Big harpoon is ‘solution to space junk’

Airbus is testing a big harpoon to snare rogue or redundant satellites and pull them out of the sky.

The 1m-long projectile would be attached, through a strong tether, to a chase spacecraft.

Once the target was captured and under control, the chase vehicle would then drag its prey down into the atmosphere to burn to destruction.

Airbus has been working on the concept for a number of years now, developing ever bigger systems.

It is a response to the growing problem of orbital junk – old pieces of hardware that continue to circle the globe and which now pose a collision threat to operational satellites.

  • UK ‘space drones’ look to Proton ride
  • Old satellites will need ‘rapid disposal’
  • Space junk mission prepares for launch

    Something in the region of 20,000 items of 10cm or larger are currently being tracked.

    The latest Airbus harpoon is being designed with the capability to capture one of the biggest rogue items of the lot – Europe’s defunct Envisat Earth observation platform.

    This 8-tonne behemoth died suddenly in orbit in 2012. “Envisat is the outlier,” explained advanced project engineer Alastair Wayman.

    “If we can design a harpoon that can cope with Envisat, then it should be able to cope with all other types of spacecraft including the many rocket upper-stages that remain in orbit.”

    The testing at the aerospace company’s facility in Stevenage, UK, involves firing the harpoon, using compressed air, into a panel that is representative of the kinds of material used to build satellite structures.

    Typically, this takes the form of 3cm-thick, composite honeycomb panels that incorporate a lot of aluminium.

    “The harpoon goes through these panels like a hot knife through butter,” said Mr Wayman.

    “Once the tip is inside, it has a set of barbs that open up and stop the harpoon from coming back out. We’d then de-tumble the satellite with a tether on the other end.”

    This is where harpoons should come into their own, over other methods of capture such as nets and robotic arms. A harpoon is relatively simple. You line up the target and shoot.

    “Many of these targets will be tumbling and if you were to use a robotic arm, say, that involves a lot of quite complex motions to follow your target,” Mr Wayman explained.

    “Whereas, with the harpoon, all you have to do is sit a distance away, wait for the target to rotate underneath you, and at the right moment fire your harpoon. And because it’s a really quick event, it takes out a lot of the complexity.”

    You still have to bring the tumbling satellite under control using thrusters on the chase vehicle – but computer simulations show this should be possible.

    The European Space Agency, which is responsible for Envisat, is considering all options at the moment, and the demonstration missions that fly in the next few years will almost certainly go for easier, more cooperative targets first. Indeed, a miniature version of the Airbus harpoon is set to launch next month on a mission called RemoveDebris.

    This demonstrator satellite, developed at the Surrey Space Centre, will carry its own piece of junk which it will release and then attempt to retrieve. It will trial a net, but will perform a harpoon test as well to further knowledge about how such systems will behave in the weightless environment of space.

    For the big harpoon back in Stevenage, it is now ready to move to its next development stage. This will involve firing the projectile over a distance of 25m, the sort of separation over which the real flight model would have to work.

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

Big harpoon is ‘solution to space junk’

Airbus is testing a big harpoon to snare rogue or redundant satellites and pull them out of the sky.

The 1m-long projectile would be attached, through a strong tether, to a chase spacecraft.

Once the target was captured and under control, the chase vehicle would then drag its prey down into the atmosphere to burn to destruction.

Airbus has been working on the concept for a number of years now, developing ever bigger systems.

It is a response to the growing problem of orbital junk – old pieces of hardware that continue to circle the globe and which now pose a collision threat to operational satellites.

  • UK ‘space drones’ look to Proton ride
  • Old satellites will need ‘rapid disposal’
  • Space junk mission prepares for launch

    Something in the region of 20,000 items of 10cm or larger are currently being tracked.

    The latest Airbus harpoon is being designed with the capability to capture one of the biggest rogue items of the lot – Europe’s defunct Envisat Earth observation platform.

    This 8-tonne behemoth died suddenly in orbit in 2012. “Envisat is the outlier,” explained advanced project engineer Alastair Wayman.

