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

Tiangong-1 Splashes Down in the Pacific Ocean

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.

 

 

Further Reading: Vandenburg Air Force Base,

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

In mid-March, the Chinese Tiangong-1 Space Station is Going to Come Crashing Back Down to Earth… Somewhere

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

To add a little perspective to this analysis, the company also indicated the following:

“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!

Further Reading: Aerospace.org, ESA, Xinhuanet

Let’s Clean up the Space Junk with Magnetic Space Tugs

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!

Further Reading: ESA

What is Low Earth Orbit?

Beginning in the 1950s with the Sputnik, Vostok and Mercury programs, human beings began to “slip the surly bonds of Earth”. And for a time, all of our missions were what is known as Low-Earth Orbit (LEO). Over time, with the Apollo missions and deep space missions involving robotic spacecraft (like the Voyager missions), we began to venture beyond, reaching the Moon and other planets of the Solar System.

But by and large, the vast majority of missions to space over the years – be they crewed or uncrewed – have been to Low-Earth Orbit. It is here that the Earth’s vast array of communications, navigation and military satellites reside. And it is here that the International Space Station (ISS) conducts its operations, which is also where the majority of crewed missions today go. So just what is LEO and why are we so intent on sending things there?

Definition:

Technically, objects in low-Earth orbit are at an altitude of between 160 to 2,000 km (99 to 1200 mi) above the Earth’s surface. Any object below this altitude will being to suffer from orbital decay and will rapidly descend into the atmosphere, either burning up or crashing on the surface. Objects at this altitude also have an orbital period (i.e. the time it will take them to orbit the Earth once) of between 88 and 127 minutes.

The layers of our atmosphere showing the altitude of the most common auroras. Credit: Wikimedia Commons

Objects that are in a low-Earth orbit are subject to atmospheric drag since they are still within the upper layers of Earth’s atmosphere – specifically the thermosphere (80 – 500 km; 50 – 310 mi), theremopause (500–1000 km; 310–620 mi), and the exosphere (1000 km; 620 mi, and beyond). The higher the object’s orbit, the lower the 1atmospheric density and drag.

However, beyond 1000 km (620 mi), objects will be subject to Earth’s Van Allen Radiation Belts – a zone of charged particles that extends to a distance of 60,000 km from the Earth’s surface. In these belts, solar wind and cosmic rays have been trapped by Earth’s magnetic field, leading to varying levels of radiation. Hence why missions to LEO aim for attitudes between 160 to 1000 km (99 to 620 mi).

Characteristics:

Within the thermosphere, thermopause and exosphere, atmospheric conditions vary. For instance, the lower part of the thermosphere (from 80 to 550 kilometers; 50 to 342 mi) contains the ionosphere, which is so-named because it is here in the atmosphere that particles are ionized by solar radiation. As a result, any spacecraft orbiting within this part of the atmosphere must be able to withstand the levels of UV and hard ion radiation.

Temperatures in this region also increase with height, which is due to the extremely low density of its molecules. So while temperatures in the thermosphere can rise as high as 1500 °C (2700 °F), the spacing of the gas molecules means that it would not feel hot to a human who was in direct contact with the air. It is also at this altitude that the phenomena known as Aurora Borealis and Aurara Australis are known to take place.

The Exosphere, which is outermost layer of the Earth’s atmosphere, extends from the exobase and merges with the emptiness of outer space, where there is no atmosphere. This layer is mainly composed of extremely low densities of hydrogen, helium and several heavier molecules including nitrogen, oxygen and carbon dioxide (which are closer to the exobase).

In order to maintain a Low-Earth Orbit, an object must have a sufficient orbital velocity. For objects at an altitude of 150 km and above, an orbital velocity of 7.8 km (4.84 mi) per second (28,130 km/h; 17,480 mph) must be maintained. This is slightly less than the escape velocity needed to get into orbit, which is 11.3 kilometers (7 miles) per second (40,680 km/h; 25277 mph).

Despite the fact that the pull of gravity in LEO is not significantly less than on the surface of Earth (approximately 90%), people and objects in orbit are in a constant state of freefall, which creates the feeling of weightlessness.

Uses of LEO:

In this history of space exploration, the vast majority of human missions have been to Low Earth Orbit. The International Space Station also orbits in LEO, between an altitude of 320 and 380 km (200 and 240 mi). And LEO is where the majority of artificial satellites are deployed and maintained. The reasons for this are quite simple.

For one, the deployment of rockets and space shuttles to altitudes above 1000 km (610 mi) would require significantly more fuel. And within LEO, communications and navigation satellites, as well as space missions, experience high bandwidth and low communication time lag (aka. latency).

For Earth observation and spy satellites, LEO is still low enough to get a good look at the surface of Earth and resolve large objects and weather patterns on the surface. The altitude also allows for rapid orbital periods (a little over one hour to two hours long), which allows them to be able to view the same region on the surface multiple times in a single day.

