Liquid Propellant Mass Measurement in Microgravity

The Modal Propellant Gauging (MPG) experiment has demonstrated sub-1% gauging accuracy under laboratory conditions on both flight hardware and subscale tanks. Recently, MPG was adapted for flight on Blue Origin's New Shepard vehicle and has flown twice, achieving equilibrated, zero-g surface configurations of propellant simulant at three different fill fractions. Flight data from MPG missions on New Shepard P7 and P9 show agreement between known and measured propellant levels of 0.3% for the fill fractions investigated in the present study. Two approaches for estimating zero-g propellant mass are described here. Both approaches rely on measuring shifts in modal frequencies of a tank excited by acoustic surface waves and subject to fluid mass loading by the propellant. In the first approach, shifts in the lowest mode frequency (LMF) are measured and associated with liquid fill-level changes. In the second approach, 1-g modal spectra at a range of known fill levels are used in a cross-correlation calculation to predict fill levels associated with a zero-g modal spectrum. Flight data for both approaches are consistent with finite element predictions using a simple fluid–structure interaction model. In both settled and unsettled microgravity environments, MPG meets or exceeds NASA Roadmap goals for in-space propellant mass gauging.

Space Flight Cultivation for Radish (Raphanus sativus) in the Advanced Plant Habitat

In preparation of a flight experiment, ground-based studies for optimizing the growth of radishes (Raphanus sativus) were conducted at the ground-based Advanced Plant Habitat (APH) unit at the Kennedy Space Center (KSC), Florida. The APH provides a large, environmentally controlled chamber that has been used to grow various plants, such as Arabidopsis, wheat, peppers, and now radish. In support of National Aeronautics and Space Administration (NASA)'s goals to provide astronauts with fresh vegetables and fruits in a confined space, it is important to extend the cultivation period to produce substantial biomass. We selected Raphanus sativus cv. Cherry Belle as test variety both for preliminary tests and flight experiments because it provides edible biomass in as few as four weeks, has desirable secondary metabolites (glucosinolates), is rich in minerals, and requires relatively little space. We report our strategies to optimize the growth substrate, watering regimen, light settings, and planting design that produces good-sized radishes, minimizes competition, and allows for easy harvesting. This information will be applicable for growth optimization of other crop plants that will be grown in the APH or other future plant growth facilities.

Research Flights on Blue Origin's New Shepard

Blue Origin's New Shepard launch vehicle made its first flight above the Kármán Line, returning safely to Earth in November 2015. At the time when this paper is being written (February 2021), the system has conducted 14 flights, including 10 with research and education payloads aboard. More than 100 payloads have exercised a wide range of capabilities and interfaces, from small cubesat-form factor student payloads to large custom payloads of nearly 100 kg. Investigations have spanned a wide range of high-altitude and microgravity research objectives, as well as raising technology readiness level (TRL) on diverse hardware. This paper summarizes New Shepard's payload missions to date, and presents standardized and custom accommodations, both in the shirtsleeve cabin and directly exposed to the space environment.

The Impact of Hindlimb Suspension on the Rat Eye: A Molecular and Histological Analysis of the Retina

The Spaceflight Associated Neuro-ocular Syndrome (SANS) is hypothesized to be associated with microgravity-induced fluid shifts. There is a need for an animal model of SANS to investigate its pathophysiology. We used the rat hindlimb suspension (HS) model to examine the relationship between the assumed cephalad fluid shifts, intraocular (IOP) pressure and the molecular responses in the retina to the prolonged change in body posture. Long evans rats were subjected to HS up to 90 days. Animals completing 90-day suspension were further studied for recovery periods up to 90 additional days in normal posture. With respect to baseline, the average IOP increase in HS animals and the rate of change varied by cohort. Transcriptomics evidence supported a response to HS in the rat retina that was affected by age and sex. Several molecular networks suggested stress imposed by HS affected the retinal vasculature, oxidative and inflammation status, pigmented epithelium and glia. The CSNK1A1-TP53 pathway was implicated in the response in all cohorts. Sex-specific genes were involved in cytoprotection and may explain sex-dependent vulnerabilities to certain eye diseases. These results support the hypothesis that changes in the biology of the retina subjected to simulated microgravity involve both the neural and vascular retina.

