Verification of the Outer Space Treaty with Cosmic Protons
Abstract
The Outer Space Treaty (OST) was opened to signatures in 1967, and since then 117 countries, including China, the United States, Russia, have become part of it. Among other stipulations the treaty bans the placement of nuclear weapons in outer space. Recently the US government has raised worries that Russia is testing nuclear-armed anti-satellite weapon (ASAT) components, with the possibility that it will place a nuclear weapon in space. Such a device, if detonated, would destroy most of the satellites in the Low Earth Orbit (LEO). This danger is compounded by the lack of a verification mechanism for the OST. No methodologies of verification have been proposed in the open peer reviewed literature. This study presents a concept and a feasibility study for verifying a satellite's compliance to the OST by observing the neutrons induced by spallation from the $\sim$GeV protons in the inner Van Allen radiation belts. The calculations show that a 9U CubeSat sized detection platform can identify a thermonuclear weapon from the distance of 4 km in approximately one week of observation. This conceptual study will stimulate and inform future research and development of verification platforms for OST.
Summary
This paper addresses the critical issue of verifying compliance with the Outer Space Treaty (OST), which bans the placement of nuclear weapons in outer space. The lack of a verification mechanism for the OST is a major concern, especially given recent worries about Russia's development of nuclear-armed anti-satellite weapons (ASATs). The paper proposes a novel concept for verifying a satellite's compliance by detecting neutrons produced by spallation reactions induced by GeV protons from the inner Van Allen radiation belts interacting with the uranium radiation case of a thermonuclear weapon. The methodology involves using a 9U CubeSat-sized detection platform with a directional neutron detector. The detector consists of two planes of 30x30 pixels, each containing an EJ-276 scintillator surrounded by CVD single-crystal diamond detectors for anti-coincidence. The system leverages the natural proton flux in the Van Allen belts to interrogate the suspect satellite, avoiding active interrogation methods. The directional information of detected neutrons is used to suppress backgrounds from atmospheric albedo neutrons and other sources. Monte Carlo simulations using Geant4 were performed to model the detector response and estimate detection times. The study concludes that the proposed system can identify a thermonuclear weapon from a distance of 4 km in approximately one week of observation. This work serves as a feasibility study and a starting point for future research and development of OST verification platforms.
Key Insights
- •The paper introduces a novel approach to OST verification by leveraging naturally occurring cosmic protons in the Van Allen radiation belts for passive interrogation.
- •It demonstrates the feasibility of detecting a thermonuclear weapon on a satellite using a relatively small (9U CubeSat) detection platform.
- •The anti-coincidence veto system using diamond detectors effectively suppresses background signals from MeV electrons and protons in the harsh radiation environment of LEO. A threshold of E_veto > 0.6 MeV is used to reject proton tracks.
- •Directional neutron detection using a two-plane detector array is crucial for discriminating between spallation neutrons from the suspected satellite and background neutrons, achieving 87% retention of vertical spallation neutrons while rejecting all neutrons from all other sources using a cut cos(θ_error) > 0.95.
- •The estimated detection time is approximately one week from a distance of 4 km, based on a neutron yield of Y≈9.1×10^10 neutrons in approximately 6 hrs of observation.
- •A significant limitation is the dead time introduced by vetoing pixels due to high proton and electron fluxes, which reduces the live time to approximately 77%.
- •The paper acknowledges the need for future work to address challenges such as the high hit rate, radiation environment, outgassing, and thermal effects on sensor components.
Practical Implications
- •This research has direct implications for arms control and international security by providing a potential technological solution for verifying compliance with the OST.
- •Governments and international organizations responsible for enforcing arms control treaties would benefit from this research.
- •Engineers and researchers can use the proposed concept as a starting point for developing and deploying space-based verification systems.
- •The paper opens up future research directions, including optimizing detector design, exploring alternative detector materials, and developing advanced signal processing techniques to improve detection sensitivity and reduce detection times. Further research is needed to consider the effects of shielding on the neutron flux and new detection signatures that will be generated.
- •Constellations of smaller CubeSats could be used to reduce detection times, potentially enabling near real-time verification capabilities. A constellation of ten 9U CubeSat inspectors, brought to a proximity of 1 km to the suspected satellite, could reduce measurement times to just 1 hour.