Can you spot the space walker in this picture? Stunning photo shows size of ISS

The ISS in all its glory. Photo / Terry Virts / Twitter

Spacewalking astronauts ventured out on Sunday, for the third time in just over a week, to complete a tricky cable job at the International Space Station. In one stunning shot, Terry Virts revealed the enormity of the station against the darkness of space as his fellow astronaut, Butch Wilmore, floated almost unseen.

"Can you spot the space walker in this picture?" Virts tweeted. "He's very small compared to the enormous starboard truss of the #ISS."

Virts also posted a space selfie and commented: "Mission Accomplished - three #spacewalks, 800' of cable, four antennas, three laser reflectors, one greased robotic arm."

Photo / Terry Virts / Twitter

Still thinking about that #awesome #spacewalk yesterday with #AstroButch! pic.twitter.com/67NoEn504U

— Terry Virts (@AstroTerry) March 2, 2015

But not everything went to plan. Dramatically, right before Sunday's spacewalk, engineers spotted problems with American astronaut Wilmore's suit.

Though it had functioned perfectly during the first two spacewalks, on Sunday morning, a pressure sensor briefly malfunctioned before he floated out.

A mechanical gauge, however, was operating fine. Mission Control told Wilmore he would need to pay extra attention to how his suit was feeling throughout the seven-hour excursion.

Can you spot the space walker in this picture? He's very small compared to the enormous starboard truss of the #ISS. pic.twitter.com/Td7pzc4Hmb

— Terry Virts (@AstroTerry) March 2, 2015

Meanwhile, Nasa said a small amount of water got into Virts' helmet once he was back in the air lock and the chamber was being repressurised on Wednesday.

The space agency was forced to spend two days analysing his suit after the water leak occurred at the end of an outing earlier this week.

Engineers concluded it was the result of condensation, and a safe and well understood circumstance that had occurred several times before with the same spacesuit.

Virts was never in danger, according to Nasa, so they cleared his spacesuit for the last of three spacewalks to install cable.

In 2013, another astronaut nearly drowned because of a flooded helmet.

Italian astronaut Luca Parmitano barely got back into the space station after a considerable amount of water filled his helmet during a spacewalk.

The water escaped from his suit's cooling system and Nasa spent months investigating the mishap, before clearing the way for more spacewalks.

The camera doesn't do it justice - floating in space, looking down on creation, seeing new color shades. #spacewalk pic.twitter.com/or8godwZSO

— Terry Virts (@AstroTerry) March 1, 2015

On Wednesday, the amount of water seepage in Virts' helmet was significantly smaller and occurred at the end of the spacewalk when Virts was already inside.

"They're very different occurrences," said Alex Kanelakos, a spacewalk officer in Mission Control.

The advance work, involving nearly 800 feet of cable over three spacewalks was carried out to create new crew capsules commissioned by Nasa.

A pair of docking ports will be flown up later this year, followed by the capsules themselves, with astronauts aboard, in 2017.

The astronauts successfully routed 364 feet on their first two excursions, on February 21 and last Wednesday.

They carried out complicated work on Sunday, yet managed to complete their task an hour early making it a five and a half-hour spacewalk and 20 hours altogether on three outings.

Neither Virts nor Wilmore had experienced any more suit trouble during their task. Mission Control joked by radio: "You guys have done an outstanding job even for two shuttle pilots."

The spacewalk, 418km above the Earth, unfolded 50 years to the month of the world's first spacewalk by Soviet cosmonaut Alexei Leonov on March 18, 1965.

Nasa hasn't conducted such a quick succession of spacewalks since its former shuttle days, and the amount of cable work is unprecedented.

More spacewalks will be needed once the docking ports start arriving in June.

Wilmore is due to return to Earth next week following a five and a half-month mission. Virts is midway through his expedition.

A Russian Soyuz spacecraft carried them both up, with Nasa paying for the multimillion- dollar tickets.

To save money and reduce reliance on the Russian Space Agency, Nasa has hired Boeing and SpaceX to develop spacecraft capable of transporting astronauts to the space station.

- Daily Mail