NASA-STD-3001 Technical Brief

Relevant Technical 

Requirements

Design for Ionizing 

Radiation Protection

OCHMO-TB-020

Rev F

NASA-STD-3001 Volume 1, Rev C

[V1 4029] As Low as Reasonably Achievable 

(ALARA) Principle 

[V1 4030] Career Space Permissible Exposure 

Limit for Space Flight Radiation 

[V1 4031] Radiation Limits – Solar Particle 

Events 

[V1 4032] Crew Radiation Limits for Nuclear 

Technologies 

[V1 4033] Crew Radiation Limits from 

Galactic Cosmic Radiation

NASA-STD-3001 Volume 2, Rev D

[V2 6095] Ionizing Radiation Protection Limit

[V2 6098] Radiation Environments 

[V2 6161] Intravehicular Area Monitoring of 

Space Radiation Exposure

[V2 6162] Personal Monitoring of Space 

Radiation Exposure

[V2 6163] Area Monitoring of Radiation 

Exposure from Nuclear Technologies

[V2 6164] Alerting of Elevated Exposure 

Rates

[V2 6165] External Space Weather 

Monitoring

Executive Summary

During any mission, crewmembers face threats of 

ionizing radiation from a variety of sources. 

Technical requirements outlined in NASA-STD3001 state that individual crewmember’s total 

career effective radiation dose during spaceflight 

radiation exposure is not to exceed 600 

millisieverts (mSv). Additionally, short-term 

radiation exposure to solar particle events is 

limited to an effective dose of 250 mSv per event 

to minimize acute effects. Design choices and 

shielding strategies can be implemented to 

reduce the threat posed by radiation and ensure 

crew safety and health.

Houston We Have a Podcast: 

Jason Weeks and Steve Platts discuss the ways NASA 

is collecting radiation data to better understand the 

risks and possible mitigation strategies for humans 

traveling through deep space. 

Ep128: Space Radiation | NASA
NASA-STD-3001 Technical Brief

OCHMO-TB-020 Design for Ionizing Radiation Protection

NASA Office of the Chief Health & Medical Officer (OCHMO)

This Technical Brief is derived from NASA-STD-3001 and is for reference only.

It does not supersede or waive existing Agency, Program, or Contract requirements.

Background

12/05/2023

Rev F 2

Risks of Radiation Exposure

Long Term Health Impact – Post Mission

Carcinogenesis 

Radiation exposure may cause increased cancer 

morbidity or mortality risk for astronauts. There is also a 

risk of changes in cognition, motor function, and 

behavior or neurological disorders.

In Mission Risk

Acute Radiation Syndromes from SPEs

Acute radiation syndromes, such as nausea, vomiting, 

and fatigue, may occur due to in mission radiation 

exposure, as well as skin injuries and depletion of bloodforming organs. Effective shielding and environmental 

monitoring minimizes this risk. See shielding guidelines.

Trapped particles are a third type of radiation 

that is a risk in certain circumstances 

(International Space Station (ISS): South 

Atlantic Anomaly (SAA); Lunar: Van Allen belts). 

These medium-to-low energy protons and 

electrons are a secondary source of exposure 

that contribute to long-term health effects (not 

acute). However due to short passes through 

the SAA and Van Allen belts, and the fact that 

typical SPE shielding is effective against trapped 

particles, additional radiation shielding is not 

required.

Occurs continuously, omni-directional, varying 

in flux with solar cycle. Lower GCR levels occur 

during solar maximum.

Shielding is NOT effective due to secondary 

radiation produced in shielding and tissue.

Countermeasures: Biological uncertainties 

cloud understanding of effectiveness of 

possible mitigations.

Solar Particle Events (SPE) – low to medium energy protons

Infrequent events occurring most often during 

solar cycle maximum (~22-year cycles) – peak

activity during solar maximum.

Lunar surface provides significant protection 

vs. free space. Shielding (5-20 g/cm2

aluminum and polyethylene) IS effective, 

optimization to reduce weight.

Countermeasures: Shielding, monitoring, 

accurate event determination, dosimetry, and 

timely reporting to alert crew to seek shelter 

are essential for crew safety.

