Abstract
The Advanced Plant Habitat (APH) is the largest research plant growth facility deployed on the International Space Station (ISS). APH is a fully enclosed, closed-loop plant life support system with an environmentally controlled growth chamber designed for conducting both fundamental and applied plant research during experiments extending as long as 135 days. APH was delivered to the ISS in parts aboard two commercial resupply missions: OA-7 in April 2017 and SpaceX-11 in June 2017, and was assembled and installed in the Japanese Experiment Module Kibo in November 2018. We report here on a 7-week-long hardware validation test that utilized a root module planted with both Arabidopsis (cv. Col 0) and wheat (cv. Apogee) plants. The validation test examined the APH’s ability to control light intensity, spectral quality, humidity, CO2 concentration, photoperiod, temperature, and root zone moisture using commanding from ground facilities at the Kennedy Space Center (KSC). The test also demonstrated the execution of programmed experiment profiles that scheduled: (1) changes in environmental combinations (e.g., a daily photoperiod at constant relative humidity), (2) predetermined photographic events using the three APH cameras [overhead, sideview, and sideview near-infrared (NIR)], and (3) execution of experimental sequences during the life cycle of a crop (e.g., measure photosynthetic CO2 drawdown experiments). Arabidopsis and wheat were grown in microgravity to demonstrate crew procedures, planting protocols and watering schemes within APH. The ability of APH to contain plant debris was assessed during the harvest of mature Arabidopsis plants. Wheat provided a large evaporative load that tested root zone moisture control and the recovery of transpired water by condensation. The wheat canopy was also used to validate the ability of APH to measure gas exchange of plants from non-invasive gas exchange measurements (i.e., canopy photosynthesis and respiration). These features were evaluated by executing experiment profiles that utilized the CO2 drawdown technique to measure daily rates of canopy photosynthesis and dark-period CO2 increase for respiration. This hardware validation test confirmed that APH can measure fundamental plant responses to spaceflight conditions.
Highlights
The Advanced Plant Habitat (APH) facility was designed and built by NASA and Orbital Technologies Corporation (ORBITEC, Sierra Nevada Corp., Madison, WI, United States) to conduct both fundamental and applied plant research in reduced gravity (Figure 1)
This paper describes the results of a hardware validation technology demonstration of the APH facility after its assembly on International Space Station (ISS)
The calculated APH CQY is higher than that measured in the Biomass Production System (BPS), probably because the wheat plants in the BPS were self-shaded. It is slightly (4–8%) higher than the CQY of wheat grown under High Pressure Sodium (HPS) lamps at 1g. The reason for these differences is that the gas exchange data collected includes error in the estimated incident radiation at the top of the canopy, error in the photosynthetic and respiration rates introduced by neglecting the leak rate correction, and errors from assuming that Arabidopsis did not contribute to the photosynthetic CO2 uptake measured in the APH
Summary
The Advanced Plant Habitat (APH) facility was designed and built by NASA and Orbital Technologies Corporation (ORBITEC, Sierra Nevada Corp., Madison, WI, United States) to conduct both fundamental and applied plant research in reduced gravity (Figure 1). The APH facility is a research, plant growth chamber that can grow plants under complete environmental control (i.e., spectral quality, light intensity, temperature, relative humidity, CO2 and ethylene concentration) for life cycles as long as 135 days (Morrow et al, 2016). It incorporates a root module watering design that is similar to those developed for ADVASC and BPS: a substrate-based water delivery system that actively controls matric potential of the root zone (Morrow and Crabb, 2000; Link et al, 2003; Morrow et al, 2004). The SC was sealed within a large, gas impermeable Tedlar bag (SKC, Inc., Eighty Four, PA, United States) (Figure 2E), and packed in foam for launch to the ISS
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