Gravitational Environment Research Articles

Tethered spacecraft in asteroid gravitational environment

Relative equilibria of a pendulum attached to the surface of a uniformly rotating celestial body are considered. The locations of the tether anchor that correspond to a given spacecraft position are defined. The domains, where the spacecraft can be held with the help of such a pendulum, are also described. Stability of the found relative equilibria is studied.

Stability of gene expression in human T cells in different gravity environments is clustered in chromosomal region 11p15.4

In the last decades, a plethora of in vitro studies with living human cells contributed a vast amount of knowledge about cellular and molecular effects of microgravity. Previous studies focused mostly on the identification of gravity-responsive genes, whereas a multi-platform analysis at an integrative level, which specifically evaluates the extent and robustness of transcriptional response to an altered gravity environment was not performed so far. Therefore, we investigated the stability of gene expression response in non-activated human Jurkat T lymphocytic cells in different gravity environments through the combination of parabolic flights with a suborbital ballistic rocket and 2D clinostat and centrifuge experiments, using strict controls for excluding all possible other factors of influence. We revealed an overall high stability of gene expression in microgravity and identified olfactory gene expression in the chromosomal region 11p15.4 as particularly robust to altered gravity. We identified that classical reference genes ABCA5, GAPDH, HPRT1, PLA2G4A, and RPL13A were stably expressed in all tested gravity conditions and platforms, while ABCA5 and GAPDH were also known to be stably expressed in U937 cells in all gravity conditions. In summary, 10–20% of all transcripts remained totally unchanged in any gravitational environment tested (between 10−4 and 9 g), 20–40% remained unchanged in microgravity (between 10−4 and 10−2 g) and 97–99% were not significantly altered in microgravity if strict exclusion criteria were applied. Therefore, we suppose a high stability of gene expression in microgravity. Comparison with other stressors suggests that microgravity alters gene expression homeostasis not stronger than other environmental factors.

Quantum principle of sensing gravitational waves: From the zero-point fluctuations to the cosmological stochastic background of spacetime

We carry out a theoretical investigation on the collective dynamics of an ensemble of correlated atoms, subject to both vacuum fluctuations of spacetime and stochastic gravitational waves. A general approach is taken with the derivation of a quantum master equation capable of describing arbitrary confined nonrelativistic matter systems in an open quantum gravitational environment. It enables us to relate the spectral function for gravitational waves and the distribution function for quantum gravitational fluctuations and to indeed introduce a new spectral function for the zero-point fluctuations of spacetime. The formulation is applied to two-level identical bosonic atoms in an off-resonant high-$Q$ cavity that effectively inhibits undesirable electromagnetic delays, leading to a gravitational transition mechanism through certain quadrupole moment operators. The overall relaxation rate before reaching equilibrium is found to generally scale collectively with the number $N$ of atoms. However, we are also able to identify certain states of which the decay and excitation rates with stochastic gravitational waves and vacuum spacetime fluctuations amplify more significantly with a factor of $N^2$. Using such favourable states as a means of measuring both conventional stochastic gravitational waves and novel zero-point spacetime fluctuations, we determine the theoretical lower bounds for the respective spectral functions. Finally, we discuss the implications of our findings on future observations of gravitational waves of a wider spectral window than currently accessible. Especially, the possible sensing of the zero-point fluctuations of spacetime could provide an opportunity to generate initial evidence and further guidance of quantum gravity.

Dynamic gene expression response to altered gravity in human T cells

We investigated the dynamics of immediate and initial gene expression response to different gravitational environments in human Jurkat T lymphocytic cells and compared expression profiles to identify potential gravity-regulated genes and adaptation processes. We used the Affymetrix GeneChip® Human Transcriptome Array 2.0 containing 44,699 protein coding genes and 22,829 non-protein coding genes and performed the experiments during a parabolic flight and a suborbital ballistic rocket mission to cross-validate gravity-regulated gene expression through independent research platforms and different sets of control experiments to exclude other factors than alteration of gravity. We found that gene expression in human T cells rapidly responded to altered gravity in the time frame of 20 s and 5 min. The initial response to microgravity involved mostly regulatory RNAs. We identified three gravity-regulated genes which could be cross-validated in both completely independent experiment missions: ATP6V1A/D, a vacuolar H + -ATPase (V-ATPase) responsible for acidification during bone resorption, IGHD3-3/IGHD3-10, diversity genes of the immunoglobulin heavy-chain locus participating in V(D)J recombination, and LINC00837, a long intergenic non-protein coding RNA. Due to the extensive and rapid alteration of gene expression associated with regulatory RNAs, we conclude that human cells are equipped with a robust and efficient adaptation potential when challenged with altered gravitational environments.

