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Health challenges including behavioral problems in long-duration spaceflight
Correspondence Address: Source of Support: None, Conflict of Interest: None DOI: 10.4103/0028-3886.259116
Keywords: Behavioral health in space, remote healthcare, space medicine
Over the past six decades of human spaceflight, the ability to live and work in Low Earth Orbit (LEO) and on short sojourns to the lunar surface for several days has been demonstrated. During this period, human spaceflight was dominated by the United States (US) and the Union of Soviet Socialist Republics (USSR).[1] The objective during the 1960s was a “space race,” with landing a man on the moon as the ultimate goal. The US focused its successive missions on short duration missions, designed to build on the success of each platform with the eventual landing of man on the moon on July 20, 1969. The Soviet approach was focused on longer duration missions over successive space stations. US missions were measured in days, whereas the Soviet missions were measured in weeks and months. In 1987, cosmonauts Vladimir Titov and Musa Manarov spent nearly 366 days onboard the Mir Space Station, and in 1994, Valeri Polyakov spent nearly 438 days on board Mir, a record that still stands today. US astronauts spent 84 days on Skylab 4 mission in 1975; the longest US record until the International Space Station (ISS) program. In 2015, Scott Kelly and Mikhail Kornienko spent 346 days on the ISS [Figure 1].[2]
Most missions of long-duration have been less than or equal to 1 year with one outlier – Polyakov in 1994. These missions have been conducted in LEO with the Earth in full view, and with protocols and capabilities to return to definitive care on Earth in the event of an emergency. The ISS always has two Soyuz Transfer Modified attached to docking ports in case of a need to return to Earth, a ballistic entry to the Steppes of Kazakhstan. Emergency returns, in the case of a significant medical emergency or if the crew has to abandon the ISS, must be coordinated with the ground prior to a return.[3],[4] Future long-duration missions will be conducted with knowledge obtained from the LEO missions and the lunar landings of 50 years ago. Scientific knowledge from life sciences research and aerospace medicine practice provides a wealth of knowledge on physiological and psychological changes in outer space to practitioners and mission designer's today.[5],[6],[7],[8],[9] Selection of appropriate individuals and matching them into highly productive crews have resulted in successful missions. Living and working in space requires life support systems to maintain health and human performance.[9],[10] Medical systems onboard, to support the crew's medical needs from basic first aid and ambulatory care to emergent care, must exist. The size and capability of the onboard medical system is dependent on the available volume in the spacecraft and the mission profile (distance from the Earth and time in orbit). This system must be linked to the expertize available at the terrestrial Mission Control Centers to support the appropriate medical needs of the crew.[11],[12] Although crews have always been in contact with select personnel on the ground, including physicians through private medical conferences (PMCs), there are times when the communication is limited.[11],[12] As the international community contemplates long-distance and long-duration missions beyond LEO to the Moon, Mars, or beyond, this proven model of care fundamentally has to change, and the length of time it takes to interact with Earth will be a key driver. [Figure 2] illustrates the distance from the Earth to the Moon (239,800 miles (380,000 km)). One-way delay in communications is measured at 1.25 s or 2.50 s roundtrip. The distance from the Earth to Mars varies depending on where the planets are in relation to one another. At their closest, the distance is 34.8 million miles (54.6 million km) and the farthest about 250 million miles (401 million km) or an average of 140 million miles (225 million km). The distance between the two planets has a direct impact on mission planning and communications. Due to the distance, communications between a spacecraft on the surface of Mars and a control center on the Earth can be 3 to 22 min one-way. This is because of the distance between the two planets and the speed of light. This causes latency in communications. This means that real-time or synchronous communications cannot be accomplished. This is one of the many significant challenges that humans will have to experience in long-distance and long-duration missions. Several more challenges are highlighted below. The implication is that Mars-bound crews must have a complex medical system onboard to address their medical needs.[13] Such an autonomous system will have a significantly delayed communications capability.
In addition to the delay in communications, access to definitive care is possible from LEO but not on a transit mission to the Moon, Mars, or any other destination. [Figure 3] illustrates the view of the Earth from the cupola on the ISS.
