Inflatable StarShade Will Be Used to Image Earthlike Exoplanets

John Mather, NASA Goddard Space Flight Center, is designing the first family of ISEE’s (Inflatable Starshade for Earthlike Exoplanets) with sizes from 35 to 100 meters in diameter. A starshade would enable any telescope to observe exoplanets, a top priority for astronomy worldwide. Compared with other starshade concepts, they aim for a lower mass, cost and complexity, while still providing high performance and science yield (over 100 targets).

The project received funding as a Phase I award under NASA’s Innovative Advanced Concepts (NIAC) program in January 2025.

The starshades would be compatible with the 6 meter diameter Habitable Worlds Observatory (HWO) now being planned, as well as the world’s largest telescope, the 39 meter diameter European Extremely Large Telescope now being built in Chile, working as part of the HOEE, (Hybrid Observatory for Earthlike Exoplanets), and other future telescopes. They need to observe oxygen at visible wavelengths and ozone at UV. The Habitable Worlds Observatory (HWO) was proposed for 2041. HWO’s main objective would be to identify and directly image at least 25 potentially habitable worlds. It would then use spectroscopy to search for chemical biosignatures in these planets’ atmospheres, including gases such as oxygen and methane, which could serve as critical evidence for life.

The Hybrid Observatory for Earth-like Exoplanets (HOEE), which was a 2022 NASA NIAC Phase I award. They proposed the first hybrid observatory, combining a 100 meter diameter starshade in space with a telescope on the ground. The Hybrid Observatory for Earth-like Exoplanets (HOEE) would convert the largest ground-based telescopes now under construction (Giant Magellan Telescope, Thirty Meter Telescope, and Extremely Large Telescope) into the most powerful planet finders yet designed. An ultra-lightweight redesign will be developed that can be built or assembled in space. The objective is to cut the starshade mass by more than a factor of 10. There is no reason to require thousands of kg to support 400 kg of thin membranes. A 2025 paper analyzed the design and performance. The HWO is expected to take cost $11 billion and launch in the first half of the 2040’s.

Key optical tolerance results confirm that the 99-m starshade is significantly less affected (improved contrast by 100 to 1000×) by optical tolerances compared with smaller starshades such as HWO, considering the proportional perturbation sizes. The next steps involve addressing mechanical design requirements and deploying the starshade into space. Future research will explore inflatable structures to achieve a highly compact and deployable mission within reasonable mass and fuel budgets. These advancements pave the way for uniquely exploring the habitable worlds and future cosmic mysteries through hybrid space-ground observatories.

Integrated photonic-based coronagraphic systems for future space telescopes Photonic technologies could potentially doubling exo-Earth yield. There is work on photonic coronagraphs and potential of hybridized designs which combine both classical coronagraph designs and photonic technologies into a single optical system. Researchers presented two possible systems.

1. a hybrid solution which splits the field of view spatially such that the photonics handle light within the inner working angle and a conventional coronagraph that suppresses starlight outside it. 2. a hybrid solution where the conventional coronagraph and photonics operate in series, complementing each other and thereby loosening requirements on each subsystem. As photonic technologies continue to advance, a hybrid or fully photonic coronagraph holds great potential for future exoplanet imaging from space.

New 2025 Inflatable Starshades

An ISEE, positioned between a target star and the telescope, would block the starlight without blocking the exoplanets. Starshades have perfect optical efficiency, they work with any telescope, and they can block the starlight much better than the requirement, for a star over 10 billion times brighter than the target.

The competing technology uses a nearly perfect and perfectly stable space telescope like HWO, with an internal coronagraph, to keep the starlight away from the image of the planet. Coronagraphs have the key advantages that they are compact, testable, and have instant availability. However, tested coronagraphs have not yet met the contrast requirement. Moreover, there is no possibility of an ultraviolet coronagraph. If the extreme picometer stability and optical perfection requirements on HWO and its coronagraph could be relaxed by using it with a starshade, then HWO itself could be built at much lower cost and risk. If UV observations of exoplanets are essential, then a 35 m starshade with HWO is the only possible solution.

The HWO will be NASA’s next great observatory, and it will include a high performance coronagraph to observe exoplanets. This choice changed the landscape for the competing starshade technology. A starshade mission could still become necessary if: A. The HWO and its coronagraph cannot be built and tested as required; B. The HWO must observe exoplanets at UV wavelengths, or a 6 m HWO is not large enough to observe the desired targets; C. HWO does not achieve adequate performance after launch, and planned servicing and instrument replacement cannot be implemented; D. HWO observations show us that interesting exoplanets are rare, distant, or are hidden by thick dust clouds around the host star, or cannot be fully characterized by an upgraded HWO; or E. HWO observations show that the next step requires UV data, or a much larger telescope, beyond the capability of conceivable HWO coronagraph upgrades.

An inflatable starshade would overcome the main obstacle to starshades: their mechanical design. Starshades have never been flown, they have strict shape and edge requirements, and they must be propelled and precisely positioned. Prior designs based on discrete elements can be scaled up to the size required for HWO (35-60 m) and HOEE (100 m), but they are massive and hard to test leading to high cost and risk. The mass budget aims for 250 kg for the 35 m HWO case, 650 kg for the 60 m case and 1700 kg for the 100 m HOEE case.We will extend our ideas and produce detailed designs and finite element models, suitable for strength, stiffness, stability, and thermal analysis. They will develop small-scale laboratory test equipment and verify solutions to issues like bonding large sheets of high-strength material into inflatable systems. Deliverable items would include mass/power budgets, strength and stiffness, and lab tests of critical items. They will update mission concepts for HWO and HOEE based on the starshade parameters.

Depending on progress with the HWO mission, starshades could be required to complete our knowledge of exoplanets. An inflatable starshade could make them possible.