Behind the scenes of the Watchtower Protocol

We go into a brief background of the aspects associated the motivation behind Watchtower and why Watchtower is a solution to not only pricing-risk for space assets but also and most importantly space sustainability.

Space Situational Awareness (SSA)

There is a myriad object in Earth’s orbit that could possibly pose a threat to existing satellites such as communications, remote sensing for climate science and more, including their launches. SSA denotes to keeping track of these objects and predicting where they will be at any given time. Unlike typical surveillance that looks from space on the Earth’s surface (also known as remote sensing), SSA mostly involves surveillance of the orbital corridors around Earth.

Why is it important to surveil our surveilers? Most terrestrial based services heavily rely on satellites located in our orbital corridors today more than since 1950s when all this started. For example, most big technology companies rely on some Global Navigation Service System (GNSS) like the GPS, GLONASS, BDS, etc. Global supply chains on sea, air and road heavily rely on this too but on top of that they also rely on communication satellites normally located in lower orbits. These communication satellites are also vital when it comes to emergency & disaster management — an ever increasing need with the rise in natural disasters due to human activity affecting our changing climate. Then there’s remote sensing satellites required to monitor our planet and provide valuable data needed to determine the impact of human activity on the climate as well as to more daily necessities like weather forecasting. This is just a sliver of the uses satellites play in our every day lives and is a rabbit hole in themselves.

The major organisations involve in surveillance of space are:

• U.S. Strategic Command (USSTRATCOM) Space Surveillance Network: This is global network of ground-based sensors and tracking systems that keep an up-to-date space object data catalog, owned by the U.S. Military.
• USSTRATCOM SSA Sharing Program: This is a program that encourages data exchange with other organisations that track space objects and/or debris, also owned by the U.S. Military.
• ESA SSA Programme: This is a program that helps develop capabilities to track objects that could potentially disturb other satellites and/or other ground-based infrastructure, owned by the European Union.
• Russian Military Space Surveillance Network (SKKP): This is Russia’s equivalent of USSTRATCOM Space Surveillance Network that also catalogs space objects, tracks and predicts their state or configuration in orbit, owned by the Russian Federation.
• Space Data Association (SDA): This is an international organisation of satellite operators working together to enhance the accuracy and timeliness of collision warning notifications, controlled by the larger players in the space sector such as the U.S., Russia, China and the EU.

These aren’t the only networks, China, India, and a few other countries have growing networks performing similar functions and collaborating with each other.

SSA is a large field within the space community and with a myriad actors ensuring that there is proper surveillance of our orbital corridors, and this doesn’t include deep space surveillance that pick up objects on the outskirts of our solar system or beyond. The biggest issue with SSA is agreeing on the location of an object also known as uncertainty in state estimation. This occurs because space is closely aligned with defense organisations as the industry really spun out of the Cold War between the U.S. and former Soviet Union. This culture has percolated within the space community & indirectly through human bias, created a siloed & suspicious culture. Therefore, most organisations today are reliant on gated, siloed and black boxed organisations that aren’t willing to be transparent of their activities.

But, to build a Foundation (or) a United Federation of Planets, here and today, we need transparency — especially when it comes to surveying our orbits as well as beyond and as such legacy organisations built for a different epoch while helpful may not necessarily suit — and this is where the WatchtowerDAO comes in, to promote transparency while respecting privacy, sustainability and censorship-resistance on permissionless public digital infrastructure to ensure we all agree on the location of space objects to aid in better state estimations.

Conjunction Assessment

Conjunction Assessment (CA) is the process of screening, assessing, and mitigating a conjunction event of a protected space asset, such as a satellite, against a space object which could be another satellite or other space debris. A conjunction or conjunction event is the closest point of approach between two space object trajectories [2]. The typical process of CA consists of three phases:

1. CA screenings involve identifying any close approaches or possible conjunction events between a “primary” — from the perspective of the observer/screener (generally the protected asset) — and any other “secondary(ies)” space objects.
2. CA risk assessment is the process of examining any of these screened close approaches that may signify a clear and present danger and will require mitigation.
3. CA mitigation involves easing the conjunction event by creating and executing a mitigation action which generally insinuates a change in trajectory of the protected asset. This mitigation action either reduces the risk of collision completely or to a lesser extent as to not create a snowballing effect of collisions or Kessler syndrome [3].

