Microgravity Research Research Articles

Development and characterization of a low intensity vibrational system for microgravity studies

Extended-duration human spaceflight necessitates a better understanding of the physiological impacts of microgravity. While the ground-based microgravity simulations identified low intensity vibration (LIV) as a possible countermeasure, how cells may respond to LIV under real microgravity remain unexplored. In this way, adaptation of LIV bioreactors for space remains limited, resulting in a significant gap in microgravity research. In this study, we introduce an LIV bioreactor designed specifically for the usage in the International Space Station. Our research covers the bioreactor’s design process and evaluation of the short-term viability of cells encapsulated in hydrogel-laden 3D printed scaffolds under 0.7 g, 90 Hz LIV. An LIV bioreactor compatible with the operation requirements of space missions provides a robust platform to study cellular effects of LIV under real microgravity conditions.

MicroGravity Explorer Kit (MGX): An Open-Source Platform for Accessible Space Science Experiments

The study of microgravity, a condition in which an object experiences near-zero weight, is a critical area of research with far-reaching implications for various scientific disciplines. Microgravity allows scientists to investigate fundamental physical phenomena influenced by Earth’s gravitational forces, opening up new possibilities in fields such as materials science, fluid dynamics, and biology. However, the complexity and cost of developing and conducting microgravity missions have historically limited the field to well-funded space agencies, universities with dedicated government funding, and large research institutions, creating a significant barrier to entry. This paper presents the MicroGravity Explorer Kit’s (MGX) design, a multifunctional platform for conducting microgravity experiments aboard suborbital rocket flights. The MGX aims to democratize access to microgravity research, making it accessible to high school students, undergraduates, and researchers. To ensure that the tool is versatile across different scenarios, the authors conducted a comprehensive literature review on microgravity experiments, and specific requirements for the MGX were established. The MGX is designed as an open-source platform that supports various experiments, reducing costs and accelerating development. The multipurpose experiment consists of a Jetson Nano computer with multiple sensors, such as inertial sensors, temperature and pressure, and two cameras with up to 4k resolution. The project also presents examples of codes for data acquisition and compression and the ability to process images and run machine learning algorithms to interpret results. The MGX seeks to promote greater participation and innovation in space sciences by simplifying the process and reducing barriers to entry. The design of a platform that can democratize access to space and research related to space sciences has the potential to lead to groundbreaking discoveries and advancements in materials science, fluid dynamics, and biology, with significant practical applications such as more efficient propulsion systems and novel materials with unique properties.

A review of applications of handling particular materials under microgravity

Microgravity research has been carried out by researchers around the world for many years. By using space flight experiments (the International Space Station) and ground-based experiments (the Microgravity Sounding Rocket, a landing tower, and weightless aircraft), the investigations under microgravity conditions are thought to be beneficial to human life in terms of chemical, physical, and biological aspects, and more. It has become a very important tool for scientific research and industrial applications today. This paper reviews the work in this area with special reference to the applications in chemical engineering processes such as particle conveying and flow and material science under different gravity levels, including microgravity environments. It has been demonstrated that gravity has a strong effect on particle conveying and flow. Reduced gravity can make materials more cohesive, which further influences particle conveying. Actually, the effect of gravity can be ignored when the gravity level is less than 0.0001g. In the field of material science, the microgravity environment can accelerate the formation process of materials, like crystal growth, and then lead to a better structure.

Challenges and progress in applying space technology in support of the sustainable development goals

The global community, with coordination from the United Nations, is energized to pursue the Sustainable Development Goals (SDGs), a list of 17 important aspirations that summarize the key challenges of our era. The SDGs apply to every nation and represent an international effort to eliminate extreme poverty, ensure access to safe drinking water, strengthen food security, and produce clean and reliable energy, among other pursuits. Space technology is already being used around the world to advance progress toward the SDGs and monitor their related Indicators. This paper explores how six technologies related to space—satellite Earth observation, satellite communication, satellite navigation and positioning, human spaceflight and microgravity research, space technology transfer, and basic scientific research—are being used to realize the vision that the SDGs represent. The paper also discusses the obstacles that limit the application of these technologies for the SDGs and provides an overview of potential paths to overcome these barriers. The paper finally studies the historical and potential roles that four distinct types of entities involved in global sustainable development—governments, non- and inter-governmental organizations, entrepreneurial companies, and universities— have played or may play in the application of space technologies towards the SDGs.

