Europe’s Mars rover takes shape

So, here it is. Europe’s Mars rover. Or rather, a copy of it.

This is what they call the Structural Thermal Model, or STM. It is one of three rovers that will be built as part of the European Space Agency’s ExoMars 2020 mission to search for life on the Red Planet. And, no, we’re not sending all three to the Red Planet.

The STM is used to prove the design. It will go through a tough testing regime to check the rover that does launch to Mars – the “flight model” – will be able to cope with whatever is thrown at it.

What’s the third robot for? It stays on Earth and is used to troubleshoot any problems. If mission control needs to re-write a piece of software to overcome some glitch on the flight rover, the patch will be trialled first on the “engineering model” before being sent up to the Red Planet.

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    It’s getting real, then. After all the delays and arguments, the ExoMars hardware is at last taking shape.

    The STM, which has been assembled at the Airbus factory in Stevenage in the UK, is about to be boxed up and sent to a facility in Toulouse for environmental testing.

    “We’re going to ‘shake and bake’ it to demonstrate that the rover can survive all of the vibrations and acoustic loading during the rocket launch, all of the shocks of deployment, and then all of the thermal stresses it will experience – all the highs and lows – both when it’s in deep space and on the surface,” explained engineer Abbie Hutty.

    “This is where we qualify our design, proving that it meets the requirements.”

    Esa member states will meet on 8 May for the Critical Design Review. This will consider every aspect of the venture and is really the last chance to change some aspect of the mission. There may be some tinkering at the edges, but the broad scope will not alter.

    There have been recent difficulties related to the “Analytical Drawer”, which will hold ExoMars’ life-seeking instruments. A leak was found in the test model for this box and a membrane also failed. “But, OK, this is why you do testing,” said ExoMars project scientist Jorge Vago.

    “Overall, I think we’re on a good track to complete everything we need to do. We have margin. It could be better, but we’re not working double shifts and on weekends, which is what you see on most projects towards the end.”

    ExoMars is a joint venture with the Russians. They’re building the descent module – the mechanism that gets the rover down to the surface once it enters the planet’s atmosphere.

    A structural model of this system is also in production, and when the rover STM completes its Toulouse exams, the two will have a fit check in Moscow and undergo another round of testing as a combined unit.

    A couple of developments in the rover’s capabilities are worth reporting. It’s now been confirmed the robot will be able to wheel-walk.

    This is a driving mode that sees the vehicle lift up its wheels and take steps – as opposed to just rolling forward. It would allow ExoMars to tip-toe out of a sand trap, if it gets caught in one. Nasa’s Spirit rover was snared in this way and the mission lost as a consequence.

    Wheel-walking was in the initial spec for ExoMars and then withdrawn for cost reasons. I’m pleased to report that member states have found the money to put it back on the rover.

    The other key capability that needs a similar response is autonomous navigation. This self-driving system would permit the robot to plot its own path across the surface of Mars, independently avoiding hazards such as large rocks and trenches.

    Without it, controllers back on Earth have to direct every move, and that’s a very slow process.

    “Clearly we need it, otherwise we will pay a high price in terms of the science you can do,” Dr Vago said.

    “To give you an example – if we need to move 500m, with autonomous navigation we can do that in five days. Without it, the drive might take 15 days.”

    Whether the rover gets this smart upgrade is probably going to depend on the UK and French space agencies.

    They’re the parties most interested in the technology and will have to fund it.

    Fortunately, autonomous navigation is a software complement, so even though hardware choices have to be locked down now there is still some extra time to resolve this particular issue.

    If you’re wondering where ExoMars will be sent, the decision will be made in November. Scientists will meet at Leicester University to choose between two equatorial locations, known as Oxia Planum and Mawrth Vallis.

    They’re both areas rich in clay minerals – the kinds of sediments that must have formed during prolonged rock interactions with water.

    Jonathan.Amos-INTERNET@bbc.co.uk and follow me on Twitter: @BBCAmos

Gaia telescope’s ‘book of the heavens’ takes shape

The Gaia observatory has released a second swathe of data as it assembles the most precise map of the sky.

The European Space Agency telescope has now plotted the position and brightness of nearly 1.7 billion stars.

It also has information on the distance, motion and colour of 1.3 billion of these objects.

Gaia’s “book of the heavens” will not be complete until the 2020s, but when it is the map will underpin astronomy for decades to come.

It will be the reference frame used to plan all observations by other telescopes. It will also be integral to the operation of all spacecraft, which navigate by tracking stars.

But beyond that, Gaia promises a raft of new discoveries about the properties and structure of our Milky Way Galaxy, its history and evolution into the future.

It will enable scientists to find new asteroids and planets; and to test physical constants and theories.

Gaia should even refine the techniques used to measure distances across the wider Universe, and reduce the uncertainties we currently have about the age of the cosmos.

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    Gaia was launched in December 2013 to an orbit some 1.5 million km from Earth.

    Its two identical telescopes throw their captured light on to a huge, one-billion-pixel camera detector connected to a trio of instruments.