The crew members aboard a spacecraft destined for a great distance from the Earth will experience acceleration, radiation, as well as physiological, and psychological impacts owing to confinement, remoteness, and isolation.[14] The crew members will leave not only the physical environment of Earth but also work, family, social and interpersonal environments, networks, and resources in which they lived, while on Earth. As the Earth recedes, so will all the physical, professional, and personal resources on which the crew members grew and trained. As the Earth recedes further and further, the Earth will only be seen as another small dot in the blackness of space. To ameliorate these challenges, life scientists and aerospace medicine specialists are developing specific onboard systems. These will address inflight medical and environmental monitoring. Countermeasures to meet the physiological and psychological impact on cardiovascular, musculoskeletal, neurosensory, and other human systems will be integrated.[15],[16] Research over the last several decades has provided considerable data, leading to design and evaluation of appropriate systems to meet specific needs of various programs and mission profiles. As indicated earlier, crews on the ISS and previous human spaceflight missions have been linked to the ground through a network that permits telemedicine commmnication to be established.[11],[12] This capability in LEO is synchronous (near real-time) as the bandwidth is available, and the distance for data to travel is unlike that seen in deep space travel. This permits interaction of the crew members and ground personnel to address health concerns.
The medical system on the ISS is adequate to address a wide variety of the crew's needs. Each mission has a designated crew medical officer, medical kits have necessary medications, limited diagnostic tools, and the ability to support PMCs. Furthermore, the crew member and the flight surgeon interaction is supported by the telemedicine link and a network of ground-based subject matter experts in a synchronous mode.[17] Although spaceflight can affect an individual in many ways, the focus in this communication is on performance and management of behavioral problems during long-duration flights.[9] Individuals, selected to fly in space, are chosen from a very select group of individuals through a set of international standards. This includes physical and mental health testing and evaluation.[18] The crew composition is done to match skills and individual personalities with mission objectives.[19],[20] Task selection and training are honed for each mission, with protocols for pre-flight as well as in-flight skill development and maintenance.
For crew members to be continuously monitored by ground-based medical personnel and their flight surgeons, a robust and secure communication link is a necessary requirement. This link provides the ability to support telemedicine and has been a key component of human spaceflight since the very first flight of a dog, sent into space in 1957.[11],[12] Synchronous communications permit remote monitoring and interactive PMCs. However, as the spacecraft continues to move beyond LEO, the delay in communications limits this capability. Although terrestrial medical care in some instances must be done in real-time, this is not possible in long-distance spaceflight.
Medical care systems, deployed on the spacecraft over the past six decades, have evolved to meet the needs of crew members, the mission profile, the mission duration, and the capability of the crew. The systems are designed and deployed depending on the risk assessment, the available volume in the spacecraft, and the ability of the crew to respond to medical needs.[17] As spacecrafts have grown in size and complexity, more equipment and, more capability can be accommodated. The ISS has more space available than the capsules used previously to transport crews to the LEO, the Moon, or the ISS. The larger volume and the mission profile are key elements in determining what the medical system includes.[21] In addition to the medical components of the system, other elements include environmental monitoring (water, air, and surfaces) and exercise countermeasures (treadmill, bicycle ergometer, resistive exercise, etc.).[19] These systems support the crew health and performance during the in-flight phase of spaceflight. The pre-flight selection, crew assignments, training, and work-rest schedules are all designed to support the overall mission objective (e.g., deployment of a satellite, construction of a system in space, conduct research, etc.).[18] In addition, the human spaceflight programs are also supported by a robust policy framework.[22] The medical system contains the appropriate hardware, instruments, and medications to support the mission. The medications onboard support a variety of medical events and meet the crew's needs. Over the years, the formulary has changed because of the mission, the crew compliment, and the spacecraft. Longer duration missions to Mars will require smarter medical systems with greater crew autonomy.