A Case Study of Human Roll Tilt Perception in Hypogravity.

Increased gravito-inertial acceleration, or hypergravity, such as produced in a centrifuge or in an aircraft coordinated turn, causes humans to systematically overestimate their roll tilt in the dark. This is known as the "G-excess" illusion. We have previously modified a mathematical observer model of dynamic orientation perception to replicate these illusory tilt perceptions. This modified model also made a novel, previously untested, prediction that humans would underestimate acute roll tilt in reduced gravitational environments (hypogravity). In the current study, we used aircraft parabolic flight to test this prediction in a single subject. Roll tilt perception was reported using a subjective visual vertical task in which the subject aligned an illuminated line, presented in a head mounted display, with their perceived direction of down. The same subject made reports during hypogravity parabolas (0.165 G and 0.38 G, corresponding to lunar and Martian gravity, respectively), hypergravity maneuvers (1.6 G during a pull out maneuver and 1.2 G during a coordinated turn), and 1-G control conditions (both on the ground and in straight and level flight). As hypothesized, the subject significantly underestimated roll tilt in the hypogravity environments by approximately 40% compared to 1-G reports while overestimating roll tilt in the hypergravity environments. The amount of underestimation observed was quantitatively consistent with that predicted a priori by the modified observer model. We propose the term "G-shortage" illusion for the underestimation of roll tilt in hypogravity. This illusion may have implications for aircraft pilots and astronauts.Clark TK, Young LR. A case study of human roll tilt perception in hypogravity. Aerosp Med Hum Perform. 2017; 88(7):682-687.

Propellant Management Devices for Low-Gravity Fluid Management: Past, Present, and Future Applications

This paper presents a comprehensive background and historical review of propellant management devices used throughout space flight history. The purpose of a propellant management device is to separate liquid and gas phases within a propellant tank and to transfer vapor-free propellant from a storage tank to a transfer line en route to either an engine or a receiver depot tank, in any gravitational or thermal environment. The design concept, basic flow physics, and principle of operation are presented for each type of propellant management device. The three primary capillary-driven propellant management device types of vanes, sponges, and screen channel liquid acquisition devices are compared and contrasted. For each propellant management device type, a detailed review of previous applications using storable propellants is given, which include space experiments as well as space missions and vehicles, in storable and cryogenic propellants. Future needs and recent technology developments are also discussed for future in-space cryogenic propellant management.

Rapid adaptation to microgravity in mammalian macrophage cells

Despite the observed severe effects of microgravity on mammalian cells, many astronauts have completed long term stays in space without suffering from severe health problems. This raises questions about the cellular capacity for adaptation to a new gravitational environment. The International Space Station (ISS) experiment TRIPLE LUX A, performed in the BIOLAB laboratory of the ISS COLUMBUS module, allowed for the first time the direct measurement of a cellular function in real time and on orbit. We measured the oxidative burst reaction in mammalian macrophages (NR8383 rat alveolar macrophages) exposed to a centrifuge regime of internal 0 g and 1 g controls and step-wise increase or decrease of the gravitational force in four independent experiments. Surprisingly, we found that these macrophages adapted to microgravity in an ultra-fast manner within seconds, after an immediate inhibitory effect on the oxidative burst reaction. For the first time, we provided direct evidence of cellular sensitivity to gravity, through real-time on orbit measurements and by using an experimental system, in which all factors except gravity were constant. The surprisingly ultra-fast adaptation to microgravity indicates that mammalian macrophages are equipped with a highly efficient adaptation potential to a low gravity environment. This opens new avenues for the exploration of adaptation of mammalian cells to gravitational changes.

