This op-ed originally appeared in the Aug. 27, 2018 issue of SpaceNews magazine.
The implementation and enforcement of space traffic management (STM) policies and regulations will be extremely complex and expensive for governments of spacefaring nations and all users of the near-Earth space domain. Compared to air traffic management, the challenges of managing low-orbital traffic will be orders of magnitude more sophisticated.
The underlying reasons include:
- High orbital speeds of near-Earth satellites, 25 times greater than jet aircraft
- Lack of the ability of satellite to responsively execute avoidance maneuvers
- Difficulty of assessing real-time and precise collision probabilities
- Presence of millions of uncontrolled and dangerous resident space objects (RSOs) that share the most-congested region of space as operating satellites
- Complexity of reaching an agreement with all spacefaring nations regarding space traffic issues
- Development of regulations that are fair and balanced without excessively restricting space traffic and related operations
- Creation of centralized space traffic controller and enforcement systems
- Achieving satellite operator compliance related to additional onboard traffic management hardware, operational restrictions and licensing processes
All objects in low-Earth orbits (LEOs) are traveling at speeds of over 25,000 kilometers per hour, about 25 times faster than today’s jetliners. Satellites share the same space as large and small debris, and everything is moving independently in arbitrary directions. Collisions can occur at relative speeds of up to 50,000 kilometers per hour. Today, there are roughly 1,200 operational satellites in LEO, most of which cannot change course on short notice. Many cannot maneuver at all. Add to this at least several million passive objects that are completely non-responsive regarding traffic management operations. As a result, we have control over less than 1 percent of a very dangerous population of extremely fast-moving objects all of which are sharing the same space. Clearly, a first step in achieving a complete and successful space traffic management system will be the remediation of the debris problem. Although the complete elimination of debris will not be possible, a sufficient amount of removal and control must be achieved in order to realize safe on-orbit operations for constellation operators. In other words, a permanent space debris elimination and control system must precede effective STM operations.
During the transition period, from today’s situation until an initial STM capability, there must be an international effort to bring the debris situation under control. At the same time, new LEO space systems developers must prepare for a new set of requirements regarding hardware and procedures that will satisfy anticipated STM regulations. For example, every new spacecraft bound for LEO will have to be licensed by the STM authority and incorporate transponders that continuously report the vehicle’s state vector to STM controllers. In order to respond to maneuver commands, each spacecraft will have to be capable of executing rapid avoidance maneuvers when commanded to do so. Such implementations will be expensive and add mass to each spacecraft. In fact, space operations will also become more complex.
In a fashion similar to air traffic control regulations, there will likely be “zones of exception” for satellite operators. For example, very small spacecraft, such as cubesats and microsats, may be allowed to operate under STM rules if they use “unrestricted space regions.” Such zones would be those that allow non-interference with large satellites and constellations. One of these zones might be the LEO space below altitudes of 500 kilometers. This region is seldom used for major space operations and the orbital decay rate is high. Thus, this zone would be self-cleansing since spacecraft using it would have limited lifetimes. Other “free-fly” zones might include the space above 1,300 kilometers and up to about 32,000 kilometers altitude, since there is little traffic and much more space in which to operate.
It is important to note that most satellites operating in the geosynchronous Earth orbit (GEO) belt, at about 36,000 kilometers altitude, are already under a space traffic management system. For all practical purposes, GEO spacecraft operate in, or near, the equatorial plane and move in the same direction at the same speed. Since they are synchronous with the Earth’s rotation, STM operations are achieved by simply assigning orbital slots, corresponding to longitudes, over which these satellites remain stationary relative to Earth.
It is the extremely congested LEO zone, between about 550 kilometers and 1,200 kilometers altitude that badly needs to be controlled. With more than 10,000 new satellites being prepared for launch into LEOs in the next few years, traffic may well soon be gridlocked. Thus, STM is essential in order to guarantee future access and use of the LEO zone.
Marshall Kaplan is a co-founder and chief technology officer of Launchspace Technologies Corporation. He has been studying space debris issues for more than four decades.