This scanning electron micrograph shows the crater left by the impact of a 10-micrometer particle traveling at more than 1 kilometer per second. Impacts at that speed produce some melting and erosion of the surface, as revealed by this research. Credit: MIT/Hassani-Gangaraj et al.
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 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.
The RemoveDebris satellite deployed from the International Space Station on June 20. Credit: NASA/NanoRacks/Ricky Arnold
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.
Artist's impression of all the space junk in Earth orbit. Credit: NASA
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:
Still pic from the high-speed video where ESA researchers conduct a hypervelocity test with their new FML shielding. Credit: Fraunhofer Institute for High-Speed Dynamics
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:
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.
Artist's impression of a laser removing orbital debris, based on NASA pictures. Credit: Fulvio314/NASA/Wikipedia Commons
Orbital debris (aka. space junk) is one of the greatest problems facing space agencies today. After sixty years of sending rockets, boosters and satellites into space, the situation in the Low Earth Orbit (LEO) has become rather crowded. Given how fast debris in orbit can travel, even the tiniest bits of junk can pose a major threat to the International Space Station and threaten still-active satellites.
It’s little wonder then why ever major space agency on the planet is committed to monitoring orbital debris and creating countermeasures for it. So far, proposals have ranged from giant magnets and nets and harpoons to lasers. Given their growing presence in space, China is also considering developing giant space-based lasers as a possible means for combating junk in orbit.
One such proposal was made as part of a study titled “Impacts of orbital elements of space-based laser station on small scale space debris removal“, which recently appeared in the scientific journal Optik. The study was led by Quan Wen, a researcher from the Information and Navigation College at China’s Air Force Engineering University, with the help of the Institute of China Electronic Equipment System Engineering Company.
Graphic showing the cloud of space debris that currently surrounds the Earth. Credit: NASA’s Goddard Space Flight Center/JSC
For the sake of their study, the team conducted numerical simulations to see if an orbital station with a high-powered pulsed laser could make a dent in orbital debris. Based on their assessments of the velocity and trajectories of space junk, they found that an orbiting laser that had the same Right Ascension of Ascending Node (RAAN) as the debris itself would be effective at removing it. As they state in their paper:
“The simulation results show that, debris removal is affected by inclination and RAAN, and laser station with the same inclination and RAAN as debris has the highest removal efficiency. It provides necessary theoretical basis for the deployment of space-based laser station and the further application of space debris removal by using space-based laser.”
This is not the first time that directed-energy has been considered as a possible means of removing space debris. However, the fact that China is investigating directed-energy for the sake of debris removal is an indication of the nation’s growing presence in space. It also seems appropriate since China is considered to be one of the worst offenders when to comes to producing space junk.
Back in 2007, China conducted a anti-satellite missile test that resulted in the creation over 3000 of bits of dangerous debris. This debris cloud was the largest ever tracked, and caused significant damage to a Russian satellite in 2013. Much of this debris will remain in orbit for decades, posing a significant threat to satellites, the ISS and other objects in LEO.
The chip in the ISS’ Cupola window, photographed by astronaut Tim Peake. Credit: ESA/NASA/Tim Peake
Of course, there are those who fear that the deployment of lasers to LEO will mean the militarization of space. In accordance with the 1966 Outer Space Treaty, which was designed to ensure that the space exploration did not become the latest front in the Cold War, all signatories agreed to “not place nuclear weapons or other weapons of mass destruction in orbit or on celestial bodies or station them in outer space in any other manner.”
In the 1980s, China was added to the treaty and is therefore bound to its provisions. But back in March of 2017, US General John Hyten indicated in an interview with CNN that China’s attempts to develop space-based laser arrays constitutes a possible breach of this treaty:
“They’ve been building weapons, testing weapons, building weapons to operate from the Earth in space, jamming weapons, laser weapons, and they have not kept it secret. They’re building those capabilities to challenge the United States of America, to challenge our allies…We cannot allow that to happen.”
