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The Lunar landing has drawn great interest in lunar exploration in recent years, and autonomous lunar landing navigation is fundamental to this task. AI is expected to play a critical role in autonomous and intelligent space missions, yet human experts question the reliability of AI solutions. Thus, the \gls{xai} for vision-based lunar landing is studied in this paper, aiming at providing transparent and understandable predictions for intelligent lunar landing. Attention-based Darknet53 is proposed as the feature extraction structure. For crater detection and navigation tasks, attention-based YOLOv3 and attention-Darknet53-LSTM are presented respectively. The experimental results show that the offered networks provide competitive performance on relative crater detection and pose estimation during the lunar landing. The explainability of the provided networks is achieved by introducing an attention mechanism into the network during model building. Moreover, the PCC is utilised to quantitively evaluate the explainability of the proposed networks, with the findings showing the functions of various convolutional layers in the network.

Research on developing deep learning techniques for autonomous spacecraft relative navigation challenges is continuously growing in recent years. Adopting those techniques offers enhanced performance. However, such approaches also introduce heightened apprehensions regarding the trustability and security of such deep learning methods through their susceptibility to adversarial attacks. In this work, we propose a novel approach for adversarial attack detection for deep neural network-based relative pose estimation schemes based on the explainability concept. We develop for an orbital rendezvous scenario an innovative relative pose estimation technique adopting our proposed Convolutional Neural Network (CNN), which takes an image from the chaser's onboard camera and outputs accurately the target's relative position and rotation. We perturb seamlessly the input images using adversarial attacks that are generated by the Fast Gradient Sign Method (FGSM). The adversarial attack detector is then built based on a Long Short Term Memory (LSTM) network which takes the explainability measure namely SHapley Value from the CNN-based pose estimator and flags the detection of adversarial attacks when acting. Simulation results show that the proposed adversarial attack detector achieves a detection accuracy of 99.21%. Both the deep relative pose estimator and adversarial attack detector are then tested on real data captured from our laboratory-designed setup. The experimental results from our laboratory-designed setup demonstrate that the proposed adversarial attack detector achieves an average detection accuracy of 96.29%.

We use the time-independent quantum-mechanical formulation of reactive collisions in order to investigate the state-to-state $\mathrm{H}^+ + \mathrm{HD} \to \mathrm{D}^+ + \mathrm{H}_2$ chemical reaction. We compute cross sections for collision energies up to 1.8 electron-volts and rate coefficients for temperatures up to 10000 kelvin. We consider HD in the lowest vibrational level $v=0$ and rotational levels $j=0$ to 4, and H$_2$ in vibrational levels $v'=0$ to 3 and rotational levels $j'=0$ to 9. For temperatures below 4000 kelvin, the rate coefficients strongly vary with the initial rotational level $j$, depending on whether the reaction is endothermic ($j\le 2$) or exothermic ($j\ge 3$). The reaction is also found less and less probable as the final vibrational quantum number $v'$ increases. Our results illustrate the importance of studying state-to-state reactions, in the context of the chemistry of the primordial universe., Comment: 7 pages, 9 figures

We present a detailed theoretical study of the rotational excitation of CH$^+$ due to reactive and nonreactive collisions involving C$^+(^2P)$, H$_2$, CH$^+$, H and free electrons. Specifically, the formation of CH$^+$ proceeds through the reaction between C$^+(^2P)$ and H$_2(\nu_{\rm H_2}=1, 2)$, while the collisional (de)excitation and destruction of CH$^+$ is due to collisions with hydrogen atoms and free electrons. State-to-state and initial-state-specific rate coefficients are computed in the kinetic temperature range 10-3000~K for the inelastic, exchange, abstraction and dissociative recombination processes using accurate potential energy surfaces and the best scattering methods. Good agreement, within a factor of 2, is found between the experimental and theoretical thermal rate coefficients, except for the reaction of CH$^+$ with H atoms at kinetic temperatures below 50~K. The full set of collisional and chemical data are then implemented in a radiative transfer model. Our Non-LTE calculations confirm that the formation pumping due to vibrationally excited H$_2$ has a substantial effect on the excitation of CH$^+$ in photon-dominated regions. In addition, we are able to reproduce, within error bars, the far-infrared observations of CH$^+$ toward the Orion Bar and the planetary nebula NGC~7027. Our results further suggest that the population of $\nu_{\rm H_2}=2$ might be significant in the photon-dominated region of NGC~7027., Comment: 10 pages, 8 figures, accepted 2017 April 7

