519 research outputs found
Orbit Modeling of Galilean Moons Flybys
No full textThis research aims at modeling the trajectory followed by the Galileo spacecraft during a variety of flybys about the Galilean moons. The chosen flybys have good Earth’s elevation angles and either low or high closest-approach altitudes, so that the comparison of the two can give relevant insight into the accuracy of the corresponding trajectories. By propagating the state of the spacecraft during these flybys, optimizing the nominal initial state of the spacecraft (obtained through the SPICE program) and the spherical harmonics of the moons, and estimating new harmonics, the minimum root mean square error between the resulting trajectory and the ephemerides by Jet Propulsion Laboratory (JPL) is found. The analysis of its components along the Local Orbital axes gives insight into the existing relation between them and the Earth's elevation and azimuth angles. In particular, a low-altitude flyby implies in general a higher error, but when two flybys have similar altitudes, then the Earth's elevation plays a relevant role and the flyby with the largest one is more likely to have a larger error too. The root mean square error of the fitted trajectories can vary from 15 cm to 7 m, so always less than the 9 m declared by National Aeronautics and Space Administration (NASA) as the maximum error of the moons ephemerides. Furthermore, the flybys about Ganymede and Callisto show a high error in the along-track and cross-track directions, since the radius of their sphere of influence is quite larger than that of the inner moons' ones, hence there is more time for the perturbations to influence the orbit. A by-product of this research is the estimate of the Galilean moons' gravity field, in particular the new values for their J2 and C2,2 coefficients led to the conclusion that Io is less hydrostatic, while Europa and Callisto are more hydrostatic than previously thought.Aerospace Engineerin
Contribution of PRIDE VLBI products to the joint JUICE-Europa Clipper moons’ ephemerides solution
No full textIn the coming decade, JUICE and Europa Clipper radio-science will yield the most accurate estimation to date of the Galilean moons’ physical parameters and ephemerides. JUICE's PRIDE (Planetary Radio Interferometry and Doppler Experiment) will help achieve such a solution by providing VLBI (Very Long Baseline Interferometry) observations of the spacecraft's lateral position, complementing nominal radio-science measurements. In this paper, we quantify how PRIDE VLBI can contribute to the moons’ ephemerides determination, in terms of attainable solution improvement and validation opportunities. To this end, we simulated VLBI data for JUICE, but also investigated the possibility to perform simultaneous tracking of JUICE and Europa Clipper, thus ultimately generating both single- and dual-spacecraft VLBI. We considered various tracking and data quality scenarios for both VLBI types, and compared the formal uncertainties provided by covariance analyses with and without VLBI. These analyses were performed for both global and local (i.e. per-flyby) estimations of the moons’ states, as eventually achieving a global solution first requires proceeding arc-per-arc. We showed that both single- and multi-spacecraft VLBI measurements only bring limited improvement to the global state estimation, but significantly contribute to the moons’ normal points (i.e. local states at flyby times), most notably in the out-of-plane direction. Additionally, we designed a validation plan exploiting PRIDE VLBI to progressively validate the classical radio-science solution, whose robustness and statistical realism is sensitive to modelling inconsistencies. By improving the local state estimations and offering various validation opportunities, PRIDE will be invaluable in overcoming possible dynamical challenges. It can therefore play a key role in reconstructing a global solution for the Galilean moons’ dynamics with the uncertainty levels promised by JUICE-Europa Clipper analyses. This, in turn, is critical to the accurate characterisation of tidal dissipation in the Jovian system, holding the key to the long-term evolution of the Galilean moons.Astrodynamics & Space MissionsSpace Engineerin
Policy design and the optimal location of forests in Flanders
No full textThis paper analyses the current Flemish afforestation policy and shows that this policy is likely to be non-optimal and can be improved. An important step in improving the afforestation policy in Flanders is the selection of the optimal location of a cluster of new forests as a whole. The analysis of the optimal location can provide the regulator with objective criteria, which can be used to develop optimal regulations. It is also worthwhile to consider alternative policies, such as auctions for afforestations projects. To this effect, we investigate several policy options and test these in a real-life example for the creation of new forests in East Flanders.Afforestation / policy instruments / optimal location
Determining the characteristics of icy moons' impactors: An experimental approach
No full textCrater counting is the main method used to determine the age of a planetary surface. This method relies on knowing the cratering rate to estimate the absolute age of a surface. However, two theories currently exist for impact cratering of the moons in the Saturnian system, one suggesting that the majority of the impactors are of heliocentric origin (i.e. they come from orbits around the Sun), and the other suggesting that the majority of impactors are of planetocentric origin (i.e. they originate from orbits around Saturn). The different theories result in very different surface ages of the icy moons. According to the heliocentric model, the surface of Titan would date to ~3 Ga, while according to the planetocentric model the surface of Titan could be dated between ~15 Ma and ~4 Ga, allowing for much more erosion of the surface according to Bell (2020). Given that these two orbits result in different impact velocities, this work attempts to discover if the impact velocity can be determined for impactors on icy moons based on crater characteristics, such as crater depth and diameter, by recreating impacts in the lab.Previous impact experiments have been performed with different impactors and target materials. This study aims at expanding previous research by performing tests on icy particles, something not done before. The data obtained from experiments are then used to obtain the estimated impactor diameter that created craters on the surface of these icy moons based on the expected impact velocities. This data can then be used to predict the likelihood of an impactor originating from either a heliocentric or planetocentric orbit.This work developed several methods to produce impact craters using different instruments and different surfaces. The best results were obtained either with the gas gun and ice blocks or with the drop tower and icy particles. Using the scaling relationships found in this work, it was shown that the required impactor diameter can be obtained from craters on icy moons and that a distinction can be made between planetocentric and heliocentric impactors. However, more work is needed to narrow down the scaling relationship to obtain a reasonable impactor diameter given a certain impact crater. More information about the crater, such as the transition of ice type during an impact, should be used in the future to further constrain the velocity ranges.Aerospace Engineerin
