1,721,378 research outputs found
Mcinnes, Colin Lachlan, VX46497
No full textThis record was harvested from a previous catalogue system and will be withdrawn in 2025. Information in this record may be superseded or incomplete. Visit this record in UMA's new catalogue at: https://archives.library.unimelb.edu.au/nodes/view/403522Surname: MCINNES. Given Name(s) or Initials: COLIN LACHLAN. Military Service Number or Last Known Location: VX46497. Missing, Wounded and Prisoner of War Enquiry Card Index Number: 21090.224905
Item: [2016.0049.35815] "Mcinnes, Colin Lachlan, VX46497
Orbit design for future SpaceChip swarm missions in a planetary atmosphere
No full textThe effect of solar radiation pressure and atmospheric drag on the orbital dynamics of satellites-on-a-chip (SpaceChips) is exploited to design equatorial long-lived orbits about the oblate Earth. The orbit energy gain due to asymmetric solar radiation pressure, considering the Earth's shadow, is used to balance the energy loss due to atmospheric drag. Future missions for a swarm of SpaceChips are proposed, where a number of small devices are released from a conventional spacecraft to perform spatially distributed measurements of the conditions in the ionosphere and exosphere. It is shown that the orbit lifetime can be extended and indeed selected through solar radiation pressure and the end-of-life re-entry of the swarm can be ensured, by exploiting atmospheric drag
Electrochromic orbit control for smart-dust devices
No full textRecent advances in MEMS (micro electromechanical systems) technology are leading to spacecraft which are the shape and size of computer chips, so-called SpaceChips, or ‘smart dust devices’. These devices can offer highly distributed sensing when used in future swarm applications. However, they currently lack a feasible strategy for active orbit control. This paper proposes an orbit control methodology for future SpaceChip devices which is based on exploiting the effects of solar radiation pressure using electrochromic coatings. The concept presented makes use of the high area-to-mass ratio of these devices, and consequently the large force exerted upon them by solar radiation pressure, to control their orbit evolution by altering their surface optical properties. The orbital evolution of Space Chips due to solar radiation pressure can be represented by a Hamiltonian system, allowing an analytic development of the control methodology. The motion in the orbital element phase space resembles that of a linear oscillator, which is used to formulate a switching control law. Additional perturbations and the effect of eclipses are accounted for by modifying the linearized equations of the secular change in orbital elements around an equilibrium point in the phase space of the problem. Finally, the effectiveness of the method is demonstrated in a test case scenario
Wave-like patterns in an elliptical satellite ring
Full text linkSatellite constellations are families of orbits selected to provide useful coverage patterns for telecommunications, Earth observation and navigation services. Such constellations are often assembled from families of circular orbits, which ensures a uniform spacing between satellites in each circular ring. However, there is a large class of elliptical orbits which are of practical interest including Molniya-like orbits and so-called Magic orbits [1,2]. Constellations of satellites using such elliptical orbits will then exhibit a time varying spacing between satellites as the orbital angular velocity experienced by each satellites varies around the elliptical ring. While current constellations use relatively modest numbers of satellites, future microspacecraft [3] or ‘smart dust’ type devices [4,5] may enable constellations with extremely large numbers of nodes. In this Note a continuum approach is used to model the dynamics of such constellations. A continuity equation is formed to describe the evolution of the number density of nodes as a function of both true anomaly and time. For small eccentricities, the continuity equation can be solved analytically to provide closed-form solutions which describe the evolution of the constellation for some initial distribution of nodes. The closed-form solutions can then be used to investigate pattern formation in elliptical rings. Wave-like patterns are found which circulate around the elliptical ring, with peaks in density which can in principle be used to provide enhanced coverage. A similar continuum approach with a continuity equation has been used in previous studies to develop closed-form solutions which model the time evolution of the radial distribution of constellations of microspacecraft under the action of air drag [6,7]
Orbital dynamics of "smart dust" devices with solar radiation pressure and drag
No full textThis paper investigates how perturbations due to asymmetric solar radiation pressure, in the presence of Earth shadow, and atmospheric drag can be balanced to obtain long-lived Earth centred orbits for swarms of micro-scale 'smart dust' devices, without the use of active control. The secular variation of Keplerian elements is expressed analytically through an averaging technique. Families of solutions are then identified where Sun-synchronous apse-line precession is achieved passively to maintain asymmetric solar radiation pressure. The long-term orbit evolution is characterized by librational motion, progressively decaying due to the non-conservative effect of atmospheric drag. Long-lived orbits can then be designed through the interaction of energy gain from asymmetric solar radiation pressure and energy dissipation due to drag. In this way, the usual short drag lifetime of such high area-to-mass spacecraft can be greatly extended (and indeed selected). In addition, the effect of atmospheric drag can be exploited to ensure the rapid end-of-life decay of such devices, thus preventing long-lived orbit debris
