Why Mars? An Astronaut's Perspective, op ed, John Grunsfeld, Huffington Post
"Sending humans (and all that they will need to accompany them) to Mars will require substantial launch capabilities. This need for heavy launch capabilities goes back more than half a century, thus confirming concepts by Werner von Braun and others for Mars exploration. NASA is investing in the Space Launch System (SLS) to launch its large payloads for its expeditions to Mars. But there is more than one way to launch such heavy masses into space - and go to Mars. Indeed, SpaceX and Blue Origin are both investing in their own heavy lift rockets - and SpaceX plans to start sending its own missions to Mars starting in 2018. One way or another, we're going to Mars. ... "
"... NASA is also in the planning stages for a high-power solar electric robotic mission to an asteroid. While I am in favor of learning more about asteroids (as will be done with the recently launched asteroid sample return mission OSIRIS-Rex), the stated driver for the asteroid redirect mission is technology development for Mars exploration. Redirecting this mission to Mars would allow for significantly more Mars-relevant technology development."