Satellite Deployment Research Articles

A Hidden Markov Tree Model for Flood Extent Mapping in Heavily Vegetated Areas based on High Resolution Aerial Imagery and DEM: A Case Study on Hurricane Matthew Floods

ABSTRACT Flood extent mapping plays a crucial role in disaster management and national water forecasting. In recent years, high-resolution optical imagery becomes increasingly available with the deployment of numerous small satellites and drones. However, analysing such imagery data to extract flood extent poses unique challenges due to the rich noise and shadows, obstacles (e.g. tree canopies, clouds), and spectral confusion between pixel classes (flood, dry) due to spatial heterogeneity. Existing machine-learning techniques often focus on spectral and spatial features from raster images without fully incorporating the geographic terrain within classification models. In contrast, we recently proposed a novel machine-learning model called geographical hidden Markov tree (HMT) that integrates spectral features of pixels and topographic constraint from Digital Elevation Model (DEM) data (i.e. water flow directions) in a holistic manner. This paper evaluates the model through case studies on high-resolution aerial imagery from National Oceanic and Atmospheric Administration (NOAA) National Geodetic Survey (NGS) together with DEM. Three scenes are selected in heavily vegetated floodplains near the cities of Grimesland and Kinston in North Carolina during Hurricane Matthew floods in 2016. Results show that the proposed HMT model outperforms several state of the art machine-learning algorithms (e.g. random forests, gradient-boosted model) by an improvement of F-score (the harmonic mean of the user’s accuracy and producer’s accuracy) from around 70% to 80% to over 95% on our datasets.

Towards the automated operations of large distributed satellite systems. Part 2: Classifications and tools

Recent developments have seen a trend towards larger constellations of spacecraft, with some proposals featuring constellations of more than 10.000 satellites. While similar concepts for large constellations already existed in the past, traditional satellite deployments hardly ever feature groups of more than 100 satellites. This trend towards considerably larger satellite numbers originates from non-traditional design and operations of spacecraft by non-traditional space companies. The evolution in the space sector, precipitated by new players, is often referred to as “Space 4.0” or “New Space”. It necessitates a rethinking of the way satellites and satellite constellations are planned, designed, and operated. New operational paradigms are needed to enable automatic, optimal task definition, and scheduling in a holistic approach.This is the second of two companion papers that investigate the operations of distributed satellite systems. This second article investigates the classification of distributed satellite systems and evaluates commercial tools for automated spacecraft operations, whereas the first article performed a survey of conventional and “new space”operations of spacecraft constellations.Classification metrics for constellations are derived and evaluated with respect to their informative value concerning the operation, the automation, and the scalability of the constellation. The proposed classification system is applied to the Dove and RapidEye constellation and allows for a comparison between the presented automation approaches. Commercial tools for automated spacecraft operations are evaluated for several mission task elements, such as orbit control, orbit maintenance, and collision avoidance. Subsequently, the trends, benefits, and standardization needs for operational automation are identified.

Orbit deployment and drag control strategy for formation flight while minimizing collision probability and drift

The compact form factor of nanosatellites or even smaller satellites makes them predestined for distributed systems such as formations, constellations or large swarms. However, when it comes to orbit insertion of multiple satellites, these ride share payloads have constrains in the deployment parameters such as sequence, direction, velocity and time interval. Especially for formation flight missions without propulsion, where the satellites should minimize their relative distance drift either passively or by atmospheric drag control, the initial ejection parameters must find a proper trade-off between collision probability and relative drift. Hence, this article covers short-term (first orbit) collision analysis, long-term (30 days) drift analysis and atmospheric drag control strategy for long-term distance control of multiple satellites. The collision analysis considers various orbit deployment parameters such as insertion direction and tolerance, orbital elements of insertion and time span. To cover the parameter space, a Monte Carlo simulation was conducted to identify the impact of these parameters. It showed that for collision probability the major factor is the time span between two ejections and the precision of the deployment vector. For long-term drift analysis, orbit perturbation such as atmosphere and J2 terms are considered. The result showed that for drift minimizing, minimizing the along-track variation is more substantial than reducing the time span between ejections. Additionally, a drag control strategy to reduce the relative drift of the satellites is described. The results have been applied on the S-NET mission, which consists of four nanosatellites with the task to keep their relative distance within 400 km to perform intersatellite communication experiments. The flight results for orbital drift show equal or better performance (0.1–0.7 km/day) compared to the worst-case simulation scenario, implying that orbit perturbation was chosen correctly and all orbit injection tolerances were within specified range. The drag control maneuver showed good matching to the flight results as well with a deviation for the maneuver time of approximately 10%.