Toward the Analysis of Lymphocyte Development in Space: PCR-Based Amplification of T-Cell Receptor Excision Circles (TRECs) Aboard the International Space Station

Spaceflight offers vast possibilities for expanding human exploration, whereas it also bears unique health risks. One of these risks is immune dysfunction, which can result in the reactivation of latent pathogens and increased susceptibility to infections. The ability to monitor the function of the immune system is critical for planning successful long-term space travel. T lymphocytes are immune cells that develop in the thymus and circulate in the blood. They can detect foreign, infected, or cancerous cells through T cell receptors (TCRs). The assembly of TCR gene segments, to produce functional TCR genes, can be monitored by measuring the presence of TCR excision circles (TRECs), circular fragments of DNA that are by-products of this assembly process mediated by the V(D)J recombination machinery. In this study, we used polymerase chain reaction (PCR) on the International Space Station (ISS) to detect TRECs in murine peripheral blood. We were able to detect TRECs in the blood of normal healthy mice of different ages, with an efficiency comparable to that achieved in ground controls. As expected, we were unable to detect TRECs in the blood of immunodeficient mice. These results are the first step in optimizing a specific, rapid, safe, and cost-effective PCR-based assay to measure the integrity of mammalian immune systems during spaceflight.

A Rapid Fabrication Methodology for Payload Modules, Piloted for the Observation of Queen Honey Bees (Apis mellifera) in Microgravity

Microgravity experiment modules for living organisms have been instrumental to space research, yet their design remains complex and costly. As the private space sector enables more widely available payloads for researchers, it is increasingly necessary to design experimental modules innovatively so that they are proportionately accessible. To ease this bottleneck, we developed a rapid fabrication methodology for producing custom modules compatible with commercial payload slots. Our method creates a unified housing geometry, based on a given component layout, which is fabricated in a digital design and subtractive manufacturing process from a single lightweight foam material. This module design demonstrated a 25–50% reduction in chassis weight compared with existing models, and is extremely competitive in manufacturing time, simplicity, and cost. To demonstrate the ability to capture data on previously limited areas of space biology, we apply this methodology to create an autonomous, video-enabled module for sensing and observing queen and retinue bees aboard the Blue Origin New Shepard 11 (NS-11) suborbital flight. To explore whether spaceflight impacts queen fitness, results used high-definition visual data enabled by the module's compact build to analyze queen-worker regulation under microgravity stress (n = 2, with controls). Overall, this generalizable method for constructing experimental modules provides wider accessibility to space research and new data on honey bee behavior in microgravity.

APL JANUS System Progress on Commercial Suborbital Launch Vehicles: Moving the Laboratory Environment to Near Space

Multiple private companies are building suborbital reusable launch vehicles possessing vastly different designs. Many of these companies originally focused on space tourism; however, revolutionary applications for scientific and engineering research as well as technology demonstrations and instrument development are emerging. The dramatic reduction in cost over traditional launch systems as well as a guaranteed (and rapid) safe payload return enable many new launch vehicle applications. These new capabilities will essentially move the laboratory environment up to the edge of space. To make use of these novel launch vehicles, the John Hopkins University Applied Physics Laboratory has established a Commercial Suborbital Program with a core system (JANUS) to support and enable many future suborbital missions. This program has already conducted six suborbital flight missions to establish vehicle interfaces and analyze the suitability and limits of each flight environment. Additionally, this program has also been selected by the NASA Flight Opportunities Program for five additional operational suborbital missions. Here we present the results of our completed missions as well as descriptions of future selected missions scheduled for 2021–2023.