Microgravity Effects on Glioma Cells: A Comprehensive Review.

High-grade gliomas (HGGs) represent a formidable challenge in neuro-oncology due to their aggressive nature and resistance to current therapeutic interventions, which include surgery, radiation, chemotherapy, and emerging immunotherapies. Despite these efforts, the prognosis for patients remains poor, emphasizing the urgent need for novel treatment strategies. One promising avenue of exploration is microgravity, a condition experienced during spaceflight and simulated in laboratories on Earth, which induces significant physiological changes in cells and tissues. This review synthesizes relevant literature and provides a comprehensive overview of microgravity's effects on glioma cells, encompassing alterations in cell proliferation, apoptosis, gene expression, and a comparative analysis of its impact on other cancer cell types. Studies utilizing simulated microgravity techniques such as clinostats and rotating wall vessels have demonstrated that glioma cells exhibit reduced viability, altered growth patterns, and enhanced activation of apoptotic pathways compared to controls under normal gravity conditions. These findings are significant given the inherent resistance of gliomas to apoptosis; a process critical for the effectiveness of conventional therapies. Despite the challenges in accurately replicating the microgravity environment of space on Earth, simulated microgravity studies have elucidated molecular mechanisms underlying cellular responses. These mechanisms include DNA damage, impaired DNA repair mechanisms, and modulation of apoptotic pathways, which suggest potential vulnerabilities that could be targeted to improve therapeutic outcomes in glioma treatment. Moving forward, further research is essential to deepen our understanding of the specific molecular pathways involved in microgravity-induced effects on glioma cells. This knowledge could pave the way for the development of innovative therapeutic strategies aimed at enhancing apoptosis and overcoming treatment resistance in HGGs. Ultimately, microgravity research offers promising opportunities to advance neuro-oncology by identifying new therapeutic targets and improving clinical outcomes for patients with HHG.

Serum multi-omics analysis in hindlimb unloading mice model: Insights into systemic molecular changes and potential diagnostic and therapeutic biomarkers

Microgravity, in space travel and prolonged bed rest conditions, induces cardiovascular deconditioning along with skeletal muscle mass loss and weakness. The findings of microgravity research may also aid in the understanding and treatment of human health conditions on Earth such as muscle atrophy, and cardiovascular diseases. Due to the paucity of biomarkers and the unknown underlying mechanisms of cardiovascular and skeletal muscle deconditioning in these environments, there are insufficient diagnostic and preventative measures. In this study, we employed hindlimb unloading (HU) mouse model, which mimics astronauts in space and bedridden patients, to first evaluate cardiovascular and skeletal muscle function, followed by proteomics and metabolomics LC-MS/MS-based analysis using serum samples. Three weeks of unloading caused changes in the function of the cardiovascular system in c57/Bl6 mice, as seen by a decrease in mean arterial pressure and heart weight. Unloading for three weeks also changed skeletal muscle function, causing a loss in grip strength in HU mice and atrophy of skeletal muscle indicated by a reduction in muscle mass. These modifications were partially reversed by a two-week recovery period of reloading condition, emphasizing the significance of the recovery process. Proteomics analysis revealed 12 dysregulated proteins among the groups, such as phospholipid transfer protein, Carbonic anhydrase 3, Parvalbumin alpha, Major urinary protein 20 (Mup20), Thrombospondin-1, and Apolipoprotein C-IV. On the other hand, metabolomics analysis showed altered metabolites among the groups such as inosine, hypoxanthine, xanthosine, sphinganine, l-valine, 3,4-Dihydroxyphenylglycol, and l-Glutamic acid. The joint data analysis revealed that HU conditions mainly impacted pathways such as ABC transporters, complement and coagulation cascades, nitrogen metabolism, and purine metabolism. Overall, our results indicate that microgravity environment induces significant alterations in the function, proteins, and metabolites of these mice. These observations suggest the potential utilization of these proteins and metabolites as novel biomarkers for assessing and mitigating cardiovascular and skeletal muscle deconditioning associated with such conditions.

