The Spring Institute

Overview

Here's what the PLANT-B Mission is all about.

Closed Terrestrial Ecosystem

We are investigating not just one plant or animal, but a whole ecosystem of plants, microbes, and microinvertebrate animals to understand how the space environment impacts communities.
A Custom 3U Cube Satellite

Our small satellite, just 10 x 10 x 30cm, will be inserted into a low-earth orbit similar the one the ISS uses. It will have an orbital period of about 90 minutes.
Passive Light & Thermal Management

A major innovation we propose is the total elimination of the need for life support. Using novel materials and shading techniques, the temperature and light levels will be maintained in a livable range.
Characterize the Orbital Environment

If we want to put ecosystems in space, we have to ensure they function in that environment. If given a controlled environment, can they adapt to the existing light/temperature/gravity conditions?

Introduction

Plant-B is a mission to design and build a 3U cube satellite capable of passively lighting and heating a ~0.7L terrarium for 2-5 years while in orbit around the Earth.

The mission will investigate the unique orbital environment (in terms of light cycle and intensity, radiation, temperature, and microgravity) and observe the behavior of a sealed, self-sustaining terrarium that consists of a multitrophic system of plants and microorganisms (including invertebrate animals and bacteria/fungi).

Despite the massive increase in satellite launch cadence, there is a relative paucity of biological payloads. The Spring Institute for Forests on the Moon addresses this gap with the innovative PLANT-B mission: a CubeSat featuring novel approaches to entirely passive light and thermal management of its terrarium payload, maintaining a self-sustaining ecosystem without supplemental life support. As light and thermal management typically comprise a large part of the mass, power, and financial budgets of satellite missions, eliminating these costs hugely expands not just the range of experiments that can be conducted, but the affordability of said experiments. Aligned with our commitment to open science, the design, simulations, and methodologies used in the PLANT-B mission will be made publicly accessible, catalyzing future endeavors in space biology.

Plant Selection

We need to select plants for this terrarium that are suited to the "orbital environment":

90 minute light cycle

We have some control over the photoperiod, i.e. should it be 60 minutes of light and 30 minutes of dark or vice versa.
Can't do 45-45, because that orbit would require the satellite to be almost touching the earth!

There will be a series of experiments to determine the ideal plant composition for the terrarium, but this is the first:

What type of photosynthesis is best suited for this photoperiod?

C3 Photosynthesis: C3 plants typically deal better with longer periods of light exposure and may not be as efficient with rapid light-dark transitions.

C4 Photosynthesis: C4 plants also photosynthesize during periods of light, with some advantages over C3 plants. They have a more efficient process under high light intensity and high temperatures, reducing water loss. However, C4 plants are not generally better adapted to rapid changes in light-dark periods than C3 plants.

CAM Photosynthesis: CAM plants typically separate their photosynthetic processes into day and night, taking in CO2 during the night and using it during the day. This process is an adaptation to arid conditions to reduce water loss during the hot day. With a light-dark cycle of 60/30 minutes, they might not have enough time to carry out their usual processes efficiently.

No plant is particularly well-suited for a cycle of 60 minutes of light and 30 minutes of darkness, as it's quite an unusual cycle for most plants. The continuous transition between light and darkness can lead to a high metabolic cost due to the need for constant adjustment. It's also worth mentioning that photosynthesis is not an instantaneous process; it takes time for the machinery involved in photosynthesis to start and stop.

However, if we had to choose the best option, it would likely be a C3 or C4 plant, as they could potentially adapt to this cycle better than a CAM plant. C4 plants might have an edge over C3 plants if the light intensity during the 60-minute periods is high, due to their additional carbon fixation mechanism that allows them to operate more efficiently under high light intensity and high temperatures.

If we chose 30 minutes of light and 60 minutes of dark, CAM plants would have more time to fix carbon.