The Circadian-clock Regulates the Arabidopsis Gravitropic Response

For long-term space missions, it is necessary to understand how organisms respond to changes in gravity. Plant roots are positively gravitropic; the primary root grows parallel to gravity's pull even after being turned away from the direction of gravity. We examined if this gravitropic response varies depending on the time of day reorientation occurs. When plants were reoriented in relation to the gravity vector or placed in simulated microgravity, the magnitude of the root gravitropic response varied depending on the time of day the initial change in gravity occurred. The response was greatest when plants were reoriented at dusk, just before a period of rapid growth, and were minimal just before dawn as the plants entered a period of reduced root growth. We found that this variation in the magnitude of the gravitropic response persisted in constant light (CL) suggesting the variation is circadian-regulated. Gravitropic responses were disrupted in plants with disrupted circadian clocks, including plants overexpressing Circadian-clock Associated 1 (CCA1) and elf3-2, in the reorientation assay and on a 2D clinostat. These findings indicate that circadian-regulated pathways modulate the gravitropic responses, thus, highlighting the importance of considering and recording the time of day gravitropic experiments are performed.

Shared Metabolic Remodeling Processes Characterize the Transcriptome of Arabidopsis thaliana within Various Suborbital Flight Environments

The increasing availability of flights on suborbital rockets creates new avenues for the study of spaceflight effects on biological systems, particularly of the transitions between hypergravity and microgravity. This paper presents an initial comparison of the responses of Arabidopsis thaliana to suborbital and atmospheric parabolic flights as an important step toward characterizing these emerging suborbital platforms and their effects on biology. Transcriptomic profiling of the response of the Arabidopsis ecotype Wassilewskija (WS) to the aggregate suborbital spaceflight experiences in Blue Origin New Shepard and Virgin Galactic SpaceShipTwo revealed that the transcriptomic load induced by flight differed between the two flights, yet was biologically related to traditional parabolic flight responses. The sku5 skewing mutant and 14-3-3κ:GFP regulatory protein overexpression lines, flown in the Blue Origin and parabolic flights, respectively, each showed altered intra-platform responses compared to WS. An additional parabolic flight using the F-104 Starfighter showed that the response of 14-3-3κ:GFP to flight was modulated in a similar manner to the WS line. Despite the differing genotypes, experimental workflows, flight profiles, and platforms, differential gene expression linked to remodeling of central metabolic processes was commonly observed in the flight responses. However, the timing and directionality of differentially expressed genes involved in the conserved processes differed among the platforms. The processes included carbon and nitrogen metabolism, branched-chain amino acid degradation, and hypoxic responses. The data presented herein highlight the potential for various suborbital platforms to contribute insights into biological responses to spaceflight, and further suggest that in-flight fixation during suborbital experiments will enhance insights into responses during each phase of flight.

Using Tapered Channels to Improve LAD Performance for Cryogenic Fluids: Suborbital Testing Results

Improvement of cryogenic fluid storage and transfer technology for in-space propulsion and storage systems is required for long-term space missions. Screened channel liquid acquisition devices (LADs) have long been used with storable propellants to deliver vapor-free liquid during engine restart and liquid transfer processes. The use of LADs with cryogenic fluids is problematic due to low temperatures associated with cryogenic fluids. External heat leaks will cause vapor bubbles to form within the LADs that are difficult to remove in the existing designs. A tapered LAD channel has been proposed to reliably remove vapor bubbles within the device without costly thrusting maneuvers or active separation systems. A model has been developed to predict bubble movement within tapered LAD channels, and subsequent ground testing was completed with a simulant fluid to provide model validation data. Suborbital microgravity testing of tapered LAD technology was recently completed with two different simulant fluids and demonstrated that the concept can passively expel vapor bubbles within the channel. Two additional suborbital flights have been funded to further develop this technology by investigating the performance of larger scale versions of the design.