Zero-G Lab: A multi-purpose facility for emulating space operations

During orbital rendezvous, the spacecraft typically approach in the same orbital plane, and the phase of the orbit eventually aligns. Potential rendezvous and docking missions need to be emulated and tested in an on-ground facility for micro-gravity research prior to meeting the harsh conditions of space environment. For orbital docking, the velocity profile of the two spacecraft must be matched. The chaser is placed in a slightly lower orbit than the target. Since all these tasks are quite complex and the realization of space missions are very expensive, any space-related hardware or software’s performance must be tested in an on-ground facility providing zero gravity emulation before initiating its operation in space. This facility shall enable emulation conditions to mimic pseudo zero gravity. It is of critical importance to be equipped with all the necessary ”instruments and infrastructure” to test contact dynamics, guidance, navigation and control using robotic manipulators and/or floating platforms. The Zero-G Laboratory at the University of Luxembourg has been designed and built to emulate scenarios such as rendezvous, docking, capture and other interaction scenarios between separate spacecraft. It is equipped with relevant infrastructure including nearly space-representative lightning conditions, motion capture system, epoxy floor, mounted rails with robots, capability to integrate on-board computers and mount large mock-ups. These capabilities allow researchers to perform a wide variety of experiments for unique orbital scenarios. It gives a possibility to perform hybrid emulations with robots with integrated hardware adding pre-modeled software components. The entire facility can be commanded and operated in real-time and ensures the true nature of contact dynamics in space. The Zero-G Lab also brings great opportunities for companies/startups in the space industry to test their products before launching the space missions. The article provides a compilation of best practices, know-how and recommendations learned while constructing the facility. It is addressed to the research community to act as a guideline to construct a similar facility.

Rational and design of the REMOTE trial: An exploratory, pilot study to analyze REtinal MicrOcirculaTion in wEightlessness.

"Spaceflight associated neuro-ocular syndrome" (SANS) represents a challenging health condition in modern space medicine. Forty-eight percent of astronauts are diagnosed with SANS after long-term space missions. The pathophysiological mechanism seems to be multifactorial, and yet remains unknown. In this proof-of-concept study we plan to investigate retinal microcirculatory changes in weightlessness and aim to identify their role in the development of SANS. Healthy individuals will take part in a parabolic flight campaign, which recreates fractioned total weightlessness periods. The airplane is specifically equipped, and designed for the execution of parabolic flight maneuvers and scientific research in microgravity. Retinal microcirculation will be assessed with a modified fundus camera, which allows dynamic vessel analysis. We will additionally measure intra-ocular pressure and hemodynamic changes during each phase of the flight. Blood samples will be analyzed at baseline, one hour and 24 hours after exposure to weightlessness. This pilot study aims to investigate the feasibility of retinal microcirculation assessment during varying gravity. Results of this study may generate insights whether venous stasis in the eye, surrogated by the dilatation of retinal vessels and increase in intraocular pressure as signs of venous insufficiency, may potentially contribute to the development of SANS.

The Past, Present and Future of UK Human Spaceflight

This paper provides a broad review of the UK’s interest in human spaceflight (HSF), covering its past, present and possible future. It looks at the origins of the national interest, starting with the British science fiction “visionaries” HG Wells and AC Clarke from the early 1900s. Considering what might have been if governments had more fully invested in UK HSF activity during the 1960-80s, it notes that despite a positive cultural enthusiasm the UK appears to have been held back by institutional scepticism and a lack of government financial commitment - this attitude strongly contrasted with that of other developed nations, particularly Germany, France and Italy. Following a sudden reversal of government policy for human space activity post-2008, a deeper HSF involvement by the UK now seems achievable, depending on sufficient funding - ESA’s 2022 selection of three new British astronaut candidates is a very positive step-forward. The paper broadly considers the opportunities via the combination of human and robotic exploration (HRE) with direct microgravity research on the ISS and the forthcoming private space labs in LEO, plus participation in NASA-led “Artemis” lunar exploration. The latter could involve applied UK space industry initiatives, possibly including lunar navigation and communications satellite construction, Gateway space-station services, plus potential nuclear power sources for a future Moonbase. Space-based solar power with HSF support, expanding space tourism activity, then the future exploration of the Moon and Mars may then be followed by ISRU exploitation and commercial space mining. The paper concludes with a revue of the importance and need for HSF for space research and exploration, it’s “value for money”, potential long-term futures and the contribution HSF makes to the “Big History” of humanity as a space-faring species. Keywords: Astronauts, Human spaceflight (HSF), Arthur C Clarke, European Space Agency (ESA), UK Space Agency, Tim Peake, Artemis, SUSIE, ISS, Orion, Argonaut, Moonbase, World History

