Gravity Assist Research Articles

Geostationary Orbit Transfer with Lunar Gravity Assist from Non-equatorial Launch Site

We show that it is possible to launch a satellite to Geostationary Equatorial orbit (GEO) from the non-equatorial launch site (Naro Space Center in South Korea) even though that is located in the mid-latitudes of the northern hemisphere. When launched from this site, the equatorial inclination after separation will be 80°. We use a lunar gravity assist (LGA) transfer to avoid the excessive ∆V costs of plane change maneuvers. There are eight possible paths for the LGA; there are four paths consisting of Earth departures and free-return types, and there are two nodes of the Moon’s orbit (ascending and descending). We analyze trajectories over five launch periods for each path using a high-fidelity orbit propagation model. We show that the LGA changes the orbital energy of the “cislunar” free-returns more than for the “circumlunar” free-returns, resulting in less geostationary insertion ∆V for the cislunar free-returns. We also show that the geometrical ∆V variation over the different paths is greater than the seasonal ∆V variation. Our results indicate that an ascending departure and cislunar free-return at the descending node have lower ∆V requirements than the other paths, and lower than described in several previous studies.

Validation of modified diuretic drainage times criteria in congenital hydronephrosis

The value of diuretic renography drainage times in congenital hydronephrosis (AHN) decision making is controversial. Recently, a group suggested a modification to the classically described diuretic drainage time cut-off values. They found that a drainage half-time (T1/2)<5min was normal whereas a T1/2 exceeding 75min predicted pyeloplasty. In addition, they reported on the benefit of a delayed drainage image obtained with gravity assistance. We sought to evaluate the ability of these modified T1/2 criteria to predict pyeloplasty, alone or in combination with a delayed drainage image referred to as Global Washout (GWO). We retrospectively reviewed 113 patients, including consecutive pyeloplasties for AHN from 2004 to 2018. Patients who underwent pyeloplasty due to low differential renal function (DRF)<30% or infection were excluded. The control group comprised high grade AHN managed non-operatively. The initial renal ultrasound and MAG 3 Lasix renogram were reviewed for grade, differential renal function (DRF), T1/2 and GWO. A ROC curve was used to evaluate the T1/2 and GWO cut-off points that can predict pyeloplasty, using a p-value of less than 0.05. The pyeloplasty group consisted of 62 patients and the control group consisted of 51 patients. Two patients (3%) in the pyeloplasty group had a T1/2 < 5min whereas 21 (34%) had T 1/2>75min (p<0.001). In the control group, 25 patients (49%) had T 1/2<5min and none had T1/2 >75min (P<0.001). The ROC curve for T1/2 < 5min demonstrated 94% sensitivity and 51% specificity whereas a T1/2 >75min demonstrated 100% specificity and 34% sensitivity. Analysis of the GWO using a ROC curve revealed that a cut-off of 50% GWO has 100% specificity and 52% sensitivity for pyeloplasty. Overall, a T1/2>75min or GWO <50% predicted 53% of pyeloplasties (Fig A) and was absent in all conservatively managed cases. The limitations of the present study include its retrospective nature. Secondly, the lack of a gold standard diagnostic test for uretero-pelvic junction obstruction hampers objective quantification of diagnostic test utility performance. We confirm the utility of the modified diuretic half-time criteria and delayed gravity assisted imaging. A T1/2>75min or GWO <50% are indicators of severity whereas a T1/2 of <5min or GWO >90% is reassuring. Gravity assisted delayed imaging can be especially helpful in cases with indeterminate T 1/2 times and should be included in the standard assessment of hydronephrotic kidneys. These parameters can be used to tailor the frequency and invasiveness of imaging within observation protocols.

