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Closed Ecosystems in Space

Published onSep 23, 2018
Closed Ecosystems in Space

Since the beginning of time, man has dreamed of living among the stars.

Unfortunately, space is a very inhospitable environment for man. Space travelers face radiation, extreme temperatures, and a vacuum that would boil the blood in their veins if not for the protection of a space suit. Clever engineering has yielded decent solutions to all of these problems. Unfortunately, other challenges, such as providing food, water, and oxygen without requiring frequent supply missions, have not been solved.

One potential solution is to construct space vehicles that act as closed ecosystems, recycling waste and carbon dioxide into nutrients and oxygen. Such systems are well-studied on Earth but on-orbit demonstrations have been few due to the high cost, technical difficulty and risk associated with launching and maintaining such a system in a space environment. CubeSats, which are lower cost and more risk tolerant than traditional satellites, may offer an opportunity to increase the number of such experiments.

Achieving this goal will require a simplified model ecosystem which includes all the organisms necessary to be self-sustaining for months or years on end. Such an ecosystem can be found in the form of the EcoSphere™, a desk toy consisting of bacteria, algae, and Halocaridinia Rubra shrimp in a snowglobe-sized glass sphere. These organisms are sealed in the sphere with no possibility for mass exchange between the internal environment of the EcoSphere™ and the surrounding environment, and represent a balanced ecosystem with the algae producing O2 from CO2 and serving as a food source for the shrimp and the bacteria breaking down the shrimp’s waste products into inorganic nutrients which fertilize the algae.

The flow of nutrients and waste products inside the EcoSphere.

There are several challenges and potential show-stoppers that must be addressed before designing a satellite to carry an EcoSphere™ into space. Specific challenges include surviving the vibration environment of launch, maintaining the inhabited capsule at within the survivable temperature range of all the organisms it contains, and monitoring organism populations in the capsule without mass transfer across the capsule boundary. These challenges have already been addressed through analysis and experimentation as part of a previous project (write up forthcoming). There exists one issue that analysis, simulation, and experimentation on Earth does not seem to be able to answer.

An EcoSphere. The air bubble at the topic is plainly visible.

The EcoSphere™ is not completely full of water and must contain a bubble of air to serve as a reservoir for O2 and CO2. The concern has been raised that in a microgravity environment, the shrimp may find themselves trapped in this air bubble and may not survive as a result.

This is where zero gravity testing comes in. It is my hope to fly an EcoSphere on the 2019 MIT Media Lab zero gravity flight. The EcoSphere would be instrumented with an array of camera which would record the behavior of the water and shrimp inside the EcoSphere when in microgravity. If microgravity testing indicates that the shrimp would not become trapped in an air bubble, the next step for this project would be the development of a CubeSat capable of hosting an EcoSphere™ in LEO (Tentatively named ShrimpSat of the International Shrimp Space Station if an international collaborator can be found). A successful mission would offer the potential for low-cost experimentation with and advancement of closed ecosystems in a space environment and bring biological experimentation in space within reach for most university small satellite programs.

A CAD rendering of an EcoSphere as a payload in a 3U CubeSat

Over the next two weeks or so, my efforts will be concentrated on:

  • Identifying suitable cameras and lenses for documenting the experiment

  • Think about how to mount the cameras and CAD a prototype

  • Investigate whether there is value in being able to rotate the EcoSphere to simulate spacecraft motion during deployment

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