NASA is now mulling over the idea of using commercial rockets to launch a critical mission around the Moon next year instead of using the massive rocket that the agency has been building for the last decade. Such a drastic change would not only upend flight plans for this particular mission, but it could also have big implications on how ambitious space travel programs are conducted in the future.

The impetus for this new commercial focus is to maintain the agency’s launch schedule. NASA’s rocket, the Space Launch System, or SLS, is taking much longer to make than expected and probably won’t be ready to fly by its current target launch date of June 2020, whereas other commercial vehicles already on the market are ready to fly right now.

Making this revision would not be a simple swap. NASA would need not one commercial rocket but two in order to make the mission happen. The agency will also need to develop new technologies and figure out how to piece together certain vehicles in space in order to ensure that its mission can actually make it all the way out to the Moon.

It’s a process that will take a lot of time and effort, and there’s no guarantee that it can be done by next year. But if NASA can pull off this monumental shift to commercial vehicles, the agency may just demonstrate a new method of deep-space travel that relies on multiple launches of smaller vehicles and doesn’t necessarily require massive rockets to succeed. That could ultimately save NASA lots of time and money, freeing up funds to do more ambitious things.

Space tugs

For this upcoming mission, NASA wants to send two heavy spacecraft out on a three-week trip around the Moon next year: an empty crew capsule called Orion and a piece of cylindrical hardware that provides power and support to the capsule called the European Service Module. Together, the two vehicles need a lot of fuel to break free of Earth’s gravity and reach the extreme distance of the Moon. The SLS is so powerful that it will be capable of sending the pair all the way out to that distance in just one launch.

But if NASA decides to fly commercial, there isn’t a vehicle available right now that’s powerful enough to send both Orion and its module together to the Moon’s vicinity. The two most powerful commercial rockets in the US include SpaceX’s Falcon Heavy and the Delta IV Heavy from the United Launch Alliance. While both are impressive vehicles, neither can match what the SLS will do when it’s complete.

That’s why two rockets would be needed. One rocket would launch Orion and the European Service Module together into Earth’s orbit where they would essentially stay “parked” for a bit. Another rocket would then launch what is known as a space tug, which is essentially another rocket with its own fuel and engine attached. The tug and Orion would hook up together in orbit, and the tug’s engine would ignite, propelling the vehicles all the way to the Moon. “It’s much like a tractor on a farm that pulls trailers or farm equipment,” Dallas Bienhoff, founder of the Cislunar Space Development Company, which focuses on building out deep-space infrastructure, tells The Verge. “It’s a propulsion unit.”

This concept of using space tugs for deep-space travel has been touted for decades. NASA began studying the concept in the 1960s and ‘70s, with one NASA official describing them as needed for “imparting velocities to other bodies in space.” Ultimately, the upper portions of rockets can be considered space tugs, as these vehicles push payloads to their intended orbits. However, space tugs can be launched on their own, remaining in space in order to attach to other vehicles and propel them where they need to go.

Space tugs could change how NASA has been doing its deep-space human missions for decades. “One of the issues that we have as a space industry, which has led us to the Space Launch System, is we insist on putting all of the mass per mission on a single launch,” says Bienhoff, who also researched technologies needed for space tugs at Boeing. Launching all of your hardware this way can get cumbersome. Earth’s gravitational pull is pretty strong, so sending heavy equipment far away from our planet requires a lot of extra power, and, in turn, a lot of extra fuel. Getting all of that fuel into space requires a big rocket, and the bigger your rocket gets, the more fuel you need to lift both the rocket and the payload off of Earth. So the cycle goes, with larger and larger amounts of cargo requiring bigger rockets for deep space.

As rockets grow in size, they become more complex and more expensive to launch. And expense has certainly become a problem for the SLS. It’s estimated that NASA has spent $14 billion over the last decade to develop the rocket, and the vehicle still isn’t finished. Once it’s complete, it’s expected to only launch once or twice a year for about $1 billion a flight. In comparison, the Delta IV Heavy costs around $350 million per launch, while the Falcon Heavy starts at just under $100 million. Just two launches of either of those vehicles cost well under one launch of the SLS.

