ESA's Venus Express prepares for last-gasp descent
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The longest-serving Venus spacecraft is beginning a plunge into the atmosphere of the solar system's hottest planet on Wednesday, after a hugely successful eight-year mission.
Esa's Venus Express has far outperformed expectations, with initial estimates for the mission expecting it to last not even two years at 500 days.
But now, as the spacecraft runs out of fuel the mission is finally being brought to a close in the most dramatic of fashions - by sending it into the atmosphere of one of the most volatile planets we know.
On Wednesday, Esa's hugely successful Venus Express spacecraft will begin lower and lower forays into the harsh Venusian atmosphere (illustration shown). The series of aerobraking maneuvers will see the spacecraft lowered to an altitude of just 80 miles (130 kilometres) above the surface - but it's unknown if it will survive
Venus Express was launched back on 9 November 2005 and arrived at Venus on 11 April 2006.
'EARTH'S TWIN' VENUS
Venus is slightly smaller than Earth but has a similar mass.
It is the second closest planet to the sun at a distance of about 67 million miles (108 million kilometres).
One day on Venus lasts as long as 243 Earth days.
Its thick and toxic atmosphere is made up mostly of carbon dioxide and nitrogen, with clouds of sulphuric acid droplets.
It's believed that its atmosphere contributed to a runaway greenhouse effect that made the planet inhospitable.
The planet's extreme high temperatures of almost 480°C (900°F) make it seem an unlikely place for for life as we know it.
It has since been orbiting Venus in an elliptical 24-hour loop that begins a distant 40,000 miles (66,000 km) over the south pole, affording incredible global views.
Its orbit then takes it to an altitude of around 155 miles (250 km) above the surface at the north pole, close to the top of the planet's atmosphere.
Each orbit, however, required more and more fuel to be spent as the spacecraft battled against radiation exerted from the sun to maintain its speed.
Now the fuel supplies necessary to maintain the orbit are running low, reports The Conversation.
In May, routine science operations of the spacecraft ceased, with efforts shifted to making lower passes through the atmosphere.
From 18 June until 11 July so-called 'experimental aerobraking' will take place, with the spacecraft's altitude gradually lowered.
'We have performed previous short "aerodrag" campaigns where we've skimmed the thin upper layers of the atmosphere at about 165 kilometres [100 miles], but we want to go deeper, perhaps as deep as 130 kilometres [80 miles], maybe even lower,' says Patrick Martin, Venus Express mission manager
It is not known, however, if the spacecraft will survive these risky operations - the fuel may or may not run out, while the electrical components may not handle the strain.
Whatever the outcome, the endeavour will provide some invaluable science about the composition of the Venusian atmosphere.
Shown here is the minimum altitude the spacecraft is expected to reach. The spacecraft has been in orbit around Venus for eight years but, as it is running out of fuel, a decision was made to send it on a risky but potentially science rich mission deep into the atmosphere of Venus
It will also prove a useful experiment into the limits of aerobraking.
EXPLORING VENUS: INTO THE FIRE
Venus Express is not the first spacecraft to journey this far into the Venusian atmosphere.
That honour is bestowed to a series of Soviet spacecraft in the 1960s, 70s and 80s called the Venera probes.
About a dozen were sent on daring missions to the surface of Venus, with only a handful being successful.
The intense heat and atmospheric pressure crushed each of the probes in up to about an hour once they had penetrated the atmosphere - but a few managed to survive long enough to return data and images.
The Venera probes were succeeded by the Vega spacecraft, high-altitude balloons that were sent into the atmosphere of Venus on scientific missions.
Aerobraking can be used as a way of getting into orbit around planets without having to carry quite so much fuel, thus reducing the launch mass.
But spacecraft are typically not subjected to intense aerobraking, instead only 'brushing' the atmosphere of a planet.
If Venus Express survives this mission, it could allow for more extreme aerobraking manoeuvres in future - allowing for spacecraft to carry more advanced instruments at the expense of additional fuel is not needed.
But if the spacecraft is still healthy afterwards, its orbit will be raised again to an altitude of 300 miles (475 kilometres) in mid-July.
Limited operations will continue for several more months but, by the end of the year at the latest, the fuel will have been exhausted.
This will mean that as 2014 draws to a close, the decay of the spacecraft's orbit will continue until it deteoriates completely; there is no chance of it surviving into 2015, according to Esa.
In its time orbiting Venus, Esa's spacecraft has returned huge amounts of scientific data. This included observational evidence for past and present volcanoes on the surface, possibly accounting for the runaway greenhouse effect that gave the planet its thick atmosphere and scorching temperature
In its eight years it has found volcanoes on Venus, tracked extreme weather, seen evidence of extraterrestrial lightning and much more.
With a suite of seven instruments, the spacecraft has provided a comprehensive study of the ionosphere, atmosphere and surface of Venus.
'Venus Express has taught us just how variable the planet is on all timescales and, furthermore, has given us clues as to how it might have changed since its formation 4.6 billion years ago,' says Håkan Svedhem, Esa's project scientist.
And there could be more surprises in store yet, if its communication equipment survives the foray through the atmosphere and is able to send data back to Earth.
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