The experimentation phase on board the Eu:CROPIS satellite developed by the German Aerospace Center (Deutsches Zentrum für Luft- und Raumfahrt; DLR) came to an end on 31 December 2019. The compact satellite has been in an orbit around Earth that passes over the north and south poles for over one year. On board are four experiments, of which the DLR-developed RAdiation Measurement In Space (RAMIS) instrument, the NASA PowerCell experiment, and the SCalable On-BoaRd Computing Experiment (SCORE) computer, which was supplied by DLR, have yielded extensive datasets. Unfortunately, the eponymous Eu:CROPIS experiment (Euglena and Combined Regenerative Organic-Food Production in Space) could not be initiated due to a software problem. With this research satellite, DLR tested for the first time a particularly weight-saving compact satellite design with innovative lightweight structures for cost-effective missions.
Radiation measured around the world
The RAMIS radiation measuring device allowed data to be recorded almost all around the world. Two identical measurement devices for recording incident radiation were attached to the satellite's exterior and interior for this experiment, which was devised by the DLR Institute of Aerospace Medicine in Cologne. These measured both changes in Earth's outer radiation belt, which is mainly populated by electrons, and the variation of galactic cosmic rays as a function of orbital position and the shielding provided by Earth's magnetic field. DLR radiation researcher Thomas Berger, who heads the team working on RAMIS, is very satisfied with the measurements: "We have acquired a lot of data from the satellite's interior and exterior with little radiation shielding, allowing us to make a perfect comparison. These data, which have now been available for a year, provides us with a dataset that is almost unique for this orbit and will give us many scientific insights." Among other aspects, the recorded data form the basis for determining the location and intensity of the outer radiation belt, which will primarily be used for verifying radiation belt models.
Bacteria under the gravitational conditions found on the Moon and Mars
The Eu:CROPIS mission has also delivered valuable results for DLR's partner, the US space agency NASA. In the PowerCell experiment, bacteria were able to create biological matter that could also be produced during a stay on the Moon or Mars. Eu:CROPIS generated the gravitational conditions of the Moon and Mars by rotating at different speeds. The Moon’s gravity is 0.16 times that of Earth, while gravity on Mars is 0.38 times Earth’s gravitational attraction.
DLR on-board computer and lightweight construction in space
SCORE is the first on-board computer to be developed by DLR. SCORE and the principle of the scalable COBC (Compact On-Board Computer) were tested in space for the first time during the Eu:CROPIS mission. The on-board computer carried out the image processing for the external cameras located beneath the solar arrays. These checked whether the panels had deployed correctly. The computer is still working reliably under the special conditions found in space. A modular, scalable computer system has the advantage that it can be adapted to the specific requirements of future missions more easily, making the development process more cost-effective and less time-consuming. "In addition to the experiments, we have also built a particularly lightweight, compact satellite which allowed the use of many innovative examples of technologies, such as 3D-printed components and a carbon fibre reinforced polymer (CFRP) pressure tank for the very first time," says Project Leader Olaf Eßmann of the DLR Institute of Space Systems.
Searching for greenhouse solutions
In January 2019, a regular software update resulted in problems communicating with the two greenhouses inside the satellite, which were transitioned into safe mode by the update. Following extensive error analysis and tests on an experimental set-up on Earth, the mission team of engineers and scientists made several attempts during 2019 to resume communications with the experiment. "For example, we rebooted various modules on the satellite, but unfortunately were unable to fix the communications issues," explains Eßmann. The greenhouse part of the Eu:CROPIS mission marked a first step towards testing how biological life support systems could be used as technology for supplying food on long-term missions. Two greenhouses hosting a symbiotic community of bacteria, single-celled algae (Euglena) and synthetic urine as a fertiliser were intended to grow tomatoes under the gravitational conditions found on the Moon and Mars. An attempt at activating the experiment revealed that the greenhouses and their technologies are still functional, but that irrigation cannot be initiated. This means that the tomato seeds and the Euglena, which are currently dormant, cannot be activated. “This is regrettable," says the Principal Investigator of the experiment, biologist Jens Hauslage of the DLR Institute of Aerospace Medicine. "Nonetheless, we can say that the principle works because the ground-based model is functional, and through our work on Eu:CROPIS we have developed a long-term testbed for biological research in space."
Tomatoes for lunar and Mars habitats
Despite the fact that the eponymous experiment could not be activated, scientists from all the institutes involved have learned fundamental lessons for future DLR compact satellites and will use this experience in the design of subsequent missions. Other flight options are currently being explored to implement the biological part of the experiment under lunar conditions. The Eu:CROPIS mission has thus contributed towards generating new insights and given engineers and biologists experience of innovations that can be harnessed in future.
Flexible construction in different sizes
The Eu:CROPIS compact satellite was constructed under the leadership of the DLR Institute of Space Systems in Bremen. The DLR Institute of Composite Structures and Adaptive Systems in Braunschweig developed the spacecraft structure and the pressure tank. Power is supplied via four solar panels, each with an area of one square metre. DLR scientists were able to draw upon their experience of developing standard components for satellites during the preparations for the mission. Depending on the payload, they are able to design and construct satellites of different sizes quickly, cost-effectively and flexibly. This component-oriented design is a unique feature that can be used to support many different research missions. Eu:CROPIS lifted off from Vandenberg Air Force Base in California on 3 December 2018 on board a Falcon 9 launch vehicle. Starting from its relatively low orbit 600 kilometres above Earth, the satellite will gradually lose altitude over the next two decades, and eventually burn up in Earth's atmosphere.
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