Human missions to...

http://science.nbcnews.com/_news/2013/04/16/17780686-nasas-mars-bound-mega-rocket-ahead-of-schedule-on-budget?lite

The booster, in its initial configuration, uses solid rocket boosters on two sides based on the space shuttle's design, with an upper stage taken from United Launch Alliance's well-tried Delta 4 rocket.

What's key is for the United States to stay true to the goal of getting to Mars. That ambition, set by President Barack Obama during his first term, is the guiding force behind the development of SLS and Orion. If a future administration alters that objective, all bets are off.