The Space Superfoods: Spirulina and Chlorella
For decades, space agencies like NASA, ESA, and Roscosmos have investigated microalgae as a promising food source for space travel. The ideal space food must be nutrient-dense, easily producible in controlled environments, and provide significant sustenance without requiring extensive resources. Two types of microalgae have risen to prominence in this research.
The Blue-Green Powerhouse: Spirulina
Spirulina, a cyanobacterium scientifically known as Arthrospira platensis, is one of the most widely recognized microalgae in astronaut diets. Its history as a food source dates back to the ancient Aztecs, who harvested it from Lake Texcoco. Its high nutritional value caught the attention of modern scientists, and it was officially recognized as a space food candidate in the mid-20th century.
Spirulina is prized for several key nutritional benefits that are critical for astronaut health during long missions:
- High Protein Content: Spirulina is composed of 57–70% protein by dry weight, offering a complete and easily digestible protein source rich in essential amino acids.
- Vitamins and Minerals: It contains an impressive array of vitamins, including B-vitamins, Vitamin K, and Vitamin E, along with essential minerals like iron, magnesium, and calcium.
- Antioxidants and Bioactive Compounds: The powerful antioxidant phycocyanin gives Spirulina its blue-green color and provides anti-inflammatory effects.
Spirulina has been used in actual space experiments. The European Space Agency (ESA) has included it in their Micro-Ecological Life Support System Alternative (MELiSSA) project, a closed-loop system designed to recycle waste into food, oxygen, and water. Astronauts have even tested Spirulina-fortified cereal bars in space. Ongoing experiments, like the recent Space Algae-2 project, are further studying Arthrospira platensis to understand its genetic stability and evolution in long-term spaceflight conditions.
The Green Workhorse: Chlorella
Another vital microalga is Chlorella, a unicellular green alga. Early Soviet space missions famously experimented with Chlorella cultures, successfully demonstrating that it could grow in orbit. Its use in space continues to be an area of intense research.
Key aspects of Chlorella that make it suitable for space food include:
- Protein and Nutrient Density: Like Spirulina, Chlorella boasts a high protein content, along with an abundance of vitamins, particularly Vitamin A and omega-3 fatty acids.
- Oxygen Production: In addition to its food potential, Chlorella's high photosynthetic efficiency is invaluable for producing oxygen and removing CO2 from the cabin atmosphere.
As part of a recent initiative, the German Aerospace Center (DLR) launched a Photobioreactor to the International Space Station (ISS) to cultivate Chlorella vulgaris. This bioreactor is designed to convert the astronauts' exhaled CO2 into both oxygen and edible biomass, with estimates suggesting that algae could one day replace up to 30% of an astronaut's food.
Comparison: Spirulina vs. Chlorella for Astronauts
While both microalgae are considered superfoods for space, their characteristics differ slightly, making them suitable for different applications.
| Feature | Spirulina (Arthrospira platensis) | Chlorella (Chlorella vulgaris) |
|---|---|---|
| Species Type | Cyanobacterium (blue-green algae) | Green Algae |
| Protein Content | 57-70% (dry weight) | 51-58% (dry weight) |
| Digestibility | Highly digestible due to soft cell walls | Less digestible due to hard cellulose cell walls, requiring processing |
| Key Nutrients | Excellent source of iron, B-vitamins, and antioxidants | Rich in Vitamin A, omega-3 fatty acids, and antioxidants |
| Space History | Tested by NASA and part of ESA's MELiSSA project | Studied extensively since early Soviet missions and tested on ISS |
| Primary Role | Direct nutritional supplement, food incorporation | Food supplement, and powerful oxygen production via bioreactors |
Algae's Dual Role: Food and Life Support
The most compelling reason for using algae in space is their ability to close the loop on life support systems. On Earth, we rely on a complex ecosystem to produce food and clean our air. In the confined environment of a spacecraft or lunar base, microalgae serve as a highly efficient, compact substitute for this natural process.
In a Bioregenerative Life Support System (BLSS), microalgae cultivated in photobioreactors use the astronauts' exhaled CO2, sunlight, and recycled wastewater to perform photosynthesis. This process not only generates a food source but also produces a continuous supply of fresh oxygen. This makes microalgae a far more sustainable option for long-term missions compared to resupplying food and oxygen from Earth, which is both expensive and logistically challenging.
The Future of Algae in Space Exploration
Research into microalgae for space is continually advancing. Scientists are investigating other species, such as Haematococcus pluvialis, for specific, high-value compounds like the potent antioxidant astaxanthin, which could serve as a valuable dietary supplement during long voyages. Studies are also addressing key challenges, including understanding how microgravity and cosmic radiation affect algal growth and genetic stability over time.
For future missions to the Moon and Mars, microalgae could be instrumental in establishing self-sufficient colonies. Experiments exploring the use of microalgae as a biofertilizer to help grow plants in lunar and Martian regolith have already shown promising results. The knowledge gained from these experiments could one day allow astronauts to cultivate their own sustainable food supply, reducing reliance on Earth resupplies and paving the way for permanent off-world habitation. NASA Studies Algae for Life Support
Conclusion: Microscopic Heroes of Space Travel
The question of which algae is eaten by astronauts reveals a fascinating intersection of biology, nutrition, and advanced technology. The current focus on species like Spirulina and Chlorella highlights their dual importance as both a superfood supplement and a key component of regenerative life support systems. As humans venture farther into the solar system, these tiny, efficient organisms will be instrumental in ensuring the health and sustainability of future deep-space exploration and colonization efforts, proving that even the smallest organisms can play the biggest role in our journey among the stars.
