The LightSail 2 spacecraft represents a significant milestone in the development of solar sailing technology, demonstrating a novel way to navigate through space using only the power of sunlight. Funded and developed by the Planetary Society, this small, innovative spacecraft continues to inspire both the space industry and the public alike. This article provides a detailed examination of LightSail 2, including its background, design, mission objectives, and broader significance to space exploration.

Background of Solar Sailing

Solar sailing is a propulsion method that relies on photons from the Sun to push a large, reflective sail attached to a spacecraft. While photons do not have mass, they possess momentum that can be transferred to the sail. Over time, this small but continuous push accelerates the spacecraft without the need for traditional fuel. Solar sailing is seen as an ideal method for long-term missions, particularly for deep space exploration, where carrying conventional propellant becomes impractical.

The idea of solar sailing has been around for decades, with early theoretical work dating back to the 1920s, but it wasn’t until the 21st century that the technology became practical for space missions. LightSail 2 followed its predecessor, LightSail 1, which served as a proof-of-concept for the concept of solar sailing. Both spacecraft were developed by the Planetary Society, a nonprofit organization that advocates for space exploration.

The LightSail Program

The LightSail program, initiated by the Planetary Society, is a crowdfunded project that aimed to demonstrate the feasibility of solar sailing in Earth’s orbit. The program consists of two primary missions:

• LightSail 1: Launched in May 2015, this was a suborbital test of solar sailing technology. LightSail 1 was a CubeSat that demonstrated successful deployment of a solar sail but did not operate long enough to test sustained propulsion. The mission provided valuable insights that led to the development of LightSail 2.
• LightSail 2: Launched in June 2019, LightSail 2 built upon its predecessor’s success and sought to achieve sustained propulsion using solar sails, something that had never been achieved by a small satellite before.

Spacecraft Design

LightSail 2 is a small, cube-shaped spacecraft known as a CubeSat, measuring just 10 x 10 x 30 centimeters when stowed. Despite its compact size, LightSail 2 features a large solar sail with an area of 32 square meters (about the size of a boxing ring). This sail is made of Mylar, a lightweight, reflective material ideal for capturing sunlight.

The spacecraft’s design consists of the following key components:

• Solar Sail: The most important feature of LightSail 2, the sail consists of four triangular segments that unfold in space. Once deployed, these segments form a large, continuous surface that catches sunlight.
• Attitude Control System (ACS): To maneuver the spacecraft and adjust its orientation relative to the Sun, LightSail 2 uses an attitude control system that relies on electromagnetic torque rods. These rods interact with Earth’s magnetic field to turn the spacecraft, allowing it to optimize its angle to the sunlight.
• Telemetry and Communications: LightSail 2 communicates with Earth through a small radio, transmitting data back to mission controllers and allowing them to monitor its performance.
• Power Supply: The spacecraft is powered by small solar panels that convert sunlight into electricity, providing energy for its systems.

LightSail 2 is an entirely autonomous spacecraft. Once it was launched, the spacecraft’s mission operations team sent commands to deploy the solar sail. From there, LightSail 2 relied on its onboard systems to navigate and maintain its sail position for optimal solar propulsion.

Mission Objectives

The primary mission objective of LightSail 2 was to demonstrate controlled solar sailing in Earth’s orbit. More specifically, the spacecraft sought to raise its orbit using sunlight alone. This would be achieved by adjusting the sail’s angle relative to the Sun, a technique known as “tacking” in sailing. By turning the sail to capture as much sunlight as possible during certain parts of its orbit, LightSail 2 could incrementally increase its altitude.

Additional mission goals included:

• Testing CubeSat Solar Sailing: LightSail 2 sought to prove that solar sailing could be effectively implemented in a small satellite, opening up new possibilities for cost-effective space missions.
• Engaging the Public: A secondary goal of the mission was to inspire the public and demonstrate the power of citizen-funded space exploration. LightSail 2 was largely funded by donations from space enthusiasts around the world.
• Providing Data for Future Missions: By collecting telemetry and operational data, LightSail 2’s mission would provide insights into solar sailing technology that could benefit future space missions, both government-funded and private.

