The Space Launch System is a so-called super heavy-lift rocket, which puts it a category ahead of SpaceX’s venerable Falcon Heavy, and which also makes it the most powerful rocket ever created. It will be created in several stages, each increasing the maximum launch capacity, until it eventually reaches its total capacity of roughly 130 metric tons delivered to Low Earth Orbit, and eventually beyond. Right now, NASA engineers are welding together the engine section of the system, which comes in at more than 25 feet in diameter! It will feature four RS-25 rocket engines, the engines from the Space Shuttle, but a later upgrade to a more efficient, modern version is planned.
First, NASA plans to send humans back to the Moon, perhaps as early as 2021, by using the SLS to launch the upcoming Orion crew capsule. Next, it wants to get on with all the ambitious asteroid and comet projects it’s been pondering, from sample retrieval to full-on landing. Finally it wants to send more robots, and eventually human beings, to Mars. With the SLS, NASA will theoretically be able to deliver on these promises without having to go against national spending policy.
On the other hand, the second answer to why it needs the SLS is: we don’t. The aforementioned Saturn V cost something like $480 million to launch ($185M adjusted from 1970 dollars) and the SLS is projected to cost about the same. So, all this time and advancement since the days of Wernher Von Braun, and we get roughly the same launch capacity for about the same cost? And for more than seven billion invested in development? Many have suggested that the SLS, incredible though it will be, is the product of politics, not scientific need.
The idea behind building bigger rockets is either that you can get the same amount of stuff higher than before (like, all the way to Mars at a decent speed) or get more stuff than before to the same height. In the latter case, the assumption has always been that bigger rockets, while more expensive on a per-launch basis, should yield more efficient results. But there has been quite a bit of questioning as to the efficiency of this design, especially given that its funding seems to be coming from the same pool as the Commercial Crew Development program, aimed at building newer and better crew vehicles. In fact, the SLS has taken so much money that it could end up harming the very projects it is meant to launch.
Regardless, the SLS is coming, so we might as well hope that it turns into an indispensable part of NASA’s arsenal. But as the frankly incredible construction project moves forward, for now, we can simply watch and enjoy the show.