In an official report NASA stated that manned missions are easier to execute on Mars than on any asteroid.
If NASA was to plan any manned mission to an asteroid, it would be a bigger challenge to execute the plan than in Mars, the U.S. Space Agency stated. Though Mars is further away than any near-Earth asteroid, it would still be more difficult to send people to these asteroids.
Experts say this is because more knowledge of the Red Planet has been acquired over the last few years, owing to the various Mars missions NASA has launched. Moreover, mapping out the path on an asteroid is practically not possible as of now because NASA is yet to determine a way to track where these asteroids are heading.
"There are still no good asteroid targets for such a mission, a necessary prerequisite for determining mission length and details such as the astronauts' exposure to radiation and the consumables required," states a December 2012 report from the U.S. National Research Council (NRC).
NASA has for a long time been working on a way to land astronauts on Mars. They planned on using, Earth's natural satellite, the Moon as a stepping stone and planned a mission called Constellation which was to go underway in 2020. However, in 2010 President Obama cancelled Constellation after finding in behind schedule and under funded.
Instead Obama voted for sending astronauts to a near-Earth asteroid by 2025 and later work on sending these astronauts to Mars by 2030.
"Despite isolated pockets of support for a human asteroid mission, the committee did not detect broad support for an asteroid mission inside NASA, in the nation as a whole or from the international community," write the authors of the report, which is called "NASA's Strategic Direction and the Need for a National Consensus."
Currently the space agency is working on launching its own steroid-sampling mission, called Osiris-Rex, in 2016.
