What are the ground based microgravity analogs?

The notions analog and model are simultaneously used with microgravity. Microgravity analogs only replicate microgravity effects on physiological responses, while a microgravity model is a platform used as a prototype or to imitate microgravity. These analogs are mostly used to conduct experiments for long duration of time. Ground microgravity analogs are: 

• long-duration bedrest 

• water immersion

Long-duration bedrest is an analog to microgravity that grants an easier access for hours to weeks in which human subjects are possible to study. It is mostly employed to simulate microgravity effects on various physiological systems, particularly on bone-studies, muscle and the cardio-vascular system of humans. Initially, the investigations of bone-loss used horizontal bedrest, and later on head-down tilt (HDT) bedrest was used for a better result that has similar effects on spaceflight. There are various HDT angles that could be used; it varies from 6⁰ through 12⁰ and 18⁰. The limitation of this platform is that subjects rarely (if ever), develop motion sickness during or after; which constitute a great discrepancy between this analog and spaceflight.

Figure 1. Types of Long Duration Bedrest

Water immersion is a model of microgravity that makes it possible to carry out bones and cardio-vascular studies on human subjects for days, and possibly months. This platform is an easier access to microgravity analog. Immersion reproduces microgravity induced changes in human body’s motor and cardio-vascular systems, and affects other physiological functions. A challenge to water immersion is that there is discomfort and possible risks of long-term skin contact with the liquid environment. Therefore dry immersion was developed that constitutes of head-out water immersion with subjects kept dry with the use of a waterproof, highly elastic fabric that creates artificial conditions similar to microgravity via floatation (Figure 2). Immersion is the main model for training of working operations in weightlessness. The limitation to the use of water immersion is that there is discomfort and possible risks of long-term skin contact with the liquid environment. The limitation to both water and dry immersion is that subjects do not develop motion sickness. 

Figure 2. Types of Water Immersion

From comparison of data, similarity has been observed in the HDT bedrest and dry immersion, although it is also suggested that dry immersion has an influence that is stronger than HDT bedrest. The microgravity analog platforms make it possible to have human subjects for experimental purposes, without the need to travel to space! 

Further reading

Abdulrashid, F.A., Oluwafemi, F.A., Hussaini, S.J., Daniel, I.B., Isah, B., Ademu, A., Otum, A.O., Polok, A.C., Dumbiri, C.O., 2020. Possible solutions to the effects of space environment on astronauts’ physiology, London Journals Press, LJER 20 (5). 

Oluwafemi, F.A., Neduncheran, A., 2022. Analog and simulated microgravity platforms for life sciences research: Their individual capacities, benefits and limitations. Advances in Space Research. https://doi.org/10.1016/j.asr.2022.01.007. 

What are Ground based microgravity simulators?

Ground based microgravity simulators mimic the true or real microgravity environment.  Various microgravity simulators that are frequently used by gravitational researchers are based on different physical principles. These simulators provide long enough periods for the sample to remain under simulated microgravity. Ground-based microgravity simulators are used as for preliminary real microgravity screening studies. The current ground microgravity simulators are:

·      Clinostats

·      Random Positioning Machines (RPM)

·      Rotating Wall Vessels (RWV)

·      Magnetic Levitation Devices (MLD)

·      Centrifuges

 

Clinostat eliminates the effect of gravity (Figure 1). There are different types of clinostats and they differ in the number of their rotational axes, and in their modes of operation as regards the speed and direction of the rotation. The accessibility is moderately easy; can supply gravity force (g) of 10^-2 to 10^-3 for several hours and weeks. Possible experiments on clinostat are microbial responses, mammalian cell, materials, and fluid behavior in microgravity, and some clinostat types have been used on plant growth and development. The limitation with clinostat is that during long-term experiments: some samples such as plants get increased in mass, the changing weight distribution causes bending stresses.

Figure 1. One-axis clinostat with adjustable rotational axis angle.

Source: Oluwafemi and Neduncheran, 2021.

