Microgravity Acceleration Research Articles

Dynamics of fluid-filled space multibody systems considering the microgravity effects

Many fluid-filled multibody systems have been used in the aerospace field. Many previous studies on the dynamics of these systems did not consider the microgravity acceleration effects. Under the microgravity acceleration action the fluid surface tension plays a dominant role in system's complex sloshing dynamic responses. An integrated computational methodology is proposed to study the nonlinear sloshing dynamics of fluid-filled space multibody systems under the actions of microgravity accelerations. The Smoothed Particle Hydrodynamics (SPH) method is used to describe the fluid and the absolute nodal coordinate formulation (ANCF) is used to describe the flexible bodies. To consider the liquid-gas interaction in the container of the fluid-filled multibody systems, a multiphase SPH model is adopted. The continuum surface force (CSF) model is adopted to treat the liquid-gas interface tension effects. A liquid static contact angle is defined to describe the liquid-solid contact interface. Finally, the effectiveness of the proposed methodology is validated by the four examples. Some new nonlinear sloshing dynamical behaviours of the space liquid-filled flexible multibody systems under the action of different gravitational accelerations are observed.

Microgravity disturbance analysis on Chinese space laboratory

Many scientific experiments are conducted in space; therefore, it is critical to understand the microgravity environment of a space laboratory. The first Chinese cargo ship, Tianzhou-1 (TZ-1), entered space on 20 April, 2017 and later joined with the Tiangong-2 (TG-2) Chinese space laboratory. TZ-1 carried a high-precision electrostatic suspension accelerometer system (ES-ACC) for measuring the microgravity acceleration on the spacecraft and a microgravity-active vibration system (MAIS), which contained flexible quartz accelerometers (Q-ACC). The ES-ACC was able to provide a reduced-disturbance environment for the MAIS. The purpose of these two instruments was to validate novel technologies and as an opportunity to record the microgravity acceleration of TZ-1 and TG-2 in detail during spacecraft operation in different flight modes, with or without vibration isolation. The acceleration data were analyzed comprehensively in a time–frequency–amplitude spectrogram. Some periodical disturbances with orbital period and irregular signals related to certain in-orbit events were observed. After reducing those disturbances, the microgravity levels on TZ-1 and TG-2 could be resolved to better than 10−6 m/s2 in the root mean square in the frequency of 0.01–10 Hz. These accurate measurements aboard the Chinese space laboratory will provide valuable information to optimize working conditions for scientific experiments.

Flight Test Results of the Microgravity Active Vibration Isolation System in China\u2019s Tianzhou-1 Mission

The Microgravity Active vibration Isolation System (MAIS) was operated on China’s first cargo-spacecraft Tianzhou-1, which was launched on April 20, 2017 and re-entered atmosphere and burned on September 22, 2017. In this article, the flight test results of MAIS is presented. The results are evaluated in terms of the performances of microgravity acceleration and vibration attenuation under control. Firstly, the system configuration of MAIS on Tianzhou-1 is described, including operating modes, acceleration measurement, and control schemes. Then, two control performance indices, namely, microgravity acceleration and vibration attenuation, are introduced, followed by their definitions and methods of calculation. Subsequently, the flight test results of MAIS are described in detail. The microgravity acceleration under a PID (Proportional-Integral-Derivative) controller is at the order of 10−7 – 10−6 m/s2 in the frequency band of 0.01–10 Hz, and the performance of vibration attenuation reaches −20 dB at frequencies higher than 0.2 Hz. The flight test results show that MAIS in the TZ-1 mission performed well and achieved the expected control performance of microgravity vibration isolation in orbit. Finally, some experiences and lessons learned are summarized, which can serve as a benchmark reference to develop MAIS-like devices on board China’s Space Station in the near future.

Voyage to Alpha Centauri: Entanglement degradation of cavity modes due to motion

We propose a scheme to investigate whether non-uniform motion degrades entanglement of a relativistic quantum field that is localised both in space and in time. For a Dirichlet scalar field in a cavity in Minkowski space, in small but freely-adjustable acceleration of finite but arbitrarily long duration, degradation of observable magnitude occurs for massless transverse quanta of optical wavelength at Earth gravity acceleration and for kaon mass quanta already at microgravity acceleration. We outline a space-based experiment for observing the effect and its gravitational counterpart.

