Satellites Equipped With a Tether Would be Able to De-Orbit Themselves at the end of Their Life

There’s no denying it, we are facing an orbital debris problem! As of January 2019, the ESA’s Space Debris Office estimates that there are at least 34,000 pieces of large debris in Low Earth Orbit (LEO) – a combination of dead satellites, spent rocket stages, and other assorted bits of space junk. And with thousands of satellites scheduled to be launched in the next decade, that problem is only going to get worse.

This is a situation that cries out for solutions, especially when you consider the plans to commercialize LEO and start sending crewed missions to deep space in the coming years. A team of scientists from the Universidad Carlos III de Madrid (UC3M) has come up with a simple but elegant idea: equip future satellites with a tether system so they can de-orbit themselves at the end of their lives.

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Before We Ruin the Universe, We Should Follow Some Space Sustainability Guidelines

There are over 20,000 objects in orbit around Earth that are larger than 10 cm. Image Credit: European Space Agency.

There are 20,000 objects orbiting Earth at this moment that are larger than 10 cm. Out of that number, only about 2,000 are operational satellites. The other 18,000 objects are pieces of junk of varying sizes. But it’s not just junk: it’s dangerous junk.

If that doesn’t sound like a problem, keep this in mind: Thanks to SpaceX and others, we’re living in the age of cheap access to space, and we’re seeing more and more satellites boosted into orbit. The problem won’t go away on its own.

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Spot Failed Soviet Venus Probe Kosmos 482 in Earth Orbit

Venera-8

A ghost from the old Soviet space program may return to Earth in the coming years. Mimicking a campy episode of the 70s series The Six Million Dollar Man, a Soviet Venus lander stranded in Earth orbit will eventually reenter the atmosphere, perhaps as early as late 2019. Fortunately, this isn’t the “Venus Death Probe” that the Bionic Man Steve Austin had to defeat, but Kosmos 482 is part of a fascinating forgotten era of the Space Age and one you can track down in the night sky, with a little skill and patience.

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British Satellite Tests its Space Junk Harpoon

Last summer, a new type of debris-hunting satellite was released from the International Space Station (ISS). It’s known as the RemoveDebris spacecraft, a technology-demonstrator developed by Surrey Satellite Technology Ltd and the Surrey Space Center. The purpose of this satellite is to test whether satellites equipped with targeting software, a debris net and a harpoon are effective at combating space debris.

For the past few months, this spacecraft has been conducting a series of Active Debris Removal (ADR) exercises. About a week ago, according to a recent statement, the RemoveDebris satellite tested out its harpoon for the first time. As you can see from the video, the satellite successfully demonstrated its harpoon system and verified its ability to secure space debris and keep it from flying away.

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Micrometeorite Damage Under the Microscope

If there’s one thing that decades of operating in Low Earth Orbit (LEO) has taught us, it is that space is full of hazards. In addition to solar flares and cosmic radiation, one of the greatest dangers comes from space debris. While the largest bits of junk (which measure more than 10 cm in diameter) are certainly a threat, the real concern is the more than 166 million objects that range in size from 1 mm to 1 cm in diameter.

While tiny, these bits of junk can reach speeds of up to 56,000 km/h (34,800 mph) and are impossible to track using current methods. Because of their speed, what happens at the moment of impact has never been clearly understood. However, a research team from MIT recently conducted the first detailed high-speed imaging and analysis of the microparticle impact process, which will come in handy when developing space debris mitigation strategies.  Continue reading “Micrometeorite Damage Under the Microscope”

A New Solution to the Space Junk Problem. Spacecraft with Plasma Beams to Force Space Junk to Burn Up

A satellite using a bi-directional plasma thruster can direct one beam at space junk, sending it harmlessly into Earth's atmosphere. The other opposite beam can stabilize the position of the satellite itself. Image: Takahashi et. al. 2018.

Space junk is a growing problem. For decades we have been sending satellites into orbit around Earth. Some of them de-orbit and burn up in Earth’s atmosphere, or crash into the surface. But most of the stuff we send into orbit is still up there.

This is becoming an acute problem as years go by and we launch more and more hardware into orbit. Since the very first satellite—Sputnik 1—was launched into orbit in 1957, over 8000 satellites have ben placed in orbit. As of 2018, an estimated 4900 are still in orbit. About 3000 of those are not operational. They’re space junk. The risk of collision is growing, and scientists are working on solutions. The problem will compound itself over time, as collisions between objects create more pieces of debris that have to be dealt with.

