1. INTRODUCTION

A human mission to the planet Mars will be a major milestone in human history. The need and reasons for the first mission to Mars have been debated, discussed, simulated, and planned over many decades. Although there are no current approved or funded programs for a human mission to Mars, the vision of extending the time-distance constant of human exploration has brought greater effort to this endeavor in recent years. While there has been a cadre of engineers figuring out how we will get to the surface of Mars and return, one of our biggest challenges is how such a mission will affect humans in the system. This impact includes the many facets of physiological implications of long duration missions in micro and partial gravity environments, and the need for medical care with little or no intervention from the Earth; not to mention the environmental unknowns and their impact to human life, and the impact of humans living on another planetary body.

Since the 1960s, we have learned a tremendous amount about human physiology systems and human factors in low Earth orbit and on missions to the surface of the moon. For each successive mission from Vostok-1 and Project Mercury to the International Space Station (ISS) program, the practice of space medicine has evolved. Systems for monitoring health have been designed and utilized on each mission. Research has been conducted on astronauts and cosmonauts to determine the effect of the absence of gravity on the human body, including the cardiovascular system, the nervous system, the musculoskeletal system, the immune system, and the neurovestibular system (Williams D, 2002; Williams D et al., 2009). A robust and comprehensive space medicine capability has been established, which includes medical policy development, medical standards for astronaut selection, technical standards for human-rated spacecraft, medical kits for utilization on orbit, and medical care capabilities for all phases of flight (Nicogossian 2003). Living and working in space has evolved from the Mercury and Gemini program in which astronauts wore pressure suits confined within a cramped ballistic capsule to the current multi-module 1 atmosphere shirt sleeved environment of the International Space Station (ISS). The launch capability has not changed significantly over five decades but once there, the ability to function and perform scientific research and operational equipment testing is an entirely different experience.

The question remains whether or not the space medicine capability to date may be appropriate for long duration flights to Mars. Transit to Mars with an extended stay will require a new way of thinking and the development of innovative smart, intelligent medical systems. Future capability will be predicated on what has been done up to this point, incorporating both operational experience and the knowledge gained from current research programs. Mars-destined crews cannot turn around and come home. Their mission will be much like those early pioneers in the Age of Discovery. Crews must take all their supplies with them, as resupply will not be possible during flight. In addition, they may be on their own with limited or no communications with mission controllers and in the case of astronaut heath, flight surgeons and other medical expertise. Space medicine for a Mars mission will truly be an evolutionary step in clinical capability as both human health and performance will be altered during long duration flight (Baisden et al. 2008).

2. PHILOSOPHY

The philosophy of space medicine in the NASA program has been to protect crew health by minimizing risk, optimizing crew capabilities, and developing selection criteria to ensure that healthy, technically qualified individuals with demonstrated expeditionary behaviours are chosen to be astronauts (Hamilton et al. 2008). Other space faring nations have similar approaches (Bogomolov et al. 2007). Since the crew represents the healthiest of the population, and there are programs that support health stabilization prior to flight, the in-flight medical capabilities have been designed to address the medical events that might occur during short duration flights. This capability includes basic first aid, some advanced life support and a breadth of primary care capabilities. The philosophy has been to prevent in-flight illness and injury if possible, diagnose and treat medical events that can be managed safely in space and stabilize and then transport to the ground medical conditions that exceed on-orbit clinical capability. This remains a key component of space medicine today; and we have been successful in mitigating risk, maximizing mission operations, and maximizing crew health and performance.

A major factor in this approach is that crews can return to definitive care on the ground, albeit 24 hours after the event occurs. Currently both the US Space Shuttle – landing in the US or a Soyuz Transfer Module (TM) – landing on the Steppes of Kazakhstan are the only way home from the ISS. When the US Space Shuttle is retired in early 2011, the Soyuz will be the only transport for return from ISS until another vehicle comes online. A medical evacuation from the ISS through landing and subsequent transfer to definitive care for US astronauts could be considerable longer than 24 hours (Billica et al. 1991; Williams D 2003; Kirpatrick et al. 2007).