    A first tranche of measurements was released in 2016. This contained the position and brightness of “just” 1.1 billion stars, and information on the distance and motion of the two million brightest objects.

    This second data release adds 600 times more stars with distances, covering a volume 1,000 times larger and all with precisions that are 100 times better.

    “This is a unique moment,” said leading British Gaia scientist Prof Gerry Gilmore. “This is the first time that mankind has had a significant 3D map of a significant volume of the Milky Way. It really is a breakthrough moment,” he told a meeting at the Royal Astronomical Society in London.


    Gaia: How far is it to the nearest stars?

    • As the Earth goes around the Sun, relatively nearby stars appear to move against the “fixed” stars that are even further away
    • Because we know the Sun-Earth distance, we can use the parallax angle to work out the distance to the target star
    • But such angles are very small – less than one arcsecond for the nearest stars, or 0.05% of the full Moon’s diameter
    • Gaia will make repeat observations to reduce measurement errors down to seven micro-arcseconds for the very brightest stars
    • Parallaxes are used to anchor other, more indirect techniques on the ‘ladder’ deployed to measure the most far-flung distances

      Gaia measures anything that moves – which is actually everything that is out there.

      It sees stars’ “proper motion”, which is their general track across the heavens as they orbit the galaxy. The telescope also sees their “parallax” – their apparent looping behaviour, which is a function of Earth and Gaia changing their vantage point as they circle the Sun (It is the parallaxes that yield the distances).

      And what Gaia also sees is the stars’ movement along its line of sight – their so-called “radial velocity”, their true motion on the sky. Gaia delivers this data for the first time in the new release.

      “We now have seven million line-of-sight velocities of stars which is more than all other measurements ever done. This is a huge sample compared with the few hundred thousand that we had before,” said Prof Mark Cropper, from the Mullard Space Science Laboratory, University College London.

      It is the radial velocities that allow researchers to make movies of the Milky Way, to run its life forwards and backwards in time, to determine, with the aid of other Gaia information, where stars were born and where they will likely end their days. It should be possible, for example, to find our Sun’s siblings – the stars that were created in the same gas and dust cloud billions of years ago but then subsequently went their different ways.

      There will be another two big data releases in the coming years. The more Gaia works, the more precise its measurements – and the more objects it will detect. There is an expectation, for instance, that tens of thousands of planets will eventually be found in Gaia’s data.

      The scale of the venture means there is too much information for professional astronomers to scrutinise, and amateurs and schools are being asked to get involved.

      An alert system operates that throws up interesting objects that brighten or dim out of the ordinary. Some of these will be exploding stars – supernovae.

      Many UK schools are now engaged in classifying these objects.

      Meg Greet, a physics teacher from Eastbury Community School in the London Borough of Barking & Dagenham, said Gaia was a fantastic educational tool: “These long-term embedded enrichment projects, rather than school trips and one-off activities, are the things that make a genuine impact on our school-children scientists, helping them to develop their creativity, their questioning skills – the kind of things they need to become the scientists of the future.”

Space agencies aim to deliver rocks from Mars to Earth

The US and European space agencies are edging towards a joint mission to bring back rock and soil samples from Mars.

Nasa and Esa have signed a letter of intent that could lead to the first “round trip” to another planet.

The move was announced as a meeting in Berlin, Germany, discussed the science goals and feasibility of a Mars Sample Return (MSR) mission.

The venture would allow scientists to answer key questions about Martian history.

Those questions include whether the Red Planet once hosted life.

Scientists at the Mars meeting said that there was only so much they could learn from Martian meteorites and from the various rovers and static landers sent to the Red Planet.

The next step had to be a mission that would retrieve samples from the Martian surface, blast them into space in a capsule and land them safely on Earth.

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    They could then be subjected to detailed analysis in laboratories, using instruments that are too big and power-hungry to carry as part of a robotic rover’s payload and techniques that are difficult to perform from 55 million kilometres away.

    Making the announcement at the ILA Berlin Air and Space Show, which is taking place at the same time as the Mars science meeting, Dr Thomas Zurbuchen, Nasa’s associate administrator for science, said: “We want to partner with the European Space Agency, but also with other partners.”

    He said this included potential link-ups with the commercial space sector, adding: “We will at every point look at what is available in the commercial market. Nasa has no interest whatsoever in developing things that we can buy.”

    Dave Parker, director of human and robotic exploration at Esa, commented: “It’s very important that every mission we send to Mars discovers something slightly unusual. It’s on the basis of that that we tend to plan the next mission or next missions.”

    Nasa’s 2020 rover mission is expected to help pave the way for Mars Sample Return, by drilling into the surface and caching the cores in containers. But this is intended as a demonstration.

    A mission design would need to be drawn up in coming years. Previous sample return concepts envisaged a rover storing geological samples from scientifically desirable locations on Mars.

    The cached samples would then be loaded on to an ascent vehicle which would lift off from the Martian surface. After the cruise back to Earth, a descent module would parachute down through Earth’s atmosphere, delivering the first retrieved Martian samples directly into the hands of experts waiting on the ground.