 

Random Positioning Machine (RPM) consists of two independent rotating frames; one frame is positioned inside the other giving a complex orientation net change to the specimen mounted in the middle (Figure 2). RPM is one of the best substitutes as it can potentially generate results comparable to the results in true microgravity. The accessibility is moderately easy; can supply gravity force (g) of 10^-2 to 10^-3 for several hours and weeks. Possible experiments have been biological parameters such as microbial responses, plant cells and mammalian cell cultures. The limitation is that it cannot simulate microgravity properly for relatively fast cellular and molecular processes.

Figure 2. Random Positioning Machine.

Source: https://en.wikipedia.org/wiki/Random_positioning_machine 

 

Rotating Wall Vessel (RWV) has a chamber that rotates around an axle while its vessel can contain culture medium and cells (Figure 3). The cells can attach to each other to form 3D cultures, but do not attach to the wall of the chamber because they are subjected to a continuous free-fall. The accessibility is moderately easy; can supply gravity force (g) of 10^-2 to 10^-3 for several hours and weeks. RWV is used increasingly in studies of microbial responses and mammalian cell behavior. It has also been used for research on fish. A limitation to its use is that it cannot simulate microgravity properly for relatively fast cellular and molecular processes. 

Figure 3. Rotatory Cell Culture System.

Source: https://en.wikipedia.org/wiki/Rotary_Cell_Culture_System 

 

Magnetic Levitation Device (MLD) simulates microgravity by allowing the isolation of magnetic and gravitational effect (Figure 4). It is used to balance gravity, as magnetic forces counteract the force of gravity that results from a magnetic gradient and the diamagnetic susceptibility of the object that together produce a force that can be equivalent to gravity. The accessibility is moderately easy; can supply gravity force (g) of 10^-2 for several minutes to hours. Possible samples are diamagnetic materials – water and biological tissue (as they are repelled from magnetic fields). It levitates cellular organelles (e.g. hypocotyls, rhizoids, statoliths in roots), seedlings and bacteria. It has also been used to research on frog and frogs’ eggs. The limitation to its use is that it can be used for only diamagnetic substances.

Figure 4. Magnetic Levitation Device (MLD)

Source: https://hackaday.com/2017/10/08/hovering-questions-about-magnetic-levitation/

 

Centrifuges actually provide hypergravity but it’s also utilized to simulate microgravity (Figure 5). Although it sounds somewhat counter-intuitive, that there can be the exploration of microgravity effects by the application of centrifuges. There is a reduced gravity paradigm (RGP) that is based on the fact that adaptations seen going from a hypergravity level to a lower gravity level are similar to changes seen going from gravity (1g) to microgravity. The accessibility of centrifuges are moderately easy; can supply gravity force (g) of 10^-3 for several minutes to months (if is a large diameter centrifuge). Possible samples are plants, cells, small animals, physical science and technological experiments, which all depends on the capacity of the centrifuge. The limitation to centrifuge use for microgravity simulator is that it cannot simulate microgravity properly for relatively fast cellular and molecular processes. 

 Figure 5. Centrifuge

Source: https://en.wikipedia.org/wiki/Centrifuge

 

Hence, the microgravity simulatory platforms are therefore more accessible for experimental purposes than the orbital or sub-orbital platforms.

 

Further reading

Oluwafemi, F.A., Neduncheran, A., 2022. Analog and simulated microgravity platforms for life sciences research: Their individual capacities, benefits and limitations. Advances in Space Research. https://doi.org/10.1016/j.asr.2022.01.007.

 

Oluwafemi, F.A., Neduncheran, A., 2021. Real and simulated microgravity platforms: Their individual capacities, benefits and limitations. 71^st International Astronautical Congress (IAC) – The CyberSpace Edition, 12-14 October, 2020. IAC-20-A2,5,10,x56924. 

 

What are the non-orbiting microgravity facilities?

