Finding new ways to travel through space is not easy and this is why tests are important – even though some snags might happen. NASA’s Advanced Composite Solar Sail System was launched in April, and in early September was fully deployed. The system appears to be working, but as one of the four booms deployed it had a slight bend in it.

This doesn’t seem to be a development that will compromise the mission but it would have been better if it had not happened. Still, the Advanced Composite Solar Sail System test is not just about sailing using sunlight – it is also about how the technology behaves in space, so this is good to know.

“While the solar sail has fully extended to its square shape roughly half the size of a tennis court, the mission team is assessing what appears to be a slight bend in one of the four booms. This likely occurred as the booms and sail were pulled taut to the spacecraft during deployment. Analysis indicates that the bend may have partially straightened over the weeks since boom deployment, while the spacecraft was slowly tumbling,” the mission team wrote in a statement.

“The primary objective of the Advanced Composite Solar Sail System demonstration is to test deployment of the booms in space to inform future applications of the composite boom technology for large-scale solar sails and other structures. 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.”

Since the deployment of the sail, the spacecraft has been tumbling. The team has to turn off the attitude control as it might have interfered with the successful deployment. “Attitude” is not a typo – it’s the system that controls the orientation of the spacecraft with respect to its direction. With that switched off, the spacecraft can slowly and safely tumble. It will be reactivated when the next phase of testing begins.

Solar sails use the power of light to propel a spacecraft forward. Photons, the particles of light, have no mass but they can impart momentum. A tiny amount, for sure, but as long as your sail is large as well as extremely thin and light, it can be sufficient to move your spacecraft. Space agencies and private organizations have tested several solar sail designs over the last several decades.