    Dr Caroline Smith, head of Earth sciences collections at London’s Natural History Museum, is attending the Berlin meeting. “I would say it’s a reinvigoration of the process,” she told BBC News.

    “Numerous studies have said the only way it’s going to be achieved is through international co-operation. So I think this is a really good message from Nasa and Esa, that we are really going to work together to achieve this – the next frontier of exploration of the Solar System.”

    She added: “There’s a real buzz in the room. I’ve spoken to my colleagues and they’ve said: ‘Wow, we’re really going to do this’!”

    Protecting the planet

    If life existed in the past on the Red Planet, it would likely have been microbial in nature. Scientists want to first know whether conditions were right for life to get started in the past and, if so, whether evidence of fossil microbes remains. They also want to resolve whether there’s life on the Red Planet now. “We’ll only be able to conclusively answer those questions by bringing samples back,” she explained.

    The current high levels of cosmic radiation on Mars’ surface – a consequence of its thin atmosphere – would create a hostile environment for any organisms. But there are ways life might be able to cling on. The possibility that organisms live in the Martian subsurface today means the mission would be subject to strict quarantine, or “planetary protection”, measures.

    “We have to be careful we’re not contaminating Mars with material from our planet, and we want to make sure we’re not accidentally contaminating the samples in a way that would interfere with experiments we want to do on Earth,” explained Dr Smith. She added: “If there’s something hazardous on Mars, we don’t want to accidentally release that into Earth’s biosphere.

    “We are used to handling hazardous materials, whether they be biological or nuclear. There are technologies that exist to be able to handle these in a safe way.”

    Dr Zurbuchen said the sample return mission could also be crucial for later planned human exploration of Mars, which he said Nasa should start thinking about in the 2030s.

    “I can imagine a lot of scenarios where the samples are actually critical for how we explore as humans,” he said.

    For example, scientists want to sample dust from both the atmosphere and soil, because it could have an important impact. If future human “bases” were to rely on solar cells, atmospheric dust might block out sunlight – hampering electricity generation.

    It might also cause problems inside the crew habitats. Dr Smith commented: “If that dust is ubiquitous, and gets everywhere and you’ve got people living there who are breathing in the dust, is it going to be a potential hazard to astronauts?”

    While rocks relevant to the life question are an obvious target for sample return, igneous rocks formed by magma from Mars’ interior are also on the wish-list. “By collecting igneous rocks, we get to understand the geochemical evolution of the planet Mars, we get to know when lavas were being erupted,” said Caroline Smith.

    Analysis of these rocks could help provide a much more accurate chronology for the Red Planet, which currently relies in part on values worked out from studies of the Moon.

    In 2009, Nasa and Esa agreed to collaborate on the Mars Joint Exploration Initiative, which would have culminated in the recovery of samples in the 2020s. But in 2011, Nasa cancelled its participation amid a budgetary squeeze.

    The 2nd International Mars Sample Return Conference is taking place from 25-27 April 2018 in Berlin.

    Follow Paul on Twitter.

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Map records UK’s small ups and downs

The subtle warping of the land surface across the entire UK has been mapped in detail for the first time.

This view of changing topography was built from more than 2,000 radar images acquired by the European Union’s Sentinel-1 satellites.

It should prove an invaluable tool for policymakers, and for industries working on big infrastructure projects.

The map reveals areas of subsidence and uplift, some of which, like those above old mine workings, could be hazardous.

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    Having detailed knowledge of their whereabouts, however, means the risks can now be properly assessed and mitigated.

    For example, it can be seen how sections of the proposed route for the High Speed 2 rail link go across land that is still responding to the presence of coal pits at depth.

    Some of the ground above disused tunnels is descending, while other locations are rebounding as water fills abandoned cavities.

    The motion may be only millimetres per year, but it still needs to be recognised and factored into construction plans.

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      The deformation map was assembled using a technique called satellite interferometry.

      By overlaying repeat radar pictures of the same location, it becomes possible to discern even the smallest changes in a scene.

      Developed some 25 years ago, the approach always worked best where the spacecraft could see specific hard features time and time again.

      These “persistent scatterers” would be objects like the corners of city buildings. But a few years ago scientists from the University of Nottingham found a way to also capture changes where “soft” features, such as vegetation, dominated the landscape.

      Using this Intermittent Small Baseline Subset (ISBAS) analysis, it is now possible to frame a full picture of Britain that incorporates both urban and rural terrain.

      Geomatic Ventures Limited (GVL) is the company that has been spun out from the university to commercialise the technology. Its chief technical officer, Dr Andy Sowter, told BBC News: “Persistent scattering interferometry relies on points that absolutely persist through all observations, but with the Sentinel satellites we now have so many images that we can use points that persist only perhaps through two-thirds of the observations.

      “In the past this data would have been thrown away, but we’re able to be more selective, and that allows us to get at the full dynamic landscape for the first time.”

