The skin-tight, pressurised suit would not only support the astronaut, but would give them much more freedom to move during planetary exploration. An electric current triggers the coils to contract and essentially shrink-wrap the garment around the astronaut's body. To take the suit off, a modest force is applied, returning the suit to its looser form.
Now MIT researchers are one step closer to engineering such an active, 'second-skin' spacesuit. Professor Dava Newman and her colleagues have engineered active compression garments that incorporate small, spring-like coils that contract in response to heat. The coils, which are made from a shape-memory alloy, are incorporated in a tourniquet-like cuff, to which a current is applied to generate heat.
At a certain trigger temperature, the coils contract to their 'remembered' form, tightening the cuff in the process. In subsequent tests, the group found that the pressure produced by the coils equalled that required to fully support an astronaut in space.
“With conventional spacesuits, you’re essentially in a balloon of gas that’s providing you with the necessary one-third of an atmosphere to keep you alive in the vacuum of space,” says Newman. “We want to achieve that same pressurisation, but through mechanical counter-pressure — applying the pressure directly to the skin, thus avoiding the gas pressure altogether."
While skintight spacesuits have been proposed in the past, there’s been one persistent design hurdle: how to squeeze in and out of a pressurised suit that’s engineered to be extremely tight. That’s where shape-memory alloys may provide a solution. Such materials only contract when heated, and can easily be stretched back to a looser shape when cool.
Some 14 types of shape-changing materials — ranging from dielectric elastomers to shape-memory polymers — were considered by the researchers before they settled on nickel-titanium shape-memory alloys. When trained as tightly packed, small-diameter springs, this material contracts when heated to produce a significant amount of force, given its slight mass, which is ideal for use in a lightweight compression garment.
Shape-memory alloys like nickel-titanium can essentially be 'trained' to return to an original shape in response to a certain temperature. To train the material, coil designer and co-researcher, Bradley Holschuh first wound raw shape memory alloy fibre into extremely tight, millimetre-diameter coils then heated these to 450°C to set them into an original, or 'trained' shape. At room temperature, the coils may be stretched or bent, much like a paper clip. However, at a certain 'trigger temperature (in this case, as low as 60°C), the fibre will begin to spring back to its trained, tightly coiled state.
The researchers applied an array of coils to an elastic cuff, attaching each coil to a small thread linked to the cuff. They then attached leads to the coils’ opposite ends and applied a voltage, generating heat. Between 60 and 160°C, the coils contracted, pulling the attached threads, and tightening the cuff.
“These are basically self-closing buckles,” Holschuh says. “Once you put the suit on, you can run a current through all these little features, and the suit will shrink-wrap you, and pull closed.”
A challenge is finding a way to keep the suit tight. The researchers are currently studying potential mechanisms to lock or clip the coils in place, thus avoiding the need to maintain high temperatures, which would otherwise by totally impractical.
Holschuh, who is currently considering several ways to thread the coils through the spacesuit, believes there are other, more earthbound applications of this technology, including the integration of cuffs as tourniquets into battle fatigues equipped with sensors that detect injury.