14 research outputs found
Flyby Anomaly Test Integrating Multiple Approaches (FATIMA)
FATIMA is a mission concept for a small satellite to investigate the flyby anomaly - a possible velocity increase that has been observed in some earlier satellites when they have performed gravitational swingy maneuvers of the earth
Orbital Debris-Debris Collision Avoidance
We focus on preventing collisions between debris and debris, for which there
is no current, effective mitigation strategy. We investigate the feasibility of
using a medium-powered (5 kW) ground-based laser combined with a ground-based
telescope to prevent collisions between debris objects in low-Earth orbit
(LEO). The scheme utilizes photon pressure alone as a means to perturb the
orbit of a debris object. Applied over multiple engagements, this alters the
debris orbit sufficiently to reduce the risk of an upcoming conjunction. We
employ standard assumptions for atmospheric conditions and the resulting beam
propagation. Using case studies designed to represent the properties (e.g. area
and mass) of the current debris population, we show that one could
significantly reduce the risk of nearly half of all catastrophic collisions
involving debris using only one such laser/telescope facility. We speculate on
whether this could mitigate the debris fragmentation rate such that it falls
below the natural debris re-entry rate due to atmospheric drag, and thus
whether continuous long-term operation could entirely mitigate the Kessler
syndrome in LEO, without need for relatively expensive active debris removal.Comment: 13 pages, 8 figures. Accepted for publication in Advances in Space
Researc
LightForce Photon-Pressure Collision Avoidance: Efficiency Assessment on an Entire Catalogue of Space Debris
The potential to perturb debris orbits using photon pressure from ground-based lasers has been confirmed by independent research teams. Two useful applications of this scheme are protecting space assets from impacts with debris and stabilizing the orbital debris environment, both relying on collision avoidance rather than de-orbiting debris. This paper presents the results of a new assessment method to analyze the efficiency of the concept for collision avoidance. Earlier research concluded that one ground based system consisting of a 10 kW class laser, directed by a 1.5 m telescope with adaptive optics, can prevent a significant fraction of debris-debris collisions in low Earth orbit. That research used in-track displacement to measure efficiency and restricted itself to an analysis of a limited number of objects. As orbit prediction error is dependent on debris object properties, a static displacement threshold should be complemented with another measure to assess the efficiency of the scheme. In this paper we present the results of an approach using probability of collision. Using a least-squares fitting method, we improve the quality of the original TLE catalogue in terms of state and co-state accuracy. We then calculate collision probabilities for all the objects in the catalogue. The conjunctions with the highest risk of collision are then engaged by a simulated network of laser ground stations. After those engagements, the perturbed orbits are used to re-assess the collision probability in a 20 minute window around the original conjunction. We then use different criteria to evaluate the utility of the laser-based collision avoidance scheme and assess the number of base-line ground stations needed to mitigate a significant number of high probability conjunctions. Finally, we also give an account how a laser ground station can be used for both orbit deflection and debris tracking
Improved orbit predictions using two-line elements
The density of orbital space debris constitutes an increasing environmental
challenge. There are three ways to alleviate the problem: debris mitigation,
debris removal and collision avoidance. This paper addresses collision
avoidance, by describing a method that contributes to achieving a requisite
increase in orbit prediction accuracy. Batch least-squares differential
correction is applied to the publicly available two-line element (TLE) catalog
of space objects. Using a high-precision numerical propagator, we fit an orbit
to state vectors derived from successive TLEs. We then propagate the fitted
orbit further forward in time. These predictions are compared to precision
ephemeris data derived from the International Laser Ranging Service (ILRS) for
several satellites, including objects in the congested sun-synchronous orbital
region. The method leads to a predicted range error that increases at a typical
rate of 100 meters per day, approximately a 10-fold improvement over TLE's
propagated with their associated analytic propagator (SGP4). Corresponding
improvements for debris trajectories could potentially provide initial
conjunction analysis sufficiently accurate for an operationally viable
collision avoidance system.
