TruSat as a Space Sustainability Tool
This section introduces the challenges to the long-term sustainability of spaceflight, and locates TruSat within an emerging space sustainability ecosystem.
Transparency and Trust Challenges to Space Sustainability
Space sustainability is about preserving the use of outer space, and all of its socioeconomic benefits, for present and future generations. The primary threat to the long-term usability of space is Earth-orbital debris: non-functional spacecraft, pieces of spacecraft discarded in the course of space missions, and fragments from collisions between spacecraft, and from spacecraft destroyed by weapons tests. While outer space is infinitely large, the orbital positions around Earth suitable for the myriad space applications on which we depend are finite and increasingly congested.
Global public awareness and concern about space sustainability is rising with the deployment of the first of thousands of satellites comprising so-called “mega-constellations” to provide broadband internet service from low Earth orbit (“LEO”). To put these constellations in perspective, the satellites planned for deployment by just three companies would add approximately 16,000-46,000 satellites to the LEO environment in the 2025-2030 time horizon; roughly a ten-to-twenty-five-foldincrease above the present population of operational satellites. 1
As LEO grows increasingly congested, so grows the risk not only of collisions—betweenoperational satellites or debris—but also catastrophic, cascading chains of collisions rendering vital swaths of Earth orbits unusable for generations.
In recent years, government regulators, industry, and civil society have identified (and required, insome cases) sustainability measures to lessen the chances of satellite operations generating orbital debris. 2 Many are implemented well before launch, such as spacecraft design and testing regimes intended to prevent “bricks:” defective satellites that are essentially debris upon launch. Other pre-launch sustainability measures go to mission design, including the altitude of operations; satellites at higher altitudes remain in orbit for decades, or even centuries, unless boosted to a disposal orbit. Whereas such pre-launch sustainability measures are vital to the long-term sustainability of space flight, measures whose implementation can be verified on the ground are not the primary focus of TruSat. Instead, TruSat is designed for space sustainability measures that involve orbital operations, including the disposal of a satellite at the end of its operational life, and decisions whether or not to maneuver to avoid a collision risk. Verifying implementation of such measures requires knowledge of satellites’ orbital positions atvarious points in time. Such information about orbital positions, used to predict potential collisions between satellites or debris, is commonly referred to as space situational awareness (“SSA”). 3
Collision avoidance maneuvers present a particularly acute imperative for standards and verification. Unlike air traffic, which is subject to formal, mandatory collision avoidance regimes, no comparable system exists for space traffic management (“STM”). In orbit, collision avoidance rests on voluntary decisions by satellite operators to maneuver to avoid a potential collision, and relatively loose coordination between operators. A small number of national governments collect SSA data for national security purposes, and screen their orbital object catalogs for “conjunctions:” predictions for objects to pass close enough to be a collision risk. For example, the United States Department of Defense utilizes a variety of sensors to track objects in orbit, and provides conjunction warnings to satellite operators with which it has entered into space situational awareness sharing agreements. Well-resourced satellite operators may supplement government-provided SSA information with commercial SSA services, as well as their own proprietary location data from on-board GPS and ground station telemetry.
