Thus, flight missions are crucial for gaining essential insight into how biology will fare in such a unique and hostile environment. However, even facilities that model GCRs by consecutively exposing biological samples to single, high-energy particles cannot overlap both radiation and microgravity to mirror the conditions of space. Attempts to model the space environment are limited to particle accelerators and single-element radiation sources to simulate cosmic radiation, and rotating wall vessels or similar instruments to simulate microgravity.
Unfortunately, it is nearly impossible to mimic the complex conditions of space using facilities on Earth. Additionally, many bacteria have been shown to display increased virulence and antibiotic resistance when exposed to the space environment. For example, in plants, a cellular-level phenomenon called gravitropism causes roots to grow downward, but in space, their roots grow randomly. Reduced gravity can have effects at the subcellular level as well, affecting gene expression and cell growth pathways. Microgravity also induces health risks such as muscle atrophy and bone density loss in humans. Ionizing radiation causes damage to biology through several means, including direct DNA damage like double-strand breaks and indirect damage such as that caused by reactive oxygen species. Beyond the Earth’s magnetosphere, biology will be exposed to a constant, low-flux shower of high-energy ionizing radiation, such as that from galactic cosmic rays (GCRs) and solar particle events (SPEs).
The deep space environment is characterized by ionizing radiation and reduced gravity, both of which can have detrimental effects on biology. Since then, long-duration missions have been confined to LEO, such as those to the International Space Station (ISS). The last time NASA performed space biology experiments beyond low Earth orbit (LEO) was during the Apollo 17 mission in 1972. The goal of this Perspective is to provide a brief introduction to examples of past and current technologies in space biology research, and how they influence the development of biosensor technologies for future missions to deep space. This goal is unachievable unless we can ensure the safety and health of the astronaut crew and other terrestrial biology on those missions. NASA currently has plans to return humans to the Moon and eventually land crewed missions on Mars. They will utilize biosensors that can better elucidate the effects of the space environment on biology, allowing humanity to return safely to deep space, venturing farther than ever before. Several have been deployed in LEO, but the next iterations of biological CubeSats will travel beyond LEO.
CubeSats also provide a low-cost alternative to larger, more complex missions, and require minimal crew support, if any. Small satellites such as CubeSats are capable of querying relevant space environments using novel, miniaturized instruments and biosensors. However, given the constraints of the deep space environment, upcoming deep space biological missions will be largely limited to microbial organisms and plant seeds using miniaturized technologies. These LEO missions have studied many biological phenomena in a variety of model organisms, and have utilized a broad range of technologies. Although many biological experiments have been performed in space since the 1960s, most have occurred in LEO and for only short periods of time.
In light of future missions beyond low Earth orbit (LEO) and the potential establishment of bases on the Moon and Mars, the effects of the deep space environment on biology need to be examined in order to develop protective countermeasures.
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