NASA spent billions on its SLS mega-rocket to take humans to the moon. It finally admitted it is 'unaffordable.'

• NASA officials have said their SLS mega-rocket program is "unaffordable."
• The program has long been criticized for a lack of transparency over its growing budget.
• Officials agree the SLS budget "needs to be improved," but it's not clear how, per a government report.

Senior NASA officials have admitted their Space Launch System (SLS), which aims to help humans build a base on the moon, is "unaffordable," according to a US government watchdog. 

When built, SLS will be the most powerful rocket ever created by the space agency. But costs are spiraling out of control.

NASA aims for its Orion spacecraft and its associated booster, collectively referred to as SLS, to play a crucial role in its Artemis missions to bring humans back to the lunar surface for the first time in over 50 years. 

The agency had a big win last year when SLS flew around the moon on its maiden voyage. But the program has long come under fire for its ever-expanding budget and its lagging deadlines.

"Senior agency officials have told us that at current cost levels the SLS program is unsustainable and exceeds what NASA officials believe will be available for its Artemis missions," the Government Accountability Office (GAO) said in a report published Thursday. 

The exact costs are unclear

The GAO says NASA has spent $11.8 billion since 2011 on the development of the integrated SLS rocket.

But there's a wild variation in numbers reported about the actual cost of this program, which depends on whether the development of the Orion spaceship — which predates SLS — and other running costs are included.

One estimate, drawn from NASA's Congressional Budget justification, puts that number at about $50 billion, when including costs linked to developing the Orion capsule since 2006, for instance, per the Planetary Society.

And the spending doesn't stop here. NASA has requested another $11.2 billion for the next five years to further improve and produce the next iterations of the rocket, per the report. 

Further SLS and Orion improvements are making up a substantial chunk of the agency's relatively small budget — about a seventh of the $27.2 billion budget it has requested in 2024, per the Planetary Society. By comparison, the proposed defense budget for 2024 is about 30 times larger. 

This is in stark contrast to private companies like Elon Musk's SpaceX, which are pushing to reduce their own rockets' launch costs. 

While officials have admitted their spending on the program "needs to be improved," it is not yet clear how they aim to achieve this, per the report. 

SLS is NASA's workhorse for lunar missions

The rocket is at the center of NASA's moon strategy in the upcoming Artemis mission because it is the only rocket that's built to fit within those missions, Brendan Rosseau, a teaching fellow of space economy at Harvard Business School, previously told Insider.

Over the next few years, NASA has planned a series of missions that will put boots on the moon at first, before aiming to establish a lunar base. 

The plan is for SLS to carry people to the orbit of the moon, where it will meet up with a lunar lander that can pick up astronauts and bring them down to the lunar surface.

NASA's people carrier, the Orion spacecraft, is at the center of these missions. And it was specifically designed to fit with the SLS booster, and not another rocket, per Rosseau

"NASA's worked really hard on it. It seems like they're going to stick with this for a while now," Rosseau previously said. 

NASA's SLS is an anomaly

Part of the criticism for the SLS program is that it sticks out as a "bit of an anomaly" in NASA's latest approach to project development, Rosseau previously said.

Driven by a political will to bring down the cost of space exploration, NASA has been moving away from developing its tech in-house over the past few decades, instead preferring to issue one-time contracts to commercial providers who can deliver a service for a set price. 

This move to a commercial-first mindset has been crucial to the development of the private space industry. 

It has led to stiff competition, with SpaceX moving forward with the development of its own Starship mega-rocket, after it landed a $2.9 billion contract to create a lunar lander for NASA's Artemis missions.

The agency also recently awarded a $3.4 billion contract to Blue Origin to develop a lunar lander for another Artemis mission.

"If you look at the price tag and how long it's taken to develop and the problems that it's had, maybe it's evidence that buying services from the commercial sector really is the way to go," Rosseau said. 

It may have been a political gambit, rather than a business decision, that drove SLS's continued investment, Rosseau previously said.

"Some cynics would say that it was congressional appropriators and senators with parochial interests who really wanted NASA to be building a giant rocket just for the jobs in their districts," he said. 

Still, the SLS is the only rocket of that power class that has demonstrated that it can work.

SpaceX attempted its first fully stacked launch of Starship in April, which ended in a fireball when the spacecraft failed to separate from its booster while in flight. 

NASA is working to bring costs under control, but it's not clear how

NASA has said it is now aiming to pare back its costs using a four-point strategy: "(1) stabilize the flight schedule, (2) achieve learning curve efficiencies, (3) encourage innovation, and (4) adjust acquisition strategies to reduce cost risk," the report states. 

Still, per the report, NASA "has not yet identified specific program-level cost-saving goals which it hopes to achieve."

The agency said moves have been made to reach those goals, but it's not clear whether they've led to savings so far, per the report. 

There's reason to question whether NASA can achieve its cost-saving goals, Ars Technica senior space editor Eric Berger wrote Thursday. 

A recent plan from NASA to reduce the cost of SLS's rocket engines by 30% down to $70.5 million has been criticized by NASA's general inspector, Paul Martin, who said the budget did not include project management and overhead costs. 

The engines would still also be far more expensive than equivalent private engines, per Berger. Blue Origin's BE-4 engines, for instance, are manufactured for less than $20 million, and SpaceX wants to bring its Raptor to a cost under $1 million per engine.