      It has to be said, there are groups in the satellite interferometry community that are yet to be convinced by ISBAS. These teams believe that tracking change in vegetated areas is still a major challenge.

      “While this initial map shows the potential power of Sentinel-1 for deformation monitoring on a nationwide-scale, many in the community have legitimate concerns about the reliability of these particular results, especially outside urban areas,” commented Prof Tim Wright from the University of Leeds.

      The resolution of the map is about 90m. It will not show the movement in someone’s backyard, but it can notice the major deformation features.

      The map will be scoured for widespread compaction of soils, landslides, eroding coastlines, and the subsidence over landfill and underground works.

      For the public release of the map, GVL has highlighted some examples of interest.

      These include a 500m-wide zone of depression at Kennington Park, part of the Northern Line tube extension in London. This subsidence is most probably related to the sinking of a shaft that was completed in November 2017.

      In the far north of Scotland, GVL has been monitoring the peatlands of Caithness and Sutherland – the so-called Flow Country. Subsiding bogs release greenhouse gases and so the satellite imagery is a way to keep a check on the UK’s climate commitments.

      “Probably the weirdest example we’ve come across is the 2cm per year uplift at a place called Willand in Devon. It’s a small place on the M5 motorway. We’ve spoken to the Environment Agency and the British Geological Survey, and right now we can’t explain it. We don’t know why it’s going up,” said Dr Sowter.

      The map was put together over a two-year period from 2015 to 2017. But it is essentially now an operational product that could easily be updated every three months.

      What makes this kind of offering possible is the avalanche of data being delivered from orbit by the EU’s Sentinel satellite series. Six spacecraft have so far been launched to image the Earth in a variety of ways, not just radar. A further 14 are already funded to fly.

      All the data is deliberately free and open so that outfits such as GVL can exploit it and innovate new business applications.

      Dr Josef Aschbacher is the director of Earth observation at the European Space Agency, which procures and manages the Sentinels for the EU.

      Speaking here at the European Geosciences Union (EGU) General Assembly in Vienna, Austria, he projected an explosion of data in the years ahead.

      “Today we are producing 14 terabytes of data from the Sentinels alone. We are producing more data from our satellites than all the images and videos being uploaded to Facebook every day,” he told BBC News.

      He said his agency expected to be archiving some 100 petabytes of data by 2026 – all of it available to drive new services such as deformation mapping.

      Jonathan.Amos-INTERNET@bbc.co.uk and follow me on Twitter: @BBCAmos

Tiangong-1: Defunct China space lab comes down over South Pacific

China’s defunct Tiangong-1 space lab mostly broke up on re-entering the Earth’s atmosphere above the South Pacific, Chinese and US reports say.

It re-entered the atmosphere around 00:15 GMT on Monday, China’s Manned Space Engineering Office said.

Tiangong-1 was launched in 2011 to carry out docking and orbit experiments.

It was part of China’s efforts to build a manned space station by 2022, but stopped working in March 2016.

What do we know about where it came down?

The rather vague “above the South Pacific” is the line from space officials.

Experts had struggled to predict exactly where the lab would make its re-entry – and China’s space agency wrongly suggested it would be off Sao Paulo, Brazil, shortly before the moment came.

The European Space Agency said in advance that Tiangong-1 would probably break up over water, which covers much of the Earth’s surface.

It stressed that the chances of anyone being hit by debris from the module were “10 million times smaller than the yearly chance of being hit by lightning”.

It’s not clear how much of the debris reached the Earth’s surface intact.

Why did the space lab fall like this?

Ideally, the 10m (32ft)-long Tiangong module would have been taken out of orbit in a planned manner.

Traditionally, thrusters are fired on large vehicles to drive them towards a remote zone over the Southern Ocean. This option appears not to have been available after the loss of command links.

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    Thirteen space agencies, under the leadership of the European Space Agency, used radar and optical observations to follow Tiangong’s path around the globe.

    Tiangong means ‘Heavenly Palace’

    • The module was launched in 2011 to practise rendezvous and docking
    • Two astronaut crews visited in Shenzhou capsules – in 2012 and 2013
    • They included China’s first female astronauts Liu Yang and Wang Yaping
    • China plans a more permanent space station in the next decade
    • It has developed a heavy-lift rocket, Long March 5, for the purpose

      Is this the biggest space hardware to fall out of the sky?

      Tiangong was certainly on the large size for uncontrolled re-entry objects, but it was far from being the biggest, historically:

      • The US space agency’s Skylab was almost 80 tonnes in mass when it came back partially uncontrolled in 1979. Parts struck Western Australia but no-one on the ground was injured
        • Nasa’s Columbia shuttle would also have to be classed as an uncontrolled re-entry. Its mass was more than 100 tonnes when it made its tragic return from orbit in 2003. Again, no-one on the ground was hit as debris scattered through the US states of Texas and Louisiana

          Astrophysicist Jonathan McDowell believes Tiangong is only the 50th most massive object to come back uncontrolled.

          Skip Twitter post 2 by @planet4589

          By my calculations, Tiangong-1 will be the 50th most massive uncontrolled reentry from Earth orbit in history.

