For experiments with biological samples, such as plants, the drop tower has become more attractive in recent years as fast molecular readouts, such as phosphoproteomics and secondary messenger signaling that play a role during the first seconds of a microgravity response, came more into focus. The major constraints are the short time and the up to 50 g of landing acceleration, which does not make drop towers suitable for every experimental hardware. With 6,000–10,000€ per drop, it is one of the cheapest microgravity platforms and the turnaround time of 2–3 drops per day widely surpasses that of other platforms. The free fall in the vacuum tube of a drop tower generates up to 5 s of exposure to high-quality microgravity or up to 10 s when a catapult is used to propel the experiment into the drop tower. is by far the most expensive low-gravity platform to perform experiments, but is a unique experimental platform for microgravity research. These experimental platforms differ in their time of microgravity provided, the mode of operating the hardware, the quality of microgravity, and the price (Fig 1, Table 1). A drop capsule in free fall, a plane during a parabolic flight, a sounding rocket, or a satellite creates a centrifugal force, which compensates the gravitational pull of the Earth with residual acceleration forces in the range of 10 −2–10 −6 g. Only free fall can achieve real microgravity. However, these platforms only provide what we call simulated microgravity and not real microgravity, and, depending on the biological system that is studied, the interpretation of results might be challenging. Over time, more sophisticated tools, such as clinostats and random positioning machines, were developed. Instead, scientists had to rely for a long time on changing or randomizing the gravity vector by turning plants from a vertical into a horizontal position (gravitropic stimulus), or by using centrifuges (hypergravity). When Charles Darwin published his first work on plant tropisms in 1880, he or his fellow researchers did not have the opportunity to perform experiments in real microgravity. Facilities to conduct experiments in simulated or real microgravity To compare space-based microgravity research and to highlight this unique environment, we take a look at some other facilities that are used to provide a low-gravity environment for research and at their costs and constraints. In this article, we look at the socioeconomic aspects of this research and the impact it had in recent years and will have in the future, and at the costs equated to other, equally ambitious research projects. Recently published review articles have summarized the achievements of decades of plant research in microgravity (see Further Reading). Now, 150 years later, a human-inhabited satellite, the International Space Station (ISS), has become a reality and plant research is one of the numerous scientific disciplines that is being studied there. He already foresaw two aspects of space facilities: their dependency on sustainable food supply and their astronomical price: The Brick Moon required 12 Mio bricks and cost US$250,000, an astronomical sum by the time he wrote his story. Hale described how the low gravity on board enabled plants to evolve at high speed, providing the inhabitants of the Brick Moon with plenty of food. “The Brick Moon” by Edward Everett Hale, published in 1869 in the Atlantic Monthly, is the first science fiction story of an artificial satellite.
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