Such concerns are quite common, and represent a bit of a stumbling block when it comes to the use of directed-energy platforms in space. While orbital lasers would be immune to atmospheric interference, thus making them much more effective at removing space debris, they would also lead to fears that these lasers could be turned towards enemy satellites or stations in the event of war.
As always, space is subject to the politics of Earth. At the same time, it also presents opportunities for cooperation and mutual assistance. And since space debris represents a common problem and threatens any and all plans for the exploration of space and the colonization of LEO, cooperative efforts to address it are not only desirable but necessary.
Artist's impression of all the space junk in Earth orbit. Credit: NASA
Since the 1960s, NASA and other space agencies have been sending more and more stuff into orbit. Between the spent stages of rockets, spent boosters, and satellites that have since become inactive, there’s been no shortage of artificial objects floating up there. Over time, this has created the significant (and growing) problem of space debris, which poses a serious threat to the International Space Station (ISS), active satellites and spacecraft.
While the larger pieces of debris – ranging from 5 cm (2 inches) to 1 meter (1.09 yards) in diameter – are regularly monitored by NASA and other space agencies, the smaller pieces are undetectable. Combined with how common these small bits of debris are, this makes objects that measure about 1 millimeter in size a serious threat. To address this, the ISS is relying on a new instrument known as the Space Debris Sensor (SDS).
This calibrated impact sensor, which is mounted on the exterior of the station, monitors impacts caused by small-scale space debris. The sensor was incorporated into the ISS back in September, where it will monitor impacts for the next two to three years. This information will be used to measure and characterize the orbital debris environment and help space agencies develop additional counter-measures.
The International Space Station (ISS), seen here with Earth as a backdrop. Credit: NASA
Measuring about 1 square meter (~10.76 ft²), the SDS is mounted on an external payload site which faces the velocity vector of the ISS. The sensor consists of a thin front layer of Kapton – a polyimide film that remains stable at extreme temperatures – followed by a second layer located 15 cm (5.9 inches) behind it. This second Kapton layer is equipped with acoustic sensors and a grid of resistive wires, followed by a sensored-embedded backstop.
This configuration allows the sensor to measure the size, speed, direction, time, and energy of any small debris it comes into contact with. While the acoustic sensors measure the time and location of a penetrating impact, the grid measures changes in resistance to provide size estimates of the impactor. The sensors in the backstop also measure the hole created by an impactor, which is used to determine the impactor’s velocity.
This data is then examined by scientists at the White Sands Test Facility in New Mexico and at the University of Kent in the UK, where hypervelocity tests are conducted under controlled conditions. As Dr. Mark Burchell, one of the co-investigators and collaborators on the SDS from the University of Kent, told Universe Today via email:
“The idea is a multi layer device. You get a time as you pass through each layer. By triangulating signals in a layer you get position in that layer. So two times and positions give a velocity… If you know the speed and direction you can get the orbit of the dust and that can tell you if it likely comes from deep space (natural dust) or is in a similar earth orbit to satellites so is likely debris. All this in real time as it is electronic.”
The chip in the ISS’ Cupola window, photographed by astronaut Tim Peake. Credit: ESA/NASA/Tim Peake
This data will improve safety aboard the ISS by allowing scientists to monitor the risks of collisions and generate more accurate estimates of how small-scale debris exists in space. As noted, the larger pieces of debris in orbit are monitored regularly. These consists of the roughly 20,000 objects that are about the size of a baseball, and an additional 50,000 that are about the size of a marble.
However, the SDS is focused on objects that are between 50 microns and 1 millimeter in diameter, which number in the millions. Though tiny, the fact that these objects move at speeds of over 28,000 km/h (17,500 mph) means that they can still cause significant damage to satellites and spacecraft. By being able to get a sense of these objects and how their population is changing in real-time, NASA will be able to determine if the problem of orbital debris is getting worse.