    “If we can design a harpoon that can cope with Envisat, then it should be able to cope with all other types of spacecraft including the many rocket upper-stages that remain in orbit.”

    The testing at the aerospace company’s facility in Stevenage, UK, involves firing the harpoon, using compressed air, into a panel that is representative of the kinds of material used to build satellite structures.

    Typically, this takes the form of 3cm-thick, composite honeycomb panels that incorporate a lot of aluminium.

    “The harpoon goes through these panels like a hot knife through butter,” said Mr Wayman.

    “Once the tip is inside, it has a set of barbs that open up and stop the harpoon from coming back out. We’d then de-tumble the satellite with a tether on the other end.”

    This is where harpoons should come into their own, over other methods of capture such as nets and robotic arms. A harpoon is relatively simple. You line up the target and shoot.

    “Many of these targets will be tumbling and if you were to use a robotic arm, say, that involves a lot of quite complex motions to follow your target,” Mr Wayman explained.

    “Whereas, with the harpoon, all you have to do is sit a distance away, wait for the target to rotate underneath you, and at the right moment fire your harpoon. And because it’s a really quick event, it takes out a lot of the complexity.”

    You still have to bring the tumbling satellite under control using thrusters on the chase vehicle – but computer simulations show this should be possible.

    The European Space Agency, which is responsible for Envisat, is considering all options at the moment, and the demonstration missions that fly in the next few years will almost certainly go for easier, more cooperative targets first. Indeed, a miniature version of the Airbus harpoon is set to launch next month on a mission called RemoveDebris.

    This demonstrator satellite, developed at the Surrey Space Centre, will carry its own piece of junk which it will release and then attempt to retrieve. It will trial a net, but will perform a harpoon test as well to further knowledge about how such systems will behave in the weightless environment of space.

    For the big harpoon back in Stevenage, it is now ready to move to its next development stage. This will involve firing the projectile over a distance of 25m, the sort of separation over which the real flight model would have to work.

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

Plastic particles found in bottled water

Tests on major brands of bottled water have found that nearly all of them contained tiny particles of plastic.

In the largest investigation of its kind, 250 bottles bought in nine different countries were examined.

Research led by journalism organisation Orb Media discovered an average of 10 plastic particles per litre, each larger than the width of a human hair.

Companies whose brands were tested told the BBC that their bottling plants were operated to the highest standards.

The tests were conducted at the State University of New York in Fredonia.

  • Read the full scientific report [PDF]

    Sherri Mason, a professor of chemistry at the university, conducted the analysis and told BBC News: “We found [plastic] in bottle after bottle and brand after brand.

    “It’s not about pointing fingers at particular brands; it’s really showing that this is everywhere, that plastic has become such a pervasive material in our society, and it’s pervading water – all of these products that we consume at a very basic level.”

    Currently, there is no evidence that ingesting very small pieces of plastic (microplastics) can cause harm, but understanding the potential implications is an active area of science.

    Commenting on the results, Prof Mason said: “It’s not catastrophic, the numbers that we’re seeing, but it is concerning.”

    Experts have told the BBC that people in developing countries where tap water may be polluted should continue to drink water from plastic bottles.

    • ‘Shame and anger’ at plastic pollution
    • Earth is becoming ‘Planet Plastic’
    • Plastic pollution in seven charts

      Contacted to comment on the findings, the companies behind the brands have insisted that their products meet the highest standards for safety and quality.

      They also point to the absence of any regulations on microplastics and of the lack of standardised methods of testing for them.

      Last year, Prof Mason found plastic particles in samples of tap water and other researchers have spotted them in seafood, beer, sea salt and even the air.

      This latest work comes amid growing international attention on plastic, fuelled by the BBC’s acclaimed Blue Planet 2 series in which Sir David Attenborough highlighted the threat of plastic waste in our oceans.

