A copy of the full analysis can be downloaded by clicking on the link at the bottom of this blog entry.
The Problem of Space Traffic Management
Description of the Problem
As we saw in the previous section, Distribution and Size of Space Activity, satellite activity encompasses a large portion of space activity. The primary function of satellites (displayed in Figure 6) is the provision of communications and information services. The ongoing provision of such services by satellites requires the use of two forms of common pool resources in outer space: (i) slots in LEO or GEO in which to orbit and (ii) room in the radiofrequency spectrum in which to transmit and receive signals.
In “An Integrated Approach to Orbital Debris Research and Management”,Marshall H. Kaplan provides details on the general coordination problems associated with managing space activities in LEO.
The flight paths of low-orbiting satellites ... are not coordinated and the selection of orbits is not centrally controlled by any international agency. .... the management of space traffic presents a daunting challenge. At the moment, we lack much of the required technology, there is little international cooperation or collaboration regarding space traffic planning and the political environment is not amenable to creating an all-inclusive space traffic control architecture. Consider the physical separation of air traffic into commercial and military categories with completely different flight rules. While satellites may be restricted to low-latitude flight paths, they must overfly all longitudes as they circle the earth. In fact, some of the most popular orbits are shared by civil, commercial and military satellites.
As previously mentioned, most of the satellite activity that occurs in outer space is concentrated within narrow portions of low earth orbit (LEO) and geostationary orbit (GEO). Brian Weeden discusses the nature of this concentration in activity, together with the resultant congestion problems.
The orbital mechanics of these specific regions of space [LEO and GEO] provide unique benefits, and the common engineering solutions used by almost all space actors result in a clustering of satellites at certain altitudes in LEO and at the same altitude in GEO. Thus, as an increasing number of countries place satellites into LEO and GEO, those regions have begun to exhibit the efficiency problems stemming from appropriators responding to marginal private costs instead of marginal social costs as commonly found in CPRs.
The congestion in GEO is particularly acute due to its small size, high demand, and the need for all satellites in the region to use the same or similar portions of the radiofrequency spectrum.
Solutions to the space traffic management problem may address any of several issues:
- Collision avoidance of air traffic in orbit
- Collision avoidance of air traffic travelling to and from space
- Radiofrequency spectrum allocation to avoid transmission interference problems
Collision Avoidance of Space Traffic
Marshall Kaplan indicates that “future satellites that operate in this region will need quick-response maneuvering capabilities that most current space systems do not carry” in order to better avoid collisions with other spacecraft. He also notes that “some form of space-born technology that complies with yet-to-be-established international protocols should ensure clear traffic lanes among the several national systems that share the space.” Finally, he makes a distinction between (i) managing traffic to and from space and (ii) managing traffic in orbit and suggests that in-orbit traffic should probably come first. After an in-orbit traffic management system has been successfully established, then traffic to and from orbit can be integrated into that system.
Unsurprisingly, the International Academy of Astronauts, in their “Cosmic Study on Space Traffic Management,”
The question arises, whether to introduce certain internationally recognized descent corridors and possibly even impact areas which are not frequently used by other traffic, and which could be dedicated to space traffic.
The Academy also proposes the use of traffic management rules, similar to those used for roadway and air traffic management. Specifically, they propose an “international inter-governmental agreement” that
• Provides traffic management rules based on the use of the database for the purpose of collision avoidance, including:
° Safety provisions for launches
° Safety provisions for human spaceflight (including space tourism)
° Zoning (selection of orbits)
° Right of way rules for in-orbit phase(s)
° Prioritization with regard to maneuver
° Specific provisions for GEO (harmonized with ITU rules)
° Specific rules for LEO satellite constellations
° Debris mitigation mechanisms
° Safety provisions for re-entries
° Environmental provisions (pollution of the atmosphere/troposphere, etc.).
• Clarifies "space objects", including legal distinction between valuable objects and valueless space debris.
• Clarifies "fault" or liability in case of damage caused in outer space with regard to the implications of traffic rules.
