With AMAA: Aerospace, Space & Defense returning to place mission-critical additive manufacturing applications under the spotlight, our pre-event series returns to focus on speakers from across the sector examining where 3D printing is moving from design freedom into functional hardware.
Among them is Ryan Watkins, a Research Engineer specializing in mechanics at NASA Jet Propulsion Laboratory, who detailed how 3D printed titanium lattice structures are being used in the baseline design for Mars Sample Return impact protection. His presentation focused on how lattice structures can be engineered as force-limiting crushables, protecting Martian sample tubes during a hard-impact Earth landing without parachutes or powered descent.
Watkins explained how additive manufacturing is being used to produce crushable lattice structures for the Mars Sample Return campaign, a multi-mission effort involving NASA and the European Space Agency (ESA). The campaign began with the landing of the Perseverance rover on Mars in 2021, where the rover has been collecting geological samples in sealed tubes for eventual return to Earth.
The Mars Sample Return campaign, a multi-mission effort involving NASA and the European Space Agency (ESA), began with the landing of the Perseverance rover on Mars in 2021. Since then, the rover has been collecting geological samples in sealed tubes for eventual return to Earth.
Watkins said the sample container’s worst-case design load is around 50 meters per second, equivalent to approximately 110 mph. To protect the sample tubes during this impact, the current baseline design uses a 3D printed titanium crushable structure inside the Earth Entry System. The component is designed to attenuate impact energy and limit the force transmitted to the sample tubes.
Turning lattice complexity into function
Watkins argued that lattices have often served as a “muse” for the 3D printing community, showcasing the complexity that additive manufacturing can produce. Lattices, multi-length-scale structures made from repeating unit cells, are common in nature and already used in aerospace for lightweight panels and energy absorbers.
Conventional metal lattice structures have historically been limited by manufacturing constraints. Aluminum foams and honeycombs, for example, can be used for energy absorption, but their geometry, material options, and integration methods are relatively restricted.
According to Watkins, metal additive manufacturing changes this design space by allowing engineers to select specific unit cells, conformally map lattices to complex geometries, tune properties across a structure, and integrate lattice regions directly into solid bodies. This removes some of the design compromises associated with bonding conventional foams or honeycombs into a larger assembly.
Designing a force limiter for Mars samples
For the Mars Sample Return application, the lattice crushable is intended to act as a force limiter. The design target is to keep the crush load below the force that would damage or break the sample tubes, while still absorbing enough energy to survive the Earth impact event.
When compressed, a crushable lattice first responds linearly, then buckles or plastically collapses into a stress plateau. During this plateau, the structure continues to compress while maintaining a relatively constant load.
That plateau behavior is central to its use as an energy absorber. The area under the load-displacement curve corresponds to the energy absorbed by the lattice. However, the design must avoid densification, where the void space has been crushed out and the structure becomes much stiffer. If densification occurs too early, the lattice can no longer reliably limit the load transmitted to the samples.
This creates two main design requirements. The unit cell must be much smaller than the overall structure to produce a flatter load plateau, and the lattice must have a low relative density to maximize crush stroke. Relative density refers to the ratio of solid material volume to the total lattice volume.
Manufacturing at the limits of metal 3D printing
Metal 3D printers typically operate across roughly two orders of magnitude in length scale. In JPL’s laser powder bed fusion process, for example, printable ligament thicknesses are around one millimeter, while the overall print volume is on the order of 200 mm. Producing effective crushable lattices means working near the lower limit of printable feature resolution. This can introduce material quality challenges, including premature fracture caused by surface roughness or internal defects such as voids.
JPL’s work therefore focused heavily on balancing internal material quality with surface finish. Watkins noted that process parameters can often be tuned either to reduce internal defects or to improve surface finish, but optimizing one can compromise the other. Because surface roughness is generally easier to address after printing than internal defects, the team prioritized internal quality during printing and then used post-processing to improve the lattice surface.
Chemical etching proved especially useful. The process reduced surface roughness and could reach the complex internal geometry of lattice structures. It also helped reduce relative density, turning printed structures into more effective crushables. In one example, Watkins described a 3D printed aluminum honeycomb with an as-printed relative density of around 30%. After etching, surface roughness was reduced by 50%, while relative density fell by 75%, bringing the structure to approximately 8% relative density. At that level, the honeycomb behaved more like a functional crushable.
JPL has since extended this approach across multiple geometries and materials. Watkins said beam-based lattices can reach around 2% relative density in materials including Aluminum 6061, RAM2, Ti-6Al-4V, and more exotic alloys such as nickel titanium.
Selecting the right unit cell
Beyond manufacturing, Watkins emphasized that lattice design itself remains a major challenge. The design space is large because engineers can choose from many possible unit cell types, then vary their aspect ratio, relative density, and other geometric parameters.
Rather than selecting a unit cell because it appears in a research paper or is commonly used in additive manufacturing, Watkins argued for a more strategic approach based on application-specific performance.
This led to the development of UnitcellHub, a suite of design tools used to explore lattice behavior. One part of the platform, UnitcellEngine, is a Python-based tool that includes CAD features, meshing, and finite element simulation. It can take a unit cell definition and output predicted properties such as relative density, stiffness, stress propagation, and thermal conductance.
The associated database contains around 15,000 simulated unit cell point designs, generated from parameter sweeps across unit cell types and modifications. These results feed into UnitcellApp, a graphical user interface for exploring lattice performance data.
Although crushing is a nonlinear response, Watkins said linear simulation results can still help reduce the design space. In the Mars Sample Return case, JPL used predicted yield behavior as a precursor to crushing performance, focusing on bending-dominated titanium lattices.
The target crush strength was in the range of two to three MPa. This allowed the team to reduce the initial design space from more than 30 unit cell types to two candidates in a manufacturable relative-density range of around 2% to 4%. After printing test structures at around 3% relative density, the team selected a diamond unit cell. Kelvin cells showed global failure modes that produced sharp load drops during crushing, which was undesirable for a force-limiting component.
From additive showcase to mission hardware
Watkins concluded that lattice structures are now part of the baseline design for a NASA flagship mission and have passed multiple design reviews. The remaining work is focused on final qualification.
The presentation positioned additive manufacturing as a route to mechanical performance that would be difficult to achieve with conventional metal foams or honeycombs. For aerospace, space, and defense applications, the Mars Sample Return work shows how 3D printed lattices can move beyond lightweighting or demonstration parts and into mission-critical impact protection.
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Featured image shows JPL 3D Printed Part Springs Forward. Photo via NASA.