The non-orbiting microgravity platforms grant experimental samples access to true (real) microgravity. This microgravity is not mimicked (simulated). These platforms include:

·      Drop towers

·      Suborbital Rocket (Sounding Rocket)

·      Parabolic Flight in Specialized Airplane

·      Balloon 

Drop-towers are vertical structures that allow free-fall of payloads under vacuum to generate microgravity conditions. The accessibility is moderate. The time of the free-fall is determined by the height of the tower, which can get up to several meters. Drop tower supply gravity force (g) of 10^-2 to 10^-6; the supply of microgravity can only range from 2 to 10 seconds; possible experiments are on cells, microbes, gravitropic reactions in fungi, and for other electrophysiological studies; the limitation is that the duration of study is very short (Figure 1).

Figure 1: Drop-tower, Bremen, Germany. Source: https://en.wikipedia.org/wiki/Drop_tower

 

Suborbital or sounding rockets are rockets launched on ballistic trajectory in vacuum with a free-fall at a high altitude. The accessibility is moderate. Sounding rockets can achieve up to a height of about 145 km; have possible gravity force (g) of 10^-3 to 10^-4; the supply of microgravity ranges from 10 to 20 minutes; possible experiments can be on membrane transport, cell morphology and physiology, free-flow electrophoresis, gene expression, signal transduction pathways, and other experiments in biotechnology; the limitations are the associated costs and how to recover the modules of experiment from the remote sites (Figure 2).

Figure 2: Sounding Rocket. Source: https://en.wikipedia.org/wiki/Sounding_rocket

 

Parabolic flight in specialized airplane is another platform aimed to attain free-fall conditions in an aircraft in a ballistic trajectory of a parabola. The accessibility is moderate. The parabolic flight maneuvers to get to an altitude of at least 3 km. Parabolic flight supplies gravity force (g) of 10^-2 to 10^-3; supplies microgravity for about 20 to 30 seconds in a cyclic manner; possible experiments had been signal transduction in human immune cells and osteoblasts, neuron responses in experimental animals and protein crystallization; the limitation is that hypergravity acceleration interrupts the microgravity phase (Figure 3).

Figure 3: Parabolic flight in Specialized Airplane. Source: https://en.wikipedia.org/wiki/Reduced-gravity_aircraft

 

Latex high-altitude balloons used for meteorological measurements allow for a simple and moderate cost approach to achieving microgravity conditions. An example is the use of a capsule carried aloft in helium weather balloon. An altitude of more than 25 km can be achieved and then the capsule carrying the experiment will be separated from the balloon for free-falls towards the Earth. This free-fall grants access to the microgravity conditions that is required for the experiment payload. On-board are: sensors to measure the capsule’s acceleration, cameras, and sub-transmitters. These experimental balloons can supply gravity force (g) of up to ±10^-4; can provide microgravity for 30 to 60 seconds. Parachute recovery system must be deployed to safely recover the capsule and the experimental data. Possible experiment was observing behaviors and brain activities of fishes; and the limitation is that only a small mass of payload could be accommodated, and launching of helium weather balloons necessitates detailed checks over the local weather, environmental conditions, wild-life and aviation regulations (Figure 4).

Figure 4: Microgravity Experimental Balloon. Source: https://en.wikipedia.org/wiki/Hot_air_balloon

 

The benefits of the access to the non-orbital microgravity platforms cannot be overemphasized over the socioeconomic benefits granted via the experiments.

 

Further reading

Oluwafemi, F.A., Neduncheran, A., 2022. Analog and simulated microgravity platforms for life sciences research: Their individual capacities, benefits and limitations. Advances in Space Research. https://doi.org/10.1016/j.asr.2022.01.007.

 

Oluwafemi, F.A., Neduncheran, A., 2021. Real and simulated microgravity platforms: Their individual capacities, benefits and limitations. 71^st International Astronautical Congress (IAC) – The CyberSpace Edition, 12-14 October, 2020. IAC-20-A2,5,10,x56924.

What are the orbiting microgravity facilities?

