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.