      The research into bottled water involved buying packs from 11 different global and national brands in countries chosen for their large populations or their relatively high consumption of bottled water. These were:

      Leading international brands:

      • Aquafina
      • Dasani
      • Evian
      • Nestle Pure Life
      • San Pellegrino

        Leading national brands included:

        • Aqua (Indonesia)
        • Bisleri (India)
        • Epura (Mexico)
        • Gerolsteiner (Germany)
        • Minalba (Brazil)
        • Wahaha (China)

          To eliminate any risk of contamination, purchases in shops and deliveries to courier companies were recorded on video. Some packs in the US were ordered over the internet.

          The screening for plastic involved adding a dye called Nile Red to each bottle, a technique recently developed by British scientists for the rapid detection of plastic in seawater.

          Previous studies have established how the dye sticks to free-floating pieces of plastic and makes them fluoresce under certain wavelengths of light.

          Prof Mason and her colleagues filtered their dyed samples and then counted every piece larger than 100 microns – roughly the diameter of a human hair.

          Some of these particles – large enough to be handled individually – were then analysed by infrared spectroscopy, confirmed as plastic and further identified as particular types of polymer.

          Particles smaller than 100 microns – and down to a size of 6.5 microns – were much more numerous (an average of 314 per litre) and were counted using a technique developed in astronomy for totalling the number of stars in the night sky.

          The make-up of these particles was not confirmed but Prof Mason said they can “rationally expected to be plastic”.

          This is because although Nile Red dye can bind to substances other than plastic – such as fragments of shell or algae containing lipids – these would be unlikely to be present in bottled water.

          Since the study has not been through the usual process of peer review and publication in a scientific journal, the BBC has asked experts in the field to comment.

          Dr Andrew Mayes, of the University of East Anglia and one of the pioneers of the Nile Red technique, told us it was “very high quality analytical chemistry” and that the results were “quite conservative”.

          Michael Walker, a consultant to the Office of the UK Government Chemist and founder board member of the Food Standards Agency, said the work was “well conducted” and that the use of Nile Red has “a very good pedigree”.

          Both of them emphasised that the particles below 100 microns had not been identified as plastic but said that since the alternatives would not be expected in bottled water, they could be described as “probably plastic”.

          One obvious question is where this plastic may be coming from. Given the amount of polypropylene, which is used in bottle caps, one theory is that the act of opening a bottle may shed particles inside.

          To check that the process of testing was not itself adding plastic to the bottles, Prof Mason ran “blanks” in which the purified water used to clean the glassware and the acetone used to dilute the Nile Red dye were themselves investigated.

          Small quantities of plastic were found in them – believed to be from the air – but these were subtracted from the final results.

          A surprise to researchers was the wide variety of findings – 17 of the 259 bottles tested showed no evidence of plastic but all of the rest did, with big differences even within brands.

          A few bottles were found to have thousands of particles – the vast majority being the smaller ones that are “probably plastic” – but others from the same pack had virtually none.

          We contacted the companies involved and most responded.

          Nestle told us its own internal testing for microplastics began more than two years ago and had not detected any “above trace level”. A spokesman added that Prof Mason’s study missed key steps to avoid “false positives” but he invited Orb Media to compare methods.

          Gerolsteiner also said it had been testing its water for microplastics for a number of years and that the results showed levels “significantly below the limits for particles” set for pharmaceutical companies. It said it could not understand how Prof Mason’s study reached its conclusions.

          It also said its measures exceeded industry standards but added that microparticles are “everywhere” so “the possibility of them entering the product from ambient air or packaging materials during the bottling process can therefore not be completely ruled out”.

          Coca-Cola said it had some of the most stringent quality standards in the industry and used a “multi-step filtration process”. But it too acknowledged that microplastics “appear to be ubiquitous and therefore may be found at minute levels even in highly treated products”.

          Danone said it could not comment on the study because “the methodology used is unclear” but added that its own bottles had “food grade packaging”.

          It pointed out that there are no regulations on microplastics or a scientific consensus on how to test for them, and it also highlighted a much smaller German study last year that found plastic particles in single use bottles but not above a statistically significant amount.

          PepsiCo said Aquafina had “rigorous quality control measures sanitary manufacturing practices, filtration and other food safety mechanisms which yield a reliably safe product”.

          It described the science of microplastics as “an emerging field, in its infancy, which requires further scientific analysis, peer-reviewed research and greater collaboration across many stakeholders”.

