Ascent Performance Research Articles

Influence of Ice Accretion on Stratospheric Airship in the Non-Forming Ascending Process

Ice accretion on stratospheric airships, which affects the net buoyancy and reduces the ascent speed, thereby leading to component failure and further necessitating flight termination, has received considerable attention. In this study, the formation of ice occurred when the airship hit supercooled water droplets during the non-forming ascending process. Theoretical descriptions of an ice accretion model, a thermal model, and a dynamic model for airships were established to estimate the flight performance with ice mass. Then, validation of the simulation and the cloud chamber test was carried out, which indicated that the temperature, liquid water content (LWC), and pressure considerably influenced the ice mass. A lower temperature had a positive effect on ice accretion. The mass of ice accretion increased with the increase in LWC. Ice did not form easily under low pressure due to evaporation and sublimation. Finally, the effects of the ambient LWC and initial helium mass were analyzed. It was shown that an LWC of 0.5 g/m3 resulted in severe degradation of the ascent performance. When the initial helium mass was not sufficient, the airship landed due to ice accumulation. However, redundant inflation increased the ice mass and lowered the cruising altitude.

Lean, fast and strong: Determinants of functional performance in the elderly

BackgroundThe current literature indicates that functional capacity is associated with physical performance and body composition measurements in older adults. However, it is not clear which tests can best explain the functional capacity in this population. This study aimed to investigate the physical performance and body composition determinants of functional capacity in older adults. MethodTwenty-four older adults (66.4 ± 4.7y) undertook body composition (body fat and muscle), rate of torque development (0–50 and 0–200 ms); countermovement jump (height, power and impulse); leg-press and seated-leg-curl 5-repetition maximum; and functional-performance tests (Timed-up-and-go, stair ascent and stair descent). FindingsTimed-up-and-go correlated with countermovement jump (height, R2 = 0.303; power, R2 = 0.198; and impulse, R2 = 0.224) and 5-repetition maximum (seated-leg-curl, R2 = 0.172). Stair ascent correlated with body fat (R2 = 0.213), rate of torque development (0–50 ms/body fat, R2 = 0.301; 0–200 ms, R2 = 0.197; 0–200 ms/body fat, R2 = 0.340), countermovement jump (height, R2 = 0.325; power/body fat, R2 = 0.413; impulse/body fat, R2 = 0.422) and 5-repetiton maximum (leg-press/body fat, R2 = 0.384; seated-leg-curl/body fat, R2 = 0.341). Stair descent correlated with rate of torque development (0–50 ms/body fat, R2 = 0.164; 0–200 ms, R2 = 0.203; 0–200 ms/body fat, R2 = 0.213), countermovement jump (height, R2 = 0.458; power, R2 = 0.212; power/body fat, R2 = 0.358; impulse, R2 = 0.218; impulse/body fat, R2 = 0.369) and 5-repetition maximum (leg-press/body fat, R2 = -0.227; seated-leg-curl/body fat, R2 = 0.209; seated-leg-curl, R2 = 0.181). InterpretationHigher body fat is associated with weaker stair ascent performance. An increase in the correlation coefficient was observed for the countermovement jump, rate of torque development, and 5-repetition maximum tests when normalized by body fat compared to the absolute values. Countermovement jump height presented the highest correlation to timed-up-and-go and stair descent, while impulse/body fat for stair ascent.

Effect of Descent Velocity upon Muscle Activation and Performance in Two-Legged Free Weight Back Squats.

Background: The aim of this study was to investigate the effect of descent velocity during two-legged full back squats upon muscle activation and squat ascent performance. Methods: Eleven healthy resistance-training males (age: 24 ± 6 years, body mass: 89.5 ± 21.5 kg, height: 1.84 ± 0.10 m) performed 4-repetition maximum (4-RM) two-legged full squats with slow, normal, and fast descent phases. Kinematics and muscle activity of ten muscles divided into five regions were measured. Results: The main findings were that maximal and minimal velocity were lower and maximal velocity occurred later in the slow condition, while there was no difference in second peak velocity or ascent displacement when compared with the normal and fast conditions. Furthermore, no differences in muscle activation were found as an effect of the descent velocity. Conclusion: It was concluded that the slow descent velocity had a negative effect upon the ascent phase, because of the lower peak velocity and peak force increasing the chance of failure. The lower velocities were not caused by lower pre-activation of the muscles but were probably a result of potentiation and/or utilization of stored elastic energy and/or the stretch reflex.