MIT Zero-G outreach initiative: Using experiment design and virtual reality to inspire the next generation of space scientists and engineers

MIT's Space Exploration Initiative offers a course on project development, prototyping, and deployment readiness for parabolic flights, culminating in an annually chartered research flight with Zero-G. MIT's Resource Exploration and Science of our Cosmic Environment (RESOURCE) team participated in the course in the fall of 2021 with a Zero-G flight in May of 2022 testing technology for a virtual reality platform to enable science on Lunar rover exploration missions. In parallel with the scientific effort, the team developed the MIT Zero-G Outreach Initiative (0G-OI), an outreach program to engage with the Cambridge Public School's (CPS) grade 7 classes to teach them about research in microgravity, parabolic flight, and experiment design. The goal of the outreach program is to inspire the next generation of space scientists and engineers using virtual reality.The CPS grade 7 curriculum covers ‘Mysteries of the Universe’ where students consider the role of gravity in the solar system. They also complete a unit on roller coasters in which they learn about key ideas of force, motion, and energy through the context of roller coasters. The 0G-OI Initiative ties these two units together through five videos covering: 1) an overview of the initiative, 2) the basics of parabolic flight and how we perceive gravity, 3) an overview of gravity and its function in the universe, 4) why and what we can study in microgravity and 5) how to design an experiment for microgravity. The students then design their own experiments for microgravity. These are down-selected to the top 5 experiments that are reviewed by an astronaut to select one experiment to fly on the MIT chartered Zero-G parabolic flight. The flight and the experiment are filmed in VR video by the MIT RESOURCE team. Each participating school is provided with an Oculus Quest 2 VR headset and a flight day is held at each school where the students experience the Zero-G flight and see the results of their experiment in an immersive VR environment. Using this initial setup, the 0G-OI can be run annually in parallel with MIT's SEI parabolic flight course.Some key development parameters included keeping the educational videos under 10 min, that having an astronaut select the winning experiment provided incentive and finally, using VR, as this technology is commonly associated with gaming and entertainment. Lessons learned focused on improvements to scheduling and coordination with Zero-G, in-person programming and classroom experience optimization. The 0G-OI aims to develop a lasting relationship with the CPSs and make the exciting experience of parabolic flight and space exploration an accessible experience.

The Design, Realization, and Validation of the Scheme for Quantum Degenerate Research in Microgravity

In microgravity, atoms can be prepared to a lower temperature and manipulated with a longer time. The Cold Atom Physics Research Rack (CAPR) in Chinese Space Station, which aims to prepare quantum degenerate gas for deep cooling and quantum simulation in microgravity, has been designed, realized, and validated. We built an integrated CAPR, consisting of a physical system, an all-fiber 780nm laser system and a low phase noise 1064nm fiber laser system, and an electrical driving and controlling system. With the CAPR, a <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">87</sup> Rb quantum degenerate gas with 1.2ⅹ10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">5</sup> atoms and a temperature below 30nK was achieved on ground. In this article, we also show the robustness of the rack, based on the experimental results before and after the simulation of the vibration and impact during the launch.

Applications for oral research in microgravity - lessons learned from burning mouth syndrome and ageing studies.

The negative consequences of microgravity for the human body are central aspects of space travel that raise health problems. Altered functions of the same systems and treatment options are common points of spaceflight physiology, age-related diseases, and oral medicine. This work emphasizes the convergence of knowledge between pathophysiological changes brought on by aging, physiological reactions to microgravity exposure, and non-pharmacological and non-invasive treatment methods that can be used in spaceflight. Sarcopenia, peripheral nerves alterations, neuromotor plaque in the masticatory muscles, lingual, labial, and buccal weakness, nociplastic pain in oral mucosal diseases, and microgravity, as well as soft tissue changes and pathologies related to chewing and swallowing, corticomotor neuroplasticity of tongue, and swallowing biomechanics, are of particular interest to us. Neurologic disease and other pathologies such as recovery from post-stroke dysphagia, nociplastic pain in glossodynia, sleep bruxism, and obstructive sleep apnea have been studied and, in some cases, successfully treated with non-invasive direct and transcranial magnetic stimulation (TMS) methods in recent decades. An interdisciplinary team from medical specialties, engineering, and biophysics propose an exploratory study based on the parallelism of ageing and space physiology, along with experiment scenarios considering TMS and non-invasive direct methods.