Management of in flight contingencies is based upon near constant communication of the crew on Earth-orbiting spacecraft with ground controllers. Should an astronaut on ISS become ill or injured, the onboard crew medical officer can discuss the situation in real-time with the flight surgeons at Mission Control and utilize onboard medical kits to provide appropriate diagnostic and therapeutic interventions. The Apollo astronauts had a telecommunication link from the moon to the Earth. Although, there was a slight delay in the transmission, the link was sufficient to address medical concerns during these flights (Nicogossian et al. 2001). Real-time communication between the Earth and Mars is more problematic with delays up to 22 minutes one way. This will be a significant challenge in the management of medical events requiring real-time communication and guidance between the flight surgeon on Earth and the crew medical officer on the Martian surface. Developing the appropriate level of medical autonomy will thus become the normal approach to crew operations (Hamilton et al. 2008).

In all missions prior to the development of the ISS, medical care was provided in-flight using small medical kits with somewhat limited capabilities that were designed to diagnose and treat the most probable in-flight medical events. When the Space Station Freedom (SSF) program started in the 1980s, the medical care capability was designed as a comprehensive system (Billica et al. 1991). This system was called the Crew Healthcare System (CHeCS). CHeCS represented a major facility-class payload and had a number of medical subsystems to address a wide variety of medical scenarios. The philosophy was to 'stand and fight', to provide the clinical capability, and to address a wide range of medical issue with onboard diagnostic systems such as a x-rays and basic blood chemistries. In addition to a breadth of therapeutic services including dental procedures, minor surgical capability, hyperbaric treatment for EVA-related decompression sickness and a capability for storing a deceased crewmember were also part of CHeCS. The CHeCS also included subsystems for environmental monitoring and exercise countermeasures to mitigate the impact of microgravity on the cardiovascular and musculoskeletal system (See Figure 1).

However, as the SSF program grew in size, scope and cost, it was constantly under the budgetary scrutiny. In the early 1990s, President Clinton made overtures to Russia about a joint space station program. This program became known as the ISS, the complex station was redesigned and the medical 'system' reverted to a 'kit-based' approach. The initial phase of this joint program with Russia involved a stint by US astronauts on the Russian Mir Space Station. This Phase 1 program helped NASA, Russia, and the other partners establish an international approach to medical care (Grigoriev et al., 2009). This program provided an outstanding test-bed for evaluating techniques and approaches, and provided operational lessons learned from first-hand experience with a number of on-orbit events including a fire, leaking toxic chemicals (ethylene glycol) in station modules, and loss of cabin pressure (spacecraft collision). These kinds of events can be adequately simulated, however, the experienced gained from an actual event provided a strong impetus to provide enhanced in-flight medical capability.

3. CHANGING PARADIGM

Sending a group of humans on a mission to Mars will require new ways of thinking, new ways of doing things, new technologies and highly collaborative international partnerships. The ISS Program has been extremely effective in developing and extending international collaboration in space medicine and operational oversight. Some technologies needed for a Mars mission exist today while others have not yet been developed or are envisioned in the minds of the expert researchers, engineers and clinicians tasked to send humans farther into space and keep them there for longer periods on exploration-class missions. The philosophy of space medicine for a Mars mission will likely need to be completely rewritten. A new philosophy will be system-based. Medical care on a Mars mission will require autonomous operations and have an underlying informatics structure (Williams et al. 2000). All medical capabilities, including limited diagnostic and therapeutic supplies like pharmaceuticals would be packaged and taken to the surface of Mars; or technologies would have to be developed to re-use or create a manufacturing capability on the surface. Depending on the length of the mission, the medical supplies on board would have to match the mission profile. A three-year mission would require a different philosophy than those lasting days or months.

This does not imply that what has been achieved to date will be of no value. A retrospective review of what has been done will be a cornerstone of space medicine support for a human mission to Mars.

4. FOCUS AREAS

There are a number of focus areas that must be considered and addressed prior to sending humans on a mission to Mars. These areas include vehicle design, risk assessment, crew selection, medical care capabilities, communications, training, and research. An underlying theme to all of these is medical policy and ethics.

Ethics in the case of humans on a Mars mission includes a discussion about crew selection based on health criteria and what is ethically correct. For instance, should all crewmembers have their appendix removed prior to the mission? Crews will be subjected to an increase in a variety of research testing due to the mission profile and duration. This research must be balanced between health maintenance and appropriate countermeasures.