Experimental Study of a Loop Heat Pipe with Direct Pouring Porous Wick for Cooling Electronics

A pouring silicate wick was manufactured to explore the influence of process and physical properties on the production and performance of loop heat pipes (LHP). This paper theoretically analyzed the advantages of pouring porous wick and introduced the technology of pouring silicate directly on evaporator. Based on this, the heat transfer performance of copper-methanol LHP system with pouring porous wick was tested under different positions. The results showed that with the input of multiple heat sources, the LHP could start up and maintain a stable temperature from 40 W to 160 W. When the vapor grooves were located above the compensation chamber, it was difficult to start up positively. By adding gravity assistance, the system could obtain more stable liquid supply and vapor flow, so as to realize start up. In the variable heat load test, the LHP showed good adaptability to the change of heat load. The thermal resistance of the system decreased with the increase of heat load. The thermal resistance of the evaporator almost unchanged and was always lower than 0.05 °C/W, which indicated that the pouring porous wick in the evaporator had good heat load matching.

Effects of taping techniques on arch deformation in adults with pes planus: A meta-analysis.

To investigate effects of taping techniques on arch deformation in adults with pes planus. The following databases were searched up to March 2020, including Web of Science, Pubmed, EBSCO, CNKI and Cochrane Library. Heterogeneity and publication bias were assessed by I2 index and funnel plots, respectively. In addition, Cochrane scale was used to evaluate the quality of research. Navicular height for three antipronation taping techniques significantly increased immediately post tape compared with baseline (mean difference = 4.86 mm, 95% CI = 2.86-6.87 mm, Z = 4.75, p < 0.001). The highest increase was observed in Augmented low-Dye (ALD). Modified low-Dye (MLD) was second only to ALD (p<0.001). Navicular height after walking for 10 min was much higher than baseline (p<0.001), with MLD decreased smaller than ALD. ALD was the most effective taping technique for controlling foot arch collapse immediately post tape compared with baseline, followed by MLD. By contrast, MLD could possibly performed better than ALD in maintaining immediate navicular height after walking for 10 min. Low-Dye could make resting calcaneal stance position closer to neutral position. Although positive effects of Navicular sling, low-Dye and Double X taping interventions were observed, they could not maintain this immediate navicular height effect after a period of higher intensity weight-bearing exercise.

Functional Outcome of Open Latarjet Procedure in Non-Athletic Middle-Aged Patients.

Introduction:The movement and steadiness of the shoulder joint is due to both the dynamic and static stabilisers. Recurrent anterior shoulder instability is common due to the Bankart lesion or the Hill Sachs lesion. The bone loss and soft tissue failure due to these lesions causing instability is well compensated by Latarjet procedure which acts by triple blocking effect of the bone graft, the sling effect of the conjoint tendon of subscapularis and the ligament of the coracoacromial ligament stump.Materials and methods:Middle-aged patients with recurrent anterior shoulder dislocation and a mid-range instability on clinical assessment with an isolated glenoid bone loss of 20% or Bankart lesion with engaging Hill Sachs lesion were selected for the study. The surgical procedure included a subscapularis split to expose the glenoid. The coracoid graft harvested was prefixed with Kirschner wires and placed flush over the glenoid ensuring no medial or lateral overhang and fixed with 4.0mm cancellous screws with the washer. The functional outcome was measured with the ROWE score and ASES score and the movements were evaluated.Results:A total of 24 patients fulfilled the inclusion criteria. Post-operatively at final follow-up, the mean ROWE score was 97.08 ±8.45 and the mean ASES score was 94.4±9.10. One patient had screw breakage as a complication and another had restriction of movement which was managed with physiotherapy.Conclusion:Open Latarjet is an effective procedure for recurrent anterior shoulder instability in non-athletic middle-aged patients as a excellent functional outcome was achieved with this technique. We therefore recommend open Latarjet as an alternative to arthroscopic treatment in developing countries where patient affordability and the availability of the resources are the issues.

Aligned Millineedle Arrays for Solar Power Seawater Desalination with Site-Specific Salt Formation.

