Back in the day, Apollo space missions were all about putting humans into space. The sixth and final lunar landing by Apollo 17, in December of 1972, however, marks the last time humans have ventured beyond low earth orbit (e.g., farther than a few hundred miles from the surface of our planet).
Unmanned spaceflight has supported studies of the Sun, comets, asteroids, and moons, while reaching every planet in the solar system. The New Horizons mission is still on its way to Pluto, which has recently been demoted from planet status.
Human spaceflight is a much costlier and difficult problem. In the November 2009 issue of "Physics World," David Clements points out that, for the cost of a human mission to Mars, we could send about 600 rovers. Addressing the safety of the crew can also compromise scientific options. Robotic missions can attempt riskier investigations and do not have the same highly challenging food, water, air, and environmental protection requirements. Additionally, they may not require a return trip to Earth. Human explorers, though, offer a level of agility, versatility, and intelligence that robots cannot yet match.
The debate rages, then, as to whether or not human spaceflight is a necessary and/or preferred space exploration objective. Some say that humans are uniquely qualified for some types of scientific investigation. At some point, many believe that space science requires direct human interaction and experience with the subject of study. Experiments on the physiological effects of space on humans certainly cannot be performed as part of an unmanned mission. Some may even take the stand that human spaceflight is an investment in the future of our humanity. The counter opinion is that human spaceflight is the ultimate reality TV spectacle â€“ more about the human interest and national pride that it generates than it is about scientific advancement. In other words, the pursuit of human spaceflight is more about the rewards for being the first to reach new frontiers than it is about the scientific achievements of doing so.
For the U.S. space program, it looks like NASA is siding with the proponents of human spaceflight. In the January 2010 issue of "Science" magazine, Andrew Lawler reports that President Obama wants to shift NASA efforts towards development of a heavy-lift launcher which would support taking humans to the moon, asteroids, and the moons of Mars. The longer term objective would be for humans to reach the Red Planet itself. This is a major shift from the current Constellation program, which aims to develop a replacement for the Space Shuttle to get humans to and from the space station (an extension of the current low-earth orbit focus for human missions) and possibly beyond. Instead, this new approach, would target an initial launch date as early as 2018 for the proposed heavy-lift vehicle. Europe, Japan, and Canada would be asked to work on a moon base solution (e.g., moon base modules and lunar lander). Commercial companies would assume the job of getting supplies and maybe even people to the international space station.
Certainly the appropriate objectives and policy for space exploration will certainly always be debated. In reality, the outcome will likely always include some combination of both manned and unmanned spaceflight. Space study, and the technology development to support it, results in not only scientific gains, but also economic and cultural benefits. What's important is that our leaders recognize the need for space science and support appropriate forums to discuss topics such as these and develop a strategy that best achieves the agreed upon goals.