Space Shuttle Discovery is towed from the shuttle landing facility to the orbiter processing facility at Kennedy Space Center on April 20, 2010 in Cape Canaveral, Florida. Discovery's landing attempts at KSC were scrubbed yesterday due to unacceptable weather conditions. Discovery is returning from a successful mission to the International Space Station. (Photo by Matt Stroshane/Getty Images). CAPE CANAVERAL, FL – APRIL 20 2010

An F/A-18 Hornet assigned to Strike Fighter Squadron One Five One (VFA-151) emerges from a cloud created when it broke the sound barrier in the skies over the Pacific Ocean, July 7, 1999. (Photo by John Gay/US Navy)

Aerobatic aircrafts fly during a performance at the Airshow Zhengzhou 2017 in Zhengzhou, capital of central China's Henan Province on April 27, 2017. The 5-day air show kicked off in Zhengzhou on Thursday, aiming to build a general aviation gathering center for business and communications. (Photo by Li An/Xinhua via ZUMA Wire)

Two dummy tanks being pushed along a road by German soldiers. (Photo by Hulton Archive/Getty Images). Circa 1925

A boy wearing a Lebanon's Hezbollah military outfit and carrying a toy gun walks during the funeral of three Hezbollah fighters who were killed while fighting alongside Syrian army forces in Syria in Nabatieh town, southern Lebanon, October 27, 2015. The fighters names are Hussein Hassan Shreifie, Ali al-Akbar Mohamad Khashfeh and Mohamad Saeed Fawaz. (Photo by Ali Hashisho/Reuters)

The summit of one of Europe's tallest mountains glows like the flame of a candle as the sun rises on a clear morning. The Matterhorn, famous for appearing on bars of Toblerone chocolate bars, reflects the vivid orange light at 5.37am. (Photo by Margarethe Jaeger/Solent News & Photo Agency)

A model falls while displaying a design from Wu Xuewei and Wu Xuekai, winners of the Asahi Kasei China Fashion Designer Award during China Fashion Week held in Beijing, China, Friday, October 29, 2010. (Photo by Ng Han Guan/AP Photo)

A tear rolls down the cheek of Karima el-Mahroug, also known as Ruby, a Moroccan woman at the center of ex-Premier Silvio Berlusconi's s*x-for-hire trial, as she reads a statement to reporters during a protest outside the court house, in Milan, Italy, Thursday, April 4, 2013. The Moroccan woman at the center of ex-Premier Silvio Berlusconi's s*x-for-hire trial has denounced what she says is psychological warfare being waged against her by Italian prosecutors. Ruby, read out a lengthy statement Thursday to a gaggle of reporters in front of Milan's courthouse denying she was a prostitute and insisting that prosecutors hear her side of the story. (Photo by Luca Bruno/AP Photo)