MESSENGER Heads Past Venus, Next Stop: Venus

NASA’s MESSENGER made its closest approach to Venus today, coming within 2,990 kilometers (1,860 miles) of its surface. The spacecraft used this close encounter with Venus’ gravity well to alter its trajectory as it travels towards its final destination: Mercury. This won’t be its final encounter with our twin planet, though. MESSENGER will meet up with Venus again in June 2007. It’ll finally make its first encounter with Mercury in January 2008, but won’t be in a final orbit until 2011.
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Night Side Atmosphere on Venus

Mars may get most of the news, but don’t forget there’s a spacecraft orbiting Venus too. New images released from ESA’s Venus Express spacecraft show new details about our twin planet’s atmosphere. These night-side infrared images reveal thermal radiation emanating from beneath the planet’s thick obscuring cloud deck. The clouds themselves are stretched out because of high-speed winds in the atmosphere.
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Science Updates from Venus Express

ESA’s Venus Express spacecraft concluded its in-orbit commissioning phase last week, and the agency has declared it ready to enter the operational phase of its science mission. All of its instruments are performing well, except for the Planetary Fourier Spectrometer (PFS), which has a malfunction. The mirror used to target the instrument is locked in the “close” position, preventing the instrument from being able to gather data.
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Double Vortex at Venus’ South Pole

New images from ESA’s Venus Express confirm that the cloud-covered planet has twin atmospheric vortexes at its southern pole. Previous missions to Venus saw stormy southern skies, but these images map out the shape of the double vortex in detail. High velocity winds take only 4 days to spin around Venus. This “super rotation” combines with the natural recycling of hot air to create this vortex structure. Scientists aren’t exactly sure why it’s creating a double vortex, though.
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Venus Express is in the Final Orbit

Artist’s view of Venus Express at Venus. Image credit: ESA. Click to enlarge
After a month of maneuvering, ESA’s Venus Express has reached its final science orbit. The spacecraft made its final maneuver on May 6, firings its engines to tighten its orbit to one that ranges between 66,000 and 250 km (41,000 and 155 miles) above the planet. Its scientific instruments will now be turned on and tested over the course of May. This will make the spacecraft ready for its science phase, due to begin on June 4, 2006.

Less than one month after insertion into orbit, and after sixteen loops around the planet Venus, ESA’s Venus Express spacecraft has reached its final operational orbit on 7 May 2006.

Already at 21:49 CEST on 6th May, when the spacecraft communicated to Earth through ESA’s ground station at New Norcia (Australia), the Venus Express ground control team at ESA’s European Spacecraft Operations Centre (ESOC) in Darmstadt (Germany) received advanced confirmation that final orbit was to be successfully achieved about 18 hours later.

Launched on 9 November 2005, Venus Express arrived to destination on 11 April 2006, after a five-month interplanetary journey to the inner solar system. The initial orbit – or ‘capture orbit’ – was an ellipse ranging from 330 000 kilometres at its furthest point from Venus surface (apocentre) to less than 400 kilometres at its closest (pericentre).

As of the 9-day capture orbit, Venus Express had to perform a series of further manoeuvres to gradually reduce the apocentre and the pericentre altitudes over the planet. This was achieved by means of the spacecraft main engine – which had to be fired twice during this period (on 20 and 23 April 2006) – and through the banks of Venus Express’ thrusters – ignited five times (on 15, 26 and 30 April, 3 and 6 May 2006).

“Firing at apocentre allows the spacecraft to control the altitude of the next pericentre, while firing at the pericentre controls the altitude of the following apocentre,” says Andrea Accomazzo, Spacecraft Operations Manager at ESOC. “It is through this series of operations that we reached the final orbit last Sunday, about one orbital revolution after the last ‘pericentre change manoeuvre’ on Saturday 6 May”.

Venus Express entered its target orbit at apocentre on 7 May 2006 at 15:31 (CEST), when the spacecraft was at 151 million kilometres from Earth. Now the spacecraft is running on an ellipse substantially closer to the planet than during the initial orbit. The orbit now ranges between 66 000 and 250 kilometres over the Venus and it is polar. The pericentre is located almost above the North pole (80º North latitude), and it takes 24 hours for the spacecraft to travel around the planet.

“This is the orbit designed to perform the best possible observations of Venus, given the scientific objectives of the mission. These include global observations of the Venusian atmosphere, of the surface characteristics and of the interaction of the planetary environment with the solar wind,” says Hakan Svedhem, Venus Express Project Scientist. “It allows detailed high resolution observations near pericentre and the North Pole, and it lets us study the very little explored region around the South Pole for long durations at a medium scale,” he concluded.

