The benefits of very low earth orbit for earth observation missions

Very low Earth orbits (VLEO), typically classified as orbits below approximately 450 km in altitude, have the potential to provide significant benefits to spacecraft over those that operate in higher altitude orbits. This paper provides a comprehensive review and analysis of these benefits to spacecraft operations in VLEO, with parametric investigation of those which apply specifically to Earth observation missions. The most significant benefit for optical imaging systems is that a reduction in orbital altitude improves spatial resolution for a similar payload specification. Alternatively mass and volume savings can be made whilst maintaining a given performance. Similarly, for radar and lidar systems, the signal-to-noise ratio can be improved. Additional benefits include improved geospatial position accuracy, improvements in communications link-budgets, and greater launch vehicle insertion capability. The collision risk with orbital debris and radiation environment can be shown to be improved in lower altitude orbits, whilst compliance with IADC guidelines for spacecraft post-mission lifetime and deorbit is also assisted. Finally, VLEO offers opportunities to exploit novel atmosphere-breathing electric propulsion systems and aerodynamic attitude and orbit control methods. However, key challenges associated with our understanding of the lower thermosphere, aerodynamic drag, the requirement to provide a meaningful orbital lifetime whilst minimising spacecraft mass and complexity, and atomic oxygen erosion still require further research. Given the scope for significant commercial, societal, and environmental impact which can be realised with higher performing Earth observation platforms, renewed research efforts to address the challenges associated with VLEO operations are required

Development and psychometric properties of the “Suicidality: Treatment Occurring in Paediatrics (STOP) Risk and Resilience Factors Scales” in adolescents

Suicidality in the child and adolescent population is a major public health concern. There is, however, a lack of developmentally sensitive valid and reliable instruments that can capture data on risk, and clinical and psychosocial mediators of suicidality in young people. In this study, we aimed to develop and assess the validity of instruments evaluating the psychosocial risk and protective factors for suicidal behaviours in the adolescent population. In Phase 1, based on a systematic literature review of suicidality, focus groups, and expert panel advice, the risk factors and protective factors (resilience factors) were identified and the adolescent, parent, and clinician versions of the STOP-Suicidality Risk Factors Scale (STOP-SRiFS) and the Resilience Factors Scale (STOP-SReFS) were developed. Phase 2 involved instrument validation and comprised of two samples (Sample 1 and 2). Sample 1 consisted of 87 adolescents, their parents/carers, and clinicians from the various participating centres, and Sample 2 consisted of three sub-samples: adolescents (n = 259) who completed STOP-SRiFS and/or the STOP-SReFS scales, parents (n = 213) who completed one or both of the scales, and the clinicians who completed the scales (n = 254). The STOP-SRiFS demonstrated a good construct validity—the Cronbach Alpha for the adolescent (α = 0.864), parent (α = 0.842), and clinician (α = 0.722) versions of the scale. Test–retest reliability, inter-rater reliability, and content validity were good for all three versions of the STOP-SRiFS. The sub-scales generated using Exploratory Factor Analysis (EFA) were the (1) anxiety and depression risk, (2) substance misuse risk, (3) interpersonal risk, (4) chronic risk, and (5) risk due to life events. For the STOP-SRiFS, statistically significant correlations were found between the Columbia-Suicide Severity Rating Scale (C-SSRS) total score and the adolescent, parent, and clinical versions of the STOP-SRiFS sub-scale scores. The STOP-SRiFS showed good psychometric properties. This study demonstrated a good construct validity for the STOP-SReFS—the Cronbach Alpha for the three versions were good (adolescent: α = 0.775; parent: α = 0.808; α = clinician: 0.808). EFA for the adolescent version of the STOP-SReFS, which consists of 9 resilience factors domains, generated two factors (1) interpersonal resilience and (2) cognitive resilience. The STOP-SReFS Cognitive Resilience sub-scale for the adolescent was negatively correlated (r = − 0.275) with the C-SSRS total score, showing that there was lower suicidality in those with greater Cognitive Resilience. The STOP-SReFS Interpersonal resilience sub-scale correlations were all negative, but none of them were significantly different to the C-SSRS total scores for either the adolescent, parent, or clinician versions of the scales. This is not surprising, because the items in this sub-scale capture a much larger time-scale, compared to the C-SSRS rating period. The STOP-SReFS showed good psychometric properties. The STOP-SRiFS and STOP-SReFS are instruments that can be used in future studies about suicidality in children and adolescents