          The full Orb Media report can be found at www.OrbMedia.org

          Follow David on Twitter

          View comments

Plastic particles found in bottled water

Tests on major brands of bottled water have found that nearly all of them contained tiny particles of plastic.

In the largest investigation of its kind, 250 bottles bought in nine different countries were examined.

Research led by journalism organisation Orb Media discovered an average of 10 plastic particles per litre, each larger than the width of a human hair.

Companies whose brands were tested told the BBC that their bottling plants were operated to the highest standards.

The tests were conducted at the State University of New York in Fredonia.

  • Read the full scientific report [PDF]

    Sherri Mason, a professor of chemistry at the university, conducted the analysis and told BBC News: “We found [plastic] in bottle after bottle and brand after brand.

    “It’s not about pointing fingers at particular brands; it’s really showing that this is everywhere, that plastic has become such a pervasive material in our society, and it’s pervading water – all of these products that we consume at a very basic level.”

    Currently, there is no evidence that ingesting very small pieces of plastic (microplastics) can cause harm, but understanding the potential implications is an active area of science.

    Commenting on the results, Prof Mason said: “It’s not catastrophic, the numbers that we’re seeing, but it is concerning.”

    Experts have told the BBC that people in developing countries where tap water may be polluted should continue to drink water from plastic bottles.

    • ‘Shame and anger’ at plastic pollution
    • Earth is becoming ‘Planet Plastic’
    • Plastic pollution in seven charts

      Contacted to comment on the findings, the companies behind the brands have insisted that their products meet the highest standards for safety and quality.

      They also point to the absence of any regulations on microplastics and of the lack of standardised methods of testing for them.

      Last year, Prof Mason found plastic particles in samples of tap water and other researchers have spotted them in seafood, beer, sea salt and even the air.

      This latest work comes amid growing international attention on plastic, fuelled by the BBC’s acclaimed Blue Planet 2 series in which Sir David Attenborough highlighted the threat of plastic waste in our oceans.

      The research into bottled water involved buying packs from 11 different global and national brands in countries chosen for their large populations or their relatively high consumption of bottled water. These were:

      Leading international brands:

      • Aquafina
      • Dasani
      • Evian
      • Nestle Pure Life
      • San Pellegrino

        Leading national brands included:

        • Aqua (Indonesia)
        • Bisleri (India)
        • Epura (Mexico)
        • Gerolsteiner (Germany)
        • Minalba (Brazil)
        • Wahaha (China)

          To eliminate any risk of contamination, purchases in shops and deliveries to courier companies were recorded on video. Some packs in the US were ordered over the internet.

          The screening for plastic involved adding a dye called Nile Red to each bottle, a technique recently developed by British scientists for the rapid detection of plastic in seawater.

          Previous studies have established how the dye sticks to free-floating pieces of plastic and makes them fluoresce under certain wavelengths of light.

          Prof Mason and her colleagues filtered their dyed samples and then counted every piece larger than 100 microns – roughly the diameter of a human hair.

          Some of these particles – large enough to be handled individually – were then analysed by infrared spectroscopy, confirmed as plastic and further identified as particular types of polymer.

          Particles smaller than 100 microns – and down to a size of 6.5 microns – were much more numerous (an average of 314 per litre) and were counted using a technique developed in astronomy for totalling the number of stars in the night sky.

          The make-up of these particles was not confirmed but Prof Mason said they can “rationally expected to be plastic”.

          This is because although Nile Red dye can bind to substances other than plastic – such as fragments of shell or algae containing lipids – these would be unlikely to be present in bottled water.

          Since the study has not been through the usual process of peer review and publication in a scientific journal, the BBC has asked experts in the field to comment.

          Dr Andrew Mayes, of the University of East Anglia and one of the pioneers of the Nile Red technique, told us it was “very high quality analytical chemistry” and that the results were “quite conservative”.

          Michael Walker, a consultant to the Office of the UK Government Chemist and founder board member of the Food Standards Agency, said the work was “well conducted” and that the use of Nile Red has “a very good pedigree”.

