Everyone understands that solar energy is abundant and practically limitless here on Earth. The same principle applies to spacecraft operating in the inner Solar System. In space, the Sun not only provides electrical energy but also emits a continuous stream of solar wind.

Solar sails have the capability to harness this wind and offer propulsion for spacecraft. NASA is on the verge of testing a new solar sail design that could enhance the effectiveness of solar sails even further.

Solar pressure is prevalent throughout the entire Solar System. While it diminishes with distance, it remains present and impacts all spacecraft, including satellites. For longer-duration space missions, solar pressure can cause substantial deviations in a spacecraft’s path. It also affects a spacecraft’s orientation, necessitating specific design considerations to address these challenges.

Despite its hindrances, solar pressure can be turned into an advantage.

Several solar sail spacecraft have been launched and tested, starting with Japan’s Ikaros spacecraft in 2010. Ikaros demonstrated that radiation pressure from the Sun, in the form of photons, can be utilized to control a spacecraft. The most recent solar sail spacecraft is the Planetary Society’s LightSail 2, launched in 2019, which successfully completed a mission lasting over three years.

One of the key advantages of solar sail spacecraft is their extremely lightweight and perpetual propulsion systems that do not require refueling. This characteristic allows solar sail spacecraft to conduct missions cost-effectively and for extended periods, despite some inherent limitations.

The viability of solar sail technology has been demonstrated, but further technological advancements are necessary for optimal effectiveness. A critical component of a solar sail spacecraft is its booms, which provide structural support to the sail material. The lighter and stronger the booms are, the more efficient the spacecraft will be. Despite being significantly lighter than other spacecraft components, the weight of the booms remains a limiting factor.

NASA is preparing to launch a new solar sail design featuring an advanced support structure. Known as the Advanced Composite Solar Sail System (ACS3), this design utilizes carbon fibre and flexible polymers to create stiffer and lighter booms compared to previous iterations.

While solar sails boast numerous advantages, they face a crucial drawback in their deployment process. These sails are launched in compact packages that must be unfurled in space before becoming operational, a task riddled with complexities and uncertainties that put significant pressure on ground crews anxiously awaiting the outcome.

The upcoming launch of ACS3, accompanied by a twelve-unit (12U) CubeSat built by NanoAvionics, aims to demonstrate successful boom deployment and validate the spacecraft’s overall functionality. The ACS3 team envisions potential maneuvers with the spacecraft, adjusting its orbit by angling the sails once the boom deployment is achieved. This undertaking could pave the way for the development of larger sails capable of generating increased thrust.

The ACS3 boom design represents a breakthrough in addressing the long-standing issue of cumbersome and inefficient booms. Keats Wilkie, NASA’s ACS3 principal investigator at Langley Research Center, highlighted the challenges associated with current boom designs and emphasized the need for large, stable, and lightweight booms that can be compactly stowed for solar sail spacecraft.

The upcoming launch of ACS3, scheduled on an Electron rocket from Rocket Lab’s launch complex in New Zealand, is slated to reach a Sun-synchronous orbit 1,000 km (600 miles) above Earth. Upon arrival, the spacecraft will initiate the unfurling process of its booms and deployment of the sail, which is expected to take around 25 minutes and provide a photon-gathering area of 80 square meters. This significantly larger sail area compared to LightSail 2’s 32 square meters signifies a step forward in solar sail technology advancement.

During the deployment process, onboard cameras will monitor the shape and symmetry of the sail to gather crucial data for future sail designs.

Alan Rhodes, the lead systems engineer for the mission at NASA’s Ames Research Center, highlighted the compact and versatile nature of the new composites boom design, emphasizing its potential to inspire novel applications and configurations in the aerospace industry.

The ACS3 project falls under NASA’s Small Spacecraft Technology program, aimed at rapidly deploying small missions to demonstrate unique capabilities. With the innovative composite and carbon fibre booms featured in the ACS3 system, the potential for supporting sails as large as 2,000 square meters opens up new opportunities for significant scientific missions.

Rhodes emphasized the enduring nature of the Sun as a boundless propulsion source, providing a sustainable alternative to traditional fuel-based missions. The versatility and potential of solar sails to power expansive scientific endeavors underscore the importance of continued advancements in solar sail technology.

While solar sail spacecraft may not offer immediate thrust comparable to chemical or electrical propulsion systems, their constant and unwavering propulsion capabilities enable unique positioning for solar observations and serve as critical early warning systems for solar hazards like coronal mass ejections. Moreover, the lightweight and robust nature of the new composite booms presents possibilities for diverse applications beyond spacecraft propulsion, such as supporting extraterrestrial habitats and communication systems.

Rudy Aquilina, the project manager for the solar sail mission at NASA Ames, emphasized the transformative potential of solar sail technology and lightweight composite booms in reshaping the future of space exploration and inspiring innovative missions yet to be conceived.