          — Jonathan McDowell (@planet4589) March 25, 2018

          Report

          End of Twitter post 2 by @planet4589

          China has launched a second lab, Tiangong-2, which continues to be operational. It was visited by a re-fuelling freighter, Tianzhou-1, just last year.

          China’s future permanent space station is expected to comprise a large core module and two smaller ancillary modules, and will be in service early in the next decade, the Asian nation says.

          A new rocket, the Long March 5, was recently introduced to perform the heavy lifting that will be required to get the core module in orbit.

Antarctica ‘gives ground to the ocean’

Scientists now have their best view yet of where Antarctica is giving up ground to the ocean as some of its biggest glaciers are eaten away from below by warm water.

Researchers using Europe’s Cryosat radar spacecraft have traced the movement of grounding lines around the continent.

These are the places where the fronts of glaciers that flow from the land into the ocean start to lift and float.

The new study reveals an area of seafloor the size of Greater London that was previously in contact with ice is now free of it.

The report, which covers the period from 2010 to 2016, is published in the journal Nature Geoscience.

“What we’re able to do now with Cryosat is put the behaviour of retreating glaciers in a much wider context,” said Dr Hannes Konrad from the University of Leeds, UK.

“Our method for monitoring grounding lines requires a lot of data but it means you could now basically build a permanent service to monitor the state of the edges of the continent,” he told BBC News.

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    Although the end product is quite simple, the process of getting to it is quite a complex one.

    Viewed from above, the position of grounding lines is not always obvious.

    The glaciers themselves are hundreds of metres thick, and where they begin to float as they come off the continent can be hard to discern in simple satellite images.

    But there are radar techniques that can find their location by spotting the up and down tidal movement of a glacier’s floating ice. This, however, is just a snapshot in time.

    What Dr Konrad and colleagues have done is use these known positions and then combine the data with knowledge about the shape of the underlying rock bed and changes in the height of the glaciers’ surface to track the evolving status of the grounding lines through time.

    The new study triples the coverage of previous surveys.

    On the face of it, the results are pretty much as expected.

    Of the 1,463km² of grounded ice that has been given up, most of it is in well documented areas of West Antarctica where warm ocean water is known to be infiltrating the undersides of glaciers to melt them.

    Dr Konrad explained: “If you take 25m per year as a threshold, which is sort of the average since the end of the last ice age, and you say anything below this threshold is normal behaviour and anything above it is faster than normal – then in West Antarctica, almost 22% of grounding lines are retreating more rapidly than 25m/yr.

    “That’s a statement we can only make now because we have this wider context.”

    The new data-set confirms other observations that show the mighty Pine Island Glacier, one of the biggest and fast-flowing glaciers on Earth, and whose grounding line had been in major retreat since the 1940s, appears now to have stabilised somewhat.

    The line is currently going backwards by only 40m/yr compared with the roughly 1,000m/yr seen in previous studies. This could suggest that ocean melting at the PIG’s base is pausing.

    Its next-door neighbour, Thwaites Glacier, on the other hand, is seeing an acceleration in the reversal of its grounding line – from 340m/yr to 420m/yr.

    Thwaites is now the glacier of concern because of its potential large contribution to global sea-level rise. And the UK and American authorities will shortly announce a major joint campaign to go and study this ice stream in detail.

    Elsewhere on the continent, 10% of marine-terminating glaciers around the Antarctic Peninsula are above the 25m/yr threshold; whereas in East Antarctic, only 3% are.

    The significant stand-out in the East is Totten Glacier, whose grounding line is retreating at a rate of 154m/yr.

    Overall, for the entire continent, 10.7% of the grounding line retreated faster than 25m/yr, while 1.9% advanced faster than the threshold.

    One fascinating number to come out of the study is that grounding lines in general are seen to retreat 110m for every metre of thinning on the fastest flowing glaciers. This relationship will constrain computer models that try to simulate future change on the continent.

    Leeds co-author Dr Anna Hogg said: “The big improvement here is Cryosat, which gives us continuous, continent-wide coverage, which we simply didn’t have with previous radar missions.

    “Its capabilities have allowed us to build up a picture of retreat rates, especially at the steeply sloping margins of the continent, which is where these changes are taking place. We have eight years of coverage now and it’s guaranteed in the future for as long as Cryosat keeps working,” she told BBC News.

    Since conducting the study at Leeds, Dr Konrad has now moved to the Alfred Wegener Institute in Bremerhaven, Germany.

    Jonathan.Amos-INTERNET@bbc.co.uk and follow me on Twitter: @BBCAmos

Space junk demo mission launches

A UK-led experiment to tackle space junk has been sent into orbit.

It takes the form of a small satellite that will practise techniques for tracking debris and capturing it.

The RemoveDebris system is heading to the International Space Station where astronauts are expected to set the experiment running in late May.

Space junk is an ever-growing problem with more than 7,500 tonnes of redundant hardware now thought to be circling the Earth.

