The Stratolaunch plane, the world's largest, does its 2nd test fight as it comes in for a landing after it performed a 4hr test flight in Mojave, California, U.S., April 29, 2021. The largest airplane ever to take flight made its sophomore voyage on Wednesday (April 29), soaring into clear skies over California's Mojave desert. REUTERS/Gene Blevins

The Stratolaunch plane, the world's largest, does its 2nd test fight as it comes in for a landing after it performed a 4hr test flight in Mojave, California, U.S., April 29, 2021. Stratolaunch's massive carrier aircraft, nicknamed 'Roc', is designed to transport hypersonic vehicles and facilitate easy access to space. REUTERS/Gene Blevins

The Stratolaunch plane, the world's largest, performs a 4hr test flight in Mojave, California, U.S., April 29, 2021. The carbon-composite carrier aircraft has a massive 385 foot (117 meter) wingspan, and can climb to altitudes of 35,000 feet, according to Stratolaunch. REUTERS/Gene Blevins

The Stratolaunch plane, the world's largest, performs a 4hr test flight in Mojave, California, U.S., April 29, 2021. The carbon-composite carrier aircraft has a massive 385 foot (117 meter) wingspan, and can climb to altitudes of 35,000 feet, according to Stratolaunch. REUTERS/Gene Blevins

The Stratolaunch plane, the world's largest, comes in for a landing over Virgin Orbit 747 Cosmic Girl after it performed a 2nd test flight in Mojave, California, U.S., April 29, 2021. REUTERS/Gene Blevins

The Stratolaunch plane, the world's largest, performs a 4hr test flight in Mojave, California, U.S., April 29, 2021. REUTERS/Gene Blevins