What are Solar Sails

Solar sails are a flight-proven spacecraft design. They use large, highly reflective, lightweight sails to reflect sunlight. Though particles of light, photons, have no rest mass, they do have momentum. The momentum of the photons is converted to momentum for the spacecraft. The continuous photon pressure from the Sun’s rays, combined with gravitational forces, provide thrust without any need for heavy, expendable propellants. Solar sails can operate for much longer periods than conventional chemical and electric propulsion systems.

Solar Sailing History

The Solar Cruiser Mission is leveraging solar sail technology advancements from the last decade. Such advancements have been made possible by test flights of smaller sails such as:

NASA’s NanoSail-D Mission
Japan’s Aerospace Exploration Agency’s Interplanetary Kite-craft Accelerated by Radiation Of the Sun (IKAROS) Mission
The Planetary Society’s LightSail Missions
NASA’s Near-Earth Asteroid (NEA) Scout and ACS3

The Solar Cruiser:

Mission Design & Purpose

The Solar Cruiser Mission was initiated by NASA’s heliophysics division to expand our ability to study the Sun. Reasons to develop the Mission include:

Technology demonstration of larger solar sail
Learning how to sail in the unique orbital environment of L1
Carrying sun-monitoring equipment closer to the Sun than current instruments
Earlier warnings for solar storms that impact astronauts and satellites

Much like the innovation of sails allowed ocean going ships to travel further and more efficiently than humans rowing, solar sails have the potential to revolutionize space exploration by using solar radiation pressure instead of fuel. NASA selected the Solar Cruiser Technology Demonstration Mission to develop the largest solar sail ever flow. The Solar Cruiser spacecraft’s 1653m² is made from a 2.5-micron thick material that is thinner than a human hair. The sail is deployed with four 29.5-m, lightweight, composite booms. It is kept stable with embedded Reflective Control Devices, composed of a thin film that can be switched from reflective to transmissive with an applied voltage. Solar Cruiser will use an Active Mass Translation device to actively adjust the spacecraft center of (light) pressure relative to its center of mass to keep the sail stable and to support steering and navigation. This mission will advance our understanding of how to build, deploy and fly solar sails capable of carrying useful payloads on long-duration missions.

Solar sailing will allow the Solar Cruiser to fly in new and unique orbits and collect observations from novel vantage points. Specifically, Solar Cruiser was proposed to maintain a position sunward of Lagrange point L1. The Earth-Sun L1 point is where where Earth’s and the Sun’s gravity are balanced along the Sun-Earth-line. Because the solar radiation pressure applies a steady force on solar sails, the Solar Cruiser would actually fly closer to the Sun than the L1 point. This sunward point is referred to as ‘L1 prime’, ‘effective L1’ or more properly ‘displaced L1’. Orbiting displaced L1 for any significant duration is not possible with chemical propellant rockets. From displaced L1, the Solar Cruiser would use solar sailing to raise it’s orbit to a higher inclination. This mission would advance our ability to fly new types of missions with more efficient resource usage.

Studying the Sun is important for our scientific understanding of the universe. Our Sun is the only star we can get close to, NASA’s Heliophysics Division initiated the mission to get better observations. Our Sun sends out a steady outpouring of particles and energy as well as a constantly writhing magnetic system. This extensive, dynamic solar atmosphere surrounds the Sun, Earth, the planets, and extends far out into the solar system. Solar Cruiser would join a fleet of 31 spacecraft observing aspects of the Sun.

Monitoring the Sun at displaced L1 is of interest not only for basic science, but also for astronauts and satellite safety. Coronal mass ejections from the Sun cause fluctuations in the solar wind, and occasionally these events are strong enough to disrupt communications satellites, overload long-distance power lines, interfere with navigation systems and radio communication, pose dangers to astronauts, and other threats. Because solar sails at L1 would fly closer to the Sun than other L1 satellites, they offer advanced warning. NOAA continues to fund the Solar Cruiser development.

Even without the Sunshade, the Solar Cruiser is an important mission to fly. Given the urgent need to address runaway warming on earth, the Solar Cruiser is even more important.

Solar Cruiser would be the first Sunshade Element

The Planetary Sunshade would be a constellation of objects near Earth-Sun Lagrange 1 that block a fraction of the earth’s sunlight. These objects would need to maintain their position over time and block a predictable amount of sunlight. Solar sail craft are a great tool for this task.

The Solar Cruiser mission would be very valuable for the development of the Planetary Sunshde concept because it would demonstrate solar sailing at displaced L1 and increase our understanding of larger solar sail technology. There’s no substitute for real world experience.

Watch Les Johnson describe the Solar Cruiser

Current Status of Solar Cruiser: Stalled

Despite the Solar Cruiser's importance to science and investment to date, it is not currently funded to fly.

NASA’s Science Mission Directorate Program Management Council met on June 28, 2022, to evaluate whether the Solar Cruiser project was ready to proceed to the next phase, in which the spacecraft would have been built. The Council determined that the project had not demonstrated an ability to meet its launch readiness date and stay within the established cost requirements. As a result, the project was not confirmed, meaning it would not move forward. (Credit: Planetary Society)

Although the Solar Cruiser mission has not yet been approved to advance to phase C of its development life, its team continues to develop and advance these key technologies as well as the demonstration of a sail deployment of this size. As of now, NASA has spent $30M on the Solar Cruiser mission. NOAA has also invested in the technology and continues to support mission development.

If NASA was to fly this mission, launch opportunities are available as early as 2028.

Planetary Sunshade Next Steps

Given the importance of researching and developing a sunshade, congress should allocate the necessary funds to fly the Solar Cruiser.

The Sunshade Foundation believes that the solar Cruiser mission has demonstrated flight readiness within reasonable margins and should continue to receive funding.

The Planetary Sunshade Foundation asks Congress to fully fund the Solar Cruiser mission. There is strong precedent for this advocacy and its success. In the past decade, US citizens organized by the Planetary Society have grown the planetary exploration budget by $1.5B. They advocated for the including cameras on the Voyager missions, creating the New Horizons mission to Pluto, and is currently lobbying to get the VERITAS mission to Venus back on track, to name a few. Our voices can play a critical role in making the Solar Cruiser mission a reality.

How you can help

In the United States, we have the ability to educate our congressional representatives about the importance of the Solar Cruiser mission. But we can’t do it alone! If you’d like to be involved in this effort, get in touch!

Advocacy

NASA’s Solar Cruiser Mission