Perspective on quantum bubbles in microgravity

Progress in understanding quantum systems has been driven by the exploration of the geometry, topology, and dimensionality of ultracold atomic systems. The NASA Cold Atom Laboratory (CAL) aboard the International Space Station has enabled the study of ultracold atomic bubbles, a terrestrially-inaccessible topology. Proof-of-principle bubble experiments have been performed on CAL with an radiofrequency-dressing technique; an alternate technique (dual-species interaction-driven bubbles) has also been proposed. Both techniques can drive discovery in the next decade of fundamental physics research in microgravity.

The Einstein Elevator

Development of space proven technologies, fundamental research in microgravity and preparation of future space missions all benefit from next generation drop tower facilities like the Einstein-Elevator. The facility is being made available within a DFG core facility center in Hannover.

Toward "Electrochemical/Materials Processing for Space Engineering" Symp

Several symposium have been hosted such as “Electrochemistry in Space”, 236th ECS Atlanta(2019) and “ISRU”, Call for Papers: ACS Earth and Space Chemistry for Special Issue: Materials of the Universe : the Final Chemical Frontier(2020). However, their scopes are rather shifted to space exploration concept, primarily led by the Space Agency. Those are not geared toward training graduate students for the future space engineering using basic science, especially Space Environmental Utilization Research is not intensively covered. It is our thought that the Electrochemical Society (ECS) shall organize such an interdisciplinary education & research program collaborating with TMS society (Light Metal and Materials Processing Divisions). The research subjects on Space Energy & Resources must be newly stimulated to make recognize and support the field of Electrochemical/Materials Processing, encompassing:[1] Basic Science with Drop Tower, Rocket & ISS(for example: Nucleation & Growth of Ice in Space, Gas Electrode Behavior)[2] Microgravity Research like Protein or Semiconductor Crystallization[3] Energy Conversion and Storage System for Space Engineering(Unitized Regenerative FC), LIB, Nuclear Battery)[4] Sensor System for Rover Eng. & X-ray Astrophysics[5] Life Supporting System including Desalination Technology and CO2 Reduction[6] ISRU, Materials Processing/Thermodynamic Measurement with ELF[7] Computational Chemistry/Interfacial Reaction Dynamics[8] Ion Transfer through Cell Membrane in Bio-physics[9] Global Environmental Observation System[10] Others

Joint Cartilage in Long-Duration Spaceflight.

This review summarizes the current literature available on joint cartilage alterations in long-duration spaceflight. Evidence from spaceflight participants is currently limited to serum biomarker data in only a few astronauts. Findings from analogue model research, such as bed rest studies, as well as data from animal and cell research in real microgravity indicate that unloading and radiation exposure are associated with joint degeneration in terms of cartilage thinning and changes in cartilage composition. It is currently unknown how much the individual cartilage regions in the different joints of the human body will be affected on long-term missions beyond the Low Earth Orbit. Given the fact that, apart from total joint replacement or joint resurfacing, currently no treatment exists for late-stage osteoarthritis, countermeasures might be needed to avoid cartilage damage during long-duration missions. To plan countermeasures, it is important to know if and how joint cartilage and the adjacent structures, such as the subchondral bone, are affected by long-term unloading, reloading, and radiation. The use of countermeasures that put either load and shear, or other stimuli on the joints, shields them from radiation or helps by supporting cartilage physiology, or by removing oxidative stress possibly help to avoid OA in later life following long-duration space missions. There is a high demand for research on the efficacy of such countermeasures to judge their suitability for their implementation in long-duration missions.

