Garbage men race on their tricycles along the track during the garbage men bicycle race at Ban Jelacic square in Zagreb, Croatia, 19 August 2020. Zagreb's authorities organised a street festival named “Cest is the best” despite the coronavirus pandemic in Croatia with some 219 infected people. (Photo by Antonio Bat/EPA/EFE)

A man carrying vegetables is stopped by police at a barricade on a road during a 21-day nationwide lockdown to limit the spreading of coronavirus disease (COVID-19) in Chennai, India, March 25, 2020. (Photo by P. Ravikumar/Reuters)

South Korean environmental activists wearing masks symbolizing the coronavirus attend a prevention campaign as South Koreans take measures to protect themselves against the spread of coronavirus (COVID-19) on March 30, 2020 in Seoul, South Korea. South Korea has called for expanded public participation in social distancing, as the country witnesses a wave of community spread and imported infections leading to a resurgence in new cases of COVID-19. According to the Korea Center for Disease Control and Prevention on Monday, 78 new cases were reported. The total number of infections in the nation tallies at 9,661. (Photo by Chung Sung-Jun/Getty Images)

A robot, developed by start-up firm Asimov Robotics, holds a tray with face masks and sanitizer after the two robots were launched to spread awareness about the coronavirus, in Kochi, India, March 17, 2020. (Photo by Sivaram V/Reuters)

People wearing face masks to prevent the spread of coronavirus gather in a discotheque in Madrid, Spain, early Saturday, July 25, 2020. Nightlife is becoming the new target of Spanish authorities attempting to contain a spike in coronavirus infections since the country ended a lockdown. The Catalonia regional government has shut nightlife venues in Barcelona, and on Friday officials in Madrid said they were considering a similar step. (Photo by Manu Fernandez/AP Photo)

Newlyweds celebrate their wedding surrounded by friends on Red Square in Moscow on November 11, 2020, amid the ongoing coronavirus disease pandemic. (Photo by Natalia Kolesnikova/AFP Photo)

A girl poses in antlers ahead of a curfew on pub in Nottingham, a city in central England’s Midlands region on September 21, 2020 as Freshers' Week got underway. Revellers were also pictured out in Birmingham, which was plunged into a local lockdown amid a surge in coronavirus cases. (Photo by Ashley Kirk/The Sun)

“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)