Cosmic radiation poses a major health risk to people in space. Its effect on the human body is a crucial and potentially limiting factor for planned future long-term manned missions in space. In order to more accurately characterise this radiation risk and devise possible protective measures, the German Aerospace Center (Deutsches Zentrum für Luft- und Raumfahrt; DLR) will send the Matroshka AstroRad Radiation Experiment (MARE) as part of the NASA Exploration Mission 1 (NASA EM-1) in 2020 to the Moon, over 50 years after the first lunar landing. The MARE experiment will mark the first time that two female radiotherapy phantoms – both fitted with radiation detectors and one with a radiation protection vest – are sent on a space flight.
The European Service Module (ESM) for NASA’s Orion spacecraft arrived in the United States at the beginning of November. The two phantoms, Helga and Zohar – equipped by DLR – will sit in the passenger seats during Orion's first flight to the Moon in 2020. The two phantoms – anatomically correct analogues of human torsos manufactured by CIRS, Norfolk, Virginia from tissue-equivalent materials of variable realistic density spanning the entire range of bone, soft tissue and lungs – are each made up of 38 slices. They represent two female astronauts and are equipped with over 5600 passive dosimeters and 16 active detectors that will detect and measure the radiation during the flight. The only difference between the 'twins' is that Zohar will be wearing a radiation protection vest (AstroRad), while Helga will not. DLR, which is carrying out MARE together with the Israeli Space Agency (ISA), its Israeli industry partner StemRad, Lockheed Martin and NASA, is currently fitting sensors to the two phantoms in Cologne. "This will be the first time that the level of radiation to which astronauts are exposed during a crewed flight to the Moon is measured with such precision," says Thomas Berger, Scientific Lead of the MARE experiment at the DLR Institute of Aerospace Medicine.
The phantoms are 95 centimetres tall. Their interiors contain organs and bones made of tissue-equivalent plastics with varying densities. "Helga and Zohar are being used to simulate a fully representative adult female body,” says Berger. "We chose female phantoms for our experiment because the number of women astronauts is increasing.” He and his team already measured radiation in space during the Matroshka experiment – a male phantom that was exposed to radiation both inside and outside the International Space Station (ISS) from 2004 to 2011. DLR is also currently measuring the level of radiation exposure within the European research laboratory Columbus, as part of the DOSIS 3D experiment. "In space, astronauts are exposed to a number of risks, such as the effects of microgravity, psychological aspects and above all the possible long-term damage caused by galactic cosmic radiation as well as the short-term radiation impact of a solar particle event."
Equipment fitted with thousands of detectors
The two 'passengers' are now being prepared for the MARE experiment at the DLR Institute of Aerospace Medicine. On the one hand, 1400 sensor locations are fitted with small passive dosimeters consisting of crystals. Secondly, the sensors of the active detectors are integrated into the most radiation-sensitive organs of the body – lungs, stomach, uterus and bone marrow. While the passive dosimeters will continuously measure and record the total radiation dose from launch until return to Earth, the active, battery-operated detectors will be switched on during launch and then record radiation exposure in a time-resolved manner. "We will therefore be able to read the various detectors and evaluate the data acquired during the mission upon the return to Earth."
Measurements with and without a radiation protection vest
The data acquired by 'unshielded' Helga will also help determine the effectiveness of the novel radiation protection vest (AstroRad) developed by the industry partner StemRad, which is sponsored by the Israeli Space Agency (ISA). AstroRad will cover the upper body, as well as the uterus and blood-forming organs, and be worn by the Israeli phantom Zohar during the entire flight. By comparison, it can then be determined to what extent the vest will protect an astronaut against harmful radiation.
Before the up to 42-day flight to the Moon and return to Earth can begin, Helga and Zohar must still undergo some more tests. During an initial test at the DLR Institute of Space Systems in Bremen, Helga was subjected to the vibrations that she will experience during the flight of the Space Launch System (SLS) currently being developed by NASA. A preliminary check will be performed in the US next spring to determine how Helga and Zohar will be attached to the passenger seats in the Orion capsule. It will test how the phantoms will sit on the seats in the Orion capsule that have been built and adapted for them at DLR.
MARE's complexity and international collaboration involving numerous universities and research institutions in Austria, Belgium, Poland, Hungary, the Czech Republic, Greece, Switzerland, Japan and the US makes it the largest experiment to determine radiation exposure for astronauts ever to leave near-Earth orbit. It will provide fundamental data for assessing the radiation risks during future crewed flights to the Moon.