A recent, high-profile conjunction between an Earth observation satellite operated by the European Space Agency (“ESA”) and a satellite in the Starlink constellation operated by SpaceX offers some insight into the informal, ad hoc, and voluntary nature of space traffic management. In late August, 2019, the U.S. Department of Defense assessed a potential conjunction between ESA’s Aeolus satellite and SpaceX’s Starlink44 4 As the probability of a collision came within 1 in 1,000—ten times higher than ESA’s internal threshold for collision avoidance maneuvers—ESA operators contacted their SpaceX counterparts, who declined to execute a maneuver. 5 Half an orbit before the potential collision, ESA triggered a series of thruster burns to provide a safe buffer between Aeolus and Starlink44. 6 In a subsequent statement, SpaceX indicated that its decision not to maneuver was based on earlier SSA data placing the collision risk at approximately 1 in 50,000, and that “a bug in our on-call paging system prevented the Starlink operator from seeing the follow on correspondence on this probability increase.”7 Commenting on the incident, ESA’s Head of Space Safety reflected: “This example shows that in the absence of traffic rules and communication protocols, collision avoidance depends entirely on the pragmatism of the operators involved.” 8
The Aeolus-Starlink44 conjunction illustrates two realities about the present state of space traffic management. First, there is no regulatory authority directing satellite operators to maneuver to avoid collisions; it is up to each operator of a maneuverable satellite to decide whether or not to maneuver. Maneuvers use fuel, thereby diminishing the useful life of the satellite and the revenue it may generate. As such, the operator’s decision whether or not to maneuver is essentially a business decision, balancing of the costs of a maneuver with the probability and costs of a collision. Second, the collision risk is uncertain even for operators with access to the highest resolution SSA data and analysis. Whereas the SSA information made publicly available by the U.S. Department of Defense initially placed the Aeolus-Starlink44 collision probability at approximately 1 in a million, ESA had access to more refined information provided by the Department of Defense pursuant to an SSA sharing agreement. 9
Crucially, as satellite operators evaluate probabilistic conjunction warnings and weigh the costs of a maneuver against the probability and costs of a collision, their incentives are not aligned with the common interest in the long-term sustainability of spaceflight. This is because satellite operators would not be made to internalize the full costs of a collision in orbit. This externality is a function of present legal and practical realities of the space domain. Satellite operators generally obtain insurance coverage for their own economic losses, such as the loss of a satellite damaged in a collision and the corresponding loss of revenue. However, the present implementation of the international legal framework for outer space makes it highly unlikely that private satellite operators would be made to bear the broader costs of a collision: to operators of other satellites damaged in a collision, or from the loss of orbits littered with debris. For one, liability for damage caused by a space object to thirdparties under international law runs to the national government(s) responsible launching the object into orbit, and few such governments have shown an appetite for indemnification arrangements to pass this liability down to the private operator responsible for a collision.
As a practical matter, third party liability for collisions in orbit is predicated on “fault.” 10 While “fault” is not defined in the relevant treaties, establishing that a satellite operator was at fault for a collision would almost certainly require an account of the relevant satellites’ orbits trusted by all parties to the dispute. By way of analogy, establishing fault in an automobile collision relies upon eyewitness accounts of the movements of each vehicle prior to the collision. There are few “eyewitnesses” as to the orbital behavior of satellites, and it is doubtful that all parties to a dispute would trust them. Substantial doubts have been raised about the trustworthiness of a national government as a sole source of SSA data, given that national interests may not always be aligned with transparency in orbital behavior. 11 In addition, for nationalsecurity reasons, agencies such as the U.S. Department of Defense do not share the sensor data or the algorithms underlying its SSA data, limiting the ability for independent validation of results. Similarly, cases can be foreseen in which commercial providers of SSA data and analytics may not be trusted by all parties in a dispute involving one or more of their customers.
To summarize the problem space to which TruSat is addressed: a tenfold increase in the LEO satellite population will increase the frequency of conjunctions (i.e., predictions that satellites will pass close enough to present a collision risk), and thus the frequencyof operators’ business decisions whether or not to maneuver to avert collisions. The true costs of a collision are not accounted for in operators’ decision calculus because it is exceedingly unlikely that a private satellite operator would bear the costsof to third parties of a collision under the international legal framework for space, as presently implemented. Among the practical reasons for this externality are the absence of an accessible source of SSA data trusted by all parties to determine faultin a collision. Given this remote possibility of liability to third parties, insulating private satellite operators from the true costs of collisions, and the costs to operators of maneuvers, operators may find an incentive to “roll the dice,” gambling with the long-term sustainability of outer space, rather than to execute a precautionary maneuver.
The Emerging Space Sustainability Ecosystem
As explained in the foregoing section, the space liability framework does not supply sufficient incentivesfor an operator faced with a conjunction warning to resolve uncertainty in favor of a precautionary maneuver. At present, the court of public opinion may be closer to minds of satellite operators weighing a maneuver than a court of law or arbitral tribunal. With public awareness of space sustainability challenges rising with the advent of “mega-constellations,” constellation operators in particular are touting their sustainability practices, for public relations purposes, and possibly also to preempt theconcerns of their regulators. 12 This desire on the part of satellite operators—soon to be competing for internet customers—to positioning their brands as responsible, sustainable stewards of the space environment, may prove to be a more potent lever for bringing the incentives of satellite operators into alignment with the collective interest in the long-term sustainability of outer space.