The Speed of Light in a Novel Gravitational Environment

In this paper, a review of the experiments, developments and ideas which have been presented on this topic together with its natural extension to the description of gravity, the ultimate dominating mystery of the universe, was taken out. A parallel mechanism was proposed between the emission of light and of neutrino by quantum leaps of electrons between the fixed energy levels of atomic orbits. The analysis of the neutron-proton mix of existing nuclides provides a rule for the calculation of the neutrino flux from matter and suggests both a medium for the transmission of light and a solution to the problem of gravitation.

The need for accurate redshifts in supernova cosmology

Recent papers have shown that a small systematic redshift shift (Δ z∼ 10−5) in measurements of type Ia supernovae can cause a significant bias (∼1%) in the recovery of cosmological parameters. Such a redshift shift could be caused, for example, by a gravitational redshift due to the density of our local environment. The sensitivity of supernova data to redshift shifts means supernovae make excellent probes of inhomogeneities. We therefore invert the analysis, and try to diagnose the nature of our local gravitational environment by fitting for Δ z as an extra free parameter alongside the usual cosmological parameters. Using the Joint Light-curve SN Ia dataset we find the best fit includes a systematic redshift shift of Δ z = (2.6+2.7−2.8) × 10−4. This is a larger shift than would be expected due to gravitational redshifts in a standard Λ-Cold Dark Matter universe (though still consistent with zero), and would correspond to a monopole Doppler shift of about 100 km s−1 moving away from the Milky-Way. However, since most supernova measurements are made to a redshift precision of no better than 10−3, it is possible that a systematic error smaller than the statistical error remains in the data and is responsible for the shift; or that it is an insignificant statistical fluctuation. We find that when Δ z is included as a free parameter while fitting to the JLA SN Ia data, the constraints on the matter density shifts to Ωm = 0.313+0.042−0.040, bringing it into better agreement with the CMB cosmological parameter constraints from Planck. A positive Δ z∼ 2.6×10−4 would also cause us to overestimate the supernova measurement of Hubble's constant by Δ H0 ∼ 1 kms−1Mpc−1. However this overestimation should diminish as one increases the low-redshift cutoff, and this is not seen in the most recent data.

Direction-dependent arm kinematics reveal optimal integration of gravity cues.

The brain has evolved an internal model of gravity to cope with life in the Earth's gravitational environment. How this internal model benefits the implementation of skilled movement has remained unsolved. One prevailing theory has assumed that this internal model is used to compensate for gravity's mechanical effects on the body, such as to maintain invariant motor trajectories. Alternatively, gravity force could be used purposely and efficiently for the planning and execution of voluntary movements, thereby resulting in direction-depending kinematics. Here we experimentally interrogate these two hypotheses by measuring arm kinematics while varying movement direction in normal and zero-G gravity conditions. By comparing experimental results with model predictions, we show that the brain uses the internal model to implement control policies that take advantage of gravity to minimize movement effort.

Treadmill exercise within lower-body negative pressure attenuates simulated spaceflight-induced reductions of balance abilities in men but not women.

Spaceflight causes sensorimotor adaptations that result in balance deficiencies on return to a gravitational environment. Treadmill exercise within lower-body negative pressure (LBNP) helps protect physiological function during microgravity as simulated by bed rest. Therefore, we hypothesized that treadmill exercise within LBNP would prevent balance losses in both male and female identical twins during 30 days of 6° head-down tilt bed rest. Fifteen (seven female and eight male) identical twin sets participated in this simulation of microgravity. Within each twin pair, one twin was randomly assigned to an exercise group that performed 40 min of supine treadmill exercise within LBNP set to generate 1.0–1.2 body weight, followed by 5 min of static feet-supported LBNP, 6 days per week. Their identical sibling was assigned to a non-exercise control group with all other bed rest conditions equivalent. Before and immediately after bed rest, subjects completed standing and walking rail balance tests with eyes open and eyes closed. In control subjects, standing rail balance times (men: −42%, women: −40%), rail walk distances (men: −44%, women: −32%) and rail walk times (men: −34%, women: −31%) significantly decreased after bed rest. Compared with controls, treadmill exercise within LBNP significantly attenuated losses of standing rail balance time by 63% in men, but the 41% attenuation in women was not significant. Treadmill exercise within LBNP did not affect rail walk abilities in men or women. Treadmill exercise within LBNP during simulated spaceflight attenuates loss of balance control in men but not in women.