Ranging from old rocket bodies and defunct spacecraft through to screws and even flecks of paint – this material poses a collision hazard to operational missions.

RemoveDebris will showcase technologies that could be used to clean up some of this techno-garbage.

The 100kg demonstrator left Earth on Monday onboard a SpaceX Falcon 9 rocket. It should arrive at the ISS on Wednesday.

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    The satellite will be stored at the station for a number of weeks, before being released by the orbiting platform’s robotic arm to begin a series of manoeuvres.

    RemoveDebris carries its own “junk” – two small cubesats that it will eject and then track.

    For one of these, the “mother” satellite will demonstrate the laser ranging (Lidar) and camera technology needed to monitor and characterise debris in orbit; for the the other cubesat, it will actually try to snare the object with a net.

    There will also be a demonstration of a small harpoon.

    The RemoveDebris satellite will extend a boom with a target on the end.

    The sharp projectile will be fired at this to learn more about how such devices move and impact a surface in micro-gravity.

    At the end of its mission, RemoveDebris will deploy a large membrane.

    This “sail” will increase the drag from air molecules high in the atmosphere and act to pull the satellite down to Earth much faster than would otherwise be the case.

    The project, which draws on expertise from across Europe, is led from the University of Surrey’s Space Centre.

    Its principal investigator is Prof Guglielmo Aglietti. He said the jury was still out on the best way to capture and remove space junk.

    “As you know, there are other people who are going with the idea of a robotic arm. All these different technologies have their advantages and disadvantages,” he told BBC News.

    “For example, the ones we are testing – the net and the harpoon – are simple and low cost, but could be considered more risky in certain circumstances than a robotic arm.

    “On the other hand, if your piece of debris is spinning very fast, it becomes very difficult to capture it with a robotic arm and an approach with a net could work better.”

    He added: “The reason we are doing this mission this way is because it is low cost. In my opinion, whether or not there are going to be real missions to remove debris will depend on cost. And I worry that if they are extremely expensive, people will think about other priorities.”

    The entire RemoveDebris project is costing €15m (£13m). Half of this is coming from the European Commission; the other half is coming from the 10 partners involved.

    These include Airbus, which supplied the harpoon technology, and Surrey Satellite Technology Limited, which assembled the spacecraft.

    The mission has been organised through NanoRacks, a Houston, US, company that specialises in deploying small satellites from the space station.

    Jonathan.Amos-INTERNET@bbc.co.uk and follow me on Twitter: @BBCAmos

Dozen black holes found at galactic centre

A dozen black holes may lie at the centre of our galaxy, the Milky Way, researchers have said.

A new analysis provides support for a decades-old prediction that “supermassive” black holes at the centres of galaxies are surrounded by many smaller ones.

However, previous searches of the Milky Way’s centre, where the nearest supermassive black hole is located, have found little evidence for this.

Details appear in the journal Nature.

Charles Hailey from Columbia University in New York and colleagues used archival data from Nasa’s Chandra X-ray telescope to come to their conclusions.

They report the discovery of a dozen inactive and low-mass “binary systems”, in which a star orbits an unseen companion – the black hole.

The supermassive black hole at the centre of the Milky Way, known as Sagittarius A* (Sgr A*), is surrounded by a halo of gas and dust that provides the perfect breeding ground for the birth of massive stars. These stars live, die and could turn into black holes there.

In addition, black holes from outside the halo are believed to fall under the influence of Sgr A* as they lose their energy, causing them to be pulled into its vicinity, where they are held captive by its force.

Some of these bind – or “mate” – to passing stars, forming binary systems.

Previous attempts to detect this population of black holes have looked for the bright bursts of X-rays that are sometimes emitted by black hole binaries.

Faint and steady

“The galactic centre is so far away from Earth that those bursts are only strong and bright enough to see about once every 100 to 1,000 years,” said Prof Hailey.

Instead, the Columbia University astrophysicist and his colleagues decided to look for the fainter but steadier X-rays emitted when these binaries are in an inactive state.

“Isolated, unmated black holes are just black – they don’t do anything,” said Prof Hailey.

“But when black holes mate with a low mass star, the marriage emits X-ray bursts that are weaker, but consistent and detectable.”

A search for the X-ray signatures of low-mass black hole binaries in the Chandra data turned up 12 within three light-years of Sgr A*.

By extrapolating from the properties and distribution of these binaries, the team estimates that there may be 300-500 low-mass binaries and 10,000 isolated low-mass black holes surrounding Sgr A*.

Prof Hailey said the finding “confirms a major theory”, adding: “It is going to significantly advance gravitational wave research because knowing the number of black holes in the centre of a typical galaxy can help in better predicting how many gravitational wave events may be associated with them.”

Gravitational waves are ripples in the fabric of space-time. They were predicted by Albert Einstein’s general theory of relativity and detected by the Ligo experiment in 2015. One way these ripples arise is through the collision of separate black holes.

European Space Agency teams with ICEYE Finnish start-up

The European Space Agency is to work with Finnish start-up ICEYE on ways to exploit its novel radar satellites.

