Solar sails

Also known as Solar sail, Solar sailing

Solar sails are large, very thin reflective membranes that change a spacecraft's speed or orbit using the small, steady push of sunlight rather than fuel. Japan's IKAROS (2010) and NASA's LightSail 2 (2019) showed the method works in space, but the push is very small and the sail must unfold and survive in orbit.

Research and prototypesDemonstratedReviewed 22 Oct 2026
AI illustration · Illustrative scene, not a photograph of the specific device or experiment.

In plain language

Light carries momentum, so when it hits a surface it pushes on that surface. Sunlight pushes on a spacecraft all the time, but the force is tiny. A solar sail is a large, lightweight reflective sheet that is folded up for launch and then unfolded in space, so that the sunlight's push adds up over many hours and days.

Japan's IKAROS spacecraft flew a sail about 14 metres square in 2010. NASA's LightSail 2 used a 32 square metre sail and changed its orbit around Earth in 2019. NASA's ACS3 mission in 2024 tested a lighter boom design, but it did not meet its main goal of showing that the sail could push the spacecraft. Sails are slow, because they push gently and constantly, and they only work if the sail unfolds reliably after launch.

Technical explanation

Solar radiation pressure gives a sail a thrust that is proportional to its area and falls with distance from the Sun. Because the force is so small, a sail needs a large area and a low mass per unit area. IKAROS's sail was a square polyimide membrane with a side of about 14 metres and a thickness of 7.5 micrometres, on a spacecraft of about 310 kilograms at liftoff (JAXA). JAXA estimated the solar-pressure thrust at 1.12 millinewtons. It described this as the expected value and derived it from orbit determination, which fits the orbit data to a model rather than measuring the force directly. JAXA also reported that light pressure deforms the sail in orbit, so the effective sail area and optical behaviour can differ from design values.

Mechanical design is a recurring constraint. The ACS3 mission used carbon-fibre-reinforced polymer booms, each about 7 metres long, to hold a sail of about 81 square metres, and NASA says the booms are 75% lighter than previously flown metallic deployable booms (NASA). NASA's 2026 state-of-the-art report says the sail was deployed before the spacecraft was decommissioned in 2026, but the main objective of showing the sail's propulsive capability was not achieved. During IKAROS's deployment, ground data were lost for about an hour (JAXA). JAXA's project page reports that IKAROS entered hibernation mode in May 2015; the sources reviewed here do not confirm its current status.

In low Earth orbit, atmospheric drag can outweigh the sail's push. NASA's 2026 report says LightSail 2's sail could overcome drag entirely on some occasions, and the spacecraft re-entered in late November 2022. Degradation is a separate concern: a 2025 Cal Poly master's thesis found that atomic oxygen erodes aluminised Mylar drag-sail material, and that vacuum ultraviolet added no further measured deterioration at the exposures tested. Those are laboratory results, not long-term in-orbit data.

What the evidence says

Each statement is typed by the strength of its evidence and linked to the source that supports it.

Demonstrated Shown in a published experiment, test or shipping product.

IKAROS carried a square polyimide sail about 14 metres per side and 7.5 micrometres thick, on a spacecraft of about 310 kilograms at liftoff.

Sources: [2] · Spacecraft specification table

Ground data from IKAROS were lost for about one hour during sail deployment.

Sources: [1] · Confirmation of photon acceleration · medium confidence

LightSail 2, a 3U CubeSat with a 32 square metre sail, changed its orbital altitude around Earth with solar sailing, which NASA says showed that solar sail technology can be used in low Earth orbit.

Sources: [3] · Section 13.3.1, High TRL Drag Sails

NASA's ACS3 sail was deployed before the spacecraft was decommissioned in 2026, but the main objective of showing the sail's propulsive capability was not achieved.

Sources: [3] · Section 13.3.1, High TRL Drag Sails

NASA's NEA Scout was launched on 16 November 2022, and NASA reports that its project team could not communicate with the spacecraft after launch.

Sources: [5] · Mission description

In a 2025 Cal Poly master's thesis, aluminised Mylar drag-sail material exposed to atomic oxygen in ground tests showed degradation that was modelled against atomic oxygen fluence, and vacuum ultraviolet added no further deterioration at the exposures tested.

Sources: [6] · Abstract · medium confidence

Reported, unverified Stated by a company or team but not independently confirmed.

JAXA estimated IKAROS's solar-pressure thrust at 1.12 millinewtons from orbit determination. It described this as the expected value, not a direct measurement.