As a sustainable and clean water production technology, solar thermal water evaporation has been extensively studied in the past few years. One challenge is that upon operation, salt would form on surface of the solar absorbers leading to inefficient water supply and light absorption and thus much reduced water vaporization rate. To address this problem, a simple solar evaporator based on an array of aligned millineedles for efficient solar water evaporation and controlled site-specific salt formation is demonstrated. The maximum solar evaporation rate achieved is 2.94kg m-2 h-1 under one Sun irradiation in brine of high salinity (25wt% NaCl), achieving energy conversion efficiency of 94.5% simultaneously. More importantly, the spontaneously site-specific salt formation on the tips of millineedles endows this solar evaporator with salt harvesting capacity. Rationally separating the clean water and salt from brine by condensation and gravity assistance, this tip-preferential crystallization solar evaporator is not affected by the salt clogging compared with conventional 2D solar evaporators. This study provides new insights on the design of solar evaporators and advances their applications in sustainable seawater desalination and wastewater management.

A “space-ball” experiment to specify the nature of gravity in the solar system

The high sensitivity of a planet's gravity assist (GA) to changes in test-body impact parameter prompts a space experiment that tests the nature of gravitational fields in the solar system. The Sun, Earth, and Venus can serve as a space-borne laboratory with a primitive space probe (“space ball”) as a test body moving on a ballistic trajectory from Earth to Venus, producing GA, and backward to Earth's orbit. We show that in Newton and Einstein (Schwarzschild) gravity, the probe's final positions, which are reached concurrently, may differ markedly, and an Earth-based observer can definitively measure that difference.

The Sling Effect: Croatia and SEE After the Fall of the Berlin Wall

The concentration of real convergence in a short period before the Great Recession (2001-2008) is a characteristic shared by many countries, but it was particularly pronounced in Croatia, Serbia, Bosnia and Herzegovina and Bulgaria. Bulgaria managed to converge after the Great Recession, but convergence in other mentioned countries was meagre; Slovenia even diverged since 2010. Direct effects of post-Yugoslav wars belong to the past, but indirect effects may have had more persistent effects: a lost decade of the &#8217;90s led to weak institutional development and the creation of the local form of state capitalism, which provides weak fundamentals for economic growth. Monetary policy and exchange rate regimes in the region are mostly centred around stable exchange rates and strive for the introduction of the Euro (Bulgaria and Croatia joined the ERM II in 2020). However, the impact of exchange rate regimes on long-run economic growth is neutral. Preference for credibility building monetary regimes is a legacy of the past. Financial predictability served as a shock absorber and a substitute for good institutions in order to attract inflows of international capital, which flooded ex-communist countries after the emerging markets crisis in the late &#8217;90s. However, when the wave of capital inflows stopped in the Great Recession, more fundamental growth factors emerged, explaining the slow convergence of the majority of SEE countries in the second decade of the 21st century.

Influence of Geometrical Changes in an Adiabatic Portion on the Heat Transfer Performance of a Two-Phase Closed Thermosiphon System

In this study, a modified non-uniform adiabatic section in a Two-Phase Closed Thermosiphon (TPCT) is proposed where the uniform section was replaced by convergent and divergent (C-D) sections. The heat transfer analysis was performed on the modified TPCT and their findings were compared with standard TPCT. The deionized water (DI) in the proportion of 30 vol% is filled in both the TPCTs. Further, the heat transfer performance analysis was carried out for three different orientations, such as 0°, 45° and 90°, and heat input was varied from 50 to 250 W. The effect of these geometrical changes and inclination angles on the heat transfer performance of both the TPCT were evaluated to compare the thermal resistance, wall temperature variation and heat transfer coefficient. The non-dimensional numbers such as Weber (WE), Bond (BO), Condensation (CO) and Kutateladze (KU) were investigated based on heat fluxes for both TPCTs. By introducing the convergent-divergent section nearer to the condenser, the pressure before and after the C-D section was increased and decreased. This enhances the heat transfer in the evaporator slightly up to 2% and 1.4% at horizontal and 45° orientation, respectively, in Non-Uniformed Adiabatic Section (NUAS) TPCT when compared to Uniformed Adiabatic Section (UAS) TPCT. The thermal resistance of NUAS TPCT was reduced by up to 4.5% relative to UAS TPCT in horizontal and 45°. The results of the non-dimensional number also confirmed that NUAS TPCT provided better performance by enhancing 2% more pool boiling characteristics, interaction forces and condensate returns. Several factors such as gravity assistance, fluid accumulation, pressure drop and thermal resistance exert an influence on the heat transfer performance of the proposed NUAS TPCT at various orientation angles. However, different type of cross-sectional variations subjected to orientation changes may also get influenced by several other parameters that in turn affect the heat transfer performance distinctly.