Converting public awareness and concern for space sustainability, and the concomitant value to private spacecraft operators of branding their activities as sustainable, intosustainable orbital operations, requires two basic elements:
- Standards: Responsible, sustainable space operations must be defined in a measurable, verifiable way.
- Assessment: Operations must actually be graded for conformity with sustainability standards. The assessment function requires both:
- a. a mutually trusted source of data about the orbital behavior of satellites, and
- b. analysis capacity to measure orbital behavior against sustainability standards.
Governments are signaling a policy preference for standards for sustainable orbital operations, but are unlikely to lead in their formulation. In June of 2018 the United States President issued Space Policy Directive-3, National Space Traffic Management Policy, signaling “A STM framework consisting of best practices, technical guidelines, safety standards, behavioral norms, pre-launch risk assessments, and on-orbit collision avoidance services is essential to preserve the space operational environment.” 13 A year later, In June of 2019 the United Nations Committee on the Peaceful Uses of Outer Space adopted the Guidelines for the Long-term Sustainability of Outer Space Activities(“LTS Guidelines”), 14 the culmination of nearly a decade of intergovernmental negotiations and representing a global political consensus on the importance of space sustainability. In September of 2019, the European Union announced the formation of a “Safety, Security and Sustainability of Outer Space (3SOS) public diplomacy initiative to “reach a common understanding of all space actors in all parts of the world on responsible and sustainable behavior.” 15 The United Nations’ LTS Guidelines illustrate why governmental and intergovernmental initiatives are unlikely to produce specific, measurable, verifiable standards for orbital operations, but instead create fertile conditions for other players in the emerging space sustainability ecosystem to do so. Negotiated and adopted by consensus in a global intergovernmental forum, the LTS Guidelines are much too general to enable spacecraft operators or the consuming public to delineate sustainable from unsustainable operations.
Non-governmental actors are beginning to step in to fill this crucial gap. Prominent among them are the recently-formed Space Sustainability Rating (“SSR”), a collaboration of the World Economic Forum, the MIT Media Lab, the University of Texas at Austin, the European Space Agency, and Bryce Space and Technology. SSR seeks to establish standards for a space sustainability certification much like LEED certification in the construction sector, providing brand and other business incentives for meeting sustainability standards. 16 The Secure World Foundation, with a mission of “promoting cooperative solutions for space sustainability,” is another example of non-governmental leadership in convening spacecraft operators and civil society experts toward defining sustainable orbital operations. Most recently, the Space Safety Coalition was formed in September of 2019, with a diverse membership spanning the space industry and civil society, and published the first iteration of its Best Practices for the Sustainability of Space Operations. 17 Whereas the September 16, 2019 iteration of the Best Practices does not prescribe measurable standards for collision avoidance, it does signal that “future efforts may be warranted to... Address maneuver prioritization in the event that two spacecraft with maneuver capabilityconjunct....” It is foreseeable that voluntary standards for sustainable orbital operations will emerge from these multi-stakeholder initiatives in the near future. There is ample precedent for voluntary technical standards for space operations being subsequently adopted and mandated by national regulators. 18
The efficacy of voluntary space sustainability standards as an incentive for responsible orbital operations depends on accountability through independent assessment. Whereas many space sustainability practices can be verified on the ground, prior to launch, independent verification of emerging standards for sustainable orbital operations will involve interpretations of SSA information to measure satellite operations against standards. This independent analysis capacity is beginning to emerge; Professor Moriba Jah’s ASTRIA Lab at the University of Texas at Austin is a prominent example. With his expertise in astrodynamics and access to the supercomputer resources of the University of Texas, Professor Jah has demonstrated a capacity and willingness to analyze SSA data to call attention to unsustainable operations in orbit.
