Spaceflight Insider

Construction of SLS’ Pathfinder begins

Artist concept of the core stage pathfinder. Photo Credit: NASA/MSFC

Artist’s concept of the core stage pathfinder. Photo Credit: NASA/MSFC

Pathfinder. The word evokes images of stalwart explorers and machines that pave the way for future exploration and settlement. It is also the name of the 213-foot (64.9-meter) mockup of NASA’s new super-heavy-lift booster, the Space Launch System or “SLS”. Work on the 230,000-pound (104,326-kilogram) simulator will help NASA prepare for the first flight of the massive new rocket.

NASA is planning to use SLS, along with the space agency’s new crew-rated spacecraft, Orion, to send astronauts to deep space destinations. The target NASA has placed firmly in the rocket’s crosshairs is the planet Mars. The space agency hopes to carry out this mission sometime in the 2030s. Meanwhile, the Asteroid Redirect Mission may serve as an interim step, taking place sometime in the mid-2020s.

At present, the rocket’s core stage, along with its prerequisite flight hardware, is being produced at the agency’s Michoud Assembly Facility (MAF) located in Louisiana. When complete, the mockup will stand an impressive 200 feet (61 meters) in height.

Asteroid Redirect MIssion with Orion spacecraft NASA image posted on SpaceFlight Insider

NASA hopes to send a crew to an asteroid towed into lunar orbit using SLS as early as the mid-2020s. Image Credit: NASA

The core stage is, predominantly, a huge fuel tank which holds the cryogenic liquid hydrogen and liquid oxygen that fuel SLS’ four RS-25 engines.

Pathfinder is more than just for show, however. It will be used to validate how the stage will be transported to locations where the rocket will be tested, built, and eventually launched. Transportation of the rocket’s core stage and other operations will also be demonstrated via the device.

“This hardware is an excellent proving ground for the core stage—from manufacturing and assembly to the launch site,” said Shane Carpenter, an engineering lead working on the core stage pathfinder project. “We don’t want the first time we transport the core stage to be with flight hardware. That’s why having a pathfinder is critical to the program.”

The company tapped to build Pathfinder is not Boeing, SLS’ primary contractor, rather it is Radiance Technologies and Dynetics—both of Huntsville, Alabama. According to a release issued by NASA, the businesses will now build, assemble, and transport Pathfinder, which will be constructed at the Dynetic’s facility in Huntsville.

“It is a privilege to work with Radiance on this critical project for NASA to help ensure the success of the nation’s future heavy-lift rocket,” said David King, Dynetics CEO. “As NASA’s industry partners, we’re prepared to take on the challenge and appreciate NASA’s confidence in our ability to do so.”

Don’t expect this to be a ‘high-fidelity’ model of NASA’s new booster, however. Bereft of its engines and avionics, it will serve, in many cases, to “fit check” structures and locations for when the actual booster is transported to various locations. If everything goes as scheduled, the pathfinder should be ready for NASA to use as early as 2017.

The mockup’s first customer, NASA’s Pegasus barge, will ensure that modifications to the barge be able to accommodate the rocket. Some of the changes made to the iconic vessel include a new 165 section (bringing the length of the barge to 310 feet / 94.5 meters).

NASA plans to increase the lifting capability of SLS from 70 to 105 and eventually 130 metric tons. Image Credit: NASA / MSFC

NASA plans to increase the lifting capability of SLS from 70 to 105 and eventually 130 metric tons. Image Credit: NASA / MSFC

The simulated core stage has a similar weight, center of gravity, outer mold line, and length as that of an actual stage.

“We look forward to working with these companies on such an important project for SLS,” said David Adcock, Stages pathfinder project lead at Marshall. “We want to ensure that the form and fit of the entire process for the core stage is successful, and any issues are addressed, before the flight hardware leaves Michoud. It helps reduce risk and keeps us on schedule.”

After it is finished with Pegasus, pathfinder will be sent to the B-2 test stand at NASA’s Stennis Space Center. The stand is currently being refurbished for use with SLS’ core stage in 2017. Once finished there, it’s on the road again, this time to Kennedy Space Center in Florida.

Once it arrives in the Sunshine State, the pathfinder will be raised vertically in the Vehicle Assembly Building. Like many facilities at NASA centers, the VAB is undergoing extensive renovations in preparation for use with SLS.

If the space agency’s efforts pay off, and if political support for the program can be maintained, the Block I version of SLS should take to the skies in late 2018. That flight, Exploration Mission 1, will be a test of SLS and NASA’s new crew-rated spacecraft, Orion, as a single unit. Orion will then venture into cislunar space on a 21-day test flight.

The Block I configuration of SLS should have a lifting capability of 70 metric tons (77 tons). It is powered by four Aerojet Rocketdyne RS-25 rocket engines—modified versions of the Space Shuttle Main Engines. Two Orbital ATK five segment solid rocket boosters will be mounted to either side of the core stage and provide the extra-added thrust required to get the stack out of Earth’s gravitational well.

If things work out as planned, the next version of SLS, the Block 1B, will be equipped with a more powerful upper stage. The Block 1B should have the ability to lift an additional 35-metric-tons (38-tons).

After that, a Block 2 version of SLS is planned. It will have new boosters, which could either be solid or liquid fueled. Whichever is selected, NASA is planning to take SLS to the next level with this version of the rocket. With a planned lifting capability of 130 metric tons (143 tons), this version of SLS should provide the agency with the launch vehicle required to re-ignite its deep space ambitions.

Video courtesy of NASA’s Marshall Space Flight Center


Jason Rhian spent several years honing his skills with internships at NASA, the National Space Society and other organizations. He has provided content for outlets such as: Aviation Week & Space Technology,, The Mars Society and Universe Today.

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