Future Visions for Scientific Human Exploration

Today, humans explore deep-space locations such as Mars, asteroids, and beyond, vicariously here on Earth, with noteworthy success. However, to achieve revolutionary breakthroughs that have punctuated history of science since dawn of Space Age has always required humans as the discoverers, as Daniel Boorstin contends in this book of same name. During Apollo 17, human explorers on lunar surface discovered genesis rock, orange glass, and humans in space revamped optically crippled Hubble Space Telescope to enable some of greatest astronomical discoveries of all time. Science-driven human exploration is about developing opportunities for such events, perhaps associated with challenging problems such as whether we can identify life beyond Earth within universe. At issue, however, is how to safely insert humans and spaceflight systems required to allow humans to operate as they do best in hostile environment of deep space. The first issue is minimizing problems associated with human adaptation to most challenging aspects of deep space space radiation and microgravity (or non-Earth gravity). One solution path is to develop technologies that allow for minimization of exposure time of people to deep space, as was accomplished in Apollo. For a mission to planet Mars, this might entail new technological solutions for in-space propulsion that would make possible time-minimized transfers to and from Mars. The problem of rapid, reliable in-space transportation is challenged by celestial mechanics of moving in space and so-called rocket equation. To travel to Mars from Earth in less than time fuel-minimizing trajectories allow (i.e., Hohmann transfers) requires an exponential increase in amount of fuel. Thus, month-long transits would require a mass of fuel as large as dry mass of ISS, assuming existence of continuous acceleration engines. This raises largest technological stumbling block to moving humans on site as deep-space explorers, delivering masses required for human spaceflight systems to LEO or other Earth orbital vantage points using existing or projected fleet of Earth-to-orbit (ETO) launch vehicles. Without a return to Saturn V-class boosters or an alternate path, one cannot imagine emplacing masses that would be required for any deep-space voyage without a prohibitive number of Shuttle-class launches. One futurist solution might involve mass launch systems that could be used to move consumables, including fuel, water, food, and building materials, to LEO in pieces rather than launching integrated systems. This approach would necessitate development of robotic assembly and fuel-storage systems in Earth orbit, but could provide for a natural separation of low-value cargo (e.g., fuel, water).