Yarman’s approach predicts anomalous gravitational bending of high-energy gamma-quanta

We predict anomalous gravitational bending of gamma rays using the gravitational framework of Yarman’s approach, abbreviated hereinafter as “YARK” from the initials of the co-authors to designate their teamwork. In contrast to the metric layout of the general theory of relativity (GTR), YARK theory is founded directly on the energy conservation law pertaining to interaction between masses. Despite the fact that predictions made respectively by GTR and YARK regarding cornerstone astrophysical observations appear remarkably identical to each other, the philosophies behind them are irreconcilably different. To test which theory comes closer to the reality, one should propose ways to distinguish their success at the experimental level. Note that bending of light in GTR represents a purely metric effect, which cannot depend on the energy of photons, whereas YARK conceptually allows the deflection of photons across a gravitational environment contingent upon either their wave-like or corpuscular-like behavior. In the case of “wave-like propagation”, which we deem particular to low-energy photons (including the visible range), YARK arrives at the same results as GTR; whereas for high-energy gamma-quanta, which we deem to signify “corpuscular-like propagation”, the deflection in a gravitational field practically vanishes in YARK. Given this opportunity to test YARK theory against GTR, we discuss possible experimental setups relevant to the subject.

Lower Body Negative Pressure Treadmill Exercise Attenuates Simulated Space Flight‐Induced Reductions of Balance Abilities in Males but not Females

Spaceflight causes sensorimotor adaptations that result in balance deficiencies upon return to a gravitational environment. Lower Body Negative Pressure (LBNP) treadmill exercise has been shown to protect against deconditioning in various other physiological systems during simulated spaceflight. Therefore, we hypothesized that LBNP treadmill exercise prevents balance losses in both male and female identical twins during 30 days of 6° head‐down‐tilt (HDT) bed rest. Fifteen (8M and 7F) identical twin sets participated in 30 days of bed rest. Within each twin pair, one twin was randomly assigned to an exercise group that performed 40 min of supine LBNP treadmill exercise set to generate 1.0–1.2 body weight, followed by 5 min of static LBNP, 6 days/wk. Their identical sibling was assigned to a non‐exercise control group. Before and immediately after bed rest, subjects completed standing and walking rail balance tests with eyes open and eyes closed. In control subjects, standing rail balance times (men: −42%, women: −40%), rail walk distances (men: −44%, women: −32%), and rail walk times (men: −34%, women: −31%) significantly decreased after bed rest. Compared to controls, subjects in the LBNP treadmill exercise group showed significantly attenuated losses of standing rail balance time, with prevention of 63% of the loss in men, but without a significant prevention in women (41%). In addition, LBNP treadmill exercise mitigated decreases in rail walk time in men, but not in women. Therefore, treadmill exercise within LBNP during spaceflight may maintain balance control; yet this protective effect may, to some extent, depend on gender.Support or Funding InformationThis study was funded by NASA grants NAG 9‐1425, NCC2‐1133, NNX10AM18G, and NNX13AJ12G, NIH grant to the UCSD GCRC M01 RR00827. BRM was supported by National Space Biomedical Research Institute through NCC 9‐58. We thank our outstanding twins and staff at the UCSD General Clinical Research Center, as well as the UCSD Faculty Mentorship Program and the 2015 Julia Brown Research Scholarship.

