The destruction of a single satellite could be catastrophic for our orbital endeavours. Image Credit: ESA
In 1978, NASA scientists Donald J. Kessler and Burton G. Cour-Palais proposed a scenario where the density of objects in Low Earth Orbit (LEO) would be high enough that collisions between objects would cause a cascade effect. In short, these collisions would create debris that would result in more collisions, more debris, and so on. This came to be known as the Kessler Syndrome, something astronomers, scientists, and space environmentalists have feared for many decades. In recent years, and with the deployment of more satellites than ever, the warning signs have become undeniable.
Currently, there is an estimated 13,000 metric tons (14,330 US tons) of “space junk” in LEO. With the breakup and another satellite in orbit – the Intelsat 33e satellite – the situation will only get worse. This broadband communications satellite was positioned about 35,000 km (21,750 mi) above the Indian Ocean in a geostationary orbit (GSO). According to initial reports issued on October 20th, the Intelsat 33e satellite experienced a sudden power loss. Hours later, the U.S. Space Forces (USSF) confirmed that the satellite appeared to have broken up into at least 20 pieces.
A map of space debris orbiting Earth. Credit: European Space Agency
October 4th, 2022, will be an auspicious day as humanity celebrates the 65th anniversary of the beginning of the Space Age. It all began in 1957 with the launch of the Soviet satellite Sputnik-1, the first artificial satellite ever sent to orbit. Since that time, about 8,900 satellites have been launched from more than 40 countries worldwide. This has led to growing concerns about space debris and the hazard it represents to future constellations, spacecraft, and even habitats in Low Earth Orbit (LEO).
This has led to many proposed solutions for cleaning up “space junk,” as well as satellite designs that would allow them to deorbit and burn up. Alas, there are still questions about whether a planet surrounded by mega-constellations is sustainable over the long term. A recent study by James A. Blake, a research fellow with the University of Warwick, examined the evolution of the debris environment in LEO and assessed if future space operations can be conducted sustainably.
Credit: Christian Scheckhuber/Wikipeia Commons (left); UC3M (right)
According to the latest numbers from the ESA’s Space Debris Office (SDO), there are roughly 6,900 artificial satellites in orbit. The situation is going to become exponentially crowded in the coming years, thanks to the many telecommunications, internet, and small satellites that are expected to be launched. This creates all kinds of worries for collision risks and space debris, not to mention environmental concerns.
For this reason, engineers, designers, and satellite manufacturers are looking for ways to redesign their satellites. Enter Max Justice, a cybersecurity expert, former Marine, and “Cyber Farmer” who spent many years working in the space industry. Currently, he is working towards a new type of satellite that is made out of mycelium fibers. This tough, heat-resistant, and environmentally friendly material could trigger a revolution in the booming satellite industry.
Radar images acquired of China's Tiangong-1 space station by the Tracking and Imaging Radar system, which is operated by Germany’s Fraunhofer FHR research institute at Wachtberg. Credit: Fraunhofer FHR
Over the weekend, multiple space agencies’ had their instruments fixed on the skies as they waited for the Tiangong-1 space station to reenter our atmosphere. For the sake of tracking the station’s reentry, the ESA hosted the 2018 Inter Agency Space Debris Coordination Committee, an annual exercise that consists of experts from 13 space agencies taking part in a joint tracking exercise.
And on April 2nd, 02:16 CEST (April 1st, 17:16 PST), the US Air Force confirmed the reentry of the Tiangong-1 over the Pacific Ocean. As hoped, the station crashed down close to the South Pacific Ocean Unpopulated Area (SPOUA), otherwise known as the “Spaceship Cemetery”. This region of the Pacific Ocean has long been used by space agencies to dispose of spent spacecraft after a controlled reentry.
The confirmation came from the Joint Force Space Component Command (JFSCC) on April 2nd, 0:400 CEST (April 1st, 19:00 PST). Using the Space Surveillance Network sensors and their orbital analysis system, they were able to refine their predictions and provide more accurate tracking as the station’s reentry time approached. The USAF regularly shares information with the ESA regarding its satellites and debris tracking.
