The recent increase in launches to meet growing demands for communications and observation satellites is adding more and more spacecraft to orbit every year. This is especially true in the more congested low-Earth orbit (LEO).
With a sharp focus on making space safe and sustainable for the current as well as future generations, organizations such as Astroscale are responding to an emerging market of commercial on-orbit services for active and defunct satellites in orbit. These plans go beyond just maintenance and lifespan extensions, including the refueling of spacecraft as well as the active removal of space debris.
Headquartered in Japan, Astroscale is one of several private companies innovating in this space. Its Active Debris Removal by Astroscale-Japan (ADRAS-J) surveying mission, which launched on a Rocket Lab Electron rocket last week, aims to demonstrate the necessary operations and technology that will underpin the delivery of new on-orbit services.
Space debris, more colloquially referred to as “space junk,” can take several forms, ranging from satellites that have reached the end of their operational life to discarded rocket stages that have performed their duties. Some rocket stages, including those from twentieth-century missions, have been discarded into a “graveyard orbit” that sits at least 300 kilometers above geostationary orbit (GEO) at 35,800 kilometers. The industry’s attention is, however, on the busier LEO.
The ADRAS-J spacecraft approaches the unresponsive upper stage of an H-IIA rocket. (Credit: Astroscale)
Different factors contribute to orbital decay, including the orbital altitude, atmospheric drag, the ballistic coefficient of the object, and even the “weather” in space. For this reason, spacecraft maintain a supply of propellant for periodic station-keeping. The decay period increases exponentially with higher altitudes, with decay times surpassing 10 years as you go beyond 500 kilometers.
Satellites in LEO typically have a five-year lifespan, while those in GEO often operate for up to 15 years. In late 2022, the Federal Communications Commission (FCC) took steps to mitigate the growing debris within 2,000 kilometers of Earth by lowering the timeframe from 25 to five years in which operators of FCC-licensed satellites should deorbit their satellites after mission completion.
The FCC issued a landmark $150,000 fine to the Dish Network satellite company in October 2023 for failing to dispose of its EchoStar-7 into a higher “graveyard orbit” at the end of its lifespan in GEO. The satellite achieved less than half of the required 300-kilometer raise due to insufficient propellant amounts.
Modern launch vehicle operators are acutely aware of the importance of debris mitigation and will precisely control the deorbit of their spent stages. For example, Falcon 9 second stages perform retrograde burns to safely deorbit after payload deployment. Similarly, Rocket Lab’s Electron kick-stage fires its Curie engine one final time to deorbit itself while the second stage reduces its own altitude so that nothing is left in orbit except the deployed satellites.
Starlink satellites will use their ion-powered ion thrusters to lower their orbit at the end of their useful life, and at altitudes below 600 kilometers, the satellites will leave no persistent debris, even if a satellite fails while in orbit. When the Perigrine-1 mission suffered an anomaly earlier this year, Astrobotic made the decision to preserve cislunar space from potential debris and utilized the lander’s remaining propellant to target a path in which the land would re-enter Earth’s atmosphere and subsequently burn up and disintegrate.
Infographic showing orbital debris decay. (Credit: ULA)
Despite these responsible mitigation steps, LEO remains populated with hundreds of thousands of pieces of debris, including end-of-life spacecraft which have run out of power and can neither communicate nor reorient themselves. These objects are the focus of the ADRAS-J mission.
ADRAS-J Mission
Rocket Lab’s ‘On Closer Inspection’ mission launched atop an Electron rocket from Launch Complex 1 in Mahia, New Zealand, on Feb. 19 at 3:52 AM NZDT (14:52 UTC on Feb. 18), carrying the ADRAS-J, which masses 180 kilograms.
The goal of the mission is to safely approach, characterize, and fly an observational orbit path around a large uncommunicative piece of space debris in LEO — the upper stage of a discarded Japanese H-IIA rocket.
Other demonstration missions similar to ADRAS-J have previously either deployed a target object as part of the demonstration or were able to communicate with it. The difference between previous demonstration missions and ADRAS-J is the non-communicative, non-powered, and uncontrollable nature of the rocket stage.
With no GPS or other data being transmitted from the object, the initial identification and approach will be based on limited ground-based data. After this, onboard visual and other sensors will locate the stage and determine the relative distance and altitude of the stage before performing a safe approach.
ADRAS-J craft approaches the discarded upper stage of an H-IIA rocket. (Credit: Astroscale)
ADRAS-J will approach at around 600 kilometers altitude using a series of corkscrew-style “safety ellipse” maneuvers. Once near the stage, it will execute a series of “Rendezvous and Proximity Operations,” which demonstrate the technology needed for a precise rendezvous with a large target object.
