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


          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

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

UK will lead European exoplanet mission

A telescope to study the atmospheres of planets beyond our Solar System will be launched by the European Space Agency in the late 2020s.

The mission, to be known as Ariel, was selected by the organisation’s Science Programme Committee on Tuesday.

The venture will be led scientifically from the UK by University College London astrophysicist Giovanna Tinetti.

“In the next decade we will see many, many planets being discovered – thousands, actually,” she said.

“All this is amazing, but we want to go beyond that and start to understand the nature of those planets, how they formed, how they evolved, and ultimately to put our Solar System in the bigger picture,” the principal investigator told BBC News.

Ariel will use a metre-sized mirror and instrumentation designed to analyse, in visible and infrared light, the chemical make-up of the gases that shroud distant worlds, or exoplanets as they are known.

This information should provide insights on how certain types of planets come to form around particular stars.

Prof Tinetti explained: “We want to sample lots of planets – some that are small like the Earth or very big like Jupiter; and at different temperatures – extremely hot, warm or temperate – around very different types of stars.

“We want to sample all the extremes and the more normal cases, because what we want to try to understand is the ‘standard model’ for planets, if such a model even exists.”

Ariel (Atmospheric Remote-Sensing Infrared Exoplanet Large-survey)

Ariel is the latest selection in Esa’s Medium Class portfolio. To win the launch opportunity in 2028, the proposal had to beat competition from an X-ray telescope (Xipe) and a mission to study energetic particles around the Earth (Thor).

A detailed technical assessment will now be conducted before the Ariel project is formally “adopted” – Esa legal-speak for “final go-ahead”. This sign-off, which should happen in the next two years, paves the way for manufacture of the flight hardware.

Ariel is the third exoplanet venture chosen by Esa in recent years.

Already coming down the line is a small telescope called Cheops that should go up next year to better measure the size of these far-off worlds; and this will be followed in 2026 by Plato, a telescope that aims to find “true Earths” – planets the same size as our home world that orbit at the same distance from Sun-like stars.

And the Americans, too, have their dedicated planet-hunters, with the newest, the Transiting Exoplanet Survey Satellite (Tess), launching in the next few weeks.

But at some point, the science of exoplanets has to move beyond simply finding and counting objects; their chemical compositions and physical conditions have to be determined.

The telescope that will start to make big inroads into this problem is the James Webb observatory, the successor to Hubble.

Due in orbit next year, it will study planetary atmospheres in exquisite detail with its 6.5m-diameter mirror. But the US space agency-led mission will probably only get to look at perhaps 150-200 exoplanets in its first five years of operation because of all the other demands on its time from astronomers.

Ariel, on the other hand, will have the single quest and that should see it characterising in the region of 500-1,000 planets during its primary years in orbit.

Steady platform

And one aspect that would work in Ariel’s favour is the absence of any moving parts in its build, commented Plato team-member Dr Don Pollaco from Warwick University, UK.

“The issue with all of these planet experiments is that the signals you are looking for are so incredibly small that any systematics in the instrument itself will dominate the signal,” he explained.

“And the systematics are often associated with bits that move. So the great thing about Ariel is that it is fixed-format – nothing changes,” he told BBC News.

Ariel is likely to cost Esa about €460m (£405m) for the spacecraft chassis, the launch vehicle and operations. As is customary for science missions like this, the agency’s individual member states pick up the cost of the scientific payload.

The UK will have the technical lead on the project and the instrumentation therefore will be assembled at the Rutherford Appleton Laboratory at Harwell in Oxfordshire.

Dr Graham Turnock, the chief executive of the UK Space Agency, said: “It is thanks to the world-leading skills of our innovative space community that a UK-led consortium has been chosen to take forward the next ESA science mission. This demonstrates what a vital role we continue to play in European collaboration on research in space.

“The Ariel mission is a prime example of the scientific innovation underpinning the wider economy. It relies on the UK’s science and engineering expertise, which are at the forefront of the government’s Industrial Strategy.”

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