Over the past few years, and especially in the last few months, the issue of space traffic management (STM) has been discussed from the U.S. Senate floor to White House press briefings. The common theme across the government is the lack of action on space traffic management. One of the underlying issues not being addressed is: You cannot manage what you can’t measure. A fundamental tenet of any STM system is detecting, identifying, and accurately tracking all objects within the management domain. Any near-Earth management domain must include all large debris objects. We have yet to develop the needed technologies and systems to anticipate conjunctions among active satellites and large debris objects effectively. In other words, STM today does not exist but is, in fact, the “wild west.”
Near-Earth space is big, but is it big enough to sustain safe flight with the rapidly growing population of active satellite constellations and orbiting debris? Gen. James Dickinson, head of the U.S. Space Command, recently stated that his organization is tracking nearly 35,000 objects, a very small subset of the actual number of low-orbiting things. This number represents a 22% increase from just a few years ago. If you consider the total number of space objects, the challenges may well seem insurmountable, and they currently are.
As of September 2021, the European Space Agency’s Space Debris Office offered a few relevant historical facts:
- The number of successful rocket launches since the space age began in 1957 is roughly 6,100.
- The number of satellites placed into Earth orbit is roughly 12,000, with about 7,500 still in orbit.
- The number of satellites still functioning is about 4,700.
- The number of large debris objects regularly tracked by the U.S. Space Surveillance Network and maintained in their catalog is more than 29,000.
- The number of break-ups, explosions, collisions or anomalous events resulting in fragmentation is over 600.
- The total mass of all space objects in Earth orbits is over 9,600 tons.
- The number of orbiting debris objects greater than 10 centimeters in size, estimated via statistical models, is 36,500. There are 1 million objects between 1 and 10 centimeters in size and 330 million objects between 1 millimeter and 1 centimeter.
Thanks to insufficient sensor coverage, one of the biggest challenges we face is comprehensive Space Domain Awareness. This challenge is quite different and more complex than air domain and maritime domain awareness. Yes, there are systems (either developed or in development), but none are integrated at a sufficient level to provide comprehensive space domain awareness. Most STM discussions focus on the roughly 35,000 objects being tracked, but this is only 0.01% of the total population. The hazards to sustained spaceflight safety lie in millions of untrackable objects.
Any multipronged approach to STM should include a debris remediation effort to eliminate the 5-centimeter and smaller objects from altitudes between 600 kilometers and 1,200 kilometers, plus provide 4 pi steradian sensor coverage to detect and track larger objects. The largest pollutant is the smaller but sufficiently large objects that can damage operating spacecraft with single collisions. These orbiting derelicts are too small to be tracked, and the resulting damage to satellites cannot be verified or recorded. Nevertheless, there is sufficient evidence that such debris is the most dangerous because of its density, relative encounter speeds and the fact that it cannot be tracked. It is the presence of these objects that will cause most of the serious damage to satellites. Continually and selectively removing portions of the 1-millimeter to 10-centimeter-size objects is necessary for flight safety and permanent access to space. Thus, permanent stability and safety in orbit will require removal operations that effectively and permanently limit the number of small objects.
The discussion and proposed approach need to be focused on three primary goals to deal with all aspects of Space Domain Awareness: 1. Track what needs to be tracked from a national security perspective; 2. Track what can be tracked from a spaceflight perspective; and 3. Use an active debris removal system to get rid of the rest.
Marshall Kaplan is chief technology officer of Launchspace Technologies Corp. Gurpartap Sandhoo is the Robert A. Heinlein Distinguished Visiting Professor of Astronautics at the U.S. Naval Academy
