TOO Close for comfort

APOGEE STAFF

The sheer volume of objects entering low Earth orbit is raising alarm in many quarters, inspiring scary renderings of space paths impossibly cluttered by sharp, shiny objects and prompting calls for space traffic management modeled on systems for controlling transit through air and sea.

The most serious danger today, though, may lie not in the proliferation of new satellites — those that enable civilization as we know it through instant communication, precise location and sharp surveillance — but in the space ambitions of decades past. In many ways, for government and private operators keeping an ever-sharper eye on all the stuff in orbit, tomorrow presents less of a threat than yesterday. The reason: Advances in technology mean that, typically, the latest satellites and satellite constellations, even though they can number in the thousands, are closely tracked, follow widely known pathways, can maneuver to get out of the way and include a plan for leaving orbit.

Compare this to the looming hulks that dominate a Top 50 list of risky objects in low Earth orbit (LEO), where outer space begins at about 100 kilometers up and most space activity occurs. The Top 20 on this list are from Russia, nearly all of them derelict rocket bodies. Most of the rest are Russian, too, except for a dozen objects combined from the United States and the People’s Republic of China (PRC). The list’s Russian derelicts date to 1974, and many weigh around 10 tons each. Lacking propulsion or any working systems, they can’t get out of the way. Some are tumbling out of control as they circle the Earth around 850 kilometers up. Reliable for their time but with little in the way of advanced technology, the big aluminum tubes wrapped in solar arrays have been likened in design to a hot dog in a bun. And as dangerous as they remain individually, many are moving in clusters, creating what Darren McKnight with space tracking company LeoLabs calls “one bad neighborhood.”

“You keep rolling the dice and it’s going to come up snake eyes,” said McKnight, senior technical fellow with the Menlo Park, California, company, and a member of the Space Debris Committee of the International Academy of Astronautics. “They’re big, they have a big, exposed area, so the numbers are against you.” About 75% of high-risk conjunctions, or close approaches, involve rocket bodies, McKnight said in a report he presented on debris hazard trends to a March 2024 aerospace conference in Florence, Italy.

Spacefaring nations grew concerned through the years about the trash they had left in orbit, and a 25-year rule — any spacecraft in LEO should be limited to an orbital lifetime as short as practicable with deorbiting no more than 25 years after completion of mission — gained wide acceptance by the early 2000s. After that, fewer nations would leave new rocket bodies to linger, with one prominent exception: the PRC, now No. 2 behind the U.S. as a global space power and moving up fast. “I wish the news was just, ‘Russia has not done that much,’ ‘The U.S. has not done that much,’ but China made up for it over the last 20 years,” McKnight told Apogee. “They’ve put up more mass per year than the rest of the world combined.”

I wish the news was just, ‘Russia has not done that much,’ ‘The U.S. has not done that much,’ but China made up for it over the last 20 years. They’ve put up more mass per year than the rest of the world combined.”
~ Darren McKnight, LeoLabs

There are a number of ways to rank the most dangerous objects in space, but McKnight’s Top 50 list draws from 11 other lists developed by experts in nine countries and highlights as a priority those objects with the potential to create damaging debris fields. In this case, size matters. A key calculation: Risk equals probability of collision (PC) multiplied by mass. By this measure, the Chinese have barely cracked the Top 50 yet. “No, but they’re working their way into it,” McKnight said. “They’re still doing it. Some of their worst ones on there are from 2019, 2020.” The most recent launch of a Russian rocket on the list was 1992. The PRC has escaped international condemnation. “There isn’t any; the Chinese do a really good job of deflecting issues.” The PRC also showed the world the dangers a debris field can present when it conducted an anti-satellite test in 2007, firing a missile into a derelict Fengyun 1C weather satellite and blowing the two objects into some 3,500 pieces, 70% of which still are in orbit. With the velocity and angle of the strike, the missile and the satellite took on the properties of liquid as they broke apart and — rather than bouncing off one another — continued forward in pieces on their respective trajectories.

The PRC also stymies efforts to make space safer by standing silent as other nations work to share what they know about objects in orbit. “Showing and sharing” your work in space operations is a key to safety, McKnight said. In this regard, “most Chinese constellations have not been as forthright and consistent,” he said. “Showing your work means explaining equations, models, thresholds for maneuver, timing for maneuvers, and constants used, then sharing your work means providing maneuver plans and propagated ephemeris [assigned location] to others.”