A further fly-around phase will then determine the target’s spin rate and axis before ADRAS-J completes its objectives by settling into a stable position a short distance away from the stage, aligned with the stage’s orientation.
Different navigational techniques and sensors are used to progressively approach the target object; VISCam (smart image processing, enabling object location detection), IRCam (using infrared), and LIDAR (using light in the form of a pulsed laser to measure distances). The latter is used to make a final approach to align with the object and demonstrate that the craft could be held at a maintained close distance.
The inspection stage enables images to be captured every 30 seconds, and the data collected by ADRAS-J will directly inform Astroscale’s other ongoing programs that focus on orbital debris clearance and maintenance.
The Japan Aerospace Exploration Agency (JAXA) selected this mission as the initial phase of their Commercial Removal of Debris Demonstration Project. The second phase will progress onto the actual capture and removal of a debris object, but has yet to be contracted.
The mission is intended to prompt global discussions with governments and companies in the space industry on the implementation of Active Debris Removal (ADR) and will be following measures and processes outlined in the “Guidelines on a License to Operate a Spacecraft Performing On-Orbit Servicing” that was issued by the Japanese government in November 2021. These were the first guidelines of their kind and the result of consultation with various space agencies, ministries, and industry experts, including leading private space companies.
Astroscale has been uniquely focused on the safe removal of space debris since its creation in 2013 and is responsible for the entire lifecycle of this project — from design and construction to testing, launch, and subsequent operations.
ADRAS-J will be the first debris management mission to target an object of this size, with the H-IIA stage sitting at 11 x four meters. This stage launched the Greenhouse Gases Observing Satellite in 2009 and is part of an expendable launch system that has launched payloads since 2001, including the XRISM space telescope and SLIM lunar lander.
Other orbital debris management missions
The technology on ADRAS-J is leveraged from Astroscale’s End-of-Life Services by Astroscale Demonstration (ELSA-D) mission which completed close rendezvous operations between two semi-cooperative spacecraft in May 2022 where one spacecraft was equipped with a magnetic docking plate.
ELSA-D was developed via a partnership between the European and UK Space Agencies and satellite operator OneWeb and is set to be succeeded by the multi-spacecraft (ELSA-M) variant. ELSA-M intends to demonstrate a second capture and removal in the same mission as well as the advanced capture of objects that are in an uncontrolled spin or tumble.
Artists impression of COSMIC capturing its client (Credit: Astroscale)
Astroscale’s Clearing Outer Space Mission through Innovative Capture (COSMIC) is planned to be an evolution from the ELSA-M variant and will provide deorbiting functionality for defunct satellites as a commercial service to satellite operators. COSMIC is expected to launch in 2025 as part of the UK’s ADR initiative. It passed a system requirements review in late 2023 and is currently undergoing a preliminary design review of functionality, such as the proposed robotic arm and de-tumbling methods.
ClearSpace is another innovative UK organization that is leading a consortium, with the backing of the UK Space Agency, to design and execute a mission to clear up orbital debris.
Their mission, known as Clearing of the LEO Environment with Active Removal (CLEAR), entered the design review stage last October and intends to remove two UK-registered defunct objects from LEO that have been inactive for more than ten years. The CLEAR spacecraft will feature unfolding robotic arms that will be used to capture and release target objects. CLEAR is currently projected to launch in the second half of 2026 on a Vega C rocket from French Guiana.
Other low-cost methods explored include Millennium Space’s wide drag tape that massed less than one kilogram. The tape could be released by craft to self-deorbit cheaply and quickly. Of the two satellites deployed during the DRAGRACER mission in 2020, the satellite with the 70-meter drag tape deorbited within eight months, while the other satellite is estimated to take at least seven years before it deorbits.
Artist’s impression of one of the DRAGRACER satellites deploying the 70-meter Terminator Tape developed by Tethers Unlimited. (Credit: Millennium Space)
Are Earth’s orbits becoming too crowded?
Between 1957 and 2012, the number of satellites launched per year stayed reasonably consistent, as the United Nations noted in their “For All Humanity” review, at approximately 150. This period includes the pioneering years of human spaceflight and the development of the International Space Station (ISS) and global communications satellites. The number of satellite launches per year has increased exponentially in the last decade, however, exceeding 2000 by 2022.
Space is vast, but some are concerned that the volume of expired objects in orbit is increasing the potential for them to become a hazard to other spacecraft and the risk of their orbits decaying in less predictable ways. Communications satellite constellations such as Starlink and Kuiper will be major contributors, with both constellations eventually hoping to have thousands of satellites in their constellations.