Combining astrometry and JUICE-Europa Clipper radio science to improve the ephemerides of the Galilean moons
No full textContext. The upcoming JUICE and Europa Clipper missions targeting Jupiter s Galilean satellites will provide radio science tracking measurements of both spacecraft. Such data are expected to significantly help estimating the moons ephemerides and related dynamical parameters (e.g. tidal dissipation parameters). However, the two missions will yield an imbalanced dataset, with no flybys planned at Io, condensed over less than six years. Current ephemerides solutions for the Galilean moons, on the other hand, rely on ground-based astrometry collected over more than a century which, while being less accurate, bring very valuable constraints on the long-term dynamics of the system. Aims. An improved solution for the Galilean satellites complex dynamics could however be achieved by exploiting the existing synergies between these different observation sets. Methods. To quantify this, we merged simulated radio science data from both JUICE and Europa Clipper spacecraft with existing ground-based astrometric and radar observations, and performed the inversion in different configurations: either adding all available ground observations or individually assessing the contribution of different data subsets. Our discussion specifically focusses on the resulting formal uncertainties in the moons states, as well as Io s and Jupiter s tidal dissipation parameters. Results. Adding astrometry stabilises the moons state solution, especially beyond the missions timelines. It furthermore reduces the uncertainties in 1/Q (inverse of the tidal quality factor) by a factor two to four for Jupiter, and about 30- 35% for Io. Among all data types, classical astrometry data prior to 1960 proved particularly beneficial. Overall, we also show that ground observations of Io add the most to the solution, confirming that ground observations can fill the lack of radio science data for this specific moon. Conclusions. We obtained a noticeable solution improvement when making use of the complementarity between all different observation sets. The promising results obtained with simulations thus motivate future efforts to achieve a global solution from actual JUICE and Clipper radio science measurements. Astrodynamics & Space Mission
Policy options for afforestation in Flanders.
No full textThis paper analyses current and alternative afforestation policy instruments in Flanders. First we select forest sites that maximize net social benefits given a constraint on the total area of new forests and then we select policy instruments that yield this optimal combination of sites. For each policy option, we calculate the associated costs for landowners and government as well as net social benefits for society. Our empirical illustration shows that the welfare gain is considerable if the afforestation subsidy is conditioned on an objective criterion rather than a case-by-case approach. Our results also show that it is worthwhile to consider alternative policy instruments, such as auctions, not previously used in Belgian legislation.Afforestation; Policy instruments; Optimal location;
Auctioning Conservation Contracts: An Application to the Flemish Afforestation Policy
No full textThis paper studies the possibility of using auctions as a policy instrument in conservation programs. In particular, it provides insight into the main concerns that need to be dealt with when implementing conservation auctions. To show the cost saving potential of this policy instrument, we also calculate the social welfare improvement that can be obtained for an afforestation project in Flanders. Creation-Date: 2006-03Auctions; Conservation contracts; Afforestation
Policy options for afferorestation in Flanders
No full textThis paper analyses current and alternative afforestation policy instruments in Flanders. First we select forest sites that maximize net social benefits given a constraint on the total area of new forests and then we select policy instruments that yield this optimal combination of sites. For each policy option, we calculate the associated costs for landowners and government as well as net social benefits for society. Our empirical illustration shows that the welfare gain is considerable if the afforestation subsidy is conditioned on an objective criterion rather than a case-by-case approach. Our results also show that it is worthwhile to consider alternative policy instruments, such as auctions, not previously used in Belgian legislation.Afforestation / policy instruments / optimal location
The development and application of economic valuation techniques and their use in environmental policy - A survey
No full textThis paper is concerned with the issue of how to introduce monetary valuation into public decision-making. This issue is closely related to introducing rational procedures into public decision-making (Pearce, 2001). All public decision-making involves choice. To economists, rational choice means making the 'best' use of available resources, i.e. choose that option that has the lowest opportunity cost or the lowest value to be sacrificed. Costs and benefits of any project should therefore be weighed as well as compared to cost and benefits of alternative projects. This implies that all impacts of these projects need to be expressed in the same unit to make comparison possible. Money seems to be the most obvious numéraire. We discuss some of the most popular economic valuation techniques and their potential role in public decision-making. Due to the high cost and time that is needed to perform original valuation studies and the limited knowledge of decision-makers with these techniques, we recommend that the Flemish Administration primarily invests in performing high-quality transfer studies.Valuation, Cost-benefit Analysis, Travel Cost Method, Contingent Valuation Method
On the origin of the moons of Jupiter
No full textThe origin of the Galilean moons have puzzled the scientists for centuries. The most recent theories affirm that they formed within a circumplanetary disk (CPD), a disk of gas and dust very similar to the protoplanetary disk (PPD), from which the planets formed. However, there are still many uncertainties on this CPD, such as its size, mass, the contribution of the young Jupiter, the young Sun and many more. In this project, an innovative way of simulating this CPD has been undertaken. With the help of the software ProDiMo, thermo-chemical simulations of the disk have been carried out. Originally designed to simulate PPDs, for the first time it has been applied to the tinier CPD. The software has proven itself to work well even with CPDs. The results are coherent with the current theories and, with this new approach, more clarity has been added to the formation process of the Galilean moons. This helps us to understand the origin of our solar system and to refine the research methods for possible habitable exomoons outside of the solar system border.Aerospace Engineerin
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