• Sets delimitation for the launch phase and clarifies the concept of "launching State".
• Provides a framework and main features for national licensing regimes (including insurance provisions), which implement the provisions of the agreement.
• Sets forth an enforcement mechanism (e.g. renouncement of access to information) and dispute settlement.
• Clarifies institutionalized interlinks with ICAO, ITU and other relevant organizations.
The Academy also proposes that systems currently in place used to manage aircraft traffic in international airspace and/or to manage ocean traffic in international waters be used as the foundation to establish a management system for spacecraft traffic in outer space.
Allocation of Radiofrequency Spectrum
Brian Weeden notes that mechanisms have been used to allocate spectrum use in GEO to avoid spectrum interference due to congestion of frequencies, but no similar mechanisms are currently used to manage LEO, due to their high costs relative to the low potential benefits.
This congestion [in GEO] made it economically feasible to create exclusion mechanisms in the form of international and national legal mechanisms to regulate and allocate the spectrum used by GEO satellites… [T]hese exclusion mechanisms have led to a fairly efficient use of GEO and correspondingly less of a space debris problem relative to LEO.
Although there have been general discussions of developing similar regulatory exclusion mechanisms for the most congested parts of LEO, these discussions have yet to gain traction. This is largely due to the high cost of putting such mechanisms in place and the lack of measureable economic benefits from LEO that would justify such expenditures…
Similarly to the proposal for the extension of current systems to manage aircraft and watercraft in international waters to the management of spacecraft in outer space, the International Academy of Astronauts proposes that the current system for allocating and managing spectrum use in GEO be extended to the management of spectrum use in LEO.
As the level of activities and number of players involved in the use of outer space increases, the coordination and congestion problems will only increase.
In general, the same types of management systems already in use for airplanes and ships (traveling in international territories) should be able to be extended to manage spacecraft in outer space. There are, however, a few complications that make spacecraft more difficult to manage than airplanes or ships. First, many spacecraft, such as satellites, aren’t able to change velocity or direction (easily), which makes it much more difficult to avoid collisions between objects in orbit. More specifically, the International Academy of Astronauts indicates that
In outer space, the ability to change velocity is the exception, rather than the rule. Even more important, objects on Earth can be at rest for indefinite time spans, but an object can last in outer space only if it is in orbital motion which is usually very fast compared to our everyday experience.
There are laws of physics which govern the motion of any object in space and must be taken into account in all efforts to regulate space traffic.
Another complication involves the current liability regime in outer space, which says that no other party has the authority to interfere with the operation of spacecraft owned by other parties (more on this in the next section). This law might need to be revisited and reconsidered in the context of a global space traffic management system.
On a different note, the addition of more private/commercial (i.e., non-government) traffic in outer space might create a need for prioritization of rights of way. For example, should spacecraft being used for space tourism have all the same rights as spacecraft being used for communications purposes? What type of rights should military craft have over non-military (government or civilian) craft? Such types of conflicts will need to be addressed.
Additionally, I think the idea of using a repeated interaction game is extremely appropriate to manage space traffic. The fixed costs associated with launching and maintaining craft in space make it almost assured that any party who participates in space will do so on a continued and/or repeated basis. The threat of losing access to outer space due to rogue behavior should give managing authorities strong leverage to keep parties in line. Leverage will further increase to the extent that parties who access outer space also access air space. In these cases, rogue behavior could potential lead to sanctions on the rogue party’s access to both outer space and air space.
Finally, I think that perhaps the most difficult negotiations for access to outer space will involve the exploitation of space resources. All three sets of tensions will come into play when it comes to exploiting resources in space: (i) private versus social, (ii) present versus future, and (iii) exploration versus exploitation.