Remote sensing of phytoplankton decline during the late 1980s and early 1990s in the South China Sea

ABSTRACT The duration of a single satellite deployment is insufficient to detect long-term trends in phytoplankton biomass. By integrating data from different platforms, we quantified the phytoplankton trends in the South China Sea (SCS) from the early-to-mid 1980s to the present. We focused on winter data because the sea surface temperature (SST) in winter has been increasing over the past three decades. We included data from three different eras: (1) the Coastal Zone Colour Scanner (CZCS) period (1979–1983), (2) the Sea-viewing Wide Field-of-view Sensor (SeaWiFS) period (1998–2002), and (3) the Moderate Resolution Imaging Spectroradiometer (MODIS) period (2010–2014). There was a decline in phytoplankton (approximately 0.15 mg m−3) over the entire SCS from the CZCS period to the SeaWiFS period. The largest reduction (over 0.3 mg m−3) occurred in the northern and western SCS. After the SeaWiFS period, the phytoplankton increased by approximately 0.05 mg m−3. The largest increase was observed to the west of Luzon Strait, extending towards the east coast of Hainan Island. The fluctuations in phytoplankton from the early-to-mid 1980s to the present were consistent with the variation in the wind field rather than with the continued increase in SST. The wind speed decreased from the CZCS period to the SeaWiFS period and increased from the SeaWiFS period to the MODIS period. Moreover, the nutrient variations induced by the mixed-layer depth also contributed to the fluctuations in phytoplankton.

Incorporation of Unmanned Aerial Vehicle (UAV) Point Cloud Products into Remote Sensing Evapotranspiration Models.

In recent years, the deployment of satellites and unmanned aerial vehicles (UAVs) has led to production of enormous amounts of data and to novel data processing and analysis techniques for monitoring crop conditions. One overlooked data source amid these efforts, however, is incorporation of 3D information derived from multi-spectral imagery and photogrammetry algorithms into crop monitoring algorithms. Few studies and algorithms have taken advantage of 3D UAV information in monitoring and assessment of plant conditions. In this study, different aspects of UAV point cloud information for enhancing remote sensing evapotranspiration (ET) models, particularly the Two-Source Energy Balance Model (TSEB), over a commercial vineyard located in California are presented. Toward this end, an innovative algorithm called Vegetation Structural-Spectral Information eXtraction Algorithm (VSSIXA) has been developed. This algorithm is able to accurately estimate height, volume, surface area, and projected surface area of the plant canopy solely based on point cloud information. In addition to biomass information, it can add multi-spectral UAV information to point clouds and provide spectral-structural canopy properties. The biomass information is used to assess its relationship with in situ Leaf Area Index (LAI), which is a crucial input for ET models. In addition, instead of using nominal field values of plant parameters, spatial information of fractional cover, canopy height, and canopy width are input to the TSEB model. Therefore, the two main objectives for incorporating point cloud information into remote sensing ET models for this study are to (1) evaluate the possible improvement in the estimation of LAI and biomass parameters from point cloud information in order to create robust LAI maps at the model resolution and (2) assess the sensitivity of the TSEB model to using average/nominal values versus spatially-distributed canopy fractional cover, height, and width information derived from point cloud data. The proposed algorithm is tested on imagery from the Utah State University AggieAir sUAS Program as part of the ARS-USDA GRAPEX Project (Grape Remote sensing Atmospheric Profile and Evapotranspiration eXperiment) collected since 2014 over multiple vineyards located in California. The results indicate a robust relationship between in situ LAI measurements and estimated biomass parameters from the point cloud data, and improvement in the agreement between TSEB model output of ET with tower measurements when employing LAI and spatially-distributed canopy structure parameters derived from the point cloud data.

