Part I

The National Research Council was tasked with evaluating the risks of landing humans safely to work on Mars. Their report highlights a number of unique aspects in transit to the red planet, as well as once humans step out onto the surface. In this first of two parts summarizing some key points, their report touches on the logistics of traveling to a site and then driving around the neighborhood.

Every 2 years from 2001 to 2011, with the dates dictated by launch windows, another spacecraft, launched by NASA and/or NASA’s international partners, is intended to visit Mars. Some spacecraft will orbit the planet, while others will land on the Martian surface.

The NASA Mars Exploration Program Office (within the NASA headquarters Office of Space Science) has established the Mars Exploration Program/Payload Analysis Group (MEPAG), consisting of more than 110 individuals from the Mars community, with representatives from universities, research centers and organizations, industry, and international partners. The MEPAG participants propose the objectives, investigations, and measurements needed for the eventual exploration of Mars, focusing on four principal exploration goals. These goals fall under four broad categories:

  • Life determine if life ever arose on Mars.
  • Climate determine the climate on Mars.
  • Geology determine the evolution of the surface and interior of Mars.
  • Prepare for the eventual human exploration of Mars.

While there is currently no funded human mission to Mars, nor even a baseline reference human mission, one of the goals of the MEPAG is to ensure that sufficient information is developed in a timely manner to support such a mission, once it has been funded.

What measurements must be made on Mars prior to the first human mission? These measurements would provide information about the risks to humans so that NASA scientists and engineers can design systems that will protect astronauts on the surface of Mars.

How can robotic exploration missions sent to Mars aid NASA in assessing the risks to astronauts posed by possible environmental, chemical, and biological agents on the planet? Of critical importance is whether it will be necessary to return Martian soil and/or air-borne dust samples to Earth prior to the first human mission to Mars to assure astronaut health and safety.

Sending astronauts to the Red Planet, having them land, conduct a mission on the surface, and then return safely to Earth will be an enormous undertaking.

A long-stay mission would require that astronauts spend 16 to 20 months in orbit around Mars or on the surface, with total mission duration being 21/2 to 3 years. On a short-stay mission, astronauts would be able to remain in orbit around Mars or on the surface for only 30 to 45 days before they would have to embark on the return journey to Earth. If they stayed longer, Earth and Mars would move out of optimum alignment and the return to Earth would require an excessive amount of propellant.

Unless provisions can be made to counter the microgravity environment (by means of exercise protocols or by inducing artificial gravity) and harsh radiation conditions in space, the potential negative effects on health of the longer transit time (short-stay mission) may be prohibitive.

Once the astronauts are on the Martian surface, there are a variety of operational scenarios that could be conducted by NASA. The simplest would be that astronauts land and never leave a stationary habitat. The most complex scenario could include astronauts using large, pressurized rovers to travel long distances from a base habitat to conduct extravehicular activities (EVAs).

Even though there is no baseline mission defined for human missions to Mars, it is likely that rovers of some form will be used to perform functions critical to the safety of the astronauts. For example, human assistant rovers may carry life support equipment, while others robots, such as slow-moving scientific rovers, will likely perform mission-critical functions.

On the human missions to Mars, rovers will need capabilities far beyond what is currently planned. Human assistant rovers would have to be able to keep pace with an astronaut walking on the surface of Mars, to operate for a long time, to have an extended range, and to navigate rough terrain quickly. These needs would be especially important for a long-stay mission, where there might be many hundreds of astronaut EVAs that would require a robotic assistant to traverse hundreds of kilometers over the course of the mission. Such human assistant rovers would require kilowatts of continuous electric power during the EVA. Compact sources of power at that capacity do not exist today.

Vehicles using standard wheels can typically roll over objects one-third the diameter of the wheel being used. This suggests that if human transport and scientific rovers will use 1-meter wheels, the mission planners will need to know the distribution of rocks one-third of a meter and larger in the landing and operation zone. Imaging rocks this size requires a pixel resolution of 10 cm. NASA should map the three-dimensional terrain morphology of landing operation zones for human missions to characterize their features at sufficient resolution to assure safe landing and human and rover locomotion

Part II

The National Research Council was tasked with evaluating the risks of landing humans safely to work on Mars. Their report highlights a number of unique aspects in transit to the red planet, as well as once humans step out onto the surface. In this first of two parts summarizing some key points, their report goes beyond the logistics and looks at the novel weather and biology that might face astronauts working within an extended stay mission.

