By Ken Eppens
Founder and CEO, OrbitGuardians.com
19% of tracked space objects threaten GPS and other GNSS satellites. While there are many fewer objects in MEO than in LEO, the risk in the former is arguably greater because GPS is so critical to almost all of our technology.
GNSS satellites, especially GPS satellites, are critical to the well-being and smooth functioning of economies and national security. This is especially true in Europe and the United States, which do not have complementary terrestrial systems able to provide vital positioning, navigation and timing (PNT) services when signals from space are not available.
While the probability of debris damage to GNSS in medium Earth orbit (MEO) is much less than for satellites in low Earth orbit (LEO), the consequences of such an event would be much, much higher. The loss of one satellite would be a concern; that of multiple satellites, a major problem. The unthinkable chaos, national security damage, and severe economic impacts to the $21 trillion U.S. GDP make the risk unacceptable.
For those who think we need not worry about the low probability of collisions at MEO, the Galileo collision avoidance maneuver in March 2021 should be a wakeup call. The problem is here. We need to act now.
Much like a nuclear fission reaction, the problem of space debris starts small then grows exponentially, as each collision creates more pieces that, in turn, can collide with other objects.
The 100 million debris objects orbiting Earth are the result of 6,500 space missions spanning 60+ years and more than 400 debris-generating events. Alarmingly, in the next eight years, this tragic legacy shall be eclipsed as more than 100,000 more satellites (17 times as many as there are now) are slated for launch.
The MEO debris environment is 100 times less dense than the LEO. The spatial density of orbital debris in LEO (up to 2,000 km), shown in Figure 1, suggests that LEO is the likely location where a runaway chain reaction will initiate. This could easily result in a region of space so dangerous that it would effectively deny access to MEO, where the GPS constellation resides.
While the debris situation at MEO is much better, there are still 4,021 tracked debris objects that could impact GPS and other GNSS satellites. Because future orbital debris collisions in LEO will be responsible for more debris in MEO, the situation is guaranteed to get worse. The dead and debris objects in highly elliptical, or Molniya, orbits, shown in Figure 2, could be responsible for such collisions pushing LEO debris into MEO.
Contributions to the general MEO debris population come from launch systems and other factors. Early GPS satellites (Block II/IIA/IIR) used internal orbital-insertion motors to avoid leaving uncontrolled stages in the operational orbit range when moving from transfer orbit to MEO. For survivability reasons, they were also deployed with sufficient fuel to make several major orbital moves. Unfortunately, later versions used separate orbital-insertion stages, which were left drifting in the orbital neighborhood and carried less fuel, resulting in fewer possible maneuvers to avoid collisions.
Using the CelesTrak visualization interface to extract space situational awareness data captured by the Combined Force Space Component Command’s 18th Space Control Squadron (18 SPCS) reveals a much more dire image of MEO. Of the 21,266 total tracked objects in Earth’s orbit, 157 are active GNSS satellites, as shown in Figure 3.
However, a total of 4,021 objects reside or pass through MEO, which are either active (331), dead (668), debris (1,761), rocket bodies (1,100) or unknown (161) objects, as shown in this video.
These 4,021 objects represent 19% of the total number of tracked objects from the 18 SPCS space catalog. While the total 21,266 tracked objects is a far cry from the 100 million objects NASA’s Orbital Debris Program Office represents, one can imagine that a significant portion of untracked debris objects, under 10 cm in size, reside or pass through MEO as well. This is significant, according to NASA, which says that objects with a diameter of 1 cm to 10 cm are the most dangerous due to the lack of tracking data, which essentially makes them invisible.
False Sense of Security
The growing orbital-debris concern is a threat too big to ignore. Unfortunately, to date attempts to manage space traffic have amounted to passive measures, such as establishing policy, characterizing the environment, and creating orbital protection guidelines. Even the highly touted, $6 billion U.S. “Space Fence” is a passive measure that contributes nothing active to solve the problem. Not at all a “fence,” it is merely a way to detect the larger and more dangerous debris.
These efforts may, in all actuality, be counterproductive if they instill a false sense of security in the public and government leaders that the problem is being adequately addressed.
A Proactive Solution
Since 1978, the orbital debris population has been touted as our biggest space problem. It is important to do as much as we can with policies and procedures to keep the problem from getting worse faster. However, even if we humans were to completely resist our seemingly natural impulse to pollute everywhere we go, collisions with existing debris would continue to increase the number of dangerous objects in orbit.
Active debris removal (ADR) is the only solution. The sooner it begins, the safer we will all be. Like the oceans and cyberspace, orbital space suffers from the tragedy of the commons. Everyone wants to use it, but no one owns it. No one is responsible for ensuring it is cared for and maintained. As a result, user behavior is difficult to control, and the environment often suffers. Government action, presumably supporting the best interests of all users, is the default answer.
The proposed Space Debris Act of 2021 is a great start. It paves the way for persistent funding and creates an industry responsible for safeguarding humanity’s orbital infrastructure. It would introduce tax credits to incentivize non-government funding contributions and reduce the price of debris removal, so that satellite operators and the emerging space tourism industry can afford to clean up space where they plan to operate.