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A Satellite With a Harpoon, Net and Drag Sail to Capture Space Junk is in Orbit and Will be Tested Soon

After almost seventy years of spaceflight, space debris has become a rather serious problem. This junk, which floats around in Low Earth Orbit (LEO), consists of the spent first rocket stages and non-functioning satellites and poses a major threat to long-term missions like the International Space Station and future space launches. And according to numbers released by the Space Debris Office at the European Space Operations Center (ESOC), the problem is only getting worse.

In addition, space agencies and private aerospace companies hope to launch considerably more in the way of satellites and space habitats in the coming years. As such, NASA has begun experimenting with a revolutionary new idea for removing space debris. It is known as the RemoveDebris spacecraft, which recently deployed from the ISS to conduct a series of Active Debris Removal (ADR) technology demonstrations.

This satellite was assembled by Surrey Satellite Technology Ltd. and the Surrey Space Center (at the University of Surrey in the UK) and contains experiments provided by multiple European aerospace companies. It measures roughly 1 meter (3 feet) on a side and weighs about 100 kg (220 lbs), making it the largest satellite deployed to the ISS to date.

The purpose of the RemoveDebris spacecraft is to demonstrate the effectiveness of debris nets and harpoons at capturing and removing space debris from orbit. As Sir Martin Sweeting, the Chief Executive of SSTL, said in a recent statement:

“SSTL’s expertise in designing and building low cost, small satellite missions has been fundamental to the success of RemoveDEBRIS, a landmark technology demonstrator for Active Debris Removal missions that will begin a new era of space junk clearance in Earth’s orbit.”

Aside from the Surrey Space Center and SSTL, the consortium behind the RemoveDebris spacecraft includes Airbus Defense and Space – the world’s second largest space company – Airbus Safran Launchers, Innovative Solutions in Space (ISIS), CSEM, Inria, and Stellenbosch University. The spacecraft, according to the Surrey Space Center’s website, consists of the following:

“The mission will comprise of a main satellite platform (~100kg) that once in orbit will deploy two CubeSats as artificial debris targets to demonstrate some of the technologies (net capture, harpoon capture, vision-based navigation, dragsail de-orbitation). The project is co-funded by the European Commission and the project partners, and is led by the Surrey Space Centre (SSC), University of Surrey, UK.”

For the sake of the demonstration, the “mothership” will deploy two cubesates which will simulate two pieces of space junk. For the first experiment, one of the CubeSats  – designated DebrisSat 1 – will inflate its onboard balloon in order to simulate a larger piece of junk. The RemoveDebris spacecraft will then deploy its net to capture it, then guide it into the Earth’s atmosphere where the net will be released.

The second CubeSat, named DebrisSat 2, will be used to test the mothership’s tracking and ranging lasers, its algorithms, and its vision-based navigation technology. The third experiment, which will test the harpoon’s ability to capture orbiting space debris, is set to take place next March. For legal reasons, the harpoon will not be tested on an actual satellite, and will instead consist of the mothership extending an arm with a target on the end.

The harpoon will then be fired on a tether at 20 meters per second (45 mph) to tests it accuracy. After being launched to the station back on April 2nd, the satellite was deployed from the ISS’ Japanese Kibo lab module on June 20th by the stations’ Canadian robotic arm. As Guillermo Aglietti, the director of the Surrey Space Center, explained in an interview with SpaceFlight Now before the spacecraft was launched to the ISS:

“The net, as a way to capture debris, is a very flexible option because even if the debris is spinning, or has got an irregular shape, to capture it with a net is relatively low-risk compared to … going with a robotic arm, because if the debris is spinning very fast, and you try to capture it with a robotic arm, then clearly there is a problem. In addition, if you are to capture the debris with a robotic arm or a gripper, you need somewhere you can grab hold of your piece of debris without breaking off just a chunk of it.”

The net experiment is currently scheduled for September of 2018 while the second experiment is scheduled for October. When these experiments are complete, the mothership will deploy its dragsail to act as a braking mechanism. This expandable sail will experience collisions with air molecules in the Earth’s outer atmosphere, gradually reducing its orbit until it enters the denser layers of Earth’s atmosphere and burns up.

This sail will ensure that the spacecraft deorbits within eights weeks of its deployment, rather than the estimated two-and-half years it would take to happen naturally. In this respect, the RemoveDebris spacecraft will demonstrate that it is capable of tackling the problem of space debris while not adding to it.