Spaceflight affects human systems in many ways. The neurovestibular system is the first system that is affected when an individual reaches orbit.[23],[24] Almost all are affected by space motion sickness (SMS) in the first few days. SMS affects each individual differently. The condition, characterized by vertigo, nausea, fatigue, dizziness, and disorientation can be mild, moderate, or severe. Regardless of the discomfort level, it can affect crew performance. Once an individual has arrived in LEO, their physiology begins to adapt.[25] Musculoskeletal, neurovestibular, ocular, and cardiovascular changes can affect crew health.[26],[27],[28],[29],[30],[31] Other changes include work/rest schedule, sleep shifting (sleep deprivation), changes in circadian rhythm, fatigue, food, hygiene, noise levels, social interaction, and sense of confinement and isolation. Understanding of these events is often anecdotal reported in crew diaries or books that crew members write after they have retired. Aside from private medical records, methodical evaluation of the crew members from a mental health perspective has not been conducted. Personal medical records are protected. However, the following are documented events that have occurred on the Mir Space Station.
These illustrations demonstrate how even a well-trained crew can be pushed to their limits. They become physically and mentally exhausted. Each event could have resulted in a catastrophic failure. The immediate response and post-event analysis have served as useful scenarios in the subsequent system design and crew training. Asthenia can make the individual hypersensitive, irritable, and hypoactive. Some of these conditions can be managed with modifications to the work schedule and a synchronous dialogue with ground controllers. Systems and protocols that have been developed, tested, and integrated into spaceflight are helpful. Historically, most individuals adapt in a relatively quick manner to the spaceflight environment. Adherence to countermeasure protocols assists in a normal physiologic and psychologic state upon return to Earth. In LEO, the crew members can interact with ground controllers, flight surgeons, family, and friends. As crews travel farther distances from Earth, they will become both more isolated and autonomous. Their behavior and performance will change. Crew members will have their vehicle, equipment, and other crew members as the only physical resources they can rely on. The physical and psychological environment will be continuously changing, requiring constant adaptation. Interactions with the ground will evolve. The crew commander's challenge to maintain the crew efficiency will have elements in common with Shackelton's phenomenal accomplishment in overcoming the loss of their ship Endeavour in the Antarctic in the early 20th century and the subsequent rescue of every member of the crew.[34]
Analog environments can provide excellent testbeds but are limited in their ability to emulate the microgravity environment. Such environments include bedrest studies, submarines, expeditions to the Antarctic, and environments where participants are often isolated. There is a significant amount of research on isolation and responses from humans during extended stays in confined extreme environments.[35],[36] NASA has used the Antarctic as a research and technology testbed for more than 40 years from testing plant growth chambers to studying personal and group dynamics.[35] NASA has used the underwater habitat aquarius as a platform for ground-based research and training [Figure 4].[37],[38]
The Russians built an analog system at the Institute for Biomedical Problems in Moscow, Russia. Called Mars 500, the facility provides crews an opportunity to live and work in isolation, emulating a long-duration mission to Mars.[38] Analog environments provide a unique terrestrial testbed for evaluating a variety of systems, technology, and protocols, as well as serve as a training area. A broad range of crew dynamics and medical preparedness have been studied in these environments.[20],[39],[40]
The collective experience of all human spaceflight is in the region of the Earth and the Moon. Researchers and policymakers have begun to design medical care systems to support human exploration of Mars. Such systems will be autonomous and include artificial intelligence and an expanded formulary.[41],[42],[43],[44] As the experience base for exploration of Mars and other celestial sites evolves over the coming decades, concomitant with advances in medicine, the onboard medical care systems will also embrace new technologies and new treatment modalities.
Health and wellbeing of individuals in space are paramount to a mission's success. Historically, the systems that have been used to support in-flight medical issues have been linked to the ground through a telemedicine capability. As these individuals travel a great distance from the Earth, they will be isolated with no real-time communications. This implies that whatever health issues arise, the onboard systems must be able to support it. If it is not an emergency then Earth-based expertise can be provided.[43],[44],[45],[46],[47],[48],[49] The crew dynamics, as well as neurovestibular, and physiological and psychological challenges will occur and the experiential base we have today will lead us to new systems and approaches for tomorrow. The evidence of tomorrow will help us further develop and build smart medical systems to address those yet undiscovered challenges of long-duration, long-distance spaceflight.[47],[48],[49],[50],[51] Acknowledgments The men and women who fly in space and those who tirelessly support them from the ground. Financial support and sponsorship Nil. Conflict of interest The authors are all employed by NASA.
[Figure 1], [Figure 2], [Figure 3], [Figure 4]
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