Knowing what the debris situation is like up there is also intrinsic to finding ways to mitigate it. This will not only come in handy when it comes to operations aoard the ISS, but in the coming years when the Space Launch System (SLS) and Orion capsule take to space. As Burchell added, knowing how likely collisions will be, and what kinds of damage they may cause, will help inform spacecraft design – particularly where shielding is concerned.
“[O]nce you know the hazard you can adjust the design of future missions to protect them from impacts, or you are more persuasive when telling satellite manufacturers they have to create less debris in future,” he said. “Or you know if you really need to get rid of old satellites/ junk before it breaks up and showers earth orbit with small mm scale debris.”
The interior of the Hypervelocity Ballistic Range at NASA’s Ames Research Center. This test is used to simulate what happens when a piece of orbital debris hits a spacecraft in orbit. Credit: NASA/Ames
Dr. Jer Chyi Liou, in addition to being a co-investigator on the SDS, is also the NASA Chief Scientist for Orbital Debris and the Program Manager for the Orbital Debris Program Office at the Johnson Space Center. As he explained to Universe Today via email:
“The millimeter-sized orbital debris objects represent the highest penetration risk to the majority of operational spacecraft in low Earth orbit (LEO). The SDS mission will serve two purposes. First, the SDS will collect useful data on small debris at the ISS altitude. Second, the mission will demonstrate the capabilities of the SDS and enable NASA to seek mission opportunities to collect direct measurement data on millimeter-sized debris at higher LEO altitudes in the future – data that will be needed for reliable orbital debris impact risk assessments and cost-effective mitigation measures to better protect future space missions in LEO.”
The results from this experiment build upon previous information obtained by the Space Shuttle program. When the shuttles returned to Earth, teams of engineers inspected hardware that underwent collisions to determine the size and impact velocity of debris. The SDS is also validating the viability of impact sensor technology for future missions at higher altitudes, where risks from debris to spacecraft are greater than at the ISS altitude.
In the future, derelict satellites could be grappled and removed from key orbits around Earth with a space tug using magnetic forces. Credit: Philippe Ogaki
After 50 years of sending rockets, satellites, and payloads into orbit, humanity has created something of a “space junk” problem. Recent estimates indicate that there are more than 170 million pieces of debris up there, ranging in size from less than 1 cm (0.4 in) to a few meters in diameter. Not only does this junk threaten spacecraft and the ISS, but collisions between bits of debris can cause more to form, a phenomena known as the Kessler Effect.
And thanks to the growth of the commercial aerospace industry and the development of small satellites, things are not likely to get any less cluttered up there anytime soon. Hence why multiple strategies are being explored to clean up the space lanes, ranging from robotic arms and nets to harpoons. But in what may be the most ambitious plan to date, the ESA has proposed creating space tugs with powerful magnets to yank debris out of orbit.
The concept comes from Emilien Fabacher, a researcher from the Institut Supérieur de l’Aéronautique et de l’Espace at the University of Toulouse, France. His concept for a magnetic tug seeks to address one type of space debris in particular – inoperable satellites. These uncontrolled, rapidly spinning objects often weigh up to several tons, and are therefore one of the most significant collision hazards there is.
Illustration showing the problem of space debris. Credit: ESA
When applied to the problem of orbital debris, magnetic attraction is an attractive solutions for the safe deorbiting of spent satellites. For starters, it relies on technology that is standard issue aboard many low-orbiting satellites, which is known as magnetorquers. These electromagnets allow satellites to adjust their orientation using the Earth’s magnetic field. Hence, debris-chasing satellites would not need to be specially equipped in advance.
What’s more, this same magnetic attraction or repulsion technology is being considered as a safe method for allowing multiple satellites to maintain close formations in space. Such satellites – like NASA’s Magnetospheric Multiscale mission (MMS), the Landsat 7 and the Earth Observing-1 satellites, and the ESA’s upcoming LISA mission – are either operational or soon will be around Earth.