Sources: [1] · Confirmation of photon acceleration · medium confidence

NASA says ACS3's composite booms are about 7 metres long, reinforced with carbon fibre, and 75% lighter than previously flown metallic deployable booms.

Sources: [4] · Mission overview · medium confidence

Proposed A design or plan that has not yet been built or tested.

The Breakthrough Starshot concept proposes a laser-pushed gram-scale nanocraft and says its light propulsion system is on a scale significantly exceeding any currently operational analogue.

Sources: [7] · Concept overview

Limitations and open problems

  • Thrust is very small. IKAROS's estimated solar-pressure thrust was 1.12 millinewtons, so orbit changes build slowly.
  • Deployment is hard to get right. IKAROS lost ground data for about an hour during deployment, and ACS3 did not meet its main propulsion objective.
  • Light pressure changes the sail's shape in orbit, so the thrust and effective area can differ from design values.
  • Atmospheric drag in low Earth orbit can outweigh the sail's push. LightSail 2's sail overcame drag only on some occasions.
  • Atomic oxygen erodes aluminised Mylar in laboratory tests. The sources reviewed here include no long-term in-orbit measurements of membrane degradation.

Possible future uses

Speculative

Ideas, not predictions. None of these has been demonstrated.

  • Slow, propellant-free orbit changes for small spacecraft that need to move between orbits without carrying fuel.
  • End-of-life removal of satellites from orbit, using a sail to increase drag or light pressure on the spacecraft.
  • Laser-pushed interstellar sails, such as the Breakthrough Starshot concept. This is a proposal only and is not demonstrated.

Timeline

  1. 21 May 2010JAXA launches IKAROS, a small solar power sail demonstrator with a sail about 14 metres square. Sources: [1], [2]
  2. 9 Jul 2010JAXA reports photon acceleration confirmed by orbit determination, with a solar-pressure thrust of 1.12 millinewtons described as the expected value. Sources: [1]
  3. Jun 2019LightSail 2, a 3U CubeSat with a 32 square metre sail, is launched and deployed from the Prox-1 satellite, then changes its orbit around Earth by sunlight. Sources: [3]
  4. 16 Nov 2022NASA's NEA Scout launches on a CubeSat that was to be propelled by a solar sail. NASA later reports that the project team could not communicate with the spacecraft after launch. Sources: [5]
  5. 23 Apr 2024NASA launches ACS3, a 12U CubeSat testing composite booms for a solar sail. Sources: [4], [3]
  6. 2026NASA decommissions ACS3 after the sail is deployed but its main propulsive objective is not met. Sources: [3]

Futures this could help bring about

AI illustration
How far away?

A probe to another star

Science demonstrated · 1 of 8 steps done

Related breakthroughs

Glossary

Solar radiation pressure
The small, steady force that sunlight exerts on a surface, because light carries momentum.
Orbit determination
Working out a spacecraft's path from tracking measurements, such as the Doppler shift of its radio signal.
Boom
A long, thin support arm that holds a sail flat and under tension.
Atomic oxygen
A reactive form of oxygen found in low Earth orbit that can erode many polymer materials.

Sources

  1. government report
    Small Solar Power Sail Demonstrator 'IKAROS' Confirmation of Photon Acceleration
    JAXA, 9 Jul 2010. Accessed 22 Oct 2026.
  2. government report
    Small Solar Power Sail Demonstrator "IKAROS"
    JAXA, 2026. Accessed 22 Oct 2026.
  3. government report
    Small Spacecraft Technology State of the Art, Chapter 13: Deorbit Systems (2026)
    NASA, May 2026. Accessed 22 Oct 2026.
  4. government report
    Advanced Composite Solar Sail System: Using Sunlight to Power Deep Space Exploration (ACS3)
    NASA, 19 Feb 2026. Accessed 22 Oct 2026.
  5. government report
    NEA Scout
    NASA Science, 2026. Accessed 22 Oct 2026.
  6. other
    Low Earth Orbit Drag Sail Degradation Due to Atomic Oxygen and Ultraviolet Radiation
    Hannah Rost. California Polytechnic State University (Cal Poly), master's thesis, Jun 2025. Accessed 22 Oct 2026.
  7. other
    Starshot concept
    Breakthrough Initiatives, 2026. Accessed 22 Oct 2026.

Revision history

3 changes since this profile was created.

Changes on 22 Oct 2026
Published on owner instruction (owner requested space, food and water topics)dc4cd89
Sources and claims re-checked against originals409337d
Initial profile drafted from primary sourceseaac9eb