We discuss additional optimization and the computational requirements for
applying all-on-all conjunction analysis to the whole TLE catalog, present and
near future. Finally, we outline a scheme for debris-debris collision avoidance
that may become practicable given these developments.Comment: Submitted to Advances in Space Research. 13 pages, 4 figure
LightForce Photon-Pressure Collision Avoidance: Updated Efficiency Analysis Utilizing a Highly Parallel Simulation Approach
This paper provides an updated efficiency analysis of the LightForce space debris collision avoidance scheme. LightForce aims to prevent collisions on warning by utilizing photon pressure from ground based, commercial off the shelf lasers. Past research has shown that a few ground-based systems consisting of 10 kilowatt class lasers directed by 1.5 meter telescopes with adaptive optics could lower the expected number of collisions in Low Earth Orbit (LEO) by an order of magnitude. Our simulation approach utilizes the entire Two Line Element (TLE) catalogue in LEO for a given day as initial input. Least-squares fitting of a TLE time series is used for an improved orbit estimate. We then calculate the probability of collision for all LEO objects in the catalogue for a time step of the simulation. The conjunctions that exceed a threshold probability of collision are then engaged by a simulated network of laser ground stations. After those engagements, the perturbed orbits are used to re-assess the probability of collision and evaluate the efficiency of the system. This paper describes new simulations with three updated aspects: 1) By utilizing a highly parallel simulation approach employing hundreds of processors, we have extended our analysis to a much broader dataset. The simulation time is extended to one year. 2) We analyze not only the efficiency of LightForce on conjunctions that naturally occur, but also take into account conjunctions caused by orbit perturbations due to LightForce engagements. 3) We use a new simulation approach that is regularly updating the LightForce engagement strategy, as it would be during actual operations. In this paper we present our simulation approach to parallelize the efficiency analysis, its computational performance and the resulting expected efficiency of the LightForce collision avoidance system. Results indicate that utilizing a network of four LightForce stations with 20 kilowatt lasers, 85% of all conjunctions with a probability of collision Pc > 10 (sup -6) can be mitigated
LightForce: An Update on Orbital Collision Avoidance Using Photon Pressure
We present an update on our research on collision avoidance using photon-pressure induced by ground-based lasers. In the past, we have shown the general feasibility of employing small orbit perturbations, induced by photon pressure from ground-based laser illumination, for collision avoidance in space. Possible applications would be protecting space assets from impacts with debris and stabilizing the orbital debris environment. Focusing on collision avoidance rather than de-orbit, the scheme avoids some of the security and liability implications of active debris removal, and requires less sophisticated hardware than laser ablation. In earlier research we concluded that one ground based system consisting of a 10 kW class laser, directed by a 1.5 m telescope with adaptive optics, could avoid a significant fraction of debris-debris collisions in low Earth orbit. This paper describes our recent efforts, which include refining our original analysis, employing higher fidelity simulations and performing experimental tracking tests. We investigate the efficacy of one or more laser ground stations for debris-debris collision avoidance and satellite protection using simulations to investigate multiple case studies. The approach includes modeling of laser beam propagation through the atmosphere, the debris environment (including actual trajectories and physical parameters), laser facility operations, and simulations of the resulting photon pressure. We also present the results of experimental laser debris tracking tests. These tests track potential targets of a first technical demonstration and quantify the achievable tracking performance
The emergence of gravity as a retro-causal post-inflation macro-quantum-coherent holographic vacuum Higgs-Goldstone field
We present a model for the origin of gravity, dark energy and dark matter:
Dark energy and dark matter are residual pre-inflation false vacuum random zero
point energy (w=-1) of large-scale negative, and short-scale positive pressure,
respectively, corresponding to the "zero point" (incoherent) component of a
superfluid (supersolid) ground state. Gravity, in contrast, arises from the 2nd
order topological defects in the post-inflation virtual "condensate" (coherent)
component. We predict, as a consequence, that the LHC will never detect exotic
real on-mass-shell particles that can explain dark matter. We also point out
that the future holographic dark energy de Sitter horizon is a total absorber
(in the sense of retro-causal Wheeler-Feynman action-at-a-distance
electrodynamics) because it is an infinite redshift surface for static
detectors. Therefore, the advanced Hawking-Unruh thermal radiation from the
future de Sitter horizon is a candidate for the negative pressure dark vacuum
energy.Comment: 8 pages, no figures. To appear in Proc. DICE2008 From Quantum
Mechanics through Complexity to Spacetime: the role of emergent dynamical
structures. Castello Pasquini/Castiglioncello (Tuscany), September 22-26,
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