Papers by Keyword: Microgravity

Abstract: Space traveling, extra-planetary exploration and even colonization requires to replicate our capabilities of manufacturing under non-entirely known environments and conditions. With the recent, yet always present, interest on colonizing spaces like the Moon or even Mars, space-based Additive Manufacturing (AM) has been considered for enabling space inhabitants to build their own tools. However, the same manufacturing techniques that are commonly used on Earth are not entirely applicable in space, especially during the considerably long traveling stage. Thus, several works have reported the study of how AM could be used in microgravity or near-zero g conditions by using the International Space Station as a laboratory. Unfortunately, the costs for doing such experiments are prohibitive, which is why experimentation in microgravity conditions on Earth is promising. In this paper, we explore the possibility of applying light-sensitive resin under Microgravity conditions using a Drop Tower facility and we propose a microgravity liquid printing technique. Our preliminary experiments focused on studying movement and extrusion velocities, extrusion nozzle diameter, UV light power, extrusion, and solidification times. The experimental runs (one catapult launch and four drops) let us find promising, although not entirely conclusive, data and practices to be considered in future works using this methodology. As expected, there is a similarity to liquid extrusion on Earth given that the initial shape and speed of extrusion influences the liquid material. Our findings also suggest that an initial contact point would help to increase the contact force due to surface tension and that the extrusion and solidification times are less than 5 seconds, which implies faster printing processes than in earth gravity conditions because the microgravity provides us less layer mixing during extrusion. The hardware, material and Microgravity drop tests used confirm the feasibility of this technique and they become an initial step for this printing process and liquid materials.

Abstract: 3D Printing in space has shown obvious advantages in several fields such as on-ground or in-situ manufacturing, space supplies, reducing spares and transportation, emergency response and promoting deep space exploration. This paper analyzes the application modes and technology development trend of 3D Printing in space. Based on the investigation of the current situation, technical plans and the potential development of 3D Printing in space, the article proposed a technical path suitable for the development of 3D printing in space.

Abstract: Water mist technology has been developed and regarded as a promising substitute fire-extinguishing agent in spacecraft. In this paper, a numerical simulation method is introduced to investigate the effect of water mist size, velocity and flow rateon the fire suppressionefficiencyin microgravity. The fire extinguishing efficiency is better for the finer water mist in microgravity due to better heat transfer and more rapid vaporization. The evaporation cooling is the dominant mechanism of fire suppression in microgravity.As for the water mist velocity, the performance of fire suppression is affected slightly in microgravity. The results on the effect of water flow rate show that the flow rate should be higher than a critical value to suppress the fire effectively.

Abstract: Boiling is known to be a very efficient mode of heat transfer in earth gravity, however, in microgravity bubble behavior is different because the buoyancy effects are replaced by surface tension effects such as Marangoni convection. The modeling of nucleate boiling with the effect of Marangoni convection in 0 g is accomplished by using Phase Field Method. Numerical simulation is carried out of single nucleating vapor bubble on a heated wall with and without Marangoni convection. The results show that the flow field consists of a major vortex that recirculates colder fluid from the upper region, pulling it toward the hot surface to the point where the bubble meets the heated surface. This type of flow pattern has been observed in various experiments.

Abstract: The manned spacecraft is a typically confined space in microgravity and it suffers severe fire risks. This paper studies on the distribution of the fire parameters in space-confined microgravity to find a more rational way to install the fire detectors. The experiments are carried out in the ground simulation experiment platform for fire based on the International Space Station. Based on the functional simulation principle, this paper maintains Gr (Grashof number) and increases Re (Reynolds number) to simulate microgravity environment in such a full-scale platform. The results show that Fire Detector 5 on the center of the side wall and Fire Detector 7 on the corner of the ceiling are the best installing locations for smoke detection. And, temperature detection is not appropriate in manned spacecraft. Namely, the way to install the fire detectors in manned spacecraft should be different from that in normal gravity.

Abstract: This paper provides an analysis of the formation of intermetallic phases in AlSi7Fe1 alloy in samples processed onboard the ISS. Based on axial 2D cross-sections obtained from regions of pure diffusive growth and also solidified with forced melt flow, the sizes and distribution of intermetallic β-Al₅FeSi phases were determined for different solidification velocities. In diffusive case the phases are larger and more homogeneously distributed than in case of induced melt flow. Additionally, especially for lower solidification velocity, the enrichment of Si and Fe in the centre part of the sample results in a few but rather large β-Al₅FeSi particles.

