Engineers in the UK took inspiration from nature for their recent spacecraft study. People’s wounds heal themselves, and perhaps so too will future spacecraft. No, really.

Granted, this blogger doesn’t have first-hand experience in building a spacecraft or in actually being a spacecraft, but I feel safe in declaring that spacecraft life wouldn’t be best described as “easy.” Building spacecraft is a complex task, even more so when the lives of astronauts are at stake. They are precision pieces of engineering. And without any in-mission help, it has to survive in the airless environment of space, where it is exposed to extreme temperatures and cosmic radiation. Once a spacecraft is in orbit, engineers have minimal-to-no chance of repairing anything that breaks.

This is why engineers working for the European Space Agency (ESA) have developed new processes that mimic human reactions so that spacecraft can someday heal themselves.

“When we cut ourselves, we don’t have to glue ourselves back together; instead we have a self-healing mechanism. Our blood hardens to form a protective seal for new skin to form underneath,” said Dr. Christopher Semprimoschnig, a materials scientist at the ESA’s European Space Technology Research Centre (ESTEC) in the Netherlands.

The ESA scientist, who oversaw last month’s study, imagined such cuts as “analogous to the ‘wear-and-tear’ suffered by spacecraft.” Temperature extremes can cause small cracks to open in the superstructure, as can impacts by micrometeoroids — small dust grains traveling at remarkable speeds per second. Throughout a mission’s lifetime, cracks build up to weaken the spacecraft until a catastrophic failure becomes inevitable.

The engineering may prove to be difficult, but the beauty of the concept itself is in its simplicity, Science a Go Go noted. Semprimoschnig and the Bristol team replicated the human process of healing small cracks before they can progress into anything more serious; they did it by replacing a few percent of the fibers running through a resinous composite material, similar to that used to make spacecraft components, with hollow fibers containing adhesive materials.

Ironically, for the material to be self-repairable, the hollow fibers had to be made of glass. “When damage occurs, the fibers must break easily otherwise they cannot release the liquids to fill the cracks and perform the repair,” Semprimoschnig said.

In humans, the air chemically reacts with the blood, thus hardening it. In space’s airless environment, alternate mechanical veins have to be filled with liquid resin and a special hardener that leak out and mix when the fibers are broken. Both must be runny enough to fill the cracks quickly and harden before it evaporates.

The illustration above shows different pictures of this resin-filled hollow fiber self-healing composite. Clockwise from top left: 30μm diameter hollow fibers, time-lapse sequence of healing process, infusion into damage site. (Credit: ESA)

The report offered these technical details about the materials used in the study:

Polymeric structural joints or polymeric composites are susceptible to cracks that may either form on the surface or deep within the material (fibre [sic]/matrix interface) where inspection/detection is often impossible. Once these cracks have formed they will weaken the material further and may lead to major damage.

Imagine now for instance a polymer matrix like an epoxy where micro/nano-encapsulated healing agents and a catalytic chemical agent are incorporated. When a crack spreads now through the matrix it will sooner or later encounter a microcapsule and break it. Due to capillary forces the healing agent will flow along the open crack front and will inevitably come into contact with the catalyst. This will trigger the self- healing reaction (polymerisation) that will close the crack. Thus (nearly) no evidence will be noticeable after the healing process

“We have taken the first step but there is at least a decade to go before this technology finds its way onto a spacecraft,” said Semprimoschnig, who believes that larger scale tests are now needed.

This arguably is not a new idea — consider, on a smaller scale, self-healing tires— is rather a new application of a long-standing idea. However, as the scientists said, self-healing spacecraft could promise “a new era of more reliable spacecraft, meaning more data for scientists and more reliable telecommunication possibilities for us all.”

The promise of self-healing spacecraft opens up the possibility of longer duration missions. The benefits are two-fold: 1) Doubling the lifetime of a spacecraft in orbit around Earth would roughly halve the cost of a mission, according to the ESA; and 2) Doubling spacecraft lifetimes means that mission planners could contemplate missions to far-away destinations within the solar system that currently are too risky.

The negative side to a humanistically self-healing spacecraft: the reality is kinda’ creepy, no?

Perhaps this is intended to be a fix for all that space junk in orbit?

The full ESA report

References

“Spacecraft, heal thyself”
European Space Agency announcement, Jan. 20, 2006

Houston, We Don’t Have A Problem
Science a Go Go, Jan. 23, 2006

Step made in self-healing spacecraft
United Press International (via Monsters & Critics), Jan 21, 2006

Additional Reading

Self-healing spacecrafts
by Roland Piquepaille
ZDNet, Jan. 21, 2006

Self-Healing Spacecraft? Tiny Tubes Ooze Epoxy
by Ben Harder
National Geographic, Jan. 27, 2006