3D-printing specialist Relativity Space raised $650 million to step up work on a fully reusable rocket that will attempt to challenge Elon Musk’s SpaceX in less than three years, the company announced on Tuesday.

The money will be used “to accelerate some of the production ramp rate and get to a higher launch cadence as quickly as we can, because the demand is certainly there for it,” Relativity Space CEO Tim Ellis told CNBC.

Relativity’s new capital will be focused on its Terran R rocket, a launch vehicle that would be similar in size and power to SpaceX’s workhorse Falcon 9 rocket.

Terran R will carry 20 times more to orbit than Relativity’s Terran 1 rocket, the latter of which the company is on track to launch for the first time by the end of this year. Additionally, Ellis said Terran 1’s backlog of customer orders makes it “the most pre-sold rocket in history before launch.”

The raise, which Ellis described as “war chest doubled,” was led by Fidelity and comes eight months after Relativity brought in $500 million in a round led by Tiger Global. The $650 million in equity added BlackRock, Centricus, Coatue and Soroban Capital as new Relativity investors, with a host of existing investors – including Fidelity, Tiger, Baillie Gifford, K5 Global, Tribe Capital, XN, Brad Buss, Mark Cuban, Jared Leto and Spencer Rascoff – building on prior stakes.

Relativity has now raised $1.34 billion in capital since its founding in 2015, with its valuation climbing from to $4.2 billion from $2.3 billion in November. Its headcount has grown to 400 people, with Ellis saying the company plans to “add several more hundred this year.”

“We’ve signed up to create a lot of value, certainly remaining the second most highly valued space company in the world,” Ellis said, as SpaceX commands an industry-leading $74 billion valuation.

Relativity is building the first iteration of its Terran 1 rocket and has manufactured 85% of the vehicle for the inaugural launch. It uses multiple 3D-printers, all developed in-house, to build Terran 1 and will do the same for Terran R.

The rockets are designed to be almost entirely 3D-printed, an approach which Relativity says makes it less complex, and faster to build or modify, than traditional rockets. Additionally, Relativity says its simpler process will eventually be capable of turning raw material into a rocket on the launchpad in under 60 days.

“We’re just seeing in the market that there needs to be another quickly-moving, disruptive launch company that’s actually skating to where the puck is going,” Ellis said.

He added that Relativity “never seriously considered the SPAC path,” believing his company doesn’t yet need to go public and can tap “almost limitless capital” in the private markets. A SPAC or special purpose acquisition company is a blank-check company that raises funding from investors to finance a merger with a private company to take it public.

Ellis noted that Relativity received higher fundraising offers than the one it accepted from Fidelity, but went with the firm as the lead due to its prestige and reputation.

Relativity Space ranked No. 23 on this year’s CNBC Disruptor 50 list.

Relativity’s Terran 1 rocket is designed to carry 1,250 kilograms to low Earth orbit. That puts Terran 1 in the middle of the U.S. launch market, in the “medium-lift” section between Rocket Lab’s Electron and SpaceX’s Falcon 9 in capability.

But Terran R would go head-to-head with Falcon 9: Targeting a capability of more than 20,000 kilograms to low Earth orbit, almost as tall at 216 feet in length, slightly wider with a 16-foot diameter, and a similarly sized nosecone to carry satellites to space.

SpaceX’s rocket features nine Merlin engines in the booster, each capable of about 190,000 pounds of thrust, while Relativity’s Terran R booster will feature seven Aeron R engines that it says will be capable of 302,000 pounds of thrust each. Earlier this year Relativity completed a full duration test firing of a pathfinder engine, using liquid oxygen and liquid methane as its fuel.

Musk’s company ships its Falcon 9 boosters via highways from its headquarters in California, and Ellis said Relativity will similarly send its Terran R boosters over land to the coast of Texas, before putting them on a barge to its engine testing facility in Mississippi and then on another barge to Florida.

Relativity is aiming to launch the first Terran R mission in 2024 from Cape Canaveral’s LC-16 launchpad, where its first Terran 1 missions will also launch. While Relativity is “nearly out of physical space” in the headquarters it moved into last summer, Ellis said the company has the core infrastructure in place needed to manufacturing Terran R. It has five large scale 3D-printers and five smaller “development” printers, and plans to add two more development bays in the near future. But Ellis noted that the company completed work on a new 3D-printer head, which more than doubles its print speed.

“It’s not just adding more printer hardware. We’re also continuously using the data and learning of printing to actually speed up the process and also make changes to the printer design themselves,” Ellis said.

Ellis emphasized that Terran R has been a part of the plan since Relativity’s early days, as the company has seen strong “market interest and demand for creating this vehicle.” Although he declined to disclose the name of the customer, Relativity has a “prominent” initial buyer for Terran R launches.

“We’ve actually been developing [Terran R] this the whole time, so in many ways I feel like this is a weight off my shoulders, a big reveal,” Ellis said. “We just needed to get enough traction and resources to be in the spot where now we’re going big.”

Ellis said he is a “huge fan” of SpaceX’s next-generation Starship rocket, which Musk’s company is developing to be fully reusable – hoping to make space travel more akin to air travel.

“We need a vehicle that’s going to take people to Mars,” Ellis said. “[Starship] is huge and I think that capability is necessary.”

As Terran R aims to be fully reusable, Ellis described it as “more a miniature Starship than a Falcon 9 rocket.” While SpaceX reuses the boosters of its Falcon 9 rockets, it has not been able to reuse the upper stages that carry satellites on to orbit. Relativity wants Terran R to be a “fresh look at what is the best possible” rocket by designing it to be fully reusable from the beginning.

Terran R’s booster, or first stage, will use its engines to land standing upright and has features “that would be nearly impossible to produce without 3D-printing.” Ellis said Relativity’s long-term goal is to “get to hundreds to thousands of reuses” per rocket. Reusing the second stage will be the next challenge, with Relativity building it “out of a more exotic 3D-printed metal” to make it lighter and able to endure the intense temperatures of reentering the Earth’s atmosphere.

“First stage reuse or even second stage may not work perfectly on the very first try, but every single launch attempt that we’re bringing in revenue we’re able to continue to develop reusability further,” Ellis said.

A fully reusable rocket would also be able to deliver cargo quickly from one point on the Earth to another, a use the U.S. military has shown great interest in already with SpaceX’s Starship.

“I think point-to-point space transportation is an interesting market that we’re looking at” with Terran R, Ellis said.

More broadly, Ellis remains focused on helping to “build an industrial base on Mars” and believes both 3D-printing and fully reusable rockets are key to making that happen.

“No one else is doing full reusability and I think that that’s a bit depressing – there needs to be more companies actually trying to make the future happen in a big way,” Ellis said. “What we’re doing is extremely hard ,but we also have the best and most experienced team in the industry.”