International Space Station
The International Space Station (ISS) is a habitable artificial satellite, in low Earth orbit with an altitude between 330 and 435 km. The ISS consists of pressurised modules, external trusses, solar arrays and other components. Launched in 1998 and having more than 15 years of continuous human presence on board, it allows unlimited microgravity time for scientific experiments. The station has been built with the participation of NASA for the US, ESA for Europe, JAXA for Japan, Roscosmos for Russia and CSA for Canada.
The ISS is an in-orbit scientific lab with experiments running mainly in Life Science and Physics (material science, fluid physics, astrophysics…) but also in other domains such as technology testing.
ISS as a Life Science Research labThe ISS capacities have been used a lot for life science experiments. At first research was focused on understanding the effect of microgravity and space on the human body and plants in order to pursue further space exploration. Then experiments have allowed significant discoveries in many areas of biology with on ground applications. The long duration of microgravity has allowed studies in numerous fields of interest for pharmaceutical, cosmetic and biotech companies. These fields include stem cell proliferation and viability, tissue engineering, drug screening capabilities, protein crystal growth. On other topics there have been studies on plants, insects and other organisms.
The different racks dedicated to life science give access to different types of incubators, glove box, freezer and centrifuge (for 1g reference) allowing a large variety of experiments to be run.
ISS as a Physics Research labIn the ISS, some racks are dedicated to physical sciences and enable, for example, the production of high quality optical fiber and semiconductors. The Fluid Science Laboratory has also made possible the study of the behavior of liquids in microgravity with applications in the cleaning of oil spills or the improvement of metal manufacturing. Studies on alloys have been made possible by the development of special furnaces and compact Xray machines (for non-destructive testing). In microgravity conditions, sedimentation and buoyancy effects become negligible. It makes some phenomenon such as combustion more stable and therefore easier to model in these conditions.
The external platforms on the ISS allow the exposure of material and technology to outer space.
By following a parabolic flight path, the aircraft gives its occupants the sensation of weightlessness. During a given amount of time (depending on the aircraft type), towards the top of the parabola, the aircraft is free-falling with its payload. During this time the aircraft does not exert any ground reaction force on its contents, causing the sensation of weightlessness. In addition to allowing future astronauts to train in microgravity conditions before going to space, many experiments are run in such flights. The microgravity time is sufficient for some experiments in physics and in biology. The parabolic flight has the advantage of allowing the scientist on board and giving the possibility to repeat the experiment up to 30 times per flight. This allows to test many parameters and get sufficient statistical data for analysis.
Parabolic flights for Life Science experimentsIn some cases, biological changes can be observed within a few seconds of exposure to microgravity. In these cases, parabolic flights are the perfect platform to run the full experiment and easily repeat it in order to collect enough data for analysis. Such experiments can be linked to gene expression and studies of some effects on cells such as T-cells. In other cases, the flight allows to test experiment material before going on longer missions on the International Space Station for example.
Parabolic flights can also be very useful to run experiments directly on any human subjects. Indeed, a simple medical form is sufficient to fly, without any training requirements.
Parabolic flights for Physics experimentsMany physics experiments are run on parabolic flights with subjects linked to fluid and material science. The time of microgravity on a parabolic flight is sufficient to study cavitation effects or combustion for example. On such a flight, it is possible to use relatively large and heavy experiment set-ups. With the presence of the experimenter interacting directly with its experiment, it is possible to adapt during the experiment.
The parabolic flight can be sufficient for physics experiments. When it is not the case, it is still often used to make sure the experiment works before it is sent to the International Space Station.
Most drop towers function in the same way, with the experiment placed in a capsule which falls in a vacuum tube. As the capsule is free falling in vacuum, everything contained inside is in microgravity. Measurements can be taken during the fall, upon impact or after, duration of microgravity is typically between 2 and 10 seconds.
Drop towers can be used for experiments requiring very short time of microgravity and no human presence. A majority of the experiments are therefore in physics, fluid physics in particular. For these experiments, the drop tower has the advantage of being able to relaunch the experiment very quickly in order to multiply the amount of results obtained.
Simulating Microgravity – Random Positioning Machine
By connecting a container to two independent axes, which are then rotated with random speeds in all directions, the random position machine (RPM) allows to simulate microgravity. Due to the random motion, the sample experiences gravity from every direction. Thus, after some time the average of the gravity affecting the sample goes to zero. In this way, the random positioning machine simulates microgravity for objects inside its container. This is sometimes also referred to as 3D clinostat.
These machines are also capable of simulating ‘partial gravity’. This provides all gravity levels from 0g up to 0.9g. Partial gravity is achieved by changing the random motion pattern in such a way that, on average, the sample experiences some influence of Earth’s gravity. It is used for simulating e.g. the 0.38g Mars’ gravity or 0.17g Moon’s gravity, but also for determining e.g. the gravity level at which organisms or cells change behavior.
This type of machine is mainly used for research in life science with applications in cell biology, microbiology, regenerative medicine, tissue engineering and stem cell research.