Microbial biomanufacturing for space-exploration-what to take and when to make

Abstract

As renewed interest in human space-exploration intensifies, a coherent and modernized strategy for mission design and planning has become increasingly crucial. Biotechnology has emerged as a promising approach to increase resilience, flexibility, and efficiency of missions, by virtue of its ability to effectively utilize in situ resources and reclaim resources from waste streams. Here we outline four primary mission-classes on Moon and Mars that drive a staged and accretive biomanufacturing strategy. Each class requires a unique approach to integrate biomanufacturing into the existing mission-architecture and so faces unique challenges in technology development. These challenges stem directly from the resources available in a given mission-class-the degree to which feedstocks are derived from cargo and in situ resources-and the degree to which loop-closure is necessary. As mission duration and distance from Earth increase, the benefits of specialized, sustainable biomanufacturing processes also increase. Consequentially, we define specific design-scenarios and quantify the usefulness of in-space biomanufacturing, to guide techno-economics of space-missions. Especially materials emerged as a potentially pivotal target for biomanufacturing with large impact on up-mass cost. Subsequently, we outline the processes needed for development, testing, and deployment of requisite technologies. As space-related technology development often does, these advancements are likely to have profound implications for the creation of a resilient circular bioeconomy on Earth.

Fig. 1. Approaches to in situ biomanufacturing (bio-ISM) depending on off-world mission-class.

The context-specific off-world mission-classes 1 to 4 are defined in (a), mapped as quadrants on qualitative spectra for the availability of in situ resources and logistic resupply. The most ubiquitous surface-accessible in situ resources for the Moon and Mars are compared in (b) in form of gases and solids, broken down into their molecular compositions (SNOPs: sulfur, nitrogen, oxygen, phosphorus. Note that SNOPs and mineral oxides exclude otherwise listed compounds. Compositions and amounts (where given) are rough estimates, based on current knowledge^–. MMt: million metric tons). Biomanufacturing concepts-of-operations (CONOPS), outlined in (c), are color-coded for the operational mode: outgoing from initial cargo (black lines), CONOPS can rely on either loop-closure (LC, blue lines), in situ resource utilization (ISRU, orange lines), or both (LC+ISRU, green lines).

Fig. 2. Breakdown of environmental control and life support systems into components by type of system and composition thereof.

The make-up of the inventory and hence the operational expenses are dependent on the mission-design scenario. Panel (a) provides an overview of parameters for five exemplar space-travel scenarios: ‘I’ and ‘II’ correspond to single sorties (N) to the Moon and Mars, respectively, using standard surface operation duration, while ‘III’ and ‘IV’ correspond to multi-sortie campaigns with the same 5400 days of total surface operation as in ‘V’. Based on these parameters and equivalency factors for Volume (V_eq), Power (P_eq), Cooling (C_eq), Crew-Time (CT_eq), and Location (L_eq) the ESM can be calculated for each scenario (as per Eq. 1 in section 2 of the SI). Panels (b–e) visualize the inventory breakdown by the expense-type contributing to the total ESM (b), type of system-component classified by associated resource (c), and composition of the inventory item (d and e): the bar-charts in panels (b–d) show the breakdown in ESM units (on the left, in mass [kg]), and the fractional breakdown of each scenario (on the right, unit-less), while in panel (e) the absolute (left, in mass [kg]) and fractional (right, unit-less) inventory breakdown in terms of material composition is visualized. An alternative representation of the data presented in (d and e) is given in Fig. S1c. ESM equivalent systems mass—for more information see BOX 1.

Fig. 3. Breakdown of available routes for bioproduction of inventory items from carbon dioxide—either as in situ or recovered resource.

Connecting lines represent possible paths for carbon-compound conversion of intermediates to products. Usability of different feedstocks is tied to nutritional mode of the microbial host organism (more than one nutritional mode is possible for certain organisms). Classes of products are assigned to respective microbes in respect of their metabolism as well as not represented ‘shadow-characteristics’ of the chassis (e.g., aerobic/anaerobic, prokaryotic/eukaryotic, metabolic rate, robustness, etc.), rather than ability to (naturally) derive the respective compounds. Products may or may not comprise some of the initial feedstocks, hence consecutive runs through this chart to up-cycle carbon are conceivable.