The International Space University Team of more the 40 geoscientists, scientists, and engineers thought about going to Mars in 2009. The human race has evolved, grown and expanded through the exploration of Earth. After initial steps on the Moon, our next challenge is to explore the solar system. Mars shows potential for both scientific discovery and future human settlement, and so is a prime candidate for the next leap of human exploration. Such a bold endeavor will be a driver for an unprecedented worldwide cooperative effort and the catalyst for a new era of international, intercultural and interdisciplinary human relations.
Scientific and technological progress will also accelerate as mankind is ushered into a new era of space exploration. Currently proposed Mars missions have identified a number of challenges such as high levels of radiation, harsh climate, fine-grained dust, and limited launch windows. Recently discovered lava tubes on Mars present potential solutions to some of these issues, but raise a variety of intriguing new challenges.
These subsurface tubes have been envisioned before in movies and express many of difficulties involved that encompass not only technological and engineering considerations, but also legal, ethical and societal issues such as planetary protection and crew safety. This report assesses the feasibility of overcoming such challenges through the exploitation of Mars caves.
This report reviews existing reference missions and identifies areas of further research essential for adapting mission architectures to utilize caves. Cave suitability is considered with respect to size, type, location and their potential to mitigate hazards. They are also assessed with respect to their potential for scientific work adhering to astrobiology guidelines and the search for extraterrestrial life. This report compares surface and subsurface habitat options.
Engineering challenges arising from the use of caves are addressed along with proposals for alternate architecture solutions. Mission analysis is conducted to determine the transit trajectory and define two possible mission scenarios with surface crews of 6 and 12 crew members. Different types of habitat are described and evaluated. An architecture for precursor missions is provided utilizing surface rovers, cargo delivery rovers and pressurized human transport vehicles. The implications of sub-surface operations on thermal control, communications and power systems are investigated with recommendations given. Crew selection, training methods and life support system solutions are also addressed.
Literature suggests a low radiation environment within Martian caves, allowing for extended duration missions. The ACCESS Mars Team concludes that using lava tubes as human habitats is not merely a viable habitat solution for a Mars expedition, but also potentially more beneficial than proposed surface solutions.
The authors have concluded that while several types of caves exist on Mars, lava tubes are the most feasible option for establishing a permanent settlement. The rationale for using specifically lava tubes includes adequate capacity to accommodate the habitat, structural stability, known occurrence on the planet, thermal stability, and accessibility (via orientation of entrance) for both robots and humans. Lava tubes offer significant protection from many harmful surface hazards such as minimizing the radiation dosage absorbed by crewmembers by almost three orders of magnitude as compared to a surface stay. This ratio assumes that the Martian regolith provides between 2-3 m of shielding as recommended in Chapter 2.
Lava tubes also present significant protection against meteorites and dust storms. Rare cave instabilities may threaten crewmembers, but a significant disaster could be mitigated via proper training and site selection. The lava tube location ought to be selected via access to ice, proximity to alternative energy sources, minerals of interest for use in the ISRU, proximity to suitable landing sites, and access to regions demonstrating scientific promise. Selection of a cave using these parameters will pave the way for an initial human settlement on Mars.
Site selection involves consideration of planetary protection guidelines before exploring „keep-out‟ zones. This necessitates robotic precursor missions prior to the construction of the initial settlement. Further lava tube requirements include a roof thickness ratio of 4:1, no major fractures in surrounding rocks, large natural openings, and a smooth floor. These lava tubes will be found via remote sensing
equipment on orbiting satellites.
Further precursor missions to acquire more data and explore potential cave options include both small- and large-wheeled and walking robots, tethered robots, hopping microbots, rotorcrafts, and flyers. These rovers will have the most difficulties exploring caves with vertical entrances, but will provide valuable information regarding cave location and access to resources needed before a crew can be sent to the planet. These rovers will also be advantageous for completing scientific goals - specifically for exploring "keep-out‟ zones identified from planetary protection strategies.
A significant element in the infrastructure for settling on Mars is the habitation, involving all habitat systems and subsystems including robotics, power, thermal management, communications, navigation, habitat structure and layout, LSS, and crew training and psychology. The successful implementation of our goals includes a meticulous operations phase combining precursor missions, habitat construction, and continuous human exploration. Each of these phases is considered for a base reference mission with comparisons drawn for an alternative mission scenario in Chapter 5.
Arguably, the most complex element of the human cave program is the habitat program and layout. In a cave system, the threat of radiation is removed and the weight of the exterior shell can be reduced significantly by employing inflatables or thin-walled structures. Without any constraints on rigidity, the habitat layout can accommodate greater freedom and spatial recognition over a long-duration mission. Based on a predetermined rating scale, we
recommend inflatable structures for both the surface and subsurface habitats. Crew psychology is important for a cave environment because of potentially curtailed daylight cycles and confinement. Both preflight psychological preparation and the design of in-situ countermeasures are necessary.
The reference mission uses a conjunction class fast transfer to reach Mars orbit with a subsequent entry, descent, and landing to reach the selected cave site within an accuracy of 10 km. Both surface and subsurface navigation systems are vital to cave settlement. Wireless networks are recommended for both rover and crewmember communication below the surface. Subsurface navigation may incorporate LiDAR and a cellular network. During surface
operations, access networks, inter-spacecraft networks, and surface networks manage the data interlinks. Surface navigation can be managed via a GPS or GNSS-based local area positioning system. Furthermore, subsurface power and thermal systems could use nuclear and solar energy
sources to power both the habitat and the rovers.
Specific importance will be placed on international cooperation, increased robustness of critical mission elements, and possible utilization of private-public partnership between commercial organizations and national space agencies. Crew-members on a human mission that ventures to another planet will most certainly face many hazards. A stakeholder analysis identified governments, space agencies, large aerospace companies, and the public (taxpayers and mass & social media) as key targets that must be persuaded to accept a higher level of risk before the commencement of such a bold mission. This acceptance may require a change in the current perception of the risk involved with exploratory tasks.
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