Abstract
The development of artificial gravity has the potential to enhance long-duration missions and further exploration by reducing the negative effects of microgravity on astronaut health, such as muscle atrophy and bone loss. One of the greatest limitations of artificial gravity is human tolerance. Scientists have already created concepts that could potentially create artificial gravity. One of these concepts included a large rotating space station that creates an inertial force that mimics the effects of a gravitational force. They rotate at a rate of around 4 rpm, which is considered the human tolerance limit. However, there were restrictions that came along with this concept, such as, mass balancing the spacecraft to eliminate rotational imbalance and cost.
Introduction In zero gravity, astronauts’ bones weaken by up to 2% per month due to reduced weight-bearing. This loss only affects astronauts upon their return to earth, due to their weakened bones, there is an increased risk of fractures. Bones constantly reshape their structure depending on the stress that’s put on them. On earth, gravity applies a constant mechanical force to the skeletal system that causes bones to maintain a specific density to support the body. In space, bones no longer have to support the body against gravity. Finding a solution to this problem is crucial for future space exploration, as on long-duration flights, bone loss can be a serious impediment. This study aims to investigate the potential creation of artificial gravity as a solution to the adverse health effects of prolonged spaceflight. The specific objectives of this research are to:
1- Find theories and methods as to how artificial gravity can be created with little to no negative impact on human health.
2- Further investigate the physiological effects of prolonged microgravity on astronauts.
3- Analyze the possible effects artificial gravity would have on long-duration space missions and astronauts’ health.
Literature Review
Microgravity is a measure of the degree to which an object in space is subjected to acceleration, it’s often used equivalently with zero gravity. Exposure to microgravity for a prolonged period may negatively affect the body. Some effects such as loss of bone mineral density can be long lasting, while other effects can me temporary and minor, such as facial puffiness due to fluid shifts. Dr. Janani Iyer, a project scientist at NASA stated that microgravity poses risks to the central nervous system, suggesting that countermeasures may be needed for long-duration space travel. As of 2000, some of these countermeasures include subcutaneous injections of erythropoietin (a hormone that your kidney naturally makes to stimulate the production of red blood cells.) to prevent decreases in erythrocyte mass and vigorous in-flight regimens to reduce loss of bone mineral density. NASA created a general approach to the development of countermeasures which summarized the steps that have been incorporated into their countermeasure’s evaluation and validation project. These are the steps given: 1- Conduct research to understand the basic nature of the physiological problem. 2- Formulate a countermeasure strategy based upon that physiological understanding. 3- Test the countermeasure and demonstrate its efficiency on the ground. 4- Lastly, validate the countermeasure in space. However, no single countermeasure has yet to be validated as clinically efficacious. Working in microgravity presents many increased risks for bone fracture and the necessity for wound healing. Technically nothing certain is known about how microgravity will affect fracture management and healing during long-duration space missions. Recent research focusing on calcium metabolism showed an approximate 50% increase in the level of calcium absorption, calcium excretion and bone resorption after a 3-month space mission. However, subjects lost around 250 mg of bone calcium per day, which would be approximately 22,500 mg lost in the three-month mission. Mainly stress-bearing bones such as the spine, neck, femur, pelvis and trochanter lost bone mineral density. Loss of bone mineral density begins within a few days and symptoms only show a year later. Long duration space missions in earth’s orbit offers the opportunity to achieve crucial data by clinical research. Thesa data can then be used to create hypotheses on how to protect astronauts from injury and death. Selecting astronauts with a higher bone mass may not prevent mineral density loss but instead prevent the aftermaths of decreased bone mineral density. Bone mass can be measured by bone densitometry and bone turnover rates as measured by markers of bone density in serum and urine determined before the initiation of a mission. Previous experiments using animals have been done to simulate weightlessness. For example, rats have been used in microgravity experiments, but the results aren’t reliable as rats and humans have different bone architectures. Young rats exposed to 18 days of rear-leg unloading developed an irregular gait, signifying permanent damage to the neuromuscular pathway. Changes in their microcirculation occur as a result of cephalad fluid shift and upon their return to earth, reloading-induced edema and ischemic tissue necrosis may occur. Adaptation to the lower force load in microgravity renders muscle tissue to structural failure when back to earth. While exercise-based protocols have been deemed effective, there is no proof of it preventing any inevitability. However, bicycle ergometry and treadmill exercises counteract the tendency to attain the weak dorsiflexion stance in microgravity, which accelerates loss of thick filaments. Among all the negative health effects that accompany microgravity, the cardiovascular and pulmonary systems’ greatest problem is orthostatic hypotension, this is a fall in blood pressure. Symptoms include dizziness, blurred vision (also known as the spaceflight-associated neuro-ocular syndrome SANS), and syncope which can occur when one stands up or stands stationary in one position. The main cause of orthostatic hypotension is the deterioration of peripheral vascular resistance due to microgravity, over two-thirds of astronauts suffer orthostatic hypotension upon their return to earth.