Debris is not, of course, limited to retired craft and stages. NASA estimates that there are about 100 million particles of debris that are larger than one millimeter in size, of which around 25,000 are larger than 10 centimeters — the size of a softball.
The ISS adjusts its course if the possibility of a collision with debris exceeds one in 10,000 and has course-corrected over thirty times since 1999, according to NASA.
Illustration of the concentration of orbital debris from LEO to GEO. (Credit: NASA OPDO)
The greatest concentration of debris is between 750 and 1,000 kilometers in altitude, with the most debris orbiting within 2000 kilometers of the surface. The time that this debris could stay in space will range from a few years to over a century, depending on its altitude. Each year, somewhere between 200 and 400 of larger-tracked objects re-enter Earth’s atmosphere, though less than 100 of these objects are large enough to survive this process and reach the surface in some form.
The primary concern among scientists is “Kessler Syndrome,” named after NASA Scientist Donald Kessler, who wrote an influential paper in 1978 in which he warned that collisions in congested space could cause a domino effect of additional impacts that cascade to the point where LEO could become an untraversable debris field for many years.
It is estimated that a third of all cataloged debris can be traced to just two such “fragmentation events” in space. The most severe incident occurred in 2009 when the Iridium 33 satellite collided with the Russian Cosmos 2251 military satellite, which had exceeded its five-year lifespan and was no longer active. The United States military subsequently developed a process that includes daily screenings of all active satellites in orbit to anticipate and react to the risk of colliding objects.
The collision created almost 2000 pieces of debris over 10 centimeters in size, some of which have since decayed from orbit, while half of the Iridium debris and much of the Cosmos debris will remain in orbit for another 10 to 20 years.
The second incident was the intentional explosion of the Fengyun-1C meteorological satellite in 2007 during a Chinese anti-satellite missile test. At around 32,400 kilometers per hour, the force of the impact was enough to destroy the satellite without explosives.
The explosion subsequently created 3000 pieces of sizeable debris (which are still regularly tracked as a potential risk to the ISS) and around 150,000 particles, of which more than half could remain in orbit at around 850 kilometers for decades; the majority likely to remain into the next century.
Other types of space debris and asteroids
One final type of space debris is unexpected and lost items, such as lost items from an extravehicular activity (EVA) like hammers and tools.
Astronauts have been accidentally losing items, including tool bags, bolts, and spatulas since Ed White lost his spare thermal glove in 1965 during the first-ever American spacewalk outside the Gemini 4 capsule. Another tool bag was recently lost during an EVA to replace ISS solar array parts in November 2023 and is expected to burn up in the atmosphere this March.
Asteroid 99942 Apophis will make a sweeping pass closer to Earth than satellites in geostationary orbit in April 2029 and another in 2036. At 340 meters in width, this is the closest approach by an asteroid of this size for which we’ve had advance notice. With a path that will be inclined away from the equator, experts have ruled out any impact with objects in GEO (nor will it impact Earth for at least the next 100 years). The repurposed OSIRIS-REx spacecraft, now dubbed OSIRIS-APEX, that previously returned a sample of asteroid Bennu will study this asteroid for 18 months as it passes by.
Space tugs and trucks
Space tugs often deliver satellites to their final destination, such as further out in GEO, enabling them to preserve onboard propellant.
This will be an advancement from Northrop Grumman’s Mission Extension Vehicles (MEV), conceived almost a decade prior by Vivisat. With a 15-year lifespan, the vehicle design includes docking, servicing or deorbiting, undocking, and moving on to a new object.
MEV-1 approaching the Intelsat 901 satellite before docking. (Credit: Northrop Grumman)
MEV-1 attached itself to Intelsat 901 in 2020, taking over attitude and propulsion control to reposition the satellite into GEO, returning it to service for five years. MEV-2 simply acted as an additional fuel tank and engine for the Intelsat 10-02 satellite. The company has since shifted focus to a Mission Robotic Vehicle, which will deploy a series of Mission Extension Pods and could launch as early as this year.
With the biggest threat being the larger objects that still linger in LEO, the next generation of space tugs, such as Impulse Space’s forthcoming Helios tug, could potentially have a role to play in this new market at lower altitudes too.
Tom Mueller, CEO of Impulse Space, recently told NSF, “I would love to have this vehicle refuel in LEO, remove an object, and then stay up there, refuel again, and keep removing. One Helios, along with propellant depots, could really improve the efficiency of removing those big objects.”
(Lead image: Render of the ADRAS-J spacecraft in orbit. Credit: Astroscale)
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