The Problem of Orbital Debris
Description of the Problem
Nodir Adilov, Peter J. Alexander, Brendan M. Cunningham in “Earth Orbit Debris: An Economic Model”define and describe the problem of orbital debris in the following passage, and they also provide the information in Figure 10:
Orbital debris is space pollution. NASA … defines debris as non-functional human-made space objects. Initially, debris is created from the upper stages of expended launch vehicles when a satellite is launched... Additional debris is created by the satellites themselves, both as they reach the end of their productive lives and break up, and as the result of impact with debris or with other satellites, among other things…
Orbital debris has degrees of persistence: a few days if the debris is less than 125 miles above the earth’s surface; a few years if the debris is between 125 and 370 miles; decades if the debris is between 370 and 500 miles; centuries if the debris is greater than 500 miles, and essentially forever if the debris is at greater altitudes, especially as one approaches GEO altitudes. Thus, at very low altitudes (less than 125 miles) space is quickly self-cleansing, however, peak debris density in LEO occurs at 550 miles, which suggests centuries would pass before the region is self-cleaned (assuming no additional debris is added during that time)…
Unlike standard terrestrial pollution, debris propagates additional pollution. Thus, for example, a collision between a satellite and a piece of debris, or even between two pieces of debris, creates additional debris which further increases the likelihood of other debris creating collisions. Kessler (1991) proposed the possibility of a sufficiently dense debris cloud that would lead to a cascade of collisions, ultimately rendering space unusable. The probability of such an event is unknown, although the probabilities increase in the density of the debris field. A recent National Academy of Sciences report states that:
...the current orbital debris environment has already reached a “tipping point.” That is, the amount of debris, in terms of the population of large debris objects, as well as overall mass of debris currently in orbit, has reached a threshold where it will continually collide with itself, further increasing the population of orbital debris. This increase will lead to corresponding increases in spacecraft failures, which will only create more feedback into the system, increasing the debris population growth rate. The increase thus far has been most rapid in low earth orbit (LEO), with geosynchronous earth or- bits (GEOs) potentially suffering the same fate, but over a much longer time period. The exact timing and pace of this exponential growth are uncertain, but the serious implications of such a scenario require careful attention...
From NASA’s “Orbital Debris Quarterly News: January 2014”
The most obvious consequence of orbital debris is the greater risk of collisions in space. Collisions between active spacecraft and even the smallest pieces of debris can cause damage to spacecraft. Attempts to avoid or mitigate damage from collisions between debris and spacecraft have increased the costs of using outer space. In particular, Brian Weeden notes
This increased risk raises the private costs of operating satellites now through greater expenditures of fuel and interruptions of mission from avoidance maneuvers and, in the future, through increased production costs in designing and maintaining satellites…
“The mere presence of debris itself also causes problems,” according to Lawrence D. Roberts, “Addressing the Problem of Orbital Space Debris: Combining International Regulatory and Liability Regimes.”
Its presence is especially harmful to astronomical instruments both on Earth and in space. The debris often generates undesired reflections that disturb photographic analysis and produce misleading spectral images of targets under investigation.
Solutions to the orbital debris problem may address any of several issues:
- How to remove existing debris from orbit;
- How to minimize the creation of new debris;
- How to improve collision avoidance measures; and/or
- How to address damages caused by collisions with new and existing debris
The Removal of Existing Debris from Orbit
Perhaps the most obvious way of solving the existing debris problem would be to remove it from space. Unfortunately, Active Debris Removal (ADR) is difficult, costly, and legally challenging. First, while even the smallest pieces of debris can cause damage, currently only the largest pieces of debris are capable of being identified and tracked. Second, the actual capture and removal of space objects is a nontrivial undertaking from a technological perspective. As The Aerospace Corporation describes it,
Removing large objects from orbit, usually by causing them to re-enter the Earth’s atmosphere, is difficult. Almost no spacecraft are designed to be physically grappled once they are in orbit, and they may have antennas, solar arrays, or other fragile projections.
They may be tumbling or spinning, making them difficult to grapple and control. Many of these old satellites and rocket upper stages weight thousands of pounds, making them difficult to move. Some of the objects have been in orbit for decades and so may not be as sturdy as when launched or may contain fuel that could be triggered to explode.
