Microgravity

What is microgravity?

Gravity

Everything is subject to gravity. On earth, gravity gives weight to objects and therefore determines almost all physical, chemical and biological phenomena.

Microgravity

In microgravity or weightlessness, since there are no contact forces upon the object, the gravitational pull does not exert any resulting force.

Free fall

Humans found a trick to experience microgravity on earth: free fall.

So if you are in an elevator with a broken rope, you would experience microgravity inside the falling elevator.

How to produce microgravity

To produce microgravity on Earth, we need to produce free falling conditions. Here are the options we have:

1. Drop towers

A drop tower is a tower in which you drop objects from the top. While the objects are in free fall (in a vacuum), they experience microgravity.

Pros:

  • Excellent quality of microgravity (10-6g)
  • Access shortly before and after drop
  • Quick turnaround time
  • Reduced safety requirements
  • Low cost

Cons:

  • Very short microgravity duration (5-10 seconds)
  • High forces while landing

2. Parabolic flights

Parabolic flights are performed by specially equipped airplanes that climb with a very high angle, before dramatically reducing their thrust. Therefore, the plane “falls” freely along a parabolic trajectory.

Pros:

  • Short time between application and performing an experiment
  • Relatively gentle launch and landing
  • Large experiments possible
  • Scientists can fly with their experiment
  • Low cost

Cons:

  • Quality of microgravity is lower (10-2g)
  • Short continuous microgravity duration (20 seconds)

3. Suborbital spaceflights

In suborbital spaceflights a spacecraft (mostly a rocket) is launched to the boundaries of space (beyond the so-called karman line at 100km altitude) and falls back to Earth.

Pros:

  • Short time between application and performing and experiment
  • Relatively gentle launch and landing
  • Lower cost than orbital
  • Very late access to rocket before launch

Cons:

  • Microgravity duration still comparably short (5-10 minutes)

4. Orbital spaceflights

In orbital flights, a spacecraft is launched into space and accelerated so fast that it does not fall back down to Earth, but literally falls around Earth. Imagine standing on a fictional very high mountain (with no atmosphere) and throwing a baseball so fast that it does not land on the ground, because the ball’s trajectory matches up exactly with the curvature of the planet and therefore is in free fall forever. This is called “launching something into orbit”.

The most prominent example for an orbital platform is the International Space Station (ISS). Also, every satellite is an orbital platform. In addition, many more so-called free-flyers will be orbiting Earth in the near future. These are independent capsules (like the SpaceX Dragon Capsule) or spacecrafts (e.g. the Sierra Nevada’s Dream Chaser) orbiting Earth.

Pros:

  • Nearly endless microgravity (ISS is in orbit since two decades)
  • More space (in case of ISS)
  • Interaction with astronauts possible

Cons:

  • Still very expensive
  • Longer time between experiment setup and start of microgravity

5. Artificial Microgravity Simulators

In addition to free fall, there are machines that can at least partly simulate the effects of microgravity. The most common examples are Clinostats and Random Positioning Machines.

A Clinostat is a device that uses rotation to negate the effects of gravitational pull on biological samples. Through the rotation the cells or plants experience a gravitational pull that is averaged over 360 degrees, thus approximating a weightless environment.

A Random Positioning Machine, or RPM, rotates biological samples along two independent axes to change their orientation in complex way thereby eliminating the effects of gravity.

Pros:

  • Shortest time between application and performing an experiment
  • Can be done in a lab 24/7
  • Near endless duration
  • Very low cost

Cons:

  • Not real microgravity
  • Very little experiment volume

Why do research and manufacturing in microgravity

Research in microgravity helps to understand the inner workings of biological and physical systems and therefore enables advancements in pharmaceutical development, bio technology, agriculture and material science. The unique properties of the microgravity enviroment even allow better manufacturing of certain materials, such as more efficient fiber cables.

Systems and processes affected by microgravity:

Surface wetting and
interfacial tension

Multiphase flow
and heat transfer

Fire and
combustion

Solidification

Changes in
organisms

Benefits for Life Sciences

Growing cell cultures in three dimensions

Unlike on Earth, where cells mostly lie flat on the bottom of a petri dish, they form complex 3D structures in microgravity —similar to tissues in the human body— offering a more effective model for studying behavior of cells, advancing regenerative medicine, and testing the effects of new drugs against e.g. cancer or osteoporosis.

Modeling human diseases

Microgravity leads to immune dysfunction, bone loss, cardiovascular deconditioning and loss of skeletal muscle. These body responses mimic outcomes linked to aging and attenuating chronic human diseases on Earth. Thus, microgravity helps analyzing and testing of therapeutics in accelerated models of aging or disease.

Analyzing proteins and large molecules

The structures of proteins and other large molecules define how they work. Crystallization is a crucial method for studying macromolecular structure. Many molecules form larger and better organized crystals in microgravity, which helps scientists study the functions of molecules important for health and disease— e.g. natural proteins and hormones or medicines. Pharmaceutical companies could improve drug design for innovations in drug manufacturing, storage, specificity and efficacy.

Advancing nanofluidics and biotechnology

Microgravity has significant effects on fluid dynamics and helps studying the complex factors linked to biomedical devices involving fluids — especially at nanoscale level, where forces like diffusion are substantial. Microgravity thus helps e.g. to improve drug delivery systems or healthcare diagnostic tools.

Studying plant biology

Microgravity helps understand the inner workings of plants . Gravity-sensing mechanisms within plants are critical to their survival on Earth. Adaptive processes of plants in microgravity help advance studies and agricultural applications such as improved crop yield, increased biofuel production, and development of new varieties.

Benefits for Physical Sciences

Materials science

The fluid dynamics of materials affect the properties of their solidified/crystallized final state — like metal alloys and semiconductors. This enables development of new materials and better manufacturing processes for products on Earth such as building materials and electronics. Also, magnetic field studies on the internal structure of materials carry potential to improve the design of ground structures for better earthquakes resistance.

Complex fluid physics

Microgravity enables insights into the interactions of small particles, such as molecules. Studying how particles move without buoyancy helps better understand the underlying rules that govern their interactions. For instance, studying the way certain fluids move and behave in response to a magnetic field might help improve the design of products such as brake systems, seat suspensions and airplane landing gear.

Fluid dynamics

Buoyancy depends on gravity and is absent in microgravity. This allows scientists to study underlying causes of fluid motion (e.g. diffusion, viscosity) that are overshadowed by buoyancy in ground studies. This effect may be critical to improving formulation chemistry for pharmaceuticals, improving nanofluidics technologies for medical devices and enabling new water and energy conservation solutions.

Interfacial phenomena

Some interactions at the interface between a liquid and a solid are easier to study in microgravity. Results from the study of these boundaries are important to understand the growth of bacteria in food-processing industries to avoid bacterial contamination of food. A lack of gravity-induced phase separation might as well allow creation of advanced materials and alloys.

Combustion

Microgravity affects important aspects of combustion such as flame ignition, propagation and quenching. These insights can be used to develop methods to increase efficiency in ground use of combustion processes (including power generation and propulsion) and improve fire safety and environmental impacts of combustion.

In-orbit production

The reduced fluid movement in microgravity also allows the creation of commercially relevant materials, such as optical fibers. Eliminating gravity reduces or eliminates imperfections in crystal lattices, improving transmission capabilities of the fibers and promising broad applications across multiple industries.

Case studies

Watch the exciting research being done in microgravity

SpaceX CRS-19

SpaceX CRS-18

SpaceX CRS-17

SOURCE: ISS NATIONAL LAB