2.2. Pillow Assembly, Layout, and Processing

All pillows were assembled at Kennedy Space Center, FL and prepared for flight as described in detail by Massa et al., 2017 [34]. Briefly, the Veggie pillows contained 250 mL of autoclaved, porous, arcillite substrate with controlled release fertilizer (Nutricote 18-6-8, type 100, Florikan ESA, Sarasota, FL, USA) mixed at 7.5 g/L dry substrate. Two surface sanitized seeds were attached with guar gum to germination wicks in each plant pillow. The mixed crop pillow layout for each study is shown in Figure 2.

Veggie technical demonstrations on ISS (VEG-03D, VEG-03E, and VEG-03F) showing the pillow and plant layout for each. The ‘*’ indicates pillows returned from ISS for analysis. ‘OL’ is ‘Outredgeous’ red romaine lettuce; ‘WG’ is ‘Waldmann’s Green’ leaf lettuce; ‘Mizuna’ is mizuna mustard greens.

The Veggie production system is a small plant growth chamber. Designed and built by ORBITEC (Madison, WI, US) to grow crops in space, it is equipped with LED lighting, a passive watering system and a fan to generate airflow [25,26]. The SN 002 system was launched to the ISS in 2014 aboard Space X CRS-3, while the SN 001 unit was launched aboard Orbital ATK OA-7 in 2017. A HOBO (honest observer by onset) data logger (Onset, Bourne, MA, US) was placed in the Veggie units used for VEG-03D and VEG-03E to record humidity, dew point, and temperature data (Figure S1). HOBO data were not collected from VEG-03F.