NASA’s Solar Sail System Update: Progress And Challenges

NASA released an update regarding the Advanced Composite Solar Sail System, revealing a slight bend issue in one of the four booms. This defect, which appears to have occurred during the deployment phase, doesn’t seem to be a major problem.

The mission was launched on April 23, 2024, aboard a Rocket Lab’s Electron rocket from New Zealand. Nearly four months later, on August 29, the spacecraft deployed its booms, unfurling the 9-meter reflecting sail.

A self-correcting bend

The bend occurred in one of the supporting composite booms during the sail tensioning phase, when the arms and structure were pulled toward the spacecraft to ensure optimal tension for full sail deployment.

Initial analysis indicates that the bend may have partially straightened over the weeks as the solar sail settled after deployment.

Views from the four B&W wide-angle cameras, each camera showing a reflective sail quadrant supported by composite booms in the lower half of the image and solar panels can be seen in the upper half. Credits: NASA

Engineers will continue to monitor the situation, but they anticipate that the slight anomaly will not prevent the system from performing its planned sailing maneuvers.

Solar sail technology: how it works

NASA is developing new deployable structures and materials technologies for solar sail propulsion systems with the goal of radically reducing the cost of future space missions.

Solar sails employ the pressure of sunlight for propulsion: when photons impact on the sail surface they transfer momentum to the spacecraft, eliminating the need for conventional rocket propellant.

Looking at one, it is evident that solar sails are always large when fully extended; the justification lies in the physics of thrust. Because solar pressure is low, solar sails must be large to maximize the useful area for efficiently generating thrust.

Illustration of how a fully extended solar sail appears after deployment. Credits: NASA — *Animation showing how a fully extended solar sail looks after deployment. Credits: NASA*

The composite booms are 7 meters long and are made of a polymer material that is flexible and reinforced with carbon fiber. This makes the structure very stiff and resistant to warping due to temperature changes.

Attitude Control System Awaiting Reactivation

Mission operators are now working to reposition the spacecraft. During the deployment of the solar sail, the mission team had disabled the attitude control system to better manage the dynamics of the spacecraft as the sail opened.

This system is critical to maintaining the correct orientation of the spacecraft relative to various references in space, such as the Sun or ground stations. For example, it allows the solar panels to be properly aligned with the sun to optimize energy harvesting and ensure stable communications with Earth.

*Engineers at NASA’s Langley Research Center test deployment of the ACS3’s solar sail. Credits: NASA*

Currently, the spacecraft is in a low-energy mode. The mission prioritizes conserving energy resources, particularly to maintain reliable communications with the ground control center, until the solar panels are optimally aligned.

When the attitude control system is reactivated, operators will be able to take new measurements of the shape and behavior of the sail to ensure accurate calibration before the first sailing maneuvers.

These maneuvers will mark a key phase of the mission: the practical test of the sail’s ability to perform autonomous movements using only solar pressure. If successful, the ACS3 could represent a revolution for future space exploration.

Towards more distant exploration

The data already collected from the deployment of the sail and its slow stabilization is very promising. Even with the bending of the boom, the mission has already demonstrated the effectiveness of composite materials and automated deployment technology.

Solar sails, moreover, can operate indefinitely, limited only by the durability of the solar sail materials and spacecraft electronic systems in the space environment. This technology is particularly attractive for missions designed to explore distant regions of the solar system where refueling would be impractical.