The missing ingredient in this emerging space sustainability ecosystem is a widely-trusted source of data suitable for assessing orbital operations against sustainability standards. As explained in Section II.A., U.S. Government SSA data suffers the same trust deficit as any SSA data sourced from a single national government, and the Government reserves the right to restrict its use. Private commercial providers of SSA data rely on satellite operators for their revenue and do not have incentives for calling out non-conforming orbital behavior. TruSat is designed to fill this gap through a new approach to SSA uncoupled from government or commercial interests.
TruSat as a New Approach to Transparency and Trust in SSA
To fill the trusted data gap, TruSat is designed to enable space sustainability advocates to task a global network of citizen satellite observers to track satellites of interest, utilizing ubiquitous consumer hardware, and to assemble observations from around the planet into a trusted record of orbital positions suitable for measuring orbital behavior against sustainability standards. Whereas the initial releases of TruSat are an experiment in producing reliable orbit predictions from amateur visual observations, the TruSat architecture is sensor-agnostic and could support inputs from a range of academic, commercial, or governmental institutions. The TruSat System comprises three elements:
- Software for prioritizing satellite observations, assisting amateur satellite observers, and processing observations into orbital predictions. As detailed in Section III, TruSat’s Proof of Satellite engine utilizes the physics of orbital mechanics to calculate accurate, actionable orbital positions from amateur visual observations of a satellite from multiple points on Earth. It achieves accuracy through diversity (of observers, geography) rather than relying on exquisite sensors.
- Observers who make and report satellite observations. TruSat is sensor-agnostic and can utilize visual observations made with hardware ranging from binoculars and a stopwatch to digital cameras, software-enabled consumer telescopes and internet-remote telescopes (e.g., iTelescope). As outlined in Section V, while the v0.1release of the TruSat software will require observers to utilize external software to convert visual observations into initial orbit determinations (IODs), subsequent releases will add support for direct inputs from a range of methods (e.g., automated IOD extraction from a digital image).
- An interface with the space sustainability community for aligning the System’s satellite observation priorities with sustainability priorities. During TruSat’s initial, experimental phase, the TruSat Partners—institutions committed to maintaining and advancing TruSat as a space sustainability tool—will be responsible for aligning the System’s observation priorities with broader space sustainability goals, in accordance with the procedures set forth in the TruSat Charter.
Community-sourcing orbital object location data through visual observations of satellites is not new. In fact, Operation Moonwatch, a global citizen-science initiative to track the first artificial satellites at the dawn of the space age, was the original SSA network. 19 More recently, the SeeSat community has been tracking satellites fordecades—with tools ranging from binoculars and a stopwatch to relatively advanced digital camera equipment—and posting the angles-only visual observations (“IOD” or other reporting formats) to an internet mailing list. 20 TruSat is designed to scale this method of satellite tracking from hobby to a source of truth in orbital behavior trusted by all space actors. What is most fundamentally new about TruSat is its open, decentralized, and automated architecture designed to remedy the trust challenges of existing public sources of SSA data. TruSat’s trust architecture is summarized by comparison to existing SSA sources in the subsection that follows, and detailed in Section III.
Leveraging Blockchain Technology in Service of Openness, Transparency, and Trust
The trust deficit of existing sources of SSA data, as applied to space sustainability applications, results from the combination of two attributes. First, as the data is controlled by a single government or business, from sensor to analysis, trustin the results is limited to trust in that institution. The application of SSA data to assessing compliance with sustainability standards presents a more difficult trust equation than the case of a satellite operator keeping planning a maneuver. The latter may have built up confidence and trust in given SSA data providers over the course of a long working relationship, and have access to multiple sources of SSA data to verify accuracy. The legitimacy of sustainability standards assessment, by contrast, rests on trust by a much broader, global set of stakeholders. Finding a single institution trusted by all stakeholders in all cases borders on impossible. Irrespective of an institution’s track record for accurate results, perceptions of institutional interests in a given case can undermine trustin the data produced by that institution. Compounding this structural trust challenge is the reality that the proprietary nature of SSA systems—with many utilized primarily for national security missions—does not permit independent verification of the results.
