In the almost 60 years since we’ve started launching humans into space, more than 550 have been , . That isn’t a lot of people when you’re looking for research data. Additionally, obtaining data on space travel can be costly and has limitations. For example, certain data collecting methodologies are not possible in space, like magnetic resonance imaging (fMRI). This means that data needs to be collected before and after the astronauts go into space. In certain cases, data collected after space travel is time sensitive and getting data too late can affect the analyses made from that data. This presents some potential obstacles for research. Real space data like this is not necessarily pro-active in the sense that we are putting humans in space in order to determine possible detrimental effects.
Fortunately scientists have developed analogues to mimic certain aspects of space travel here on earth. This allows scientists to gather data and study the effects of space on the brain and other aspects of the human body in a safe controlled environment. Of course, no technique is a perfect analogue for space, but they can give us a better understanding of what the factors are that we are dealing with in order to help us create countermeasures.
So what are the analogues?
Parabolic Flight (PF):
Parabolic flight was first introduced in the 1950’s as a way to train astronauts in microgravity.
Figure 1. The illustration shows the general trajectory of a parabolic flight. It shows that several gravities are created during flight; hypergravity, microgravity, and Earth gravity. It also shows the general time course for each gravity. Data from Van Ombergen et al, 2017.
Figure 1 illustrates a general parabolic flight pattern and the relatively short timespan in which to experience microgravity. Parabolic flight offers several different gravities for study, including normal gravity (1g), hypergravity (1.5-1.8g), and microgravity (0g). Additionally, different flight alterations can offer Martian gravity (.38g) and lunar gravity (.16g). Microgravity or zero gravity (0g) is roughly 20-25 seconds in length , . This is often repeated 30-60 times.
Dry immersion was first used in the 1970’s as a way to test the effects of weightlessness. Dry immersion is a technique where a subject is immersed in thermo-neutral water. The subject is covered with a waterproof fabric in order to keep them completely dry and prevents contact with the water. This method recreates the supportlessness, confinement, immobilization, centralization of bodily fluids, and reduced muscle movement (hypokinesia) that astronauts face in space ,.
Figure 2. An image showcasing dry immersion. Image from Navasiolava et al., 2011.
They can be horizontal as in Figure 2 or upright such as sitting or standing. Immersions can last anywhere from a few days up to a few weeks.
Head Down Bed Rest (HDBR):
The use of bed rest to study the effects of inactivity on the human body has been conducted since the late 1940’s. However, using the head down method to simulate the body in space wasn’t used until the 1970s . It entails immobilizing a subject at a six degree angle which causes cephalic fluid (cerebrospinal fluid in brain) shifting , . This method is meant to recreate the immobilization, isolation, and monotony that astronauts are subjected to in space. However, unlike space, this method still allows for gravitation as well as a sense of balance.
Figure 3. Subjects are confined to beds at a six degree angle. Image from nasa.gov.
What these analogues allow scientists to do is to learn what the risks and effects of space are on the human body in a controlled environment. They offer more opportunities for testing then would be available just using real astronauts alone. The accumulation of this sort of data will enable the development of better and safer ways for people to travel in space. If our future is in the stars, then we better figure out how to prevent problems before we get there.
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 Astronaut/Cosmonaut Statistics [Internet]. [publisher unknown] [place unknown] [updated 2019 Jan 16; cited 2019 Jan 15]. Available from: https://www.worldspaceflight.com/bios/stats.php
 Van Ombergen, A., Demertzi, A., Tomilovskaya, E., Jeurissen, B., Sijbers, J., Kozlovskaya, I.B., Parizel, P.M., Van de Heyning, P.H., Sunaert, S., Laureys, S., Wuyts, F.L. The Effect of Spaceflight and Microgravity on the Human Brain. Journal of Neurology. 2017, 264(1): S18-S22.
 Karmali, F., Shelhamer, M. The Dynamics of Parabolic Flight: Flight Characteristics and Passenger Percepts. Acta Astronautica. 2008, 63(5-6): 594-602.
 Navasiolava, N. M., Custaud, M., Tomilovskaya, E. S., Larina, I.M., Mano, T., Gauquelin-Koch, G., Gharib, C., Kozlovskaya, I.B. Long-Term Dry Immersion: Review and Prospects. European Journal of Applied Physiology. 2011, 111(7): 1235-1260.
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