Dewatering of super absorbent polymers: Alternatives to thermal desorption by liquid phase extraction using dimethyl ether

The high saturation potential of highly hygroscopic desiccants makes their drying potential reuse an energetically unfavorable challenge. Perhaps there are other ways beyond dehydration the extract saturated water from these structures. That was the premise of the proposed experiments in which an existing method was redesigned in which condensed Dimethyl Ether (DME) was used aqueous fluids from commercial grade superabsorbent polymers (SAPs) similar to those found in commercial diapers. It was hypothesized that liquid extraction could be energetically less intensive than thermally dehydrating the SAP. By toggling between pressures above and below 0.6 MPa at room temperature, using gravity assistance, and nitrogen gas as driving forces, the DME condenses and interacts with the saturated SAP. The system successfully dewatered both DI water and saline saturated SAP. Roughly 90% of deionized water and ~80% of artificial urine are extractable from SAP when the chamber was pressurized 3 times. The salts in the artificial urine also conveyed in the aqueous extract and not concentrated in the dehydrated SAP. Energy assessments linked with each DME loading consumed 12.6 kJ or ~5 kJ/g of water extracted, more than required for thermal evaporation. The dehydrated superabsorbent polymer structure appears morphologically different by microscopy, but it can re-swell up to 35 times its dry mass in water and 15 times its mass in artificial urine. Overall, aqueous phase extraction using condensed DME dewaters saturated superabsorbent polymers allowing their reuse as other forms of desiccants but it is less efficient than by dehydration.

Low-Thrust Gravity-Assist Trajectory Design Using Optimal Multimode Propulsion Models

The complexities in using indirect optimization methods get compounded for practical co-optimization problems in the presence of continuous and discrete design variables. In this paper, realistic multimode electric propulsion systems are incorporated within the formulation of gravity-assist, low-thrust trajectory design problems. Electric thrusters operate over a large set of discrete operation modes, and each mode is characterized by specific values for power, thrust, specific impulse, and mass flow rate. Unlike the traditional methods that approximate the aggregate behavior of electric thrusters’ performance (using polynomials fits), a novel construct is proposed to incorporate optimal discrete operating modes within indirect optimization. The capability of the tool and the efficacy of the proposed methodology are demonstrated by solving a multiyear, fuel-optimal trajectory problem from Earth to asteroid Psyche via a Mars gravity-assist maneuver and using a Hall-effect SPT-140 thruster with 21 operating modes. Comparisons with the traditional polynomial-based thruster modeling are presented.

Non‐Detection of Lightning During the Second Parker Solar Probe Venus Gravity Assist

AbstractThe Parker Solar Probe (PSP) spacecraft completed its second Venus gravity assist maneuver (VGA2) on December 26, 2019. For a 20 min interval surrounding closest approach, the PSP/FIELDS Radio Frequency Spectrometer (RFS) was set to “burst mode,” recording radio spectra from 1.3 to 19.2 MHz at sub‐second cadence. We analyze this burst mode data, searching for signatures of radio frequency “sferic” emission from lightning discharges. During the burst mode interval, only four spectra were observed with strong impulsive signals, and all four could be attributed to saturation of the RFS high gain stage by in situ electrostatic plasma waves. These RFS measurements during VGA2 are consistent with previous non‐detection of radio frequency lightning signals from Venus reported by Gurnett et al. (2001, https://doi.org/10.1038/35053009).