Attitude control for satellites flying in VLEO using aerodynamic surfaces

This paper analyses the use of aerodynamic control surfaces, whether passive or active, in order to carry out very low Earth orbit (VLEO) attitude maneuver operations. Flying a satellite in a very low Earth orbit with an altitude of less than 450 km, namely VLEO, is a technological challenge. It leads to several advantages, such as increasing the resolution of optical payloads or increase signal to noise ratio, among others. The atmospheric density in VLEO is much higher than in typical low earth orbit altitudes, but still free molecular flow. This has serious consequences for the maneuverability of a satellite because significant aerodynamic torques and forces are produced. In order to guarantee the controllability of the spacecraft they have to be analyzed in depth. Moreover, at VLEO the density of atomic oxygen increases, which enables the use of air-breathing electric propulsion (ABEP). Scientists are researching in this field to use ABEP as a drag compensation system, and consequently an attitude control based on aerodynamic control could make sense. This combination of technologies may represent an opportunity to open new markets. In this work, several satellite geometric configurations were considered to analyze aerodynamic control: 3-axis control with feather configuration and 2-axis control with shuttlecock configuration. The analysis was performed by simulating the attitude of the satellite as well as the disturbances affecting the spacecraft. The models implemented to simulate the disturbances were the following: Gravitational gradient torque disturbance, magnetic dipole torque disturbance (magnetic field model IGRF12), and aerodynamic torque disturbances (aerodynamic model DTM2013 and wind model HWM14).The maneuvers analyzed were the following: detumbling or attitude stabilization, pointing and demisability. Different VLEO parameters were analyzed for every geometric configuration and spacecraft maneuver. The results determined which of the analyzed geometric configurations suits better for every maneuver

Discoverer - Making commercial satellite operations in very low earth orbit a reality

DISCOVERER is a €5.7M European Commission funded Horizon 2020 project developing technologies to enable commercially-viable sustained-operation of satellites in very low Earth orbits. Why operate closer to the Earth? For communications applications latency is significantly reduced and link budgets improved, and for remote sensing improved link budgets allow higher resolution or smaller instruments, all providing cost benefits. In addition, all applications benefit from increased launch mass to lower altitudes, whilst end-of-life removal is ensured due to the increased atmospheric drag. However, this drag must also be minimised and compensated for. One of the key technologies being developed by DISCOVERER are materials that encourage specular reflection of the residual atmosphere at these altitudes. Combined with appropriate geometric designs these can significantly reduce drag, provide usable lift for aerodynamic attitude and orbit control, and improve the collection efficiency of aerodynamic intakes for atmosphere breathing electric propulsion systems, all of which are being developed as part of DISCOVERER. The paper provides highlights from the developments to date, and the potential for a new class of aerodynamic commercial satellites operating at altitudes below the International Space Station

Concepts and Applications of Aerodynamic Attitude and Orbital Control for Spacecraft in Very Low Earth Orbit