Prior to any of these phases happening, data preparation is extensively carried out to ensure reliable CA. Therefore, the four aspects to CA are:

1. required input data,
2. CA screenings,
3. CA risk assessments and,
4. CA mitigation [1].

The aim of the Watchtower Protocol & DAO is to commence solving the space debris problem by addressing this second phase — CA risk assessment. We propose an open-source auction-based approach to determining the risk associated with a screened conjunction event. This risk assessment evaluation activity feeds the concept of pricing risk by extending the evaluation activity as a basis for decision making. There are a myriad of methods proposed for calculating and assessing satellite collision likelihood with their own merits and tolerances but, probability of collision or Pc is clear-cut, the oldest and widely accepted metric and is currently the industry standard endorsed by space agencies worldwide like NASA, academia and other space situational awareness actors both commercial and non-commercial [4].

Probability of Collision (Pc)

Probability of Collision (Pc) is a metric to identify high-risk conjunction events between space objects. There are many CA risk metrics in academic literature [5] that are useful but when making a choice on a specific CA collision likelihood metric, certain requirements need considering that are technical or otherwise such as:

• The fitness of risk bearing concerning CA risk,
• The simplicity of conceptually comprehending the parameter and how it is calculated
• The consensus within the space industry particularly the CA community
• The easiness and workability of computation
• And the capacity to characterise the likelihood of collision in a way that corresponds with the risk posed.

Pc is straightforward to calculate by any amateur and trained computational data scientist and can be calculated accurately in many difficult situations especially with modern computing techniques. It is relatively easy to translate and interpret by those making decisions regarding CA mitigation. It is the preferred parameter by the NASA’s CARA program as well as civilian, commercial, and military CA sectors.

While Pc is a well adopted metric, there are issues associated with the parameter. The main opposition to using Pc is the occurrence of probability dilution. Probability Dilution is the phenomenon when low Pc values indicate a low collision scenario that supports the notion of ceasing a mitigation action but are not necessarily a guaranteed safety outcome. State estimation data are used to characterise miss distances at Time of Closest Approach (TCA) and any uncertainties in the state estimation data are carried over into the calculation which eventually move into the CA risk parameter, Pc. Another issue is that Pc can be calculated either numerically or analytically. The numerical methods make fewer assumptions but are computationally demanding whilst analytical methods make more assumptions and computationally efficient. There are also issues associated with regularization and interpretation of input data to calculate Pc. There is a need to examine and prepare the required input data sets whilst choosing the appropriate calculation approach to that specific conjunction event scenario.

The Watchtower protocol aims to solves this by creating the first foundational infrastructure lego block — a market to price CA risk with an auction mechanism to coordinate computational data scientists or guardians around the world via a cryptographic token. Guardians assess the risk of screened conjunction events and those that perform well earn tokens based on the auction mechanism. This is the CA risk-pricing market — the first of three parts of the Watchtower protocol.

If you’d like to be involved in building this out or have more questions, get in touch. Best way is either via twitter or discord.

References

[1] “Spectrum Commons,” Wikipedia, 2021. [Online]. Available: https://en.wikipedia.org/wiki/Spectrum_commons_theory. [Accessed: 27-Aug-2021].

[2] NASA, “Satellite Safety,” 2021. [Online]. Available: https://satellitesafety.gsfc.nasa.gov/cara.html. [Accessed: 26-Aug-2021].

[3] D. J. Kessler and B. G. Cour-Palais, “COLLISION FREQUENCY OF ARTIFICIAL SATELLITES: THE CREATION OF A DEBRIS BELT.,” J Geophys Res, vol. 83, no. A6, pp. 2637–2646, 1978.

[4] NASA, NASA Spacecraft Conjunction Assessment and Collision Avoidance Best Practices Handbook, 1st ed. NASA, 2020.

[5] M. D. Hejduk, “Satellite Conjunction Assessment Risk Analysis for ‘Dilution Region’ Events: Issues and Operational Approaches,” Sp. Traffic Manag. Conf., 2019.