SUPER-RESOLUTION FOR SENTINEL-2 IMAGES

Abstract. Obtaining Sentinel-2 imagery of higher spatial resolution than the native bands while ensuring that output imagery preserves the original radiometry has become a key issue since the deployment of Sentinel-2 satellites. Several studies have been carried out on the upsampling of 20 m and 60 m Sentinel-2 bands to 10 meters resolution taking advantage of 10 m bands. However, how to super-resolve 10 m bands to higher resolutions is still an open problem. Recently, deep learning-based techniques has become a de facto standard for single-image super-resolution. The problem is that neural network learning for super-resolution requires image pairs at both the original resolution (10 m in Sentinel-2) and the target resolution (e.g., 5 m or 2.5 m). Since there is no way to obtain higher resolution images for Sentinel-2, we propose to consider images from others sensors having the greatest similarity in terms of spectral bands, which will be appropriately pre-processed. These images, together with Sentinel-2 images, will form our training set. We carry out several experiments using state-of-the-art Convolutional Neural Networks for single-image super-resolution showing that this methodology is a first step toward greater spatial resolution of Sentinel-2 images.

Optimisation problems and resolution methods in satellite scheduling and space-craft operation: a survey

ABSTRACT The fast development in the production of small, low-cost satellites is propelling an important increase in satellite mission planning and operations projects. Central to satellite mission planning is the resolution of scheduling problem for an optimised allocation of user requests for efficient communication between operations teams at the ground and spacecraft systems. The aim of this paper is to survey the state of the art in the satellite scheduling problem, analyse its mathematical formulations, examine its multi-objective nature and resolution through meta-heuristics methods. Finally, we consider some optimisation problems arising in spacecraft design, operation and satellite deployment systems.

The orbit deployment strategy of OOS system for refueling near-earth orbit satellites

Extend lifetime of near-earth orbit satellites by on-orbit refueling has significant economic benefits, while the orbit deployment strategy of the on-orbit servicing (OOS) system which implements the refueling task directly affects the efficiency of on-orbit refueling mission. Three orbit deployment modes were proposed, including ground deployment, low earth orbit (LEO) deployment and the same orbit deployment. For the client satellites to be refueled on near-earth orbit including LEO, medium earth orbit (MEO) and geosynchronous orbit (GEO), the three deployment modes were compared quantitatively based on two evaluation indicators: the refueling response time and the economic benefits. The comparing results showed that for MEO and GEO client satellites, it is appropriate to adopt the same orbit deployment mode, while for LEO client satellites, ground deployment mode is more suitable. As the maximum economic benefits can be earned to refuel GEO client satellites, the orbit deployment scheme of OOS system for refueling GEO client satellites was further studied. A new architecture of OOS system called “1+N” consist of 1 fuel storage station and N refueling vehicles was proposed. The fuel storage station carries a great deal of fuel, running on orbit steadily. The refueling vehicles maneuver on GEO and implement the refueling operations for GEO client satellites. If the vehicles run out of fuel, they arrive at the station to be refueled. The weight and orbital altitude of fuel storage station, the number, weight, orbital altitude and orbital phase of refueling vehicles are the key parameters of the orbit deployment scheme. The mathematical model for optimizing the scheme was constructed, which takes shorten the refueling response time and lower the cost of OOS system as multi-objective. The calculation process of the optimization was explained. By analyzing the optimization results, the optimal orbit deployment scheme of OOS system containing 1 fuel storage station and 4 to 6 refueling vehicles was proposed.

Review of Control Methods and Strategies of Space Tether Satellites

Space tether satellites systems are one of the most promising directions in the modern space industry. Such systems consist of two or more spacecraft connected to each other by very long tethers. Great extension and variable configuration of the system in the orbital flight conditions provide some dynamic features, which are not typical of conventional spacecraft. The concept of the tethered satellite system (TSS) promises to revolutionize many aspects of space exploration and exploitation. It provides not only numerous possible and valuable applications, but also challenging and interesting problems related to their dynamics, control, and physical implementation. The overarching theme of the paper is to show various control methods of the tethered satellites system (TSS) that have been undertaken recently, and also to emphasize on the importance of the TSS control method as an important aspect in the tether concepts, design, and missions. This review article presents the historical background and recent hot topics for the space tethers, and introduces the dynamics and control of TSSs in a progressive manner, from basic operating principles to the state-of-the-art achievements. The paper introduces the strategies and methods applied in controlling the TSS not excluding their advantages and disadvantages during the tether satellite deployment, retrieval, and station keeping procedures. At the end of the paper, a conclusion is made about the effectiveness of the control methods in stabilizing the libration and vibration motions of the TSS.

