The technology focus areas for ARGO are excavation, site preparation, construction, and in-situ resource utilization (ISRU). ARGO can provide simulated lunar and martian vacuum pressures, temperatures, and regolith conditions.  In the case of excavation and construction technologies for the lunar surface, this may include the vacuum pressure, cryogenic temperatures, and solar simulated thermal effects.

The ARGO system consists of a large sum of capabilities that is continuing to be developed and improved. The ARGO system is a capability set that acts as a proving ground for lunar and martian technology development for both NASA and its national and international partners. The ARGO system includes the ASSIST chamber (a ~1.47 m x 1.47 m x 1.18 m vacuum chamber capable of 3.39×10^-6 torr or greater pressures), the ARGO gantry (a 4 axis X/Y/Z and E axis gantry for tool manipulation and additive construction), a -200 °C cryogenically cooled thermal shroud (using AL325 and AL600 Cryomech cryocoolers), heated additive construction build plates and regolith simulant bins, a residual gas analyzer, multiple 15 kW power supplies, a 10 kW induction power supply, and a solar simulator lamp. These capabilities can be paired with one another within the ASSIST chamber to allow technologies to advance their TRL within a relevant environment. ARGO has already been utilized on multiple projects including MMPACT, REACT, and GaLORE.

ARGO consists of several individual capabilities:

• The Atmospherically Sealed Simulator for In-situ System Testing (ASSIST) as a 1 atm to high vacuum chamber
• A 4-axis gantry with a 90 kg payload size
• Cryogenic capabilities utilizing two sizes of helium loop cryo refrigerators
• Two 15 kW power supplies
• Pellet extruder E-axis payload for the gantry
• Rotary motion E-axis payload for the gantry
• Various regolith bins and heated build plates
• Various cameras and supporting equipment

ASSIST is a dedicated Dirty Thermal Vacuum (DTVAC) chamber capable of pressure ranges between 760 torr (atmospheric) and 3.5×10^-6torr to allow testing with regolith and volatiles in a simulated lunar or martian pressure environment. Many dirty thermal vacuum chamber systems are either large, facility-based chambers with long test turnaround times, high upkeep costs, and expensive access fees, or they are significantly smaller with limited technology demonstration volume and configuration capabilities. ASSIST fits between these two extremes with a large internal volume but quick turnaround testing.

• The internal dimensions of the chamber are 1.47 m x 1.47 m x 1.18 m (58 in x 58 in x 46.5 in).
• The front face of the chamber is a full-sized door, allowing test fixtures to utilize the entire inner dimensions of the chamber and be placed using a forklift.
• The chamber can support payloads up to 3130 kg (6900 lbm) and a maximum floor loading pressure of 6.7 MPa (970 psi).
• Additionally, the chamber has ¼-20 internal threaded blind holes on the left, right, and back internal surfaces to allow for mounting shelving, test fixtures, or wire track.
• These fastener points are rated to 445 N (100 lbf) shear load and are spaced on a 15.24 cm x 15.25 cm (6 in x 6 in) grid pattern.
• Three walls of the enclosure are equipped with circulating coolant channels that regulate the wall temperature to mitigate the risk of exceeding the temperature limit of 150 °C imposed by the elastomeric seals of the flanges.

Fig. 3 ASSIST Chamber

ASSIST Port List:

Below is a list of all vacuum ports on the ASSIST chamber. The chamber drawing is provided in Appendix A.

• Front Door
  • 2x 0.5 m x 0.5 m (20 x 20 in) view windows
• Left
  • 4x KF50
  • 2x ISO250-K
• Right
  • 4x KF50
  • 1x ISO250-K
• Back
  • 2x KF40 (equipped with vacuum and venting system valves)
  • 2x KF25 (equipped with a medium and high vacuum gauge)
  • 1x ISO160-K
  • 2x ISO250-K
  • 1x ISO250-K (equipped with EBT2400 turbomolecular pump)
  • 1x ISO350-K
• Top
  • 4x KF50
  • 2x KF50 on 21 cm (8.5 in) riser tubes (equipped with vacuum relieve valves)
  • 2x ISO160-F
  • 2x ISO250-K
  • 1x 25.4 cm (10 in) diameter fused silica viewport
• Bottom
  • 1x ISO160-F

ASSIST Pressure Range

Fig. 5 shows the chamber pressure during an automated pump down procedure. At ~9 x 10^-1 torr, ASSIST begins operations to open the gate valve to the turbo molecular pump and begin pumping to high vacuum pressures. The chamber can be set to achieve either the lowest possible high vacuum pressure or a specific medium vacuum pressure (down to 1 torr) with a control band range (for example +/- 3 torr). This feature can be used to achieve martian-like atmospheric pressures.