          Both of them emphasised that the particles below 100 microns had not been identified as plastic but said that since the alternatives would not be expected in bottled water, they could be described as “probably plastic”.

          One obvious question is where this plastic may be coming from. Given the amount of polypropylene, which is used in bottle caps, one theory is that the act of opening a bottle may shed particles inside.

          To check that the process of testing was not itself adding plastic to the bottles, Prof Mason ran “blanks” in which the purified water used to clean the glassware and the acetone used to dilute the Nile Red dye were themselves investigated.

          Small quantities of plastic were found in them – believed to be from the air – but these were subtracted from the final results.

          A surprise to researchers was the wide variety of findings – 17 of the 259 bottles tested showed no evidence of plastic but all of the rest did, with big differences even within brands.

          A few bottles were found to have thousands of particles – the vast majority being the smaller ones that are “probably plastic” – but others from the same pack had virtually none.

          We contacted the companies involved and most responded.

          Nestle told us its own internal testing for microplastics began more than two years ago and had not detected any “above trace level”. A spokesman added that Prof Mason’s study missed key steps to avoid “false positives” but he invited Orb Media to compare methods.

          Gerolsteiner also said it had been testing its water for microplastics for a number of years and that the results showed levels “significantly below the limits for particles” set for pharmaceutical companies. It said it could not understand how Prof Mason’s study reached its conclusions.

          It also said its measures exceeded industry standards but added that microparticles are “everywhere” so “the possibility of them entering the product from ambient air or packaging materials during the bottling process can therefore not be completely ruled out”.

          Coca-Cola said it had some of the most stringent quality standards in the industry and used a “multi-step filtration process”. But it too acknowledged that microplastics “appear to be ubiquitous and therefore may be found at minute levels even in highly treated products”.

          Danone said it could not comment on the study because “the methodology used is unclear” but added that its own bottles had “food grade packaging”.

          It pointed out that there are no regulations on microplastics or a scientific consensus on how to test for them, and it also highlighted a much smaller German study last year that found plastic particles in single use bottles but not above a statistically significant amount.

          PepsiCo said Aquafina had “rigorous quality control measures sanitary manufacturing practices, filtration and other food safety mechanisms which yield a reliably safe product”.

          It described the science of microplastics as “an emerging field, in its infancy, which requires further scientific analysis, peer-reviewed research and greater collaboration across many stakeholders”.

          The full Orb Media report can be found at www.OrbMedia.org

          Follow David on Twitter

          View comments

Huge black hole blasts out ‘double burp’

Astronomers have caught a massive black hole letting out a “double burp” after bingeing on hot gas.

When cosmic gas comes near one of these sinkholes, it gets sucked in – but some of the energy is released back into space in the form of a burp.

Now, the Hubble and Chandra space telescopes have detected a new belch emerging from a black hole located about 800 million light-years away.

But they saw a remnant of another belch that occurred 100,000 years earlier.

“Black holes are voracious eaters, but it turns out they don’t have very good table manners,” Julie Comerford, from the University of Colorado, Boulder, told the 231st American Astronomical Society meeting in Washington DC.

“There are a lot of examples of black holes with single burps emanating out, but we discovered a galaxy with a supermassive black hole that has not one but two burps.”

The burp itself consists of a stream of high-energy particles that is kicked back from the black hole.

Supermassive black holes are the largest type and are found at the centres of nearly all big galaxies. X-ray emission from the galaxy in question – called SDSS J1354+1327 – was picked up by the Chandra telescope, allowing researchers to pinpoint the location of its central black hole.

Hubble was able to show them that a cloud of blue-green gas extending away from the black hole represented the aftermath of an earlier burp. They found that electrons had been stripped from atoms in the cone of gas and surmise that this was caused by a burst of radiation from the vicinity of the black hole.

In the meantime, it had expanded 30,000 light-years away from the black hole itself.

But the astronomers found a little loop in the images; the sign of a new belch emerging from the cosmic sinkhole.

“This new burp is actually moving like a shockwave that is coming out very fast,” said Dr Comerford.

