It’s been a few months since launch, and NASA’s solar sail mission isn’t looking so good; ground teams have so far failed to deploy its massive Sun-gliding system. The mission is designed to test new materials and deployable structures for solar sail propulsion as a form of space travel, but the mission’s success could be in jeopardy.

The Advanced Composite Solar Sail System launched on April 23 on board Rocket Lab’s Electron rocket. Nearly a week into its journey, the microwave oven-sized cubesat made contact with ground control from its Sun-synchronous orbit, which is around 600 miles (966 kilometers) above Earth’s surface. Things were going smoothly until NASA began deployment operations.

During an initial attempt to unfurl, the mission’s solar sail paused when an onboard power monitor detected higher-than-expected motor currents, NASA wrote in a recent update. NASA engineers are analyzing data from the spacecraft to understand what may have caused the sudden glitch. The spacecraft’s communications, power, and attitude control are operating normally in the meantime, according to NASA.

“Mission operators have been able to download data from the spacecraft during brief, planned communications windows when it passes in range of mission control at Santa Clara University in California,” NASA wrote. “The team is conducting analysis and assessing all spacecraft systems before resuming deployment operations.”

Solar sails run on photons from the Sun, harnessing energy produced by light and using it to propel spacecraft forward. As the photons hit the spacecraft’s sails, it causes small bursts of momentum that propel it farther away from the star. If a spacecraft is able to surpass the drag from Earth’s atmosphere, it could potentially reach very high altitudes.

NASA’s solar sail mission is meant to test new materials and deployable structures for the experimental propulsion systems, including new composite booms that are used to unfurl the sail. The composite booms are made from a polymer material; they’re lightweight while still being stiff and resistant to bending and warping when exposed to different temperatures. They work the same way as a sailboat’s boom, except they are designed to catch the propulsive power of sunlight rather than wind.

If unfurled, the solar sail will stretch across 30 feet (9 meters) per side. The sail needs to be large enough to generate sufficient thrust, while also being at a high enough orbit to gain altitude and overcome atmospheric drag using the subtle force of sunlight on the sail. The force exerted by the Sun’s light is roughly equivalent to the weight of a paperclip resting on your palm, according to NASA.

The mission’s initial flight phase is designed to last for around two months and it includes a series of pointing maneuvers to demonstrate orbit raising and lowering using only the pressure of sunlight acting on the sail. NASA is hoping its solar sail technology can help the space agency reach further destinations across the cosmos, and help deepen our understanding of the solar system.

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