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Op-ed | Proliferated LEO is risky but necessary

The red lines in this video screenshot are tracks of debris that Indian satellite Microsat-R may have produced when it struck the antisatellite weapon placed in its path by India’s military defense organization on March 27. Credit: Analytical Graphics Inc.

“All problems become smaller when you confront them instead of dodging them.” — William F. Halsey

Once a safe haven, the space above Earth’s atmosphere is congested and contested — and the problem is getting worse. A determined adversary can disable or eliminate a satellite it views as a threat. As the national security of the United States and its allies becomes increasingly reliant on space-based capabilities, we need to move toward resilient constellations that can absorb satellite losses without losing the mission. Proliferated LEO — the building of large constellations of small satellites in low Earth orbit — is an essential strategy for achieving this resilience. But it does come with its own challenges.

The commercial space industry is leveraging the miniaturization of satellite technology, shrinking costs and increased competition in launch to create a projected huge increase in commercial satellites in lower orbits. It is now feasible for proliferated LEO constellations to provide persistent, global internet coverage with very low latency. OneWeb, SpaceX, Amazon, Telesat, and Samsung are among those pursuing large LEO constellations comprising hundreds to thousands of small satellites. The U.S. Federal Communications Commission has already agreed to license more than 10,000 such satellites with hundreds more under review. The Defense Department is leveraging this trend with DARPA’s Blackjack and Casino programs and a new communications transport layer being pursued by the Space Development Agency.

The world is moving inexorably to proliferated constellations. This is a logical progression and generally a good thing. But like many good things, it is not without risks.

The risk, simply put, is that space will become too congested to be safe. Space is vast but the orbital real estate suitable for satellite constellations is finite. This is especially true for LEO compared to higher orbits.

An Indian PDV-Mk II missile lifts en route to intercept and destroy Microsat-R. Credit: Government of India Credit: Government of India

The Earth’s most heavily utilized orbits will certainly grow more congested and become a riskier place to operate when the DoD’s newly planned proliferated LEO (pLEO) constellations and commercial pLEO constellations are added to the multitude of inoperative satellites, spent rocket stages, and softball size or larger pieces of orbital debris we can currently track. Because of the high velocities involved — in excess of 27,000 kilometers per hour — any one of the hundreds of thousands of pieces of space debris currently too small to track can cause significant damage. (As we move toward the Space Fence, we will be able to track the golf ball size objects, which will allow potentially better planning and operational safety actions).

The volumes available in space increase exponentially as orbits increase in altitude. So, LEO is far more susceptible to congestion than medium Earth orbit or geostationary or highly inclined orbits. However, the current trend is to move from orbits with large volumes of space that help mitigate congestion to lower orbits with much smaller volumes of space which accentuate congestion. As a result, we are on a path toward exponential increases in the risk of in-orbit collisions. The projected space object densities in LEO are straining our current capabilities to reliably model the risks.

Adding to the complexity of this problem is the reality that smaller pieces of space junk are created by violent breakup events and inadvertent (and possibly intentional) collisions that supply new pieces of debris. With each collision, the population of space debris increases, thereby increasing the odds of collisions. To date there have been nearly 200 accidental explosions of satellites, creating a huge amount of space debris. Micrometeoroids also will be a significant threat as the numbers of satellites increase so significantly. In 1978, NASA scientist Donald J. Kessler predicted that space debris collisions would trigger a cascade effect, rendering low Earth orbit activities untenable for decades, with created debris increasing exponentially in time by successive collisions. Last March, India conducted a successful ‘kinetic kill’ antisatellite test when it fired a ground-launched missile at one of its satellites orbiting at 325 kilometers. India wrongly assumed that the low altitude would cause the debris to rapidly reenter and decay within weeks. However, 125 objects were cataloged in orbit with apogees up to 2,200 kilometers. Forty-six objects remained in orbit a full five months after the test and 17 objects are still being tracked as of early this year. This surely is an example of the unpredictability of debris created by a kinetic event, intentional or unintentional.