Spacecraft operations below 450km, namely Very Low Earth Orbit (VLEO), can offer significant advantages over traditional low Earth orbits, for example enhanced ground resolution for Earth observation, improved communications latency and link budget, or improved signal-to-noise ratio. Recently, these lower orbits have begun to be exploited as a result of technology development, particularly component miniaturisation and cost-reduction, and concerns over the increasing debris population in commercially exploited orbits. However, the high cost of orbital launch and challenges associated with atmospheric drag, causing orbital decay and eventually re-entry are still a key barrier to their wider use for large commercial and civil spacecraft. Efforts to address the impact of aerodynamic drag are being sought through the development of novel drag-compensation propulsion systems and identification of materials which can reduce aerodynamic drag by specularly reflecting the incident gas. However, the presence of aerodynamic forces can also be utilised to augment or improve spacecraft operations at these very low altitudes by providing the capability to perform coarse pointing control and trim or internal momentum management for example. This paper presents concepts for the advantageous use of spacecraft aerodynamics developed as part of DISCOVERER, a Horizon 2020 funded project with the aim to revolutionise Earth observation satellite operations in VLEO. The combination of novel spacecraft geometries and use of aerodynamic control methods are explored, demonstrating the potential for a new generation of Earth observation satellites operating at lower altitudes

Development and psychometric properties of the “Suicidality:Treatment Occurring in Paediatrics (STOP) Risk and Resilience Factors Scales” in adolescents

Suicidality in the child and adolescent population is a major public health concern. There is, however, a lack of developmentally sensitive valid and reliable instruments that can capture data on risk, and clinical and psychosocial mediators of suicidality in young people. In this study, we aimed to develop and assess the validity of instruments evaluating the psychosocial risk and protective factors for suicidal behaviours in the adolescent population. In Phase 1, based on a systematic literature review of suicidality, focus groups, and expert panel advice, the risk factors and protective factors (resilience factors) were identified and the adolescent, parent, and clinician versions of the STOP-Suicidality Risk Factors Scale (STOP-SRiFS) and the Resilience Factors Scale (STOP-SReFS) were developed. Phase 2 involved instrument validation and comprised of two samples (Sample 1 and 2). Sample 1 consisted of 87 adolescents, their parents/carers, and clinicians from the various participating centres, and Sample 2 consisted of three sub-samples: adolescents (n = 259) who completed STOP-SRiFS and/or the STOP-SReFS scales, parents (n = 213) who completed one or both of the scales, and the clinicians who completed the scales (n = 254). The STOP-SRiFS demonstrated a good construct validity—the Cronbach Alpha for the adolescent (α = 0.864), parent (α = 0.842), and clinician (α = 0.722) versions of the scale. Test–retest reliability, inter-rater reliability, and content validity were good for all three versions of the STOP-SRiFS. The sub-scales generated using Exploratory Factor Analysis (EFA) were the (1) anxiety and depression risk, (2) substance misuse risk, (3) interpersonal risk, (4) chronic risk, and (5) risk due to life events. For the STOP-SRiFS, statistically significant correlations were found between the Columbia-Suicide Severity Rating Scale (C-SSRS) total score and the adolescent, parent, and clinical versions of the STOP-SRiFS sub-scale scores. The STOP-SRiFS showed good psychometric properties. This study demonstrated a good construct validity for the STOP-SReFS—the Cronbach Alpha for the three versions were good (adolescent: α = 0.775; parent: α = 0.808; α = clinician: 0.808). EFA for the adolescent version of the STOP-SReFS, which consists of 9 resilience factors domains, generated two factors (1) interpersonal resilience and (2) cognitive resilience. The STOP-SReFS Cognitive Resilience sub-scale for the adolescent was negatively correlated (r = − 0.275) with the C-SSRS total score, showing that there was lower suicidality in those with greater Cognitive Resilience. The STOP-SReFS Interpersonal resilience sub-scale correlations were all negative, but none of them were significantly different to the C-SSRS total scores for either the adolescent, parent, or clinician versions of the scales. This is not surprising, because the items in this sub-scale capture a much larger time-scale, compared to the C-SSRS rating period. The STOP-SReFS showed good psychometric properties. The STOP-SRiFS and STOP-SReFS are instruments that can be used in future studies about suicidality in children and adolescents

