurements. The design of the control is achieved as a trade between simplicity and performance. Stabilization and Sun pointing are achieved via the successive application of the classical Bdot control law and a quaternion feedback control. For the purpose of Sun pointing, a simple quaternion estimation scheme is implemented based on geometric arguments, where the need for a costly optimal filtering algorithm is alleviated, and a single line of sight (LoS) measurement is required ? here the Sun vector. Beyond the three-axis Sun pointing mode, spinning Sun pointing modes are also described and used as demonstration modes. The three-axis Sun pointing mode requires reaction wheels and magnetic control while the spinning control modes are implemented with magnetic control only. In addition, a simple scheme for angular rates estimation using Sun vector and Earth magnetic measurements is tested in the case of gyro failures. The various control modes performances are illustrated via extensive simulations over several orbits time spans. The simulated models of the dynamical space environment, of the attitude hardware, and the onboard controller logic are using realistic assumptions. All control modes satisfy the minimal Sun pointing requirements allowed for power generation.Space EngineeringAerospace Engineerin
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