The team behind an attempt to break the world manned balloon altitude record says its flight will begin from Cornwall on Tuesday.
The pair will be making their ascent on an open flight deck
British pilots Andy Elson, from Somerset, and Colin Prescot, from Hampshire, aim to break a 42-year-old record.
They hope to ascend 132,000 feet (25 miles or 40 kilometres) into the stratosphere with the 1,270 ft (387 metres) tall QinetiQ 1 balloon.
The revolutionary craft is expected to launch between 0600 BST and 0800 BST on Tuesday from QinetiQ's vessel Triton - a prototype trimaran warship - off St Ives.
Made from 1.7 tonnes of super thin polyethylene, the envelope is designed to carry 44 million cubic ft (1.25 million cubic m) of helium.
The record attempt should be completed within nine hours, although the duo will carry enough oxygen on board the platform for 11 hours.
"The Qinetiq 1 balloon and flight platform is being loaded on to the deck of our ship, RV Triton, in readiness for launch," a spokesman for QinetiQ, the UK science and technology research company sponsoring the mission, said on Sunday.
Scientists from the Russian research company Zvezda are also en route to mission control in St Ives.
They will be on board prior to launch to help the pair dress in the spacesuits that will be vital to their survival.
The conditions on the open platform will resemble those on the surface of Mars, with temperatures dropping as low as -70 Celsius (-94 Fahrenheit), then rising to around -25 C (-13 F) and with high levels of radiation.
The Met Office has been monitoring the weather and on Saturday provided the pilots with forecast data allowing them to pinpoint the preferred conditions to launch and fly the balloon.
"Obviously we're quite excited, but once we sail from Falmouth it might all begin to sink in a little bit," said Mr Elson.
Colin Prescot said: "I'm feeling calm, but very pleased that we're getting the weather at last.
"I will be rehearsing everything in my mind during the next day."
The current height record for a balloon journey stands at 113,740 feet (34,668 metres).
It was set in 1961 by two American navy officers, following a launch from an aircraft carrier in the Gulf of Mexico.
People who want to watch the launch have been advised not to go to St Ives, already packed with holidaymakers.
Devon and Cornwall police have advised would-be spectators to go to the many vantage points along the north Cornwall coast.
"People will be able to see the balloon from miles away," said a police spokesman.
St Ives Council has said there will be signs guiding people to vantage points, as well as extra staff to help spectators.
And British Airways has agreed to divert a Concorde flight when the world record bid goes ahead.