In the end, the RemoveDebris spacecraft will test a number of key technologies designed to make orbital debris removal as simple and cost-effective as possible. If it proves effective, the ISS could be receiving multiple RemoveDebris spacecraft in the ftureu, which could then be deployed gradually to remove larger pieces of space debris that threaten the station and operational satellites.

Conor Brown is the external payloads manager of Nanoracks LLC, the company that developed the Kaber system aboard the Kibo lab module to accommodate the increasing number of MicroSats being deployed from the ISS. As he expressed in a recent statement:

“It’s wonderful to have helped facilitate this ground-breaking mission. RemoveDebris is demonstrating some extremely exciting active debris removal technologies that could have a major impact to how we manage space debris moving forward. This program is an excellent example of how small satellite capabilities have grown and how the space station can serve as a platform for missions of this scale. We’re all excited to see the results of the experiments and impact this project may have in the coming years.”

In addition to the RemoveDebris spacecraft, the ISS recently received a new tool for detecting space debris. This is known as the Space Debris Sensor (SDS), a calibrated impact sensor mounted on the exterior of the station to monitor impacts caused by small-scale space debris. Coupled with technologies designed to clean up space debris, improved monitoring will ensure that the commercialization (and perhaps even colonization) of LEO can begin.

Further Reading: Spaceflight Now, RemoveDEBRIS

Did You Know That a Satellite Crashes Back to Earth About Once a Week, on Average?

This past weekend, a lot of attention was focused on the Tiangong-1 space station. For some time, space agencies and satellite trackers from around the world had been predicting when this station would fall to Earth. And now that it has safely landed in the Pacific Ocean, many people are breathing a sigh of relief. While there was very little chance that any debris would fall to Earth, the mere possibility that some might caused its share of anxiety.

Interestingly enough, concerns about how and when Tiangong-1 would fall to Earth has helped to bring the larger issue of orbital debris and reentry into perspective. According to the SDO, on average, about 100 tonnes of space junk burns up in Earth’s atmosphere every year. Monitoring these reentries and warning the public about possible hazards has become routine work for space debris experts.

This junk takes the form of defunct satellites, uncontrolled spacecraft, the upper stages of spent rockets, and various discarded items (like payload covers). Over time, this debris is slowed down by Earth’s upper atmosphere and then succumbs to Earth’s gravitational pull. Where larger objects are concerned, some pieces survive the fiery reentry process and reach the surface.

Radar images acquired by the Tracking and Imaging Radar system – one of the world’s most capable – operated by Germany’s Fraunhofer FHR research institute. Credit: Fraunhofer FHR

In most cases, this debris falls into the ocean or lands somewhere far away from human settlement. While still in orbit, these objects are tracked by a US military radar network, the ESA’s Space Debris Office, and other agencies and independent satellite trackers. This information is shared in order to ensure that margins of error can be minimized and predicted reentry windows can be kept narrow.

For the SDO team, these efforts are based on data and updates provided by ESA member states and civil authorities they are partnered with, while additional information is provided by telescopes and other detectors operated by institutional and private researchers. One example is the Tracking and Imaging Radar (TIRA) operated by the Fraunhofer Institute for High Frequency Physics and Radar Techniques near Bonn, Germany.

This is a challenging task, and often subject to a measure of imprecision and guesswork. As Holger Krag, the head of ESA’s Space Debris Office, explained:

“With our current knowledge and state-of-the-art technology, we are not able to make very precise predictions. There will always be an uncertainty of a few hours in all predictions – even just days before the reentry, the uncertainty window can be very large. The high speeds of returning satellites mean they can travel thousands of kilometres during that time window, and that makes it very hard to predict a precise location of reentry.”

Tiangong-1 as seen in a a composite of three separate exposures taken on May 25, 2013. Credit and copyright: David Murr.

Of the 100 tonnes that enters our atmosphere every year, the vast majority are small pieces of debris that burn up very quickly – and therefore pose no threat to people or infrastructure. The larger descents, of which there are about 50 per year, sometimes result in debris reaching the surface, but these generally land in the ocean or remote areas. In fact, in the history of spaceflight, no casualties have ever been confirmed by falling space debris.

The ESA also takes part in a joint tracking campaign run by the Inter Agency Space Debris Coordination Committee, which consists of experts from 13 space agencies. In addition to the ESA, this committee includes several European space agencies, NASA, Roscosmos, the Canadian Space Agency, the Japanese Aerospace Exploration Agency, the Indian Space Research Organization, the China National Space Agency, and the State Space Agency of Ukraine.

