A rocket launch. The tall vessel, akin to a solitary skyscraper, stands alone on the launchpad. The thunderous roar of thrusters travels across miles of empty concrete. The ground shakes. The audible roar in your ear and the palpable vibration underfoot steadily rises, in unison with the overhead countdown. Hundreds of on-lookers stand in excitement, witnessing the launch at a safe distance. Seated in the capsule, confined by restraints, are the astronauts themselves. Modern-day heroes with movie-star smiles, contagious confidence, and uniforms proudly brandishing the Star-Spangled Banner. Years of training, sacrifice, and rigorous military or scientific backgrounds have prepared them for this moment. But wait. The scene changes. Now enter affluent tech entrepreneurs — the likes of Sir Richard Branson, Jeff Bezos and others. These faux voyagers have geared up for launches of their own, competing with one another to enter “space” on a technicality. Neither flight will rise beyond 50 to 60 miles, and neither will last more than 20 minutes. No orbit. No prolonged microgravity. No long-duration exposure to the detrimental effects of space. Real spaceflight, borne by real astronauts, is far from bragging rights. And far from benign. The deleterious effects of prolonged microgravity on human physiology are immense, affecting countless body functions. The cardiovascular system experiences cranial fluid shifts, leading to cardiac atrophy and vascular remodeling. These fluid shifts cause chronically elevated intracranial pressure and resultant optic disc edema, a phenomenon known as Visual Impairment and Intracranial Pressure (VIIP). This has led to altered vision in astronauts, with some changes lasting even upon their return to Earth. Similarly, the musculoskeletal system is not spared. Progressive bone loss and sarcopenia (muscle loss) are seen, despite best efforts at daily resistive exercise and anti-resorptive agents. The proximal femurs of healthy young astronauts may lose up to 10% of bone mass over 6 months in space, with recovery upon return to Earth taking upwards of 3 to 4 years. Cartilage in the intervertebral discs and joint surfaces also experiences changes. Intervertebral disc height is lost, with chondrocytes changing morphology and their normal ratio of secreted collagen proteins. These alterations to human physiology do not only occur at the macrosystem level. Countless derangements in hematological and immunological systems affect our smallest cells and signaling molecules. A phenomenon known as neocytolysis, the selective destruction of the youngest red blood cell populations, contributes to anemia and the challenge of acclimating on return to Earth. Immune system deregulation prompts changes in cell populations and cytokine ratios. While our bodies experience hindered leukocyte migration, extravasation, and phagocytic ability, microbes simultaneously experience increased pathogenicity and virulence in space. Multiple viral species, such as herpes, have reactivated in healthy astronauts during spaceflight. Similarly, countless astronauts suffer chronic upper respiratory symptoms for the duration of flight. Healthy male astronauts have even been found to sustain urinary tract infections, which are normally atypical infections for this demographic on Earth. In light of these known phenomena, the medical and aerospace communities are tasked with a challenge. As the societal and economic will for longer duration spaceflight — and possibly even semi-permanent settlement – continues to grow, how will we address these impacts on human physiology? Prior to prematurely ambitious plans for a long-duration mission to Mars, a long-term Moonbase, colonizing asteroids, etc., we must continue researching these conditions and creating countermeasures. How do we address a major injury in space? If we sustain major trauma, hemorrhage or fractures, do these heal reliably in microgravity? Or are the normal molecular cascades of inflammation, early repair and tissue remodeling too altered? And this does not address the more distant future of humans in space. In the scene of a multi-generational settlement, how does prolonged microgravity affect pregnancy and fetal development? Are the normal developmental axes of cranial-caudal, dorsal-ventral, organogenesis and appropriate limb budding possible? Or fraught with complication? Initial research on mouse and rat populations suggests distorted longitudinal growth and altered mRNA expression at the growth plate. Could this dictate a limit on long-duration spaceflight or extraterrestrial settlement at a site with different gravity from Earth? None of this even touches upon the potentially damaging effects of long-term interstellar radiation once we exit the protective envelope of Earth’s magnetosphere. Now return to the scene of the rocket launch. The thrusters burn crimson, and the ground rattles. On one side are the highly trained, dedicated astronauts embarking to explore for their country and humanity. On the other are the tech billionaires, prepping for flights to soar slightly higher than hot-air balloons. Their launches seemed successful, fun, and all they could wish for. But they are not astronauts. They have not sacrificed so much of their lives for dreams of discovery. Astronauts are the modern-day adventurers upon whose backs our knowledge of the final frontier has been built. This knowledge has wrought more questions than answers and questions addressing the myriad changes to our physiology. In the not-so-distant future, our extraterrestrial exploits will become less limited by physics and rocket technology. We will be limited by our human biology. It is imperative to study, design, and implement countermeasures for safe and lasting exploration amongst the stars, rather than simply jockeying with rivals to cross the symbolic Kármán line. Source
