Belgium's Crown Princess Elisabeth, center, marches past the Royal tribune with cadets of the military school during the National Day parade in Brussels, Wednesday, July 21, 2021. Belgium celebrates its National Day on Wednesday in a scaled down version due to coronavirus, COVID-19 measures. (Photo by Olivier Matthys/AP Photo)

Principal of the Royal Ballet, Natalia Osipova, performs outside the Edinburgh International Conference Centre in Edinburgh, England on November 21, 2018, where she is starring in the new contemporary ballet “The Mother”. (PHoto by Jane Barlow/PA Wire via ZUMA Press)

Indian Hindu sadhus (holy men) from the Juna Akhara take part in a religious procession towards Sangam area, during the first “royal entry” for the Kumbh Mela in Allahabad on December 25, 2018. (Photo by Sanjay Kanojia/AFP Photo)

Rummaging in a bin for scraps, this fox in Barnet, north London, England found itself trapped in the lid on May 23, 2019. Luckily the Royal Society for the Prevention of Cruelty to Animals were able to free it. (Photo by RSPCA/PA Wire Press Association)

The Duchess of Cambridge comes down a slide during a visit to the LEGO Foundation PlayLab at the Carlsberg Campus, University College Copenhagen, Denmark, on day one of a two-day working visit with The Royal Foundation Centre for Early Childhood on Tuesday, February 22, 2022. (Photo by John Sibley/PA Wire Press Association)

Dancers Amy Hadley and Bethany Kingsley-Garner from the Scottish Ballet wait backstage during the dress rehearsal of the current production of “Sleeping Beauty” at the Theatre Royal on December 16, 2011 in Glasgow, Scotland. (Photo by Jeff J Mitchell/Getty Images)

“NASA's Pathfinder, Pathfinder Plus, Centurion and Helios Prototype were an evolutionary series of solar- and fuel-cell-system-powered unmanned aerial vehicles. AeroVironment, Inc. developed the vehicles under NASA's Environmental Research Aircraft and Sensor Technology (ERAST) program. They were built to develop the technologies that would allow long-term, high-altitude aircraft to serve as “atmospheric satellites”, to perform atmospheric research tasks as well as serve as communications platforms”. – Wikipedia

Photo: The solar-electric Helios Prototype flying wing is flies over the Hawaiian islands of Niihau and Lehua during the first solar-powered test flight July 14, 2001 from the U.S. Navy's Pacific Missile Range Facility on Kauai, HI. The 18-hour flight was a functional checkout of the aircraft's systems and performance in preparation for an attempt to reach sustained flight at 100,000 feet altitude later in the summer. (Photo Courtesy of NASA/Getty Images)

The Haʻikū Stairs, also known as the Stairway to Heaven or Haʻikū Ladder, is a steep hiking trail on the island of Oʻahu. The trail began as a wooden ladder spiked to the cliff on the south side of the Haʻikū Valley. It was installed in 1942 to enable antenna cables to be strung from one side of the cliffs above Haʻikū Valley to the other. A building to provide a continuous communication link between Wahiawā and Haʻikū Valley Naval Radio Station was constructed at the peak of Puʻukeahiakahoe, elevation about 2,800 feet (850 m). The antennae transmitted very low frequency radio signals from a 200,000-watt Alexanderson alternator in the center of Haʻikū valley. The signals could reach US Navy submarines as far away as Tokyo Bay while the submarines were submerged.