Galactic Cosmic Rays (GCR) – penetrating protons and heavy nuclei

Space Radiation Environment Overview
NASA-STD-3001 Technical Brief

OCHMO-TB-020 Design for Ionizing Radiation Protection

NASA Office of the Chief Health & Medical Officer (OCHMO)

This Technical Brief is derived from NASA-STD-3001 and is for reference only.

It does not supersede or waive existing Agency, Program, or Contract requirements.

Background

12/05/2023

Rev F 3

Space Radiation Environment Overview

Probability of Space Radiation Events

• GCR dose & SPE probability are anti-correlated over 11-year solar cycle.

• Near or long-term prediction of SPE occurrence is not accurate, however the dose-rates for the 

large majority of past SPEs show real-time responses and should be adequate to reduce 

exposures to well below NASA dose limits.

• In an effort of prudence and preparation, current plans are in place for 1 in 100 (centennial) and 

1 in 1000 (millennium) SPE events.

• To better understand risk of GCR exposure, dose rates are calculated utilizing simulators which 

retrospectively estimate secondary particle fluence as well as ambient dose equivalent rates 

and effective dose rates at any point in the atmosphere. Further information can be found in 

the reference article: Numerical calculation of the radiation exposure from galactic cosmic rays 

at aviation altitudes with the Professional Aviation Dose Calculator (PANDOCA) core model 

(Matthia, Meier, & Reitz, 2014).
NASA-STD-3001 Technical Brief

OCHMO-TB-020 Design for Ionizing Radiation Protection

NASA Office of the Chief Health & Medical Officer (OCHMO)

This Technical Brief is derived from NASA-STD-3001 and is for reference only.

It does not supersede or waive existing Agency, Program, or Contract requirements.

Background

Radiation Technical Requirements Overview

NASA updated the astronaut Space Flight Radiation Permissible Exposure Limit, the solar particle event 

technical requirements, and added a nuclear technologies technical requirement. The graphic below 

provides a summary. The technical requirements are all based on dose (mSv) with a relationship to Risk of 

Exposure-Induced Death (REID) for cancer mortality. 

12/05/2023

Rev F 4

[V1 4030] Career Space Permissible Exposure Limit for Space Flight Radiation An individual 

crewmember’s total career effective radiation dose due to spaceflight radiation exposure shall be less 

than 600 mSv. This limit is universal for all ages and sexes. From NASA-STD-3001 Volume 1, Rev C

The NASA effective dose for determining the technical requirement threshold limit is calculated using the 

NASA Q (based on the NASA cancer model of 2012), 35-year-old female model parameters (tissue 

weighting factors, phantom, etc.) for both males and females. Individual astronaut risk of exposureinduced death (REID) calculations are calculated using the appropriate NASA Q (based on the NASA cancer 

model of 2012) sex and age model parameters. See next page.

The 600 mSv and 3% mean risk of cancer mortality was set to avoid exceeding cancer risk from various or 

lifestyle factors, such as smoking, lack of exercise, unhealthy diets, etc.
NASA-STD-3001 Technical Brief

OCHMO-TB-020 Design for Ionizing Radiation Protection

NASA Office of the Chief Health & Medical Officer (OCHMO)

This Technical Brief is derived from NASA-STD-3001 and is for reference only.

It does not supersede or waive existing Agency, Program, or Contract requirements.

Background

Radiation Technical Requirements Overview

The table below provides an example of a notional crewmember with three flights and their total dose 

exposure and mean REID calculations for both female and male.

12/05/2023

Rev F 5

This graph illustrates the 

maximum excess risk 

based on the NASA 

spaceflight radiation 

exposure technical 

requirement and 

provides a comparison to 

lifestyle factors.
NASA-STD-3001 Technical Brief

OCHMO-TB-020 Design for Ionizing Radiation Protection

NASA Office of the Chief Health & Medical Officer (OCHMO)

This Technical Brief is derived from NASA-STD-3001 and is for reference only.

It does not supersede or waive existing Agency, Program, or Contract requirements.