Abstract: In the frame of ESA-MAP (Microgravity Application Promotion) project entitled XRMON (In situ X-Ray MONitoring of advanced metallurgical processes under microgravity and terrestrial conditions), a microgravity (μg) experiment in the XRMON-GF (Gradient Furnace) setup was successfully launched in 2012 on board MASER 12 sounding rocket. During this experiment, in situ and real time observations of the formation of the solidification microstructures in diffusive conditions were carried out for the first time by using X-ray radiography. In addition, two reference experiments with the same control parameters but in ground-based conditions were performed to enable us a direct comparison with the μg experiment and therefore to enlighten the effects of gravity upon microstructure formation. This communication reports on fragmentation phenomenon observed during those experiments. For 1g upward solidification, fragmentations mainly take place in the upper part of the mushy zone. After their detachments, dendrite fragments are carried away by buoyancy force in the bulk liquid where they are gradually remelted. For μg experiment and horizontal solidification, this type of fragmentation is not observed. However, a great number of fragmentations are surprisingly revealed by in situ observation in the deep part of the mushy zone, when the liquid fraction is very small. Moreover, as soon as they are detached, the dendrite fragments move toward the cold part of the mushy zone, even in the case of μg experiment. The observations suggest that sample shrinkage may be at the origin of this fragment motion.

Abstract: A special type of divorced eutectic growth mode (symbiotic growth) in a ternary Al-Mn-Si alloy, triggered by addition of titanium boride (TiB2) has been studied under both ground and microgravity conditions. During directional solidification, α (AlMnSi) particles nucleate ahead of the planar solidification front and are pushed and later engulfed by the interface forming a banded particle layer structure. The presence of fine titanium boride particles (clusters) in front of the growing α (AlMnSi) particles makes the interaction between the intermetallic α (AlMnSi) particles and solidification front much more complex than most proposed models for particle/interface interactions. Microgravity experiments can eliminate the gravity related effects and thus provide an opportunity to better understand the formation mechanism of symbiotic growth. In this study, hypoeutectic Al-1Mn-3Si alloys with addition of 0.33 wt% TiB2 were directionally solidified in ESA Solidification and Quenching Furnace (SQF) on board of the International Space Station (ISS). The ground experiment was conducted in a replica of this furnace prior to the microgravity experiments. Non-destructive X-ray tomography and its 3D reconstruction software was used to characterize the particles and their distribution. Comparison between ground and microgravity experiment results is presented. The particle pushing and engulfment of symbiotic growth is discussed based on a particle pushing and engulfment model.

Abstract: This paper gives an overview of the experiments on-board the International Space Station (ISS) performed so far by the CETSOL team. Al-7 wt% Si alloys with and without grain refiners were solidified in microgravity. Detailed grain structure analysis showed columnar growth in case of non-refined alloy, but the existence of a columnar to equiaxed transition (CET) in refined alloy. One main result is a sharp CET when increasing the solidification velocity and a progressive CET for lowering the temperature gradient. Applying a front tracking model this behavior was confirmed numerically for sharp CET. Using a CAFE model both segregation and grain structures were numerically modeled and show a fair agreement with the experimental findings.

Abstract: During solidification of metallic alloys, thermosolutal natural convection plays a significant role in grain nucleation, subsequent growth and morphology, as well as the formation of casting defects. In this work, an Al-5wt%Ti-1wt%B inoculated Al-20wt%Cu alloy was solidified, near-isothermally, using a Bridgman-type gradient furnace, while being monitored in real-time via in-situ X-radiography as part of a parabolic flight microgravity campaign. Each parabola consisted of a transition through 24 seconds of hypergravity (1.8 g), followed by 22 seconds of microgravity, and a then a further 24 seconds of hypergravity. Solidification was controlled such that nucleation occurred coincident with the onset of microgravity. This allowed for the effects of microgravity on equiaxed nucleation and initial growth, followed by continuing solidification in hypergravity, to be observed, as well as the effect on the semi-coherent grain structure when transitioning between the two.