Positive attributes of space exploration include identifying potentially habitable planets, locating non-renewable resources and driving technological advancement; however, space exploration has negative attributes, such as exposure to radiation and vacuum, and a high cost of access. The continued exploration of space by humans demonstrates that the rewards outweigh the risks.
Space exploration missions can use manned and unmanned spacecraft, with each having its own unique positive and negative attributes.
Manned spacecraft, such as the International Space Station and the now-defunct Space Shuttle, offer scientists the opportunity to perform orbital experiments that examine the physiological and psychological effects of living in micro-gravity on the human body. These experiments, and the data gained as a result, can spur technological innovations that aim to increase the safety and efficiency of human space exploration. The negative attributes of manned spacecraft missions include danger of exposure to high levels of radiation while in orbit, loss of spacecraft and crew due to human error or mechanical malfunction and the high cost of putting humans and life support systems into orbit. As of 2015, the farthest a manned spacecraft has ever traveled is around the far side of the moon.
Unmanned spacecraft, such as the Lunar Prospector, Mars Reconnaissance Orbiter and Stardust, allow for deeper space exploration that is currently out of reach for manned missions. Unlike manned missions, unmanned space exploration missions do not require human life support systems, which allows for more equipment, sensors and fuel, and thus a greater range and exploration potential. The negative attributes of unmanned spacecraft include high cost of launch and mission management, and risk of damage or failure.
Many technologies developed by NASA and other space exploration agencies have found uses on Earth. Since 1973, NASA has published more than 1,800 reports highlighting technologies it has created or helped to develop. Today, satellite technology provides the backbone for GPS navigation systems, weather prediction, storm tracking and much of the world's communications network. However, private enterprise might have developed these technologies and launched satellites at less cost to taxpayers.
More than 20 astronauts have been killed during spaceflight missions, while others were killed performing related work on the ground. However, the number of lives lost during space exploration has been relatively low compared to other less extensive ventures on Earth that have spun off fewer overall gains in technology and knowledge. Falling space junk poses a threat to humans on Earth. So far, however, such debris has burned up in the atmosphere, fallen into the ocean or crashed in remote areas without doing harm.