The return to the Moon is just around the corner. The launch window opens for NASA's Artemis I mission opens this Wednesday, 16 November 2022, at 07:04 (CET). After several postponements, it is now set to go – taking humankind back to the Moon almost exactly 50 years after the last Apollo flight in December 1972. On board are the #LunaTwins of the German Aerospace Center (Deutsches Zentrum für Luft- und Raumfahrt; DLR). The two astronaut phantoms, Helga and Zohar, of the MARE experiment will measure the cosmic radiation on the journey to the Moon and back. Both phantoms endured the waiting time prior to launch well thanks to a sophisticated power-saving strategy. A flight lasting approximately 26 days now lies ahead of them. The Orion capsule containing the#LunaTwins is expected back on Earth on 11 December 2022.
"Helga and Zohar are fit for flight," says Thomas Berger from the DLR Institute of Aerospace Medicine. "We planned for the possibility of a longer waiting time prior to launch, and both mannequins are also designed for the long flight time lasting several weeks." Once the new SLS heavy-lift rocket launches the flight test on schedule tomorrow from NASA's Kennedy Space Center in Florida, an extensive flight programme will begin. This will involve the Orion spacecraft, with the two mannequins on board, entering lunar orbit and travelling up to half a million kilometres from Earth – further than any spacecraft fit for a human crew has ever flown. "During this journey, the radiation levels will be significantly higher than on Earth or even on the International Space Station. The MARE experiment will be the first to comprehensively record exactly how much higher," Berger continues.
Passive and active radiation sensors
The two measuring mannequins are modelled on the female body, including reproductive organs, in order to measure the radiation dose experienced by organs that are particularly sensitive to it. The female astronaut phantoms, each consisting of 38 slices, are 95 centimetres tall and weigh 36 kilograms. Zohar weighs 62 kilograms when taking into account the AstroRad radiation protection vest that will be tested during the flight. Inside the two phantoms are organs and bones made of tissue-equivalent plastics that mimic the varying density of bones, soft tissue and lungs. More than 12,000 passive radiation detectors made of small crystals have been installed in these ‘organs’ and on the mannequins’ surfaces, as well as 16 active detectors from DLR in the body's most radiation-sensitive organs – including the lungs, stomach, uterus and bone marrow. The passive radiation measuring devices (dosimeters) do not require any current, measure continuously and thus provide a value of the total radiation exposure throughout the entire mission. By reading out the crystals, a three-dimensional image of the human body is created, revealing the total radiation exposure to different parts of the bones and organs during a lunar flight.
The active, battery-operated detectors integrated in the two phantoms will record the radiation exposure with a temporal resolution of five minutes. This will allow the researchers to understand under which conditions and during which phases of the mission radiation exposure affects the body parts. To account for the possibility of increased waiting time prior to the launch of Artemis I, a particularly ingenious power-saving method was implemented for the DLR detectors. "Our active radiation detectors, called M-42, are in a type of sleep mode prior to launch, requiring almost no power from the batteries," explains DLR researcher Thomas Berger, who is leading the MARE experiment. "Only at launch do acceleration sensors activate the devices and the radiation measurements begin."