Psychosocial risk factors for suicidality in children and adolescents

Suicidality in childhood and adolescence is of increasing concern. The aim of this paper was to review the published literature identifying key psychosocial risk factors for suicidality in the paediatric population. A systematic two-step search was carried out following the PRISMA statement guidelines, using the terms ‘suicidality, suicide, and self-harm’ combined with terms ‘infant, child, adolescent’ according to the US National Library of Medicine and the National Institutes of Health classification of ages. Forty-four studies were included in the qualitative synthesis. The review identified three main factors that appear to increase the risk of suicidality: psychological factors (depression, anxiety, previous suicide attempt, drug and alcohol use, and other comorbid psychiatric disorders); stressful life events (family problems and peer conflicts); and personality traits (such as neuroticism and impulsivity). The evidence highlights the complexity of suicidality and points towards an interaction of factors contributing to suicidal behaviour. More information is needed to understand the complex relationship between risk factors for suicidality. Prospective studies with adequate sample sizes are needed to investigate these multiple variables of risk concurrently and over time

Inductive Plasma Thruster (IPT) design for an Atmosphere-Breathing Electric Propulsion System (ABEP)

Challenging space missions include those at very low altitudes, where the atmosphere is source of aerodynamic drag on the spacecraft, therefore an efficient propulsion system is required to extend the mission lifetime. One solution is Atmosphere-Breathing Electric Propulsion (ABEP). It collects atmospheric particles to use as propellant for an electric thruster. This would minimize the requirement of limited propellant availability. The system could be applied to any planet with atmosphere, enabling new mission at these altitude ranges for continuous orbiting. Challenging is also the presence of reactive chemical species, such as atomic oxygen in Earth orbit. Such components are erosion source of (not only) propulsion system components, i.e. acceleration grids, electrodes, and discharge channels of conventional EP systems (RIT and HET). IRS is developing within the DISCOVERER project an intake and a thruster for an ABEP system. This paper deals with the design and first operation of the inductive plasma thruster (IPT) developed at IRS. The paper describes its design aided by numerical tools such as HELIC and ADAMANT. Such a device is based on RF electrodeless discharge aided by externally applied static magnetic field. The IPT is composed by a movable injector, to variate the discharge channel length, and a movable electromagnet to variate position and intensity of the magnetic field. By changing these parameters along with a novel antenna design for electric propulsion, the aim is to achieve the highest efficiency for the ionization stage by enabling the formation of helicon-based discharge. Finally, the designed IPT is presented and the feature of the birdcage antenna highlighted

On the exploitation of differential aerodynamic lift and drag as a means to control satellite formation flight

For a satellite formation to maintain its intended design despite present perturbations (formation keeping), to change the formation design (reconfiguration) or to perform a rendezvous maneuver, control forces need to be generated. To do so, chemical and/or electric thrusters are currently the methods of choice. However, their utilization has detrimental effects on small satellites’ limited mass, volume and power budgets. Since the mid-80s, the potential of using differential drag as a means of propellant-less source of control for satellite formation flight is actively researched. This method consists of varying the aerodynamic drag experienced by different spacecraft, thus generating differential accelerations between them. Its main disadvantage, that its controllability is mainly limited to the in-plain relative motion, can be overcome using differential lift as a means to control the out-of-plane motion. Due to its promising benefits, a variety of studies from researchers around the world have enhanced the state-of-the-art over the past decades which results in a multitude of available literature. In this paper, an extensive literature review of the efforts which led to the current state-of-the-art of different lift and drag-based satellite formation control is presented. Based on the insights gained during the review process, key knowledge gaps that need to be addressed in the field of differential lift to enhance the current state-of-the-art are revealed and discussed. In closer detail, the interdependence between the feasibility domain/the maneuver time and increased differential lift forces achieved using advanced satellite surface materials promoting quasi-specular or specular reflection, as currently being developed in the course of the DISCOVERER project, is discussed