This failure to share reflects a general absence of dialogue with the PRC that creates conditions for “miscommunication, misperception, misinterpretation, and then things could go wrong,” Lt. Gen. John E. Shaw, then deputy commander of U.S. Space Command (USSPACECOM) and now retired, said during the Summit for Space Sustainability in New York during June 2023. Traffic watchers at Vandenberg Space Force Base in California issue warnings of close approaches in orbit to satellite operations and national agencies, including the government of the PRC. They’re known as conjunction data messages. But when messages are sent to Chinese email addresses, “We never get a response. Never,” Shaw told the summit, as reported by SpaceNews. “Even the Russians know how to communicate with us. We don’t have anything like that with the Chinese, and that’s the biggest hindrance to transparent operations.” The Chinese deviated from that pattern recently, “proactively” reaching out to the U.S. twice on space-safety issues, Space Force Gen. Stephen Whiting, commander of USSPACECOM, told the Space Symposium in Colorado Springs, Colorado, during April 2024.

Transparency is the mission of the 18th Space Defense Squadron (SDS), the space watchers of Space Force, whose duties include maintaining Space-Track.org. This comprehensive catalog is available to anyone who logs in, and its Space Scoreboard keeps a running count that in September 2024 listed 10,400 active payloads, 17,100 objects under analysis and 18,900 “debris,” for a total of 46,400 objects. That’s actually just a fraction of all the manmade objects in space — only those that are 10 centimeters in size, as big as a softball, or larger. As for the smaller objects, there are 1 million manmade objects in space ranging from 1 centimeter up to 10 centimeters and a whopping 130 million objects 1 millimeter to 1 centimeter in size, the European Space Agency estimated in 2022. These numbers constantly change with new launches, objects leaving orbit, breakups, collisions and other events.

The 18th SDS monitors and identifies the changes, according to a November 2023 report at the Space Force website, spaceforce.mil. The squadron processes information on plans and observations submitted by civil, commercial and military satellite operators worldwide, and from the ground-based and space-based sensors of the Department of Defense’s Space Surveillance Network. On a classified level, the Space Force also shares potential threats from adversaries with U.S. allies and partners. To predict fragmentations, one of their tasks, the 18th SDS tracks changes in orbital parameters that can signal whether a satellite is releasing gas or undergoing structural stress. The squadron’s clustering algorithms collate objects that have similar properties, such as size, shape and orbital path, to identify potential fragmentation debris. Once debris is identified, the 18th SDS incorporates it into conjunction assessments and shares potential collision risks through Space-Track.org.

“We’d like to know every instance, and this is hard with all the data from 47,000 objects on orbit that could hit 46,999 other objects — that’s a big math problem,” Space Force Gen. B. Chance Saltzman, chief of space operations, told Apogee at the Space Symposium in Colorado Springs, Colorado, in April 2023. “Not to mention the debris that’s small enough we can’t track. Do I think it’s inevitable? Yeah, there’s going to be collisions. Do I think we can watch and prioritize the things that we’re most sensitive about? I do. I have that capability and that’s exactly what we’re trying to do.”

USSPACECOM and its component commands will continue to keep watch over defense and national security interests in space, but responsibility for tracking everything else is shifting to the Department of Commerce — an effort that will enable the command to focus more on what’s happening in the domain. “Our challenges center on ensuring the warfighter has relevant and timely data to execute missions in a very complex and changing environment,” Army Gen. James H. Dickinson, then commander of USSPACECOM and now retired, said in October 2022 after the shift was announced.

Do I think it’s inevitable? Yeah, there’s going to be collisions. Do I think we can watch and prioritize the things that we’re most sensitive about? I do. I have that capability and that’s exactly what we’re trying to do.”
~ Space Force Gen. B. Chance Saltzman

Increasingly, the job of watching and analyzing objects in space will fall to the commercial sector, Space Force Col. Daniel Kimmich told Defense News in March 2024. Noting the rapid proliferation of civilian and defense constellations, Kimmich said, “We have to rely on commercial … selling that information to government so we have a complete picture so we’re not solely reliant on systems we built.” The transition to the Commerce Department is called the Traffic Coordination System for Space, and an early demonstration phase is known as the Consolidated Pathfinder project. Three companies were chosen to carry out the project: COMSPOC of Exton, Pennsylvania; Slingshot Aerospace of El Segundo, California; and LeoLabs.

With its sixth radar complex activated last year in western Australia, LeoLabs provides satellite tracking services to customers including the Japan Air Self-Defense Force, Starlink broadband system and Planet with its more than 200 Earth-imaging satellites. Starlink and operators of other modern satellites can track their own spacecraft because they’re equipped with GPS. But what about all the other stuff? “What they need is information for operational payloads that don’t play nice with others, like the Chinese, or secondaries like rocket bodies and fragments,” McKnight said. “That’s why it’s critically important for them to have our services.” The military is turning to commercial providers like these for their innovation, efficiency and flexibility. Despite a national defense policy that requires it, the handoff is taking time when it comes to the space situational awareness services that LeoLabs provides. “We’re trying to get them used to the idea that they don’t need to control and own the logistics; that’s where the costs are,” McKnight said. “They’re just not comfortable. It’s like having kids and letting them have cellphones. Back in my day, we didn’t have cellphones. Well, guess what, things have changed. So, we’re in transition.”

