The Space Launch System (SLS), as it is currently known, will be the most powerful launcher ever built – more powerful even than the Saturn V rockets that put men on the Moon.
On top of the SLS, Nasa plans to put its Orion astronaut capsule, which is already in development.
The agency says the first launch should occur towards the end of 2017.
This will be an uncrewed test flight, and it is estimated the project will have cost $18bn (£11.4bn) by that stage.
"The next chapter of America's space exploration story is being written today," said Nasa's top official, General Charles Bolden.
"President Obama has challenged us to be bold and dream big, and that's exactly what we do.
"While I was proud to fly in the space shuttle, tomorrow's explorers will dream of one day walking on Mars."
The SLS will borrow many technologies developed for the recently retired space shuttle programme. These include the shuttle orbiter's main engines.
But whereas the reusable spaceplane had three such power units on its aft, the SLS main core stage in its full-up configuration will have five.
A further stage on top will provide additional muscle, as will shuttle-like strap-on boosters. Although, again, these will be bigger than those used on the shuttle.
The initial design calls for the SLS to be able to put 70 tonnes in a low-Earth orbit (LEO), the altitude of the space station. Some 130 tonnes is the eventual target.
It feels a little old school, to have that kind of booster, but it's better than mucking around on the ground, isn't it?
[Source: BBC News]