4.1 Vehicle Design A human mission to the Martian surface will take many months of transit time, most likely in a spacecraft that is still on the drawing board. The design of the spacecraft will be based on a variety of factors driven by the need to protect the human in the system (Davis 1999). Space medicine experts will drive medical policy to develop the medical and technical standards that lead to the creation of design requirements for new inter-planetary spacecraft and systems that will optimize human health and performance. This includes protection from radiation exposure, maintenance of air and water quality, sophisticated closed-loop environmental systems, mitigation of occupational issues such as noise within the vehicle as well as design that incorporates human factors. Space faring nations have done a relatively good job of designing and building spacecraft to date and have significant experience that may be incorporated into new designs.

There have been constraints on weight, volume, utilization of vehicle resources and the amount of crew interaction involved. A medical device that weighs 200 pounds, takes up five cubic feet, and requires ten hours of maintenance a week is not operationally feasible. All spacecraft have had weight and volume constraints associated with the cost of delivering payload to orbit. The medical care system for a Mars transit vehicle and associated surface modules must meet medical requirements and standards but must also fit into a limited footprint within the vehicle.

The volume and capabilities of the medical system for the transit vehicle and the medical system for the surface modules may be complementary but they will also be used to support different scenarios.

The vehicles and modules or landing craft will provide a miniature biosphere sufficient to maintain habitability for a crew of five to seven individuals.

4.2 Risk Assessment Space-faring nations should attempt to mitigate space exploration risks by minimizing or removing known threats, vulnerabilities of the systems (albeit human or vehicular), and their long-term implications to and potential consequences to the health of the space explorers. The space program should evolve along the lines of an occupational health program for timely and proper risk management. Risks that astronauts face during space travel are internal (biomedical or vehicular), external (meteorites or radiation), and systemic (the result of a cascade of events). Risk analysis should be a continuous undertaking since mission planners and stakeholders will be learning more about various obstacles astronauts will be facing in space. Risk analysis must be accomplished by methods that not only include probabilistic analysis, but also worst case scenario and probabilistic tree analysis. Risk analysis relies on databases that are developed from research protocols carried out on Earth using special simulations and analogs duplicating individual or multiple space flight environmental parameters, in space studies, and post space flight follow-up (Nicogossian et al. 2006).

4.3 Crew Selection Individuals who fly in space are chosen from a select group of individuals. They are chosen based on the application of evidence-based medical assessments and the unique combination of technical and behavioral competencies critical to mission success in long duration spaceflight. Current standards will likely be modified based on additional evidence-based clinical research aboard the ISS (Bogomolov et al. 2007). In addition, data from analogs will be extremely helpful in developing new standards. Our experience has indentified the impact that living and working in low Earth orbit has on the human body. While no human has gone beyond the moon, we understand the challenges that might occur during a transit to Mars and what life on the surface might be like. As a result, the selection of crewmembers will be based on operational experience, scientific and clinical data collected to date.

The crew will be extremely isolated during the mission and will heavily rely on the onboard systems for health and safety. Communication with the Earth will occur, but will be delayed or absent depending on distance and location. Therefore, the selection criteria must include a consideration of psychological and behavioral health issues related to crew performance (Williams et al., 2005).

4.4 Medical Care Capabilities Spaceflight affects human physiology in a variety of ways, and may affect the pathophysiology of disease processes. The body readily acclimates to microgravity with many of these changes presenting clinical challenges on return to normal gravity or a partial gravity environment (Williams et al. 2009; Nicogossian 2003). Extensive countermeasures research and implementation of protocols to maintain crew health have helped ameliorate some of the deleterious effect on the human body (Nicogossian et al. 1995). The purpose of the medical care systems or facility on board a Mars transit vehicle and that of surface module or habitat must maximize the safety, health and performance of the crew (Hamilton et al., 2008). The medical care capability must also support radiation protection, monitoring of the environment (air quality, water quality, noise, radiation, etc) and exercise countermeasures to minimize the deleterious effect of microgravity. An optimal capability for the long duration must support the crew for a period of perhaps multi-years in duration. A capability to address behavioral health and psychological support will also be key elements of the medical care system.

The medical system developed and integrated into a Mars mission will be more robust and more intelligent than any medical care system used in space or any other analog to date. The system will include intelligent or smart systems that will function autonomously with little or no interaction from ground controllers.

