1. Introduction

On January 14, 2004, a new U. S. Vision for Space Exploration (VSE) was announced (NASA, 2004). The VSE included sending humans to Mars. In January 2007, NASA Headquarters commissioned The Mars Architecture Working Group (MAWG) to develop the Mars Design Reference Architecture 5.0 (DRA 5.0). In February 2007, the Mars Exploration Program Analysis Group (MEPAG) chartered the Human Exploration of Mars Science Analysis Group (HEM-SAG) to develop the scientific goals and objectives for the human exploration of Mars. MEPAG selected James B. Garvin (NASA Goddard Space Flight Center) and Joel S. Levine (NASA Langley Research Center) as the HEM-SAG co-chairs. Garvin and Levine selected 27 scientists from the U. S. and Europe to serve on HEM-SAG (See Table 1 for a list of the HEM-SAG membership). The scientific goals and objectives for the human exploration of Mars developed by HEM-SAG were incorporated in the Human Exploration of Mars Design Reference Architecture 5.0 (DRA 5.0) (Drake, 2009a, b). The HEM-SAG goals and objectves for the human exploration of Mars are based on the MEPAG Mars Scientific Goals, Objectives, and Priorities: 2006 (MEPAG, 2006) (Grant, 2006: http://mepag.jpl.nasa.gov/reports/index.html).

The results of the HEM-SAG panel are presented in five papers in this issue (see Levine et al., 2010a,b,c,d,e).

2. HEM-SAG Conclusions for a Human Mission to Mars Based on Scientific Investigations

The Mars Architecture Working Group (MAWG) asked HEM-SAG to address several key questions that will significantly impact the architecture/engineering design of the human missions to Mars:

3. Why Mars?

Mars is both a unique and complex world. Many of the same processes/mechanisms have operated/operate on both Earth and Mars. Processes/mechanisms common to both Earth and Mars include (1) an early heavy bombardment is found in the geological record of both planets, (2) impact craters are recorded on the surface of both planets, (3) planetary dipole magnetic fields existed on both planets (Mars lost its planetary dipole field in its early history), (4) evidence of widespread and extensive volcanism are found on both planets, (5) the presence of past (Mars) and present (Earth) liquid water on the surface, (6) the existence of geochemical cycles on both planets, and (7) the condensation of atmospheric gases forming polar caps (water vapor on Earth and carbon dioxide on Mars).

Measurements indicate that Earth and Mars experienced very divergent paths of evolution. The geological record suggests that the atmosphere/climate of Mars changed significantly over its history. Early Mars may have possessed a much denser atmosphere, perhaps with an atmospheric pressure in excess of 1000 millibars, the surface pressure of the Earth’s present-day atmosphere. A denser atmosphere on Mars would have permitted liquid water on its surface. Present-day Mars has a thin (6 millibars) cold atmosphere, devoid of any surface liquid water. Why has Mars changed so drastically over its history? How and why has the habitability of Mars changed over its history? Is there a message in the history of Mars to better understand the future of the Earth?

Some recent discoveries abut Mars that have impacted plans for the human exploration of Mars (Beaty and Zurek, 2010):

4. Why Humans?

Humans have unique capabilities for performing scientific measurements, observations and sample collecting. Human attributes to exploration include: intelligence, adaptability, agility, dexterity, cognition, patience, problem solving in real-time, in situ analyses - more science in less time!

Humans are unique scientific explorers. Humans could obtain previously unobtainable scientific measurements on the surface of Mars. Humans possess the abilities to adapt to new and unexpected situations in new and strange environments, they can make real-time decisions, have strong recognition abilities and are intelligent. Humans could perform detailed and precise measurements of the surface, subsurface and atmosphere while on the surface of Mars with state-of–the-art scientific equipment and instrumentation brought from Earth. The increased laboratory ability on Mars that humans offer, would allow for dramatically more scientific return within the established sample return limits. The HEM-SAG envisions that the scientific exploration of Mars by humans would be performed as a synergistic partnership between humans and robotic probes, controlled by the human explorers on the surface of Mars. Robotic probes could explore terrains and features not suitable or too risky for human exploration. Under human control, robotic probes could traverse great distances from the human habitat covering distances/terrain too risky for human exploration and return rock and dust samples to the habitat from great distances.