Orbiting microgravity facilities are microgravity platforms that are real or true. This microgravity is not mimicked. The orbiting microgravity platforms are the:

 

·      manned orbiting systems

·      unmanned satellites

      

An example of the manned orbiting systems is the International Space Station (ISS) that accommodates man for living and working (e.g. experimental) purposes. The panels on the ISS are large solar panels to power it (Figure 1). The ISS is based on partnership amongst many space agencies: NASA of USA, CSA of Canada, ESA of European countries, Roscosmos of Russia and JAXA of Japan. Russian MIR space station is another of this type. These platforms orbit at about 400 km altitude; supply gravity force (g) of up to 10^-5 to 10^-6; experiment in diverse fields of research are possible; the duration of the experiments can range from months to years as the microgravity supply is constant; the limitation is the high cost.

 

Figure 1: The International Space Station. Source: 

Tarantola, A. (2022). https://en.wikipedia.org/wiki/Small_satellite#/media/File:Estcube-1_2012-12-27.jpg

Due to the limited access (scarceness and high cost) to manned orbiting systems, unmanned miniaturizing and automating experiments are designed called autonomous microgravity laboratory satellites. These are called SmallSats (Figure 2). This does not require human intervention. This type of laboratory operates as Nanosatellites or CubeSats that are controlled by users on the ground by proprietary software that are installable on laptops and smart phones. The data and experimental results are normally transmitted to the ground-station. The flying of microgravity experiments as a stand-alone automatic satellites occur at above 300 km altitude; supply gravity force (g) of 10^-5 to 10^-6; experiments on plants, microbes and chemical reactions are possible; the duration of the experiments can range from weeks to years as the microgravity supply is constant; the limitation is that launch opportunities are limited.

Figure 2. A Nanosatellite. Source: Wikipedia (2023). https://golden.com/wiki/Nanosatellite-NMV8DXY

The benefits of the access to these platforms cannot be overemphasized over the socioeconomic benefits of the experiments.

 

Further reading

Oluwafemi, F.A., Neduncheran, A., 2022. Analog and simulated microgravity platforms for life sciences research: Their individual capacities, benefits and limitations. Advances in Space Research. https://doi.org/10.1016/j.asr.2022.01.007.

 

Oluwafemi, F.A., Neduncheran, A., 2021. Real and simulated microgravity platforms: Their individual capacities, benefits and limitations. 71^st International Astronautical Congress (IAC) – The CyberSpace Edition, 12-14 October, 2020. IAC-20-A2,5,10,x56924.

 

Tarantola, A. (2022). https://en.wikipedia.org/wiki/Small_satellite#/media/File:Estcube-1_2012-12-27.jpg

 

Wikipedia (2023). Small satellites. https://golden.com/wiki/Nanosatellite-NMV8DXY

What are the currently available microgravity platforms?

 

The major characteristics of the space environment are: microgravity and radiation. But someone may ask; can microgravity be experienced on the Earth? The answer is yes! This is because there are so many platforms or facilities that can supply microgravity on the Earth; these are known as terrestrial microgravity platforms. There are four major classifications of microgravity platforms or facilities (Figure 1):

-orbiting microgravity facilities (this supplies real or true microgravity); 

-non-orbiting microgravity facilities (this supplies real or true microgravity);  

-ground microgravity analogs; and 

-ground microgravity simulators.

     Figure 1: Microgravity Platforms 

The choice of the platform to use depends on so many factors. The focus of the specific experiment is the key to selecting the right platform. Some factors that may determine the choice of a particular platform can include: accessibility (most platforms are scarce and expensive); type of the experimental sample [size or volume, plant, animal, cells, microorganisms, solid, materials, chemical (hazardous or not) etc.]; the duration of microgravity supplied by the platform (e.g. seconds, minutes, hours, days, months); microgravity quality in g (10^-2, 10^-3, 10^-4, 10^-5, or 10^-6); and accessible altitude (for orbiting and non-orbiting platforms).

