Space Radiation Dosimeter by Free-Space PADLES in ISS JEM Exposed area (Free-Space PADLES) - 10.25.17

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Science Objectives for Everyone
Free-Space Passive Dosimeter for Life-Science Experiment in Space (Free-Space PADLES) is an investigation that uses a Sealed Free-Space Dosimeter to measure radiation doses outside the International Space Station (ISS). The obtained results are used for verification of the ISS hull wall shielding contribution, and a benchmark study to develop existing simulation codes and space radiation models for present, and future, human space flight activities.
Science Results for Everyone
Information Pending

The following content was provided by Aiko Nagamatsu, Ph.D., and is maintained in a database by the ISS Program Science Office.
Information provided courtesy of the Japan Aerospace and Exploration Agency (JAXA).
Experiment Details

OpNom: Sealed area dosimeter

Principal Investigator(s)
Aiko Nagamatsu, Ph.D., Japan Aerospace and Exploration Agency, Tsukuba, Japan

Tsuyoshi Ito, Japan Aerospace Exploration Agency, Tsukuba, Japan
Jun Shimada, Japan Aerospace Exploration Ageny, Japan
Chiemi Matsumura, Tsukuba, United States
Tetsuro Mizuno, JAMSS, United States
Keiichi Kitajo, Japan Aerospace Exploration Agency (JAXA), Japan
Ken Shimada, Japan Aerospace Exploration Agency (JAXA), Japan

Japan Aerospace Exploration Agency (JAXA), Tsukuba, Japan

Sponsoring Space Agency
Japan Aerospace Exploration Agency (JAXA)

Sponsoring Organization
Japan Aerospace Exploration Agency

Research Benefits
Scientific Discovery, Space Exploration

ISS Expedition Duration
September 2014 - March 2016

Expeditions Assigned

Previous Missions
From Increment 17, five experiments using the PADLES system started in 2008. The experiments include: area radiation monitoring in Kibo (Area PADLES), dose measurements of biological samples exposed to space radiation (Bio PADLES), personal radiation dosimetry for Asian crew members (Crew PADLES), various kinds of international cooperative experiments with ISS partners, such as the Matroshka project conducted by the German Aerospace Center in Cologne, the ALTCRISS project conducted by the National Institute of Nuclear Physics (Dosimetric PADLES), and measurement of the directional dependence of radiation doses inside the Kibo module (Experiment PADLES).

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Experiment Description

Research Overview

  • Until now, radiation dose measurements (dosimetery) in the exposed areas outside of the ISS were conducted with a limited number of experiments. Specifically, the distributions in higher linear energy transport (LET) regions were not measured in great detail. In order to measure ISS hull wall shielding contribution and effects, a set of radiation measuring results need to be made simultaneously inside and outside of the ISS. Under the vacuum environment of low earth orbit, the track formation sensitivity for space radiation particles of CR-39 plastic nuclear track detectors, in the PADLES detectors that measure higher LET regions, decreases with a change of internal gas pressure. Therefore the dosimeter cases need to be able to hold an equivalent air pressure inside as to what would be found on Earth (1 atmosphere), with radiation shielding to be as thin as possible in order to evaluate the radiation dose measurement.
  • Free-Space PADLES is intended to fly onboard the ISS to verify the space radiation environment in the outside exposed area, with exclusive dosimeter cases featuring various shielding thickness to estimate the shielding effects for space radiation particles. Free-Space PADLES is launched and returned as a pressurized cargo by Cygnus or Dragon spacecraft, and packed inside a Crew Transfer Bag (CTB). The Free-Space PADLES are installed on the Multi-Purpose Experiment Platform (MPEP) in the JEM Pressurized Module (PM), and then moved outside of the ISS Japanese Experiment Module (JEM) through the JEM airlock. After the Small Satellite Orbital Deployer (J-SSOD) deploys the small satellites, the JEMRMS robot arm moves, and keeps a measurement position for the exposed Free-Space PADLES for up to approximately 2 months. After exposure to the vacuum environment of Low Earth Orbit, the PADLES dosimeters are transported back inside ISS through JEM Airlock, and stored for return to Earth.
  • The dosimetric results obtained by dosimeters are published in JAXA’s PADLES database (, and are used to support the planning of life-science experiments on board Kibo, as well as to modify simulation codes of space-radiation models for future manned space activities beyond the earth.

Information Pending

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Space Applications
Protecting crew members from radiation is a major challenge on the ISS and for future deep-space missions. Free-Space PADLES studies the radiation environment outside of the Kibo module of the ISS, providing important insight into radiation exposure. Results from this investigation, as well as previous PADLES investigations, help engineers design new types of radiation monitoring and shielding for future space exploration.

Earth Applications
The sealed dosimeters in this investigation are used in radiation medicine experiments on Earth as well as for testing of radiation shielding. Workers at high-energy accelerators and other radioactive sources use similar dosimetric methods to measure their radiation exposure. Results from this investigation may lead to new measures to protect workers on Earth from radiation exposure, including at nuclear power plants and in cancer treatment centers.

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Operational Requirements and Protocols
Information Pending

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Decadal Survey Recommendations

Information Pending

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Results/More Information

Information Pending

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Related Websites
ISS Space radiation environment data-base (PADLES-DB)

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