Space tugs could also help save on cost in the future by simply staying in space when they are finished with their tugs. For instance, a tug that drags hardware to the Moon could then travel back to low Earth orbit and wait for a refill. Another rocket could then bring up propellant from Earth, dock with the tug, and transfer fuel over. That would allow the space tug to drag some other object out into deep space, which is a task it can do over and over again, saving on extra launches.

In-space assembly

Of course, another capability that’s needed for all of this to work is a way to dock with these tugs. NASA administrator Jim Bridenstine has acknowledged that the crew capsule Orion, as it’s designed now, does not have the capability to rendezvous and dock with a tug. “Between now and June of 2020, we would have to make that a reality,” he said during a Senate hearing, referring to docking.

However, this kind of in-space docking is not a novel practice. Russia’s Soyuz capsule has long been automatically docking with the International Space Station, bringing crews to the orbiting lab. SpaceX’s Crew Dragon also just demonstrated its ability to dock with the ISS on a recent test flight without crew input, using a suite of sensors and lasers to come in close and gently ram itself onto a port on the outside of the station. “The LIDAR and machine vision systems that are used for Crew Dragon to autonomously dock with station are some of the sensors you might use to do manufacturing and assembly in space,” Andrew Rush, CEO and president of Made In Space, a company developing ways to 3D print and build in space, tells The Verge.

Attaching critical pieces together in space allows engineers to get around big rockets, too. Rather than sending everything up in one piece, you can launch smaller pieces and then connect the hardware together once it’s in orbit. That way, you don’t have to completely build your spacecraft on the ground first. This has been a problem for certain complex missions, like NASA’s future space observatory, the James Webb Space Telescope, which doesn’t exactly fit fully inside the rocket it’s launching on. The spacecraft is so big and complex that it has to launch to space folded up and then unfurl over the course of two weeks. If that process goes awry, the telescope may not work properly in space, putting an end to a more than $9.66 billion mission.

But with in-space assembly or additive manufacturing in space, there isn’t a need to build the entirety of a vehicle on Earth first. “By spreading the equipment over a couple of launches, and then using in-space manufacturing and assembly, we can actually accomplish this in a much more cost-effective way than if we launched that sort of monolithic spacecraft,” says Rush.

The risks

All of these changes come with a price, though. Docking and in-space assembly are considered risky maneuvers, according to Bridenstine. “Docking crewed vehicles in Earth orbit to get to the Moon adds complexity and risk that is undesirable,” he wrote in a memo to NASA employees. Additionally, launching hardware in pieces means multiple rockets would be needed for one deep-space mission, and that doesn’t sit well with some people. A few experts and lawmakers argue that performing more launches opens up more opportunities for risk since one of the launches could fail and jeopardize the mission. “The perspective of the committee is let’s go, and let’s go hard... as opposed to piecemeal,” Rep. Frank Lucas (R-OK) said this week during a hearing of the House science committee.

Using commercial launch vehicles won’t be easy for this mission, either. Currently, engineers are verifying Orion for this upcoming launch, running simulations based on the SLS design. In order to swap to commercial vehicles, they would have to shelve all of that work and start running new simulations based on data from the new vehicles. It would also completely change the flight profile, which would require extra work to prepare. “If the mission profile changes, which seems inevitable given the lesser capabilities of every other vehicle compared to SLS, a lot of that work is no longer relevant,” an employee at Lockheed Martin working on Orion, who did not want to speak publicly in case of retaliation, tells The Verge. So meeting the June 2020 launch date seems unlikely.

Then there is political opposition that will most certainly prevent this change from taking place. Lawmakers in Congress, particularly those from Alabama where the SLS is being built, will likely fight to keep the Orion vehicle on the massive NASA rocket. And since Congress ultimately approves NASA’s budget and dictates how the agency can use federal funds, lawmakers could mandate that Orion stay on the SLS.

By making this change, NASA has the opportunity to demonstrate an entirely new type of approach for sending humans to deep space — one that has never been used before. While launching in pieces may be more complex, it could save on money and time, which are two things that NASA does not have in abundance. Perhaps NASA’s future mission to the Moon won’t be reliant on massive rockets, but smaller vehicles that launch more frequently and accomplish the same tasks.