Martian lower thermospheric variations are complex due to internal surface dust storms and external solar activities. However, limited Martian measurement data are restricted to observe and understand its variations in the past. In this paper, multisatellite accelerometer-derived densities and the Mars Climate Database are used to investigate seasonal variations, gravity waves, and coupling effects with the internal and external inputs, including Mars Global Surveyor, Mars Reconnaissance Orbiter, Mars Odyssey, and Mars Atmosphere and Volatile EvolutioN Mission. The diurnal and seasonal structures are reconstructed by the data, and the phase of the cycles is formed by solar heating/ionizing processes. Both amplitude and phase are impacted by surface dust activities during autumn and winter, for which density increases about 1.5-3.5 times compared to spring and summer seasons. A parameterized model that includes a newly introduced dust index is proposed to well fit and reinterpret the seasonal cycles. Furthermore, the coupling process between internal atmospheric gravity waves (IAGWs) and dust activities are investigated and explained. During dust storm times/seasons, the IAGWs exhibit both narrower amplitude peaks and deposit their energy at higher altitudes relative to "clear sky" times. The IAGWs could extend their energies into higher layers beyond exobase due to a thermospheric layer expansion (i.e., density increase) during dust seasons. Plain Language Summary The new spacecraft Mars Atmosphere and Volatile EvolutioNMission aims to observe Mars lower thermosphere from 100 to 200 km, namely, the lower thermosphere. The daily and yearly variations of the Mars thermospheric density are illustrated for the first time with this data. An improved fitting function is proposed for the yearly density variations. We found that the yearly variations are explained by seasonal solar illumination changes experienced by Mars during its orbit, which can be fit by a superposition of sine and cosine functions. The amplitude of the variations is impacted by surface dust storms during dust seasons (Mars northern autumn and winter). The behaviors of the vertically propagating internal atmospheric gravity waves (IAGWs) are investigated in different seasons. The interaction between these IAGWs and lower atmosphere dust storms is analogous to ocean waves hitting a beach, where the changes in the lower atmosphere dust function like the changing ocean depth close to shore that allow the ocean waves (i.e., IAGWs) to propagate more energy onto the shore (into the upper atmosphere).

The robustness of the Sandia Inertial Terrain‐Aided Navigation (SITAN) algorithm has a pivotal influence on underwater vehicles' Gravity‐Aided Inertial Navigation Systems (GAINS). An abrupt glitch of the accuracy of the GAINS will evolve into a disaster when vehicles pass through areas of smooth gravity. In order to resolve vulnerability issues of initial error and linearization error, we propose the Correlation SITAN algorithm with Weight‐Reducing Iteration Technique (CSITAN + WRIT), in which the correlation process equals Terrain Contour Matching (TERCOM). The CSITAN algorithm is a Multipoint‐based Extended Kalman Filtering (MEKF) method, which can work in real time. First, we need to derive the state equation and observation equation of the Multipoint‐based SITAN algorithm based on the principle of the traditional SITAN algorithm. Then the accuracy of the state prediction can be improved, and the linearization error can be reduced by the correlation method based on TERCOM. Finally, the WRIT is utilized to reduce the possible influence of gross errors existing in the results of the MEKF and to extract a value with higher precision. The experimental results show that CSITAN + WRIT can achieve better accuracy and higher success rate of matching and can improve the possibilities of the occurrence of large matching errors than traditional SITAN methods in areas with smooth gravity. Copyright © 2017 Institute of Navigation

Temperature profiles retrieved using the first set of data of the Emirates Mars InfraRed Spectrometer obtained during the science phase of the Emirates Mars Mission are used for the analysis of migrating thermal tides in the Martian atmosphere. The selected data cover a solar longitude (LS) range of 60°–90° of Martian Year 36. The novel orbit design of the Hope Probe leads to a good geographic and local time coverage that significantly improves the analysis. Wave mode decomposition suggests dominant diurnal tide and important semi‐diurnal tide with maximal amplitudes of 6 and 2 K, respectively, as well as the existence of ∼0.5 K ter‐diurnal tide. The results agree well with predictions by the Mars Planetary Climate Model, but the observed diurnal tide has an earlier phase (3 hr), and the semi‐diurnal tide has an unexpectedly large wavelength (∼200 km).

Internal gravity waves (IGWs) play an important role in the planetary atmospheres, which transfer energy and momentum from the lower layers to the upper atmosphere. However, the IGW perturbations and behaviors are not clear in the Mars upper atmosphere, particularly for the horizontal internal gravity waves (hIGWs). In this study, the hIGWs in the upper atmosphere of Mars are estimated and investigated for the first time using both accelerometer (ACC)‐derived mass density and Neutral Gas and Ion Mass Spectrometer‐measured neutral density from Mars Atmosphere and Volatile EvolutioN (MAVEN) mission. The results show that the amplitudes of hIGWs variations are significantly affected by the dust storms and increase with the altitudes. The larger amplitudes are triggered in Martian Year (MY) 34 during a global dust event. The characteristics of Ar and CO2 hIGWs variations are similar. Furthermore, the trend of the CO perturbations seems to follow the CO2. However, the dust storms play little role in shaping hIGWs of atomic O. The hIGWs show the stable waveform with the increasing altitudes.

The precise autonomous navigation for deep space exploration by combination of multi-source observation data is a key issue for probe control and scientific applications. In this paper, the performance of an integrated Optical Celestial Navigation (OCN) and X-ray Pulsars Autonomous Navigation (XNAV) system is investigated for the orbit of Mars Pathfinder. Firstly, OCN and XNAV single systems are realised by an Unscented Kalman Filter (UKF). Secondly, the integrated system is simulated with a Federated Kalman Filter (FKF), which can do the information fusion of the two subsystems of UKF and inherits the advantages of each subsystem. Thirdly, the performance of our system is evaluated by analysing the relationship between observation errors and navigation accuracy. The results of the simulation experiments show that the biases between the nominal and our calculated orbit are within 5 km in all three axes under complex error conditions. This accuracy is also better than current ground-based techniques.

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The Martian atmosphere is the host of small-scale vertical fluctuations that have been observed by multiple Martian orbiters (

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