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[Jez]

'Supermodel' satellite set to fly
By Jonathan Amos
Science reporter, BBC News
Neil Wallace reveals the inner workings of Goce's ion engine

Europe is set to launch one of its most challenging space missions to date.

The Goce satellite will map minute variations in the pull of gravity experienced across the planet.

Scientists will use its data to improve their understanding of how the oceans move, and to frame a universal system to measure height anywhere on Earth.

The super-sleek spacecraft will go into orbit on a modified intercontinental ballistic missile from the Plesetsk Cosmodrome in north-west Russia.

http://news.bbc.co.u...ure/6919016.stmLift-off for the Rockot vehicle is timed for 1421 GMT on Monday.

Most satellites launched into space are ugly boxes. The European Space Agency's (Esa) Goce satellite is very different.

"This is the most beautiful satellite that has ever been built - and for good reason," enthused one of the scientists who conceived the mission, Reiner Rummel, from the Technical University of Munich, Germany.

Goce's striking good-looks are a requirement of the extremely testing environment in which it will have to operate.

The arrow shape and fins are necessary to keep the spacecraft stable as it flies through the wisps of air still present at an altitude just under 270km.

This orbit is much lower than for most Earth observation missions but will be essential if Goce is to sense the very subtle gravity anomalies that exist across the planet.

"Our current knowledge of the Earth's gravity is incomplete," explained Danilo Muzi, Esa's Goce programme manager.

"Gravity is the force we experience daily; it keeps our feet on the ground. But there is this general misconception that it is constant everywhere on the globe, which is not true. If we go to the North Pole we will weigh more than if we are at the equator." Goce data will be used to construct an idealised surface called a geoid



This extraordinary phenomenon is explained in part by the shape of the planet. It is not a perfect sphere - it is flatter at the poles, fatter at the equator. Its interior layers are also not composed of uniform shells of homogenous rock - some regions are thicker or denser.

This leads to an irregular distribution of mass; and as everything that has mass is pulled by gravity, its tug becomes irregular, too.

The variations, though, are miniscule - almost imperceptible.

Meeting the measurement challenge in itself resulted in two years' delay for the Gravity Field and Steady-State Ocean Circulation Explorer (Goce). Engineers have had to work through immense technical difficulties.

At the heart of the spacecraft is a device known as a gradiometer.

"This is a very complex instrument," said Andrea Allasio, who led the production of the satellite at Thales Alenia Space in Italy. "It is, for sure, the most sophisticated gradiometer which has ever been prepared for a satellite."

It consists of three pairs of "proof masses", or accelerometers. They are aligned at 90 degrees, across each axis. The entire set-up is mounted inside an ultra-stable casing.  

As Goce bumps through the Earth's gravity field, the accelerometers will sense the fantastically small disturbances.

"We have one comparison that we often make," explained Rune Floberghagen, Esa's Goce mission manager.

"Imagine a snowflake, which has a fraction of a gram, slowly falling down on to the deck of a supertanker. The acceleration that the supertanker experiences from that snowflake is comparable to the sensitivity of our instrument," he told BBC News.

There is however a potential showstopper: the low altitude Goce must fly to get the detail it seeks in the gravity signal. The constant buffeting the satellite receives from the residual air still present in the thermosphere would ordinarily drown out the data.

So Goce employs an ion engine to maintain a steady path - a sort of cruise control. The engine is throttled up and down, producing exquisite levels of thrust by accelerating charged atoms of xenon through nozzles at the rear of the spacecraft.

"We are an enabling technology on this mission; it couldn't happen without us," said Neil Wallace from Qinetiq, the UK technology firm which supplied the engine. "But then this mission has many such technologies."