Nonlinear control of a subscale submarine in emergency ascent

This paper presents a nonlinear parametric model and proof-of-concept motion control system for a scale model submarine undertaking an emergency ascent. An energy-based model is presented that represents the underactuated submarine in a non-neutrally buoyant state. This model is then used to synthesize a control law using Port-Hamiltonian theory and interconnection and damping assignment passivity-based control. Lyapunov analysis is used to demonstrate stability of the closed-loop system, and a simulation-based study is presented to demonstrate performance of the control law. The results demonstrate that a closed loop non-linear controller is able to improve the quality of emergency rise by automatically compensating for some parasitic effects in the hydrodynamics that can compromise ascent performance.

Functional resistance training can increase strength, knee torque ratio, and functional performance in elderly women.

Functional resistance training can increase strength, knee torque ratio, and functional performance in elderly women. The aim of the present study was to understand the effects of closed kinetic chain exercises with constant load on muscular strength, the knee torque conventional ratio (hamstring:quadriceps – H:Q), and functional capacity in the elderly. Nine untrained healthy elderly women participated in experimental resistance training. Ten-repetition maximum (10RM) for the deadlift, isokinetic maximum voluntary concentric contraction, and functional capacity were assessed before and after the 7-week resistance-training program. Magnitude based inference analysis was used to examine the differences in muscle strength and functional performance. Therefore, the smallest worthwhile change was calculated and 90% confidence intervals were also determined to characterize muscle strength and functional performance. The analysis demonstrated an increase in the deadlift and knee flexor torque (60o/sec) after the experimental intervention. Furthermore, stair ascent, knee extensor torque (120o/sec), knee flexor torque (120o/sec), and knee ratio (60o/sec) also presented a positive effect in the same training period. Conversely, knee extensor torque (60o/sec), and knee ratio (120o/sec) did not show conclusive responses. In conclusion, resistance training with functional closed kinetic chain exercises and constant volume load (i.e., 65% of 1-repetition maximum) can increase deadlift 10RM, isokinetic concentric torque, the conventional H:Q ratio, and stair ascent performance in elderly women.

Self-efficacy, pain, and quadriceps capacity at baseline predict changes in mobility performance over 2years in women with knee osteoarthritis.

This study examined the extent to which baseline measures of quadriceps strength, quadriceps power, knee pain and self-efficacy for functional tasks, and their interactions, predicted 2-year changes in mobility performance (walking, stair ascent, stair descent) in women with knee osteoarthritis. We hypothesized that lesser strength, power and self-efficacy, and higher pain at baseline would each be independently associated with reduced mobility over 2years, and each of pain and self-efficacy would interact with strength and power in predicting 2-year change in stair-climbing performance. This was a longitudinal, observational study of women with clinical knee osteoarthritis. At baseline and follow-up, mobility was assessed with the Six-Minute Walk Test, and stair ascent and descent tasks. Quadriceps strength and power, knee pain, and self-efficacy for functional tasks were also collected at baseline. Multiple linear regression examined the extent to which 2-year changes in mobility performances were predicted by baseline strength, power, pain, and self-efficacy, after adjusting for covariates. Data were analyzed for 37 women with knee osteoarthritis over 2years. Lower baseline self-efficacy predicted decreased walking (β=1.783; p=0.030) and stair ascent (β=-0.054; p<0.001) performances over 2years. Higher baseline pain intensity/frequency predicted decreased walking performance (β=1.526; p=0.002). Lower quadriceps strength (β=0.051; p=0.015) and power (β=0.022; p=0.022) interacted with lesser self-efficacy to predict worsening stair ascent performance. Strategies to sustain or improve mobility in women with knee osteoarthritis must focus on controlling pain and boosting self-efficacy. In those with worse self-efficacy, developing knee muscle capacity is an important target.