Third, all proposed methods for capturing and removing debris from space are extremely expensive. And fourth, there are legal issues involved. In particular, according to Steven A. Hildreth and Allison Arnold in “Threats to U.S. National Security Interests in Space: Orbital Debris Mitigation and Removal,”
Article VIII of the 1967 Outer Space Treaty declares that space objects continue to belong to the country or countries that launched them. The launching state retains “jurisdiction and control” for a space object while it is in outer space, on a celestial body, and upon its return to Earth. The launching state never loses authority over the object, and no other nation has the legal authority to remove or otherwise interfere with it without authorization from the state of registry.
As briefly mentioned above, the International Academy of Astronauts suggests a reconsideration of laws regarding space debris as they apply to ownership status, which would go a long way towards easing legal liability restrictions on dealing with space junk. More explicitly, the Academy’s suggestion is a call for
Distinction between Valuable Spacecraft and Worthless Space Debris: UNCOPUOS should start discussing whether or not space debris are space objects in the sense used in space law treaties. If it is decided that space debris are space objects, an additional protocol should be elaborated stating what provisions of the treaties apply to valuable spacecraft and which provisions apply to space debris. If it is decided that space debris are not space objects, the protocol should determine under what conditions space debris may be removed or re-orbited in order to prevent collisions or close encounters with valuable spacecraft.
Minimizing the Creation of New Debris
If the debris that currently exists in outer space cannot be affordably removed, at least we can try to minimize the amount of future debris created. The fact that existing debris will continue to propagate through further collisions with itself means that the amount of newly created debris cannot be entirely eliminated. However, in an attempt to minimize the creation of new man-made debris in outer space, the UN Office for Outer Space Affairs issued Space Debris Mitigation Guidelines in 2010. These Guidelines provide the following proposed measures:
Guideline 1: Limit debris released during normal operations
Guideline 2 Minimize the potential for break-ups during operational phases
Guideline 3: Limit the probability of accidental collision in orbit
Guideline 4: Avoid intentional destruction and other harmful activities
Guideline 5: Minimize potential for post-mission break-ups resulting from stored energy
Guideline 6: Limit the long-term presence of spacecraft and launch vehicle orbital stages in the low-Earth orbit (LEO) region after the end of their mission
Guideline 7: Limit the long-term interference of spacecraft and launch vehicle orbital stages with the geosynchronous Earth orbit (GEO) region after the end of their mission
An additional method of minimizing the creation of new debris in space, namely “Earth Orbit Debris: An Economic Model.”the competitive market to choose the optimal levels of launches and debris creation rate.” However, their claim that a Pigouvian tax will solve the problem fails to consider the point made earlier by Brian Weeden. He noted that the majority of space activity is undertaken on behalf of government, and public actors don’t necessarily respond to market incentives (such as taxes used to decrease activity levels). It follows that until a larger portion of space activity is undertaken on behalf of private/commercial actors, a tax scheme shouldn’t necessarily be expected to lead to an efficient outcome.was offered by Nodir Adilov, Peter J. Alexander, and Brendan M. Cunningham in
Improving Collision Avoidance Capabilities
One of the keys to improving our ability to avoid collisions with orbital debris is improved information collection and tracking information on orbital debris and on global space activities. In other words, what we need is better space situational awareness. In “Space Situational Awareness Fact Sheet,”Brian Weeden defines Space Situational Awarenes (SSA) as
the ability to accurately characterize the space environment and activities in space. Civil SSA combines positional information on the trajectory of objects in orbit (mainly using optical telescopes and radars) with information on space weather. Military and national security SSA applications also include characterizing objects in space, their capabilities and limitations, and potential threats.
SSA is an inherently international and cooperative venture. It requires a network of globally distributed sensors as well as data sharing between satellite owner‐operators and sensor networks. SSA also forms the foundation of space sustainability as it enables safe and efficient space operations and promotes stability by reducing mishaps, misperceptions, and mistrust.