And of course, at altitudes between 160 and 1000 km from the Earth’s surface, objects are not subject to the intense radiation of the Van Allen Belts. In short, LEO is the simplest, cheapest and safest location for the deployment of satellites, space stations, and crewed space missions.

Issues with Space Debris:

Because of its popularity as a destinations for satellites and space missions, and with increases in space launches over the past few decades, LEO is also becoming increasingly congested with space debris. This takes the form of discarded rocket stages, non-functioning satellites, and debris created by collisions between large pieces of debris.

The existence of this debris field in LEO has led to growing concern in recent years, since collisions at high-velocities can be catastrophic for space missions. And with every collision, additional debris is created, creating a destructive cycle known as the Kessler Effect – which is named after NASA scientist Donald J. Kessler, who first proposed it in 1978.

In 2013, NASA estimated that there may be as much as 21,000 bits of junk bigger than 10 cm, 500,000 particles between 1 and 10 cm, and more than 100 million smaller than 1 cm. As a result, in recent decades, numerous measures have been taken to monitor, prevent, and mitigate space debris and collisions.

For instance, in 1995, NASA became the first space agency in the world to issue a set of comprehensive guidelines on how to mitigate orbital debris. In 1997, the U.S. Government responded by developing the Orbital Debris Mitigation Standard Practices, based on the NASA guidelines.

NASA has also established the Orbital Debris Program Office, which coordinates with other federal departments to monitor space debris and deal with disruptions caused by collisions. In addition, the US Space Surveillance Network currently monitors some 8,000 orbiting objects that are considered collision hazards, and provides a continuous flow of orbit data to various agencies.

The European Space Agency’s (ESA) Space Debris Office also maintains the Database and Information System Characterizing Objects in Space (DISCOS), which provides information on launch details, orbital histories, physical properties and mission descriptions for all objects currently being tracked by the ESA. This database is internationally recognized and is used by almost 40 agencies, organizations and companies worldwide.

For over 70 years, Low-Earth Orbit has been the playground of human space capability. On occasion, we have  ventured beyond the playground and farther out into the Solar System (and even beyond). In the coming decades, a great deal more activity is expected to take place in LEO, which includes the deployment of more satellites, cubesats, continued operations aboard the ISS, and even aerospace tourism.

Needless to say, this increase in activity will require that we do something about all the junk permeating the space lanes. With more space agencies, private aerospace companies, and other participants looking to take advantage of LEO, some serious cleanup will need to take place. And some additional protocols will surely need to be developed to make sure it stays clean.

We have written many interesting articles about orbiting the Earth here at Universe Today. Here’s What is the Orbit of Earth?, How High is Space?, How Many Satellites are in Space?, The Northern and Southern Lights – What is an Aurora? and What is the International Space Station?

If you’d like more info on low Earth orbit, check out the types of orbit from the European Space Agency website. Also, here’s a link to NASA’s article about Low Earth Orbit.

We’ve also recorded an entire episode of Astronomy Cast all about Getting Around the Solar System. Listen here, Episode 84: Getting Around the Solar System.

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NASA Invests In Radical Game-Changing Concepts For Exploration

Every year, the NASA Innovative Advanced Concepts (NIAC) program puts out the call to the general public, hoping to find better or entirely new aerospace architectures, systems, or mission ideas. As part of the Space Technology Mission Directorate, this program has been in operation since 1998, serving as a high-level entry point to entrepreneurs, innovators and researchers who want to contribute to human space exploration.

This year, thirteen concepts were chosen for Phase I of the NIAC program, ranging from reprogrammed microorganisms for Mars, a two-dimensional spacecraft that could de-orbit space debris, an analog rover for extreme environments, a robot that turn asteroids into spacecraft, and a next-generation exoplanet hunter. These proposals were awarded $100,000 each for a nine month period to assess the feasibility of their concept.

Continue reading “NASA Invests In Radical Game-Changing Concepts For Exploration”

How Do Astronauts Avoid Debris?

So, just how do we keep our space stations, ships and astronauts from being riddled with holes from all of the space junk in orbit around Earth?

We revel in the terror grab bag of all the magical ways to get snuffed in space. Almost as much as we celebrate the giant brass backbones of the people who travel there.

We’ve already talked about all the scary ways that astronauts can die in space. My personal recurring “Hail Mary full of grace, please don’t let me die in space” nightmare is orbital debris.

We’re talking about a vast collection of spent rockets, dead satellites, flotsam, jetsam, lagan and derelict. It’s not a short list. NASA figures there are 21,000 bits of junk bigger than 10 cm, 500,000 particles between 1 and 10 cm, and more than 100 million smaller than 1 cm. Sound familiar, humans? This is our high tech, sci fi great Pacific garbage patch.

