SpaceX will attempt to catch both parts of its huge Starship rocket after it launches on its next test flight on Friday.
Elon Musk's company will use the mechanical arms - nicknamed chopsticks - on its launch tower to grab the rocket parts mid-air as they return to Earth.
If successful, this will be the first full recovery of a rocket that's been to space, paving the way for making Starship reusable so it can fly repeatedly.
Nasa will be closely watching the flight: the SpaceX rocket is set to play a vital part in its Artemis programme, which will see astronauts land on the Moon.
The 124m-tall rocket is scheduled to blast off from the Starbase launchpad in Texas at 1645 local time (2245 GMT) with a 75-minute-long launch window.
After six and a half minutes, the first planned catch will be attempted when the bottom part of the rocket - the Super Heavy booster - returns to the launch tower.
The top part of the rocket, called the Ship, will continue its journey to space and deploy 26 satellites. These will form part of the Starlink constellation that provides high speed internet from space.
The Ship is then due to complete 14 orbits around the Earth before returning for the second catch attempt about 22 and a half hours after taking off.
Until now, SpaceX has managed to catch the Super Heavy Booster on three earlier test flights.
But the upper stage of the rocket, which only reached orbit for the first time in September, has never been grabbed by the chopsticks. Instead it's splashed down in the ocean.
SpaceX said it would only decide to try to catch the Ship after carefully assessing the vehicle while it's in space.
If any problems are detected there are various points during the flight when the rocket stage can be brought down in the ocean.
Building a fully reusable rocket is a long-held ambition for SpaceX.
In 2015, it became the first company to vertically land part of a rocket with its Falcon 9 booster.
Falcon 9 rockets now fly more than a hundred times a year, and the ability to reuse the bottom part of the rocket has dramatically cut the costs of launch.
But landing an entire Starship rocket could take this to the next level, says Prof Malcolm Macdonald, President of Royal Aeronautical Society.
"A successful double catch would be visually spectacular, but full reusability has the potential to fundamentally change the economics of accessing space," he said.
"One successful flight will not prove that model, but it could mark an important transition: from demonstrating that Starship can fly, to demonstrating how Starship could operate."
After SpaceX went public earlier this year, its shareholders will be carefully monitoring this flight, as will the US Space Agency.
The progress of Starship has direct implications for Nasa's attempt to land humans on the Moon in 2028 - a highly ambitious timeline.
SpaceX has been given a Nasa contract to configure the Ship into a lander that will eventually take astronauts down to the lunar surface.
But it's not the only company working with the US Space Agency. Blue Origin, owned by rival tech billionaire Jeff Bezos, also has a contract to use its New Glenn rocket and lander for the Moon touch down.
Both companies will also play a key role in Artemis III, which is currently planned for summer 2027- another challenging schedule.
This mission will see four astronauts in Nasa's Orion spacecraft attempt to dock with both SpaceX and Blue Origin's landers.
Starship will need to make a lot of progress in the coming months to meet these commitments - the pace of the rocket's development has been far slower than SpaceX had intended.
But Blue Origin also has much work to do. The company suffered a major setback earlier this year when its rocket exploded, totally destroying its launchpad in Florida.
Blue Origin had said they would be back in action by the end of this year, but a return to flight has now been delayed to early in 2027.
Nasa is under pressure to meet its timelines. Its administrator Jared Isaacman has said America is in a race with China to get to the Moon. China plans to land its Taikonauts on the lunar surface by 2030.
