Uncrewed Systems Technology 047 l Aergility ATLIS l AI focus l Clevon 1 UGV l Geospatial insight l Intergeo 2022 report l AUSA 2022 report I Infinity fuel cell l BeeX A.IKANBILIS l Propellers focus I Phoenix Wings Orca

88 stack at once, which would be wasteful, and we get extremely high usage rates of the reactants.” Also, since PEMFC life is directly affected by humidifying the reactants, Infinity also provides an in-stack means of humidifying the hydrogen and oxygen while also reducing or eliminating any gas in the product water. At the opposite end of the stack from the vents is a series of cells that expose the incoming hydrogen and oxygen to the product water before it exits the stack, humidifying the gases. That section also includes an electrochemical means of reacting dissolved or visible reactants that might be present in the product water, minimising downstream water management, particularly for zero- gravity applications. External balance of plant The exact arrangement of mechanical and electronic parts comprising the external BoP is not standardised in design terms. For instance, in the recent Blue Origin flight, most of those components were mounted directly on the fuel cell’s end plates to eliminate the need for external piping. “Putting everything, including the valves and pressure regulators, right on the end plates made everything smaller and lighter, and kept overall packaging really tight, which is really important for any kind of spacecraft,” Smith says. “Earlier in development, we would just use thick pieces of stainless steel for our end plates, because that was low-risk and we didn’t want to have to design too much new technology into an end plate. But what we’ve evolved towards now are end plates that sometimes actually contain the BoP – so the BoP is integrated not just onto but inside the end plate.” The productionised PEMFCs will probably therefore use end plates with fluid ports running through them, to allow pressure regulators and valves to function. Infinity is also considering alternatives to stainless steel for manufacturing its end plates, such as carbon composite for further weight reduction when the application calls for it, for instance in air or space flight. As a final note about the end plates, Smith notes that the tie rods used for tightening the stack are likely to remain in all future iterations, as they provide ideal control and repeatability over the compression across the cell, particularly compared with alternative approaches such as straps. “We’ve used stainless steel and titanium tie rods, and both work well and are very safe,” he adds. December/January 2023 | Uncrewed Systems Technology Both stainless steel and titanium tie rods can be used, enabling precise and repeatable stack compression as needed for the mission environment, the size of the stack and so on