Until beginning of June, Venus Express will continue its ‘orbit commissioning phase’, started on 22 April this year. “The spacecraft instruments are now being switched on one by one for detailed checking, which we will continue until mid May. Then we will operate them all together or in groups” said Don McCoy, Venus Express Project Manager. “This allows simultaneous observations of phenomena to be tested, to be ready when Venus Express’ nominal science phase begins on 4 June 2006,” he concluded.

Original Source: ESA Portal

Venus Express Tests its Engine

Venus Express main engine firing in space. Image credit: ESA Click to enlarge
One hundred days after beginning its cruise to Venus, ESA’s Venus Express spacecraft successfully tested its main engine for the first time in space.

The main engine test is a critical step in the mission. In fact, it is due to its powerful thrust that Venus Express will be able to ‘brake’ on arrival at Venus. The spacecraft must slow down in order to be captured in orbit around the planet.

The engine was fired during the night of 16/17 February, starting at 01:27 CET (00:27 UT) and the ‘burn’ lasted for about three seconds. Thanks to this engine burn, the spacecraft changed its velocity by almost three metres per second.

About one hour later, the data received from the spacecraft by the Venus Express ground control team (via ESA’s New Norcia antenna in Australia) revealed that the test was successful.

The engine performed as expected. The spacecraft reacted correctly to the push and was able to recover the control of its attitude and to correctly point its high-gain antenna back to Earth to communicate with ground control.

All data recorded during the burn will now be carefully analysed by Astrium (who built the spacecraft) and ESA’s engineers to study the performance of the engine in detail.

The next big milestone is the Venus Orbit Insertion manoeuvre on 11 April 2006, which will require the main engine firing sequence to operate for about 51 minutes in the opposite direction to the spacecraft motion. This braking will allow the spacecraft to counteract the pull of the Sun and Venus, and to start orbiting the planet.

Venus Express is currently at a distance of about 47 million kilometres from Earth.

Original Source: ESA Portal

Shadows Cast By Venus

Venus at the beach on Nov. 19th. Image credit: Pete Lawrence. Click to enlarge
It’s often said (by astronomers) that Venus is bright enough to cast shadows.

So where are they?

Few people have ever seen a Venus shadow. But they’re there, elusive and delicate?and, if you appreciate rare things, a thrill to witness.

Attention, thrill-seekers: Venus is reaching its peak brightness for 2005 and casting its very best shadows right now.

Amateur astronomer Pete Lawrence of Selsey, UK, photographed the elusive shadow of Venus just two weeks ago. It was a quest that began in the 1960s:

“When I was a young boy,” recalls Lawrence, “I read a book written by Sir Patrick Moore in which he mentioned the fact that there were only three bodies in the sky capable of casting a shadow on Earth. The sun and moon are pretty obvious, but it was the third that fascinated me — Venus.”

Forty years passed.

Then, “quite by chance a couple of months ago,” he continues, “I found myself in Sir Patrick’s home. The conversation turned to things that had never been photographed. He told me that there were few, if any, decent photographs of a shadow caused by the light from Venus. So the challenge was set.”

On Nov. 18th, Lawrence took his own young boys, Richard (age 14) and Douglas (12), to a beach near their home. “There was no ambient lighting, no moon, no manmade lights, only Venus and the stars. It was the perfect venue to make my attempt.” On that night, and again two nights later, they photographed shadows of their camera’s tripod, shadows of patterns cut from cardboard, and shadows of the boy’s hands?all by the light of Venus.

The shadows were very delicate, “the slightest movement destroyed their distinct sharpness. It is difficult,” he adds, “for a cold human being to stand still long enough for the amount of time needed to catch the faint Venusian shadow.”

Difficult, yes, but worth the effort, he says. After all, how many people have seen themselves silhouetted by the light of another planet?

If you’d like to try, this is the week. Your attempt must come before Dec. 3rd. After that, the crescent moon will join Venus in the evening sky, and any shadows you see then will be moon shadows.

Instructions: Find a dark site (very dark) with clear skies and no manmade lights. Be there at sunset. You’ll see Venus glaring in the southern sky: diagram. When the sky fades to black, turn your back on Venus (otherwise it will spoil your night vision). Hold your hand in front of a white screen?e.g., a piece of paper, a portable white board, a white T-shirt stretched over a rock?and let the shadow materialize.

Can’t see it? Venus shadows are elusive. “Young eyes help,” notes Lawrence, whose teenage sons saw the shadows more easily than he did.

Shadows or not, before you go home, be sure to look at Venus directly through binoculars or a small telescope. Like the moon, Venus has phases, and this week it is a lovely crescent. Aside: If Venus is at peak brightness, shouldn’t it be full? No. Venus is full when it is on the opposite side of the sun, fully illuminated yet far from Earth. Venus is much brighter now, as a crescent, because Earth and Venus are on the same side of the sun. Venus is nearby, big and bright.

