US astronaut Scott Kelly and Russian
cosmonaut Mikhail Kornienko have arrived for the start of a 12-month
tour of duty on the International Space Station.
It will be the longest continuous stay anyone has had aboard the 400km-high (250 mile) orbiting platform.
Their Soyuz capsule docked successfully at 01:33 GMT on Saturday, Nasa said.
Scientists hope to get a keener idea of the effects on the human body of living in microgravity for extended periods.
The space agencies say the data will be invaluable as they plan towards eventually mounting a mission to Mars.
Mr
Kelly and Mr Kornienko launched from Baikonur in Kazakhstan in the
Soyuz vehicle at 01:42 local time on Saturday (19:42 GMT Friday).
They were joined on the flight up by cosmonaut Gennady Padalka, but his tour will only last the normal six months.
Although
Mr Kelly and Mr Kornienko will set an endurance record for this space
station, some of the stays aboard the old Russian Mir platform were much
longer.
Four cosmonauts lived on Mir at various times for more
than a year, with Valeri Polyakov spending a mammoth 437.7 days in orbit
in 1994-95.
"The last time we had such a long duration flight was almost 20 years
and of course all… scientific techniques are more advanced than 20
years ago,'' Mr Kornienko was quoted as saying by the AP wire service in
the pre-launch press conference.
"And right now we need to test
the capability of a human being to perform such long-duration flights.
So this is the main objective of our flight - to test ourselves."
Mr
Kelly added: "One of the differences here is that we're doing it as an
international partnership, and if we're going to go beyond low-Earth
orbit again, perhaps to Mars, because of the cost and the complexity it
will most likely be an international mission, so we see this as a
stepping stone to that."
Knowledge on how to mitigate some of the deleterious effects of
living in zero-g has improved markedly since the Mir era, and the
expectation is that Mr Kelly and Mr Kornienko will come back in a better
shape than those early pioneers.
Programmed nutrition and
exercise routines now prevent much of the bone density loss and muscle
weakness that earlier astronauts used to experience.
However,
there are other problems that doctors still need to study and
understand. They have poor data on the effects on immune function, for
example, and there is considerable concern about the damage spaceflight
causes to the eyes. This is a newly recognised phenomenon, and appears
to be related to the way fluid is redistributed in a weightless body.
Pressure is seen to build in the skull and on the optic nerve, and a
large number of astronauts return to Earth complaining that their vision
is not as good as when they went up.
By having Mr Kelly and Mr
Kornienko onboard for a year, the agencies will be able to monitor how
such complications progress beyond the normal six-month tour of duty.
Mr
Kelly's situation is made more interesting by the fact that he has an
identical twin brother, Mark Kelly, who was himself an astronaut before
retiring from the US space agency in 2011.
The pair will be used in a comparative study: one in space, one on the ground.
Relativity
theories predict that Scott Kelly should age less quickly than his
brother while speeding above the Earth - but only by a few milliseconds
over the year.
The
American space agency's Dawn spacecraft is bearing down on Ceres, the
largest object in the asteroid belt between Mars and Jupiter.
New pictures released on Monday will help navigators put the
satellite on the correct path to go into orbit around the dwarf planet
on 6 March.
The German camera team on Dawn has made a little movie showing the 950km-wide world part-rotating on its axis.
Come the end of the month, the probe's pictures will better those from Hubble.
At the moment, at a separation of just under 400,000km, they
are still only 80% as sharp as what the famous space telescope can
produce.
Ceres will be the first dwarf planet to be visited up-close.
The second encounter will come in July when Nasa's New Horizons
spacecraft flies by Pluto.
The dwarfs are a distinct class of object in the Solar System
- after the terrestrial inner planets like Earth and the gas giants
like Jupiter.
Dawn is arriving at Ceres after visiting the asteroid Vesta.
This 530km-wide rock had the look of a punctured football, the result of
a colossal collision sometime its past that ripped a big chunk out of
its southern polar region.
Ceres, on the other hand, is big enough for gravity to have pulled it into a more spherical shape.
Scientists think both bodies are fledglings that never quite made it to the big time.
In the case of Vesta, it underwent a lot of the same
processes that transformed the early Earth, such as differentiating its
insides to include an iron core.In contrast, Ceres's bid to reach the
major planet league probably stalled very quickly.
Researchers believe its interior is dominated by a rocky core
topped by ice that is then insulated by rocky lag deposits at the
surface. A big question the mission hopes to answer is whether there is a
liquid ocean of water at depth. Some models suggest there could well
be.
Dawn is supposed to undertake a 16-month study of Ceres once
it gets into orbit, but that may depend on how well the hobbled probe
performs.
It has lost two of the four reaction wheels it uses for
fine-pointing. As a result, it has to fire its thrusters to maintain a
correct attitude, but this puts a drain on its hydrazine fuel supply. If
everything keeps working, observations will be made from as low as
400km from the surface.
When time is eventually called on the mission, Dawn will be left circling Ceres.
"They've run out the models for a hundred years and it'll be a
very stable orbit. We'll become a perpetual satellite of Ceres," deputy
principal investor Carol Raymond told BBC News. Jonathan.Amos-INTERNET@bbc.co.uk and follow me on Twitter: @BBCAmos
Google
latest "moonshot" is an apt one - it is investing in a Nasa-owned
airfield to expand research into space exploration and robotics.
Planetary Ventures, an offshoot of Google, will take over management of the Moffett Federal Airfield.
The airfield is already regularly used as a landing strip for the private jets of the firm's billionaire executives.
Google has not divulged exactly how the site will be used.
But, according to a Nasa press release, the site will be used
for "research, development, assembly and testing in the areas of space
exploration, aviation, rover/robotics and other emerging technologies".
For Nasa, the sale offers rich pickings - the agreement will
provide it with $1.16bn (£731m) in rent over the initial 60-year lease
term.
"As Nasa expands its presence in space, we are making strides
to reduce our footprint here on Earth," said Nasa administrator Charles
Bolden.
And for Google, the investment represents an opportunity to restore an iconic building.
Part of the deal includes the restoration of Hangar One, an
important landmark in Silicon Valley. Built in 1933, it is one of the
world's largest free-standing structures.
There is also a golf course on the site
Planetary Ventures plans to invest more than $200m in rebuilding Hangar One and two other hangars on the site.
It will create an educational facility where the public can explore the site's legacy and the role of technology on it.
"We look forward to rolling up our sleeves to restore the
remarkable landmark Hangar One, which for years has been considered one
of the most endangered historic sites in the United States," said David
Radcliffe, vice president of real estate and workplace services at
Google.
Very little is known about Planetary Ventures, the firm
behind the deal. Press reports describe it as shell organisation for
real estate deals although the name hints at something more.
The base, previously maintained by Nasa's Ames Research Center, is located four miles from Google's Mountain View headquarters. Space projects
It is not the first time Google has invested in unusual
purchases. Two mysterious barges that appeared on the coasts of San
Francisco and Portland, Maine, last year turned out to be Google-owned.
It emerged that Google intended to use them as floating
showcases for new products such as Google Glass and its self-driving
cars.
The project was later abandoned after coastguard officials deemed them to be a fire risk.
Neither it is the first time that Google has worked with
Nasa. Back in 2005, Google built an office at Nasa's research facility
in order to co-operate on a range of projects.
More recently, the two teamed up to launch a new laboratory,
focused on advancing machine learning, also based at Nasa's research
centre.
Google founders Larry Page and Sergey Brin have a well-known
interest in aviation and space and the company has acquired firms
working on satellite technology and robotics.
The net giant also funds the Lunar X Prize, a $30m competition to land a privately funded robot on the moon.