4.5 Research Throughout human spaceflight, space life scientists and clinical researchers have longed to understand the impact of spaceflight on the human system. While significant data was collected during the human-tended missions of the American and Soviet Space Programs prior to the Shuttle and the Mir Space Station programs, it has been these two programs and the ISS research that that have been instrumental in gaining a greater understanding (Thirsk et al. 2009). That experience combined with ground-based research over the past 50 years has also helped extend our knowledge and understanding of these issues (Williams D 2002).

Research has provided a better understanding of the need for countermeasures, as well as the cardiovascular implications, neurovestibular implications, genitourinary issues (Jones et al. 2005), surgical implications (Campbell et al. 2005; Rafiq et al. 2005), and nutrition issues associated with long duration missions.

There have been a number of analog environments that have been of value in further understanding the effects of isolation, the importance of behavioral science and the need to develop new technologies to support the delivery of healthcare in extreme environments. These analogs have included winter stays in the Antarctic, Haughton Crater on Devon Island in the Canadian Arctic, the Russian MARS 500 Study, and the NASA Extreme Environment Mission Operations (NEEMO) missions. These environments provide unique experiences and research opportunities. Participating crews are isolated by design to mimic a long duration mission. During NEEMO missions, crews living in the submerged Aquarius Habitat, which is in 20 meters (11 fathoms) of water, cannot simply surface in the event of a medical issue. Similarly, crews isolated in the Antarctic must maintain a high level of autonomy as it is very challenging to conduct a rescue mission and there are limited opportunities of medical evacuation. There is consensus in the space life research community that these analog environments provide excellent venues for evaluating technologies and protocols for conducting a variety of tasks. Figure 2 illustrates the Aquarius habitat, which serves as a NASA analog.

Research on medical and surgical care technologies has been performed in many of these environments, including the evaluation of surgical robotics (Doarn et al. 2009), diagnostic ultrasound and evaluation of asynchronous telemedicine (Harnett et al. 2001). Technologies and surgical skills were also evaluated on aircraft in parabolic flight to simulate microgravity (Kirkpatrick et al. 2008).

A human mission to Mars provides a unique opportunity to create new areas of research in the basic and physical sciences. While there is a basic understanding of what might happen to the musculoskeletal system en route, even if the crew follows a prescribed exercise regimen, the changes in physiology will only be better understood once the crew arrives and can conduct the necessary research on the surface. All living systems, including bacteria will change in route. New studies and new data will be collected and transmitted back to the Earth for analysis. What we learn on the surface may also be interpreted by smart medical systems on the surface and protocols could be changed in real-time.

5. ADVANCED MEDICAL SYSTEMS MEDICAL CARE CAPABILITIES

When spacecraft crews leave the Earth and travel into space, they undergo unique physiological changes. The major body systems change and adapt to the absence of gravity. The medical selection and retention and physical conditioning programs ensure pre-flight astronaut health, they may experience illness or injury once they are in space. The extreme isolation and behavioral issues associated with leaving the Earth far behind, where it appears as a small pale blue dot that shrinks in size to a look like another star may be significant. Careful consideration must be given to behavioral issues in selecting and training crew (Williams et al. 2005).

Medical systems available to the crew in a transit vehicle must provide preventive medicine, including medical and surgical care. Once the crew has landed on the surface of Mars, a medical care capability will be enhanced beyond the transit system. This of course is predicated on the duration of the surface mission. The vehicles and habitats must also be monitored to understand the environment. Maintenance of air quality, water quality, radiation protection, noise abatement and exercise capability are all key elements of maintaining crew health.

The establishment and maintenance of a medical capability must follow a similar management structure as developed for the ISS Program (Grigoriev et al. 2009). This ensures policy development, standards for selection, oversight of crew health and assurance of crew health and safety. Currently, NASA has established a Health and Medical Technical Authority to ensure the medical capabilities are addresses. This organization will also review ethics and review research to remain cognizant and ensure the safety of the crew. The medical system(s) will also include a component of medical informatics and asynchronous telemedicine. Linkages between the crew and ground controllers on the Earth will permit monitoring and updating databases, training modules, etc. In many cases, information can be transferred from one location to the next with little crew involvement (Williams et al. 2000).

All supplies that support the medical system will be taken on the mission; it will be inventoried and managed, since there is no resupply during a transit mission. There may be opportunities for supply ships to be sent to the surface prior to crew arrival or once they arrive.