Artist’s illustration of China’s 8-ton Tiangong-1 space station, which is expected to fall to Earth in late 2017. Credit: CMSE
As with the ESA’s coordination with other space agencies and European member states, JFSCC’s efforts include counterparts in Australia, Canada, France, Germany, Italy, Japan, South Korea, and the United Kingdom. As Maj. Gen. Stephen Whiting, the Deputy Commander of the JFSCC and Commander of the 14th Air Force, indicated in a USAF press release:
“The JFSCC used the Space Surveillance Network sensors and their orbital analysis system to confirm Tiangong-1’s reentry, and to refine its prediction and ultimately provide more fidelity as the reentry time approached. This information is publicly-available on USSTRATCOM’s website www.Space-Track.org. The JFSCC also confirmed reentry through coordination with counterparts in Australia, Canada, France, Germany, Italy, Japan, South Korea, and the United Kingdom.”
The information is available on U.S. Strategic Command’s (USSTRATCOM) website – www.Space-Track.org. Holger Krag, the head of ESA’s Space Debris Office, confirmed the reentry of Tiangong-1 shortly thereafter on the ESA’s Rocket Science Blog. As he stated, the reentry was well within ESA’s earlier reentry forecast window – which ran from April 1st 23:00 UTC to 03:00 UTC on April 2nd (April 2nd, 01:00 CEST to 05:00 CEST):
“According to our experience, their assessment is very reliable. This corresponds to a geographic latitude of 13.6 degrees South and 164.3 degrees West – near American Samoa in the Pacific, near the international date Line. Both time and location are well within ESA’s last prediction window.”
Artist’s illustration of China’s 8-ton Tiangong-1 space space station. Credit: CMSE.
China’s Manned Space Agency (CMSA) also made a public statement about the station’s reenty:
“According to the announcement of China Manned Space Agency (CMSA), through monitoring and analysis by Beijing Aerospace Control Center (BACC) and related agencies, Tiangong-1 reentered the atmosphere at about 8:15 am, 2 April, Beijing time. The reentry falling area located in the central region of South Pacific. Most of the devices were ablated during the reentry process.”
As Krag noted, the ESA’s monitoring efforts were very much reliant on its campaign partners from around the world. In fact, due to when the station entered the Earth’s atmosphere, it was no longer visible to the Fraunhofer FHR institute’s Tracking and Imaging (TIRA) radar, which provides tracking services for the ESA’s Space Debris Office (SDO).
Had the station still been in orbit by 06:05 CEST (21:00 PST), it would have still been visible to the institute’s TIRA radar. Some unexpected space weather also played a role in the station’s reentry. On March 31st, the Sun’s activity spontaneously dropped, which delayed the Tiangong-1’s entry by about a day.
“This illustrates again the dependence that Europe has on non-European sources of information to properly and accurately manage space traffic, detect reentries such as Tiangong-1 and track space debris that remains in orbit – which routinely threatens ESA, European and other national civil, meteorological, scientific, telecomm and navigation satellites,” said Krag.
While news of the Tiangong-1’s orbital decay caused its share of concern, the reentry happened almost entirely as predicted and resulted in no harm. And once again, it demonstrated how international cooperation and public outreach is the best defense against space-related hazards.
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:
Artist's illustration of China's 8-ton Tiangong-1 space station, which is expected to fall to Earth in late 2017. Credit: CMSE.
China’s Tiangong-1 space station has been the focus of a lot of international attention lately. In 2016, after four and half years in orbit, this prototype space station officially ended its mission. By September of 2017, the Agency acknowledged that the station’s orbit was decaying and that it would fall to Earth later in the year. Since then, estimates on when it will enter out atmosphere have been extended a few times.
According to satellite trackers, it was predicted that the station would fall to Earth in mid-March. But in a recent statement (which is no joke) the Chinese National Space Agency (CNSA) has indicated that Tiangong-1 will fall to Earth around April 1st – aka. April Fool’s Day. While the agency and others insists that it is very unlikely, there is a small chance that the re-entry could lead to some debris falling to Earth.
For the sake of ensuring public safety, the European Space Agency’s (ESA) Space Debris Office (SDO) has been providing regular updates on the station’s decay. According to the SDO, the reentry window is highly variable and spans from the morning of March 31st to the afternoon of April 1st (in UTC time). This works out to the evening of March 30th or March 31st for people living on the West Coast.
The possible re-entry region of the Tiangong-1 space station, indicated in green. Credit: ESA/SDO
“Reentry will take place anywhere between 43ºN and 43ºS. Areas above or below these latitudes can be excluded. At no time will a precise time/location prediction from ESA be possible. This forecast was updated approximately weekly through to mid-March, and is now being updated every 1~2 days.”
