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the story So Far: 24 August, NASA said Boeing’s Starliner crew capsule, which carried astronauts Sunita Williams and Barry Wilmore to the International Space Station (ISS) as part of its first crewed test flight, was not safe enough to take them back. Instead, NASA extended Williams and Wilmore’s stay on the ISS until February 2025, when they will return in a SpaceX crew capsule launching in September 2024. Boeing’s Starliner will have to undocke and return without a crew.
What is space?
Millions of kilometres from Earth, ‘space’ is easier to identify than closer to the planet because conditions gradually change from ‘Earth-like’ to ‘space-like’. In aeronautical and astronautical circles, space begins at the Kármán line, which is 100 kilometres above sea level. Similarly, the force of gravity can be said to be close to zero several billion kilometres away from a massive body, but still exists. This is why astronauts aboard the ISS experience zero gravity, not microgravity.
Thus, space may be a vast expanse but different parts of space can expose astronauts to vastly different ambient conditions. The Van Allen radiation belts around Earth are a good example of this. They are located above the Karman line, from 640 km to 58,000 km above. They are made up of charged particles from outer space that have become trapped in the Earth’s magnetic field. Researchers explored the amount of radiation these belts exposed astronauts to during the U.S. Apollo program (which is not harmful) and then also the risk to astronauts in outer space, where the belts would not protect them. In this article, ‘space’ means above the Karman line and in microgravity conditions.
What effect does space have on the human body?
While hundreds of astronauts have been to space, they are not a large enough group for researchers to study them and reliably explain all the effects of space flight on their bodies. They have spent very varying amounts of time there and have reported different symptoms after different trips. However, some broad trends have emerged, centering on the body’s bones, digestion, eyes, heart, muscles and nerves. All of these organs and systems function in accordance with environmental conditions on Earth.
For example, bones weaken in microgravity, which may force the body to deposit ‘excess’ mineral content in the kidneys, leading to kidney stones. Food may move more slowly through the intestine and weight gain may occur. About 20% of all astronauts and 70% of those involved in long-duration spaceflight suffer from a condition called spaceflight-associated neuro-ocular syndrome (SANS): excess fluid enters the head and accumulates behind the eye, affecting vision.
Because of the body’s weightless experience, the heart has to do less work and can contract. Similarly, muscle mass and strength may decrease in other parts of the body. The blood loses more red blood cells per day than it does on land (a 2022 study In Naturopathy The rate of loss was assessed, but the cause could not be ascertained), meaning that astronauts’ diets need to be adjusted to give their bodies more energy to make more of these cells. The brain works constantly on Earth to help the body maintain its balance, sense of orientation and positional stability, receiving signals from various parts of the body, including the eyes and inner ear. These signals deviate from ‘normal’ in space and force the brain to work harder to determine proper balance.
If these symptoms are present, researchers have identified some important shared causes: radiation exposure, confined and hostile environment, distance from Earth and gravity, among others. The second of them also refers to psychological factors such as fatigue, loss of morale and a feeling of helplessness towards the needs of the astronauts’ family on Earth.
Can we counteract these effects?
The more time astronauts spend in space, the more pronounced their symptoms become. But whether the mission is short or long, space agencies require their astronauts to follow strict exercise regimes and maintain predictable routines to keep the body functioning without stress while in orbit. Agencies have also developed communication and task-management protocols that keep astronauts occupied, enabling them to take responsibility for their work and relax.
The researchers are also studying whether various nutrients and drugs are metabolized differently in space. They have already identified some changes in metabolic pathways involved in the synthesis of DNA, amino acids and phospholipids, and a condition in which there is excess iron in the body as well as decreased magnesium in the urine and potentially reduced DNA stability. 2022 reportThe researchers suggested developing a more portable optical coherence tomography machine to investigate SANS on spacecraft. If it exists, they recommended studying countermeasures to reduce “headward fluid shift”, including applying “lower body negative pressure”, exposure to artificial gravity through “human centrifugation” and taking drugs that reduce intracranial pressure.
That said, our understanding of the effects of space flight on humans is fraught with many uncertainties, according to a paper published in June 2024. Nature Communications He added that researchers still need to understand which effects of space flight are or are not of “health-related significance,” avoid overinterpreting data “given the small sample sizes and small number of studies,” establish “appropriate ground controls,” and find alternative ways to replicate their findings.
An important set of studies called “space omics” involves understanding all the ways in which the body can be affected by the space environment. A well-known example of this is NASA’s Study of twinsWhere scientists examined the differences in the bodies of two identical twins – astronauts Mark Kelly and Scott Kelly – after the latter spent a year in space. It identified about 8,600 genes that were expressed differently between them. The June 2024 paper noted that “any permutation of (these genes) could reveal biochemical pathways that hold the key to the development of therapeutic supplements and lifestyle recommendations that better protect health in space”.
The “Cell Space Atlas” of space omics | Photo credit: Nature Communications Volume 15, Article number: 4952 (2024) (CC BY 4.0)
Japan’s KAKENHI programme is studying biological responses in different parts of the space environment. Europe’s Space Omics Topical Team is developing space omics tools and methods. In the US, the ‘Supplementing Integrated Protocols for Human Exploration Research’ project allows astronauts to sign up for experiments in space that will study their health in standardised ways. Scientists around the world, including India, are working to develop research and ethics guidelines to be part of international standards for space omics processing.
How much time are humans spending in space?
Average maximum time The time an astronaut spends in space has increased from one month in the 1960s to six months in the 2020s. Each mission to the ISS can also be up to six months long.
Assuming their current trip ends on Feb. 15, 2025, Williams and Wilmore will spend 256 days in orbit. So far, 11 individuals have spent more than 300 days in space in a single mission. The record holder is Valery Polyakov of Russia (437 days from Jan. 8, 1994) and the US record holder is Frank Rubio (370 days from Sept. 21, 2022). Cosmonaut Oleg Kononenko is currently the only astronaut to have spent more than 1,000 days in space in missions. The second active astronaut on the list is Peggy Whitson of the US who has spent 675 days.
Less than a century ago, going to the moon was considered a long-duration space mission. Today, the space agencies of China, India, Japan, Russia and the United States, among others, are considering permanent stations on the moon and manned missions to Mars. These are new long-duration missions and will present new security challenges.
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