Which spaceflight biology hardware can be modelled?

Overview

The specimen environment inside flight hardware is rarely documented well enough to model.

Spaceflight biology results are interpreted against the hardware the specimens lived in, yet the physical environment inside that hardware (airflow, gas composition, temperature, humidity, light and nutrient delivery) is rarely documented well enough to be modelled. We joined the three public NASA hardware sources (the SPLASH instrument catalogue, the OSDR hardware registry and the experiment-platform field of every OSDR study), scored every specimen-housing item against a 15-item checklist of what a CFD model needs, curated the literature for the most-used hardware, and built verified OpenFOAM models of the hardware that reached CFD readiness.

01Where the hardware flies and how specimens are fed

From all catalogued hardware to the items whose public metadata support a CFD model.

The crosswalk produced 328 entities. 164 can carry space-biology payloads and 111 house live specimens during flight; only 33 of these are linked to at least one OSDR study. Mission records place bio-capable hardware on the Space Shuttle (38), on free-flying biosatellites (19) and on the ISS (18). Nutrient delivery was evidenced for fewer than half of the habitats (59 with no evidence); where evidenced, animal food and water (16), culture medium (21) and agar (11) were the commonest modes. Every assigned mode is backed by a verbatim quotation.

02Catalogue defects

Errors that propagate silently into any automated reuse of the catalogues.

27 SPLASH records (#121–#147) carry descriptive fields displaced from neighbouring rows: 29 fields were confirmed as misattributed on review. For example, a Plant Growth Unit record's specimen field describes an RNA thermal cycler, and a BRIC-Opti canister record carries the crop list and the CO₂, humidity and temperature control ranges of the Advanced Plant Habitat. The sources, schematics and study_links fields are empty in every record. 310 of 641 OSDR datasets have no experiment-platform entry; the rest use 116 free-text strings, with 9 spellings of Veggie alone.

03The MI-CFD-HW checklist

Fifteen items a CFD model of a specimen environment needs; six are critical.

An item is Tier A (CFD-ready) when every critical item is sourced; the airflow requirement is waived for sealed or passive hardware. Specimen type is almost always stated (98.20% quantitative), but airflow rate (3.60%), specimen metabolic load (0.00%) and heat load (1.80%) are almost never given. Median completeness was 0.30 using all public sources and 0.07 using SPLASH alone.

Percentages of the 111 specimen-housing items. Source: results/tables/T4c_item_missingness.csv.

04Which hardware is under-documented

Documentation tracks use, platform and hardware class, not era.

Completeness differed by hardware class (Kruskal–Wallis p = 0.00), flight platform (p = 5.9 × 10⁻⁶) and catalogue coverage (p = 1.0 × 10⁻⁶), but not by era (p = 0.27) or SPLASH status (p = 0.17). Cell and microbe culture hardware was least documented and ISS hardware best. Hardware used in OSDR studies was better documented than unused hardware (p = 5.3 × 10⁻⁸; Spearman ρ = 0.54 with the number of studies), but several used items remain below the median, and some of the most-used hardware cannot be modelled: the ISS Rodent Habitat, linked to 133 OSDR studies, has no published internal cage dimensions in any source we could open, and BRIC-PDFU, linked to 13 studies, has no published internal dimensions.

05Validating the scorer

Two blind raters, an adjudicated gold standard, and a conservative automated scorer.

Two raters scored a random sample of 12 habitats blind; they agreed on 90% of 180 cells (weighted κ = 0.89). Against the adjudicated gold standard the automated scorer never credited absent information (precision 1.00) but missed some (recall 0.69; mean completeness 0.36 versus 0.53 gold), so automated completeness is a conservative lower bound. No sampled entity was Tier A on the gold scores either.

06Hardware explorer

All 111 specimen-housing items, scored from public metadata.

Completeness is the share of the 15 checklist items found in SPLASH, the OSDR registry and linked study metadata (0–1); the bar marks it visually. Platforms are those named in the hardware's catalogue and registry text, not a flight log; feeding modes are shown only where a verbatim quotation supports them. Missing critical items are listed under each tier. Download: habitats.json.

07Literature curation

Papers, technical reports and mission documentation, one verbatim quotation per value.

Curation of 37 hardware items yielded 592 sourced parameters out of 1,081 sought (54.76%). 4 items reached Tier A (the Advanced Plant Habitat, the JAXA Aquatic Habitat, the Mice Drawer System and the Vented Fly Box), 24 remained Tier B and 9 Tier C. The commonest gap is the airflow that ventilates the specimens, missing for 15 curated items. An independent audit found all 40 of 40 sampled quotations in their sources.

G1 enclosure dimensions · G2 specimen container · F1 ventilation mode · F2 airflow rate · E1 temperature · B1 specimen. Every value, source and quotation is in hardware/*.yaml.