GRAVITY FIELD AND STEADY-STATE OCEAN CIRCULATION EXPLORER 1. The 1,100kg Goce is built from rigid materials and carries fixed solar wings. The gravity data must be clear of spacecraft 'noise'2. Solar cells produce 1,300W and cover the Sun-facing side of Goce; the near side (as shown) radiates heat to keep it cool3. The 5m-by-1m frame incorporates fins to stabilise the spacecraft as it flies through the residual air in the thermosphere4. Goce's accelerometers measure accelerations that are as small as 1 part in 10,000,000,000,000 of the gravity experienced on Earth5. The UK-built engine ejects xenon ions at velocities exceeding 40,000m/s; Goce's mission will end when the 40kg fuel tank empties6. S Band antenna: Data downloads to the Kiruna (Sweden) ground station. Processing, archiving is done at Esa's centre in Frascati, Italy7. GPS antennas: Precise positioning of Goce is required, but GPS data in itself can also provide some gravity field information


Goce's quest is to produce a snapshot of the Earth's gravity field at an unprecedented resolution. The data will inform a multitude of science disciplines:

understanding how the mass of ocean waters circulate, moving heat around the planet, will assist climate prediction

a better knowledge of the way mass is distributed inside the Earth will be useful to those who study geo-hazards such as volcanoes and earthquakes

and because gravity defines what is meant by "up", "down" and "level", the new data can underpin a truly universal system to compare heights the world over

Goce is the first of Esa's Earth Explorers, a series of spacecraft that will provide quick answers to key environmental questions.

Six missions have so far been approved; a seventh is in discussion. All will use cutting-edge space technology to acquire their data. Cryosat has been re-built and will launch later this year
Europe ice mission failure probed

The Goce mission has experienced a series of frustrating delays. It was sent to Plesetsk in August last year and should have orbited in September, but the satellite was then held on the ground because of niggling concerns about the readiness of its launcher system.

The ghost that haunts this mission is the Cryosat satellite. The Esa spacecraft built to map the world's ice fields was supposed to be first Earth Explorer but it was destroyed on launch in 2005 when its Rockot failed and ditched in the Arctic Ocean.

"From the information we have seen from Eurockot (operator) and Khrunichev (manufacturer), we have seen they have done extensive testing," said Danilo Muzi.

"On the basis of all the testing that has been done, and the fact that these tests were successful, then the confidence in the good status of the launcher has been restored," he told BBC News.

Goce will be put into a sun-synchronous orbit, meaning the spacecraft will be kept in daylight for a sustained period of time. The Breeze-KM upper-stage booster will release Goce at an altitude of about 285km.

The satellite will then gradually fall to its operational altitude of 263km, where its ion engine will maintain a steady orbit for the science campaign.

Two major data-gathering periods are planned, each lasting about six months. The first should start in early September after all the in-orbit testing is complete.

The mission will probably be extended if sufficient xenon is left, although some propellant will be needed to take the spacecraft safely out of the sky in a controlled burn-up over ocean waters.

GRAVITY FIELD AND STEADY-STATE OCEAN CIRCULATION EXPLORER 1. Goce senses tiny variations in the pull of gravity over Earth 2. The data is used to construct an idealised surface, or geoid3. It traces gravity of equal 'potential'; balls won't roll on its 'slopes'4. It is the shape the oceans would take without winds and currents5. So, comparing sea level and geoid data reveals ocean behaviour6. Gravity changes can betray magma movements under volcanoes7. A precise geoid underpins a universal height system for the world8. Gravity data can also reveal how much mass is lost by ice sheets
Jonathan.Amos-INTERNET@bbc.co.uk

[freaky2]

The first article has made me think of a very bright star I always see when I go to my friend's house. Maybe next time I can keep a watch on it to see if it moves.

[Rainmaster]

freaky2, on Mar 16 2009, 09:06 AM, said:

The first article has made me think of a very bright star I always see when I go to my friend's house. Maybe next time I can keep a watch on it to see if it moves.

Just make sure to watch where you're walking

[freaky2]

Rainmaster, on Mar 16 2009, 07:23 PM, said:

Just make sure to watch where you're walking

I already never do it

[Jez]

Any luck spotting that star again?

[freaky2]

Been buried under work for uni, no time to visit friends. Maybe this weekend

[Argento Reloaded]

I´m considering to buy a telescope for my son. He loves astronomy but I have no idea wich the best entry level type telescope I should choose. Suggestions?

[pumpdoc]

http://www.nasa.gov/multimedia/nasatv/

Anybody besides me that watches this stuff, space walks are especially cool

[Jez]

freaky2, on Mar 18 2009, 11:41 AM, said:

Been buried under work for uni, no time to visit friends. Maybe this weekend

What are you studying?