Home Use of an Upper Extremity Exoskeleton in Children with SMA: A Pilot Study

Background: People with spinal muscular atrophy (SMA) often have arm weakness resulting in restricted independence and challenges with activities of daily living. An upper extremity (UE) orthosis, the Wilmington Robotic Exoskeleton (WREX), which augments arm movement by providing gravity assistance, was provided to a small cohort of subjects for 1 year. Resulting changes in the subjects’ performance were assessed.

Hayabusa2 extended mission: New voyage to rendezvous with a small asteroid rotating with a short period

Hayabusa2 is the Japanese Asteroid Return Mission and targeted the carbonaceous asteroid Ryugu, conducted by the Japan Aerospace Exploration Agency (JAXA). The goal of this mission was to conduct proximity operations including remote sensing observations, material sampling, and a Small Carry-On Impact experiment, as well as sample analyses. As of September 2020, the spacecraft is on the way back to Earth with samples from Ryugu with no critical issues after the successful departure in November 2019. Here, we propose an extended mission in which the spacecraft will rendezvous with a small asteroid with ~30 m - ~40 m in diameter that is rotating at a spin period of ~10 min after an additional ~10-year cruise phase. We introduce that two scenarios are suitable for the extended mission. In the first scenario, the spacecraft will perform swing-by maneuvers at Venus once and Earth twice to arrive at asteroid 2001 AV43. In the second scenario, it will perform swing-by maneuvers at Earth twice to reach asteroid 1998 KY26. In both scenarios, the mission will continue until the early 2030s. JAXA recently released the decision that the spacecraft will rendezvous with 1998 KY26. This paper focuses on our scientific assessments of the two scenarios but leaves the decision process to go to 1998 KY26 for future reports. Rendezvous operations will be planned to detail the physical properties and surrounding environments of the target, one of the smallest elements of small planetary bodies. By achieving the planned operations, the mission will provide critical hints on the violent histories of collisions and accumulations of small bodies in the solar system. Furthermore, the established scientific knowledge and techniques will advance key technologies for planetary defense.

Functional outcome of open latarjet procedure for recurrent anterior shoulder instability: A prospective study

Introduction: Shoulder joint owing to its anatomy and biomechanics is the most unstable and frequently dislocated joint in our body. Anterior shoulder instability is often caused by glenoid and/or humeral bony defects in addition to soft tissue injuries. Most commonly seen in young and athletic population with high demand activities. Arthroscopic Bankart repair and open Latarjet procedure are the mainstay of treatment for recurrent anterior shoulder instability. Here we analyse the functional outcome of the shoulder joint repair following Open Latarjet procedure for recurrent anterior shoulder instability. Methods: Prospective study conducted for 2 years among 34 patients who met our criteria for open Latarjet procedure. In which coracoid process along with the conjoint tendon is transferred and fixed with non-absorbable to the margin of glenoid. This procedure provides stability by bony effect, Bankart effect and dynamic sling effect. Phased Rehabilitation was customised based on tissue quality, stability of repair. Outcome was assessed with ISIS score (Injury Severity Index Score), Rowe score, quick DASH (The Disabilities of Arm, Shoulder and Hand) score, ASES score (The American Shoulder and Elbow Surgeons Shoulder Score) and Visual analogue scale. Results: Follow up done at 2 weeks,1 month,3 month and 6 month showed progressive improvement in Range of motions, Apprehension relief, pain relief, return to normal activities and no any recurrence of instability and improved assessment scores.Conclusion: For recurrent anterior shoulder instability Open Latarjet procedure showed satisfactory result in terms of stability and range of motion mainly with significant bony defect of glenoid.

