Multi-objective imperfect selective maintenance optimization for series-parallel systems with stochastic mission duration

To improve the probability that an engineering system successfully completes its next mission, it is crucial to implement timely maintenance activities, especially when maintenance time or maintenance resources are limited. Taking series-parallel system as the object of study, this paper develops a multi-objective imperfect selective maintenance optimization model. Among it, during the scheduled breaks, potential maintenance actions are implemented for the components, ranging from minimal repair to replacement. Considering that the level of maintenance actions is closely related to the maintenance cost, age reduction coefficient and hazard rate adjustment coefficient are taken into account. Moreover, improved hybrid hazard rate approach is adopted to describe the reliability improvement of the components, and the mission duration is regarded as a random variable. On this basis, a nonlinear stochastic optimization model is established with dual objectives to minimize the total maintenance cost and maximize the system reliability concurrently. The fast elitist non-dominated sorting genetic algorithm (NSGA-II) is adopted to solve the model. Numerical experiments are conducted to verify the effectiveness of the proposed approach. The results indicate that the proposed model can obtain better scheduling schemes for the maintenance resources, and more flexible maintenance plans are gained.

The effect of mission duration on LISA science objectives

The science objectives of the LISA mission have been defined under the implicit assumption of a 4-years continuous data stream. Based on the performance of LISA Pathfinder, it is now expected that LISA will have a duty cycle of $$\approx 0.75$$ ≈ 0.75 , which would reduce the effective span of usable data to 3 years. This paper reports the results of a study by the LISA Science Group, which was charged with assessing the additional science return of increasing the mission lifetime. We explore various observational scenarios to assess the impact of mission duration on the main science objectives of the mission. We find that the science investigations most affected by mission duration concern the search for seed black holes at cosmic dawn, as well as the study of stellar-origin black holes and of their formation channels via multi-band and multi-messenger observations. We conclude that an extension to 6 years of mission operations is recommended.

Helicopter emergency medical service for time critical interfacility transfers of patients with cardiovascular emergencies

Background The goal of improving quality through centralisation of specialised medical services must be balanced against potential harm caused by delayed access to emergency treatments in rural areas. This study aims to assess the duration of transfers of critically ill patients with cardiovascular emergencies from smaller hospitals to major medical centres by a helicopter emergency medical service (HEMS) in Switzerland. Methods This retrospective observational cohort study includes all consecutive emergency interfacility transfers (IFTs) conducted by Switzerland’s largest HEMS provider between July 3rd, 2019, and March 31st, 2021. All patients with acute myocardial infarction, non-traumatic strokes, ruptured aortic aneurysms, and other acute vascular emergencies were included. The duration and distance of each HEMS IFT were compared to calculated distances and duration of travel for the same missions using ground-based transportation (GEMS). The ground-based mission distance beyond which the total mission duration of HEMS is expected to be faster than GEMS was calculated. Findings A total of 645 patients were transferred for stroke (n = 364), myocardial infarction (n = 252) and other acute vascular emergencies (n = 29). The median total mission duration from emergency call to landing at the destination was 59.9 (IQR 51.5 to 70.5) minutes. The median road distance for the same missions was 60 (IQR 43 to 72) km. Regression analysis revealed that HEMS is expected to be faster if the road distance is more than 51.3 km. Interpretation Centralisation of specialised medical services should be accompanied by a comprehensive and specialised rescue chain. HEMS in Switzerland ensures time-sensitive IFT in medical emergencies, even in topographically challenging terrain. Graphical Abstract

Trajectory options for a manned mission to Mars using high-thrust propulsion systems

An analysis has been done of performance factors (mission duration, initial mass of the interplanetary crew transfer vehicle, velocity of the re-entry into the Earth atmosphere of the descent vehicle with the crew) for a single-spacecraft manned mission to Mars using high-thrust propulsion systems. Locally optimal solutions (in terms of delta-V budgets for the transfer) were found for the Earth–Mars–Earth transfer, with varying periods of waiting in Mars orbit, minimal distance to the Sun, as well as flight paths (direct Earth–Mars–Earth transfers vs. gravity assist maneuvers at Venus during Earth–Mars or Mars–Earth transfers). The proposed classification for locally optimal solutions is applicable to both high-thrust propulsion systems and low-thrust propulsion systems. A comparison of performance factors has been done for manned Martian mission options based on liquid-propellant engines and nuclear rocket engines with a 12,5 km/s constraint on the velocity of the manned re-entry vehicle in the Earth atmosphere. Key words: Manned mission to Mars, interplanetary transfer trajectory, high-thrust, liquid-propellant rocket engine, nuclear rocket engine, mission duration, initial mass of the interplanetary vehicle, re-entry velocity of a manned vehicle for returning the crew to Earth.