The purpose of these campaigns is for space agencies to pool their respective tracking information from radar and other sources. In so doing, they are able to analyze and verify each other’s data and improve prediction accuracy for all members. The ESA hosted the 2018 campaign, which followed the reentry of China’s Tiangong-1 space station as it entered Earth’s atmosphere this weekend – the details of which are posted on the ESA’s Rocket Science blog.

“Today, everyone in Europe relies on the US military for space debris orbit data – we lack the radar network and other detectors needed to perform independent tracking and monitoring of objects in space,” said Krag. “This is needed to allow meaningful European participation in the global efforts for space safety.”

While predicting when and where space debris will reenter our atmosphere may not yet be an exact science, it does have one thing going for it – its 100% safety record. And as the Tiangong-1 descent showed, early warning and active tracking ensure that potential threats are recognized well in advance.

In the meantime, be sure to enjoy this video on the Space Debris Office’s reentry monitoring, courtesy of the ESA:

Further Reading: ESA

Spacecraft Shields Will Need to be Tough. Here’s an Aluminum Bullet Shattering a Shield at 7 km/s

After sixty years of space agencies sending rockets, satellites and other missions into orbit, space debris has become something of a growing concern. Not only are there large pieces of junk that could take out a spacecraft in a single hit, but there are also countless tiny pieces of debris traveling at very high speeds. This debris poses a serious threat to the International Space Station (ISS), active satellites and future crewed missions in orbit.

For this reason, the European Space Agency is looking to develop better debris shielding for the ISS and future generations of spacecraft. This project, which is supported through the ESA’s General Support Technology Programme, recently conducted ballistics tests that looked at the efficiency of new fiber metal laminates (FMLs), which may replace aluminum shielding in the coming years.

To break it down, any and all orbital missions – be they satellites or space stations – need to be prepared for the risk of high-speed collisions with tiny objects. This includes the possibility of colliding with human-made space junk, but also includes the risk of micro-meteoroid object damage (MMOD). These are especially threatening during intense seasonal meteoroid streams, such as the Leonids.

While larger pieces of orbital debris – ranging from 5 cm (2 inches) to 1 meter (1.09 yards) in diameter – are regularly monitored by NASA and and the ESA’s Space Debris Office, the smaller pieces are undetectable – which makes them especially threatening. To make matters worse, collisions between bits of debris can cause more to form, a phenomena known as the Kessler Effect.

And since humanity’s presence Near-Earth Orbit (NEO) is only increasing, with thousands of satellites, space habitats and crewed missions planned for the coming decades, growing levels of orbital debris therefore pose an increasing risk. As engineer Andreas Tesch explained:

“Such debris can be very damaging because of their high impact speeds of multiple kilometres per second. Larger pieces of debris can at least be tracked so that large spacecraft such as the International Space Station can move out of the way, but pieces smaller than 1 cm are hard to spot using radar – and smaller satellites have in general fewer opportunities to avoid collision.”

To see how their new shielding would hold up to space debris, a team of ESA researchers recently conducted a test where a 2.8 mm-diameter aluminum bullet was fired at sample of spacecraft shield – the results of which were filmed by a high-speed camera. At this size, and with a speed of 7 km/s, the bullet effectively simulated the impact energy that a small piece of debris would have as if it came into contact with the ISS.

Artist’s impression of all the space junk in Earth orbit. Credit: NASA

As researcher Benoit Bonvoisin explained in a recent ESA press release:

“We used a gas gun at Germany’s Fraunhofer Institute for High-Speed Dynamics to test a novel material being considered for shielding spacecraft against space debris. Our project has been looking into various kinds of ‘fibre metal laminates’ produced for us by GTM Structures, which are several thin metal layers bonded together with composite material.”

As you can see from the video (posted above), the solid aluminum bullet penetrated the shield but then broke apart into a could of fragments and vapor, which are much easier for the next layer of armor to capture or deflect. This is standard practice when dealing with space debris and MMOD, where multiple shields are layered together to adsorb and capture the impact so that it doesn’t penetrate the hull.

An common variant of this is known as the ‘Whipple shield’, which was originally devised to guard against comet dust. This shielding consists of two layers, a bumper and a rear wall, with a mutual distance of 10 to 30 cm (3.93 to 11.8 inches). In this case, the FML, which is produced for the ESA by GTM Structures BV (a Netherlands-based aerospace company), consists of several thin metal layers bonded together with a composite material.