The physical environments that might pose risks to crew safety on Mars fall into three categories: geologic, atmospheric, and radiation. The geologic features of interest in this study are airborne dust, regolith, and terrain. The two Viking landers were enveloped in a global dust storm soon after landing, and dust devils have been observed many times on Mars by Viking orbiters and landers, the Mars Pathfinder, and the Mars Global Surveyor. Windblown dust appears to be a common condition on Mars and would cause electrostatic charging of astronauts’ space suits during operations on the surface of Mars, as well as of their equipment and habitat. Despite this phenomenon, there has been no report of electrostatic damage to delicate electronics on any of the surface systems. Furthermore, neither the Viking missions nor the Mars Pathfinder mission experienced any problems due to electrostatic charging.

Objects on moist ground on Earth are said to be grounded since the conducting ground has an almost unlimited capacity to accept either positive or negative charge without changing its electric charge potential from what is essentially zero. Such natural discharge or prevention of charging is not expected to occur on Mars, because there is no near-surface liquid water.

The hazards from electrostatic discharge on Mars can range from a simple spark, equivalent to feeling a sting here on Earth after walking on certain types of carpet and reaching for a doorknob, to potentially more potent bursts between astronauts and large equipment or structures on Mars. The dry conditions and uncertainty about conductivity, charging, and discharging rates in the Mars environment create uncertainties about electrostatic effects on human operations in the Mars environment.

It would be helpful for NASA to investigate the design considerations and procedures used at the Siple research station in Antarctica, where there is little to no local electrical ground. Again, as an example of potentially innovative design solutions, two crossed-dipole antennas at Siple, each 21.4 kilometers long, occasionally charged up to the order of 20,000 volts when windborne ice particles passed over them. The danger of discharge was removed by connecting the antennas to the station buildings. The buildings prevented a charge from accumulating on the antenna conductors by acting as large capacitors that stored the charge. The electrostatic voltage on the antennas was reduced to near zero, and since ice is not a perfect electrical insulator, the charge on the buildings dispersed gradually. Sharp conducting points, the needlelike devices referred to above, were also used near the buildings to bleed off the electrical charge.

The strongest surface winds observed by in situ measurements on Mars are believed to be 30 to 50 meters per second (67 to 111 miles per hour) based on eolian deposits at the Viking I landing site. From a terrestrial perspective, these wind speeds appear to represent a significant hazard. However, when the lower atmospheric dynamic pressure on Mars, resulting from a less dense atmosphere than on Earth, is accounted for, the Earth-equivalent wind speeds are much less. Simply stated, the wind must blow nine times faster on Mars than here on Earth to achieve the equivalent dynamic pressure. In the strongest wind case mentioned above, a 30 to 50 meter per second (67 to 111 mile per hour) wind on Mars is roughly equivalent to a 3.3 to 5.5 meter per second (7.4 to 12 mile per hour) wind on Earth.

The Martian atmosphere has been determined to be composed predominantly of carbon dioxide (95 percent), with nitrogen, argon, and oxygen (all nontoxic) present in abundances greater than 0.1 percent.

Astronauts are by definition radiation workers. Radiation exposure in space will be a significant and serious hazard during any human expedition to Mars. The radiation dose received by astronauts on the surface of Mars will be a significant fraction of the total radiation exposure for the mission.

Strong oxidants detected in Martian soil by the Viking biology experiment would be inactivated by humidification inside the astronaut habitat. It is therefore essential that NASA implement proper humidification in conjunction with the filtration system as part of habitat atmosphere conditioning. Even if strong oxidants are present, if the dust level is maintained at 1 mg/m3 or less and appropriate humidification systems are in place, there will be negligible risk associated with oxidation on the Martian surface.

The probability that life-forms exist on the surface of Mars (that is, the area exposed to ultraviolet radiation and its photochemical products) is very small. However, as a previous [1997] NRC study notes, there is a possibility that such life-forms exist there “in the occasional oasis,” most likely where liquid water is present, and, furthermore, that “uncertainties with regard to the possibility of extant Martian life can be reduced through a program of research and exploration.”

It is highly unlikely that infectious organisms are present on Mars. The same NRC study that focuses on the possibility that Martian organisms could be agents of infectious disease also states as follows: “The chances that invasive properties would have evolved in putative Martian microbes in the absence of evolutionary selection pressure for such properties is vanishingly small. Subcellular disease agents, such as viruses and prions, are biologically part of their host organisms, and an extraterrestrial source of such agents is extremely unlikely.”

In light of experience gained during Apollo missions to the Moon, a previous [1993] NRC report concludes, “It would, however, be virtually impossible to avoid forward-contamination of Mars or back-contamination of Earth from human exploration.” As such, NASA should ensure proper quarantine or decontamination of equipment that may have been exposed to a Martian life-form.