Verification of the Outer Space Treaty with Cosmic Protons

TL;DR

This work proposes a passive, neutron-based verification concept for the Outer Space Treaty by exploiting spallation neutrons produced when GeV protons in the inner Van Allen belts interact with a suspect satellite's uranium radiation case. A detector system comprising two 30×30 pixel planes on a 9U CubeSat and using EJ-276 scintillators with a diamond veto detects and directionally localizes neutrons while suppressing belt protons and electrons through anti-coincidence and pulse-shape discrimination. The study shows that a single 9U inspector could confirm a thermonuclear device at ~4 km within ~7 days, with significant reductions in time possible using a constellation or closer proximity; however, it recognizes substantial engineering and policy challenges before deployment. The approach highlights the potential for a non-interrogation, physics-based verification pathway and points to follow-up work on background modeling, shielding, and practical formation-flying deployment to inform policy and future R&D.

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.

Figures (4)

• Figure 1: Plot of electron, proton flux, and spallation neutron counts versus time. (a) Electron spectra around minute 316. (b) Proton spectra around minute 316. (c) Proton flux, electron flux, and spallation neutron yields vs. time over three orbits.
• Figure 2: Model of the 9U CubeSat detector. (a) Rendering of the simulation of a single pixel of the array. The red volumes correspond to the diamond veto detectors. For purposes of clarity, the 60 nm dead layer is omitted and only axial protons are included. (b) Rendering of the full system of the two detector planes. The planes are 30$\times$30 cm$^2$, i.e. 30$\times$30 pixels big.
• Figure 3: Suppression of proton and neutron backgrounds. (a) A histogram of the distribution of EJ-276 signal vs. veto signal for incident protons, identifying the conditions for accepting neutron counts marked by the blue rectangle. (b) Distribution of $\cos(\theta_{\mathrm{error}})$ for the simulated albedo neutron flux and the flux of spallation neutrons. The $\cos(\theta_{\mathrm{error}})>0.95$ threshold cut (blue line) retains 87% of neutrons streaming from above while rejecting all neutrons from all other sources.
• Figure 4: The dependence of the estimated observation time necessary for confirming the presence of a hypothetical thermonuclear device carried by a suspect satellite vs. the measurement distance. The calculation is performed for two scenarios: a single 9U CubeSat; a constellation of 10 such CubeSats.