Patient-reported outcomes interact with muscle capacity to predict two-year stair ascent performance in women with clinical knee osteoarthritis

Patient-reported outcomes interact with muscle capacity to predict two-year stair ascent performance in women with clinical knee osteoarthritis

The effects of horizontally and vertically oriented baffles on flow structure and ascent performance of upstream-migrating fish

ABSTRACTConsiderable effort has been expended to construct culverts and fishways that allow for fish passage. However, the designs have seldom considered behaviour, energetics, and biomechanics of fish. In this study, we performed controlled experiments, in which upstream-migrating Alewife (Alosa pseudoharengus) and Brook Trout (Salvelinus fontinalis) were allowed to volitionally enter either one of two open channels. These channels were outfitted with horizontally and vertically oriented baffles. The flow structure was characterized using acoustic Doppler velocimeter measurements. The added baffles had a marked influence on the flow field, which was distinct between horizontal and vertical baffles, indicative of horizontally and vertically orientated vortices, respectively. Passage success was measured, both in terms of attraction and ascent performance under each flow condition. The results indicated that Alewife and Brook Trout staged significantly more attempts into the vertical baffled channel compared to the horizontal baffled channel. However, Alewife traversed greater distances swimming in the channel with the horizontal baffles at the lower flow condition. Brook Trout also swam further under low flow but traversed similar dtistances in both channels. This information furthers our understanding of both ascent performance and behavioural responses of fish in relation to turbulent flow and roughness orientation.

Leg Strength, Power and Stair Ascent Performance 5 Years After Unicompartmental Knee Arthroplasty

Leg Strength, Power and Stair Ascent Performance 5 Years After Unicompartmental Knee Arthroplasty

The role of lower extremity joint powers in successful stair ambulation

Ascending stairs is an important functional activity that is affected by lower extremity pathology including amputation. Although several studies have demonstrated stair ascent is more challenging than level ground walking, our understanding of the mechanics remains limited. The purpose of this study was to determine the association between lower extremity joint power generation and vertical COM acceleration (COMA) during stair ascent. Twenty-two healthy individuals underwent a biomechanical gait assessment while walking up a 16-step instrumented staircase. The association between the peak joint powers and peak COMA during stance were assessed with respect to timing and magnitude. With respect to timing, peak ankle joint power was highly correlated with peak COMA (R2=0.93), while peak knee and hip joint powers demonstrated limited association with COMA (R2=0.41 and 0.08, respectively). Only the magnitude of peak ankle power was associated with peak COMA (R2=0.3).Significant temporal and magnitude associations between peak ankle joint power and peak COMA suggest ankle power is a key contributor to COMA. Although peak knee joint power and COMA are temporally associated, the association is weaker and the occurrence of peak joint knee power is nearly 10% after peak COMA, suggesting knee joint power plays a lesser role in COMA. These combined findings indicate the role of trail limb ankle plantarflexors should be recognized in the stair ascent cycle definition and demonstrate the potential importance of a power generated by the ankle plantarflexors to normalize stair ascent performance following lower extremity amputation.

Verification of JEM Structural Compatibility with the Space Shuttle

The JEM elements are delivered to the ISS on three Shuttle flights and are assembled on orbit subsequently. The verification of JEM structural compatibility with the Space Shuttle was performed to certify its flight readiness. Structural compatibilities are required on weight and center of gravity, stiffness and structural damping, strength, and dynamic clearance. Verification results should be reviewed at several assessment stages and needs to be approved by NASA for flight certification. On the other hand, JEM is the Japanese first manned-base facility, and has complicated interface with the Space Shuttle. So several issues were found in the verification phase and have been successfully resolved by technical challenges on Lack of Ascent Performance Margin (APM), Non-linear stiffness of structural latch mechanism, Negative structural margin, and Close clearance / Interference.

