SpaceX Starship 40 departs Christmas Island for Texas via heavy-lift vessel

Like a certain extraterrestrial, SpaceX's Starship 40 is set to depart its adopted safe harbour of Christmas Island and head for home.

But, far from Hollywood special effects, a highly specialised watercraft is helping it make the 17,000 kilometre journey back to Starbase, Texas.

The Forte is a heavy-lift, semi submersible cargo carrier sailing beneath a Maltese flag.

The ABC tracked the vessel using publicly available marine traffic data from Indonesia to Christmas Island's Flying Fish Cove, where it docked late on Sunday evening.

The Forte has anchored within a few hundred metres of Starship 40, where it will sink its stern to load the floating 52-metre-long rocket directly from the water.

Islander Lisa Preston described the spectacle as awe-inspiring.

"It's quite surreal going past it on a boat and having a look at this rocket," she said.

"Then we've, as humans beings, designed this other piece of machinery that can pull that out of the ocean and semi-submerge and float itself again and sail off with the rocket.

Christmas Island Tourism Association chair David Watchorn headed out before sunrise to watch the Forte up close, calling it the biggest vessel he had ever seen at Christmas Island.

"It's huge, it pales [other ships] in significance," Mr Watchorn said.

Sad farewell

The rocket's presence on the remote Australian territory has caused lots of excitement in the tight-knit island community, especially among its youngest residents.

Space enthusiast George Pride, age 9, said it was something he and his schoolmates would never forget.

"I went like one metre away from it," he said.

Ellyse Ingwersen, age 10, said she would be sad to see it go.

"It was a really cool spaceship, I think it's like a once in a life opportunity."

Retrieved for analysis

The recovery mission comes almost a week after Starship 40 was towed to Christmas Island, more than 1,500 kilometres off Western Australia's coast.

The ship, described by SpaceX as the upper-stage attached to the world's most powerful booster, made a controlled touchdown in the Indian Ocean on July 24.

It then spent 24 days at sea as crews from the mainland battled rough weather and delays.

At the time, a spokesperson for the Australian Space Agency confirmed the federal government was assisting SpaceX in its efforts.

In an earnings call earlier this month, SpaceX chief executive Elon Musk said the flight of Starship 40 demonstrated the "core capabilities" of an orbital mission and return to Starbase for "catch".

It is expected to return to Texas for analysis by engineers.

The company hopes to launch, catch, and reuse its rockets going forward, with last month's soft splashdown a key test of its performance.

Yet in a post to his X account last week, Mr Musk admitted a catch attempt on dry land was still some way off.

"If there had been a tower out to sea where we practised landing the ship, it would have been caught," he wrote.

"First reflight (sic) of the ship will be either [the] end of this year or early next."