Investigation of flow boiling in large micro-channel heat exchangers in a refrigeration loop for space applications

Future manned space endeavors will require a new class of vehicles, capable of conducting different types of missions and enduring varying gravitational and temperature environments. Thermal management will play a vital role in these new vehicles, and is complicated by the need to tackle both low and high heat sink temperatures. The present study concerns the development of a thermal management system operating in vapor compression mode to tackle high heat sink temperatures. The specific goal of the study is to investigate the two-phase heat transfer characteristics of two large micro-channel heat exchangers that serve as evaporators in the vapor compression loop using R134a as refrigerant. Both heat exchangers feature parallel micro-channels with identical 1×1-mm2 cross-sections. The evaporators are connected in series, with the smaller 152.4-mm long heat exchanger situated upstream of the larger 609.6-mm long heat exchanger. This layout, along with broad ranges of mass velocity (152.90–530.72kg/m2s) and base heat flux (8072.93–48,437.60W/m2) produced a wide range of qualities, which facilitated systematic assessment of dominant heat transfer mechanisms using both heat transfer measurements and high-speed video. Overall, it is shown low qualities are associated with slug flow and dominated by nucleate boiling, and high qualities with annular flow and convective boiling. Important transition points between the different heat transfer regimes are identified as (1) intermittent dryout, resulting from vapor blanket formation in liquid slugs and/or partial dryout in the liquid film surrounding elongated bubbles, (2) incipient dryout, resulting from dry patch formation in the annular film, and (3) complete dryout, following which the wall has to rely entirely on the mild cooling provided by droplets deposited from the vapor core. Finally, the study provides an assessment of the accuracy of eight previous correlations in predicting the measured two-phase heat transfer coefficient for both evaporators. Only one correlation is found to provide acceptable predictions in both accuracy and trend, evidenced by a mean absolute error of 21.19%, with 69.92% and 95.12% of the predictions falling within ±30% and ±50% of the data, respectively.

Thermal analysis of hybrid single-phase, two-phase and heat pump thermal control system (TCS) for future spacecraft

An urgent need presently exists to develop a new class of versatile spacecraft capable of conducting different types of missions and enduring varying gravitational and temperature environments, including Lunar, Martian and Near Earth Object (NEOs). This study concerns the spacecraft's Thermal Control System (TCS), which tackles heat acquisition, especially from crew and avionics, heat transport, and ultimate heat rejection by radiation. The primary goal of the study is to explore the design and thermal performance of a Hybrid Thermal Control System (H-TCS) that would satisfy the diverse thermal requirements of the different space missions. The H-TCS must endure both ‘cold’ and ‘hot’ environments, reduce weight and size, and enhance thermodynamic performance. Four different operational modes are considered: single-phase, two-phase, basic heat pump and heat pump with liquid-side, suction-side heat exchanger. A thermodynamic trade study is conducted for six different working fluids to assess important performance parameters including mass flow rate of the working fluid, maximum pressure, radiator area, compressor/pump work, and coefficient of performance (COP). R134a is determined to be most suitable based on its ability to provide a balanced compromise between reducing flow rate and maintaining low system pressure, and a moderate coefficient of performance (COP); this fluid is also both nontoxic and nonflammable, and features zero ozone depletion potential (ODP) and low global warming potential (GWP). It is shown how specific mission stages dictate which mode of operation is most suitable, and this information is used to size the radiator for the H-TCS.

Computational characterization of fracture healing under reduced gravity loading conditions.

The literature is deficient with regard to how the localized mechanical environment of skeletal tissue is altered during reduced gravitational loading and how these alterations affect fracture healing. Thus, a finite element model of the ovine hindlimb was created to characterize the local mechanical environment responsible for the inhibited fracture healing observed under experimental simulated hypogravity conditions. Following convergence and verification studies, hydrostatic pressure and strain within a diaphyseal fracture of the metatarsus were evaluated for models under both 1 and 0.25 g loading environments and compared to results of a related in vivo study. Results of the study suggest that reductions in hydrostatic pressure and strain of the healing fracture for animals exposed to reduced gravitational loading conditions contributed to an inhibited healing process, with animals exposed to the simulated hypogravity environment subsequently initiating an intramembranous bone formation process rather than the typical endochondral ossification healing process experienced by animals healing in a 1 g gravitational environment. © 2015 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 34:1206-1215, 2016.

