If you want to get humans to the Moon, you're going to need an absolute monster of a rocket.

Over 50 years ago, we had the iconic Saturn V to get that job done. And its spiritual successor, NASA’s Space Launch System, is even more powerful.

It’s currently scheduled to hurl its first astronauts around the moon in 2024. But the SLS isn’t a proverbial monster just because of the 8.8-million-pound-punch of thrust it packs. Engineers designed it to be a rocket cannibal.

See, even though the SLS is picking up where the Saturn V left off, it’s using pieces of the space shuttle to do so. [♪ INTRO] Ever since Apollo 17 splashed down in 1972, no human has gotten more than about 650 kilometers from the Earth’s surface. Which sounds like a small step compared to the 386,000 kilometer leap you need to get to get to the Moon. But it is far enough away to allow astronaut-scientists to study how space works while still being relatively protected by their home planet.

And between 1981 and 2011, NASA’s space shuttle was the workhorse that got astronauts into those low Earth orbits. Whether they were conducting microgravity experiments, or launching probes into deep space, or performing maintenance on the Hubble Space Telescope, the shuttle got them where they needed to go. And how did the shuttle get anything where it needed to go?

Mostly a combination of solid fuel rocket boosters, which detached about two and a half minutes into a launch, and three liquid fuel main engines that stuck out over the back end of the orbiter. In 2010, before the shuttle fleet was mothballed, the US government knew they’d need a replacement. At least to keep shipping people and supplies to the International Space Station.

So in addition to funding a couple of programs where private companies could develop their own space-faring tech, Congress gave NASA a budget and mandate to build the SLS. And partly because all those congresspeople wanted to keep their constituents happily employed, the SLS program was instructed to make use of pre-existing technologies whenever it was practical. Including pieces of technology that had previously flown as part of the three remaining space shuttles.

But the Space Launch System wasn’t just supposed to replace the shuttle. It needed to return astronauts to the Moon, too. So engineers couldn’t just build Shuttle 2.0.

They had to kick things up a few notches. In fact, the SLS rocket was designed to be modular, with different configurations for different missions. Sending humans to the Moon?

You stick these bits on. Sending a massive space probe on an interplanetary mission? You stick these bits on.

But each configuration has the same core stage with four shuttle main engines stuck to the bottom. That’s one more than any shuttle used at a time, but hey, you don’t need as much oomph if you’re only trying to get something into low Earth orbit. And yeah, those main engines would need a little adapting and upgrading before the engineers stuck them onto the SLS.

But isn’t it cool that an engine which helped a shuttle get to space gets a second chance? I sure think so. As for the shuttle’s solid rocket boosters, some SLS configurations also use enlarged versions of those.

Combine these pieces of cannibalized space shuttle tech with the SLS’s overall paint job, and if you squint, you can kind of see the offspring of the shuttle and the Saturn V. With a mandate from Washington, NASA got to work on SLS back in 2011, with the initial goal to be mission-ready by 2017. You might have noticed that did not happen.

It took until 2022 for an SLS rocket to fly. But when it did, it broke the record for the most powerful rocket ever launched. That 2022 flight was a part of the Artemis program, in which NASA has teamed up with a global network of other space agencies to get humans back to the Moon.

They hope to do new science, look for resources, and study whether a permanent base can be built there. Now, Artemis I was an uncrewed mission. The Orion capsule that went around the Moon and back was occupied by mannequins.

But the next mission, Artemis II, will ferry real people around the Moon. That flight is tentatively scheduled for 2024, but engineers are already putting the mission’s SLS together. In September 2023, the core stage’s four Shuttle-derived engines were successfully attached.

They’ve also started fabrication of the SLS for Artemis III, which hopes to put astronaut boots back on the Moon as early as 2025. After that, NASA might use the SLS for more deep-space crewed missions, such as building a Moon base, and even going to Mars. But that “might” is pretty important.

Because the whole SLS program has been a bit controversial, mainly due to… How should I put this? …being really freaking expensive. By some estimates, its initial budget of six billion dollars had quadrupled by its first launch. And in September 2023, a government audit called the SLS an “unaffordable” means to achieve the Artemis mission goals.

There are a lot of reasons why that’s happened, but one is that the rockets are not reusable. Unlike the space shuttle, where the giant orange external tank was the only thing you had to replace each go, or emerging rocket technology from private companies. And speaking of which, SpaceX’s upcoming Starship rocket is supposed to be both reusable and more powerful than the SLS.

So why not let NASA cut its losses and save some money? Well, unfortunately for SpaceX, and for all of us, Starship blew up during its first test flight in April 2023. And as we’re filming this episode, they don’t even have a second test flight scheduled yet.

Plus, defenders of SLS argue that its use of tried-and-tested parts from the Shuttle make it much more reliable than brand-new rocket designs, which is important for a flagship mission like Artemis. So the SLS project is safe, at least for now. And even if all it does is get humans back to the Moon after 50 years, that is a big enough accomplishment to… …make the SLS our final rocket pin of the month for 2023!

You can pick yours up by heading over to dftba.com/SciShow right now! Or, you can wait for all of us at SciShow to thank you for celebrating one year of awesome rockets with us, and then you can head over. Thanks as always for learning with us.

And thanks, of course, for watching! [♪ OUTRO]