 

It has been observed that most tests in physics and microbiology require short time scales only while macrobiological tests would need long time scales. Also, physics experiments need more true (real) microgravity while biological experiments in many cases might be done in simulated or analog microgravity.

References and Further Reading

Ferranti, F., Del Bianco, M., Pacelli, C., 2021. Advantages and limitations of current microgravity platforms for space biology research. Appl. Sci. 11 (1), 68. https://doi.org/10.3390/app11010068.

 

Funmilola A. Oluwafemi and Adhithiyan Neduncheran (2022). Analog and Simulated Microgravity Platforms for Life Sciences Research: Their Individual Capacities, Benefits and Limitations. Advances in Space Research. 69, 2921-2929. ISSN 0273-1177. https://doi.org/10.1016/j.asr.2022.01.007. https://www.sciencedirect.com/science/article/abs/pii/S0273117722000199#.

What is the difference between microgravity and reduced gravity?

What is the difference between microgravity and reduced gravity?

It is well established that the major characteristics of the space environment are: microgravity and radiation. Microgravity is a state of weightlessness (like floating) or a state of very low gravitational pull, whereby only minute gravity is experienced by an object. In the real sense, there is no zero gravity, because zero gravity does not exist in the universe. The existence of microgravity starts after the Karman line (at an altitude of 100 km (62 mi) above the sea level). Each planet, moon, asteroid or any other celestial body have individual gravitational pull that is defined by their size, density, mass and proximity to other celestial bodies. The more massive the object in the solar system, the larger its gravitational field. Therefore, gravity comparism of such object to the Earth’s gravity generates the answer if there is reduced gravity or hypergravity on such a celestial body. Hence outside every celestial body and outside the Earth exists microgravity (Figure 1), but on every celestial body exists reduced gravity or hypergravity compared to the gravity of the Earth (1G). The amount of gravity depicts how a body bounces on a celestial body (video). 

    

Figure 1. The solar system

 

Figure 1 shows the solar system, the dark portion annotates where microgravity exists, while on the planets or very close to the planet (or any other celestial body) exists reduced gravity or hypergravity when compared to 1G. Table 1 explains further.

Table 1. Shows if gravity of celestial body is reduced or hypergravity compared to the Earth

Note that on the Earth exists gravity, while there are equipment or facilities that can supply microgravity or hypergravity. Therefore, microgravity can be simulated or mimicked on the Earth; while hypergravity can also be supplied by centrifuge. These simulations could be done for experimental purposes, deducing some scientific benefits. 

Further reading

Funmilola Oluwafemi (2021). Gravity Variation on the Growth of Maize Shoots.  Multidisciplinary Digital Publishing Institute (MDPI). Proceedings of 1^st Electronic Conference on Universe (ECU): General Relativity and Gravitation Section. Sciforum-042524, 22-28 February. https://doi.org/10.3390/ECU2021-10184.

Why space exploration?

The currently pressing challenges in the world include intense energy demand, growing pressures on the environment (this includes sanitation) and the economy. Increased human population, limited production resources and global climate-change are the cause. There is shortage in global food supplies that causes an urgent need to produce more food while reducing the impact on environment and ecosystem. Therefore, spreading out to one of the next-door celestial body is imperative, for a long-term survival in case something devastating that could change the course of life happens to the planet earth such as natural disaster like rogue comet or self-infliction like nuclear war, making the earth not to be habitable. Going to a celestial body implies going into the outer space environment. Figure 1 shows the summary of space exploration.  

 

Another motive to go into space is for scientific purposes that may lead to some benefits. As the basic characteristics of the space region are the presence of radiation and microgravity. Only minute gravity is in action at this region, unlike on the earth where gravity is always present. Microgravity is a degree of absolute weightlessness. Under the influence of microgravity, biological organisms (humans, animals, plants, cells, microorganisms), biological macromolecules, fluids and materials may behave differently. Most of the time, microgravity effect causes significant changes on the chosen samples during experiments. The changes that occur as a result of microgravity effect have led to findings that have been found to be of socio-economic advantages. 