For the period of weightlessness, there is a loss of hydrostatic pressure, especially in the lower limbs. Fluid shifts from extravascular to intravascular spaces and towards the upper body. Other disadvantages that occur along microgravity are prolonged reduction in central venous pressure, which resets the baroreceptors to a lower operating point limiting plasma volume expansion during efforts to increase fluid intake and a decrease in femoral vascular and renal resistance. These changes in intravascular volume leads to a change in stroke volume and cardiac output.
Artificial gravity is the creation of an inertial force in a spacecraft achieved by the linear acceleration or steady rotation of all or part of the spacecraft, with the purpose of imitating gravitational force on a board crewed spacecraft. It can act as a countermeasure to mitigate the physiological deconditioning associated with microgravity on the human body. While artificial gravity cannot address all long duration space flight related problems like radiation exposure, it is a precaution that addresses the debilitating and potentially fatal problems of cardiovascular deconditioning, muscle weakening, bone loss and neurometabolic disturbances and regulatory disorders. Artificial gravity can also be a countermeasure for the visual impairment acuity and ocular trauma seen in long-duration astronauts which is due to VIIP syndrome (Visual impairment and intracranial pressure). The theorized trigger for VIIP is that the lack of gravity, causing bodily fluids to experience weightlessness and shift is the precipitating factor leading to impairment in cerebrospinal fluid re-sorption and central nervous system venous drainage. Though this is nothing more than a hypothesis, scientists and researchers are still trying to understand the ramification of VIIP and is currently being investigated, since it is currently a critical concern preventing long-duration missions. One potential artificial gravity invention is the continuingly rotating space shuttle that generates a centrifugal force of 1 G, this provides the static crewmembers the sensation of standing vertically as if they’re on earth. Sergei Pavlovich Korolev proposed to connect two Voskhod ( A soviet crewed space program in the early 1960s) by a 300 m tether and rotate them at 1 rpm to generate 0.16 G. Wernher Von Braun also proposed a space shuttle having a diameter of 76 m rotating at 3 rpm, this would result in a suitable platform for long duration space missions such as the Mars excursion exposing the astronauts to 0.3 G. A human rated short radius centrifuge offers a more realistic upcoming opportunity for providing intermittent artificial gravity. Centrifugal force depends on both rotation and radius, changes in the artificial gravity level can be attained either by increasing or decreasing the rate of rotation which will mostly influence the physiological and psychological responses of the crew on board and increasing or decreasing the rate of radius of the structure will directly impact the cost and complexity of the space shuttle. Exercise on the other hand was introduced as a countermeasure by means of ingenious elastic, mechanical, hydraulic, pneumatic, and electric devices. This procedure works by holding the crew members down by wearing a harness that’s attached to an exercise bike or treadmill. However elastic devices cannot sustain acceleration, it can only effectively create force. On a short-radius centrifuge, crew members are generally lying horizontally with their head close to the axis or rotation and their feet directed outwards. Designs created for exercising during centrifugation include the “twin bike”, “Space cycle” and NASA research center’s human powered centrifuge. During centrifugation in space, the crew members are only exposed to the centrifugal force along their longitudinal body axis, referred to as artificial gravity.
Conclusion
The implementation of artificial gravity presents a promising avenue to mitigate the numerous adverse health effects of prolonged exposure to microgravity. Astronauts experience significant physiological deterioration in space, including bone demineralization, muscle atrophy, cardiovascular deconditioning, and neuro-ocular syndromes. These effects pose a substantial threat to the safety, functionality, and long-term viability of crewed space missions, especially those venturing beyond low Earth orbit. Artificial gravity, particularly through rotating spacecraft or centrifuge-based exercise platforms, offers a compelling solution by simulating Earth-like gravitational forces. While concepts such as Von Braun’s rotating wheel and short-radius centrifuges show potential, their implementation is constrained by engineering complexity, human tolerance limits, and financial costs. Nonetheless, the integration of artificial gravity into spaceflight systems—alongside existing countermeasures like exercise regimens and pharmaceutical interventions—could greatly enhance the sustainability of human life in space. As research continues, interdisciplinary collaboration between engineers, physiologists, and space agencies is crucial to refining these systems and validating their effectiveness. Artificial gravity may not yet be a fully realized technology, but its future role in supporting the health and performance of astronauts is indisputable. Continued development and testing will be essential in ensuring that humanity is prepared for the challenges of extended space exploration.
This is a highly insightful and well-researched paper that clearly explains the challenges of microgravity and the potential of artificial gravity as a practical solution for long-duration space missions.