Which green alga is used by space travellers as protein rich food ?

Explanation

**Step-by-Step Solution:**

1. **Identify the Question**: The question asks for the name of a green alga that is utilized by space travelers as a protein-rich food source.

2. **Recall Information about Green Algae**: Green algae are a diverse group of photosynthetic organisms, primarily found in aquatic environments. They are known for their high protein content.

3. **Specific Alga for Space Travel**: Among various green algae, one specific type is known for its use in space missions. This alga is recognized for its nutritional value, particularly its protein content.

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