Engineering

The best idea thus far.

A fleet of about 5,000 heliogyro shade craft (each weighing 13 kt and measuring 40km in diameter) positioned at Sun Earth Lagrange 1’, would achieve a 1% reduction in sunlight and reduce global average temperature by approximately 1℃. This design maximizes the use of lunar resources, which minimizes the number of launches from Earth. The 10km long blades are aluminum, and the 10km long cables are silicon. The central hub of each craft would be manufactured on Earth, containing each craft’s computer, avionics, batteries, communications, sensors and motors.

Other Sunshade Concepts

A sunshade could be constructed in many ways.

Proposals include large solar sails launched from Earth and sailed to SEL1’, millions of tiny sails, space bubbles, dust clouds, repositioned asteroids, and more. Any sunshade design must account for the solar radiation pressure and the slight instability of the SEL1’ region.

Could a sunshade be built with lunar resources?

The Planetary Sunshade Institute’s heliogyro concept works backward from the total mass and energy requirements of the system. While sunshade technology demonstrations and initial structures would almost certainly come from Earth, several factors make it very likely that lunar resources would end up being the source of the vast majority of mass.

  • The moon’s gravity is a fraction of Earth’s, so lifting mass from the surface of the moon to SEL1’ requires only about 1/35th of the fuel.
  • Components for rocket fuel (hydrogen and oxygen) exist on the lunar surface.
  • Kinetic options like a mass driver or spin launch are more feasible from the moon than Earth due to lower gravity and the absence of atmosphere.
  • Components for building a sunshade, aluminum and silicon, are abundant.
  • As the scale of an industrial supply chain increases, the incentive to find efficiencies also increases. Effectively using lunar resources offers an orders-of-magnitude efficiency, and therefore profitability, for sub-contractors.
  • The Planetary Sunshade Institute works closely with lunar industrialization company Ethos Space to advance these concepts.

Could a sunshade also generate solar power?

Large, flat structures in space can be designed to include photovoltaic panels to produce electricity. However, the heliogyro design does not generate power beyond the small amount needed to operate itself. This is because, to maximize shading with a given amount of mass, the materials are optimized for a specific purpose.

Instead of generating power directly with a sunshade, think of sunshades as one part of an industrial space economy. Before we can build sunshades at scale, we first need to manufacture solar panels from lunar resources at scale. Doing this creates the power needed to make more power, more mining, sunshades, data centers and any other use case.

What if a sunshade is no longer needed?

Sunshades are controllable. Some or all of them could be moved out of the way if not needed temporarily, and recycled when they are no longer needed permanently.

What happens if a sunshade fails?

Individual sunshade spacecraft will fail. The factory operation producing sunshades would maintain a low level of operation to replace sunshades. The orbits of sunshade elements must be designed such that failures minimize risk to other elements. Relative speeds in the SEL1 region are very low, in contrast to low earth orbit.

Positioned outside of Earth’s gravity well, sunshades maintain a delicate balance with solar radiation pressure at an equilibrium point. However, as a sunshade becomes less reflective—due to material degradation and micrometeoroid impacts—it receives less solar radiation pressure. Consequently, the sunshade is pulled closer toward the Sun rather than toward Earth.

More research is needed to explore all possible failure modes and resulting orbital trajectories.

What happens if a sunshade is hit by an asteroid?

Individual sunshade elements will be hit by micrometeoroids and asteroids. Most of these area of a sunshade is the blades, and small impacts will create small holes in the blades which are designed to prevent spreading. Asteroid strikes to more critical elements could break the sunshade element, requiring it to be replaced.

What would happen if a sunshade is hit by a solar storm? 

Impacts on electronics: The electronics of sunshade elements, like all spacecraft, must be properly shielded from solar storms.

Impacts on the sail position: The pressure exerted by the solar wind—composed of charged particles—is typically three orders of magnitude weaker than the solar radiation pressure exerted by photons. While coronal mass ejections can increase this particle pressure by a factor of 100, the force remains smaller than the light pressure for station-keeping. Consequently, solar storms have a small direct mechanical effect on a sunshade’s orbital stability.


The Planetary Sunshade Institute is a U.S.-based, registered 501(c)3 nonprofit organization.
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