A passive satellite deorbiting strategy for MEO using solar radiation pressure and the J2 effect
No full textThe growing population of space debris poses a serious risk to the future of space flight. To effectively manage the increase of debris in orbit, end-of life disposal has become a key requirement for future missions. This poses a challenge for Medium Earth Orbit (MEO) spacecraft which require a large Δv to re-enter the atmosphere or reach the geostationary graveyard orbit. This paper further explores a passive strategy based on the joint effects of solar radiation pressure and the Earth’s oblateness acting on a high area-to-mass ratio object. The concept was previously presented as an analytical planar model. This paper uses a full 3D model to validate the analytical results numerically for equatorial circular orbits first, then investigating higher inclinations. It is shown that for higher inclinations the initial position of the Sun and right ascension of the ascending node become increasingly important. A region of very low required area-to-mass ratio is identified in the parameter space of a and inclination which occurs for altitudes below 10,000 km
Orbit evolution, maintenance and disposal of SpaceChip swarms through electro-chromic control
Full text linkThe combined effect of solar radiation pressure, Earth oblateness and atmospheric drag on the orbital dynamics of satellites-on-a-chip (SpaceChips) is investigated for future swarm mission concepts. The natural evolution of the swarm is exploited to perform spatially distributed measurements of the upper layers of the atmosphere. The energy gain from asymmetric solar radiation pressure can be used to balance the energy dissipation from atmospheric drag. An algorithm for long-term orbit control is then designed, based on changing the reflectivity coefficient of the SpaceChips. The subsequent modulation of the solar radiation pressure allows stabilisation of the swarm in the orbital element phase space. It is shown that the orbit lifetime for such devices can be extended through the interaction of solar radiation pressure and atmospheric drag and indeed selected and the end-of-life re-entry of the swarm can be ensured, by exploiting atmospheric drag
Orbital dynamics of high area-to-mass ratio spacecraft under the influence of J2 and solar radiation pressure
No full textThis paper investigates the effect of planetary oblateness and solar radiation pressure on the orbit of high area-to-mass spacecraft. A planar Hamiltonian model shows the existence of equilibrium orbits with the orbit apogee pointing towards or away from the Sun. These solutions are numerically continued to non-zero inclinations and considering the obliquity of the ecliptic plane relative to the equator. Quasi-frozen orbits are identified in eccentricity, inclination and angle between the Sun-line and the orbit perigee. The long-term evolution of these orbits is then verified through numerical integration. A set of ‘heliotropic’ orbits with apogee pointing in direction of the Sun is proposed for enhancing imaging and telecommunication on the day side of the Earth. The effects of J2 and solar radiation pressure are exploited to obtain a passive rotation of the apsides line following the Sun; moreover the effect of solar radiation pressure enables such orbits at higher eccentricities with respect to the J2 only case
Self-organising satellite constellation in geostationary Earth orbit
Full text linkThis paper presents a novel solution to the problem of autonomous task allocation for a self-organizing satellite constellation in Earth orbit. The method allows satellites to cluster themselves above targets on the Earth’s surface. This is achieved using Coupled Selection Equations (CSE) - a dynamical systems approach to combinatorial optimization whose solution tends asymptotically towards a Boolean matrix describing the pairings of satellites and targets which solves the relevant assignment problems. Satellite manoeuvers are actuated by an Artificial Potential Field method which incorporates the CSE output. Three demonstrations of the method’s efficacy are given - first with equal numbers of satellites and targets, then with a satellite surplus, including agent failures, and finally with a fractionated constellation. Finally, a large constellation of 100 satellites is simulated to demonstrate the utility of the method in future swarm mission scenarios. The method provides efficient solutions with quick convergence, is robust to satellite failures, and hence appears suitable for distributed, on-board autonomy
Constellations of inclined heliotropic orbits for enhanced earth coverage
No full textThis paper proposes a mission design of a constellation for improved Earth coverage using a family of 'heliotropic' orbits. The secular effects of the Earth's oblateness is exploited to maintain the spacecraft on a family of inclined orbits with a constant Sun-pointing apogee, so that enhanced coverage is provided during daylight hours for visible light imaging, or providing communications services during peak local demand. The initial orbital elements of the constellation are designed to meet increased coverage requirements. The orbit semi-major axis is selected in the heliotropic family for repeated groundtrack on specific locations on the Earth's surface. It is also shown that a small solar sail allows having these orbits at higher eccentricity, allowing the spacecraft to spend more time in the dayside of the Earth, w hen orbiting through the apogee. Copyright© (2012) by the International Astronautical Federation
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