Fig. 5 Baseline high vacuum test with no hardware or regolith in the chamber

The ARGO system can achieve cryogenic temperatures using two sizes of thermal shrouds. The thermal shrouds are cooled by conduction from helium refrigerant loop cryocoolers. Alternatively, test hardware can also be directly coupled to the cryocoolers. Two cryocoolers are available for use on the ARGO system: the Cryomech AL600 (600 W cooling at -190 °C with a base temp of -250 °C) and the AL325 (100 W cooling at -250 °C with a base temp of -261 °C). The cryocoolers were chosen over a liquid nitrogen cooling loop due to cost and facility limitations. Helium refrigerant systems have the capability to reach lower temperatures than liquid nitrogen cooling loops, but heat rejection wattage is limited, so the shrouds within ARGO are not capable of reaching the base temperature limits of either cryocooler. Temperature ranges of test hardware that are directly coupled to the cryocoolers will vary depending on the application.

The larger shroud (called Mega-Shroud) has an internal volume of 1.4 m x 1.1 m x 1.4 m (~55 in x 43 in x 55 in). Fig. 6 shows the initial fit checking of the Mega-Shroud in the ASSIST chamber. At the time of this publication, the Mega-Shroud thermal environment has not been fully characterized. Future work will provide this thermal data.

Fig. 6 Mega-Shroud and ARGO Gantry installed into ASSIST

The smaller shroud (called Mini-Shroud) has an internal volume of 0.27 m x 0.27 m x 0.25 m (~10.6 in. x 10.6 in. x 9.8 in.) and has reached temperatures below -200°C in approximately 2 hours of cooling at vacuum pressures. Fig. 7 shows one location of the Mini-Shroud within the ASSIST chamber (other configurations are possible). In the tested configuration, the Mini-Shroud utilized the AL600 Cryomech cryocooler (mounted using the provided mounting holes shown in Fig. 8). Temperature data was recorded using three E-type thermocouples (TC) clamped to the aluminum body of the shroud. These TC locations are highlighted in Fig. 9. Fig. 10 shows the cooling rate over a 4-hour test. Temperature deltas between the wall high/low TCs and the cryocooler contact  TC could be reduced given more cooling time.

The cryocoolers may be mounted to additional test fixtures as desired. Thermal performance will be affected by the coupling area between the cryocooler and the test fixture, isolation of the fixture from the chamber wall, and total thermal mass.

Fig. 7 Cryomech AL600 (left) and Mini-Shroud assembly (right)

Fig. 8 Cryohead mounting hole pattern

Fig. 9 Thermocouple positions along the Mini-Shroud wall

Fig. 10 Mini-Shroud cooling rate using AL600 cryocooler

Visible Light:

The ARGO system includes a 4K Logitech Brio webcam that can be placed within the chamber. A USB 3.0 feedthrough is provided to pass the camera connection to the recording laptop. Photos, videos, or timelapse recordings can be obtained using this camera.

Infrared

ARGO has an FLIR A35-FOV45 with two reading ranges (-25 °C to 100 °C and -40 °C to 550 °C, +/-5 % reading accuracy). This camera can be mounted to the outside of the chamber door to observe temperatures on points of interest within the chamber through a 4.5 inch CF flange zinc-selenide view port. This viewing configuration requires the replacement of either the bottom or top view window of the door with the Window to CF Adapter. Alternative placements can be achieved using a CF