Physical and Psychological Factors Associated With Stair Negotiation Performance in Older People

An inability to negotiate stairs is a marker of disability and functional decline and can be a critical factor in loss of independence in older people. There is limited research on the underlying factors that impair performance in this important activity of daily living. We examined which physical and psychological factors are associated with stair climbing and stair descending performance in older people. Six hundred sixty-four community-dwelling people aged 75-98 years (mean age = 80.1 years, standard deviation (SD) = 4.4 years) underwent stair negotiation tests as well as tests of lower limb strength, vision, peripheral sensation, reaction time, and balance and completed questionnaires measuring psychological and health status. Many physiological and psychological factors were significantly associated with stair negotiation speed. Multiple regression analyses revealed that knee extension and knee flexor strength, lower limb proprioception, edge contrast sensitivity, reaction time involving a foot-press response, leaning balance, fear of falling, and the Short-Form 12 Health Status Questionnaire (SF-12) pain and vitality scores were significant and independent predictors of stair ascent and descent performance. The combined set of variables explained 47% of the variance in stair ascent performance and 50% of the variance in stair descent performance. Measures of strength, balance, vision, fear, and vitality also significantly discriminated between persons who did and did not require the use of the handrail when performing the tests. Discussion. In community-dwelling older people, impaired stair negotiation is associated not only with reduced strength but also with impaired sensation, strength, and balance; reduced vitality; presence of pain; and increased fear of falling.

Multidisciplinary Analysis of a Lifting Body Launch Vehicle

As part of phase 2 of the X-33 Program, NASA selected an integrated lifting body/aerospike engine configuration as the study vehicle for the conceptual analysis of a single-stage-to-orbit reusable launch vehicle. A team at NASA Langley Research Center participated in the screening and evaluation of a number of proposed vehicle configurations in the early phases of the conceptual design process. The performance analyses that supported these studies were conducted to assess the effect of the vehicle's lifting capability, linear aerospike engine, and metallic thermal protection system on the weight and performance of the vehicle. These performance studies were conducted in a multidisciplinary fashion that indirectly linked the trajectory optimization with weight estimation and aerothermal analysis tools. This approach was necessary to develop optimized ascent and entry trajectories that met all vehicle design constraints. Significant improvements in ascent performance were achieved when the vehicle flew a lifting trajectory and varied the engine mixture ratio during flight. Also, a considerable reduction in empty weight was possible by adjusting the total oxidizer-to-fuel and liftoff thrust-to-weight ratios. However, the optimal ascent flight profile had to be altered to ensure that the vehicle could be trimmed in pitch using only the flow diverting capability of the aerospike engine. Likewise, the optimal entry trajectory had to be tailored to meet thermal protection system heating rate and transition constraints while satisfying a crossrange requirement.

Impact of mission requirements and constraints on conceptual launch vehicle design

The objective of this paper is to analyse the impact of mission requirements and constraints on both the optimum vehicle design and the effects on flight path selection for two types of reusable two-stage-to-orbit launch vehicles. The first vehicle type considered provides horizontal take-off and landing capabilities and is intended to be propelled by an airbreathing propulsion system during stage 1 flight. The second vehicle type assumes a vertical launch and is accelerated by a rocket propulsion system during the booster stage ascent flight. The analysis employs a design tool for simultaneous system and mission optimization. It consists of a CAD-based preliminary vehicle design tool, aerodynamic and aerothermodynamic calculation software, flight simulation programs, and a two-level decomposition optimization algorithm enabling simultaneous system and flight optimization. The results to be presented show that the cruise flight requirement for an European launched mission of the airbreathing vehicle results in a loss of 60 % payload mass as compared to a mere accelerated ascent for a near equatorial mission into the same target orbit assuming constant take-off mass. The strong dependencies of mission requirements on both the optimal vehicle design and the ascent performance are determined for the rocket-powered vehicle type by varying the inclination and altitude of the target orbit.

Impact of knee extensor strength deficits on stair ascent performance in patients after medial meniscectomy

After arthroscopic meniscectomy the relationship between the magnitude of knee extensor strength deficits and locomotor performance during stair ascent unloaded and when carrying a 22 kg load has been tested in 31 patients. The specific locomotor adaptations related to large strength deficits were also studied. The results indicate that large deficits were significantly associated to: 1) reduced activation of the knee extensor muscles (vastus medialis and lateralis) during the first double leg support and single leg support phases, and of the hip extensors (medial hamstrings) during the second double leg support of stair ascent, 2) overactivations of the hip extensors (gluteus maximus and medial hamstrings) during single leg support, and 3) longer cycle and step durations and lower cadences. Locomotor abnormalities in movements and muscle activations were generally found in patients with strength deficits greater than 25% while patients with smaller strength deficits (less than 25%) usually could climb stairs with normal performance. These results support the use of knee extensor strength measures to predict locomotor capacities, and also highlight the importance of postoperative knee strength rehabilitation.