Look at Venus or look away from it. Either way, it’s a great view.

Original Source: NASA News Release

Podcast: Larry Esposito and Venus Express

Venus is our nearest planetary neighbour. Compared to the Earth, it’s nearly identical in size and distance from the Sun. But that’s where the similarities end. While we enjoy our comfortable temperature, pressure and atmosphere, Venus’ environment is downright hostile to life. The European Space Agency’s Venus Express blasted off for our “evil twin” planet today, and will hope to help answer the question: what went wrong? My guest today is Larry Esposito from the Laboratory for Atmospheric and Space Physics at the University of Colorado. He’s a member of the Venus Express science team.
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Liftoff for Venus Express

Venus Express atop a Soyuz rocket. Image credit: ESA. Click to enlarge.
The European spacecraft Venus Express has been successfully placed into a trajectory that will take it on its journey from Earth towards its destination of the planet Venus, which it will reach next April.

A virtual twin sister of the Mars Express spacecraft which has been orbiting the Red Planet since December 2003, Venus Express is the second planet-bound probe to be launched by the European Space Agency.

Venus Express will eventually manoeuvre itself into orbit around Venus in order to perform a detailed study of the structure, chemistry and dynamics of the planet’s atmosphere, which is characterised by extremely high temperatures, very high atmospheric pressure, a huge ‘greenhouse effect’ and as-yet inexplicable ‘super-rotation’ which means that it speeds around the planet in just four days.

The European spacecraft will also be the first orbiter to probe the planet’s surface while exploiting the ‘visibility windows’ recently discovered in the infrared waveband.

The 1240 kg mass spacecraft was developed for ESA by a European industrial team led by EADS Astrium with 25 main contractors spread across 14 countries. It lifted off on board a Soyuz- Fregat rocket, the launch service being provided by Starsem.

The lift-off from the Baikonur Cosmodrome in Kazahkstan this morning took place at 09:33 local time (04:33 Central European Time).

Initial Fregat upper-stage ignition took place nine minutes into the flight, manoeuvring the spacecraft into a low-earth parking orbit. A second firing, one hour and 22 minutes later, boosted the spacecraft to pursue its interplanetary trajectory.

Contact with Venus Express was established by ESA’s European Space Operations Centre (ESOC) at Darmstadt, Germany approximately two hours after lift-off. The spacecraft has correctly oriented itself in relation to the sun and has deployed its solar arrays.

All on-board systems are operating perfectly and the orbiter is communicating with the Earth via its low-gain antenna. In three days’ time, it will establish communications using its high-gain antenna.

Full speed ahead for Venus
Venus Express is currently distancing itself from Earth at full speed, heading on its five-month, 350 million kilometre journey inside our Solar System. After check-outs to ensure that its on-board equipment and instrument payload are in proper working order, the spacecraft will be ‘mothballed’, with contact with Earth being reduced to once daily. If needed, trajectory correction manoeuvres can go ahead at the half-way stage in January.

When making its closest approach, Venus Express will face far tougher conditions than those encountered by Mars Express on nearing the Red Planet. For while Venus’s size is indeed similar to that of Earth, its mass is 7.6 times that of Mars, with gravitational attraction to match.

To resist this greater gravitational pull, the spacecraft will have to ignite its main engine for 53 minutes in order to achieve 1.3 km/second deceleration and place itself into a highly elliptical orbit around the planet. Most of its 570 kg of propellant will be used for this manoeuvre.

A second engine firing will be necessary in order to reach final operational orbit: a polar elliptical orbit with 12-hour crossings. This will enable the probe to make approaches to within 250 km of the planet’s surface and withdraw to distances of up to 66 000 km, so as to carry out close-up observations and also get an overall perspective.

Exploring other planets to better understand planet Earth
“The launch of Venus Express is a further illustration of Europe’s determination to study the various bodies in our solar system,” stressed Professor David Southwood, the Director of ESA’s science programmes.

“We started in 2003 with the launch of Mars Express to the Red Planet and SMART-1 to the Moon and both these missions have amply exceeded our expectations. Venus Express marks a further step forward, with a view to eventually rounding off our initial overview of our immediate planetary neighbours with the BepiColombo mission to Mercury to be launched in 2013.”

“With Venus Express, we fully intend to demonstrate yet again that studying the planets is of vital importance for life here on Earth,” said Jean Jacques Dordain, ESA Director General.

“To understand climate change on Earth and all the contributing factors, we cannot make do with solely observing our own planet. We need to decipher the mechanics of the planetary atmosphere in general terms. With Mars Express, we are studying the Martian atmosphere. With Huygens, we have explored that of Saturn’s satellite Titan.