The ARGO gantry (shown in Fig.11) is a 4-axis motion system designed for additive construction, as well as other manipulation tasks within the vacuum chamber or in ambient conditions. With the gantry installed in ASSIST 1×10^-5 torr vacuum pressure was achieved. Lower pressures should be achievable given more pump-down time or the use of cryocoolers for cryo pumping the chamber. The Gantry has 4 Z-axis motors, 2 X-axis motors, 1 Y-axis motor, and 1 additional E-axis motor which can drive either a polymer pellet extruder or act as an additional rotary motion axis, as shown in Fig. 12. All motors are NEMA 34 driven by DM860I. The linear rail axes are Nook ball screw DLK120 (X&Y) and non-back driving lead screw DLT120 (Z) linear actuators. Fig. 13 shows the layout of the Gantry control system. The Gantry is operated using a Bigtreetech Octopus V1.4 Control Board and Raspberry PI 4 computer with MainsailOS for Local Area Network connection. The Gantry can be controlled via g-code text files or direct g-code inputs. Data logging for thermocouples and load cells is provided through the ARGO Gantry using an included National Instruments 4-card data acquisition system (DAQ).

The ARGO Gantry is dust tolerant with spring steel dust seals on the moving axes that prevent dust intrusion. The Gantry also has t-slot-based mounting along all axes for placement of sensors or bracketry. Operating specifications of the Gantry are shown in Table 1.

Fig. 11 ARGO Gantry (left), ARGO Gantry and Universal Build Plate (right)

Fig. 12 E-axis configured for rotary motion using NEMA 34 30:1 worm gearbox

Fig. 13 ARGO Gantry control system block diagram

Table 1 ARGO Gantry specifications

Universal Build Plate

The Universal Build Plate (shown in Fig. 14 and Fig. 15) was designed to support additive construction technology testing on a more traditional heated PEI build plate or on a lunar-like regolith surface. Two Custom Heaters & Research (CHR) 450-watt, 340 mm x 720 mm silicone heaters were placed under the build plate to either provide heating of the construction surface or act as a bake-out system.

Fig. 14 shows the Universal Build Plate with the polyethyleneimine (PEI) build surface. This surface consists of a thin PEI sheet which is adhered to a 760 mm x 760 mm x 12.25 mm (30 in. x 30 in. x 0.5 in.) cast aluminum block.

Fig. 15 shows the Universal Build Plate with the 12.5 mm deep regolith simulant bed in place of the PEI coated aluminum plate. This simulant bed was designed to support additive construction testing on a simulated lunar surface that can be cooled using the Mega-Shroud or heated using the two CHR heaters below the build plate.

The two heater pads are placed between the build plates and the Universal Build Plate’s frame and can raise the temperature of the build plates up to 100 °C. The build plate can be heated in air or under vacuum. Heating can act as a limited bake-out heater system and can reduce internal warm up time following tests at cryo temperatures.

Fig. 14 Universal Build Plate with PEI-coated aluminum plate

Fig. 15 Universal Build Plate with 12.5 mm deep regolith bed

50 mm Regolith Bed

The 50 mm Regolith Bed has a build surface of 794 mm x 720 mm and can support a depth of up to 50 mm regolith. The surface can be leveled using a screed, with excess regolith deposited into the capture channels along all four faces. The bed was also designed to be lifted either by hand or with a forklift using the yellow handles as shown in Fig. 16 . The bottom of the bed is outfitted with thermally insulative garolite plates to accommodate cryogenic cooling of the regolith surface through either radiation into an environment shroud or conduction through the bed.

Fig. 15 Universal Build Plate with 12.5 mm deep regolith bed

The ARGO system is equipped with a high voltage/current power supply server rack. This rack includes a 15 kW Keysight N8932A (200 V, 210 A) and 15 kW Keysight N8931A (80 V, 510 A). Copper transmission lines are available to feed power into the chamber. The ARGO system has several facility power options:

• 480V 3Ph 30A (1X)
• 208V 3Ph 60A (3x)
• 120V 1Ph 20A (2x circuits)
• Additional 480, 208, and 120-V sources may be available depending on other concurrent testing in the lab

Additionally, the ARGO system has an induction coil power supply capable of 10 kW and a solar simulator lamp, which is a xenon arc lamp with 7.14 kW/280k Lumens (~40 lm/W) capability. The solar simulator light can be passed through the 25.4 cm (10 in.) silica viewport on the top of ASSIST.