Argento, on Mar 20 2009, 05:39 AM, said:

I´m considering to buy a telescope for my son. He loves astronomy but I have no idea wich the best entry level type telescope I should choose. Suggestions?

That's a nice gift idea. What's your budget, Argento?

pumpdoc, on Mar 20 2009, 05:58 AM, said:

http://www.nasa.gov/multimedia/nasatv/

Anybody besides me that watches this stuff, space walks are especially cool

Yep, I love this stuff! Watching a succesfull launch also does it for me bigtime.

Yes, I want to propose to a shuttle launch.

Edited by Jez, 19 March 2009 - 11:57 PM.

[Rainmaster]

Extreme DIY: http://news.bbc.co.u...rld/7953792.stm

[Jez]

Rainmaster, on Mar 20 2009, 11:17 AM, said:

Extreme DIY: http://news.bbc.co.u...rld/7953792.stm

Gotta love it! What a feeling that would be to be involved!

[Jez]

Astronauts fail to budge stuck cargo carrier

File imageby Staff Writers
Washington (AFP) March 23, 2009
The Discovery astronauts were unable to dislodge a stuck cargo carrier system during their third and final space walk Monday, and carried on with their busy to-do list on the orbiting space station, NASA said.

Richard Arnold and Joseph Acaba, two former science teachers turned astronauts, emerged from the decompression chamber at 1537 GMT, some six minutes earlier than planned.

One of their tasks during a six-and-a-half hour walk in space was to unblock the external cargo carrier after Acaba and fellow astronaut Steven Swanson inadvertently inserted a restraining pin upside down on Saturday.

Their attempts to fully deploy the system, however, were unsuccessful and mission control told them to stop trying and secure the system with "long-duration tethers," which will protect the hardware until another attempt can be made in the future.

"Because the problem is not yet understood, Mission Control cancelled Acaba and Arnold's installation of a similar payload attachment system on the starboard side" of the ISS, NASA said.

Discovery and the International Space Station (ISS) maneuvered into lower orbit Sunday to avoid a piece of floating debris that could have passed close by during Monday's spacewalk.

Discovery's steering jets turned the shuttle and space station 180 degrees for three hours to increase drag, which altered the vessel's trajectory, lowering it by two miles (3.3 kilometers) to avoid the debris, explained NASA spokesman Bill Jeffs.

The object, which measures a little over 10 centimeters (four inches), came from a Chinese rocket launched in 1999 that broke up in March 2000.

The most important task during the third spacewalk is to reposition an equipment cart from one side to another of the Mobile Transporter, the ISS's rail line.

The cart is used in the maintenance of the station's Canadian-built robot arm and the Dextre service robot. The robot arm will move the cart to another worksite at the station for tasks to be performed in upcoming space shuttle missions.

Elsewhere on the ISS, experts were working on a water-recycling unit that processes astronauts' urine and sweat into drinking water. A replacement part was brought by the Discovery and testing began Sunday. The samples will be taken back to Earth for analysis.

The machine, which was delivered to the ISS in November -- and has not yet functioned properly -- is key to sustaining a bigger crew on the orbiting station and for long-term space expeditions, such as moon landings or missions to Mars.

Carrying large amounts of water aboard the shuttle or other space vessels is expensive and takes up room needed for other equipment.

The two astronauts will also grease the hand joints of the ISS's robot arm and will install a thermal blanket on the Dextre robot. Dextre can be attached to the robot arm to manipulate small objects for tasks usually completed by an astronaut.

One of the Discovery mission's biggest tasks was to deliver the last set of solar arrays, which were successfully unfurled Friday.

The ISS now has four solar panels, two per wing, containing 32,800 cells that convert sunlight into electricity.

They will boost the outpost's full power generation from 90 to 120 kilowatts, providing the power the space station needs to carry out scientific experiments aboard Kibo and the European Columbus laboratory.

The additions also make it possible to double the space station's crew from three to six, beginning in May.

Discovery's latest mission, which blasted off last Sunday from Florida with a crew of seven astronauts, is one of the last major efforts in a decade-long push by 16 countries to build the 100-billion-dollar outpost in space.

NASA has scheduled nine shuttle flights through 2010 to finish building the space station. Upcoming shuttle flights also include the last mission to service the orbiting Hubble telescope in May.