It is likely that the crew will need refresher training during the entire mission. This will also be addresses through just-in-time training and emphasizes the potential need for a medical simulation capabililty. Modules will be uplinked for review and use by the crew to enable continuous training. The onboard computer systems will also formulate curricula based on need.

5.1 Mars Transit Medical Care A comprehensive medical care capability for a transit mission must support a crew that will have no immediate return to the Earth and will have limited, asynchronous communications. The crew will have undergone selection and will have undergone extensive training on the medical systems available to them. While no policies or requirements have been finalized for a future mission, it is assumed that there would be physicians on board. Some have even speculated that the physician should in fact be a surgeon. Regardless of training and clinical specialty of the designated crew medical officer(s), physician astronauts must expand their skill sets to encompass all aspects of space medicine and onboard training tools are needed to provide the crew with a capability of maintaining their skills. Ground support will be able to upgrade training modules via communications to the spacecraft for use on board during the mission.

The medical systems will include a variety of subsystems, similar to the SSF's CHeCS design. The similarity is only in capability. The design of the subsystems and the technologies will be completely different. Since a return to definitive care is impossible, the healthcare system on board will be capable of diagnosing and treating anticipated illness and injury. This will include ambulatory care – basic first aid, advanced life support, an ability to respond to trauma, an ability to support minor surgical care, and an ability to provide basic dental care. A dental care capability will exist for routine care and treatment of dental illness and injury. This will also include the support tasks including pathology, imaging, decision support, basic laboratory tests, pharmaceuticals, medical consumables, and other ancillary medical supplies and equipment.

Telemedicine is an integral component of the current ISS and Shuttle program. The ability to interact with the crew in real-time via a telecommunications link is a vital tool given the limited medical capability available (Doarn et al. 1998; Nicogossian et al. 2001). The medical 'kits' for these spacecraft were designed with the knowledge that an ill or injured crewmember can be returned to the ground for definitive care. On a Mars mission, this is not possible. Therefore, the basic concepts of real-time (synchronous) telemedicine will not work. An asynchronous mode will most likely be used as information can be transmitted between the transit vehicle, or the Martian surface to the Earth in a store-and-forward mode. Therefore, medical informatics and smart medical systems will be the underlying fabric of healthcare in space (Williams et al. 2000). All medical records will be electronic. All instrumentation will have intelligence and will be linked to one another. Each will have decision support embedded to resolve issue autonomously. The healthcare system will be ergonomically designed and incorporate decision support. In other words, data from instrumentation will be interpreted and a diagnosis will be rendered.

The ultimate goal of the system is to ensure the health and safety of the crew so that they can maximize their performance and minimize risk to the vehicle, mission and crew.

5.2 Mars Surface Medical Care The surface medical care capability will be complementary to the transit system. It will include a more comprehensive facility to address a spectrum of illness and injury including trauma and decompression sickness. It will also include capabilities to support intensive care for ill or injured crewmembers. While major surgical care is unlikely, live saving surgical intervention is possible, so all the appropriate systems will be in place, including a robotic surgical system (Kirkpatrick et al. 2005, 2008).

6. CONCLUSION

As we ponder a human mission to Mars, the mission architecture, spacecraft and enabling technologies will be based on our understanding of the potential risk and the knowledge gained in the decades of experience with lunar missions and long duration missions in Earth orbit. Human spaceflight has evolved from one-man capsules to vehicles designed to transport astronauts or cosmonauts from the Earth to Mars over a distance of 55 or more million miles in months, perhaps as much as nine months. Once the spacecraft has arrived, the crew may stay for extended periods conducting exploration of the planet surface.

The risk is inherently high in spaceflight, going a great distance from the Earth, where crews watch the Earth vanish to small blue dot in the cold blackness of space, has many unknowns. However, the operational experience and research outcomes to date have helped develop a comprehensive understanding of what we might expect. Mission planners and spacecraft designers will conducted their work with the human as part of the system.

The medical care systems used during the transit phase and the surface operations will provide sufficient capabilities using appropriate technologies and information systems to support a crew that might be isolated from communications with expertise on the Earth. The crew will face new challenges and learn more about the impact of life on another celestial body. This will help refine the next generation of systems and will greatly enhance the delivery of healthcare on the Earth.