Fatigue, Emotion, and Cognitive Performance in Simulated Long-Duration, Single-Piloted Flight Missions

BACKGROUND: Fatigue of air force pilots has become an increasing concern due to changes in mission characteristics. In the current study we investigated fatigue, emotions, and cognitive performance in a simulated 11-h mission in the 39 Gripen fighter aircraft. METHODS: A total of 12 subjects were evaluated in a high-fidelity dynamic flight simulator for 12 consecutive hours. Perceived fatigue was measured by the Samn-Perelli Fatigue Index (SPFI). Emotions were assessed with the Circumplex Affect Space. Cognitive performance was assessed by five cognitive tasks. RESULTS: Significant increase in self-reported fatigue, general decrease in two positive emotional states, as well increase of one negative emotional state occurred after approximately 7 h into the mission. Self-reported fatigue negatively correlated with enthusiasm and cheerfulness (r 0.75; 0.49, respectively) and positively correlated with boredom and gloominess (r 0.61; r 0.30, respectively). Response time in the low-order task negatively correlated with enthusiasm, cheerfulness and calmness (r 0.44; r 0.41; r 0.37, respectively) and positively correlated with boredom and anxiousness (r 0.37; r 0.28, respectively). Mission duration had an adverse impact on emotions in these environmental conditions, particularly after 7 h. DISCUSSION: These results contribute to the understanding of fatigue development in general and of emotion-cognition relationships. These findings emphasize that both emotional states and the type of cognitive tasks to be performed should be considered for planning long-duration missions in single-piloted fighter aircrafts as to increase the probability of missions success. Rosa E, Gronkvist M, Kolegard R, Dahlstrom N, Knez I, Ljung R, Willander J. Fatigue, emotion, and cognitive performance in simulated long-duration, single-piloted flight missions. Aerosp Med Hum Perform. 2021; 92(9):710719.

Space Radiation Protection Countermeasures in Microgravity and Planetary Exploration

Background: Space radiation is one of the principal environmental factors limiting the human tolerance for space travel, and therefore a primary risk in need of mitigation strategies to enable crewed exploration of the solar system. Methods: We summarize the current state of knowledge regarding potential means to reduce the biological effects of space radiation. New countermeasure strategies for exploration-class missions are proposed, based on recent advances in nutrition, pharmacologic, and immune science. Results: Radiation protection can be categorized into (1) exposure-limiting: shielding and mission duration; (2) countermeasures: radioprotectors, radiomodulators, radiomitigators, and immune-modulation, and; (3) treatment and supportive care for the effects of radiation. Vehicle and mission design can augment the overall exposure. Testing in terrestrial laboratories and earth-based exposure facilities, as well as on the International Space Station (ISS), has demonstrated that dietary and pharmacologic countermeasures can be safe and effective. Immune system modulators are less robustly tested but show promise. Therapies for radiation prodromal syndrome may include pharmacologic agents; and autologous marrow for acute radiation syndrome (ARS). Conclusions: Current radiation protection technology is not yet optimized, but nevertheless offers substantial protection to crews based on Lunar or Mars design reference missions. With additional research and human testing, the space radiation risk can be further mitigated to allow for long-duration exploration of the solar system.