The capabilities LeoLabs offers include machine learning and artificial intelligence that can help reveal meaningful patterns, like, “these four satellites are maneuvering and they haven’t maneuvered in a year,” or “these ones maneuver every single month and they’ve stopped maneuvering,” McKnight said. In other words, buy the work of data wrangling, as he calls it, and leave the higher-level analysis about what it means to Space Force Guardians. The company also offers a high “revisit” rate — how often each day its global network of radars sees an object in space. With the average object, that’s four to six times, and twice that for those objects the company is tasked with keeping a closer eye on. “That means there’s less of a chance for someone to do something and [the customer] is not going to know about it.” He offered a highway analogy. “If you have two traffic cameras and you want to know which way you should take home from work today, you have no idea. Two’s not enough. But if you have 30 on the beltway, you know exactly. You’re aware of the situation.”

Information satellite operators receive from Space-Track.org and LeoLabs, and from one another, helps them decide whether they need to act, perhaps by conducting what’s known as a risk-reduction maneuver. Assessing risk is a math problem, a calculation of complex factors such as time of closest approach; orbital speed; radial, transverse and cross-track vectors; even something called the Mahalanobis Distance. Tolerance for risk, known as risk threshold, varies among operators as they give weight to considerations such as how much fuel they have, the maneuverability of their satellites and the time it would take to execute. “Some people are more risk averse than others,” McKnight said. “And so some people will wait to maneuver until the probability of collision is on the order of 1 in 10,000 and some people will do it when it’s 1 in a million. On average it’s about 1 in 100,000.”

While LeoLabs sends conjunction data messages as early as five days before a conjunction with a high probability of collision, the typical operator will maneuver two to three days before the projected time of closest approach. The longer an operator waits, the less uncertainty there is in the predictions but the greater the sweep of a maneuver. Sometimes, two satellite operators learn of a potential collision and one or both may decide to maneuver. Their individual risk thresholds may drive who acts, or whether one is transiting the other’s operational altitude, or maybe the newer spacecraft has more propulsion maneuvers. “There are a wide variety of scenarios and all of them require significant pre-event planning and during-event communications,” McKnight said. More common are conjunction data messages involving an approach by one of the far more numerous space objects that lack the ability to maneuver.

Sometimes, near misses make news, like a post in February 2024 on the social media platform X from the European Space Agency. The agency had to move a three-satellite Earth-observation constellation known as Swarm Bravo to get it “out of the way of a satellite that came too close for comfort.” The post said, “We nudged Bravo down by 1.75 cm/s just in case, and we’re thankfully safe and sound!” Also in February, a NASA research satellite known as TIMED and a derelict Russian intelligence satellite came within 10 meters of one another, according to Pamela Melroy, NASA deputy administrator. “Had the two satellites collided, we would have seen significant debris generation – tiny shards traveling tens of thousands of miles an hour waiting to puncture a hole in another spacecraft,” Melrose told the 2024 Space Symposium. “The TIMED spacecraft really scared us all.” In this case, observers could only sit and watch; neither the NASA satellite nor the Russian Cosmos 2221 was capable of maneuvering. The Chinese military satellite Yaogan 37 nearly collided with an Australian satellite in October 2023, the Australian website ABC News reported. Yaogan 37 maneuvered 16 hours before the predicted conjunction, increasing the miss distance to a safer 978 meters at closest approach. “Unfortunately, these types of critical conjunctions occur on a nearly daily basis in low Earth orbit,” said Terry van Haren with LeoLabs Australia, as reported by ABC. “Deconfliction between western satellites and Chinese and Russian systems is of course more complicated given the lack of communication and cooperation between these space users.”

Deconfliction between western satellites and Chinese and Russian systems is of course more complicated given the lack of communication and cooperation between these space users.”
~ Terry van Haren, LeoLabs Australia

In contrast to that bad neighborhood with so many old rocket bodies — some 20% of all the mass in LEO, and all about 900 kilometers up — McKnight’s good neighborhood is at about half that altitude. But it’s the belt that’s generating much of the alarm about space congestion, what he calls the Starlink Corridor. This corridor has more than twice as many manmade objects, some 6,300 of them as of April 2024, as the bad neighborhood does. But volume alone doesn’t scare McKnight. This time, he used a couple of analogies to explain. “People said, ‘Ah, we just can’t have that number,’ and I said, ‘Stop, stop. You can have a certain number of people on a dance floor if they know how to dance.’ If they don’t know how to dance, you can only have 20% of those people and you’re going to have a lot of collisions. At football games, at halftime, we have 300 college students in a marching band and nobody is hitting each other. After the game, when there’s a big upset, you have 150 people on the field and they’re flying all over the place.”