Every time we conduct a space launch, we have to de-conflict based on potential interference from LEO objects. If low Earth orbit becomes too crowded for new launches, then active space junk removal missions — no matter how far-fetched they may sound — could become the only option. But these would come at an opportunity cost for other science, civil and defense missions. If we do not pay attention and set up some rules of the road, especially for Proliferated LEO, we run the risk of cascading collisions rendering LEO unusable, and creating so much debris that we also cannot safely launch through it.

There are currently limited actions on best practices for deorbit. The real issue is the current commercial “Gold Rush” approach to pLEO, with ventures vying to be the first and build the most in order to drive competitors out of the marketplace. A possible result of this rush could be an overpopulation of pLEO space. There are guidelines, but no real rules, for eliminating space debris and removing defunct satellites from orbit. For the expanding field of cubesat and smaller satellites, we lack even clear guidelines. These tiny satellites, some weighing less than a kilogram, can’t be easily deorbited as a result of their low fuel reserves. And because they’re so small, it takes a long time for drag to pull them out of low Earth orbit. Because deorbit time is proportional to ballistic coefficient (effective drag area/ mass), small, dense objects linger in orbit longer than large light objects.

Some of the commercial companies pursuing big LEO constellations populated with mass-produced satellites are assuming 10-15% of the spacecraft they launch could die on orbit.

SpaceX launched its fifth batch of Starlink broadband satellites into low Earth orbit Feb. 17. The company now has 302 satellites in orbit with plans to launch hundreds more by year’s end. Credit: SpaceX Credit: SpaceX

Consider an historical example: Iridium, which launched its first 95 satellites between 1997 and 2002, still has 30 of those satellites in orbit because the malfunctioned before they could be brought down. Up to 23 of those defunct satellites are expected to remain there for 100 years or more.

If something similar happens with today’s planned mega-constellations, and we end up with 20,000 commercial satellites in LEO, we could also end up with 2,000 rocks orbiting with the potential to cause a collision cascade. The scenario looks even worse if we assume that some of these constellations go bankrupt, leaving space cluttered with abandoned assets waiting years or decades to decay and deorbit. Who has the responsibility to ensure the satellites from these bankrupt companies are disposed of properly? The biggest issue is that once the damage is done, it is a long wait for the problem to self-correct.

Another question that should be asked of these owner-operators of proliferated, low-cost satellite constellations is this: What assumptions have you made with regard to the ability of your “disposal” approach to handle radiation environments more hostile than are currently present? Are your satellite avionics capable of surviving a significant solar flare or coronal mass ejection event? Do you even know at what point your avionics suffer a catastrophic latch-up that leaves your satellite deaf to commands? Traditional national security space missions have, for decades, required worst-case analysis to be performed to understand how failures can occur and what to do to mitigate them. The commercial, proliferated constellation operators should have to demonstrate a similar level of understanding of their constellations and prove that their disposal approach will function in the most challenging of space environments.


“Not everything that is faced can be changed. But nothing can be changed until it is faced.” — James Baldwin

Many ideas are being floated for how to address the problem of actively removing space junk. However, it is probably cheaper to prevent the space debris from accumulating in the first place to than to remove it once it is there. Who is going to spend millions of dollars to build and launch a satellite that collects a couple of pieces of debris? It does not currently appear financially feasible.

Currently, the U.S. Space Force — via its absorption of Air Force Space Command — provides space object and debris tracking and provides potential collision warnings. In the past, this has not been a huge job. But that’s changing with the growing number of shrinking satellites being built and launched. Appropriately, there is an ongoing transition — per the Trump administration’s Space Policy Directive-3 (SPD-3) — of this responsibility to the Federal Aviation Administration and the Federal Communications Commission.

