NASA Making Better Starshades to Help Us Find Exoplanets

Starshade-based methods, both for in-space observatories like the Habitable Worlds Observer or ground-based observatories, have the potential to increase our observational capability without launching ever increasing telescope apertures. Construction of these starshades with the necessary low mass, stability, precision, launch volume, and size (>100m for some missions) remains a challenge, since loading can be significant for ultra-light structures during slewing and station keeping during observations. A key challenge to finding exoplanets is blocking the star’s light, which is about 10 billion times brighter than the planet’s reflected light.

The discovery of exoplanets in the habitable zone is one of the highest priorities in astrophysics. However, direct imaging would benefit immensely from much larger telescopes apertures than the James Webb Space Telescope, which already pushed the limit of deployable technologies and programmatic/budgetary capabilities. Large-scale space structure designs are often driven by dynamic stability requirements that are linked to precision requirements. Traditional materials inherently trade-off between stiffness and damping, which limits the operational capabilities and dynamic precision of resultant space structures. Recent advances in dissipative metamaterial and phononic crystals present an opportunity to disrupt this trade-off, creating high-stiffness and high-damping structures, as well as structures with phononic band gaps (i.e., the forbidden frequency range for the propagation of mechanical waves) for mode suppression. This study will design a starshade structure that utilizes novel dissipative and phononic metamaterials to design ultra-stable occulter structures at a fraction of the mass of traditional deployable designs. By enabling lower mass starshades with lower fuel requirements, this technology can transform our ability to discover exoplanets.

Christine Gregg discussed the project and explaining how architected metamaterials could enable on-orbit assembly of starshades, reducing the need for massive deployable systems like those in the James Webb Space Telescope.

She highlighted the role of dissipative metamaterials in managing vibrations over space-relevant temperature ranges and phononic crystals for creating “forbidden” frequency bands to prevent unwanted resonances.

The James Webb Space Telescope has been successes in observing the distant universe and exoplanets. Future missions like the Habitable Worlds Observatory will be designed to directly image Earth-sized planets around Sun-like stars. Two methods are used to block the superbright light of a star an onboard coronagraph or a separate large structure in space called a star shade.

Star shades must be repositionable for observing multiple stars, requiring rigidity to avoid wobbling during movement for efficient observations. This leads to the need for innovative materials.The guest, Christine Greg from NASA Ames Research Center, is introduced. She is working on a NIAC (NASA Innovative Advanced Concepts) proposal with a team to use meta-materials for star shades. Meta-materials involve bonding multiple materials to achieve enhanced properties, specifically increased stiffness in space to minimize wobbling after repositioning.

Christine Greg says advances in 3D printing and manufacturing have enabled meta-materials, which she defines broadly as human-designed substructures (from atomic to larger scales) that yield properties not found in nature. Her focus is on mechanical meta-materials, which offer superior stiffness-to-weight ratios, better vibration damping, or unique effects. She also touches on electromagnetic meta-materials for optical or RF applications, like cloaking, describing the field as “science fiction and magic.”

Christine emphasizes the multidisciplinary nature, involving deployables, materials, and manufacturing. She credits her large team for combining expertise, as her strengths are more in mechanical aspects than electromagnetics.

NIAC Proposal: Meta-Materials for Star ShadesChristine describes star shades as structures that block starlight to reveal faint planetary reflections, enabling the study of habitable worlds close to stars. Her NIAC proposal aims to build star shades using meta-materials, robotic assembly, and deployment, targeting the same mission as another NIAC awardee, John Mather (a Nobel Prize winner), who is exploring inflatables. The proposals are complementary, not competitive, with Mather supporting hers.

Traditional star shade designs (e.g., for HabEx or Habitable Worlds Observatory) involve a folded cylinder that unfurls into a petal-like flower to block light. Christine’s approach uses robotic agents to assemble elements in space, achieving the same shape but with enhanced dynamics. The Habitable Worlds mission requires rapid repositioning during observations, demanding tight dynamic control for a 100-meter structure—it must settle quickly without prolonged wobbling.

The key innovation is “meta-damping materials,” developed with collaborators Professor Sharif Tol (University of Michigan) and Professor Alper Erturk (University of Texas at Austin). These materials defy the usual tradeoff: higher stiffness typically means less damping. By designing the substructure with multiple materials, they achieve twice the damping for the same stiffness-per-weight ratio. This allows lighter structures that settle faster after movement, reducing mission costs (e.g., less fuel needed) and enabling more observations.For the star shade, this means rigid petals that minimize flapping during repositioning.

Compared to deployables (e.g., JPL’s unfurling design), her assembled version could offer similar performance at lower weight, as parts don’t need to survive launch loads intact. However, joints for assembly add complexity, so the NIAC Phase 1 grant focuses on estimating mass scaling and tradeoffs versus deployables or inflatables. Deliverables include recommendations on redesigning with robotic assembly for better mass efficiency.Broader Discussion on In-Space Assembly and ManufacturingThe conversation expands to in-space assembly, citing the International Space Station (ISS) as a successful example (modules assembled via space shuttle, astronauts, and robotic arms). Despite this, it hasn’t been widely repeated (though Lunar Gateway may revive it). Christine sees low-hanging fruit in assembling basic truss structures, with Earth demos and commercial robotic arms (flight-qualified, off-the-shelf) making it feasible soon.

She envisions a continuum: from one-time module docking to hundreds of operations (e.g., building long booms from sticks) or even assembling PCBs in orbit.Robotics could enhance deployables, not replace them—e.g., repositioning deployed parts. She advocates starting simple: repositioning or basic trusses.

Christine highlights other projects from NASA’s Advanced Composite Structures Lab at Ames.

Robotic building blocks: Lightweight, stiff, autonomous meta-materials like truncated cubes (cubes with corners cut off), resembling dodecahedrons. These are 3D-printed or injection-molded, forming Tinker Toy/Lego-like sets for automated construction.

Metallized structures will combine structural and electromagnetic properties. The structures can act as antennas or lenses (not just supporting them).

These use injection molding for high precision and scalability (thousands of parts), with materials like carbon-fiber-reinforced plastics (stiffer than standard 3D-print plastics), aluminum, or steel. Injection molding offers machining-level precision, enabling precise large structures (error below measurement noise). Examples include the MadCat project: a wing from injection-molded octahedra connected by bolts.She contrasts this with 3D printing in space (e.g., on ISS), favoring pre-manufactured parts sent up in “bags” for robotic assembly as a near-term step. Long-term, hybrid approaches could combine manufacturing methods based on needs.Topologically, she’s a fan of octet lattices for high stiffness (due to connectivity avoiding bending, favoring axial loads like triangles vs. squares in 3D).

Her current interest: two-unit-cell tilings (combining two geometries), expanding design space for better properties. Examples include inserting cross shapes on planes or soccer ball-like hexagons with pentagons, unlocking new topologies.