Sure, a tiny rivet or piece of scrap foil doesn’t sound very dangerous, but consider the fact that astronauts are orbiting the Earth at a velocity of about 28,000 km/h. And the Tang packets, uneaten dehydrated ice cream, and astronaut poops are also traveling at 28,000 km/h. Then think about what happens when they collide. Yikes… or yuck.

Here’s the International Space Station’s solar array. See that tiny hole? Embiggen and clarinosticate! That’s a tiny puncture hole made in the array by a piece of orbital crap.

The whole station is pummeled by tiny pieces of space program junk drawer contents. Back when the Space Shuttle was flying, NASA had to constantly replace their windows because of the damage they were experiencing from the orbital equivalent of Dennis the Menace hurling paint chips, fingernail clippings, and frozen scabs.

That’s just little pieces of paint. What can NASA do to keep Sandra Bullock safe from the larger, more dangerous chunks that could tear the station a new entry hatch?

For starters, NASA and the US Department of Defense are constantly tracking as much of the orbital debris that they can. They know the position of every piece of debris larger than a softball. Which I think, as far as careers go, would be grossly underestimated for its coolness and complexity at a cocktail party.

Artist's impression of debris in low Earth orbit. Credit: ESA
Artist’s impression of debris in low Earth orbit. Credit: ESA

“What do you do for a living?”
“Me, oh, I’m part of the program which tracks orbital debris to keep astronauts safe.”
“So…you track our space garbage?”
“Uh, actually, never mind, I’m an accountant.”

Furthermore, they’re tracking everything in low Earth orbit – where the astronauts fly – down to a size of 5 cm. That’s 21,000 discrete objects.

NASA then compares the movements of all these objects and compares it to the position of the Space Station. If there’s any risk of a collision, NASA takes preventative measures and moves the Space Station to avoid the debris.

The ISS has thrusters of its own, but it can also use the assistance of spacecraft which are docked to it at the time, such as a Russian Soyuz capsule.

NASA is ready to make these maneuvers at a moment’s notice if necessary, but often they’ll have a few days notice, and give the astronauts time to prepare. Plus, who doesn’t love a close call?

For example, in some alerts, the astronauts have gotten into their Soyuz escape craft, ready to abandon the Station if there’s a catastrophic impact. And if they have even less warning, the astronauts have to just hunker down in some of the Station’s more sturdy regions and wait out the debris flyby.

The Iridium constellation - a robust satellite network (Iridium)
The Iridium constellation – a robust satellite network (Iridium)

This isn’t speculation and overcautious nannying on NASA’s part. In 2009 an Iridium communications satellite was smashed by a dead Russian Kosmos-2251 military satellite. The collision destroyed both satellites instantly. As icing on this whirling, screaming metallic orbital-terror-cake, it added 2,000 new chunks of debris to the growing collection.

Most material was in a fairly low orbit, and much of it has already been slowed down by the Earth’s atmosphere and burned up.

This wasn’t the first time two star-crossed satellites with a love that could-not-be had a shrapnel fountain suicide pact, and I promise it won’t be the last. Each collision adds to the total amount of debris in orbit, and increases the risk of a run-away cascade of orbital collisions.

We should never underestimate the bravery and commitment of astronauts. They strap themselves to massive explosion tubes and weather the metal squalls of earth orbit in tiny steel life-rafts. So, would you be willing to risk all that debris for a chance to fly in orbit? Tell us in the comments below.

European Satellite Dodged Space Debris Hours After Reaching Orbit

Yesterday, the European Space Agency disclosed a serious problem early in the Sentinel-1A mission, which lifted off April 3 on a mission to observe the Earth. The spacecraft — which reportedly cost 280 million Euros ($384 million) to launch — came close to a collision in orbit.

“At the end of the first day after the launch (4 April): all deployments have been executed during the night and completed early in the morning at the beginning of the first ‘day shift’,” read a blog post from the Sentinel-1A team on the European Space Agency’s website.

“As the first day shift nears its end, a serious alert is received: there is a danger of a collision with a NASA satellite called ACRIMSAT, which has run out of fuel and can no longer be maneuvered. Not much information at the beginning, we are waiting for more information, but a collision avoidance maneuver may be needed.  ‘Are you kidding? A collision avoidance maneuver during LEOP [launch and early orbit phase]? This has never been done before, this has not been simulated!’ ”

Worse, as controllers looked at the data they realized there was not one, but two possible points of collision. Cue the inevitable Gravity reference, and then a solution: to essentially move the satellite out of the way. The maneuver took about 39 seconds, and safely skirted Sentinel-1A out of danger.

You can read more about the situation in the blog post. ESA’s main Twitter feed and the ESA Operations Twitter feed also first reported the near-collision yesterday, nearly a week after it occurred. It should also be noted that the Europeans (among many other space agencies) are looking at ways to reduce space debris.

The successful liftoff of Sentinel-1A in April 2014. Credit: ESA-S.Corvaja, 2014
The successful liftoff of Sentinel-1A in April 2014. Credit: ESA-S.Corvaja, 2014