08Solver verification

OpenFOAM v2606 (buoyantBoussinesqPimpleFoam) against benchmark and analytic solutions.

The solver reproduced the reference heated-cavity Nusselt numbers with second-order convergence (observed order 2.05 and 2.15 at Ra = 10⁵ and 10⁶); Richardson-extrapolated values were within 0.07% of Hortmann et al. (1990). One-dimensional diffusion matched the analytic solution to 4.6 × 10⁻⁵ (concentration scale 0–1), and the transient CO₂ balance closed to within 0.68% in every hardware run. Grid convergence indices were computed for 26 quantities on three-mesh ladders (17 converging monotonically; median fine-mesh GCI 1.50%, maximum 14.36%; full table in the supplement).

De Vahl Davis heated cavity on 64², 96² and 128² meshes. Source: results/tables/T8_verification_cavity.csv.

09Specimen environments, flight versus ground

Three-dimensional transient models of the four CFD-ready items, at 0 g and 1 g.

• Mice Drawer System. With the sourced cage through-flow and organism-level loads for a 30 g mouse, the air around the mouse carried 15.58 ppm more CO₂ than the supply, was 0.29 K warmer and had a mean age of 0.27 s. Flight and ground control differed by 0.19%: the forced flow dominates the mouse's buoyant plume (Ri = 0.01).
• Advanced Plant Habitat. At the PH-04 set-points the canopy CO₂ excess was −6.50 ppm relative to the supply in flight (s.d. 0.46) and −6.82 ppm in ground control (s.d. 0.28), a difference within the fluctuation of the transitional, fan-driven flow. At maximum fan speed it was −1.34 ppm.
• Vented Fly Box. The box exchanges gas with the cabin only through its vents, whose size is not published. With 20 mm vents the CO₂ excess at the vial plugs reached 187.94 ppm, with 60 mm vents 40.51 ppm: 4.64-fold from one undocumented parameter.
• Aquatic Habitat. At the sourced flow per aquarium, the mean age of water was 544.50 s against a nominal residence time of 441.00 s, which indicates poorly flushed regions for the assumed port positions.

End-of-run specimen-zone values on the medium mesh; ± is the temporal s.d. over the last quarter of the run. Hardware without a sourced heat load is run at 0 g only, because 1 g is identical by construction. Source: results/tables/T9_cfd_results_medium.csv.

Model viewer

Engineering drawing, animated mid-plane record, end-of-run field slices and specimen-zone time series for each run. The animations play while they are on screen (use the controls to pause or step); full VTK time series will be in the Zenodo deposit.

10Cabin telemetry: what it can and cannot test

ISS-cabin and ground-control temperature, humidity and CO₂ from the OSDR Environmental Data App.

Of the 24 missions in the OSDR Environmental Data App, 13 Rodent Research missions have flight and ground-control series of the same variables during habitation (10 with CO₂). All of them describe cabin or ground-chamber air; none measures the interior of the hardware. The ground-control series tracked the cabin with a lag of at most 1 h, and median flight − ground differences were within 0.10 °C, 1.03% relative humidity and 67.33 ppm CO₂, except in RR-3, whose ground controls were 2.00 °C warmer than the cabin (23.88 versus 21.88 °C).

Median [interquartile range] of hourly flight − ground differences. Source: results/tables/T11_flight_ground.csv; habitation windows in data/curated/eda_mission_windows.csv.

11What the models can and cannot say

Undocumented inputs can matter more than gravity.

In the four hardware items that could be modelled, the gravity contrast was small: forced ventilation dominated the mouse-cage environment, and in the plant growth chamber the flight–ground difference was within the fluctuation of the flow. This is not evidence that gravity does not matter to these environments, because the loads that would let it act (canopy and lamp heat, fly metabolic heat, the solutal buoyancy of exhaled CO₂) are exactly the inputs the public record does not provide. For hardware of this kind, interpreting a flight–ground difference as a gravity effect requires the hardware environment to be measured or modelled, and modelling requires metadata that do not yet exist publicly.

Recommendations for SPLASH and the OSDR registry

1. Adopt the MI-CFD-HW items as structured fields with units and provenance.
2. Populate the existing but empty sources, schematics and study_links fields.
3. Replace the free-text experiment-platform field of OSDR studies with a controlled reference to a hardware identifier.
4. Record, per flight, the logged temperature, humidity and CO₂ of the hardware interior.

Data & code

Every number is generated from the repository; every hardware value carries its source.

make setup      # Python venv with pinned requirements
make analysis   # catalogue → crosswalk → classification → sufficiency → meta-analysis → validation → figures
make verify     # CFD verification (Docker + OpenFOAM v2606)
make cfd        # Tier-A campaign, 0 g and 1 g, mesh ladders
make post       # drawings, results, GCI
make paper      # manuscript PDF / DOCX / HTML
make site       # this page