Discovery is due to land back on Earth on March 28 at 1742 GMT, two days after a Russian Soyuz mission takes off for the ISS carrying a crew of three, including US billionaire businessman Charles Simonyi, who has shelled out 35 million dollars for his second trip as a space tourist.

On Discovery, crew member Koichi Wakata became the first Japanese astronaut to join the ISS for a long stay. He is scheduled to remain on the orbiting station until June. The Discovery mission, delayed five times, is the first by a US space shuttle in 2009.

Edited by Jez, 24 March 2009 - 12:49 AM.

[Jez]

That lucky b#####d!!


Space tourist blasts off to ISS
The Soyuz launch went entirely according to plan

A Russian Soyuz rocket has blasted off from Kazakhstan's Baikonur cosmodrome to ferry a three-member crew to the International Space Station (ISS). Among them is US billionaire Charles Simonyi, aged 60, who is the first space tourist to make the trip twice.

The software tycoon, who has paid $35m (£24m) for his trip, will be the last tourist for the foreseeable future.

During his 13-day mission, he will help with research projects and take part in live broadcasts with schools.

'Crowded' ISS

Expedition 19 to the ISS, which also includes Russian cosmonaut Gennady Padalka and US astronaut Michael Barratt, lifted off on schedule at Baikonur.



Mr Simonyi will help astronauts with research projectsMr Padalka and Mr Barratt will form part of a new six-member crew aboard the ISS.

Until now only three astronauts lived on the station at any one time.

Doubling the number will allow more scientific research to be carried out, but it will also mean there will be less room for visitors.

Mr Simonyi said the $35m he had paid for the flight was his contribution to the exploration of space.

Watch the launch here

[Jez]

Gravity satellite feels the force
By Jonathan Amos
Science reporter, BBC News



Europe's innovative Goce satellite has switched on the super-sensitive instrument that will make ultra-fine measurements of Earth's gravity. The sophisticated gradiometer will feel the subtle variations in Earth's tug as it sweeps around the globe.

The spacecraft has also fired up the British-built engine that will help maintain its orbit.

Goce needs tiny but continuous levels of thrust to keep it stable and prevent it from falling out of the sky.

European Space Agency (Esa) mission manager Rune Floberghagen said all systems on the spacecraft had now been activated following the launch from Russia last month.

Goce is being overseen from Esa's "mission control" in Germany"The big news today is that the gradiometer is fully working; all its accelerometers have survived the launch and they are producing meaningful data," he told BBC News.

"Now we must learn to drive our super-satellite."

To acquire its data, Goce carries a set of six state-of-the-art high-sensitivity accelerometers. These have been arranged in pairs and sit across the three axes of the spacecraft.

As Goce "bumps" through Earth's gravity field, the accelerometers will sense fantastically small disturbances - as small as one part in 10,000,000,000,000 of the gravity experienced at the Earth's surface.

This exquisite measurement capability meant some very fragile mechanisms had to be built into the gradiometer, and developing these delicate technologies so they could also survive the intense shaking experienced at launch proved to be one of the major design challenges of the mission.

Monday's switch-on will be seen as vindication of the extraordinary engineering work on the gradiometer and its accelerometers, led by the Thales Alenia Space and Onera companies (France).

Gravity data can tell scientists about the nature of the Earth's interior"This was a pivotal moment in the mission, for sure," said Dr Floberghagen.

"What's very important in this first phase is that we see some consistency between the measurements from the six sensors onboard; and we do see that, which is all very exciting. But still, we need to characterise each one of these very precise sensors, and that process is not over."

The other major milestone in the commissioning of Goce has been the successful start-up of its electric propulsion system.

Built by UK technology firm Qinetiq, the T5 ion engine is a critical part of the mission. The satellite flies so low in order to get a good gravity signal that it actually brushes through the top of the atmosphere.

Without the constant force applied from the T5 unit, the drag on Goce would rapidly pull it out of orbit. But the engine's presence is also integral to the acquisition of the gravity data itself.

The buffeting from air molecules would ordinarily upset Goce's gradiometer instrument, so the British engine is designed to throttle up and down to counteract this disturbance and leave a clean signal.

