Microgravity Research Articles

A Piezoelectric Balance System With Mass Automatic Recognition Ability Based on Resonant Frequency Shift

Mass measurement in the microgravity environment is a crucial technology promoting space science experiments. Here, a piezoelectric balance (PEBL) based on resonant frequency shift is proposed to achieve mass measurement for microgravity environment. The structural and electrical designs of the PEBL are elaborated, and the theoretical modeling is accomplished to carry out parameter analysis. The finite-element method (FEM) simulation is used to analyze the vibration modes and verify the relationship between the resonant frequency shift and the measured mass, in which the working mode of the PEBL is determined; the impact resistance of the PEBL is analyzed, which shows that it can resist acceleration overload of larger than 50 times the gravity acceleration. A prototype is developed and its vibration characteristics and impedance characteristics are tested experimentally. The experiments successfully verify the effectiveness of theoretical analysis. Furthermore, an automatic mass recognition system is developed to achieve fast detection of the resonant frequency and the measured mass. The developed PEBL system achieves measurement range of 283.36 g with measurement uncertainty of about 1.22% (3.47 g). It is a suitable candidate for mass measurement in microgravity environment with merits of independence on the acceleration field, low power consumption, structure miniaturization, and configuration simplification.

Numerical simulation and experiment of a blade management device in microgravity

Currently, most satellite propulsion systems are mainly chemical propulsion, and liquid propellant is the necessary power fuel for the propulsion system. The working environment of microgravity occurs when the satellite is in orbit. According to the working characteristics of the satellite, a propellant management device of vane type is designed. The PMD is composed of a vertical guide plate and a liquid accumulator, which is applied to the propellant tank to store and manage the propellant. In this paper, the microgravity gas-liquid management and control mechanism of a propellant management device of vane type is studied by numerical simulation and tower drop test. The results of numerical simulation and tower drop test are consistent, which verifies the good fluid management characteristics of this type of propellant management device, and provides references for its engineering application and the design of this type of structure.

Bubble nucleation and growth on microstructured surfaces under microgravity

Understanding the dynamics of surface bubble formation and growth on heated surfaces holds significant implications for diverse modern technologies. While such investigations are traditionally confined to terrestrial conditions, the expansion of space exploration and economy necessitates insights into thermal bubble phenomena in microgravity. In this work, we conduct experiments in the International Space Station to study surface bubble nucleation and growth in a microgravity environment and compare the results to those on Earth. Our findings reveal significantly accelerated bubble nucleation and growth rates, outpacing the terrestrial rates by up to ~30 times. Our thermofluidic simulations confirm the role of gravity-induced thermal convective flow, which dissipates heat from the substrate surface and thus influences bubble nucleation. In microgravity, the influence of thermal convective flow diminishes, resulting in localized heat at the substrate surface, which leads to faster temperature rise. This unique condition enables quicker bubble nucleation and growth. Moreover, we highlight the influence of surface microstructure geometries on bubble nucleation. Acting as heat-transfer fins, the geometries of the microstructures influence heat transfer from the substrate to the water. Finer microstructures, which have larger specific surface areas, enhance surface-to-liquid heat transfer and thus reduce the rate of surface temperature rise, leading to slower bubble nucleation. Our experimental and simulation results provide insights into thermal bubble dynamics in microgravity, which may help design thermal management solutions and develop bubble-based sensing technologies.

Construction of microgravity biological knowledge graph and its applications in anti-osteoporosis drug prediction

Microgravity in the space environment can potentially have various negative effects on the human body, one of which is bone loss. Given the increasing frequency of human space activities, there is an urgent need to identify effective anti-osteoporosis drugs for the microgravity environment. Traditional microgravity experiments conducted in space suffer from limitations such as time-consuming procedures, high costs, and small sample sizes. In recent years, the in-silico drug discovery method has emerged as a promising strategy due to the advancements in bioinformatics and computer technology. In this study, we first collected a total of 184,915 literature articles related to microgravity and bone loss. We employed a combination of dependency path extraction and clustering techniques to extract data from the text. Afterwards, we conducted data cleaning and standardization to integrate data from several sources, including The Global Network of Biomedical Relationships (GNBR), Curated Drug–Drug Interactions Database (DDInter), Search Tool for Interacting Chemicals (STITCH), DrugBank, and Traditional Chinese Medicines Integrated Database (TCMID). Through this integration process, we constructed the Microgravity Biology Knowledge Graph (MBKG) consisting of 134,796 biological entities and 3,395,273 triplets. Subsequently, the TransE model was utilized to perform knowledge graph embedding. By calculating the distances between entities in the model space, the model successfully predicted potential drugs for treating osteoporosis and microgravity-induced bone loss. The results indicate that out of the top 10 ranked western medicines, 7 have been approved for the treatment of osteoporosis. Additionally, among the top 10 ranked traditional Chinese medicines, 5 have scientific literature supporting their effectiveness in treating bone loss. Among the top 20 predicted medicines for microgravity-induced bone loss, 15 have been studied in microgravity or simulated microgravity environments, while the remaining 5 are also applicable for treating osteoporosis. This research highlights the potential application of MBKG in the field of space drug discovery.