Background

Radiation Technical Requirements Overview

12/05/2023

Rev F 6

[V1 4031] Radiation Limits – Solar Particle Events The program shall protect crewmembers from 

exposure to the design reference Solar Particle Event (SPE) environment proton energy spectrum (sum 

of the October 1989 events) to less than a NASA effective dose of 250 mSv. From NASA-STD-3001 

Volume 1, Rev C

Recommendations for types of SPE shielding for mission location and duration

This limit is based on not adding more than 10% radiation exposure beyond the space environment 

radiation of the mission. Based on an analysis for a surface-based mission, the radiation environment 

exposure is approximately 0.5 mSv per day; and 10% of this value sets the technical requirement to 0.05 

mSv per day and ~20 mSv/mission year. This technical requirement is applied to both surface and freespace missions regardless of mission solar cycle. Exact mission assumptions should be considered when 

performing the calculation; parameters should include estimates of time in a habitat, habitat shielding, 

and EVA frequency. For missions that are leveraging nuclear sources for a propulsion system, the 

tradeoff of reduced mission duration due to faster transit which reduces 

the crew exposure to space flight radiation exposure should be 

Considered compared to the increased exposure due to the nuclear 

source. For example, if the nuclear propulsion system saved 90 days of 

exposure during the transit to Mars which equates to 

1.5 mSv/day × 90 days = 135 mSv “saved” space flight radiation 

exposure and the source generates 150 mSv, then the net 

exposure is +15 mSv.

[V1 4032] Crew Radiation Limits for Nuclear Technologies Radiological exposure from nuclear 

technologies emitting ionizing radiation to crewmembers (e.g., radioisotope power systems, fission 

reactors, etc.) shall be less than an effective dose of 20 mSv per mission year (prorated/extrapolated to 

mission durations) utilizing the ALARA principle. From NASA-STD-3001 Volume 1, Rev C
NASA-STD-3001 Technical Brief

OCHMO-TB-020 Design for Ionizing Radiation Protection

NASA Office of the Chief Health & Medical Officer (OCHMO)

This Technical Brief is derived from NASA-STD-3001 and is for reference only.

It does not supersede or waive existing Agency, Program, or Contract requirements.

Reference Data

12/05/2023

Rev F 7

Effective Dose (mSv per Mission Day) Variation with Solar Cycle

Engineering Countermeasures

• The best way to shield from ionizing 

radiation is to provide as much physical 

material between a person and the 

source of radiation as possible. Dense 

and thick materials that essentially 

absorb the high energy particles from 

incoming radiation are ideal but prove 

difficult in space travel due to their 

significant amounts of mass. 

Shielding Materials

• Aluminum and polyethylene are the most 

commonly used shielding materials. They 

provide an average 50% reduction in 

dosage levels from SPE radiation. GCR 

radiation does not respond to shielding, 

with only an average 7% reduction in 

dosage levels. Additionally, secondary 

radiation is produced within tissues, 

further reducing any benefits of GCR 

shielding.
NASA-STD-3001 Technical Brief

OCHMO-TB-020 Design for Ionizing Radiation Protection

NASA Office of the Chief Health & Medical Officer (OCHMO)

This Technical Brief is derived from NASA-STD-3001 and is for reference only.

It does not supersede or waive existing Agency, Program, or Contract requirements.

Reference Data

12/05/2023

Rev F 8

Ray Tracing tools and Effectiveness of Shielding

Effective Dose (mSv) by crew location within 

capsule*

Crew 

#1

Crew 

#2

Crew 

#3

Crew 

#4

Effective Dose E 214 210 259 231

Effective Dose (Optimized Pre-Launch Stowage) 68 65 66 66

Effective Dose (Optimized Return Stowage) 83 75 73 83

Effect of using water bags/stowage as a shelter during an SPE event 

beyond low earth orbit in a capsule

Effect of ISS Shielding on crew daily dose

Ray Tracing technology examines the 

effectiveness of shielding tools in blocking 

radiation. Evenly distributed rays are 

created to start from dose point and end 

outside the vehicle. Each ray records 

distance and respective density of the parts 

it passes. Areal mass density is calculated 

and used in transport code that evaluates 

particle flux at dose point.

*Note the different doses based on location within a vehicle
NASA-STD-3001 Technical Brief

OCHMO-TB-020 Design for Ionizing Radiation Protection

NASA Office of the Chief Health & Medical Officer (OCHMO)

This Technical Brief is derived from NASA-STD-3001 and is for reference only.

It does not supersede or waive existing Agency, Program, or Contract requirements.