“I thought of an analogy for this and I was debating whether to use it or whether it’s a little too gross… imagine someone eating dinner at their kitchen table and they’re eating and burping, eating and burping.

“You walk in the room and you notice there’s an old burp still hanging in the air from the appetiser course. Meanwhile, they’re eating the main course and they let out a new burp that’s rocking the kitchen table.”

She said the black hole was going through a cycle of feasting, burping and napping, before starting over.

The observations are important because they support previous theories – not demonstrated until now – that black holes should go through these cycles. The black holes were expected to become very bright in the process of feasting and burping and then go dark during the nap phase.

“Theory predicted that black holes should flicker on and off very quickly and this galaxy’s evidence of black holes does flicker on timescales of 100,000 years – which is long in human timescales, but in cosmological timescales is very fast,” said Julie Comerford.

The researchers think the black hole erupted twice because it consumed two separate meals. The reason for this might lie with the fact that the galaxy it’s in had collided with another galaxy nearby. This would provide plenty of cosmic gas on which a black hole could feast.

“There’s a stream of stars and gas connecting these two galaxies. That collision led gas to stream towards the supermassive black hole and feed it two separate meals that led to these two separate burps,” said the University of Colorado researcher.

The results are published in the Astrophysical Journal.

Follow Paul on Twitter.

Farthest monster black hole found

Astronomers have discovered the most distant “supermassive” black hole known to science.

The matter-munching sinkhole is a whopping 13 billion light-years away, so far that we see it as it was a mere 690 million years after the Big Bang.

But at about 800 million times the mass of our Sun, it managed to grow to a surprisingly large size in just a short time after the origin of the Universe.

The find is described in the journal Nature.

The newly discovered black hole is busily devouring material at the centre of a galaxy – marking it out as a so-called quasar.

Matter, such as gas, falling onto the black hole will form an ultra-hot mass of material orbiting around it known as an accretion disk.

“Quasars are among the brightest and most distant known celestial objects and are crucial to understanding the early Universe,” said co-author Bram Venemans of the Max Planck Institute for Astronomy in Germany.

This quasar is interesting because it comes from a time when the Universe was just 5% of its current age.

At this time, the cosmos was beginning to emerge from a period known as the dark ages – just before the first stars appeared.

“Gathering all this mass in under 690 million years is an enormous challenge for theories of supermassive black hole growth,” said co-author Eduardo Bañados, from the Carnegie Institution for Science.

The quasar’s distance is described by a property called its redshift – a measurement of how much the wavelength of its light is stretched by the expansion of the Universe before reaching Earth.

The newly discovered black hole has a redshift of 7.54. The higher the redshift, the greater the distance, and the farther back astronomers are looking in time when they observe the object.

Prior to this discovery, the record-holder for the furthest known quasar existed when the Universe was about 800 million years old.

“Despite extensive searches, it took more than half a decade to catch a glimpse of something this far back in the history of the Universe,” said Dr Bañados.

The discovery of a massive black hole so early on may provide key clues on conditions that abounded when the Universe was young.

“This finding shows that a process obviously existed in the early Universe to make this monster,” Dr Bañados explained.

“What that process is? Well, that will keep theorists very busy.”

The unexpected discovery is based on data amassed from observatories around the world. This includes data from the Gemini North observatory on Hawaii’s Maunakea volcano and a Nasa space telescope called the Wide-field Infrared Survey Explorer (Wise).

Event Horizon Telescope ready to image black hole

Scientists believe they are on the verge of obtaining the first ever picture of a black hole.

They have built an Earth-sized “virtual telescope” by linking a large array of radio receivers – from the South Pole, to Hawaii, to the Americas and Europe.

There is optimism that observations to be conducted during 5-14 April could finally deliver the long-sought prize.

In the sights of the so-called “Event Horizon Telescope” will be the monster black hole at the centre of our galaxy.

Although never seen directly, this object, catalogued as Sagittarius A*, has been determined to exist from the way it influences the orbits of nearby stars.

These race around a point in space at many thousands of km per second, suggesting the hole likely has a mass of about four million times that of the Sun.

