A new NASA spaceship is tumbling through space uncontrollably as engineers on the ground work to fix an issue that caused the $20 million craft to lose control.

The agency's Advanced Composite Solar Sail System (ACS3), a craft with four reflective 'sails' designed to test a new type of propulsion system, hit a snag when it unfurled the sails.

Engineers noticed a slight bend in one of the 'booms,' or structural beams, that support the sails, impacting its ability to stay on course.

NASA has kept ACS3's attitude control system - which controls the orientation of a spacecraft - turned off engineers assess this damage. 

As a result, the microwave-sized spacecraft is currently careening through space. 

This mission is a test of new spaceflight technology that uses the pressure of sunlight for propulsion, similar to the way a sailboat is powered by the wind. 

One day, it could reduce the extremely high cost of deep space missions. But first, NASA will have to wrangle its runaway craft. 

ACS3 launched from New Zealand aboard Rocket Lab's Electron rocket on April 23. 

Just a few months after the launch, the spacecraft's sail got stuck when an onboard power monitor detected higher-than-expected motor currents and paused the unfurling process. 

In late August, NASA successfully deployed the sails in a second attempt.

But before doing so, engineers deactivated the spacecraft's attitude control system in order to accommodate dynamic changes as the sails unfolded. It's been turned off ever since.

Now, the discovery of this bend in one of the booms has delayed reactivation of the attitude control system further, as engineers work to assess the damage.

'This likely occurred as the booms and sail were pulled taut to the spacecraft during deployment,' NASA's update stated.

'Analysis indicates that the bend may have partially straightened over the weeks since boom deployment, while the spacecraft was slowly tumbling.'

Engineers are currently working to reposition the spacecraft, keeping it in 'low power mode' until its sails are oriented toward direct sunlight. 

Once the team achieves that desired position, they will be able to re-engage the attitude control system and stop the spacecraft's constant tumbling. 

At that point, the re-oriented spacecraft will be able to point its radio antenna toward mission control on Earth and communicate with the NASA engineers on the ground.

This will allow engineers to gather even more data, calibrate the precise shape of the sail and prepare to begin its sailing maneuvers, according to NASA. 

The sailing maneuvers will be the true test of this new propulsion system. 

Engineers will angle the sails to change the spacecraft's orbit, which is critical to their ability to maneuver ACS3. 

It's currently located about 600 miles above Earth's surface - twice as high as the International Space Station.

Once the spacecraft entered sun-synchronous orbit - which allows a satellite to remain in-sync with the sun as it circles the Earth - NASA engineers disengaged the attitude control system and unfurled the sails.

The ACS3 mission was designed to test solar propulsion as a way to lower the cost of deep space missions, such as flights to Mars.

The spacecraft's four sails unfurl to form a 30-foot-wide silver square that is supported by two diagonal booms.

When light particles - or photons - from the sun impact these sails, it creates small bursts of momentum that propel the spacecraft forward, like a sailboat. 

The force exerted by the sun’s light is roughly equivalent to the weight of a paperclip resting on your palm, according to NASA, just enough to allow the spacecraft to overcome atmospheric drag and gain altitude. 

NASA isn't the first to test a solar sail propulsion system in space. 

The Planetary Society's LightSail 2 launched in 2019 and gained two miles of altitude two weeks after unfurling its 300-square-foot sail. 

But the mission ended in disaster when the spacecraft began losing altitude and ultimately burned up in Earth's atmosphere.

LightSail 2 inspired the ACS3 mission. If NASA can prove this technology works, it could significantly reduce the amount of fuel needed for deep space missions, saving the agency a lot of money. 

'Data collected from this flight test has already proven highly valuable, and the demonstration will continue producing critical information to enable future solar sail missions,' the agency wrote in a recent update.