Waste recycling is pivotal for deep space exploration or space habitation in life support systems (LSS) to enhance the material closure. This study investigated the enzymatic pretreatment and solid-state anaerobic digestion (SS-AD) of wheat straw as the major component of biomass waste in LSS for resource reclamation. Wheat straw compounds, such as cellulose, hemicellulose and lignin were significantly degraded after pretreatment with degradation at 37.47%, 46.96%, and 14.05%, respectively. SS-AD with the C/N ratio of 25 resulted in more intense lignocellulose degradation (74.20%) and more biogas yield (77.59 L/kg volatile solid) with 30 days digestion. The microbial community variation and diversity were analyzed that common fiber-degrading bacteria including Firmicutes, Bacteroidetes and Proteobacteria were dominant while the composition of the microbial genera shifted along with the digestion time. Moreover, a potential feasible strategy for biomass waste management in LSS by SS-AD was proposed. 

Lignocellulose degradation, biogas production and characteristics of the microbial community in solid-state anaerobic digestion of wheat straw waste

Waste recycling is pivotal for deep space exploration or space habitation in life support systems (LSS) to enhance the material closure. This study investigated the enzymatic pretreatment and solid-state anaerobic digestion (SS-AD) of wheat straw as the major component of biomass waste in LSS for resource reclamation. Wheat straw compounds, such as cellulose, hemicellulose and lignin were significantly degraded after pretreatment with degradation at 37.47%, 46.96%, and 14.05%, respectively. SS-AD with the C/N ratio of 25 resulted in more intense lignocellulose degradation (74.20%) and more biogas yield (77.59 L/kg volatile solid) with 30 days digestion. The microbial community variation and diversity were analyzed that common fiber-degrading bacteria including Firmicutes, Bacteroidetes and Proteobacteria were dominant while the composition of the microbial genera shifted along with the digestion time. Moreover, a potential feasible strategy for biomass waste management in LSS by SS-AD was proposed.

Controlled Ecological Life Support System (CELSS) is a closed artificial ecosystem which can regenerate oxygen, food, water and other substances for crew survival in long-term space missions. Solid organic waste is a vital resource pool for material reuse and recycling in CELSS. In this study, solid wastes including wheat straw and food waste were disposed via aerobic composting under functional microbial agent inoculation. Compared to tests with a commercial microbial agent addition and without exogenous microorganisms, system performance was promoted by the self-developed microbial agent significantly which exhibited the highest composting temperature (67.4 ± 1.5 °C) and longest thermophilic period (7 days). And treatment with self-developed microbial agent showed the highest values in volatile solid reduction, C/N reduction, germination index (124.83 ± 13.25%) and total available nutrient content (47.45 ± 1.69 g/kg), which suggested the feasibility of compost product to be used for crop cultivation. Moreover, shifts of microbial community in phylum and genus levels were observed. Microbial agent augmentation led to high quality and safe compost product after a short composting period (30 days) without leaching, which suggested an efficient way to promote the recycling and recovery of solid waste in CELSS. 

Application of functional microbial agent in aerobic composting of wheat straw for waste recycling.

Flexible exoskeletons are lightweight robots that surround the user’s anatomy to assist or oppose motion. Their structure is made of light and flexible materials, like fabrics, so the forces created by the robot are directly transferred to the user’s musculoskeletal system. Exosuits are thus sensitive to the sliding of the actuation, textile perturbations and improper fitting to the user. LUXBIT is a cable-driven flexible exoskeleton that combines fabrics and sewing patterns to promote its anatomical adaption. The exoskeleton is intended for bimanual assistance of daily tasks and long-term usage. To this end, the system reduces the pressures applied to the user and the misalignment of the actuation by stacking textile patches. The patches enhance the functioning of the base garment and promote the transference of the assistance forces. Additionally, LUXBIT has a compact actuation with deformable components to prevent the user movements from being restricted. The exoskeleton is portable by using an enhanced textile backpack. This paper shows the exoskeleton’s benefits for trajectory and muscle activity during the flexion of the shoulder and the elbow.

Assessment of a textile portable exoskeleton for the upper limbs’ flexion

As interest in space exploration grows, developing a lunar habitat has become a key component of extending missions into deep space. To guarantee reliable power management of a lunar habitat's DC microgrid, control schemes are needed that can manage the different assets (batteries, photovoltaics, loads) effectively. Proposed hierarchical control schemes are further developed into hardware solutions using Opal-RT's real-time simulation software and Power Hardware-in-the-Loop platform. Experimental results of a simulated DC microgrid and physical DC/DC components can allow better realization and performance of applications such as battery discharge control. 

Development of Hierarchical Control for a Lunar Habitat DC Microgrid Model Using Power Hardware-in-the-Loop

NASA has been tasked with implementing a bold vision of the future for human spaceflight including expanding the commercial market and operations in low-Earth orbit (LEO); launching the world's most powerful rocket and deep space crew spacecraft; incrementally establishing a sustainable presence on and around the Moon, starting by landing the first woman and the next man on the surface in 2024 while, in parallel, constructing an orbital Gateway in cislunar space. The key piece of establishing a sustainable presence in deep space is the development of habitation systems that will not only extend mission operations, but provide for living quarters that will keep the crew happy and healthy throughout their expeditions. Beyond the Gateway habitation needs, these capabilities will need to be defined and advanced to support the initial lunar surface missions and to prepare for human missions to the Mars system. The Foundation Surface Habitat (FSH) is the current concept in consideration to serve as this initial surface habitat that will extend the crew mission durations. It will provide 30–60 day habitability for a crew of four allowing for the astronauts to explore farther and longer on each visit to the lunar surface. The Transit Habitat is the current concept under study that would be capable of supporting long-duration missions. These missions could include extended operations at the Gateway or as a free-flyer facility in low-Earth orbit but ultimately, the Transit Habitat is envisioned as the crew habitat that would transport humans on long-duration deep space missions. The Transit Habitat integrated with an advanced propulsion system would serve as the in-space transportation system tasked with safely ferrying humans to and from Mars. Each of these habitation concepts is currently under study internal to NASA, but the agency is also working closely with U.S. industry through the Next Space Technologies for Exploration Partnerships (NextSTEP) activity to understand their concepts for a commercially-provided FSH and Transit Habitat as well as close coordination with our international partners to understand their desires for in-space and surface habitation. This paper will provide a status of these concepts and partnership activities as well as potential future development paths and architecture plans.

Shane Canerday

Papers

Deep Space Habitation: Establishing a Sustainable Human Presence on the Moon and Beyond

Concepts for Phased Development of a Lunar Surface Base