TruSat’s decentralized architecture removes any institution or individual from the trust equation. In place of an institutional arbiter between sensor data and orbit predictions, TruSat substitutes transparent, verifiable algorithms, which automate the process of determining and refining orbits. Unlike existing sources of SSA data, the entirety of the algorithms that translate individual observations of a satellite into an orbit prediction with a confidence assessment—the confidence factors applied, and their weighting—are transparent, allowing any orbit prediction to be independently assessed.
In the absence of an institution trusted by all stakeholders to the orbital position of satellites, TruSat dispenses with the need to trust any institution. Instead, trust in TruSat’s orbital position data derives from the transparencyof the observations and algorithms underpinning each orbit prediction, and that any attempt to tamper with the algorithms or output would be evident. This decentralized, tamper-evident architecture is enabled by building TruSat atop the Ethereum blockchain. TruSat will periodically compare its code base and database with tamper-evident blockchain records, ensuring that the algorithms in effect at any given time are those approved by the TruSat Community. Furthermore, the individual data submissionswill be secured and logged in “on-chain” transactions, with eachobserver’sability to provide weighted-contributions to the TruSat dataset be secured bypublic/private key cryptography through access to on-chain wallet credentials.
The inputs of ConsenSys Space and the TruSat Partners are limited to refining the software and communicating space sustainability observation priorities, in accordance with the TruSat Charter (see Section IV, TruSat Governance). The source code for each update to TruSat’s codebase will be available in the TruSat software repositories, ensuring the transparency of the algorithms in effect. While TruSat does not permit human input in processing satellite observations into orbit predictions, the System does rely on human input to make and report satellite observations. Section III.C. details attack vectors ranging from malicious attempts to influence orbital position data to erroneous observations, and how the TruSat software is designed to mitigate the influence of such inputs.
A Toolset for Measuring Orbital Behavior against Sustainability Standards
The easiest sustainability application for TruSat, as presently conceived, is probably verifying post-mission disposal requirements. Many regulatory authorities require that satellites in geosynchronous orbit be raised to a so-called “graveyard” orbit at the end of their useful life, to reduce the potential for collision.More recently, with the advent of “mega-constellations” comprising thousands of satellites in low Earth orbit (“LEO”), regulatory authorities have required operators to place satellites in a disposal orbit--from which the satellite will re-enter Earth’s atmosphere and burn up within one year--at the end of theiroperational life.Beyond regulatory requirements, post-mission disposal standards are likely to form part of voluntary sustainability standards.
Consider a hypothetical case in which an operator of a LEO constellation announces it has moved a satellite into a disposal orbit, in conformity with its sustainability commitments and/or regulatory requirements, and submits its own information to TruSat for verification. From an orbit prediction derived from the operator’s data, TruSat contributors around the world know where and when to look to observe the satellite, and submit their observations through the TruSat interface. From these observations around Earth, the Proof of Satellite engine generates and orbital prediction and confidence assessment, confirming or disputing the satellite operator’s claims. In this hypothetical, the satellite operator is cooperating with TruSat to obtain the benefit of independent verification of its sustainability practice. But the system does not depend on such cooperation; it could be used to verify post-mission disposal claims without satellite ephemeris data supplied by the operator.
This end of life disposal hypothetical admittedly does not make full use of TruSat’s potential as a sustainability tool. The movement of a satellite from its operational orbit to a disposal orbit is such a large change as not to require precision measurement to verify.
What use cases would make fuller use of a public eyewitness capability in orbit? Consider a conjunction scenario along the lines of the recent Aelous-Starlink44 incident. A conjunction analysis predicts maneuverable LEO satellites operated by Operators A and B have a 1 in 10,000 chance of collision in 72 hours. Assume the presence of a voluntary standard or guideline calling for any maneuverable satellite to execute a maneuver to avoid a collision risk greater than 1 in 10,000. Now imagine TruSat users on multiple continents observing both satellites, creating indelible records of their orbit tracks. Does the world watching, literally, change the decision calculus of Operators A or B? Does it lead either operator to resolve uncertainty in favor of a precautionary maneuver? Does it add to the public relations benefits of a maneuver, and add to the public relations costs of declining to maneuver?