Chemical models used to study the chemical composition of the gas and the ices in the interstellar medium are based on a network of chemical reactions and associated rate coefficients. These reactions and rate coefficients are partially compiled from data in the literature, when available. We present in this paper kida.uva.2014, a new updated version of the kida.uva public gas-phase network first released in 2012. In addition to a description of the many specific updates, we illustrate changes in the predicted abundances of molecules for cold dense cloud conditions as compared with the results of the previous version of our network, kida.uva.2011., Comment: Accepted for publication in ApJS on February 26th, 2015

We report in this review recent fully-quantum time-independent calculations of cross sections and rate constants for the gas phase ortho-to-para conversion of H$_2$ by H and H$^+$. Such processes are of crucial interest and importance in various astrophysical environments. The investigated temperature ranges was 10$-$1500 K for H+H$_2$ and 10$-$100 K for H$^+$+H$_2$. Calculations were based on highly accurate H$_3$ and H$_3^+$ global potential energy surfaces. Comparisons with previous calculations and with available measurements are presented and discussed. It is shown that the existence of a long-lived intermediate complex H$_3^+$ in the (barrierless) H$^+$+H$_2$ reaction give rise to a pronounced resonance structure and a statistical behaviour, in contrast to H+H$_2$ which proceeds through a barrier of $\sim 5000$ K. In the cold interstellar medium ($T\leq 100$ K), the ortho-to-para conversion is thus driven by proton exchange while above $\sim$300 K, the contribution of hydrogen atoms become significant or even dominant. Astrophysical applications are briefly discussed by comparing, in particular, the relative role of the conversion processes in the gas phase ({\it via} H, H$^+$, H$_2$ and H$_3^+$) and on the surface of dust particles. Perspectives concerning future calculations at higher temperatures are outlined., Comment: 34 pages, 7 fugures

Using the multipolar expansion of the electrostatic energy, we have characterized the asymptotic interactions between an oxygen atom O$(^3P)$ and an oxygen molecule O$_2(^3\Sigma_g^-)$, both in their electronic ground state. We have calculated the interaction energy induced by the permanent electric quadrupoles of O and O$_2$ and the van der Waals energy. On one hand we determined the 27 electronic potential energy surfaces including spin-orbit connected to the O$(^3P)$ + O$_2(^3\Sigma_g^-)$ dissociation limit of the O--O$_2$ complex. On the other hand we computed the potential energy curves characterizing the interaction between O$(^3P)$ and a O$_2(^3\Sigma_g^-)$ molecule in its lowest vibrational level and in a low rotational level. Such curves are found adiabatic to a good approximation, namely they are only weakly coupled to each other. These results represent a first step for modeling the spectroscopy of ozone bound levels close to the dissociation limit, as well as the low energy collisions between O and O$_2$ thus complementing the knowledge relevant for the ozone formation mechanism., Comment: Submitted to J. Chem. Phys. after revision

We present a novel chemical database for gas-phase astrochemistry. Named the KInetic Database for Astrochemistry (KIDA), this database consists of gas-phase reactions with rate coefficients and uncertainties that will be vetted to the greatest extent possible. Submissions of measured and calculated rate coefficients are welcome, and will be studied by experts before inclusion into the database. Besides providing kinetic information for the interstellar medium, KIDA is planned to contain such data for planetary atmospheres and for circumstellar envelopes. Each year, a subset of the reactions in the database (kida.uva) will be provided as a network for the simulation of the chemistry of dense interstellar clouds with temperatures between 10 K and 300 K. We also provide a code, named Nahoon, to study the time-dependent gas-phase chemistry of 0D and 1D interstellar sources., Comment: Accepted for publication in ApJS

