Mars Atmosphere and Regolith COllector/PrOcessor for Lander Ops (MARCO POLO) Atmospheric Processing Module (MARCO POLO APM)

The multi-NASA center Mars Atmosphere and Regolith COllector/PrOcessor for Lander Operations (MARCO POLO) project was established to build and demonstrate a methane/oxygen propellant production system in a Mars analog environment.  The MARCO POLO project will provide a demonstration platform for all aspects of Martian soil and atmospheric processing, beginning with the extraction of water from Martian soil, which would then be electrolyzed into hydrogen (H₂) and oxygen (O₂), and the capture of carbon dioxide (CO₂) from the Martian atmosphere to produce methane (CH₄) using H₂ from the water. The lander is designed in a modular fashion with an Atmospheric Processing Module (APM), Soil Processing Module, Water Cleanup Module, Water Processing Module, and Power Production Module.  Work at the Kennedy Space Center (KSC) has focused on the Atmospheric Processing Module (APM).  The purpose of the APM is to freeze CO₂ from a simulated Martian atmosphere at Martian pressures (~7 mbar) by using dual cryocoolers.  The resulting pressurized CO₂ and H₂ are fed to a Sabatier reactor to make CH₄ and water vapor.  The CO₂ freezer subsystem has a collection/supply design requirement of 88 g CO₂/hr., and the Sabatier subsystem has a design requirement to produce 31.7 g/hr. CH₄ fuel and 71.3 g/hr. H₂O, which would also be electrolyzed to H₂ and O₂.

The atmosphere of Mars consists of 95.32% CO₂, 2.7% nitrogen, 1.6% argon, and trace amounts of water, carbon monoxide, and several other gases. At 7 mbar, the average pressure on the Martian surface, the freezing point of CO₂ is 150 K (–123^oC), which makes it necessary to use a cryocooler as the condensation method.  Dual cryocoolers are needed to operate in tandem (one collecting CO₂ while the other is supplying the Sabatier reactor). The Sunpower Cryotel Model GT Stirling cycle cryocooler has the proper cooling capacity, low mass and power, and space flight heritage.  Lab testing of three copper cryocooler cold head designs to collect the CO₂ show that only the “Ferris Wheel” design met the APM requirements.

The full APM was designed and constructed during a series of projects at KSC.  The current APM CO₂ Freezer consists of two cryocoolers and freezing chambers, a chiller to remove heat from the cryocoolers, a vacuum pump to produce Mars pressures in the chambers, two CO₂.storage tanks, a mass flow controller for simulated Mars atmosphere, and various valves to control gas flow and cooling water flow.  Multiple optimization tests at varying flow rates showed that the CO₂ Freezer subsystem captures an average of 99 g CO₂/hr. in 1.4 hr. at a feed rate of 1.2 SLPM of Mars gas simulant, well above the required rate of 88 g/hr.  The CO₂ capture fraction averaged 79% while the CO₂ sublimation rate averaged 95 g/hr.  As the CO₂ sublimes, it is pumped into the storage tanks at the top of Figure 3.

To improve the CO₂ conversion efficiency of the Sabatier subsystem and to recover unreacted H₂, a recycling process was added. After the water product is condensed a membrane module separates the CH₄ product from residual CO₂ and H₂, then a compressor recycles the CO₂ and H₂ back through the Sabatier reactor.  Testing of the new Sabatier reactor without recycling has been promising, with 97% conversion of the CO₂ without the overheating experienced with a reactor supplied by JSC. Testing of the recycling system is currently underway with the membrane module producing pure CH₄, but without recycling the CO₂ and H₂ yet.  Integration and testing of the Sabatier subsystem and the CO₂ Freezer is planned in the near future.