When Space Exploration Technologies (SpaceX) launched its Dragon cargo capsule and docked with the International Space Station this year, the joint venture between NASA and SpaceX delivered 1,000 pounds (450kg) of supplies. According to Reuters, such launches cost between $83 million and $128 million, which comes to approximately $83,000 to $128,000 per pound to deliver food, water, toilet paper, replacement parts, new equipment, and so on. Though the successful launch and docking of the Dragon capsule captured all the attention, I wondered why we still put people in space and deliver supplies to them, when machines could function equally well without sleep, water, air, and nourishment.
The US and Russia have sent many robotic spacecraft to Mars to take photographs and analyze the atmosphere and surface. Lately, the possibility of manned missions to Mars has captured attention and sparked numerous debates. You can click here to read about the pros and cons of such a mission.
So far, though, the majority of missions to Mars have failed. An online list of past and current missions shows 25 failures out of 45 missions. One mission went awry when teams used different units -- one English and one metric. Some might argue that if we had sent people on a similar mission, they could have corrected for the problem, but that seems unlikely. The scientists and engineers on the ground didn't recognize the problem until the mission failed. When failures occur, it seems better to lose a robot than a manned vehicle, which would cost more in time, money, preparation, training, support, and lost lives.
A variety of unmanned spacecrafts could perform almost every task we would ask humans to do -- even research experiments. Advances in computers, communications, robotics, chemical sensors, vision systems, and guidance equipment make unmanned missions less expensive and easier to design.
By the way, many of the experiments performed on the ISS deal with the effects of the space environment on life -- lack of gravity, growth characteristics, long-term effects on the central nervous system, sleep-wake cycles, and so on. But if we replaced people in space with robotic craft, much of this research would not need to take place. The money that has been spent on this type of life-science work could have already put several robotic space vehicles on paths to planets or asteroids.
I'm not sure knowledge of Mars, for example, has much bearing on life on Earth, but if we have an urge to explore outer space, let's leave people on Earth and conduct experiments and gather data at a distance.