Colby Lemon

Computational Physicist · Space Radiation Effects & Space Environment Modeling

https://lemonlab.net · https://github.com/lem-n

https://www.linkedin.com/in/colbylemon · colby@lemonlab.net · 214-587-8663

Profile

Computational physicist with two decades of experience modeling Earth’s space radiation environment and its effects on satellite hardware. Deep expertise in radiation transport through matter (Geant4), internal and surface charging, and ESD susceptibility analysis across LEO, MEO, HEO, and GEO. Extensive on-orbit anomaly investigation experience for critical government and commercial satellite programs, supported by beam-line testing that validated charging models against measurement. Also a production HPC developer — C++, Fortran, Python, and Julia with MPI, OpenMP, CUDA, and PETSc — who builds the analysis tools rather than only running them.

Core Skills

Space Environment & Radiation Effects: Radiation transport through matter, internal/deep dielectric charging, surface charging, ESD susceptibility analysis, charge and dose deposition, radiation belt and South Atlantic Anomaly environments (LEO/MEO/HEO/GEO), on-orbit anomaly root-cause investigation
Radiation & Charging Codes: Geant4, FASTRAD, Ansys Charge Plus
Programming Languages: C++, Fortran, Python, Julia, MATLAB, Lua, Shell scripting
Parallel & GPU Computing: MPI, OpenMP, CUDA, JAX, PyTorch, PETSc, Kokkos, Slurm
Numerical Methods & Libraries: FEM/FEA, AMR, libMesh, PETSc
Scientific Computing: PDE solvers, MHD, CFD, plasma simulation, mathematical optimization
Performance Engineering: Profiling and bottleneck analysis, memory optimization, CPU/GPU architecture
Data & Visualization: NumPy, SciPy, HDF5, Pandas, Matplotlib
Software Engineering: Agentic coding, spec-driven development, test-driven development

Experience

The Aerospace Corporation · Space Science Applications Laboratory

El Segundo, California · 2005–Present

Three concurrent and overlapping technical roles spanning radiation effects on satellites, magnetospheric modeling, and plasma instrument development.

Spacecraft Radiation Effects and Electrostatic Discharge Analysis

Developed a 3D multi-physics model in C++ coupling Geant4 radiation transport with a finite-element Poisson solver and Ohm’s-law charge transport algorithm to simulate deep dielectric charging in spacecraft materials.
Investigated the environmental cause of on-orbit shorts on a high-LEO satellite’s solar arrays, which clustered around the South Atlantic Anomaly; narrowed the probable short locations on the array and identified design modifications to prevent recurrence.
Led the radiation-environment assessment for a serious on-orbit anomaly on a MEO mission as sole subject-matter expert, characterizing the proton and electron environments encountered and evaluating their potential effects on the satellite.
Performed high-energy electron beam testing at NASA Marshall Space Flight Center, injecting charge into insulator samples and measuring the resulting charge density by the pulsed electroacoustic (PEA) technique to validate the dielectric charging model.
Analyzed, assessed, and diagnosed satellite anomalies attributed to the space radiation environment, working directly with customers, program offices, and contractors and presenting findings to both technical and program stakeholders.
Performed pre-launch charging susceptibility analyses for payloads, solar arrays, and other components to estimate ESD risk to critical flight systems.
Built a 1D Python charging and radiation effects model for rapid-turnaround simulation of 10–15 year missions, supporting numerous on-orbit anomaly investigations and ESD failure analyses for critical government and commercial satellites.
Assessed on-orbit charging of spacecraft antenna elements with 3D FASTRAD simulations, identifying where charge accumulates and bounding worst-case charging scenarios.
Implemented adaptive mesh refinement to resolve localized charge accumulation and electric field gradients near material interfaces.
Parallelized radiation transport with MPI and the electric field solver with MPI + PETSc.
Developed a Python-driven parametric simulation framework to sweep material properties and radiation environments, enabling systematic ESD susceptibility mapping across mission-relevant conditions.
Benchmarked dense and sparse matrix solvers (NumPy, SciPy, JAX, PyTorch) for the 1D Poisson equation on high-resolution grids to identify optimal solver strategies.
Performed verification and validation of the FEM and PIC solvers in Ansys Charge Plus for simulating triboelectric charging of astronauts in the lunar environment.

Magnetospheric Dynamics Modeling

Developed a coupled magnetosphere–ionosphere–plasmasphere transport model for simulating space weather, magnetic storms, and auroral dynamics.
Validated model predictions against satellite measurements to quantify accuracy and isolate the contributions of specific physical processes.
Designed numerical experiments mapping cause-and-effect relationships between solar wind drivers and magnetospheric response.
Optimized serial performance and parallelized advection and magnetic field solvers using OpenMP, reducing wall-clock time by over 100x on shared-memory systems.
Evaluated advection solver flux limiters to balance numerical diffusion against spurious oscillations in the plasma transport equations.
Refactored legacy Fortran codebase using test-driven development; wrapped compiled Fortran with Julia to accelerate development/testing cycles; migrated significant portions to Modern Fortran and Python.
Developed a relativistic Lorentz-force particle tracer in MPI Fortran to compute electron trajectories in 3D electromagnetic fields.
Performed statistical analyses of satellite plasma and energetic particle data for process studies, model input generation, model validation, and satellite anomaly assessment (Python, NumPy, SciPy, Pandas, Matplotlib).

Plasma Instrument Design and Field Campaigns

Supported four suborbital NASA sounding rocket missions: led payload-instrument integration, monitored ground-support equipment pre-flight and in-flight, and verified instrument performance.
Designed, prototyped, fabricated, and launched a magnetic mass spectrometer for measuring plasma ion composition; flew on two sounding rockets to measure ions in the upper ionosphere and lower magnetosphere.
Built a first-principles ion optics simulation coupling magnetic field geometry with an electric field solver to optimize electrode shapes compensating for field non-uniformities.
Simulated electron and ion trajectories in CubeSat plasma-analyzer instruments to optimize performance metrics and maximize science return.

Education

Ph.D., Physics — Rice University
- Dissertation: “Simulating the Driven Magnetosphere”
M.S., Astrophysics — Rice University
B.S., Physics — University of Texas at Dallas

Selected Publications

Lemon, C. et al., Long-Term Nuclear Detonation Effects on Space Technologies and Radiation Responses, Aerospace Report No. TOR-2025-00995, 2025.

Lemon, C. L., J. L. Roeder, and J. F. Fennell, Long Term Charge Buildup and Dissipation in Spacecraft Materials, Proceedings of the 15th Spacecraft Charging Technology Conference, Kobe, Japan, 2018.

Lemon, C. L., J. L. Roeder, M. D. Looper, J. F. Fennell, M. J. Meshishnek, and M. R. Ciofalo, A 3-D Model of the Internal Charging of Spacecraft Dielectric Materials, Proceedings of the 11th Spacecraft Charging Technology Conference, Albuquerque, NM, 2010.

Lemon, C., R. Wolf, T. Hill, S. Sazykin, R. Spiro, F. Toffoletto, J. Birn, and M. Hesse, Magnetic storm ring current injection modeled with the Rice Convection Model and a self-consistent magnetic field, Geophys. Res. Lett., 31, L21801, 2004.

Lemon, C., F. Toffoletto, M. Hesse, and J. Birn (2003), Computing magnetospheric force equilibria, J. Geophys. Res., 108, 1237, doi:10.1029/2002JA009702, A6.