In other words, if any debris does fall to the surface, it could happen anywhere from the Northern US, Southern Europe, Central Asia or China to the tip of Argentina/Chile, South Africa, or Australia. Basically, it could land just about anywhere on the planet. On the other hand, back in January, the US-based Aerospace Corporation released a comprehensive analysis on Tiangong-1s orbital decay.
Their analysis included a map (shown below) which illustrated the zones of highest risk. Whereas the blue areas (that make up one-third of the Earth’s surface) indicate zones of zero probability, the green area indicates a zone of lower probability. The yellow areas, meanwhile, indicates zones that have a higher probability, which extend a few degrees south of 42.7° N and north of 42.7° S latitude, respectively.
The Aerospace Corporations predicted reentry for Tiangong-1. Credit: aerospace.org
The Aerospace Corporation has also created a dashboard for tracking Tiangong-1 (which is refreshed every few minutes) and has come to similar conclusions about the station’s orbital decay. Their latest prediction is that the station will descend into our atmosphere on April 1st, at 04:35 UTC (March 30th 08:35 PST), with a margin of error of about 24 hours – in other words, between March 30th to April 2nd.
And they are hardly alone when it comes to monitoring Tiangong-1’s orbit and predicting its descent. The China Human Spaceflight Agency (CMSA) recently began providing daily updates on the orbital status of Tiangong-1. As they reported on March 28th: “Tiangong-1 stayed at an average altitude of about 202.3 km. The estimated reentry window is between 31 March and 2 April, Beijing time.”
The US Space Surveillance Network, which is responsible for tracking artificial objects in Earth’s orbit, has also been monitoring Tiangong-1 and providing daily updates. Based on their latest tracking data, they estimate that the station will enter our atmosphere no later than midnight on April 3rd.
Naturally, one cannot help but notice that these predictions vary and are subject to a margin of error. In addition, trackers cannot say with any accuracy where debris – if any – will land on the planet. As Max Fagin – an aerospace engineer and space camp alumni – explained in a recent Youtube video (posted below), all of this arises from two factors: the station’s flight path and the Earth’s atmosphere.
Basically, the station is still moving at a velocity of 7.8 km/sec (4.8 mi/s) horizontally while it is descending by about 3 cm/sec. In addition, the Earth’s atmosphere shrinks and expands throughout the day in response to the Sun’s heating, which results in changes in air resistance. This makes the process of knowing where the station’s will make its descent difficult to predict, not to mention where debris could fall.
However, as Fagin goes on to explain, once the station reaches an altitude of 150 km (93 mi) – i.e. within the Thermosphere – it will begin falling much faster. At that point, it be much easier to determine where debris (if any) will fall. However, as the ESA, CNSA, and other trackers have emphasized repeatedly, the odds of any debris making it to the surface is highly unlikely.
If any debris does survive re-entry, it is also statistically likely to fall into the ocean or in a remote area – far away from any population centers. But in all likelihood, the station will break up completely in our atmosphere and produce a beautiful streaking effect across the sky. So if you’re checking the updates regularly and are in a part of the world where it can be seen, be sure to get outside and see it!
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:
Artist's illustration of China's 8-ton Tiangong-1 space station, which is expected to fall to Earth in late 2017. Credit: CMSE.
In September of 2011, China officially joined the Great Powers in Space club, thanks to the deployment of their Tiangong-1 space station. Since then, this prototype station has served as a crewed orbital laboratory and an experimental testbed for future space stations. In the coming years, China hopes to build on the lessons learned with Tiangong-1 to create a larger, modular station in 2023 (similar to the International Space Station).
Though the station’s mission was originally meant to end in 2013, the China National Space Agency extended its service to 2016. By September of 2017, the Agency acknowledged that they had lost control of the station and indicated that it would fall to Earth later in the year. According to the latest updates from satellite trackers, Tianglong-1 is likely to be reentering our atmosphere in March of 2018.
Given the fact that the station measures 10 by 3.35 meters (32.8 by 11 ft), weighs a hefty 8,506 kg (18,753 lb) and was built from very durable construction materials, there are naturally concerns that some of it might survive reentry and reach the surface. But before anyone starts worrying about space debris falling on their heads, there are a few things that need to be addressed.