Astronauts well-being and possibly anti-aging improved during long-duration spaceflight

This study assesses how circadian rhythms of heart rate (HR), HR variability (HRV) and activity change during long-term missions in space and how they relate to sleep quality. Ambulatory 48-h ECG and 96-h actigraphy were performed four times on ten healthy astronauts (44.7 ± 6.9 years; 9 men): 120.4 ± 43.7 days (Before) launch; 21.1 ± 2.5 days (ISS01) and 143.0 ± 27.1 days (ISS02) after launch; and 86.6 ± 40.6 days (After) return to Earth. Sleep quality was determined by sleep-related changes in activity, RR-intervals, HRV HF- and VLF-components and LF-band. The circadian amplitude of HR (HR-A) was larger in space (ISS01: 12.54, P = 0.0099; ISS02: 12.77, P = 0.0364) than on Earth (Before: 10.90; After: 10.55 bpm). Sleep duration in space (ISS01/ISS02) increased in 3 (Group A, from 370.7 to 388.0/413.0 min) and decreased in 7 (Group B, from 454.0 to 408.9/381.6 min) astronauts. Sleep quality improved in Group B from 7.07 to 8.36 (ISS01) and 9.36 (ISS02, P = 0.0001). Sleep-related parasympathetic activity increased from 55.2% to 74.8% (pNN50, P = 0.0010) (ISS02). HR-A correlated with the 24-h (r = 0.8110, P = 0.0044), 12-h (r = 0.6963, P = 0.0253), and 48-h (r = 0.6921, P = 0.0266) amplitudes of the magnetic declination index. These findings suggest associations of mission duration with increased well-being and anti-aging benefitting from magnetic fluctuations.

ChipSats for Planetary Exploration: Dynamics and Aerothermal Modeling of Atmospheric Entry and Dispersion

This paper presents an orbit-to-ground model for the atmospheric entry of ChipSats, gram-scale spacecraft that offer unique advantages over their conventionally larger counterparts. ChipSats may prove particularly useful for in-situ measurements in the upper atmosphere, where spatially and temporally varying phenomena are especially difficult to characterize. Globally distributed ChipSats would enable datasets of unprecedented detail, assuming they could survive. The model presented is used to assess the survival and dispersion of a swarm of ChipSats when deployed over the Earth, Moon, Mars, and Titan. These planetary exploration case studies focus on the Monarch, the newest-generation ChipSat developed at Cornell University, in order to evaluate technology readiness for such missions. A parametric study is then conducted to inform future ChipSat design, highlighting the role of the ballistic coefficient in both peak entry temperature and mission duration.

Master Catalogue of Lunar and Mars Exploration Missions

This paper contains catalogues of Chronology of Lunar and Mars Exploration Missions with their respective probe parameters such as launch mass, probe mass, the period of mission duration and mission degradation, mission intervals between launches. The novel feature of this catalogues are precise and verified data gathered from reliable online resources and journal articles than other resources available. These catalogues are assorted to have clearance in mission attempts and trends since the last century towards the Moon and Mars. It also encloses random graphical images generated using the data mentioned in this catalogue. The catalogues also comprise gravity assist probes and test launches. Some of the unclear data were gathered from online resources and have uncertain in data validation. This catalogue is derived from our previous complied works described in the supplementary materials section.

Ocean Zooglider: an autonomous vehicle for optical and acoustic sensing of zooplankton and suspended particles

<p><em>Zooglider</em> is an autonomous buoyancy-driven ocean glider designed and built by the Instrument Development Group at Scripps. <em>Zooglider</em> includes a low power camera with a telecentric lens for shadowgraph imaging and two custom active acoustics echosounders (operated at 200/1000 kHz).  A passive acoustic hydrophone records vocalizations from marine mammals, fishes, and ambient noise.  The imaging system (<em>Zoocam</em>) quantifies zooplankton and ‘marine snow’ as they flow through a sampling tunnel within a well-defined sampling volume. Other sensors include a pumped Conductivity-Temperature-Depth probe and Chl-<em>a</em> fluorometer.  An acoustic altimeter permits autonomous navigation across regions of abrupt seafloor topography, including submarine canyons and seamounts.  Vertical sampling resolution is typically 5 cm, maximum operating depth is ~500 m, and mission duration up to 50 days.  Adaptive sampling is enabled by telemetry of measurements at each surfacing.  Our post-deployment processing methodology classifies the optical images using advanced Deep Learning methods that utilize context metadata.  <em>Zooglider</em> permits in situ measurements of mesozooplankton and marine snow - and their natural, three dimensional orientation - in relation to other biotic and physical properties of the ocean water column.  <em>Zooglider</em> resolves micro-scale patches, which are important for predator-prey interactions and biogeochemical cycling. </p><p> </p>