Context: Dark cloud chemical models usually predict large amounts of O2, often above observational limits. Aims: We investigate the reason for this discrepancy from a theoretical point of view, inspired by the studies of Jenkins and Whittet on oxygen depletion. Methods: We use the gas-grain code Nautilus with an up-to-date gas-phase network to study the sensitivity of the molecular oxygen abundance to the oxygen elemental abundance. We use the rate coefficient for the reaction O + OH at 10 K recommended by the KIDA (KInetic Database for Astrochemistry) experts. Results: The updates of rate coefficients and branching ratios of the reactions of our gas-phase chemical network, especially N + CN and H3+ + O, have changed the model sensitivity to the oxygen elemental abundance. In addition, the gas-phase abundances calculated with our gas-grain model are less sensitive to the elemental C/O ratio than those computed with a pure gas-phase model. The grain surface chemistry plays the role of a buffer absorbing most of the extra carbon. Finally, to reproduce the low abundance of molecular oxygen observed in dark clouds at all times, we need an oxygen elemental abundance smaller than 1.6E-4. Conclusion: The chemistry of molecular oxygen in dense clouds is quite sensitive to model parameters that are not necessarily well constrained. That O2 abundance may be sensitive to nitrogen chemistry is an indication of the complexity of interstellar chemistry., Comment: 6 pages, 3 figures, accepted for publication in Astronomy & Astrophysics

A potential energy surface for the lowest quartet electronic state of lithium trimer is developed and used to study spin-polarized Li + Li_2 collisions at ultralow kinetic energies. The potential energy surface allows barrierless atom exchange reactions. Elastic and inelastic cross sections are calculated for collisions involving a variety of rovibrational states of Li_2. Inelastic collisions are responsible for trap loss in molecule production experiments. Isotope effects and the sensitivity of the results to details of the potential energy surface are investigated. It is found that for vibrationally excited states the cross sections are only quite weakly dependent on details of the potential energy surface., Comment: 21 pages, 27 figures. Version 2 is final version as accepted for publication in J. Chem. Phys

We have carried out the first quantum dynamics calculations on ultracold atom-diatom collisions in isotopic mixtures. The systems studied are spin-polarized 7Li + 6Li7Li, 7Li + 6Li2, 6Li + 6Li7Li and 6Li + 7Li2. Reactive scattering can occur for the first two systems even when the molecules are in their ground rovibrational states, but is slower than vibrational relaxation in homonuclear systems. Implications for sympathetic cooling of heteronuclear molecules are discussed., Comment: 4 pages, 3 figures

We have developed a new potential energy surface for spin-polarized K($^2$S) + K$_{2}(^3\Sigma^+_u)$ collisions and carried out quantum dynamical calculations of vibrational quenching at low and ultralow collision energies for both bosons $^{39}$K and $^{41}$K and fermions $^{40}$K. At collision energies above about 0.1 mK the quenching rates are well described by a classical Langevin model, but at lower energies a fully quantal treatment is essential. We find that for the low initial vibrational state considered here ($v=1$), the ultracold quenching rates are {\it not} substantially suppressed for fermionic atoms. For both bosons and fermions, vibrational quenching is much faster than elastic scattering in the ultralow-temperature regime. This contrasts with the situation found experimentally for molecules formed via Feshbach resonances in very high vibrational states., Comment: 11 pages, 9 figures

We have carried out quantum dynamical calculations of vibrational quenching in Li + Li_2 collisions for both bosonic 7Li and fermionic 6Li. These are the first ever such calculations involving fermionic atoms. We find that for the low initial vibrational states considered here (v less than or equal to 3), the quenching rates are not suppressed for fermionic atoms. This contrasts with the situation found experimentally for molecules formed via Feshbach resonances in very high vibrational states., Comment: 4 pages, 4 figures (with Figs. 2 and 3 in 2 files each)

Ultracold collisions between spin-polarized Na atoms and vibrationally excited Na_2 molecules are investigated theoretically, using both an inelastic formalism (neglecting atom exchange channels) and a reactive formalism (including atom exchange). Calculations are carried out on both pairwise additive and non-additive potential energy surfaces for the quartet electronic state. In both inelastic and reactive calculations, the Wigner threshold laws are followed for energies below 10^{-6} K. It is found that vibrational relaxation processes dominate elastic processes for temperatures below 10^{-3} - 10^{-4} K. For temperatures below 10^{-5} K, the rate coefficients for vibrational relaxation (v = 1 -> 0) from the full calculation are 4.8 x 10^{-11} and 5.2 x 10^{-10} cm^3 s^-1 for the additive and non-additive potentials respectively., Comment: 4 pages, LaTeX source, 3 figures