Application

12/05/2023

Rev F 9

Design Considerations

• Shielding design must implement ALARA for mission duration < 6 months with respect to SPE 

protection.

• For missions > 6 months, it is recommended that vehicle shielding be at least 20 g/cm2 to protect the 

crew from SPEs.

• Storm shelter: Additional Storm Shelter with an added 10 cm water equivalent in crew quarters to 

protect against centennial solar particle event.

• This can be achieved by rearranging items such as water containers and/or high hydrogen 

content materials.

• Timelines of SPEs allow sufficient time for re-configuration.

• Protection for a 1000-year SPE event would require ~20 cm water equivalent for shielding.

• Due to the nature of GCRs, shielding is less effective. GCR particles scatter into multiple particles when 

they strike shielding.

• Radiation alerting provides an additional layer of protection to limit exposure to SPEs (early warning 

allows for crew to safe vehicle and configure shelter).

• Real-time alert dosimetry also provides a very high level of protection for EVAs if termination 

occurs within 2 hours and there is access to shielding.

• Radiation dose monitoring provides critical occupational health information to understand the effects 

of radiation exposure.

• Designs can be evaluated and maximized for shielding effectiveness utilizing existing Shield Geometry 

Model and Shielding Analysis by computer-aided design (CAD) tools, as well as conducting Ray Tracing.

Vehicle Design Considerations

• Current engineering and design teams are researching 

the possibility of utilizing a ‘surrounded’ vs. ‘in-line’ 

architecture approach for crew habitat in hopes that 

there is a reduction in overall exposure to GCR radiation. 

A surrounded architecture approach utilizes the hub and 

spoke ideology, with a centralized node module acting as 

the core/hub at the center of the layout where crew 

activity takes place most of the time. The structure 

surrounding the core/hub would be comprised of major 

structural elements that contain logistics, equipment, 

trash, props, etc.

Source: Bailey (2012) – Deep 

Space Habitat Project
NASA-STD-3001 Technical Brief

OCHMO-TB-020 Design for Ionizing Radiation Protection

NASA Office of the Chief Health & Medical Officer (OCHMO)

This Technical Brief is derived from NASA-STD-3001 and is for reference only.

It does not supersede or waive existing Agency, Program, or Contract requirements.

Application

12/05/2023

Rev F 10

Guidelines for Space Radiation Shielding Requirements for Exploration Missions

• NASA’s Health and Medical Technical Authority has developed Shielding Requirement 

Guidelines for exploration missions that were reviewed by the Space Radiation 

Research Clinical Advisory Panel (RCAP). These Guidelines are intended to provide 

closure for vehicle design requirements.

• Analysis shows decennially large SPEs lead to doses for average spacecraft 

shielding below NASA Dose limits requiring only ALARA.

• However centennial and millennial events require a well designed “storm 

shelter”.

• Large majority (~95%) of SPEs require only ALARA considerations and do not approach 

dose limits.

• A Centennial Event (1 per 100 years) can be shielded below NASA dose limits 

with additional 10 cm water equivalent storm-shelter shielding.

• Millennial Event (1 per 1000 year) with additional 20 cm water equivalent stormshelter shielding. 

• Assuming a vehicle with 20 g/cm2 aluminum – Additional Storm Shelter with additional 

10 cm water equivalent in crew quarters to protect against centennial solar particle 

event.

• Combination of inherent and reconfigurable shielding.

• Timelines of SPEs allow sufficient time for re-configuration.

• Mission disruption is a major risk from SPEs, especially for extravehicular activities 

(EVAs).

• Spacecraft shielding requirements could be impacted by additional doses 

incurred by crew during EVA, especially on lunar surface.

• Real-time alert dosimetry provides a very high level of protection if EVA 

termination occurs within 2 hrs.

• The probability of EVA organs doses >100 mSv is less than one in a million based 

on SPE statistics of event frequency, size and energy spectra.

• Shielding guidelines could be modified by new knowledge of GCR, central nervous 

system functioning, cancer, and other risks.
NASA-STD-3001 Technical Brief

OCHMO-TB-020 Design for Ionizing Radiation Protection

NASA Office of the Chief Health & Medical Officer (OCHMO)

This Technical Brief is derived from NASA-STD-3001 and is for reference only.

