Scientists from the Indian Institute of Space Science and Technology (IIST), Thiruvananthapuram, have discovered that exposure to microgravity leads to a continuous rise in human core body temperature. Their study, published on March 29, 2025, in Life Sciences in Space Research, highlights that this increase is mainly caused by fluid redistribution in the body, which disrupts the natural process of thermal regulation during prolonged space missions.
According to the National Aeronautics and Space Administration (NASA), microgravity is defined as the condition in which people or objects appear to be weightless. It is often measured as one-millionth (10-6) of standard Earth’s gravity (9.80665 m/s2, which can vary slightly as per location, altitude, and depth).
Purpose of the Research
With many nations advancing their human spaceflight programs, protecting the health of astronauts has become a key area of study. Researchers investigate microgravity’s effects using both in-orbit and Earth-based simulations, such as parabolic flights and head-down tilt experiments. These involve both human and animal subjects, like rodents and fish. (Parabolic flights and head-down tilt (HDT) techniques are used to reverse the impact of gravity.)
Due to limited in-space data on factors such as physical inactivity, radiation, disrupted circadian rhythms, and stress from acceleration, ground-based studies and computer models are increasingly used. The IIST study employs such a model to understand how microgravity influences human body temperature overtime.
Why Thermoregulation Matters in Space
As human space missions venture farther—like Voyager 1 spacecraft which on February 1, 2025 was around 25 billion kilometres from Earth—maintaining ‘thermoregulation’, becomes vital. (Thermoregulation is the maintenance of physiologic internal body temperature of 37 ± 0.5 °C or 98.6 ± 0.9 °F, needed for the body’s metabolic processes to function correctly.)
While this is a simple process on Earth, it becomes much more complex in space. In the absence of gravity, many standard physiological functions change, including how the body generates, retains, and releases heat. According to the lead researcher, Professor Shine S.R., the redistribution of fluids inside the body is a major factor in these thermal imbalances during spaceflight.
Physical and Biological Factors in Space
Individual responses to temperature changes vary based on factors such as age, physical fitness and body fat. In space, these responses become more unpredictable due to significant physiological changes caused by microgravity. These include muscle and bone density loss, altered heart function, changes in the immune system, metabolism and cellular behaviour. For these reasons, keeping track of the space farer’s body temperature is essential throughout the mission to avoid health complications.
Developing and Validating the Computational Model
To investigate these effects in more detail, researchers at IIST developed a three-dimensional computer model to simulate how the human body regulates heat in a microgravity environment. This model accounts for various physiological shifts seen in space, including fluid redistribution, metabolic changes, and loss of muscle and bone mass. These inputs were used to improve understanding of how microgravity influences thermoregulation.
The lead author of the study, who is also a Ph.D. student at IIST, Chithramol M.K., pointed out that one of the main difficulties in constructing the model was the lack of specific metabolic data. When such data was not available, the team used standard engineering methods and careful judgment to estimate the impact of various factors.
The model incorporates mathematical formulae to track heat flow within the body in three dimensions. It includes key thermoregulation processes, such as sweating, shivering, insulation from clothing, and heat production by internal organs. Each of these mechanisms was modelled individually and then combined to give a complete picture of how the body manages temperature in space.
To test the accuracy of their model, the researchers simulated data from past missions aboard the Russian Mir space station and the International Space Station (ISS). The results of the model closely aligned with real-world data, confirming that it is reliable.
Another important feature of the model is its customisation for the Indian population. Most existing thermoregulation models are based on data from non-Indian groups, which may not always be applicable due to differences in body structure and physiology. The IIST model addresses this gap by specifically reflecting characteristics of Indian subjects.
Key Findings of the Study
The study found that microgravity causes a shift in blood flow from the lower body to the upper body, altering the internal temperature distribution of the body. Over time, astronauts tend to experience cooler hands and feet, while the head, core, and abdomen become warmer.