As an experiment, TruSat may well supply answers to some of these questions about how, if at all, introducing an unprecedented public eyewitness capability to orbital operations affects operator incentives in weighing the costs and benefits of maneuvers. As readers are no doubt experienced, the addition of speed cameras or a visible police car have a demonstrable effect on the strictness of adherence to terrestrial rules of the road. Whether this phenomenon extends to “rules of the road” that will emerge for orbital operations remains to be seen.
1. The lower range of the estimate is based upon regulatory filings and public statements by SpaceX, OneWeb, and Amazon’s Project Kuiper. The Federal Communications Commission (FCC) authorized 7,518 of the V-band satellites, and 4,409 of Ku- and Ka-band satellites comprising SpaceX’s Starlink constellation. Amazon subsidiary Kuiper, LLC has sought approval of a constellation that “will consist of 3,326 satellites in 98 orbital planes at altitudes of 590 km, 610 km, and 630 km.” Whereas OneWeb received FCC authorization for a constellation of 720 satellites in 2017 and indicated it was considering adding an additional 1,972 satellites, more recent public statements suggest the constellation will be fully operational at 648 satellites. The upper range of the estimate accounts for the October 2019 regulatory filings by SpaceX for an additional 30,000 Starlink satellites.
2. Among the space sustainability measures beyond the scope of this brief introduction are diplomatic efforts to proscribe the use and testing of debris-generating anti-satellite weapons, as well as emerging mission concepts for active debris removal (“ADR”), by which nonfunctional space objects are removed from orbit to mitigate collision risks.
3. P.J. Blount, Space Traffic Management: Standardizing On-Orbit Behavior, 113 AJIL UNBOUND 120 (2019) (defining space situational awareness as “information about what is in orbit, where it is at a given time, and who (if anyone) controls it.” ).
4. European Space Agency, ESA Spacecraft Dodges Large Constellation (September 3, 2019).
7. Jeff Foust, ESA spacecraft dodges potential collision with Starlink satellite, SPACENEWS (September 2, 2019).
8. ESA, supra note 4.
9. See Foust, supra note 7 (“[ESA Head of Space Safety] Krag, though, said that while SOCRATES uses publicly available information on spacecraft orbits, known as two-line elements (TLEs), satellite operators like ESA and SpaceX have access to more accurate orbital information provided by the Air Force ‘about one order of magnitude better than TLEs.’ That, combined with operators’ own knowledge of spacecraft positions, yielded a ‘more credible’ collision probability of 1 in 1,000 that led to the decision to perform the maneuver.”)
10. See Convention on International Liability for Damage Caused by Space Objects, Mar. 29, 1972, 961 UNTS 187.
11. See, e.g., Blount, supra note 3.
12. Constellation operator OneWeb has been particularly forward-leaning in positioning itself as a leader in space sustainability. See, e.g., OneWeb’s space sustainability website www.responsible.space; Jeff Foust, OneWeb founder Wyler calls for responsible smallsat operations, SPACENEWS (August 6, 2019).
13. For a survey of initiatives to develop STM standards, guidelines, and best practices responsive to the mandates of Space Policy Directive-3, see Michael P. Gleason, Establishing Space Traffic Management Standards, Guidelines, and Best Practices, THE AEROSPACE CORPORATION (September 2019).
15. See Jeff Foust, EU agency starts space sustainability initiative, SPACENEWS (September 15, 2019).
16. See A Sustainability rating for space debris, MIT News (May 6, 2019).
17. www.spacesafety.org; Jeff Foust, New coalition seeks to improve space safety, SPACE NEWS (Sept. 18, 2019).
18. See, e.g., Gleason, supra note 18.
19. See W. Patrick McRay, KEEP WATCHING THE SKIES! THE STORY OF OPERATION MOONWATCH AND THE DAWN OF THE SPACE AGE (Princeton University Press, 2008); Operation Moonwatch, WIKIPEDIA (retrieved September 17, 2019); David Dickinson, Citizen Science, Old-School Style: The True Tale of Operation Moonwatch, UNIVERSE TODAY (March 15, 2013).
20. SeeSat-L Home Page, http://www.satobs.org/seesat/seesatindex.html.