Figure 1: Some reasons for space exploration

New technology and research such as Global Positioning System (GPS), solar cells, accurate weather prediction and the ultraviolet filters in sunglasses and cameras have been developed to improve lives and to improve the economy on earth. New technology and research that leads to space spin-offs, which are useful on the earth. Several gadgets, materials and processes that were originally developed for space programs but found other applications back on earth are called space spin-offs. Technology developed for use in space has found uses also in health care. So many people suffer tissue or organ loss from accidents and diseases every year. Yet transplantation of tissues and organs is very limited by donor availability. Growing tissue samples outside the body is one of the main goals of the current medical research, and the space environment has great potential for advancing this research.

 

Space exploration such as on asteroids and comets have helped deflect these objects saving lives on the earth, as asteroids and comets smacks into earth. The space program allows to spot a dangerous body long enough before striking the earth and sends a spacecraft to put in a nuclear explosion nudging it off its collision course. In addition, there is a wealth of precious raw materials in space, which is an effectively rare raw material with unlimited supply as the strain on the natural resources continues to increase on earth, asteroid mining is one of these. The moon is a potential lucrative source of helium 3 (useful for certain Magnetic Resonance Imaging (MRI) and as a possible fuel for nuclear power plants); and a potential source of other rare earth elements such as tantalium and europium that are in high demand for electronics use, solar panels and any other advanced gadgetry.

 

Understanding the world, inspiration, space tourism and international collaboration to work together toward a larger goal irrespective of nationality, gender and race are some other reasons for travelling to the outer space. Space tourism is travelling to space for leisure, recreation or business purposes and it includes orbital, suborbital, and lunar space tourism. It encompasses commercial activities offering the members of the general public direct or indirect experience in outer space.

 

Due to less mass at launch and lower initial costs, a one-way mission to the moon, mars, venus or any other celestial body is advocated for than a round-trip mission. A one-way mission means not involving a return of the crew to the earth. This could help mankind reach these celestial bodies earlier. A one-way mission will however entail a different approach to design the habitat modules which will present more risks.

 

Further reading 

Afolayan, E. M., Oluwafemi, F. A., Jeff-Agboola, E. O., Oluwasegun, T., & Ayankale, J. O. (2019). Socio-economic benefits of microgravity research. Arid Zone Journal of Engineering, Technology and Environment (AZOJETE). Centre for Satellite Technology Development Special Issue: Space Science and Technology for Sustainable Development, 15(SP.i2), 57-74.

Enemali, J. O., Oluwafemi, F. A., Hussaini, S. J., Daniel, I. B., Ameh, O., Adamu, A., & Agboola, O. A. (2020). Microgravity: A tool for protein drug development. Int. J. Pharm. Sci. Rev. Res. (ISSN 0976–044X), 64(2), Article No. 14, Pages: 82-86. doi: 10.47583/ijpsrr.2020.v64i02.014.

Jaiyeola, P. O., Oluwafemi, F. A., Otum, A. O., Tomori, O. S., Bemibo, I. E., & Ayegba, A. (2020). Impact of microgravity environment on body mass: Case study of lizards. International Journal of Engineering and Applied Sciences (IJEAS), ISSN: 2394-3661, Volume-7, Issue-8.

Jayachandran, A. V. T., Oluwafemi, F. A., Israel, Y., & Akinwale, A. T. (2018). Space mining corporation: The pseudo-economic and technology model. IAC-18,A3,IP,48,x43397, Proceedings of the 69th International Astronautical Congress (IAC), Bremen, Germany, 1-5 October, 2018.

Oluwafemi. (2022). Space Food on Celestial Bodies and on the Way There (Chapter 26). In: Future Foods: Global Trends, Opportunities and Sustainability Challenges. Rajeev Bhat (Ed.). Elsevier Sciences Inc.: Wiley Blackwell, Oxford, UK. pp. 451-468. Book ISBN: 978-0-323-91001-9. https://doi.org/10.1016/B978-0-323-91001-9.00012-8.