To maximize reliability, Earth entry/landing vehicles for robotic sample return missions will comprise an aeroshell, a crushable layer that will absorb the energy of the ballistic impact landing, and a sample container inside the crushable layer; parachutes will not be used. Lightweight carbon foams are being considered for the crushable layer, but many other foams with different strengths and energy absorption capacities are available. By using foams of different materials with different mechanical properties and different relative densities, the crush behavior of the layer can be tailored. In addition to brittle crushing of carbon foams or ductile collapse of metallic foams, other energy-absorbing mechanisms are available, some of which have been tested at high strain rates for use as underbody armor on military vehicles to mitigate blast effects from improvised explosive devices. In this project, existing foam properties data at Ultramet will be used to guide the selection of candidate impact absorption material systems, which will include both brittle and ductile foams as a key element. The candidate impact absorption material systems will be built up and undergo high strain rate compression testing via the split Hopkinson bar technique. Low density and low thermal conductivity are also desirable characteristics, so density and thermal conductivity measurements will also be made. The resulting data will be used to develop a top-level design for a minimum-mass, low thermal conductivity crushable layer for sample return missions with high impact velocities.
The primary NASA application will be sample return missions from solar system locations including planets, planetary moons, dwarf planets, asteroids, and comets. Because the energy absorption characteristics of the material system can be tailored, it also has the potential to be used for landing payloads on these bodies. Likewise, for a mission to divert an asteroid from collision with Earth, this type of system could be used to transfer momentum to the asteroid over a tailorable time frame to minimize fracture/fragmentation of the target body.
Commercial applications for lightweight energy-absorbing structures include backing structures for automobile bumpers and underbody armor for military vehicles to mitigate blast effects from mines and improvised explosive devices. Temporary structures in war zones could also be protected against blast effects with this technology.