Because of this, this kind of magnetic attraction technology presents a safe and effective alternative for deorbiting space junk. As Fabacher explained in a recent ESA press release:
“With a satellite you want to deorbit, it’s much better if you can stay at a safe distance, without needing to come into direct contact and risking damage to both chaser and target satellites. So the idea I’m investigating is to apply magnetic forces either to attract or repel the target satellite, to shift its orbit or deorbit it entirely.”
Artist’s impression of the ESA’s proposed Darwin mission, six formation-flying satellites that would look for exoplanets. Credit: ESA/Medialab
The concept emerged out of a conversation Fabacher had with experts from the ESA’s technical center in the Netherlands. As part of his PhD research, he was looking into how magnetic guidance, navigation and control techniques would work in practice. This led to a discussion about how similar technology could allow swarms of satellites to attract and remove debris from orbit.
After making some calculations that combined a rendezvous simulator with magnetic interaction models, and also taking account the ever-changing state of Earth’s own magnetosphere, Fabacher and his colleagues realized they had a working concept. “The first surprise was that it was indeed possible, theoretically – initially we couldn’t be sure, but it turns out that the physics works fine,” he said.
To break it down, the chaser satellites would generate a strong magnetic field using superconducting wires that are cooled to cryogenic temperatures. These satellites would also rely on magnetic fields to maintain precise flying formations, thus allowing a swarm of chaser satellites the ability to deal with multiple pieces of debris, or to coordinate and guide debris to a specific location.
According to Finn Ankersen – an ESA expert in rendezvous and docking and formation flight – these magnetic tugs would also be able to remove space debris with a very high level of precision. “This kind of contactless magnetic influence would work from about 10–15 meters out, offering positioning precision within 10 cm with attitude precision [of] 1 – 2º,” he said.
Why Space Debris Mitigation is needed. Click for animation. Credit: ESA
The concept is being developed with support provided by the ESA’s Networking/Partnering Initiative, a program that offers support to universities and research institutes for the sake of developing space-related technologies. And it comes at a time when the issue of space debris is becoming increasingly worrisome.
Left unchecked, space debris is likely to become a very serious hazard in the coming years and decades. Already, it is estimated that the small satellite market will grow by $5.3 billion in the next decade (according to Space Works and Eurostat) and many private companies are looking to provide regular launch services to accommodate that growth.
If we intend to begin making a return to the Moon and mounting missions to Mars, we need to make sure the space lanes are clear! And given the importance of the International Space Station to scientific research and international collaboration, and with companies like Bigelow Aerospace looking to establish space habitats in orbit, something has to be done about this problem before it gets completely out of control!
Who knows? Maybe a small fleet or magnetic tugs is just what we need to clean up this mess!
A number companies are deploying satellites this year to create space-based internet services. Credit: AMNH.
SpaeeX and Tesla-founder Elon Musk has made some rather bold promises over the years. In addition to building a fleet of reusable rockets, an Interplanetary Transport System, colonizing Mars, and revolutionizing transportation, he has also made it clear that he hopes to provide worldwide broadband access by deploying a “constellation” of internet-providing satellites.
In November of 2016, SpaceX filed an application with the Federal Communications Commission (FCC) for a license to operate this constellation of non-geostationary satellites (NGS). And earlier this week, the US Senate Committee on Commerce. Science, and Transportation convened a hearing to explore this proposal for next-generation telecommunications services.
The hearing was titled, “Investing in America’s Broadband Infrastructure: Exploring Ways to Reduce Barriers to Deployment”. In the course of things, the committee heard from representatives of government and industry who spoke about the best ways to offer streamlined broadband access (especially in rural areas), the necessary infrastructure, and how to encourage private investment.
SpaceX’s proposed satellite constellation – 4,425 broadband internet satellites – could provide the entire world with high-speed internet access. Credit: ESA
Of those the committee heard from, Ms. Patricia Cooper – VP of Satellite Government Affairs for SpaceX – was on hand to underscore the company’s vision. As she stated:
“SpaceX sees substantial demand for high-speed broad band in the United States and worldwide. As the Committee is aware, millions of Americans outside of limited urban areas lack basic, reliable access. Furthermore, even in urban areas, a majority of Americans lacks more than a single fixed broadband provider from which to choose and may seek additional competitive options for high-speed service.”