Unlocking the potential: analyzing 3D microstructure of small-scale cement samples from space using deep learning

Due to the prohibitive cost of transporting raw materials into Space, in-situ materials along with cement-like binders are poised to be employed for extraterrestrial construction. A unique methodology for obtaining microstructural topology of cement samples hydrated in microgravity environment at the International Space Station (ISS) is presented here. Distinctive Scanning Electron Microscopy (SEM) micrographs of hardened tri-calcium silicate (C3S) samples were used as exemplars in a deep learning-based microstructure reconstruction framework. The proposed method aids in generation of an ensemble of microstructures that is inherently statistical in nature, by utilizing sparse experimental data such as the C3S samples hydrated in microgravity. The hydrated space-returned samples had exhibited higher porosity content (~70 %) with the portlandite phase assuming an elongated plate-like morphology. Qualitative assessment of the volumetric slices from the reconstructed volumes showcased similar visual characteristics to that of the target 2D exemplar. Detailed assessment of the reconstructed volumes was carried out using statistical descriptors, and was further compared against micro-CT virtual data. The reconstructed volumes captured the unique microstructural morphology of the hardened C3S samples of both space-returned and ground-based samples, and can be directly employed as Representative Volume Element (RVE) to characterize mechanical/transport properties.

Effect of 15 days -6° head-down bed rest on microbial communities of supragingival plaque in young men.

The microgravity environment astronauts experience during spaceflight can lead to an increased risk of oral diseases and possible changes in oral microecology. In this study, we aimed to assess changes in the microbial community of supragingival plaques to explore the effects of spaceflight microgravity environment on oral microecology. Sixteen healthy male volunteers were recruited, and supragingival plaque samples were collected under -6° head-down bed rest (HDBR) at five-time points: day 1 before HDBR; days 5, 10, and 15 of HDBR; and day 6 of recovery. Bacterial genomic DNA was sequenced using gene sequencing technology with 16S ribosomal ribonucleic acid V3-V4 hypervariable region amplification and the obtained data were analyzed bioinformatically. Alpha diversity analysis showed a significant increase in species richness in supragingival plaque samples on day 15 of HDBR compared with that at pre-HDBR. Beta diversity analysis revealed that the community composition differed among the groups. Species distribution showed that, compared with those at pre-HDBR, the relative abundances of Corynebacterium and Aggregatibacter increased significantly during HDBR, while those of Veillonella, Streptococcus, and Lautropia decreased significantly. Moreover, compared with those at pre-HDBR, the relative abundance of Leptotrichia increased significantly on day 6 of recovery, whereas the relative abundances of Porphyromonas and Streptococcus decreased significantly. Network analysis showed that the interaction relationship between the dominant genera became simpler during HDBR, and the positive and negative correlations between them showed dynamic changes. Phylogenetic investigation of communities by reconstruction of unobserved states analysis showed that the amino acid metabolism function of plaque microorganisms was more enriched during HDBR. In summary, in a 15-day simulated microgravity environment, the diversity, species distribution, interaction relationship, and metabolic function of the supragingival plaque microbial community changed, which suggests that microgravity may affect the oral microecosystem by changing the balance of supragingival plaque microbial communities and further leading to the occurrence and development of oral diseases.