A natural autonomous force added in the restricted problem and explored via stability analysis and discrete variational mechanics

With improved observational capabilities, an increasing number of binary systems have been discovered both within the solar system and beyond. By characterizing the gravitational environment near a binary star, for example, potential motions of a nearby exoplanet may be explored. The path of this comparatively small body is influenced by an underlying dynamical structure of periodic orbits which can attract, bound or repel trajectories in their vicinity. In this investigation, stability analysis is employed to examine the evolution of selected families of periodic orbits near large mass ratio binary systems in two dynamical models: the circular restricted three-body problem and an expanded model that incorporates an additional autonomous force to examine theories for three-body gravitational interactions. Discrete variational mechanics is employed to determine the natural parameters corresponding to the existence of a given orbit geometry, facilitating exploration of the effect of an additional three-body interaction on nearby periodic orbits and the conditions for reproducibility in the natural gravitational environment. Any unique effects of the additional autonomous force contribution may impact the potential motion of an exoplanet as it orbits a binary star system.

The Impact of Simulated Weightlessness on Endothelium-Dependent Angiogenesis and the Role of Caveolae/Caveolin-1

Background/Aims: The potential role of caveolin-1 in modulating angiogenesis in microgravity environment is unexplored. Methods: Using simulated microgravity by clinostat, we measured the expressions and interactions of caveolin-1 and eNOS in human umbilical vein endothelial cells. Results: We found that decreased caveolin-1 expression is associated with increased expression and phosphorylation levels of eNOS in endothelial cells stimulated by microgravity, which causes a dissociation of eNOS from caveolin-1 complexes. As a result, microgravity induces cell migration and tube formation in endothelial cell in vitro that depends on the regulations of caveolin-1. Conclusion: Our study provides insight for the important endothelial functions in altered gravitational environments.

The Astronaut-Athlete: Optimizing Human Performance in Space.

It is well known that long-duration spaceflight results in deconditioning of neuromuscular and cardiovascular systems, leading to a decline in physical fitness. On reloading in gravitational environments, reduced fitness (e.g., aerobic capacity, muscular strength, and endurance) could impair human performance, mission success, and crew safety. The level of fitness necessary for the performance of routine and off-nominal terrestrial mission tasks remains an unanswered and pressing question for scientists and flight physicians. To mitigate fitness loss during spaceflight, resistance and aerobic exercise are the most effective countermeasure available to astronauts. Currently, 2.5 h·d, 6-7 d·wk is allotted in crew schedules for exercise to be performed on highly specialized hardware on the International Space Station (ISS). Exercise hardware provides up to 273 kg of loading capability for resistance exercise, treadmill speeds between 0.44 and 5.5 m·s, and cycle workloads from 0 and 350 W. Compared to ISS missions, future missions beyond low earth orbit will likely be accomplished with less vehicle volume and power allocated for exercise hardware. Concomitant factors, such as diet and age, will also affect the physiologic responses to exercise training (e.g., anabolic resistance) in the space environment. Research into the potential optimization of exercise countermeasures through use of dietary supplementation, and pharmaceuticals may assist in reducing physiological deconditioning during long-duration spaceflight and have the potential to enhance performance of occupationally related astronaut tasks (e.g., extravehicular activity, habitat construction, equipment repairs, planetary exploration, and emergency response).

Consolidated methodology to predicting flow boiling critical heat flux for inclined channels in Earth gravity and for microgravity

The transition from single-phase to two-phase thermal systems in future space vehicles demands a thorough understanding of flow boiling critical heat flux (CHF) in reduced gravity, including microgravity. This study is a comprehensive, consolidated investigation of the complex trends of flow boiling CHF in a rectangular channel in both microgravity and for different orientations in Earth gravity. It is shown that the Interfacial Lift-off Model provides good predictions of CHF data for both gravitational environments and both single-sided and double-sided heating. CHF mechanism in Earth gravity is shown to be highly sensitive to flow orientation at very low velocities, but is consistent with the wavy vapor layer depiction of the Interfacial Lift-off Model at high velocities. The model predicts a stable vapor-liquid interface for downflow with a downward-facing heated wall at lower velocities, and wavy interface with a critical wavelength that decreases with increasing velocity at higher velocities. Predicted CHF values for microgravity fall about midway between the maxima and minima for Earth gravity. Overall, predicted values of CHF and key interfacial parameters for all orientations in Earth gravity and for microgravity converge above ∼1.5m/s, which points to a velocity threshold above which inertia begins to effectively negate gravity effects.