Cooper also cited recent FCC findings, which indicated that millions of Americans lag behind other developed nations in terms of broadband speed, access, and price competitiveness. Basically, thirty-four million American citizens do not have access to 25 megabits per second (“Mbps”) broadband service while 47% of students in the US lack the connectivity to meet the FCC’s short-term goal of 100 Mbps per 1,000 students and staff.
This is at at a time when global demand for broadband services and internet connectivity continue to grow at an unprecedented rate. According to a report prepared by Cisco in 2016 – titled “White paper: Cisco VNI Forecast and Methodology, 2015-2020” – global Internet Protocol (IP) traffic surpassed the zettabyte threshold. In other words, over 1,000 billion gigabytes of data were exchanged worldwide in a single year!
SpaceX plans to beginning launching their internet-providing satellites aboard their Falcon 9 rockets beginning next year. Credit: Ken Kremer/Kenkremer.com
By 2020, that figure is projected to double, global fixed broadband speeds are expected to nearly double, and the number of devices connected to IP networks is projected to outnumber the global population by a factor of about 3 to 1. To remedy this situation, and bring broadband access in the US up to the average for developed nations, SpaceX plans to launch 4,425 broadband satellites.
These will begin being launched in 2019 aboard the company’s fleet of Falcon 9 rockets. The launches will continue until they have reached full capacity, which is expected to be by 2024. As Cooper outlined it:
“Later this year, SpaceX will begin the process of testing the satellites themselves, launching one prototype before the end of the year and another during the early months of 2018. Following successful demonstration of the technology, SpaceX intends to begin the operational satellite launch campaign in 2019. The remaining satellites in the constellation will be launched in phases through 2024, when the system will reach full capacity with the Ka- and Ku-Band satellites. SpaceX intends to launch the system onboard our Falcon 9 rocket, leveraging significant launch cost savings afforded by the first stage reusability now demonstrated with the vehicle.”
Other details included the operational altitudes of the satellites – ranging from 1,110 to 1,325 km (690 to 823 mi) – as well as the necessary infrastructure on the ground, which would include “ground control facilities, gateway Earth stations, and end-user Earth stations.” SpaceX has also indicated that it plans to deploy an additional 7.500 satellites that will operate at lower altitudes in order to boost broadband capacity in large population centers.
Naturally, there have to be those people who hear words like “satellite constellation” and immediately think “space junk”. Certainly, the deployment of between 4,425 and 11,925 satellites in the coming years will lead to increasing concerns about “orbital clutter”. Especially when other telecommunications providers are seeking to get in on the trend – a good example being Google’s Project Loon.
Why Space Debris Mitigation is needed. Credit: ESA
And while the subject did not come up during the hearing, it will be unavoidable in the coming years and decades. But in the meantime, the idea of bringing internet access to the world – particularly the developing regions of the world where the infrastructure may not otherwise exist – has the potential of being a great social leveler. In the coming decades, it is expected that internet use will reach proportions unheard of a few decades ago.
By 2020 alone, it is estimated that the number of Internet users will reach almost 5 billion – or roughly half the world projected population of 10 billion. This represents an almost threefold increase from the number of internet users in 2010 (1.7 billion) and an almost 14 fold increase since 2000 (360 million). As such, any investment that will help ensure that this growth occurs more equally across geographic and social barriers is certainly a good one.
The committee also heard testimony from Larry Downes, the Project Director of the Georgetown Center for Business and Public Policy, and Brian Hendricks – the head of Technology Policy & Public Affairs for the Americas Region for Nokia. In addition to addressing the current sate of broadband internet in the US, they made multiple recommendations on how the non-geostationary internet satellite industry could be fostered and developed.
You can read the transcripts and check out the live webcast by going to the hearing page.
