By Sean Smith
McMurdo Sound is only accessible at the end of the Antarctic summer
A few weeks ago I was in a tiny aircraft, a Twin Otter ski-plane, flying above the vastness of the Antarctic continent.
My destination was the historic shore of McMurdo Sound, the starting point for the British attempts on the South Pole led by Shackleton and Scott, during what is now called "The Heroic Age" of Polar exploration 100 years ago.
I was with three men who were about to embark on one of the toughest endurance tests on the planet - an unsupported 850 mile (1360km) trek to the South Pole.
It is a journey that will take them across hundreds of miles of featureless ice shelf, then up one of the largest and most treacherous glaciers in the world, the Beardmore Glacier. This opens on to the immense polar plateau itself - the coldest, windiest, most inhospitable place on earth.
The Shackleton Centenary Expedition is being used to launch the £10m Shackleton Foundation to fund projects that embody the explorer's spirit of adventure and "calculated risk".
If they reach their destination they will be part of a very select band - fewer people have made this particular journey than have walked on the face of the Moon!
The team is retracing Shackleton's 1908 expedition
They are following in the footsteps of Sir Ernest Shackleton's 1908 Nimrod expedition, which turned back just 97 miles (155km) short of the South Pole.
Although unsuccessful in reaching his goal, it was Shackleton who opened the road to the pole for Roald Amundsen and Robert Falcon Scott a few years later. And turning back when the pole was within his grasp is seen by many as one of the most inspired leadership decisions in the history of exploration, for to go on would have meant certain death.
The three men on the expedition, Henry Worsley, Will Gow, and Henry Adams are descendants respectively of Shackleton's captain (Frank Worsley), brother-in-law (Herbert Dorman) and second in command (Jameson Boyd Adams).
This expedition is to complete "unfinished family business" and is the culmination of five years' planning and training involving endurance races in the Yukon and the Himalayas, and Arctic training courses in Norway and Baffin Island.
Shackleton's team spent the winter in a hut
The team has been learning the survival skills necessary to function day after day and week after week in temperatures as low as -40C and to battle the icy blizzards which could strike at any time.
They learnt how to recognise and treat frostbite and hypothermia.
And in the Alps and Greenland they learnt how to tackle the most deadly threat they will face on the journey - crevasses, the huge, hidden cracks formed when a glacier moves over an obstruction.
If one person falls down a "slot", as they're known in mountaineering jargon, the others will have to rig up an improvised rescue system.
I joined the team as they flew from Chile to Antarctica and on via ski plane towards McMurdo Sound - where we landed on the ice just a mile away from the site of Shackleton's original 1908 hut.
It had felt like a long journey, but for Shackleton's men, it would have seemed like the blink of an eye.
In 1908 the only way to get to the Antarctic was by sea, and the only time you could reach Ross Island and McMurdo was at the end of the Antarctic summer when the sea ice had melted.
Shackleton and his Nimrod crew began their voyage from the East India Docks in July 1907.
The interior of the hut is very much as it was left in 1908
The final leg from New Zealand to the Antarctic was an epic in itself, battling violent storms and treacherous pack ice before the Nimrod anchored in McMurdo Sound on Jan 28th 1908.
While the ship's captain fretted about being trapped for the winter, the crew and shore party hurried to unload the ship and build the hut that would be the expedition's base and winter quarters. By mid-February all the stores were ashore, and on 28 February the Nimrod set sail northwards.
The 15 men in the hut were now alone as the Antarctic winter set in.
With no means of communicating with the outside world, and no other human beings within thousands of miles, this was the Edwardian equivalent of an Apollo moon shot, but one that lasted years, not months.
Today Shackleton's hut is the focus of a conservation project run by the New Zealand government.
But walking across the dark volcanic rocks with the snow cone of Mt Erebus behind and the sound of penguins braying along the sea ice of the sound, it is easy to imagine yourself transported back to the early years of the last century, for this is a timeless landscape.
Going into the hut itself draws a gasp of amazement from everyone who enters.
Here are preserved clothing, equipment, bedding and foodstuffs, all arranged on the shelves as though the original occupants have just popped out for a spot of sledging or a quick constitutional.
The descendants of the original expedition team hope to reach the pole
For Henry Worsley, a Lieutenant Colonel in the Army, it is a particularly poignant moment.
He has revered Ernest Shackleton for most of his adult life. He is an ardent collector of Shackleton memorabilia and on this occasion he has brought something truly special - Ernest Shackleton's original compass from the 1908 expedition that has been loaned to him by the explorer's great grand-daughter, Alexandra.
She is hoping that the compass at least will finally make the journey that Sir Ernest was unable to do.
As Lt Col Worsley gets the compass out in the hut and hands it round, the expedition members go quiet.
It is an object with a peculiar power; a palpable link to the great explorer who has inspired these men to take up the challenge of the Antarctic for their own generation.
In the second of his articles, Sean Smith's brings us the latest information on the progress of the expedition which is also being filmed for a BBC Two Timewatch documentary in Spring 2009.