It does not supersede or waive existing Agency, Program, or Contract requirements.

Back-Up

12/05/2023

Rev F 11
NASA-STD-3001 Technical Brief

OCHMO-TB-020 Design for Ionizing Radiation Protection

NASA Office of the Chief Health & Medical Officer (OCHMO)

This Technical Brief is derived from NASA-STD-3001 and is for reference only.

It does not supersede or waive existing Agency, Program, or Contract requirements.

Major Changes Between Revisions

12/05/2023

Rev F 12

Rev E  Rev F

• Updated information and standards to be consistent with 

NASA-STD-3001 Volume 1 Rev C and Volume 2 Rev D.

Rev D  Rev E

• Updated format.

• Added additional information to be consistent with NASASTD-3001 Volume 1 Rev C and Volume 2 Rev D.

Rev C  Rev D

• Updated information to be consistent with NASA-STD-3001 

Volume 1 Rev B and Volume 2 Rev C.

Rev B  Rev C

• Added information regarding shielding materials and 

vehicle/spacecraft design considerations.

• Added information regarding frequency of radiation events.

• Added additional information about ray tracing.

• Added new HMTA proposed guidelines for space radiation 

shielding requirements.

• Overall formatting/template updates.
NASA-STD-3001 Technical Brief

OCHMO-TB-020 Design for Ionizing Radiation Protection

NASA Office of the Chief Health & Medical Officer (OCHMO)

This Technical Brief is derived from NASA-STD-3001 and is for reference only.

It does not supersede or waive existing Agency, Program, or Contract requirements.

NASA-STD-3001 Volume 1 Revision C

[V1 4029] As Low as Reasonably Achievable (ALARA) Principle All crew radiation exposures shall be 

minimized using the ALARA principle.

[V1 4030] Career Space Permissible Exposure Limit for Space Flight Radiation An individual crewmember’s 

total career effective radiation dose due to space flight radiation exposure shall be less than 600 mSv. This 

limit is universal for all ages and sexes. 

Note: The NASA effective dose for determining the standard threshold limit is calculated using the NASA Q 

(based on the NASA cancer model of 2012), 35-year-old female model parameters (tissue weighting factors, 

phantom etc.) for both males and females. Individual astronaut REID calculations are calculated using the 

appropriate NASA Q (based on the NASA cancer model of 2012) sex and age model parameters. 

[V1 4031] Short-Term Radiation Limits – Solar Particle Events The program shall protect crewmembers 

from exposure to the design reference Solar Particle Event (SPE) environment proton energy spectrum (sum 

of the October 1989 events) to less than a NASA effective dose of 250 mSv. 

[V1 4032] Crew Radiation Limits for Nuclear Technologies Radiological exposure from nuclear technologies 

emitting ionizing radiation to crewmembers (e.g., radioisotope power systems, fission reactors, etc.) shall 

be less than an effective dose of 20 mSv per mission year (prorated/extrapolated to mission durations) 

utilizing the ALARA principle. 

[V1 4033] Crew Radiation Limits from Galactic Cosmic Radiation For habitable space systems designed to 

support crew for > 60 days, the program shall protect crewmembers from exposure to the galactic cosmic 

ray (GCR) environment to less than a NASA effective dose (as defined in NASA-STD-3001, Volume 1 [V1 

4030] Career Space Permissible Exposure Limits for Spaceflight Radiation) rate of 1.3 mSv/day for systems 

in free space and to less than 0.9 mSv/day for systems on planetary surfaces.

Note: To verify the habitable space system design meets the GCR protection requirement above, the NASA 

effective dose rate is calculated using the 2009 solar minimum Badhwar O’Neill GCR model spectrum and 

take into account estimated crew time spent at lightly and more heavily shielded locations throughout the 

habitable space system. If achievable, further measures are to be taken to reduce crew exposure in 

accordance with the ALARA principle, as set forth in [V1 4029] As Low as Reasonably Achievable (ALARA) 

Principle.

NASA-STD-3001 Volume 2 Revision D

[V2 6095] Ionizing Radiation Protection Limit The program shall set system design requirements to prevent 

potential crewmembers from exceeding career space permissible exposure limits (PELs) as set forth in 

NASA-STD-3001, Volume 1.