Validation results of maximum S4 index in F-layer derived from GNOS on FY3C satellite

The first Global Navigation Satellite System (GNSS) Occultation Sounder (GNOS) compatible with both BeiDou Navigation Satellite System (BDS) and Global Positioning System was successfully launched into orbit on September 23, 2013, which was mounted on the FengYun-3C (FY3C) satellite. FY3C/GNOS has produced a lot of ionospheric radio occultation (RO) scintillation data until now. This work was conducted to verify the accuracy of the scintillation data observed by FY3C/GNOS for monitoring of the GNSS signal attenuation and early warning of the possible GNSS signal interruption, thus laying the foundation for research on ionospheric space weather. In this work, the ionospheric F-layer maximum scintillation indexes S4 (\(S4_{{{\text{max}}}}^{{\text{F}}}\)) probed by FY3C/GNOS and Constellation Observing System for Meteorology, Ionosphere, and Climate (COSMIC) are matched into data pairs by data matching criterions during January 10, 2014 and January 9, 2015, which allow the comparison and error analysis of \(S4_{{{\text{max}}}}^{{\text{F}}}\) indexes between FY3C/GNOS and COSMIC. We find that FY3C/GNOS overestimates the \(S4_{{{\text{max}}}}^{{\text{F}}}\) data compared to that of COSMIC, and the biases and standard deviations (Stds) of the differences between the two \(S4_{{{\text{max}}}}^{{\text{F}}}\) indexes (FY3C/GNOS-COSMIC) in data pairs are 0.004 and 0.063 in the whole day, 0.007 and 0.080 at nighttime, 0.001 and 0.046 at daytime, respectively. The statistical error results verify the precision consistency of the ionospheric RO scintillation data between FY3C/GNOS and COSMIC. The errors at nighttime are larger than those in the whole day and daytime, which is probably due to time-varying ionospheric irregularities after midnight and disparity of the data matching criterions. Since the deployment of FY3 series satellites, GNOS can contribute more scintillation data to the international ionospheric research and forecasting of ionospheric space weather.

Spatial Heterodyne Observations of Water (SHOW) vapour in the upper troposphere and lower stratosphere from a high altitude aircraft: Modelling and sensitivity analysis

A spatial heterodyne spectrometer (SHS) has been developed to measure the vertical distribution of water vapour in the upper troposphere and the lower stratosphere with a high vertical resolution (∼500 m). The Spatial Heterodyne Observations of Water (SHOW) instrument combines an imaging system with a monolithic field-widened SHS to observe limb scattered sunlight in a vibrational band of water (1363 nm–1366 nm). The instrument has been optimized for observations from NASA's ER-2 aircraft as a proof-of-concept for a future low earth orbit satellite deployment. A robust model has been developed to simulate SHOW ER-2 limb measurements and retrievals. This paper presents the simulation of the SHOW ER-2 limb measurements along a hypothetical flight track and examines the sensitivity of the measurement and retrieval approach. Water vapour fields from an Environment and Climate Change Canada forecast model are used to represent realistic spatial variability along the flight path. High spectral resolution limb scattered radiances are simulated using the SASKTRAN radiative transfer model. It is shown that the SHOW instrument onboard the ER-2 is capable of resolving the water vapour variability in the UTLS from approximately 12 km – 18 km with ±1 ppm accuracy. Vertical resolutions between 500 m and 1 km are feasible. The along track sampling capability of the instrument is also discussed.

