Status Report

NASA Lessons Learned: ISS Program/Radiation Exposure/Effects on Crew

By SpaceRef Editor

October 3, 2003

Filed under ISS, NASA Public Lessons Learned System (PLLS) Database, Space Physiology and Medicine, US

PLLS Database Entry: 1071

Lesson Info

Lesson Number: 1071
Lesson Date: 01-feb-1998
Submitting Organization: HQ
Submitted by: David M. Lengyel

Subject/Title/Topic(s):

International Space Station (ISS) Program/Radiation Exposure/Effects on Crew

Description of Driving Event:

Effects of Radiation Exposure on ISS Expedition Crews

Lesson(s) Learned:

Radiation exposures of U.S. astronauts recorded over several MIR missions of 115 to 180 days duration have been approximately 10.67 to 17.20 REM. If similar levels of exposure are experienced during ISS operations, the cumulative effects of radiation could affect crew health and limit the number of ISS missions to which crewmembers could be assigned.

Recommendation(s):

Determine projected ISS crew radiation exposure levels. If appropriate, based on study results, initiate a design program to modify habitable ISS modules to minimize such exposures or limit crew stay time as required.

Evidence of Recurrence Control Effectiveness:

Crew radiation exposure requirements for the primary elements of the United States On-orbit Segment (USOS), including the habitation and laboratory modules, as defined in the Primary Item Development Specifications (Section 3.3.10.3) state the design of these modules shall limit the ionizing radiation dose to crew members to 40 Roentgen equivalent man (rem) Blood Forming Organs (BFO) per year. This requirement was developed in coordination with the JSC Space Radiation Analysis Group and is more stringent than the overall NASA Flight Rule requirement (14-10) of 50 rem BFO per year. This requirement also meets the intent of the Presidential Directive concerning Federal Radiation Protection Guidance for Occupational Exposure (Federal Register Vol. 52, No. 17). Detailed analyses documented in SAIC-TN-96065 (August 1996) and SAIC-TN-9601 (January 1996) indicates that the maximum dose for any location in the USOS is less than 23 rem BFO per year.

Detailed shielding analyses performed by Khrunichev and documented in EN-10-13, Protection from Space Environment (November 1996), indicate calculated values of absorbed dose in the FGB crew-habitable zone range from 16-39 rads/year. Using a quality factor value of 1.4 obtained from NCRP Report No. 98 (Guidance on Radiation Received in Space Activities pg. 45) to convert from rads to rem gives 22-55 rem per year. Based on these analyses and the nominal crew rotation schedule (90 days on-orbit, not to exceed 180 days), ISS concludes that adequate protection is provided to the crew by the shielding and design of the ISS.

In addition, the federal guideline is an exposure of 50 rem BFO per year. The International Space Station requirement is 40 rem BFO per year. Current analysis of USOS predicts maximum exposure of 16 rem BFO per year. Although the actual crew exposure level will be monitored with actual flight data, the ISSP concludes that no redesign is necessary to consider increased shielding requirements.

Technical Reference: Letter from Boeing Environments Team dated February 12, 1998

Applicable NASA Enterprise(s):