NASA is trying for a final time to contact its record-setting Mars rover Opportunity, before calling it quits.

Key points: Opportunity was designed to last for three months but has survived for 15 years

Opportunity was designed to last for three months but has survived for 15 years It had set a record for endurance on Mars and had also travelled the furthest across the planet — 45 kilometres

It had set a record for endurance on Mars and had also travelled the furthest across the planet — 45 kilometres Opportunity's twin Spirit was pronounced dead by NASA in 2001 after becoming stuck in sand

The rover has been silent for eight months, having fallen victim of one of the most intense Martian dust storms in decades.

Thick dust darkened the sky last year and, for months, blocked sunlight from the spacecraft's solar panels.

NASA will on Tuesday (US time) issue a final series of recovery commands, on top of more than 1,000 already sent.

If there is no response by Wednesday — which NASA suspects will be the case — Opportunity will be declared dead, 15 years after arriving at the red planet.

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When did Opportunity fall silent?

Flight controllers tried to awaken the rover, devising and sending command after command for months.

The Martian skies eventually cleared enough for sunlight to reach the rover's solar panels, but there was still no response.

Now it is becoming colder and darker on Mars, further dimming prospects.

Engineers speculate the rover's internal clock may have become scrambled during the prolonged outage, disrupting the rover's sleep cycle and draining its batteries.

A growing dust storm on Mars in June, 2018 with the approximate location of Opportunity indicated by the blue dot. ( Supplied: NASA )

Opportunity was only expected to last three months

Team members are already looking back at Opportunity's achievements, including confirmation water once flowed on Mars.

Opportunity was, by far, the longest-lasting lander on Mars.

Besides endurance, the six-wheeled rover set a roaming record of 45 kilometres.

Its identical twin, Spirit, was pronounced dead in 2011 a year after it had become stuck in sand and communication ceased.

Both outlived and outperformed expectations, on opposite sides of Mars.

The golf cart sized rovers were designed to operate as geologists for just three months, after bouncing onto our planetary neighbour inside cushioning air bags in January 2004.

They were rocketed from Cape Canaveral a month apart in 2003.

It is no easier saying goodbye now to Opportunity, than it was to Spirit, project manager John Callas said.

"It's just like a loved one who's gone missing, and you keep holding out hope that they will show up and that they're healthy," he said.

"But each passing day that diminishes, and at some point you have to say enough and move on with your life."

Opportunity and Spirit were not designed to deal with severe weather like dust storms. ( Supplied: NASA )

Deputy project scientist Abigail Fraeman was a 16-year-old high school student when Opportunity landed on Mars.

She was inside the control centre as part of an outreach program.

Inspired, Dr Fraeman went on to become a planetary scientist, joined NASA's Jet Propulsion Laboratory and ended up deputy project scientist for Opportunity.

"It gives you an idea just how long this mission has lasted," she said.

"Opportunity's just been a workhorse … it's really a testament, I think, to how well the mission was designed and how careful the team was in operating the vehicle."

Global dust storms typically kick up every few years, and "we had gone a long time without one", Mr Callas said.

Unlike NASA's nuclear-powered Curiosity rover, which is still chugging along on Mars, Opportunity and Spirit were never designed to endure such severe weather.

Ground sloping downward towards the Perseverance Valley on Mars, as seen by Opportunity. ( AP: Supplied NASA )

Death in a dust storm an honourable end

Cornell University's Steve Squyres, lead scientist for both Opportunity and Spirit, considers succumbing to a ferocious storm an "honourable way" for the mission to end.

"You could have lost a lot of money over the years betting against Opportunity," Professor Squyres said.

The rovers' greatest gift, according to Professor Squyres, was providing a geologic record at two distinct places where water once flowed on Mars, and describing the conditions there that may have supported possible ancient life.

Now it is up to Curiosity and the newly arrived InSight lander to carry on the legacy, Mr Callas said, along with spacecraft in orbit around Mars.

As for Opportunity: "It has given us a larger world," Dr Callas said.

"Mars is now part of our neighbourhood."

NASA does not expect to reinitiate contact with Opportunity. ( AP: Supplied NASA )

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