Launch and Deployment

LightSail 2 was launched on June 25, 2019, aboard a SpaceX Falcon Heavy rocket as part of the U.S. Air Force’s STP-2 mission. The spacecraft was placed into an orbit about 720 kilometers above Earth. After deployment, LightSail 2 remained dormant for several days while the spacecraft was checked out and prepared for solar sail deployment.

On July 23, 2019, the sail was successfully deployed, marking the start of the mission’s primary phase. Over the following weeks, the spacecraft performed a series of maneuvers, adjusting the angle of the sail to maximize sunlight and gradually raising its orbit. This marked the first time that a small spacecraft achieved controlled solar sailing in orbit.

Achievements and Results

LightSail 2’s mission was a resounding success. The spacecraft demonstrated that solar sailing could be used to raise its orbit, and over the course of its mission, LightSail 2 increased its altitude by several kilometers. This achievement validated the effectiveness of solar propulsion in space and opened the door to future missions that could take advantage of this technology.

Some of LightSail 2’s key accomplishments include:

• First Controlled Solar Sailing in Earth Orbit: LightSail 2 became the first small spacecraft to successfully control its orbit using solar sailing, a groundbreaking achievement in the field of space propulsion.
• Public Engagement: The mission captured the imagination of the public, drawing attention to solar sailing as a viable method of space propulsion. The Planetary Society engaged its community through mission updates, educational materials, and real-time tracking of the spacecraft’s progress.
• Contribution to Solar Sailing Research: LightSail 2’s telemetry and operational data were shared with the global space community, providing valuable insights for future solar sail missions. This data will likely benefit both governmental and private efforts to develop solar sailing technology.

The Broader Significance of LightSail 2

LightSail 2’s success marks a turning point in space exploration. It demonstrated that small, low-cost spacecraft could utilize solar sailing for propulsion, significantly reducing the need for traditional propellant. This technology has far-reaching implications for future missions, particularly those aimed at deep space exploration.

Cost-Effective Propulsion

Solar sails could dramatically reduce the cost of space missions by eliminating the need to carry large amounts of fuel. For small satellites and CubeSats, which are already more affordable to build and launch than traditional spacecraft, solar sailing offers a compelling way to further reduce costs. This could open up space exploration to more universities, private companies, and other organizations that may not have access to large budgets.

Long-Duration Missions

Because solar sails do not rely on fuel, they can provide propulsion for extended periods. This makes them ideal for missions to distant destinations, such as the outer planets or even interstellar space. Solar sailing is seen as one of the most promising technologies for missions that need to operate over many years or decades.

Space Debris Mitigation

One of the most intriguing applications of solar sailing technology is its potential for mitigating space debris. Solar sails could be used to deorbit old satellites by gradually lowering their orbits, allowing them to burn up in Earth’s atmosphere. This would help address the growing problem of space debris in Earth’s orbit.

Challenges of Solar Sailing

While LightSail 2 was a major success, it also highlighted some of the challenges associated with solar sailing. For example, the spacecraft had to contend with atmospheric drag, which can slow down satellites in low Earth orbit. Additionally, solar sails require precise control and navigation, and the process of tacking can be slow, limiting the speed at which a spacecraft can change its orbit.

Furthermore, solar sails are not well-suited for missions that require high acceleration or quick maneuvers. As such, they are likely to complement, rather than replace, traditional propulsion methods in many space missions.

Summary

LightSail 2 represents a significant step forward in the field of space propulsion. By demonstrating controlled solar sailing in Earth’s orbit, it proved that small, low-cost spacecraft could use sunlight to navigate through space. The mission’s success opens up exciting possibilities for future space exploration, particularly for deep space missions and cost-effective small satellites. The data gathered from LightSail 2 will be invaluable for the continued development of solar sail technology, making it an important milestone in the history of spaceflight.