← Back to NASA Technology Projects
Active TRL 3 (started at 3, targeting 8)
The High charge (Z) and Energy TRaNsport (HZETRN) Physics Development project creates and verifies improved nuclear physics models for NASA’s HZETRN code to support accurate assessment of crew radiation exposure in heavily shielded spacecraft. An accurate and computationally efficient radiation transport code is needed to support the design of spacecraft that keep radiation exposure As Low As Reasonably Achievable (ALARA) and to verify spacecraft radiation protection requirements. NASA’s HZETRN code has a demonstrated ability to analyze highly complex vehicle geometry in space environments and is currently being used for requirements verification for Solar Particle Event (SPE) protection for Orion Multi-Purpose Crew Vehicle (MPCV), Gateway, and Human Landing System (HLS). Multiple verification and validation efforts have shown that HZETRN models in-space dose measurements very well. Detailed comparisons have also been performed between HZETRN and much slower Monte Carlo transport codes. These comparisons showed that HZETRN agreed with the Monte Carlo codes as well as they agree with each other; and all codes indicated that there is an optimal shield thickness near 20 g/cm2 for non-hydrogenous materials, beyond which dose equivalent begins to rise. However, these comparisons also showed that calculated dose equivalent for thick shields (40-100 g/cm2) in Galactic Cosmic Ray (GCR) environments can vary by as much as 30% using the world’s best codes. The HZETRN Physics Development project will improve the accuracy of thick shield transport calculations to support accurate assessment of human exposure in heavily shielded spacecraft, such as surface habitats and/or the Mars Transit Vehicle, needed for long duration lunar surface and Mars missions.
This effort will focus on the development of double-differential cross section models for pion, nucleon, and light ion production, because these are the particles that dominate the radiation environment behind thick shielding. Three efforts will begin in FY25 and be completed in FY26. A two-year study examining the cross section models currently used by HZETRN and other transport codes will be undertaken. This study will include a review of published comparisons between models and cross section measurement data and a limited number of inter-model comparisons. At the same time, development of a new double differential cross section model for pion, neutron, and proton production will begin. Also, beginning in FY25 and wrapping up in FY26, the list of particles tracked by HZETRN will be updated to ensure that the most prevalent isotopes are included. In FY27-FY30, additional cross section models for light ion production, medium ion production, and hadron production will be developed and verified with measurement data.
The HZETRN space radiation transport code was developed by NASA to address NASA’s need to predict and evaluate crew radiation exposure. HZETRN is unique, compared with other world class transport codes, in its computational speed and its proven ability to analyze detailed and highly complex vehicle geometry in space radiation environments. These features make it possible to assess multiple vehicle configurations under consideration and/or to evaluate crew exposure at multiple locations within complex spacecraft models. HZETRN has been used to assess crew exposure in ISS, Orion MPCV, Gateway, HLS, the Mars Transit Vehicle, and a variety of lunar and Mars surface habitat concepts. HZETRN has been incorporated into the On-Line Tool for the Assessment of Radiation In Space (OLTARIS), which NASA maintains; and a long list of domestic commercial and international partners have used it to assess their vehicles with their mission parameters. Improvements to HZETRN physics models and validation of the HZETRN code have been funded under the Mars Campaign Office RadWorks Activity since FY18. During that time, HZETRN2020 was completed and released; validation with ISS, Artemis-1, and Mars rover measurements was performed; and a new method for developing Double-Differential FRaGmentation (DDFRG) cross section models was developed. The current HZETRN Physics Development Project began in FY25 and will culminate in FY30 with the completion of HZETRN2030.
The resulting improved HZETRN transport code will make thick shield transport calculations more accurate, which will enable the design of heavily shielded spacecraft/habitats with optimized shielding.
Listed on TechPort itself — the most direct way to ask about this specific project.
This is early/mid-stage (TRL 3) — the most realistic path in is NASA SBIR/STTR, which funds small businesses and research institutions to develop technology aligned with NASA's needs (equity-free, phased funding). Check whether a current SBIR/STTR solicitation topic overlaps with this project's technology area, or contact the project directly (above) to ask.
None of these are guaranteed paths for this specific project — TechPort itself doesn't have an "apply" button. Reaching out to the contact(s) above with a specific question is usually the fastest way to find out what's actually open.