English (United Kingdom)

https://curated-unify.zendy.io/wp-json/zendy-region/v1/featured_content/oa?rat=en

https://curated-unify.zendy.io/wp-json/zendy-region/v1/highlighted_journal/

Global: Zendy Plus annual

Presents the access of premium content as premium feature

Premium Content

Presents the keyphrase highlighting as premium feature

Keyphrase Highlighting

Presents the summarisation as premium feature

Summarisation

Insights

Presents the pdf analysis as premium feature

PDF Analysis

Presents the zaia usage as premium feature

ZAIA

Global: Zendy Plus monthly

Global: Zendy Tools annual

Global: Zendy Tools monthly

Global: Zendy Free Plan

The goal of ultrathin lightweight photophoretic flyers, or light-flyers forshort, is to levitate continuously in Earth's upper atmosphere using onlysunlight for propulsive power. We previously reported light-flyers thatlevitated by utilizing differences in thermal accommodation coefficient (TAC)between the top and bottom of a thin film, made possible by coating their lowersurfaces with carbon nanotubes (CNTs). Such designs, though successful, werelimited due to their high thermal emissivity (>0.5), which prevented them fromachieving high temperatures and resulted in their transferring relatively lowamounts of momentum to the surrounding gas. To address this issue, we havedeveloped light-flyers with undoped germanium layers that selectively absorbnearly 80% of visible light but are mostly transparent in the thermal infrared,with an average thermal emissivity of <0.1. Our experiments show thatgermanium-coated light-flyers could levitate at up to 43% lower lightirradiances than mylar-CNT disks with identical sizes. In addition, wesimulated our experiments using a combined first-principles-empirical model,allowing us to predict that our 2-cm-diameter disk-shaped germanium-coatedlight-flyers can levitate in the mesosphere (altitudes 68-78 km) under thenatural sunlight (1.36 kW/m2). Similar ultrathin selective-absorber coatingscan also be applied to three-dimensional light-flyers shaped like solarballoons, allowing them to carry significant payloads and thereby revolutionizelong-term atmospheric exploration of Earth or Mars.

Photophoretic Light-flyers with Germanium Coatings as Selective Absorbers