SPD-3 also represents the definitive U.S. government position for space traffic management. Per the White House directive, space traffic management (which is similar to “Basic Space Situational Awareness Services” provided by the18th Space Control Squadron at Vandenberg Air Force Base) will transition to the Department of Commerce. Overall, the impact of constellations on the LEO environment are currently managed as part of the launch licensing process. Given the potential issues, we need to explicitly include best practices for failure rates and de-orbit guidelines for LEO smallsat constellations. As we move to FAA and FCC as the responsible U.S. government entities, they will have to develop policies and practices to deal with these challenges. Under Space Policy Directives 2 and 3, the FAA and FCC both solicited industry input to new launch licensing and orbital debris guidelines. These flight risk and orbital safety issues need to be part of this process.

For the junk that has been already created in space, the current mitigation approach entails using ground-based systems to map it, sending out collision avoidance messages, and maneuvering to avoid it. For now, we will have to rely on these tracking systems to keep low Earth orbit safe, and also work to prevent new missions from making the problem worse. Though tracking space junk is easier and cheaper than collecting and getting rid of debris, it is not without challenges. The Space Fence and other space junk-tracking telescopes need to be funded, built and deployed.

DARPA is developing a prototype line of cost-effective reconnaissance satellites that will set up shop in low Earth orbit, as part of a program called Blackjack. Credit: DARPA Credit: DARPA

As we build thousands of new satellites bound for LEO, we need to build in the requirements for keeping LEO viable. This will cost money, but if satellite makers don’t take the necessary steps to ensure their products won’t contribute to space junk, the increasing odds of a collision and the risk of starting a collision cascade will increase. Late last year, a newly established group of space industry leaders called the Space Safety Coalition published a list of best practices for spacecraft operators, including guidelines for limiting the impact of new satellites and preventing the growth of space debris. The guidelines call on spacecraft operators to create improved deorbiting plans and for engineers to prioritize collision-avoidance capabilities. Spacecraft owners, operators and stakeholders should exchange information relevant to safety-of-flight and collision avoidance. Both SpaceX and OneWeb have submitted plans, but no one has assessed the adequacy in the new pLEO world.


“Running away from a problem only increases the distance from the solution.” — Anonymous

Proliferated LEO is necessary for contending with the new world realities in space. As you move to LEO to take advantage of shorter distances and lower latency, you clearly need more satellites to provide the coverage you need vs. higher altitudes. Additionally, the military also proliferates for resiliency so they can absorb the loss of satellites and have the mission continue.

We can overpopulate any orbit, but it is in LEO where we face the most significant challenges. The shift to pLEO is moving fast from both government and commercial points of view. Being in a place where we can now build and launch systems that make this feasible is a good thing. The concern is that the commercial rush could over-clutter space and prevent an effective, defensive national security use of space. The evolution of all classes of smallsats, increasing launch competition, and the move to smaller lower cost launch are allowing this to happen.

So, yes, we must move to proliferated constellations, but we must do it with intelligence and care. Now is the time to make sure that this will not turn into a nightmare. We need to plan and have rules, and these rules need to be internationally accepted. We need an international organization that protects space similar to spectrum allocation. There is an urgent need to tell operators that if you put it up, you have to bring it down — or fund some kind of independent remediation fund for space similar to the federal Superfund program the United States established in the 1980s to clean up toxic waste sites. Maybe operators should be required to put up bonds based on the number of satellites they put into space.

The affordability and shorter lifetimes of proliferated LEO systems will allow the United States to effectively counter its adversaries through rapid insertion of new technology. As we move to LEO to take advantage of shorter distances and lower latency, we need more satellites to provide the same coverage as small numbers of satellites in higher altitudes. Additionally, proliferation provides resiliency, allowing the military — not to mention commercial operators — to absorb the loss of satellites and have the mission continue.

We should celebrate industry advances, but we should not deploy them without the consideration and mitigation of their corresponding risks.

Top “Tav” Taverney is a retired U.S. Air Force major general and former vice DARPA commander of Air Force Space Command.

This article originally appeared in the Feb. 24, 2020 issue of SpaceNews magazine.