What is Nasa's giant SLS rocket?

Nasa has been developing a huge rocket called the Space Launch System (SLS) to launch astronauts to the Moon - and eventually Mars. Set to make its debut in November 2021, the SLS is the most powerful launch vehicle built since the 1960s. Nasa has plans to send a man and woman to the lunar surface by 2024, in the first landing with humans since Apollo 17 in 1972. In the last 20 years, astronauts have been making routine trips to and from the International Space Station (ISS). But the Moon is nearly 1,000 times further than the ISS; getting astronauts there requires a monster rocket. The SLS is the modern equivalent of the Saturn V, the huge launcher built during the Apollo era. Like the...