ICEYE-X1 was launched in January – the first of multiple spacecraft that will go up in the coming years.

About the size of a suitcase, these are the world’s smallest synthetic aperture radar satellites and cost a fraction of traditional platforms.

The Esa/ICEYE cooperation will focus on technology development and uses for the forthcoming constellation.

It will see future satellites – in particular, their radar antenna design – being tested at the agency’s technical centre (ESTEC) at Noordwijk, Netherlands.

Esa’s Earth observation headquarters (ESRIN) at Frascati, Italy, will also assist with calibration and validation of the ICEYE data.

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    The agency is keen to see how radar images from the mini-satellites can be drawn into the European Union’s Copernicus programme, the broad system of services that depend on space data.

    Areas of interest are likely to include maritime applications such as ship monitoring, and oil-spill and iceberg detection.

    “This is how we can best help so-called ‘New Space’ companies,” said Esa’s director of Earth observation, Josef Aschbacher.

    “They don’t need us to build their radar instrument or their satellites; they’re doing that themselves, and I would say faster than if we were involved. But there is a lot of engineering expertise here at Esa that is based on radar missions of more than 20 years,” he told BBC News.

    “We want to help ICEYE grow the market by testing and evaluating their value for Copernicus which is potentially a huge customer for them.”

    Esa’s own radar missions currently in service include the Sentinel 1a and 1b spacecraft.

    • In this preliminary flood analysis exercise image, ICEYE has combined and processed Esa’s Sentinel-1 satellite data with ICEYE-X1 satellite data to visualise potential change detection capabilities. The image features the River Seine as it ran past Paris-Orly airport in France at the start of the year when water levels were extremely high.

      ICEYE-X1’s bus, or chassis, which contains the radar instrument and spacecraft sub-systems, measures 80cm by 60cm by 50cm. Its radar antenna, after being unfolded in orbit, is 3.5m in length.

      These dimensions are much smaller than those of past radar missions.

      Like all New Space companies, the Helsinki-based outfit is exploiting the use of cheap electronics normally found in consumer products to reduce both the size and cost of its designs.

      The first satellite has now taken hundreds of images from an altitude of 505km.

      ICEYE is exploring how these pictures, and the analysis of them, could best benefit commercial partners.

      Radar’s great advantage is that it senses the ground in all weathers and at night.

      ICEYE wants to couple this vision with high temporal resolution, meaning a single spot on the Earth’s surface would be surveyed several times a day. Algorithms will scour the data to detect significant changes.

      High-repeat requires a network of satellites, and ICEYE envisages perhaps 30 platforms in orbit.

      Such a constellation could observe London or Paris, say, 15 times a day.

      Spatial resolution is important, too. ICEYE-X1 has been returning 10m-resolution pictures, meaning they see any features bigger than that. But iterations of the instrument and the radar antenna are expected to bring the resolution down to 3m.

      “ICEYE-X1 has far exceeded our expectations,” said Rafal Modrzewski, CEO and co-founder of ICEYE.

      “We did expect it to perform well, obviously; but for a first spacecraft from a start-up to perform so well – it’s been a great mission and a really exciting period for us,” he told BBC News.

      ICEYE-X2 is scheduled to go up in August and ICEYE-X3 is aiming for a November launch.

      ICEYE is working with a Polish company to part-manufacture ICEYE-X2.

      For ICEYE-X3, the entire bus will come from York Space Systems, a Colorado, US, concern.

      Mr Modrzewski said his company was trying to establish how much in-house building to do versus external sourcing.

      “We’re also looking into at least one more satellite because the sooner we get our constellation up and running, the sooner it will be providing our customers and partners with the capability. But we have to be careful. We don’t want to launch too fast and then fail.”

      Jonathan.Amos-INTERNET@bbc.co.uk and follow me on Twitter: @BBCAmos

Curiosity rover: 2,000 days on Mars

Nasa’s Curiosity rover, also known as the Mars Science Laboratory (MSL), is celebrating 2,000 martian days (sols) investigating Gale Crater on the Red Planet. In that time, the robot has made some remarkable observations. Here are just a few of them, chosen by the Curiosity science team.

Looking back: In the history of the space age, some of the most dramatic planetary images ever taken have been of Earth, but photographed looking back from deep space. This image by Mastcam on the Curiosity Rover shows our planet as a faint pinpoint of light in the martian night sky. Every day scientists from across the world drive the Curiosity rover and study the Red Planet about 100 million miles from Earth.

The beginning: The first image that Curiosity took came back just 15 minutes after landing on 5 August 2012. Getting our imagery and other data relies on the timing of Mars Reconnaissance Orbiter (MRO) overpasses, a pattern which determines the structure of the martian working day, or sol. It shows a grainy Front Hazard Camera image – the team normally use these to help avoid obstacles – of our ultimate goal Mount Sharp. When this image came back we knew it was going to be a successful mission.