Effect of long-range Coulomb repulsion on adhesive particle agglomeration in homogeneous isotropic turbulence

Abstract

A computational approach to the powered Swing-By in the elliptic restricted problem

This work performs a computational investigation of the energy variations given by a powered Swing-By maneuver realized in an elliptical system. It extends previous works by giving the freedom to choose the location and the direction of the thrust vector, aspects that were not considered before in the literature. Those variations are obtained numerically as a function of the parameters related to the thrust (magnitude, direction and location of the application) and the orbital parameters of the primaries (eccentricity and true anomaly). The maneuver is realized around the smaller primary, and the energy variations are measured with respect to the main body of the system. The initial orbit of the space vehicle is defined by its periapsis distance, angle and approach velocity with respect to the smaller primary. The study is applied to a system composed of two primaries that are in elliptic orbits around the center of mass of the system. The eccentricity is varied as a free parameter, to measure its effects. The results show that the best maneuvers apply the thrust at a point inside the sphere of influence of the secondary body, but not in the periapsis of the orbit. The best direction of the thrust is not aligned with the motion of the space vehicle. The techniques studied here are applied in situations where it is desired to increase the energy of the space vehicle. Empirical equations are obtained for the energy variations, based on the simulations made in the present paper. The numerical approach makes the results more accurate and not limited to particular regions of the eccentricity.

Trajectory Design for Solar Approaching Detection Mission Using Multiple Resonant Gravity Assists of the Venus

To approach close to the Sun, direct launch from the Earth costs a lot of energy, which can be effectively reduced by the gravity assist of the Venus. In this paper, interplanetary transfer trajectories with multiple resonant gravity assists of the Venus are designed for a solar approaching detection mission. And design models for the trajectories with continuous resonant gravity assists, as well as resonant and non-resonant gravity assists combined are built. A mission launched between 2025 and 2028 is studied. The study shows that, compared with trajectory with continuous resonant gravity assists, trajectory with resonant and non-resonant gravity assists combined is useful for reducing transfer time of solar approaching detection mission. And its impact on the energy cost is not universal, which is related to the resonance ratio in the trajectory.

A Gravity Assist Mapping Based on Gaussian Process Regression

We develop a Gravity Assist Mapping to quantify the effects of a flyby in a two-dimensional circular restricted three-body situation based on Gaussian Process Regression (GPR). This work is inspired by the Keplerian Map and Flyby Map. The flyby is allowed to occur anywhere above 300 km altitude at the Earth in the system of Sun-(Earth+Moon)-spacecraft, whereas the Keplerian map is typically restricted to the cases outside the Hill sphere only. The performance of the GPR model and the influence of training samples (number and distribution) on the quality of the prediction of post-flyby orbital states are investigated. The information provided by this training set is used to optimize the hyper-parameters in the GPR model. The trained model can make predictions of the post-flyby state of an object with an arbitrary initial condition and is demonstrated to be efficient and accurate when evaluated against the results of numerical integration. The method can be attractive for space mission design.

Evidence of Subproton‐Scale Magnetic Holes in the Venusian Magnetosheath

AbstractDepressions in magnetic field strength, commonly referred to as magnetic holes, are observed ubiquitously in space plasmas. Subproton‐scale magnetic holes with spatial scales smaller than or on the order of a proton gyroradius, are likely supported by electron current vortices, rotating perpendicular to the ambient magnetic field. While there are numerous accounts of subproton‐scale magnetic holes within the Earth’s magnetosphere, there are few, if any, reported observations in other space plasma environments. We present the first evidence of subproton‐scale magnetic holes in the Venusian magnetosheath. During Parker Solar Probe’s first Venus Gravity Assist, the spacecraft crossed the planet’s bow shock and subsequently observed the Venusian magnetosheath. The FIELDS instrument suite onboard the spacecraft achieved magnetic and electric field measurements of magnetic hole structures. The electric fields associated with magnetic depressions are consistent with electron current vortices with amplitudes on the order of 1 μA/m2.