Weeden indicates that the US currently has the most complete SSA system globally, known as the Space Surveillance Network (SSN), though it does contain gaps. “Russia operates the second‐largest network of sensors and also maintains a relatively complete catalog of space objects. The Russian system is known as the Space Surveillance System (SSS).” Internationally, there are other collections of information sponsored by private and government entities. And in fact, Weeden reports that there are active efforts in the works to improve global SSA and make such information more widely available.
In March 2014, Analytical Graphics Inc. (AGI) announced it was creating a Commercial Space Operations Center (ComSpOC). AGI is in the process of negotiating contracts with optical, radar, and RF sensor operators around the world as potential data providers. The ComSpOC plans to integrate these observations into a central database and provide subscribers services such as warnings of potential conjunctions and assistance in resolving anomalies.
…The draft International Code of Conduct (ICoC) for Outer Space Activities also includes language for the voluntary sharing of information on activities and events such as launches, potential collisions, break‐ups, and risky re‐entries. The United Nations Commitiee on Peaceful Uses of Outer Space (UNCOPUOS) is also discussing improved SSA data sharing as part of its agenda item on Long‐Term Sustainability of Outer Space Activities.
Liability for Damages Caused by New and Existing Debris
There is currently a system in place for assessing liability for collisions with orbital debris. As Lawrence D. Roberts indicates in “Addressing the Problem of Orbital Space Debris: Combining International Regulatory and Liability Regimes”
The Liability Convention is the primary instrument for allocating compensation for damage caused by space objects. Article III describes the standard of liability for activities in outer space:
In the event of damage being caused elsewhere than on the surface of the [E]arth to a space object of one launching State or to persons or property on board such a space object by a space object of another launching State, the latter shall be liable only if the damage is due to its fault or the fault of persons for whom it is responsible.
However, the biggest problem with the current system is that most objects in space have not been identified, and if an untracked object collides with a spacecraft, liability cannot be determined. Improving SSA data will help expand our ability to determine liability for collisions in space with orbital debris. In the meantime, Roberts suggests that a collective fund – a liability pool – be established, endowed by past and present space actors, from which to compensate victims of collisions.
There is, however, a solution to the problem posed by this technological limitation [the present inability to track and identify large quantities of debris]: establishing a mandatory liability pool for all users of the space environment. To promote the safe use of the space environment, the amount contributed to the liability pool by those seeking to place an object in orbit would be linked to an estimate of the object's potential harm to the commons. Payments from the pool would occur in situations where authorities determine that collision with orbital debris caused damage to, or the destruction of, an orbiting object. The utility costs inherent in the commons would be transferred to the individual user, thereby maximizing social efficiency.
The liability pool would also cover the risk posed by debris currently orbiting the Earth. Currently, this risk is relatively small. Given the anticipated trend in the amount of debris, however, absent retroactive payments to the liability pool, a significant percentage of any payment into the pool would be devoted to covering risk already posed by debris present in orbit at the time of launch. Thus, it may be necessary to allocate payments into the pool on the basis of prior enjoyment of the space environment as well as present use.
Current and past users of outer space (US, Russia, China, etc.) have created the stock of debris that currently exists in outer space. This debris will increase the costs of current and future use of outer space, through increases in the costs associated with making current and future spacecraft more robust to collisions with orbital debris and more able to detect and maneuver around orbital debris. Should the past users of outer space who contributed to the creation of the current stock of man-made orbital debris be forced to compensate current and future users for their higher costs? At the very least, a pool of resources (as per Roberts’ suggestion) should be made available to compensate current and future users for damages associated with any collisions.
Based on the past history of the ingenuity of mankind, I believe that new and improved technologies will be developed to decrease the costs associated with orbital debris. In particular, I believe new technologies will
- Improve our ability to track smaller pieces of debris;
- Improve the ability of new spacecraft to better withstand collisions;
- Increase our ability to undertake active debris removal efforts; and
- Increase the ability of spacecraft to better maneuver and avoid collisions.
In the meantime, perhaps the best we can do is to continue efforts to
- Minimize the creation of new debris; and
- Enhance transparency SSA through joint (global) monitoring and information collecting efforts.