An important element of the HEM-SAG study has been to identity the unique capabilities that humans would bring to the process of exploring Mars. As a result, a common set of human traits emerged that would apply to exploration relating to the MEPAG science disciplines which include Geology, Geophysics, Atmosphere/Climate, and Biology/Life, These characteristics include: speed and efficiency to optimize field work; agility and dexterity to go places difficult for robotic access and to exceed currently limited degrees-of-freedom robotic manipulation capabilities; and most importantly the innate intelligence, ingenuity, and adaptability to evaluate real-time and improvise to overcome surprises while ensuring that the correct sampling strategy is in place to acquire the appropriate sample set.

The unique capabilities that humans would provide for each of the MEPAG science disciplines mentioned above are summarized as follows:

Geology Human explorers can perform intelligent sample selection, real time assessment of site sampling progress and strategy development to optimize science return. Human explorers can perform drilling in environments difficult for core recovery (ice, sediments, other unconsolidated materials) without human involvement. Human explorers can perform rapid assessment of subsurface and sampling/trenching (efficiency factor).

Geophysics Humans are likely to be far more efficient and skilled than robots in carrying out the careful emplacement of instruments, networks, and site surveys required to meet geophysical investigation goals and objectives. Even if rover-borne instrumentation is deployed telerobotically, that would require human oversight from the habitat. Some geophysics instrumentation must be deployed and then recovered following measurements (e.g., active seismic systems, or electromagnetic sensors). Humans would make this deployment/recovery process more efficient and perhaps even more carefully done, as well as providing instant gratification on the health and performance of the instruments.

Atmosphere/Climate Human enabled investigations on Mars would benefit atmospheric, polar cap, and ancient climate science objectives in a variety of ways. Human dexterity and efficiency would be important qualities for micrometeorological investigations where activities such as radiosonde preparation and release are not yet automated on Earth due to the dynamic interaction with surface turbulence and winds. Cognitive ability, dexterity and efficiency would be necessary attributes in the search for relevant rock outcrops and samples, providing the ability to identify sources of trace gases for studies of current climate on Mars as well as locating pristine impact glasses containing trapped gasses for the study of ancient Mars climate. These unique human capabilities would be vital to deep drilling and coring activities. Touch and sound would be used to monitor the drill performance and respond rapidly to changing subsurface conditions.

Biology/Life Earth-based investigations into the purported evidence for life in Martian meteorite ALH84001 have involved a great number of scientists utilizing many sophisticated instruments and techniques but remain controversial. Evidence of life on Mars, both past and present may be quite subtle. The selection of relevant samples and sampling environments would require the unique capabilities of humans (e.g., ingenuity, flexibility, efficiency) to interpret available clues in real time and to strategically execute a plan for investigation of hypotheses in situ. Humans bring to planetary exploration the ability to quickly analyze and assess samples before they degrade locally or on return. Samples should still be returned to Earth because of the advanced analytical capabilities of terrestrial laboratories, but the increased capabilities humans would provide on Mars, and the remarkable advances that have and would continue to be made in lab instrument miniaturization mean more science reaped without the restrictions of sample weight on return and a greater likelihood of satisfying the goals and objectives of the mission. We believe that the human element is value added to all aspects of the MEPAG Goals and Objectives. Technology development in the decades leading up to a human mission to Mars would determine the best synergistic fit between human and robotic exploration and perhaps technology challenges would be overcome to shift the balance of physical activity toward robotic assignment. However, certain uniquely human attributes could not be duplicated by or relegated to robots or to operations remotely operated by humans on a planet substantially separated in time and space from Earth. Only a human presence in Mars mission surface operations activities could facilitate and achieve the ambitious scientific goals and objectives of MEPAG.