Abstract
The Tanpopo experiment was the first Japanese astrobiology mission on board the International Space Station. It included exposure experiments of microbes and organic compounds as well as a capture experiment of hypervelocity impacting microparticles. We deployed three Exposure Panels, each consisting of 20 Exposure Units that contained microbes, organic compounds, an alanine UV dosimeter or an ionizing radiation dosimeter. The three Exposure Panels were situated on the zenith face of the Exposed Experiment Handrail Attachment Mechanism (ExHAM) that was pointing in zenith direction toward space, which was attached on a handrail of the Japanese Experiment Module (Kibo) Exposed Facility (JEM-EF) outside the International Space Station. The three Exposure Panels were one by one retrieved and returned to the ground after approximately 1, 2, and 3 years of exposure to the space environment. Capture Panels, each of which contained one or two blocks of amorphous silica aerogel, were exposed to collect hypervelocity impact microparticles. Possible captured particles may include micrometeoroids, human-made orbital debris, and natural terrestrial particles. Each year, Capture Panels containing from 11 to 12 aerogel blocks were attached to the three faces of the ExHAM (pointing to zenith, ram, and port); they remained in place for about 1 year and were then returned to the laboratory. This process was repeated three times, in total, during 2015-2018. Additional exposure of a Capture Panel facing ram was conducted between 2018 and 2019. Once the aerogel blocks were returned to the laboratory, they were encapsulated in dedicated transparent plastic cases and optically inspected by a specially designed microscopic system. Once located and recorded, hypervelocity impact signatures were excavated one by one and distributed for further detailed analyses. The apparatus, operation, and environmental factors of all the Tanpopo experiments are summarized in this article.
Highlights
The Tanpopo experiment, named after ‘‘dandelion’’ in Japanese, was the first Japanese astrobiology mission on board the International Space Station
The three Exposure Panels were situated on the zenith face of the Exposed Experiment Handrail Attachment Mechanism (ExHAM) that was pointing in zenith direction toward space, which was attached on a handrail of the Japanese Experiment Module (Kibo) Exposed Facility ( JEM-EF) outside the International Space Station
There is a gaspermeable filter underneath the sample so that it is exposed to the vacuum of the space environment, allowing the air inside the Exposure Units (EUs) to escape during space exposure
Summary
The Tanpopo experiment, named after ‘‘dandelion’’ in Japanese, was the first Japanese astrobiology mission on board the International Space Station. The possibility of organic compounds produced in space successfully being transferred to Earth via micrometeorites was tested, and organic compounds were exposed in space to estimate denaturation Another experiment was designed to capture intact microparticles and to estimate the average density of microbes at the cruising altitude of the International Space Station (ISS). Hypervelocity impacting microparticles were captured intact and are being analyzed to determine if any organic molecules are present These objectives are reviewed in an accompanying article (Yamagishi et al, 2021). We designed original Capture Panels (CPs), each of which contains one or two aerogel blocks approximately 100 · 100 · 20 mm size for intact capture of hypervelocity impacting microparticles These apparatuses used in the Tanpopo experiments are explained and the environmental conditions of space exposure are summarized below
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