Optimal control of ascent trajectories and rotary dynamics for wingless orbital stages

For a rocket type orbital stage of a space transportation system with an airbreathing first stage, an investigation on ascent performance is presented. Particular emphasis is given to the lifting capability of the wingless orbital stage because of its decisive influence on ascent performance. A rocket type orbital stage without a lifting capability can perform an ascent to an orbit only when the flight path angle is rather large for a separation condition in hypersonic flight at high altitude. However, rocket type vehicles without a wing have a limited lifting capability which enables the vehicle to achieve an ascent to an orbit even if the separation flight path inclination is small. It is shown how this capability can be utilized in an optimum manner. This concerns the optimal control of lift, thrust setting and thrust vector angle. In addition to point mass dynamics, a model including pitching moment balancing and rotary dynamics is also investigated. It is shown which effects for ascent control and performance result.

Ascent performance of an air-breathing horizontal-takeoff launch vehicle

Simulations are conducted to investigate a proposed NASA launch vehicle that is fully reusable, takes off horizontally, and uses airbreathing propulsion in a single stage. The propulsion model is based on a cycle analysis method, and the vehicle is assumed to be a rigid structure with distributed fuel, operating under a range of atmospheric conditions. The program to optimize simulated trajectories (POST) is modified to include a predictor-corrector guidance capability and then used to generate the trajectories. Significant errors are encountered during the unpowered coast phase due to uncertainty in the atmospheric density profile. The amount of ascent propellant needed is shown to be directly related to the thrust-vector angle and the location of the center of gravity of the vehicle because of the importance of aim-drag losses to total ideal velocity.

Ascent performance issues of a vertical-takeoff rocket launch vehicle

Covers advancements in spacecraft and tactical and strategic missile systems, including subsystem design and application, mission design and analysis, materials and structures, developments in space sciences, space processing and manufacturing, space operations, and applications of space technologies to other fields.

Orbital Rendezvous Systems

The sybstem requirements for orbital rendezvous systems vary greatly depending on the mission in question. A few of the mission parameters which significantly affect subsystem requirements are: 1. Launch Window. The permitted launch window may be very short in an emergency rescue mission or could be relaxed on a supply mission. The size of the launch window, in turn, affects the variation in terminal geometry, and the ascent and terminal phase performance requirements. 2. Ground Tracking and Control On-board Tracking and Control. For many earth-orbiting missions the ground track will be well covered by tracking stations which can determine a precise ephemeris for the target and/or the chaser, which, in turn, permits ground control of orbital maneuvers up to some point in the terminal phase. This procedure would not be possible, of course, for lunar orbital rendezvous. A related question is then the point in the terminal phase at which relative position and velocity data are adequate for terminal guidance. 3. Cooperative: vs. Non-cooperative Target. Rendezvous with a non-cooperative target usually requires a high powered skin tracking radar capability of acquisition at fairly extended ranges whereas a cooperative target permits use of a transponder, greatly reducing power requirements, and also pernuts cooperative attitude reorientation and corrective maneuvers of the target. 4. Manned vs. Unmanned. It, has been demonstrated by ground simulation that a pilot can visually monitor and control portions of the terminal phase of a rendezvous and docking mission, whereby the tracking and computation requirements for such missions can be greatly altered. Even within the framework of a given mission there are a number of major system parameters to be determined. For example, the question of whether tracking sensors can be fixed to the body or require isolation from vehicle motions in the acquisition and terminal phases, in turn depends on the nature and accuracy of the vehicle stabilization and control systein, and the number and location of corrective rockets which will affect the reorientation requirements to achieve velocity corrections. Furthermore, the number and size of these corrections, which depend on tracking accuracy, will affect whether or not tracking is required during such corrections. The factors which lead to a choice among radar, optical or infrared targeting during the various phases will he discussed. Finally, the discussion and comparison of various guidance laws for controlling the closing rate and lateral corrections will be discussed, including the effects on propulsion requirements and tracking accuracy requirements. In particular, proportional navigation, bang-bang correction, and orbital maneuver laws will be compared.