River pebbles: Once we had started driving (16 sols after landing), we soon came across these pebble beds. The rounded shape of the clasts shows that they formed in an ancient, shallow river, flowing from the surrounding four-billion-year-old highlands into Gale Crater. The inset Mastcam image shows one of the pebbles in close-up. Contrary to our expectations before MSL, the crust being eroded by the rivers was not all dark, primitive basalt but a more evolved composition and mineralogy. Pebbles caught up in this ancient martian river are causing us to rethink our view of how the underlying igneous crust and mantle of Mars formed.

Ancient lake: Before landing and in the early part of the mission, the team wasn’t sure what all of the terrains identified from MRO HiRISE orbital imagery were. They might have been lava flows or lake sediments, without close-up “ground truth” it was impossible to be certain. This image settled the debate and was a seminal stage in Martian exploration. Yellowknife Bay is made of layers of fine grained sand and muds, which were deposited as rivers flowed into an ancient Gale Crater lake. We made our first of 16 drill holes on sol 182 – we do this to get rock in to the spectrometers housed in the body of our rover – here at the John Klein site. The results – including identifying clays, organics and nitrogen-bearing compounds – showed us that this had been a habitable environment for microbial life. The next discovery step – Was There Life? – remains to be determined.

Deep water: The Pahrump Hills section Curiosity encountered around sol 753 was key for developing our understanding of Gale’s past environment. Here the rover observed thinly layered mudstones, which represented mud particles settling out from suspension within the deeper lake. The Gale Lake has been a long-standing, deep body of water.

An unconformity: At Mount Stimson, the rover identified from sol 980 a thick sandstone unit overlying the lake deposits, separated by a geological feature called an unconformity. This unconformity represents a time where erosive processes took over after millions of years when the lake had finally dried up – to form a new land surface. This shows evidence of events happening over “deep time”, similar to those that the pioneering geologist James Hutton described in his field work in the late 18th Century at Siccar Point on the Scottish Coast.

Desert sands: The Namib dunes encountered close up by Curiosity at sol 1192 is a small part of the great Bagnold dune field. Its the first active dunefield explored on the surface of another planet and Curiosity had to pick its way carefully along and through the field as moving sands are an obstacle for rovers. Although the Martian atmosphere is a fraction of the density of that of Earth’s, it is still capable of transporting sediment and is capable of creating such beautiful structures akin to those we see in the deserts of Earth.

Wind sculptures: The Murray Buttes, photographed by Mastcam on sol 1448, formed of the same sandstones observed at Mount Stimson and represent a lithified dune field created by dunes similar to those in the present day Bagnold dune field. These desert-formed sandstones sit above an unconformity, and this suggests that after a long period with a humid climate, the climate became drier and wind became the dominant agent shaping the environment at Gale Crater.

Dried muds: Curiosity is able to perform detailed analyses of the Gale rocks with the ChemCam laser and telescope mounted on its mast. Here on sol 1555 at Schooner Head we came across a set of ancient mudcracks and sulphate veins. On Earth, lakes typically dry up in places around their margins and here on Mars the Gale lake was no different. You can see the red crosses where we fired the laser at the rock, creating a small plasma spark, with the wavelength of light in the spark telling us the composition of the mudstone and veins.

Cloudy skies: This sequence of images was taken with Curiosity’s Navigational Cameras (NavCam) on sol 1971 as we pointed them towards the sky. Occasionally on the cloudiest of Martian days we are able to make out faint clouds in the sky. These images are processed to highlight differences, allowing us to see the clouds move across the sky. This sequence shows previously unseen cloud features with prominent zig-zag patterns visible. The three images, from start to finish, cover approximately 12 minutes on Mars.

Obligatory ‘selfie’: The Curiosity rover has gained a reputation over the years that rivals those of Instagram users for its many “selfies” taken along its traverse. These selfies are not all for show though as they help the team track the state of the rover throughout the course of the mission for changes such as wheel wear and dust accumulation. Curiosity’s self-portraits are taken using the rover’s Mars Hand Lens Imager (MAHLI) situated on its robotic arm and are generated by merging a series of high-resolution images into a mosaic. This one taken on sol 1065 at the Buckskin locality shows the main mast of Curiosity with its ChemCam telescope used to determine rock compositions, and the Mastcam cameras. In the foreground you can see that Curiosity has just been drilling, leaving a small grey pile of tailings.

Long drive: This panorama taken with the rover’s Mastcam shows Curiosity’s 18.4km drive over the last 5 years from the Bradbury landing site to its current location on the Vera Rubin Ridge (VRR). VRR was formerly known as Hematite Ridge due to the high concentrations of the iron oxide mineral hematite detected here from orbit. As hematite largely forms in the presence of water, this location was a high-priority target for the Curiosity rover science team to investigate in order to assess how the conditions in Gale Crater changed over its geological history. This key location is the perfect spot for Curiosity to spend its 2000th sol, and for all of us to look back on the many discoveries made so far in the mission.

By John Bridges, Ashwin Vasavada, Susanne Schwenzer, Sanjeev Gupta, Steve Banham, Candice Bedford, Christina Smith, Brittney Cooper & the MSL Team