One significant insight from the model was the impact of exercise on body temperature in space. It showed that during physical activity, the core temperatures of the astronaut rise more quickly than on Earth. After roughly two and a half months in space, the core temperature of an astronaut could increase from 36.3 °C to around 37.8 °C due to reduced sweating and higher metabolism. During exercise, this could rise even further, nearing 40 °C which may pose a serious risk to physiological stability.
Earth-Based Applications of the Model
While this model was developed with space missions in mind, it has further valuable uses on Earth. Thermoregulation models are already widely used in designing clothing for various climates, constructing buildings to reduce heat stress and supporting medical procedures such as cardiac surgeries where temperature control is critical.
Additionally, the model includes calculations for the Universal Thermal Climate Index, which measures how people perceive temperature based on factors like wind, humidity, and sunlight. This could help improve safety and comfort in outdoor environments.
Professor Shine emphasised that although the focus was space-related, the usefulness of the model goes far beyond. From improving safety in harsh climates to enhancing daily comfort, the ability to understand and control body temperature has broad practical value.
India’s Leap in Microgravity Research: Axiom-4 Mission
In a related development, the Indian Space Research Organisation (ISRO) has chosen seven experiments to be conducted aboard the ISS as part of the Axiom-4 (Ax-4) mission, fourth private astronaut mission to the ISS. These experiments would involve Indian astronaut group captain, Shubhanshu Shukla.
The selected projects come from national research labs and academic institutions, including the Indian Institute of Science (IISc), Institute of Stem Cell Science and Regenerative Medicine (InStem) and the University of Agricultural Sciences (UAS) in Dharwad, Karnataka.
ISRO sees this initiative as a major milestone in developing India's microgravity research capabilities, with promising applications in health care, biotechnology, materials science, and space technology.
Seven microgravity experiments have been selected for research aboard the ISS. One of them, developed by the International Centre for Genetic Engineering and Biotechnology (ICGEB) along with the National Institute of Plant Genome Research, would explore how radiation in microgravity affects edible microalgae. They are also working on sprouting salad seeds in space.
Another study from the ICGEB would compare cyanobacterial growth using urea and nitrate under microgravity conditions, focusing on their protein-level responses. Meanwhile, the UAS, Dharwad, is conducting research that could help in improving the nutrition of astronauts in space.
The IISC is leading two projects. One looks at how a microscopic organism, called a ‘tardigrade’, specifically the Paramacrobiotus species, could survive, recover and reproduce in space. The other project would examine how humans interact with electronic screens in a weightless environment.
The InStem would study how certain metabolic supplements could help with muscle regeneration when the body is in microgravity. This could support long-duration space missions.
The final experiment, a collaboration between the IIST, the Department of Space and Kerala Agricultural University, aims to understand how microgravity influences the growth and yield of food crop seeds.
Other Space Missions Supporting Microgravity Research India’s space program is actively advancing microgravity research through several key missions.
The Gaganyaan Mission, approved by the Government of India, aims to send a 3-member crew on a 3-day mission to Low Earth Orbit (400 km) and return them safely. The first unmanned trial is expected in 2025, followed by the first manned spaceflight before 2026. With this, India would become the fourth country, after the US, Russia, and China, to achieve human spaceflight capability. Gaganyaan also supports microgravity experiments in biology, medicine, and material sciences.
POEM-4 (PSLV Orbital Experimental Module-4) complements this, launched on December 22, 2024, aboard PSLV-C60 under the SpaDeX (Space Docking Experiment) mission. It utilises the spent fourth stage (PS4) of the rocket as a stable orbital platform to host microgravity experiments for up to three months, avoiding space debris and enabling proof-of-concept trials for future technologies.
According to ISRO, microgravity research has wide-reaching potential in fields like health care, biotechnology, material science, and pharmaceuticals. Conducting these studies aboard the ISS is expected to boost India’s capabilities in this field and foster a thriving microgravity research environment for future space missions.
© Spectrum Books Pvt Ltd.
