The Silk Road once connected China to the rest of the world. Now, Chinese researchers propose that silkworms could provide a lifeline for long missions to outer space by serving as meals for astronauts.
To survive for years in space, astronauts may need to bring along miniature ecosystems that provide necessities such as oxygen and food. Past research into what animal protein astronauts might live on has assessed poultry, fish, and even sea urchin larvae. All of these animals have drawbacks. Poultry needs a large amount of food and space, which is typically limited on expeditions, and it produces a lot of excrement. Fish and other aquatic life are very sensitive to water conditions, disturbances in which could delay spawning, hatching, and development.
Enter silkworms. As environmental scientist Hong Liu of Beihang University in Beijing and colleagues explained online 24 December in Advances in Space Research, the insects breed quickly, require little space and water, and generate only small amounts of excrement, which could serve as fertilizer. Plus, silkworm pupae are mostly protein, the team reported, and when it comes to essential amino acids, they contain twice as much as pork does and four times as much as eggs and milk. Even the insect's inedible silk, which makes up 50% of the weight of the dry cocoon, could provide nutrients: The material can be rendered edible through chemical processing and can be mixed with fruit juice, sugar, and food coloring to produce jam, the researchers reported. As a bonus for Chinese astronauts, or "taikonauts," silkworm pupae are already eaten in parts of China.
Liu's team calculates that given a relatively normal diet with a three-to-one ratio of plant to animal protein, each astronaut would need to consume 170 silkworm pupae and cocoons a day to fulfill their animal protein needs. That number might be difficult to raise on a cramped spaceship but could be more feasible than raising an equivalent number of chickens.
"This is an appealing line of research," says ecological engineer Mark Nelson of the Institute of Ecotechnics, an ecosystems research firm in Sante Fe, New Mexico. "It might be kind of fanciful to some, but on the other hand, space travel was considered science fiction not that many decades ago." Still, says Nelson, "whether American astronauts could overcome cultural taboos regarding eating insects is an open question."