Based on this latest test, the FML appears to be well-suited at preventing damage to the ISS and future space stations. As Benoit indicated, he and his colleagues now need to test this shielding on other types of orbital missions. “The next step would be to perform in-orbit demonstration in a CubeSat, to assess the efficiency of these FMLs in the orbital environment,” he said.

And be sure to enjoy this video from the ESA’s Orbital Debris Office:

Further Reading: ESA

A New Kind of Propulsion System That Doesn’t Need Propellant. It Converts Electricity into Thrust and Vice Versa.

The proposed "space-tie" propulsion system being patented by Spanish scientists could be useful on Satellites like the ESA's Sentinel-1, pictured. Image: ESA/ATG

Some of the best things in science are elegant and simple. A new propulsion system being developed in Spain is both those things, and could help solve a growing problem with Earth’s satellites: the proliferation of space junk.

Researchers at Universidad Carlos III de Madrid (UC3M) and the Universidad Politécnica de Madrid (UPM) in Spain are patenting a new kind of propulsion system for orbiting satellites that doesn’t use any propellant or consumables. The system is basically a tether, in the form of an aluminum tape a couple kilometers long and a couple inches wide, that trails out from the satellite. The researchers call it a space tie.

“This is a disruptive technology because it allows one to transform orbital energy into electrical energy and vice versa without using any type of consumable”. – Gonzalo Sánchez Arriaga, UC3M.

The lightweight space tie is rolled up during launch, and once the satellite is in orbit, it’s deployed. Once deployed, the tape can either convert electricity into thrust, or thrust into electricity. The Spanish researchers behind this say that the space-ties will be used in pairs.

The system is based on what is called a “low-work-function” tether. A special coating on the tether has enhanced electron emission properties on receiving sunlight and heat. These special properties allow it to function in two ways. “This is a disruptive technology because it allows one to transform orbital energy into electrical energy and vice versa without using any type of consumable,” said Gonzalo Sánchez Arriaga, Ramón y Cajal researcher at the Bioengineering and Aerospace Engineering Department at UC3M.

As a satellite loses altitude and gets closer to Earth, the tether converts that thrust-caused-by-gravity into electricity for the spacecraft systems to use. When it comes to orbiting facilities like the International Space Station (ISS), this tether system could solve an annoying problem. Every year the ISS has to burn a significant amount of propellant to maintain its orbit. The tether can generate electricity as it moves closer to Earth, and this electricity could replace the propellant. “With a low- work function tether and the energy provided by the solar panel of the ISS, the atmospheric drag could be compensated without the use of propellant”, said Arriaga.

“Unlike current propulsion technologies, the low-work function tether needs no propellant and it uses natural resources from the space environment such as the geomagnetic field, the ionospheric plasma and the solar radiation.” – Gonzalo Sánchez Arriaga, UC3M.

For satellites with ample on-board power, the tether would operate in reverse. It would use electricity to provide thrust to the space craft. This is especially useful to satellites near the end of their operational life. Rather than languish in orbit for a long time as space junk, the derelict satellite could be forced to re-enter Earth’s atmosphere where it would burn up harmlessly.

The space-tie system is based on what’s called Lorentz drag. Lorentz drag is an electrodynamic effect. (Electrodynamics enthusiasts can read all about it here.) I won’t go too deeply into it because I’m not a physicist, but the Spanish researchers suggest that the Lorentz drag can be easily observed by watching a magnet fall through a copper tube. Here’s a video.

Space organizations have shown interest in the low-work-function tether, and the Spanish team is getting the word out to experts in the USA, Japan, and Europe. The next step is the manufacture of prototypes. “The biggest challenge is its manufacturing because the tether should gather very specific optical and electron emission properties,” says Sánchez Arriaga.

The Spanish Ministry of Economy, Industry and Competitiveness has awarded the Spanish team a grant to investigate materials for the system. The team has also submitted a proposal to the European Commission’s Future and Emerging Technologies (FET-Open) consortium for funding. “The FET-OPEN project would be foundational because it considers the manufacturing and characterization of the first low-work-function tether and the development of a deorbit kit based on this technology to be tested on a future space mission. If funded, it would be a stepping stone to the future of low-work-function tethers in space” Sanchez Arriaga concluded.

In this video, Gonzalo Sanchez Arriaga explains how the system works. If you don’t speak Spanish, just turn on subtitles.