Images of the Tiangong-1 docking in Earth orbit in 2013. Credit: ESA
For starters, in the history of space flight, there has not been a single confirmed death caused by falling space debris. Tthanks to the development of modern tracking and early warning systems, we are also more prepared than at any time in our history for the threat of falling debris. Statistically speaking, you are more likely to be hit by falling airplane debris or eaten by a shark.
Second, the CNSA has emphasized that the reentry is very unlikely to pose a threat to commercial aviation or cause any impact damage on the surface. As Wu Ping – the deputy director of the manned space engineering office – indicated at a press conference back on September 14th, 2017: “Based on our calculation and analysis, most parts of the space lab will burn up during falling.”
In addition, The Aerospace Corporation, which is currently monitoring the reentry of Tiangong-1, recently released the results of their comprehensive analysis. Similar to what Wu stated, they indicated that most of the station will burn up on reentry, though they acknowledged that there is a chance that small bits of debris could survive and reach the surface. This debris would likely fall within a region that is centered along the orbital path of the station (i.e. around the equator).
To illustrate the zones of highest risk, they produced a map (shown below) which indicates where the debris would be most likely to land. Whereas the blue areas (that make up one-third of the Earth’s surface) indicate zones of zero probability, the green area indicates a zone of lower probability. The yellow areas, meanwhile, indicates zones that have a higher probability, which extend a few degrees south of 42.7° N and north of 42.7° S latitude, respectively.
The Aerospace Corporations predicted reentry for Tiangong-1. Credit: aerospace.org
“When considering the worst-case location (yellow regions of the map) the probability that a specific person (i.e., you) will be struck by Tiangong-1 debris is about one million times smaller than the odds of winning the Powerball jackpot. In the history of spaceflight, no known person has ever been harmed by reentering space debris. Only one person has ever been recorded as being hit by a piece of space debris and, fortunately, she was not injured.”
Last, but not least, the European Space Agency’s Inter Agency Space Debris Coordination Committee (IADC) will be monitoring the reentry. In fact, the IADC – which is made up of space debris and other experts from NASA, the ESA, JAXA, ISRO, KARI, Roscosmos and the China National Space Administration – will be using this opportunity to conduct a test campaign.
During this campaign, participants will combine their predictions of the reentry’s time window, which are based on respective tracking datasets obtained from radar and other sources. Ultimately, the purpose of the campaign is to improve prediction accuracy for all member states and space agencies. And so far, their predictions also indicate that there is little cause for concern.
As Holger Krag, the Head of ESA’s Space Debris Office, indicated in a press statement back in November:
“Owing to the geometry of the station’s orbit, we can already exclude the possibility that any fragments will fall over any spot further north than 43ºN or further south than 43ºS. This means that reentry may take place over any spot on Earth between these latitudes, which includes several European countries, for example. The date, time and geographic footprint of the reentry can only be predicted with large uncertainties. Even shortly before reentry, only a very large time and geographical window can be estimated.”
The Chinese Long March 3 rocket reentering the atmosphere over Hawaii. Credits: ESA/Steve Cullen (Starscape Galery)
The ESA’s Space Debris Office – which is based at the European Space Operations Centre in Darmstadt, Germany – will follow this campaign in February with an international expert workshop. This workshop (which will run from February 28th to March 1st, 2018) will focus on reentry predictions and atmospheric break-up studies and allow experts in the field of space debris monitoring to share their latest findings and research.
In the current age of renewed space exploration and rapidly improving technology, every new development in space is an opportunity to test the latest instruments and methods. The reentry of Tiangong-1 is a perfect example, where the reentry of a space station is being used to test our ability to predict falling space debris. It also highlights the need for tracking and monitoring, given that humanity’s presence in orbit is only going to increase in the coming years.
In the meantime, it would not be inadvisable to keep your eyes on the skies this coming March. While there is little chance that debris will pose a hazard, it is sure to be spectacular sight for people who live closer to the equator!
Still image taken from a movie, Space debris ? a journey to Earth, to be released April 18th, 2017. Credit: ESA
Orbital debris, otherwise known as “space junk”, is a major concern. This massive cloud that orbits the Earth is the result of the many satellites, platforms and spent launchers that have been sent into space over the years. And as time went on, collisions between these objects (as well as disintegrations and erosion) has created even more in the way of debris.