ELECTRIC PROPULSION ON GOCE Satellite carries two engines; one is back-up in case of failureT5 unit draws power from solar panels on side of spacecraftElectrons are stripped off xenon atoms to give them chargeAn electric field then hurls the xenon ions through rear nozzleXenon exits at speeds in excess of 40,000m/s to provide thrustAmount of thrust is moderated by gradiometer information
'Cruise control' for spacecraftGravity satellite leads new waveThe levels and range of thrust needed, however, are tiny - a continuously variable force of anywhere between one and 20 millinewtons during the science phase of the mission.

This is similar to the force a postcard will exert when laid down on a surface.

Put another way, you would need to strap together 650 million Goce spacecraft to achieve the same amount of thrust as Europe's mighty Ariane rocket at launch.

Commissioning last week saw both T5 "chains" (there are two engines; one is a back-up) perform precisely to specification.

The levels of thrust delivered were shown to be within 10 micronewtons of what was being demanded at any one time. The drive is also very straight, with the spacecraft deviating offline by only 0.6 of a degree.

"You work on these things for so many years that you should be cold and confident that it will all work, but there's always a risk that it won't," Neil Wallace, who leads the Qinetiq electric propulsion team, told BBC News.

"One of the tests we did was to demand a thrust ramp, from one to 20 millinewtons, as quickly as possible. This is one of the most critical requirements and the most difficult to achieve, and both chains did it perfectly."

The T5 was then switched off to allow controllers to concentrate on the gradiometer's behaviour.

"The other reason was to let the spacecraft's orbit decay. All the time we are thrusting, Goce is going up. We did one orbit at 8.3mN and we went up by 150m."

Neil Wallace reveals the inner workings of Goce's ion engineGoce was placed initially by its Rockot launcher in an orbit some 283km above the Earth. Spacecraft operators are allowing it to fall by between 150m to 200m a day.

It is now just above 275km and will continue to drop to its target science altitude of 263km.

By then, the satellite will have been put in a "closed loop" mode whereby the gradiometer and the engine will be working in tandem to fly a stable path and gather the gravity data.

Scientists will use Goce to help them construct high-resolution maps of the geoid, which, simply put, is an idealised globe with a surface of constant gravity.

Geoid information has many applications but perhaps the biggest knowledge gains will come in the study of ocean behaviour.

Understanding better how gravity pulls water - and therefore heat - around the globe will improve computer models that try to forecast climate change.

GRAVITY FIELD AND STEADY-STATE OCEAN CIRCULATION EXPLORER 1. Goce senses tiny variations in the pull of gravity over Earth 2. The data is used to construct an idealised surface, or geoid3. It traces gravity of equal 'potential'; balls won't roll on its 'slopes'4. It is the shape the oceans would take without winds and currents5. So, comparing sea level and geoid data reveals ocean behaviour6. Gravity changes can betray magma movements under volcanoes7. A precise geoid underpins a universal height system for the world

[medilloni]

Great stuff Jez,

Love the bit about "...need to strap together 650 million Goce spacecraft to achieve the same amount of thrust as Europe's mighty Ariane rocket at launch", and especially, "similar to the force a postcard will exert when laid down on a surface.".

See?  Brit's still building the best injuns  

Just a thought, why aren't NASA and other bods using this technology for powering spacecraft once they're away from the effect of gravity?  An example would be manouvering for docking to the space station - surely the weight of conventional fuel saved during lift-off would be important....

Edited by medilloni, 08 April 2009 - 09:10 AM.

[Max Mosley]

Dr Floberghagen says 'und next ve vill take over ze world!'.

Oh and are those T5s ion engines?  I thought they were being considered for some space missions as a main source of propulsion.  The thrust is small but there's no resistance in space.  Wonder how long they can fire for and what the final speed could be.  Perhaps the idea was to use hydrogen instead but there surely isn't enough of the stuff in space?

Another idea was solar sails, and they generate very small accelerations too but of course the acceleration is continuous so eventually large speeds would be obtained.

[Rainmaster]

^I love it when Murray talks dirty.

[Max Mosley]

[AutoRacer5]

Stephen Colbert won the vote to have a node on the ISS named after him, but NASA still has the final say.