It’s a make-or-break moment for NASA’s next mega-rocket: the Space Launch System.

Why it matters: The rocket — about 10 years in development and billions of dollars over budget — is expected to launch for the first time this year. Its success iskey for NASA’s plans to bring people and payloads to deep space destinations like the Moon.

• “This is the year the SLS has to show that it can work,” the Planetary Society’s Casey Dreier told me. “It had better do something. It’s been 10 years now.”

Driving the news: NASA is expected to stage what will be one of the biggest tests of the SLS yet on January 17.

• That testwill see the four engines of the huge rocket's core stage fire in unison without taking flight.
• The rocket will light up for as many as eight minutes in order to see how the booster might behave during a real launch.

What's next: The SLS is expected to launch to space for the first time in November 2021, sending an uncrewed Orion capsule around the Moon and back to Earth.

But but, but ... whether that happens on time remains to be seen.

• There isn't much margin in the schedule for possible delays and fixes that may come about as a result of the test firing or other issues, according to a Government Accountability Office report published last month.
• If the first flight of the SLS and Orion isdelayed, it could have a cascade effect on NASA's future Moon missions, including the planned 2024 crewed lunar landing, William Russell, one of the authors of the GAO report, told me.

Context: Congress directed NASA to build the SLS in 2010.

• Today there are commercial space companies — including Blue Origin and SpaceX — working to develop rockets that could launch astronauts and payloads to the Moon and beyond for cheaper than the cost of an SLS.
• Some have suggested NASA should buy a ride to the Moon aboard a commercial rocket instead of the SLS, at least at first.

The other side: Proponents of the SLS program say that even with these commercial heavy lift rockets expected to come online, NASA still needs its own launcher in order to fulfill its unique needs as an exploration agency.

• The entire system — including SLS and Orion — are built to work together, so swapping in some other kind of rocket isn't practical at this phase in development, Dreier said.
• The SLS program has also brought much-needed jobs back to NASA and the contractors — Boeing, Aerojet Rocketdyne, and Northrop Grumman — responsible for building and testing the rocket.

The bottom line: NASA's future deep space exploration plans depend on the SLS succeeding — and soon.