Crystal growth of HgZnTe alloy by directional solidification in low gravity environment

An Hg 0.84Zn 0.16Te alloy crystal was back-melted and partially resolidified during the first United States Microgravity Laboratory mission in the Marshall Space Flight Center's Crystal Growth Furnace. The experiment was inadvertently terminated at about 30% of planned completion. Nonetheless, it was successfully demonstrated that a HgZnTe alloy ingot partially grown and quenched on the ground can be back-melted and regrown in space under nearly steady-state growth conditions. An identical “ground-truth” experiment was performed following the mission and a comparison between the properties of the crystals is described. The results indicate the importance of residual microgravity acceleration (≲0.4 μg) even in the submicrogravity range for the slow solidification velocities and large density gradients.

The electrohydrodynamic stability of a liquid bridge: microgravity experiments on a bridge suspended in a dielectric gas

The electrohydrodynamic stability of a liquid bridge was studied in steady and oscillatory axial electric fields with a novel apparatus aboard a space shuttle. To avoid interphase transport, which complicates matters in terrestrial, matched-density systems, the experiments focused on a liquid column surrounded by a dielectric gas. The micro-gravity acceleration level aboard the spacecraft kept the Bond number small; so interface deformation by buoyancy was negligible. To provide microgravity results for comparison with terrestrial data, the behaviour of a castor oil bridge in a silicone oil matrix liquid was studied first. The results from these experiments are in excellent agreement with earlier work with isopycnic systems as regards transitions from a perfect cylinder to the amphora shape and the separation of an amphora into drops. In addition, the location of the amphora bulge was found to be correlated with the field direction, contrary to the leaky dielectric model but consistent with earlier results from terrestrial experiments. Next, the behaviour of a bridge surrounded by a dielectric gas, sulphur hexa fluoride (SF6), was investigated. In liquid–gas experiments, electrohydrodynamic ejection of liquids from ‘Taylor cones’ was used to deploy fluid and form bridges by remote control. Experiments with castor oil bridges in SF6 identified the conditions for two transitions: cylinder–amphora, and pinch-off. In addition, new behaviour was uncovered with liquid–gas interfaces. Contrary to expectations based on perfect dielectric behaviour, castor oil bridges in SF6 could not be stabilized in AC fields. On the other hand, a low-conductivity silicone oil bridge, which could not be stabilized by a DC field, was stable in an AC field.

Methodology for microgravity quality assessment, implementation, and verification of orbital systems: A challenge for microgravity engineering science

The present paper outlines a methodology for dealing with the various microgravity quality aspects of orbital systems. Of cardinal importance in the presented procedures of quality assessment, implementation, and verification are the microgravity acceleration characteristics, in terms of which the microgravity quality of the orbital systems considered is directly expressed and described. Therefore, particular attention is being paid to the various acceleration sources and constituents existing under typical orbital and operational conditions. It is attempted to provide a complete description of this microgravity environment in terms of its various components. For the microgravity analysis and quality assessment of a given orbital system, a global, comprehensive mathematical microgravity model is proposed, and outlined in its essential features, which yields as output the microgravity acceleration levels and field values, including the detailed spatial, temporal, and spectral distributions, and which is capable of dealing with both quasi-stationary and time-variable (incl. transient) sources and disturbances. Proven methods of implementation and of control of the microgravity environment are indicated. Principles, technical concepts, and limitations, of in-orbit accelerometric measurements are discussed. The need for adequate measurement instrumentation with sufficiently high resolution at very low frequencies (< 0.1 Hz) is acknowledged.

Organic crystal growth in low earth orbit

Six experiments were performed in the Diffusive Mixing of Organic Solutions (DMOS-2) apparatus aboard the orbiter Atlantis during the Space Transportation System mission 61-B. In four of these experiments, solutions of organic compounds were allowed to mix and form crystals while in Earth orbit. Because mass transport in the crystal growth experiments was important, an additional pair of experiments addressed fluid mixing behavior in the microgravity environment. After recovery of the apparatus, analysis revealed that convective mixing took place in those experiments involving fluids having significantly different densities. In other experiments with fluids having small density differences, diffusion controlled the mixing of the fluids, even though residual milligravity to microgravity accelerations were present during the mission. Regardless of the mass transport mechanism, the crystals formed in these experiments were not found to be superior to crystals produced in a similar manner on Earth.