In South Texas, the commercial spaceflight company SpaceX is preparing to test a huge, stainless-steel rocket. The machine could one day carry humans to the moon, Mars and beyond.

But first, it has to fly.

"It's a very complex machine; it has so many different components," says Paulo Lozano, director of MIT's space propulsion laboratory. The rocket is larger than any ever built. Success will depend upon dozens of engines, firing in perfect synchrony.

The stakes could not be higher, at least to hear SpaceX CEO Elon Musk speak about the mission.

"Eventually the Sun will expand and destroy all life," Musk said, standing before the giant rocket about a year ago. "It is very important – essential in the long-term – that we become a multi-planet species."

Musk hopes Starship will provide a critical step to becoming multiplanetary, by allowing large payloads to be carried into orbit for cheap. His goal is for Starship to someday transport the first people to Mars.

SpaceX also has a business interest in seeing its mammoth rocket fly. Starship could be used to launch large numbers of the company's internet-providing "Starlink" satellites. Starlink is seen as a key part of SpaceX's future, and Starship would allow the network to rapidly grow, says Tim Farrar, the president of TMF associates, a telecom consulting firm.

But Starship is unlike any other rocket, and SpaceX acknowledges that the first test flight will be extremely risky. That launch attempt is set to take place during a 150-minute window that opens at 8 a.m. Eastern on Monday, April 17. When the company recently posted its timeline for the flight, it replaced "liftoff" in its mission timeline with two words: "excitement guaranteed."

Starships were meant to fly

Standing at nearly 400 feet tall, Starship is made of gleaming stainless steel, an unusual choice in a business where every pound of weight matters. In fact, SpaceX started out looking at advanced, lightweight composites for Starship, Musk told the Space Studies Board of the National Academies in 2021. But he quickly realized that steel was cheap, abundant, and most importantly, incredibly tough. It could hold cryogenic rocket fuel and tolerate the grueling heat of re-entry better than other materials.

"I'm a big fan of stainless steel," he joked. "Stainless steel and I should get a room or something."

The rocket also uses an unconventional fuel choice – methane. Most high-powered rockets use hydrogen for fuel because it is lightweight and highly efficient, Lozano says.

But methane does have some advantages: It is cheaper to produce and easier to handle the hydrogen, and trace amounts of methane are present in the atmosphere of Mars. That means that a future Starship mission to the red planet might be able to refuel by drawing methane from the atmosphere or another local source.

"I think the idea, down the road, is to use methane that is found on places like Mars," Lozano says.

To make up for its extra weight, Starship depends on powerful engines called Raptors. The spacecraft itself uses six Raptors to fly, but the super-heavy booster that will lift it into space uses 33 of the engines, working together.

Again, the decision to use such a large number of engines is a trade-off, according to Lozano. It allows the rocket to produce an enormous amount of thrust, which it needs to get off the ground. But, he adds, "having that large number of rocket engines firing simultaneously – it's actually quite hard. I think that's going to be one of the biggest challenges."

In fact, the Soviet Union tried a similar approach to reach the moon at the end of the 1960s. It built a massive rocket called the N1, the first stage of which used 30 engines. However, even a single engine failure was enough to cause the rocket to explode, and four prototypes were destroyed before the Soviets eventually abandoned the program. By contrast, America used five enormous engines for the first stage of the Saturn V rocket. The reduced complexity allowed the rocket to carry astronauts to the moon.

The stainless steel rocket saves the world

Assuming everything works, Musk believes that the cheap, durable design of Starship will make it a workhorse for getting things into space. Speaking last year, Musk said he hoped Starship could be reused every six to eight hours, and the booster might be reusable, in theory at least, every hour.

In the near term, it won't be carrying interplanetary missions. Instead, SpaceX needs it to transport satellites into orbit for its satellite-based Internet service known as Starlink. Starlink is a major revenue-maker for the company and there's been strong interest from users. But the Starlink system is limited in how many subscribers it can support, says telecoms consultant Tim Farrar.

"In order to continue to grow their subscriber base, they need more capacity and that's going to require more and bigger satellites," he says.

It could take thousands of additional satellites to build a system big enough to meet the demand. Right now, SpaceX's smaller rockets can only launch a few dozen at a time. Starship can launch many more – and larger, heavier satellites that the company can use to increase profitability.

"If they can get Starship going that will clearly help a lot," he says.

NASA is also paying SpaceX around a billion dollars to develop a version of Starship to visit the moon, though that mission is likely still several years away.

The launch of Starship comes at a difficult time for the tech industry, Farrar notes. SpaceX is currently trying to raise additional capital to keep the development of Starship and Starlink going.

For now, investors seem happy to let SpaceX try out its massive potentially interplanetary rocket. But he says that if the launch fails and Starship falls further behind schedule, it could affect all of SpaceX's business, especially in the current financial climate.

"[If] people lose confidence, and people lose that belief," Farrar says, "then things are going to look very different."

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