The ASSIST chamber is outfitted with an Inficon RGA MPH200M with dedicated independent turbo and roughing pumps. This setup allows the RGA to be utilized even when ASSIST is at rough vacuum levels (≤10 torr ). The RGA has the capability to measure up to 200 AMU with an electron multiplier capability. The system may be isolated from the ASSIST chamber for ease of use without additional installation required. The system is used for monitoring of material outgassing, vacuum-based chemical processing, and environmental composition monitoring.

MMPACT – Moon-to-Mars Planetary Autonomous Construction Technology Site Prep Tool

The Moon-to-Mars Planetary Autonomous Construction Technology (MMPACT) project is currently designing and testing a multi-use site preparation tool for use in construction on the Lunar surface. This site prep tool is currently being tested within the ASSIST chamber using the ARGO Gantry, the rotary E-axis, and the Heated Regolith Bin. Testing is being conducted at vacuum pressures down to 1×10^-5 torr.

GaLORE – Gaseous Lunar Oxygen from Regolith Electrolysis

The Gaseous Lunar Oxygen from Regolith Electrolysis (GaLORE) project’s goal was to demonstrate a cold wall, molten regolith electrolysis reactor within a representative vacuum environment. In the cold-wall reactor configuration,  the molten material being electrolyzed does not contact the reactor containment housing, but instead is surrounded by a wall of “cold” granular regolith. This reduces reactor wall corrosion and the risk of an eventual breakthrough of the molten regolith.  The GaLORE reactor was placed within the ASSIST chamber and powered by both the 15 kW power supply unit (PSU) system (for electrolysis power) and the 10 kW induction coil (for melt formation heater power). Fig. 17 shows the GaLORE reactor placed in ASSIST with the induction coil system mounted around the zirconia reactor. A gaseous nitrogen purge was input into the chamber at 6.5 L/min during electrolysis to avoid a 100 % oxygen (O₂) environment within the roughing pump. At the time of GaLORE testing the turbomolecular pump was not yet installed. Due to the nitrogen purge and lack of turbo pump, the chamber’s pressure during testing was 2 torr to 6 torr. Output gas composition was measured with the RGA, and flowrate was measured with a volumetric flow meter on the roughing pump out to estimate the total O₂ produced.

GaLORE successfully produced O₂ during testing. Additional information can be found in the 2021 ASCEND paper “GaLORE (Gaseous Lunar Oxygen from Regolith Electrolysis): Technology Advances for a Cold-Walled Molten Regolith Electrolysis Reactor”

Fig. 17 GaLORE molten regolith electrolysis reactor in ASSIST during installation (left) and during test at temperatures near 1500 °C (right)

REACT- Relevant Environment Additive Construction Technology

The Relevant Environment Additive Construction Technology (REACT) project demonstrated additive construction within a Lunar-relevant environment using various regolith-polymer composite formulations. Testing was performed using the ARGO Gantry within ASSIST and at cryogenic temperatures using the Mini-Shroud. Shroud temperatures during testing were below -200⁰C with a build plate temperature below -90⁰C. Fig.18 shows a demonstration test within the cryogenic shroud at vacuum pressures. During cryogenic testing, the chamber  maintained pressures of 4×10^-4 torr or lower. Gauge limitations at the time of testing prevented the verification of testing pressures below 4×10^-4 torr. ASSIST operations conducted after the REACT tests with pressure gauges appropriate for lower pressure range have confirmed that lower pressure values are achieved under similar chamber conditions. Fig. 19 shows the data collection user interface that was used for REACT. The ARGO Gantry’s DAQ system is shown in the top window; the DAQ collects thermal data at various points of interest. 4k 60 FPS video footage of the test is recorded in the lower left. In the lower right, a FLIR thermal camera is used along with the front window to CF adapter plate to gather thermal data of the test. Additional information on the REACT project will be provided in currently in review publications [3] [4].

Fig. 18 REACT additive construction within vacuum at cryogenic environment temperatures

Fig. 19 REACT real-time data display during polymer-regolith additive construction under cryogenic vacuum conditions F