Testing 3D printed biological platform for advancing simulated microgravity and space mechanobiology research

The advancement of microgravity simulators is helping many researchers better understanding the impact of the mechanically unloaded space environment on cellular function and disfunction. However, performing microgravity experiments on Earth, using simulators such as the Random Positioning Machine, introduces some unique practical challenges, including air bubble formation and leakage of growth medium from tissue culture flask and plates, all of which limit research progress. Here, we developed an easy-to-use hybrid biological platform designed with the precision of 3D printing technologies combined with PDMS microfluidic fabrication processes to facilitate reliable and reproducible microgravity cellular experiments. The system has been characterized for applications in the contest of brain cancer research by exposing glioblastoma and endothelial cells to 24 h of simulated microgravity condition to investigate the triggered mechanosensing pathways involved in cellular adaptation to the new environment. The platform demonstrated compatibility with different biological assays, i.e., proliferation, viability, morphology, protein expression and imaging of molecular structures, showing advantages over the conventional usage of culture flask. Our results indicated that both cell types are susceptible when the gravitational vector is disrupted, confirming the impact that microgravity has on both cancer and healthy cells functionality. In particular, we observed deactivation of Yap-1 molecule in glioblastoma cells and the remodeling of VE-Cadherin junctional protein in endothelial cells. The study provides support for the application of the proposed biological platform for advancing space mechanobiology research, also highlighting perspectives and strategies for developing next generation of brain cancer molecular therapies, including targeted drug delivery strategies.

Optimization of thermocapillary-driven melting in trapezoidal and triangular geometry in microgravity

A numerical analysis of thermocapillary-driven melting in trapezoidal and triangular geometry in microgravity is presented. The phase change transition is modelled using an enthalpy-porosity-based formulation of the Navier-Stokes equations, where the solid and liquid phases are treated as a single layer with physical properties depending on the local temperature, and analyzed for the organic phase change material (PCM) n-octadecane, due to its relevance to recent and upcoming microgravity research. We describe first the melting process in rectangular geometry, which is characterized by a final diffusive stage that largely determines the melting time τM, where the solid PCM near the cold boundary melts slowly. Other geometries are proposed to optimize the process and minimize τM. By inclining the cold lateral wall, melting can be accelerated substantially. We find a maximum reduction in τM by a factor of 3 in the limiting case of a right triangle — the optimal geometry within the scope of the present work. For completeness, the process is analyzed in the symmetric trapezoids that result from inclining the hot lateral wall. An increase (reduction) of the overall melting time (rate) is observed at moderate inclination angles, associated with a PCM region dominated by weak thermal diffusion. Finally, the effect of Γ is presented in both rectangular geometry and the optimal triangular geometry, suggesting a general scaling τM∝Γ−1.25.

Use of Reduced Gravity Simulators for Plant Biological Studies.

Simulated microgravity and partial gravity research on Earth is a necessary complement to space research in real microgravity due to limitations of access to spaceflight. However, the use of ground-based facilities for reduced gravity simulation is far from simple. Microgravity simulation usually results in the need to consider secondary effects that appear in the generation of altered gravity. These secondary effects may interfere with gravity alteration in the changes observed in the biological processes under study. In addition to microgravity simulation, ground-based facilities are also capable of generating hypergravity or fractional gravity conditions whose effects on biological systems are worth being tested and compared with the results of microgravity exposure. Multiple technologies (2D clinorotation, random positioning machines, magnetic levitators, or centrifuges) and experimental hardware (different containers and substrates for seedlings or cell cultures) are available for these studies. Experimental requirements should be collectively and carefully considered in defining the optimal experimental design, taking into account that some environmental parameters, or life-support conditions, could be difficult to be provided in certain facilities. Using simulation facilities will allow us to anticipate, modify, or redefine the findings provided by the scarce available spaceflight opportunities.

NASA's Ground-Based Microgravity Simulation Facility.

Since opportunities to conduct experiments in space are scarce, various microgravity simulators and analogs have been widely used in space biology ground studies. Even though microgravity simulators do not produce all of the biological effects observed in the true microgravity environment, they provide alternative test platforms that are effective, affordable, and readily available to facilitate microgravity research. The Microgravity Simulation Support Facility (MSSF) at the National Aeronautics and Space Administration (NASA) John F. Kennedy Space Center (KSC) has been established for conducting short duration experiments, typically less than 1 month, utilizing a variety of microgravity simulation devices for research at different gravity levels. The simulators include, but are not limited to, 2D Clinostats, 3D Clinostats, Random Positioning Machines, and Rotating Wall Vessels. In this chapter, we will discuss current MSSF capabilities, development concepts, and the physical characteristics of these microgravity simulators.