NASA scientists call it "the seven minutes of terror."
Early Monday morning, at 1:31 Eastern time, a planetary rover will attempt to land safely on Mars.
After completing an eight-month journey from Earth, the U.S. spacecraft will hit the upper Martian atmosphere at a speed of 21,000 kilometres an hour. And in just seven nail-biting minutes it must come to a relatively gentle stop.
It will use a heat shield and a parachute to slow its descent. But for the final few metres, it will rely on a brand new landing system – the hovering "sky crane," a retro-rocket-equipped backpack that is supposed to gingerly lower the vehicle to the surface using three nylon cables.
If anything goes wrong in this complex, multistage landing, the $2.5-billion mission will end up as smashed bits of space junk on the Red Planet. So scientists at NASA – the U.S. National Aeronautics and Space Administration – have good reason to dread the final moments of the 563-million-kilometre trip to Mars.
During the vehicle's plunge to the surface, it will transmit a stream of data, and three nearby spacecraft – Mars Odyssey, Mars Reconnaissance Orbiter and Mars Express – will relay the information to Earth.
The on-board computer must perform each manoeuvre flawlessly because Mars is too far away to permit any direct intervention from Earth.
It will take about 14 minutes for a radio signal from the rover, nicknamed Curiosity, to reach mission-control scientists at NASA's Jet Propulsion Laboratory in Pasadena, Calif.
"By the time we get word that the craft has entered the upper atmosphere of Mars, it will have been on the surface for seven minutes – for better or for worse," said Devin Kipp, one of the engineers responsible for getting Curiosity to Mars in one piece.
Scientists, including some in Canada, have spent years preparing for the mission and have high hopes it will help unlock the secrets of the planet's distant past when water could have flowed freely on its surface.
Curiosity, officially called the Mars Science Laboratory, is the biggest and most complex rover yet sent to the Red Planet. It's packed with instruments – including a Canadian-made device – that will try to determine if the now-barren planet was once capable of supporting microbial life.
It is essentially the size of a small car – measuring three metres in length and weighing 899 kilograms.
In fact, its bulk meant that NASA engineers had to invent a radically new landing system. On previous missions, the robotic rovers, Spirit and Opportunity, were small enough to be encased in airbags and they literally bounced along the surface until coming to a stop.
The hovering sky-crane system not only allows for a larger vehicle to be placed on Mars, but it also provides for precision landing.
The plan is to touch down close to the foot of a five-kilometre-high mountain located inside a 154-kilometre-wide crater called Gale.
"It is going to be spectacular scenery," Mr. Kipp said. "You're going to see a vertical elevation on the horizon and it is going to be very different than the standard images you might have in your mind of the previous landing sites, which have been quite flat and maybe a little bit rocky."
The target crater dates back to a giant meteor impact about 3.5 billion years ago. Over time, the crater filled with sediment, possibly deposited by flowing water. Once Mars turned dry, winds gradually eroded away most of the sediment, leaving behind a gently sloping mountain of layered sedimentary rock inside Gale Crater.
By driving up the mountain, scrutinizing rock samples along the way, Curiosity should be able to provide scientists with a chronological record of the planet's early history.
But before detailed exploration can begin, mission scientists will run several weeks of operational tests on the rover's scientific equipment, which have been supplied by several countries.
The Canadian Space Agency is footing the $10-million bill for the Alpha Particle X-ray Spectrometer (APXS), which blasts rocks with alpha particles and X-rays to determine their chemical elements.
Ralf Gellert, an assistant professor at the University of Guelph, is the scientist overseeing Canada's contribution to the U.S.-led mission.
He is ready for an unprecedented mission of scientific discovery. "We will find something completely new that no one expected," Dr. Gellert said.
The nuclear-powered rover has the capacity to remain at work for many years to come.