Ship Classification in TerraSAR-X Images With Convolutional Neural Networks

Synthetic aperture radar (SAR) is an important instrument for oceanographic observations, providing detailed information of oceans’ surface and artificial floating structures. Due to advances in SAR technology and deployment of new SAR satellites, an increasing amount of data is available, and the development of efficient classification systems based on deep learning is possible. A deep neural network has improved the state of the art in classification tasks of optical images, but its use in SAR classification problems has been less exploited. In this paper, a full workflow for SAR maritime targets detection and classification on TerraSAR-X high-resolution image is presented, and convolutional neural networks (CNNs) recently proposed in the literature are cross evaluated on a common data set composed of five maritime classes, namely, cargo, tanker, windmill, platform, and harbor structure. Based on experiments and tests, a multiple input resolution CNN model is proposed and its performance is evaluated. Our results indicate that CNNs are efficient models to perform maritime target classification in SAR images, and the combination of different input resolutions in the CNN model improves its ability to derive features, increasing the overall classification score.

Construction of an upper stage flight pattern for placing a group of spacecraft into an orbit plane with the required angular distance between the satellites

The article deals with issues of constructing the flight pattern of an upper stage and its ballistic justification subject to minimization of the mission time taking into account the upper stages performance in the case of placing a group of spacecraft into the orbit plane with provision of a uniform angular distance between the satellites, and generating a motion control program to implement the chosen flight pattern. The solution of the problem is divided into two steps: the choice of a flight pattern with its project-ballistic analysis and generation of a centre-of-mass motion control program providing the required deployment of satellites. To solve the problem of the project-ballistic analysis of the flight pattern the author developed a mathematical apparatus allowing determination of a flight pattern that matches the specified criteria of time and fuel consumption by end formulae using the linear programming technique.

Potential of Commercial Human Spaceflight

The Space Race between the Soviet Union and the United States back in 1960s had propelled vast development of space technology. Although it was still nascent during that time, space technology had spurred the launch of the first human to outer space and eventually the first human to step on the Moon. Nevertheless, the much celebrated technology breakthrough in human spaceflight could not expand its benefit to society due to the dual nature of space projects. Unlike other forms of technology, spacecraft and rocketry remain to be highly confidential and special privilege of space faring nations particularly their space agencies. With receding funding growth to these space agencies especially after the end of the Space Race, this paper aims to explore the potential of commercial human spaceflight in modern days to rejuvenate the development of space technology and its challenges. The scope of this paper is limited to commercial and private initiatives of human spaceflight, but not government or space agency. Towards the end, this paper concludes that commercial human spaceflight particularly the suborbital spaceflight has the potential to develop space tourism, point-to-point transportation, science research, satellite deployment, remote sensing, education, technology demonstration and media promotion.

Deployment of Tethered Satellites in Low-Eccentricity Orbits Using Adaptive Sliding Mode Control

AbstractTethered-satellite systems have great potential in completing various space missions. However, existing researches mainly focus on the deployment of satellites in a circular orbit, whereas ...

Fractional order sliding mode control for tethered satellite deployment with disturbances

This paper proposes a fractional order sliding mode control for the deployment of tethered space systems with the consideration of uncertainty of external disturbances and unmodeled system dynamics. The proposed fractional order sliding mode control consists of two sub-sliding manifolds that are defined separately for the actuated and unactuated states. This, in turn, generates a control scheme to make all states move toward to the desired states. The stability analysis of the proposed control law indicates not only all states converge to the desired states at equilibrium but also disturbances caused by the uncertainty can be suppressed satisfactorily. Parametric studies are conducted to investigate the influences of fractional order and sub-sliding manifold of unactuated states on the performance of the proposed control law. The performance is compared with the sliding mode, PD and fractional order PD control laws for a baseline scenario of tether deployment. The proposed control law performs better than others in the settling time and the maximum pitch angle control in the presence of unwanted disturbances. Effectiveness and robustness of the proposed control law are demonstrated by computer simulations.