But as colossal as that sounds, the “edge” of the black hole – the horizon inside which an immense gravity field traps all light – may be no more than 20 million km or so across.

And at a distance of 26,000 light-years from Earth, this makes Sagittarius A* a tiny pinprick on the sky.

The Event Horizon Telescope (EHT) team is nonetheless bullish.

“There’s great excitement,” said project leader Sheperd Doeleman from the Harvard-Smithsonian Center for Astrophysics in Cambridge, Massachusetts.

“We’ve been fashioning our virtual telescope for almost two decades now, and in April we’re going to make the observations that we think have the first real chance of bringing a black hole’s event horizon into focus,” he told BBC News.

The EHT’s trick is a technique called very long baseline array interferometry (VLBI).

This combines a network of widely spaced radio antennas to mimic a telescope aperture that can produce the resolution necessary to perceive a pinprick on the sky.

The EHT is aiming initially to get down to 50 microarcseconds. Team-members talk in analogies, describing the sharpness of vision as being the equivalent of seeing something the size of a grapefruit on the surface of the Moon.

They emphasise the still complex years of work ahead, but also trail the prospect of an imminent breakthrough.

The scientists certainly have an expectation of what they ought to see, if successful.

Simulations rooted in Einstein’s equations predict a bright ring of light fringing a dark feature.

The light would be the emission coming from gas and dust accelerated to high speed and torn apart just before disappearing into the hole.

The dark feature would be the shadow the hole casts on this maelstrom.

“Now, it could be that we will see something different,” Doeleman said.

“As I’ve said before, it’s never a good idea to bet against Einstein, but if we did see something that was very different from what we expect we would have to reassess the theory of gravity.

“I don’t expect that is going to happen, but anything could happen and that’s the beauty of it.”

Over the years, more and more radio astronomy facilities have joined the project. A key recent addition is the Atacama Large Millimeter/submillimeter Array (ALMA) in Chile.

Its extraordinary state-of-the-art technology has at a stroke increased the EHT’s sensitivity by a factor of 10. Hence, the optimism ahead of April.

Even so, scientists have had to install special equipment at all the radio facilities involved in the observations.

This includes big hard drives to store colossal volumes of data, and atomic clocks to precisely timestamp it all.

Nothing happens on the spot – the hard drives must first be flown to a large computing facility at MIT Haystack Observatory in Westford, just outside Boston, Massachusetts.

“Our hard-drive modules hold the capacity of about 100 standard laptops,” said Haystack’s Vincent Fish.

“We have multiple modules at each telescope and we have numerous telescopes in the array. So, ultimately, we’re talking about 10,000 laptops of data.”

It is in Haystack’s correlator computer that the synthesis will begin.

Some very smart imaging algorithms have had to be developed to make sense of the EHT’s observations, but it will not be a quick result.

It could be the end of the year, perhaps the start of 2018, before the team releases an image in public.

Looking to the future, the scientists are already thinking about how to extend their techniques.

For example, the matter closest to the event horizon and about to disappear into Sagittarius A* should take about 30 minutes to complete an orbit.

Katie Bouman, from MIT’s Computer Science and Artificial Intelligence Laboratory, thinks it might be possible to capture this movement.

“We want to push boundaries and to try to make movies from the data,” she told BBC News.

“Maybe we can actually see some of the gas flowing around the black hole. That’s really the next stage of what we’re trying to accomplish with these imaging algorithms.”

First and foremost, the team needs good weather at the participating observing stations in April.

The strategy is to view the galactic centre at a wavelength of 1.3mm (230GHz). This has the best chance of piercing any obscuring gas and dust in the vicinity of the black hole. But if there is too much water vapour above the array’s receivers, the EHT will struggle even to see through Earth’s atmosphere.

Just getting a resolved view of Sagittarius A* would be a remarkable triumph in itself. But the real objective here is to use the imaging capability to go test aspects of general relativity.

If there are flaws to be found in Einstein’s ideas – and scientists suspect there are more complete explanations of gravity out there waiting to be discovered – then it is in the extreme environment of black holes that limitations should be exposed.

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