“And now with Venus Express, we are going to add a further specimen to our collection. Originally, Venus and the Earth must have been very similar planets. So we really do need to understand why and how they eventually diverged to the point that one became a cradle for life while the other developed into a hostile environment.”

The Venus Express mission is planned to last at least two Venusian days (486 Earth days) and may be extended, depending on the spacecraft’s operational state of health.

Twin sister of Mars Express
Venus Express largely re-uses the architecture developed for Mars Express. This has reduced manufacturing cycles and halved the mission cost, while still targeting the same scientific goals. Finally approved in late 2002, Venus Express was thereby developed fast, indeed in record time, to be ready for its 2005 launch window.

However, Venusian environmental conditions are very different to those encountered around Mars. Solar flux is four times higher and it has been necessary to adapt the spacecraft design to this hotter environment, notably by entirely redesigning the thermal insulation.

Whereas Mars Express sought to retain heat to enable its electronics to function properly, Venus Express will in contrast be aiming for maximum heat dissipation in order to stay cool.

The solar arrays on Venus Express have been completely redesigned. They are shorter and are interspersed with aluminium strips to help reject some solar flux to protect the spacecraft from temperatures topping 250ºC.

It has even been necessary to protect the rear of the solar arrays – which normally remain in shadow – in order to counter heat from solar radiation reflected by the planet’s atmosphere.

An atmosphere of mystery
Following on from the twenty or so American and Soviet missions to the planet carried out since 1962, Venus Express will endeavour to answer many of the questions raised by previous missions but so far left unanswered.

It will focus on the characteristics of the atmosphere, its circulation, structure and composition in relation to altitude, and its interactions with the planet’s surface and with the solar wind at altitude.

To perform these studies, it has seven instruments on board: three are flight-spare units of instruments already flown on Mars Express, two are from comet-chaser Rosetta and two were designed specifically for this mission.

The PFS high-resolution spectrometer will measure atmospheric temperature and composition at varying altitudes. It will also measure surface temperature and search for signs of current volcanic activity.

The SPICAV/SOIR infrared and ultraviolet spectrometer and the VeRa instrument will also probe the atmosphere, observing stellar occultation and detecting radio signals; the former will in particular seek to detect molecules of water, oxygen and sulphuric compounds thought to be present in the atmosphere.

The VIRTIS spectrometer will map the various layers of the atmosphere and conduct multi-wavelength cloud observation in order to provide images of atmospheric dynamics.

Assisted by a magnetometer, the ASPERA 4 instrument will analyse interaction between the upper atmosphere and the solar wind in the absence of magnetospheric protection such as that surrounding Earth (for Venus had no magnetic field). It will analyse the plasma generated by such interaction, while the magnetometer will study the magnetic field generated by the plasma.

The VMC camera will monitor the planet in four wavelengths, notably exploiting one of the ‘infrared windows’ revealed in 1990 by the Galileo spacecraft (when flying by Venus en route for Jupiter), making it possible to penetrate cloud cover through to the surface. The camera will also be used to monitor atmospheric dynamics, notably to observe the double atmospheric vortex at the poles, the origin of which still remains a mystery.

Original Source: ESO News Release

Venus Express Nearly Ready to Launch

Venus Express on top of its launcher. Image credit: ESA. Click to enlarge.
Following the announcement of the Venus Express launch delay due to particulate contamination found in the launcher fairing where the spacecraft was installed, ESA staff and industry teams have started an inspection of the spacecraft. This recovery ‘investigation procedure’ has so far revealed a spacecraft in good status.

Having been removed from the Soyuz rocket, the upper composite, consisting of the Venus Express spacecraft attached to the Fregat upper stage and all housed in the rocket fairing, was transported to the Baikonur cosmodrome’s Upper Composite Integration Facility in the early morning of Sunday 23 October. On Monday 24 October the fairing was removed and engineers started the inspection to assess the status of the spacecraft.

The scenario is so far very encouraging, as only fairly large particles, pieces of the insulating material initially covering the launcher’s Fregat upper stage, have been found on the body of the spacecraft. These have been easy to identify by naked eye or with UV lamps, and are being carefully removed with tweezers, vacuum-cleaners or nitrogen gas airbrushes, according to size.

In the next couple of days the inspections and cleaning of Venus Express will continue, focussing on the instrument optics and apertures. After this step, Venus Express will be ready for the electric tests, routine checks that precede the final cleaning done just before the encapsulation with the fairing. The upper composite will then be complete again and will be ready for re-integration with the launcher.

ESA and Starsem, the company responsible for the Soyuz-Fregat launcher, are merging the results of their parallel investigations and recovery measures to define a new launch date in the shortest time frame. The ESA Project team is confident that Venus Express will be launched well within the launch window, which closes on 24 November this year.

Original Source: ESA News Release