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Space Radiation Environment Measurement Program

Outline Outline of On board Devices
Major Accomplishments in Past Flights for Space Radiation Measurement
What is Space Radiation?

The National Space Development Agency of Japan (NASDA) has been engaged in execution of a Space Radiation Environment Measurement Program using a space shuttle. Its purpose is to evaluate the effects of space radiation over the on-orbit environment inside a pressurized module (inside the spacecraft filled with the air of 1 barometric pressure, the same as the condition on the ground).
A Real time Radiation Monitoring Device (RRMD) and a Bonner Ball Neutron Detector(BBND) will be flown on board a space shuttle which is to fly on the scheduled orbit of the International Space Station. A total of 4 mission flights have been planned for this program during the period between September 1996 and May 1998.

Outline of On board Devices
RRMD can conduct real-time measurement of the time and direction of incidence of high-energy radiation particles striking into a pressurized module, as well as real-time identification of the kinds of these particles. It can also transmit these data to the ground. RRMD consists of Detector Unit, Sample Holder, Control Unit and Data Recorder.
The Detector Unit is divided into two types, viz., Type II which is primarily used to measure heavy particles from carbon to iron, and Type III which is primarily used to measure light particles from proton to carbon.
RRMD Detector Unit (Type II)
The Sample Holder, which is used to store such biological specimens as colitis germs, is set in the Detector Unit.
RRMD Sample Holder
The Control Unit possesses such functions as measurement signal processing and measurement control.
RRMD Control Unit
The Data Recorder is used to record data in the South Atlantic Anomaly (SAA) zone where a larger amount of measurement data can be obtained than in any other zones.





The ratio of neutron in the total space radiation striking into spacecraft is considered to be about 20%. Real-time environment measurement of neutron energy spectrum has not been made up to today. BBND is a real-time neutron spectrum measurement device developed to establish a radiation exposure control system vital for the forthcoming manned space activities aboard the International Space Station, as well as to verify predicted values by on-orbit neutron environment measurement. This device can measure neutron energy in the range of 0.25eV `10MeV.
Measurement of neutron spectrum by BBND will be conducted on board Space Shuttle STS-89.

Major Accomplishments in Past Flights for Space Radiation Measurement

First International Micro gravity Laboratory (IML-1; January 1992)
First Material Processing Tst (FMPT; September 1992)
Second International Microgravity Laboratory (IML-2; July 1994)

On IML-1 and FMPT, the amount of space radiation inside the space shuttle was measured using a plastic track detector and a thermoluminescent detector. As a result, the level of radiation was found to differ according to such flight conditions as orbit or time element (solar activities).
On IML-2, RRMD was carried by a space shuttle for the first time. This device is able to conduct real-time measurement of the direction and time of incidence of radiation particles, as well as real-time identification of the kinds of these particles. The measurement results obtained on this mission were compared with those obtained using the above-mentioned detectors of IML-1 and FMPT. It was found that both results are well consistent with each other.
The said three missions also conducted an investigation on the effect of space radiation over such biological specimens as bacteria and cell. As a result, it was revealed that when one of the repair functions of the damaged DNA is crippled, the intensity of this effect becomes bigger in outer space, and that the repair efficiency of the DNA damaged by pre-irradiation on the ground rises higher under micro gravity.

STS-79 (September 1996)
Space radiation measurement was conducted by RRMD aboard STS-79 on the scheduled orbit of the International Space Station. Of radiation particles, those which are heavier than carbon were selected as objects of priority measurement of radiation doses. As a result, it was found that the absorbed dose rate in the South Atlantic Anomaly (SAA) zone is far much more higher than those in other zones, and that the incidence of high-energy space radiation increases at the time of passage above the polar proximity zone.
An experiment was also conducted on the biological effect by space radiation using such specimens as colitis germs and genetic DNA. The finding of this experiment reconfirmed the experiment result obtained on the FMPT mission to the effect that a specific ferment activator is required for repair of DNA damages by space radiation.

STS-84 (May 1997)
Space radiation measurement was conducted by RRMD aboard STS-84 on the same orbit as STS-79 orbited. On this mission, an investigation was made on low-energy particles, in consequence of which it was revealed that most of these particles were concentrated in SAA.
As for the biological effect by space radiation, an experiment was made using such specimens as silkworm eggs, dicty ostelium discoideums, colitis germs, radiation-resistant bacteria, and genetic DNA. At present, analyses are under way to elucidate the bodily reaction mechanism of these specimens vital for DNA repair by space radiation, the effect of the space environment over their embryonic development and differentiation, and the genetic effect exerted over the silkworm's offsprings during the process of their growth in space.

What is Space Radiation?

All kinds of atomic nucleus constituents of protons, electrons and positrons are scattered by the energy originating from the solar flare or the explosion of supernovas (fixed stars) in or around the Galaxy. The high-energy radiation consisting of these constituents are called Space Radiation or Cosmic Radiation. Cosmic ray is classified into three types with difference in originating source or domain, viz., solar cosmic ray, galactic cosmic ray and extragalactic cosmic ray.
If astronauts or biological specimens on board the Space Station, etc. are exposed to these space radiation particles for a long time, it could result in producing skin cancer or harmful effects on their genes. However, reality is that the duration of human stay in space is foreseen to become longer and longer. Thus, the continuous research on biological effects by space radiation and the establishment of effective radiation exposure control system is of paramount importance.

Experiment Themes


Name Themes Flight No.
79 84 89 91
Tadayoshi Doke (Waseda University)
Real-time Measurements of Dose Equivalent for Space Station O O O O
Takeo Goka (National Space Development Agency of Japan) Real-time Measurement of the Low Energy Range Neutron Spactral - - O -
Kazunobu Fujitaka (National Institute of Radiological Sciences) Organ Dose Measurments using a Phantom Torso - - - O
Hiroshi Watanabe (Japan Atomic Energy Research Institute) Effect of Space Environment on DNA Repair O - - -
Kazuki Harada (PL Gakuen Women's Junior Collage) Study on the Effect of Space Environments on Escherichia coli Mutant Cells O O - -
Toshiharu Yoshizawa (Kyoto Institute of Technology) Effect of Space Radiation on the Embryonic Development and Differentiation of the Silkworm, Bombyx mori - O - -
Takeo Ohnishi (Nara Medical University) Biological Effects by DNA Damage in Dictyostelium discoideum - O - -
Analysis of DNA Damage by Space Radiations - - O -
The Effects of Microgravity Environment on Mutation Frequency - - O -
The Effects of Microgravity on Repair Activity of DNA Damage - - - O
Fumihiko Tomita (Communication Research Laboratory) Synthetic Analysis of Space Radiation Environment Data O O - O
Synthetic Analysis of Space Radiation Environment Data - - O -
Masahiko Hirano(Toray Research Center) Cosmic Radiation Effects for Eukaryotic Cells - - O -
Hiroshi Yasuda(National Institute of Radiological Sciences) Dose Equivalent Analysis for Space Radiation Quality by Integrating Solid Dosimeters - - O -
Yasuhiko Kobayashi(Japan Atomic Energy Research Institute ) Effects of Space Environment on DNA Repair - - - O

(NOTE) As for the themes to be taken up for implementation on board STS-91, NASDA is currently under consultation with NASA.

Last Updated : January 23, 1998


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