Space radiation simulation using blowout plasma wakes at the SAMURAI Lab

We discuss the creation of broadband electron energy spectra using plasma wakefield acceleration at the SAMURAI Lab as part of the UCLA Particle Beam Physics Laboratory group. As the exploration and development of space increases, it will become important to efficiently replicate radiation conditions that exist in low earth orbit and planetary space. Missions such as satellite deployment and exploration of other planets, i.e. the Juno probe launched to explore Jupiter [1], require electronics that are able to withstand the electron radiation spectrum present in these locations. This requires Earth-based testing for development of robust electronics with respect to electron radiation exposure. Conventional accelerators are poorly suited for this purpose because they are designed for monoenergetic electron beams. Current simulation schemes involve the interpolation of discrete exposure tests, with time structures entirely different from space events. This idea poorly captures the radiation damage physics seen in the real world. Conversely, the wakefields produced in the blowout regime of beam plasma wakefield accelerators can be used to create the full spectrum of space radiation including high energy “killer” electrons by injecting a long bunch to excite the plasma blowout. With a long bunch (kpσz≈2) the beam will feel both accelerating and decelerating fields, resulting in an exponential or power law energy spectrum distribution seen in regions outside the Earth and Jupiter. This can be achieved at the new SAMURAI lab at UCLA resulting in broadband energy spectra with maximum energies up to 100MeV that correctly reflect the radiative conditions of space in low Earth orbit and around Jupiter.

Refining Ku-Band Rain Attenuation Prediction using Local Parameters in Tropics

Background/Objectives: Researches disclosed rain attenuation prediction models offered by ITU-R severely underestimate the signal attenuation in tropical region. Improvement can be accomplished by incorporating three in-situ parameters of prediction models. Methods/Statistical Analysis: The locally derived components are rainfall rate, rain height and specific attenuation coefficients. Beacon signal data for MEASAT-I satellite were sampled for one year. Sampling time of 1 minute was chosen for rainfall rate. Both attenuation and rainfall rate were represented in terms of annual cumulative distribution. Rain height data were gathered from related researches and visually compared with radar data of 10 convective and 30 stratiform rain events. Findings: In previous works, these components were treated separately. By combining all three components, rain attenuation prediction model with distinctive accuracy can be acquired compared to the previous results. All previous and current works exhibited significant improvement from the latest ITU-R P.618 revision 12 model. The new result closely fitted in with measured attenuation which was not present in any previous work. This was shown by RMS error of 2.02 dB at availability of 99.9% to 99.999% (0.1% to 0.001% exceedance). Application/ Improvements: Accurate representation of fade margin can be included in link budget analysis by designers for satellite deployment in tropical region.

Uncovering common misconceptions in GNSS Precise Point Positioning and its future prospect

Within the last decade, GNSS Precise Point Positioning (PPP) has generated unprecedented interest among the GNSS community and is being used for a number of scientific and commercial applications today. Similar to the conventional relative positioning technique, PPP could provide positioning solutions at centimeter-level precision by making use of the precise carrier phase measurements and high-accuracy satellite orbits and clock corrections provided by, for example, the International GNSS Service. The PPP technique is attractive as it is computationally efficient; it eliminates the need for simultaneous observations at both the reference and rover receivers; it also eliminates the needs for the rover receiver to operate within the vicinity of the reference receiver; and it provides homogenous positioning quality within a consistent global frame anywhere in the world with a single GNSS receiver. Although PPP has definite advantages for many applications, its merits and widespread adoption are significantly limited by the long convergence time, which restricts the use of the PPP technique for many real-time GNSS applications. We provide an overview of the current performance of PPP as well as attempt to address some of the common misconceptions of this positioning technique--considered by many as the future of satellite positioning and navigation. Given the upcoming modernization and deployment of GNSS satellites over the next few years, it would be appropriate to address the potential impacts of these signals and constellations on the future prospect of PPP.

Adaptive sliding mode control of tethered satellite deployment with input limitation

This paper proposes a novel adaptive sliding mode tension control method for the deployment of tethered satellite, where the input tension limitation is taken into account. The underactuated governing equations of the tethered satellites system are firstly derived based on Lagrangian mechanics theory. Considering the fact that the tether can only resist axial stretching, the tension input is modelled as input limitation. New adaptive sliding mode laws are addressed to guarantee the stability of the tethered satellite deployment with input disturbance, meanwhile to eliminate the effect of the limitation features of the tension input. Compared with the classic control strategy, the newly proposed adaptive sliding mode control law can deploy the satellite with smaller overshoot of the in-plane angle and implement the tension control reasonably and effectively in engineering practice. The numerical results validate the effectiveness of the proposed methods.