Phase Separation through Screen Channel Liquid Acquisition Devices in Microgravity

To enable future deep space exploration, orbital refueling of spacecraft is essential. However, transferring liquid in a microgravity environment is a complex process dependent on various factors. One of the basic and critical tasks is to separate phases to allow the supply of gas-free liquid from one tank to another. For this purpose, a liquid acquisition device is essential. In this work, a screen channel liquid acquisition device was designed and used to investigate phase separation and liquid removal from an experiment tank in a microgravity environment. The experiments were performed using the drop tower facility at the University of Bremen, with HFE-7500 as the test liquid under isothermal conditions. This investigation explored the interdependent effects of various phenomena, including the reorientation of liquid in the tank, capillary rise between parallel plates, flow through screen pressure variation, and bubble point breakthrough. Under subcritical conditions, the SC-LAD was found to supply gas-free liquid at the outlet, as long as the pressure drop across the screen was lower than the bubble point threshold. At the critical point, the screen started to ingest bubbles, resulting in a sharp peak in the differential pressure signal. The wetted area of the screen was obtained by analyzing images captured with a high-speed camera and used to calculate the analytical pressure drop. The experimental results were compared with the analytical solution and discussed in detail.

Non-destructive investigation of thermophysical properties on the China's space station: In-orbit experiment measurements and analysis

This paper discusses the current state of non-destructive research on the density, surface tension and viscosity of molten samples using the electrostatic levitation furnace (ELF) aboard the China Space Station (CSS). To address the challenges posed by the microgravity environment during the non-destructive testing process of containerless technology, we have developed several solutions. These include a temperature correction for infrared temperature measurement, a dual-camera position correction technique for density testing, a double electrode synchronous excitation, semi-frequency excitation and fine-sweeping approach for surface tension testing, and a signal demodulation method for viscosity testing. The uncertainties of the three thermophysical properties were 0.51 %, 3.10 %, and 9.78 %, respectively. This study highlights the feasibility and accuracy of measurements conducted in the ELF on the CSS, offering valuable insights into the behavior of molten materials under microgravity conditions. The findings from this study significantly contribute to our understanding of the thermophysical properties of molten materials.

Computation of aluminum droplet ejection and flight in microgravity

Persistent and frequent space explorations are limited by real-time parts supply and it is significant to achieve space manufacture, such as the droplet-based printing. In order to study the microgravity environment effect on droplet-based printing, this paper proposed an effective method to research the effect of space station environmental g-jitter (according to NASA experimental signal) on droplet ejection and flight process. The heat transfer, transient gravity acceleration and Marangoni effect are studied based on the improved model. The results show that the g-jitter is in the order of 10−3 magnitude and the effect on aluminum droplet ejection could be ignored when nozzle diameter (dn) is smaller than 0.1 mm and so do ground case. Combined with the ground microgravity simulation of SnPb alloy lateral ejection experiments, it can be obtained that the ejected single droplet is characterized by capillary number (Ca≤0.002), the droplet flight trajectory is dependent on the Froude number (Fr) and the laminar-turbulence transition exists during the droplet flight process. The relationship formulation between the deviation along gravity direction and the deposition distance is introduced to control and adjust the droplet flight trajectory. Moreover, the temperature effect on material property, such as surface tension and so on, has effect on the droplet breakup length. The g-jitter field enhances the Marangoni effect resulting in the deviation of droplet trajectory. In microgravity field, the computational droplet oscillation period is well coincidence with theoretical equation. Improved KIC-SST based model is available for simulating droplet-based printing in microgravity.

Enhancing cell-scale performance via sustained release of the varicella-zoster virus antigen from a microneedle patch under simulated microgravity.

The immune system of astronauts might become weakened in the microgravity environment in space, and the dormant varicella-zoster virus (VZV) in the body might be reactivated, seriously affecting their work and safety. For working in orbit for the long term, there is currently no efficient and durable delivery system of general vaccines in a microgravity environment. Accordingly, based on the previous foundation, we designed, modified, and synthesized a biodegradable and biocompatible copolymer, polyethylene glycol-polysulfamethazine carbonate urethane (PEG-PSCU) that could be mainly adopted to fabricate a novel sustained-release microneedle (S-R MN) patch. Compared with conventional biodegradable microneedles, this S-R MN patch could not only efficiently encapsulate protein vaccines (varicella-zoster virus glycoprotein E, VZV gE) but also further prolong the release time of VZV gE in a simulated microgravity (SMG) environment. Eventually, we verified the activation of dendritic cells by VZV gE released from the S-R MN patch in an SMG environment and the positive bioeffect of activated dendritic cells on lymphocytes using an in vitro lymph node model. This study is of great significance for the exploration of long-term specific immune responses to the VZV in an SMG environment.