[V2 6098] Radiation Environments The program shall specify the radiation environments to be used in 

verifying the radiation design requirements. 

[V2 6161] Intravehicular Area Monitoring of Space Radiation Exposure The program shall monitor the 

radiation exposure produced by galactic cosmic rays, solar energetic particles, trapped radiation, and 

neutrons in habitable volumes as referenced in Table 6.8-1—Space Radiation Monitoring Requirements 

Mission Location vs. Required Monitoring.

Referenced Technical Requirements

12/05/2023

Rev F 13

View the current versions of NASA-STD3001 Volume 1 & Volume 2 on the 

OCHMO Standards website
NASA-STD-3001 Technical Brief

OCHMO-TB-020 Design for Ionizing Radiation Protection

NASA Office of the Chief Health & Medical Officer (OCHMO)

This Technical Brief is derived from NASA-STD-3001 and is for reference only.

It does not supersede or waive existing Agency, Program, or Contract requirements.

NASA-STD-3001 Volume 2 Revision D

[V2 6162] Personal Monitoring of Space Radiation Exposure The program shall monitor the radiation 

exposure produced by galactic cosmic rays, solar energetic particles, and trapped radiation received by 

individual crew members as referenced in Table 6.8-1—Space Radiation Monitoring Requirements Mission 

Location vs. Required Monitoring.

[V2 6163] Area Monitoring of Radiation Exposure from Nuclear Technologies The program shall monitor 

the crew ionizing radiation exposure from nuclear technologies.

[V2 6164] Alerting of Elevated Exposure Rates The radiation monitoring system shall alert the crew and 

operations teams when radiation exposure rates exceed predefined thresholds.

[V2 6165] External Space Weather Monitoring The program shall monitor the in-situ extravehicular space 

weather environment including the external exposure rates, electron flux spectra, and proton flux spectra.

Referenced Technical Requirements

12/05/2023

Rev F 14

View the current versions of NASA-STD3001 Volume 1 & Volume 2 on the 

OCHMO Standards website
NASA-STD-3001 Technical Brief

OCHMO-TB-020 Design for Ionizing Radiation Protection

NASA Office of the Chief Health & Medical Officer (OCHMO)

This Technical Brief is derived from NASA-STD-3001 and is for reference only.

It does not supersede or waive existing Agency, Program, or Contract requirements.

Reference List

1. Chancellor, J., Scott, G., & Sutton, J. (2014). Space Radiation: The Number One Risk to Astronaut 

Health beyond Low Earth Orbit. Life, 4(3), 491–510.

2. Real Martians: How to Protect Astronauts from Space Radiation on Mars (Frazier 2017). 

https://www.nasa.gov/feature/goddard/real-martians-how-to-protect-astronauts-from-spaceradiation-on-mars

3. Space Faring: The Radiation Challenge. An Interdisciplinary Guide on Radiation and Human Space 

Flight. https://www.nasa.gov/sites/default/files/atoms/files/space_radiation_ebook.pdf

4. Countermeasures to Space Radiation. NASA Space Radiation Program (Cucinotta 2013).

5. Deep Space Habitat Project: Radiation Studies for a Long Duration Deep Space Transit Habitat. 

Engineering Directorate (Bailey 2012).

6. HMTA Proposed Guidelines for Space Radiation Shielding Requirements for Exploration Missions. 

Health and Medical Technical Authority – Human Health and Performance Directorate (Francisco 

2015).

7. Antonsen, E. Report on Virtual Radiation Risk Panel. September 24, 2020. Internal NASA document.

8. CR-HSRB-16-005: Risk of Adverse Health Outcomes and Performance Decrements Resulting from 

Space Radiation Exposure.

9. Simonsen & Semones. Agency radiation requirements and overview of radiation risk. Internal NASA 

document.

10. Matthia, D., Meier, M.M., and Reitz, G. Numerical calculation of the radiation exposure from galactic 

cosmic rays at aviation altitudes with the PANDOCA core model. Space Weather, 12(3): 161-171.

11. Artemis, meet ARTEMIS: Pursuing Sun Science at the Moon. (Oct 7 2019). 

https://www.nasa.gov/feature/goddard/2019/artemis-meet-artemis-pursuing-sun-science-at-themoon

12/05/2023

Rev F 15