SpaceX is preparing to carry four astronauts to a crowded International Space Station on Thursday, in the second routine mission since the United States resumed crewed space flight, and the first with a European.

Liftoff is planned for 6:11 am Eastern Time (1011 GMT) on April 22, from NASA's Kennedy Space Center in Florida.

The mission, called Crew-2, involves US astronauts Shane Kimbrough and Megan McArthur, along with the Japan Aerospace Exploration Agency (JAXA)'s Akihiko Hoshide, and the European Space Agency (ESA)'s Thomas Pesquet.

NASA has made history by successfully flying the mini helicopter Ingenuity on Mars, the first powered flight on another planet.

Here are some key things to know.

Proof of concept

The rotorcraft's first flight lasted 39.1 seconds as Ingenuity lifted itself to a height of 10 feet (three meters) and then returned to the Martian surface.

While it does have the capacity to fly for 90 seconds and cover a distance of up to 980 feet (300 meters), its test runs are intentionally of limited scope as they are meant to prove only that the technology works.

Ingenuity is not gathering scientific data about Mars or aiding in the search for past microbial life.

Previous technology demonstrations include the Mars Pathfinder rover, Sojourner, which was the first ever rover to explore another planet in 1997.

It is hoped that one day, future aircraft can help revolutionize exploration of celestial bodies by going further and faster than rovers, and reaching areas hard to access by land.

NASA conducted its first flight on another planet early Monday morning, a short hop for a small chopper named Ingenuity which demonstrated technology that could prove critical to the future of space exploration.

The four-pound vehicle ascended to about 10 feet above the surface of the red planet for about 40 seconds, before descending back to the ground.

The helicopter arrived on Mars along with the Perseverance rover on Feb.

NASA's experimental Mars helicopter rose from the dusty red surface into the thin air Monday, achieving the first powered, controlled flight on another planet.

The triumph was hailed as a Wright Brothers moment. The mini 4-pound (1.8-kilogram) copter named Ingenuity, in fact, carried a bit of wing fabric from the 1903 Wright Flyer, which made similar history at Kitty Hawk, North Carolina.

"We can now say that human beings have flown a rotorcraft on another planet," project manager MiMi Aung announced to her team.

Flight controllers in California confirmed Ingenuity's brief hop after receiving data via the Perseverance rover, which stood watch more than 200 feet (65 meters) away.

In the weeks following its launch in early 2006, when NASA's New Horizons was still close to home, it took just minutes to transmit a command to the spacecraft, and hear back that the onboard computer received and was ready to carry out the instructions.

As New Horizons crossed the solar system, and its distance from Earth jumped from millions to billions of miles, that time between contacts grew from a few minutes to several hours. And on April 17 at 12:42 UTC (or April 17 at 8:42 a.m. EDT), New Horizons will reach a rare deep-space milepost—50 astronomical units from the sun, or 50 times farther from the sun than Earth is.

New Horizons is just the fifth spacecraft to reach this great distance, following the legendary Voyagers 1 and 2 and their predecessors, Pioneers 10 and 11.

If there is one driving force in the commercial space industry it is economics. The whole concept of reusable booster rocket emphasizes the importance of getting launch costs down. SpaceX, the company leading the charge in trying to bring launch costs down, doesn't just recover booster rockets however. It also recovers the rocket fairings that hold the payload during launch. SpaceX's original plan was to capture the fairings as they fell back to Earth using specially equipped ships with nets to catch them before they landed in the ocean. Now, however, the company has transitioned to simply fishing fairings out of the ocean after they splash down, and that seems to be working just fine.

The economic motivation for attempting a fairing capture is simple. Salt water is corrosive, so if a fairing lands in the ocean it must be refurbished at a cost. Catching it before it hits the water would eliminate the need to refurbish it, thereby lowering the cost of reusing the fairing.

To attempt this capture, SpaceX commissioned two ships, named with their usual whimsical style: Ms.

On April 21, 1908, near Earth's North Pole, the Arctic explorer Frederick Albert Cook scrawled in his diary a memorable phrase: "We were the only pulsating creatures in a dead world of ice." These words may soon take on new significance for humankind in another dead world of hidden ice, submerged beneath the red sand of its frigid deserts. This dead world is Mars, and the desert is the planet's mid-latitude region known as Arcadia Planitia.