Flame Spread over Charring Thin Cylindrical Fuels in Oxygen Enriched Normal and Microgravity Environments

Flame Spread over Charring Thin Cylindrical Fuels in Oxygen Enriched Normal and Microgravity Environments

Microgravity Inhibits Cell Proliferation and Promotes Senescence and Apoptosis in Embryonic Stem Cells

With advancements in deep space exploration missions, long-term spaceflights pose potential hazards to the reproductive and developmental functions of astronauts. Embryonic stem cells (ESCs), which are crucial to the development and growth of individual organisms, are observably altered by a microgravity environment. However, the role and mechanisms of microgravity in other activities of ESCs are still unclear. Here, mouse embryonic stem cells (mESCs) were used to investigate and understand the effect of microgravity on their activities. Combined with the SJ-10 satellite and random position machine, which were utilized for spaceflight and microgravity simulation, respectively, the bioinformatic tools were also used to assess the effect that microgravity might have on mESC activities. Based on differentially expressed genes (DEGs) analysis, 114 DEGs were significantly up-regulated and 859 DEGs were significantly down-regulated in mESCs after being subjected to spaceflight. The activities, such as cell proliferation, senescence, and apoptosis, were selected and confirmed by Gene Ontology and Kyoto Encyclopedia of Genes and Genomes analyses. It demonstrated a reduced proliferation capability of mESCs but increased the number of senescent and apoptotic cells after being subjected to simulated microgravity. Real-time polymerase chain reaction analysis of the screened activity-related DEGs demonstrated approximately consistent trends of these gene expressions in both spaceflight and simulated microgravity, as was predicted by bioinformatics analysis. Overall, these findings suggest that microgravity inhibits the proliferation of mESCs and induces senescence and apoptosis, shedding light on the impact of microgravity on the fundamental functions of mESCs in reproductive and embryonic development.

New insights into the intestinal barrier through "gut-organ" axes and a glimpse of the microgravity's effects on intestinal barrier.

Gut serves as the largest interface between humans and the environment, playing a crucial role in nutrient absorption and protection against harmful substances. The intestinal barrier acts as the initial defense mechanism against non-specific infections, with its integrity directly impacting the homeostasis and health of the human body. The primary factor attributed to the impairment of the intestinal barrier in previous studies has always centered on the gastrointestinal tract itself. In recent years, the concept of the "gut-organ" axis has gained significant popularity, revealing a profound interconnection between the gut and other organs. It speculates that disruption of these axes plays a crucial role in the pathogenesis and progression of intestinal barrier damage. The evaluation of intestinal barrier function and detection of enterogenic endotoxins can serve as "detecting agents" for identifying early functional alterations in the heart, kidney, and liver, thereby facilitating timely intervention in the disorders. Simultaneously, consolidating intestinal barrier integrity may also present a potential therapeutic approach to attenuate damage in other organs. Studies have demonstrated that diverse signaling pathways and their corresponding key molecules are extensively involved in the pathophysiological regulation of the intestinal barrier. Aberrant activation of these signaling pathways and dysregulated expression of key molecules play a pivotal role in the process of intestinal barrier impairment. Microgravity, being the predominant characteristic of space, can potentially exert a significant influence on diverse intestinal barriers. We will discuss the interaction between the "gut-organ" axes and intestinal barrier damage, further elucidate the signaling pathways underlying intestinal barrier damage, and summarize alterations in various components of the intestinal barrier under microgravity. This review aims to offer a novel perspective for comprehending the etiology and molecular mechanisms of intestinal barrier injury as well as the prevention and management of intestinal barrier injury under microgravity environment.

The DEPLOY! Project: Development of a Deployable Pulsating Heat Pipe experiment on a parabolic flight

DEPLOY! Project aims at analysing the behaviour of Deployable Pulsating Heat Pipe (PHP) shaped as a helicoidal torsional spring in the adiabatic section on board a Parabolic Flight platform. A PHP is a passive thermal control device where the heat is efficiently transported by means of the self-sustained oscillatory fluid motion driven by the phase change phenomena. The microgravity environment allows to eliminate the buoyancy force contribution in the liquid phase momentum. Consequently, it is possible to isolate the contribution of the pressure drop caused by the 3D arrangement and infer on their effect on the PHP performance. As a result, a proper design based on the previous considerations would increase the flexibility of the PHP for use in space applications without significant reductions in efficiency. The goal of DEPLOY! is to demonstrate the functionality of a Deployable Pulsating Heat Pipe in various unfolding configurations by analysing its thermal-hydraulic response throughout a Parabolic Flight. The presented Deployable PHP is composed of an aluminium tube (inner/outer diameters 1.6mm/2.6 mm) and filled with HFE-7000. It is heated at the evaporator using a flat heater and cooled at the condenser with a water-cooled cold plate. T-type thermocouples are used to measure the wall temperature in several locations, while two pressure transducers (one located in the evaporator section and another in the condenser section of the same pipe) measure the local fluid pressure. Additionally, an IR Camera will be used to observe a section of the pipe for further analysis of the flow frequency. The device operation will be tested on ground and 0-g at different heat loads (24W, 34W), in multiple static positions corresponding to different opening angles (0°, 45°, 90°, 135°, 180°) and during its dynamic opening from 0° to 180°, thanks to a remotely controllable motion system.

