Balancing Wind and Batteries: Towards Predictive Verification of Smart Grids -- nnenum: Verification of ReLU Neural Networks with Optimized Abstraction Refinement -- Minimum-Violation Traffic Management for Urban Air Mobility -- Integrating Formal Verification and Assurance: An Inspection Rover Case Study -- Towards verifying SHA256 in OpenSSL with the Software Analysis Workbench -- Polygon Merge: A Geometric Algorithm Verified Using PVS -- Program Sketching using Lifted Analysis for Numerical Program Families -- Specification Decomposition for Reactive Synthesis -- On Symmetry and Quantification: A New Approach to Verify Distributed Protocols -- Integrating Runtime Verification into a Sounding Rocket Control System -- Verification of Functional Correctness of Code Diversi cation Techniques -- Scalable Reliability Analysis by Lazy Verification -- Robustifying Controller Specifications of Cyber-Physical Systems Against Perceptual Uncertainty -- Good fences make good neighbors: Using formally verified safe trajectories to design a predictive geofence algorithm -- Online Shielding for Stochastic Systems -- Verification of Eventual Consensus in Synod Using a Failure-Aware Actor Model -- An Infrastructure for Faithful Execution of Remote Attestation Protocols -- Verifying min-plus Computations with Coq -- Efficient Verification of Optimized Code: Correct High-speed X25519 -- A formal proof of the Lax equivalence theorem for finite difference schemes -- Recursive Variable-Length State Compression for Multi-Core Software Model Checking -- Runtime Verification of Generalized Test Tables -- Quasi-Equal Clock Reduction On-the-Fly -- On the Effectiveness of Signal Rescaling in Hybrid System Falsification.

This book constitutes the proceedings of the 13th International Symposium on NASA Formal Methods, NFM 2021, held virtually in May 2021. The 21 full and 3 short papers presented in this volume were carefully reviewed and selected from 66 submissions. The papers aim to identify challenges and provide solutions to achieve assurance in mission-critical and safety-critical systems. Examples of such systems include advanced separation assurance algorithms for aircraft, next-generation air transportation, autonomous rendezvous and docking of spacecraft, on-board software for unmanned aerial systems (UAS), UAS traffic management, autonomous robots, and systems for fault detection, diagnosis, and prognostics.