Starlink, he said, knows how to dance. He said the SpaceX-owned company that hired LeoLabs to watch its back is one of the most responsible players in space, skilled at system design and risk management. In some cases, the company can avoid conjunction through a move called duck and dodge — turning a satellite to reduce its collision cross-section without using propulsion for a maneuver. Starlink is called upon daily to prove just how well it can dance. The company was forced to swerve more than 25,000 times between December 2022 and May 2023 to avoid potentially dangerous approaches, according to a twice-yearly report SpaceX files with the Federal Communications Commission. That’s about double the number reported for the previous six-month period, an average of six per day, raising concerns that its risk-reduction maneuvers would begin to increase exponentially. “The problem with exponential trends is that they get to very large numbers very quickly,” University of Southampton astronautics Professor Hugh Lewis told Space.com for a July 2023 article. Starlink has received FCC approval for 12,000 satellites to provide broadband service around the globe and indicated it intends to seek approval for 30,000 more. Still, the company’s six-month report for the period ending December 2023 showed no increase in avoidance maneuvers. “If somebody told me I have to go hang out in a satellite for a year in an orbit, you know where I’d go? I’d go to 547 kilometers,” McKnight said. “Why would I do that? Because I trust Starlink.” That corridor also is low enough that the pull of Earth’s gravity brings debris down fast, further reducing risk, he said. “I’d much rather be there than at 865 kilometers where you have the remnants of the Fengyun test, you have the old Soviet rocket bodies, you got old U.S. weather satellites. About six of them have had small breakup events that add up to one big breakup event. And they’re going to linger for centuries.”

Greater international cooperation is required for space-tracking efforts in LEO to deliver acceptable levels of safety, experts agree. Over 95% of operational satellites in LEO by 2030 will be part of just five constellations from three countries: SpaceX and Kuiper from the U.S., Guowang and G60 from the PRC, and OneWeb from the United Kingdom, according to McKnight’s March 2024 presentation. A 2023 report from the Rand Corp. public policy research group explores the possible creation of an International Space Management Organization through the United Nations, drawing comparisons with existing entities such as the International Maritime Organization. Going forward, designing spacecraft with debris mitigation in mind and strengthening mitigation rules would make space safer, including reducing the 25-year rule to five years, many agree. “Even that’s dumb,” McKnight said. “It should be one.” Deorbiting in LEO generally means using the last bit of a satellite’s fuel to slow it down, so it falls into Earth atmosphere and burns up. Today, only France has adopted space debris mitigation as law. Even the U.S. has issued only guidelines with little follow-up once they’re agreed to before launch. The FCC reduced its standard to five years, but other regulatory agencies have not, and waivers are sometimes granted for national security purposes.

As for dealing with all the objects already in LEO, standardizing tracking and avoidance to the extent possible given the age and capabilities of each operational satellite would go a long way toward making the neighborhoods safer, McKnight said. So would “showing and sharing” — and developing debris removal technologies, a growing but largely untested commercial sector. The first mission to remove a dead rocket was launched in February 2024 aboard a rocket from U.S.-based Rocket Lab, funded by the Japanese Space Agency JAXA and featuring an inspection spacecraft from Japan’s Astroscale. In addition, the MIT Technology Review reported, the U.S. Senate passed a bill in October 2023 to investigate debris removal technology, the U.K. has selected Astroscale and ClearSpace of Switzerland to design debris removal missions, and ClearSpace plans to launch a mission for the European Space Agency in 2026 to remove from orbit a 112-kilogram piece of a European rocket. Even tractor beams, reminiscent of “Star Trek” episodes, are under study at the University of Colorado for debris removal in higher orbits. Hazards there are less than in LEO, in part because satellites are fewer, their velocity is lower and they orbit at lower angles to the Earth.

LeoLabs with its Earth-based radar is working with satellite-based imaging company Maxar of California and the University of Bern in Switzerland on questions such as debris removal priorities. This includes those giant, looming hulks. “So which ones should we go after? Stable is much easier to remove than a tumbling one,” McKnight said. “A removal mission involves several steps: rendezvous, grappling, detumbling if needed and propulsive reentry. With a tumbling object, rendezvous and grappling are both more difficult.” Bringing together all these partners’ skills may help produce the best answers. “Radar alone can’t do this, telescope alone can’t do it, space-based imagery can’t do it,” McKnight said. “But the combination, I think, is very important for the highest level of characterization.”