DMD analysis on sporadic flame behaviors in low-Lewis-number counterflow under microgravity

In order to deepen the understanding on the quasi-steady flame behaviors in counterflow field involving mixtures with low-Lewis number (Le) near lean limit, the experimental and numerical analyses for sporadic flames were carried out. The experiment was conducted with the mixture of Le 0.3 and 0.5 under microgravity environment using parabolic flights of an airplane to eliminate the effect of buoyancy for low-stretch conditions. Three-dimensional numerical simulation with simplified diffusive thermal model was carried out to investigate the three-dimensional structure of sporadic flames. The experimental observations showed the change in the conditions for sporadic flames with changes in Le. The sporadic flames of Le 0.3 could be observed under leaner conditions and endured higher stretch circumstances compared to those observed with Le 0.5. The numerical simulation also reproduced this trend and proved that Le has an important role in the conditions for sporadic flames. To understand the characteristic structure of sporadic flames, the analysis with dynamic mode decomposition (DMD) was conducted. Through this analysis, three characteristic structure modes—planar, radial, and circular—were identified. The decomposed modes showed that the domain of counterflow field could be divided into two; the area forming sporadic flames near the counterflow axis and the area splitting and transporting flame pieces at outer part of the counterflow field. The characteristic length scale was also analyzed using fast Fourier transform (FFT). FFT analysis quantified the characteristic length scale of the decomposed mode of radial and circular. It was also found that the characteristic length scale in radial and angular direction had the same value.

Effects of weightlessness on the cardiovascular system: a systematic review and meta-analysis.

Background: The microgravity environment has a direct impact on the cardiovascular system due to the fluid shift and weightlessness that results in cardiac dysfunction, vascular remodeling, and altered Cardiovascular autonomic modulation (CAM), deconditioning and poor performance on space activities, ultimately endangering the health of astronauts. Objective: This study aimed to identify the acute and chronic effects of microgravity and Earth analogues on cardiovascular anatomy and function and CAM. Methods: CINAHL, Cochrane Library, Scopus, Science Direct, PubMed, and Web of Science databases were searched. Outcomes were grouped into cardiovascular anatomic, functional, and autonomic alterations, and vascular remodeling. Studies were categorized as Spaceflight (SF), Chronic Simulation (CS), or Acute Simulation (AS) based on the weightlessness conditions. Meta-analysis was performed for the most frequent outcomes. Weightlessness and control groups were compared. Results: 62 articles were included with a total of 963 participants involved. The meta-analysis showed that heart rate increased in SF [Mean difference (MD) = 3.44; p = 0.01] and in CS (MD = 4.98; p < 0.0001), whereas cardiac output and stroke volume decreased in CS (MD = -0.49; p = 0.03; and MD = -12.95; p < 0.0001, respectively), and systolic arterial pressure decreased in AS (MD = -5.20; p = 0.03). According to the qualitative synthesis, jugular vein cross-sectional area (CSA) and volume were greater in all conditions, and SF had increased carotid artery CSA. Heart rate variability and baroreflex sensitivity, in general, decreased in SF and CS, whereas both increased in AS. Conclusion: This review indicates that weightlessness impairs the health of astronauts during and after spaceflight, similarly to the effects of aging and immobility, potentially increasing the risk of cardiovascular diseases. Systematic Review Registration: https://www.crd.york.ac.uk/prospero/, identifier CRD42020215515.

MICROGRAVITY PLANT HABITAT –PHYSICAL AND ELECTRICAL PROTOTYPING

The article explores the intricacies of the "Microgravity Plant Habitat" through an in-depth investigation of its design, functionality, and implications for space exploration and colonization. Focusing on ongoing experiments like Veggie Plant Growth System, Advanced Plant Habitat (APH), and Space Greenhouse Experiments, the paper emphasizes the vital role of plant cultivation in supporting life, nutrition, and psychological well-being during deep space missions. The article proposes a novel solution to the challenge of water distribution in microgravity by introducing a modified aeroponics technique within a two-chambered module. This innovative approach ensures even water distribution, overcoming the complexities of gravity-free water droplet behavior. The Concept Article further details the parameters, experimental setup, and expected outcomes of the proposed system, highlighting its potential for reducing mission costs, conserving resources, and enhancing space habitability. The study contributes to advancements in space agriculture, aiming to create a sustainable and efficient system for plant growth in the unique environment of microgravity. The implications extend to the development of water management strategies critical for the success of future space exploration and habitation initiatives. The article concludes by proposing corrective measures and referencing relevant research to support ongoing efforts in space-based agriculture

An apparatus to study arc-wire direct energy metal deposition additive manufacturing process in a drop tower microgravity platform.

Understanding the mechanisms and dynamics of molten metal droplet transfer within the plasma of a directed energy deposition arc process in microgravity is critical for optimizing the build process with minimal defects. This paper presents a unique experimental setup designed to investigate the transfer of molten metal droplets in the microgravity environment of a drop tower. The primary design of the apparatus revolves around accommodating, within the confines of the drop tower experimental capsule, essential components, including a high-speed camera with necessary filters for capturing molten metal droplets, a consumable electrode wire-arc setup, batteries, a linear traverse stage for single bead deposition, sensors, data acquisition systems, online communication systems, and the control system. These systems are secured to withstand the high deceleration forces at the end of a free fall in the drop tower. The arrangement has demonstrated consistent deposition outcomes, capturing clear images of droplet transfers using a high-speed camera along with voltage, current, and temperature data during the microgravity state induced by free fall. This apparatus will serve as a foundational element in establishing a viable additive manufacturing capability for space applications, as it provides fundamental insights into the transfer of molten metal droplets.

Brief Review: Virtual Reality and Physical Exercise as Countermeasures of Coping the Space Missions

Microgravity is an environment incompatible with human physiology that induces unique physiological changes to the body. Exposure to microgravity environment can cause some possible physiological hazards, such as impairment of immune function, bone mass and skeletal muscle mass, in addition to possible negative psycological alterations (depression, anxiety, apathy, and personality changes). These pysico-physiological changes negatively impact health status and quality of life and result in operational difficulties on a space mission for the astronauts. Countermeasures designed to lessen the effect of microgravity on the human body include daily physical exercise and rehabilitation, psychotherapy, specific diets, pharmaceutical treatments, and the use of technologies. Virtual reality (VR) added to physical exercise programs, in the training and preparation of the astronauts for the space missions, could have more exuberant effects. Therefore, the aim of this perspective article is to present the application of VR and physical exercise as countermeasures for training and preparation before, during and after a space missions.

Extinction of solid diffusion flame in microgravity: Details of quenching and blowoff processes

Long duration microgravity experiments aboard the International Space Station determine diffusion flame extinction limits of PMMA spheres. Upon ignition from an electrically-heated coil, the 4-cm-diameter samples are exposed to forced flows ranging from 0.2 to 80 cm/s and an oxygen ranging from 13 to 28 % in one atmosphere total pressure. Extinction is reached as oxygen concentration gradually decreases by natural depletion. Five extinction tests are presented at different flow velocities and oxygen concentrations. Quenching at low velocity is observed with the flame tip shrinking upstream and blowoff is observed when a hole forms in the flame at the forward flow stagnation point. However, these processes are not quasistatic. The quenching motion involves periodic flame tip pulsating toward downstream and shrinking upstream with a continually decreasing flame size at the end of each cycle. In blowoff, the flame base pulsates between the flame hole and the downstream location, although with far fewer cycles compared to quenching. The pulsations appear to be the result of a premixed flame front spreading into a combustible mixture. Two specific cases are discussed in more details. In the first, at very low flow velocity (∼ 0.4 cm/s) and elevated oxygen, self-sustained flame tip cyclic pulsations are observed for a lengthy period (∼15 min). In the second case with a higher flow velocity (50 cm/s), the diffusion flame is stabilized at the shoulder of the spherical sample after local stagnation point blowoff. With steady decrease in ambient oxygen due to depletion, spinning flamelets are formed. The long-duration microgravity environment makes it possible to observe these interesting and detailed extinction processes.