Trajectory design for optical on-orbit inspection missions in geostationary Earth orbit

Thermal design of a GEO communication satellite is based on worst hot and cold cases on Geostationary Orbit (GEO). However, thermal analysis on transfer process is vital due to the harsh thermal conditions. The reasons of this harsh thermal conditions are frequent change of kinematics and varying operational conditions of the equipment along geostationary transfer orbit (GTO). Main goals of this study are to comprehend the thermal effects of GTO on the satellite, to ensure that the internal and external equipment temperatures stay in the limits and improving thermal design of a GEO satellite model with outcomes of the analysis. Thermal analysis results of the satellite in GEO is also used due to comparison purposes. Orbital information and thermal analysis scenarios in GEO and GTO are summarized in the study. The generation of orbital scenarios, kinematics and radiative couplings calculation are performed in Thermica. MSC Sinda is utilized as a numerical solver for obtaining temperature results and heater duty cycles.

The 2010 National Space Policy encourages federal agencies to “actively explore the use of inventive, nontraditional arrangements for acquiring commercial space goods and services to meet United States Government requirements, including…hosting government capabilities on commercial spacecraft”. NASA's Science Mission Directorate has taken an important step towards this goal by adding an option for hosted payload responses to its recent Announcement of Opportunity (AO) for Earth Venture-2 missions. Since NASA selects a significant portion of its science missions through a competitive process, it is useful to understand the implications that this process has on the feasibility of successfully proposing a commercially hosted payload mission. This paper describes some of the impediments associated with proposing a hosted payload mission to NASA, and offers suggestions on how these impediments might be addressed. Commercially hosted payloads provide a novel way to serve the needs of the science and technology demonstration communities at a fraction of the cost of a traditional Geostationary Earth Orbit (GEO) mission. The commercial communications industry launches over 20 satellites to GEO each year. By exercising this repeatable commercial paradigm of privately financed access to space with proven vendors, NASA can achieve science goals at a significantly lower cost than the current dedicated spacecraft and launch vehicle approach affords. Commercial hosting could open up a new realm of opportunities for NASA science missions to make measurements from GEO. This paper also briefly describes two GEO missions recommended by the National Academies of Science Earth Science Decadal Survey, the Geostationary Coastal and Air Pollution Events (GEO-CAPE) mission and the Precipitation and All-weather Temperature and Humidity (PATH) mission. Hosted payload missions recently selected for implementation by the Office of the Chief Technologist are also discussed. Finally, there are technical differences specific to hosted payloads and the GEO environment that must be considered when planning and developing a hosted payload mission. This paper addresses some of payload accommodation differences from the typical NASA LEO mission, including spacecraft interfaces, attitude control and knowledge, communications, data handling, mission operations, ground systems, and the thermal, radiation, and electromagnetic environment. The paper also discusses technical and programmatic differences such as limits to NASA's involvement with commercial quality assurance processes to conform to the commercial schedule and minimizing the price that makes hosted payloads an attractive option.

The French Space Agency has developed a simple, low-cost experiment, “THERME,” which aims to assess the aging of thermal coatings by measuring solar absorptivity. This experiment is now used on-board several low-Earth-orbit (LEO) Sun-synchronous satellites. The most significant in-orbit results for thermal control coatings (white paints, second surface mirrors, and Kapton) are summarized in this paper. To use THERME on-board geostationary Earth orbit (GEO) missions, the existing THERME concept had to be modified to allow typical rigid GEO thermal coatings such as optical solar reflectors to be carried. This new concept was developed based on the LEO THERME design and was made to be as nonspecific as possible, and so it may be carried on any industrial GEO satellite. The development and qualification of this new THERME concept, the so-called “THERME GEO” or “THERME rigid,” is presented in this paper. “THERME GEO” is currently being used on two telecom satellites. All the flight models were subject to thermal and mechanical acceptance testing in accordance with the satellite specifications. These tests, as well as the first flight data, are described in this paper.

This paper presents the design and preliminary performance tests of an L-band synthetic aperture interferometic radiometer using the new sampling concept of clock scan. With the advantages of simple and deployable array structure, the concept of Clock Scanning Microwave Interferometric Radiometer (CS-MIR) has much potential to apply for the future Solar Polar Orbit (SPO) and Geostationary Earth Orbit (GEO) missions, where large antenna array with high angular resolution is the prime requirement. This L band demonstrator is developed to validate the concept of CS-MIR and solve the related technical problems.

A development of an onboard camera system for in-situ measurement of micro space debris in geostationary earth orbit is described in this paper. Distribution of small space debris in and near geostationary orbit is not known well, because they cannot be seen from groundbased facilities nor retrieving surface specimens of space crafts impacted by them is nearly impossible, different from that in low earth orbit. We had proposed a concept of in-situ debris measurement system to observe micro debris environment in and near geostationary orbit. It is a piggyback visual inspection system on geostationary satellite, which autonomously detects impacted features created on the surface of the mother satellite and sends its picture to a ground-based facility for further analyses. In this study, an experimental model of the inspection system was developed to show feasibility of such a concept of in-situ measurement of the micro debris. Some experiments are performed to verify the basic functions of it, autonomous finding and taking detailed picture of the impacted features on the target surface. Results of them successfully show the feasibility of this concept of in-situ measurement system.

Solar thermal propulsion and propulsion/power systems were identified as key technologies in the operational effectiveness and cost comparison study (OECS) sponsored by Phillips Laboratory (PL). These technologies were found to be pervasively cost effective with short transfer times and very good performance across a wide range of missions. The on-going Integrated Solar Upper Stage (ISUS) Program sponsored by PL represents development of a solar thermal propulsion/power (bimodal) system. As part of this effort, mission trades are being conducted to further define the ISUS system for geosynchronous equatorial orbit (GEO), high Earth orbit (HEO-Molniya class), and mid Earth orbit (MEO-GPS class) missions. These trades will consider launch vehicles ranging in size from a LLV3 to an Atlas IIAS that insert the ISUS into low Earth orbit (LEO). These trades will be used to define the ISUS system for the planned Engine Ground Demonstration, a space demonstration mission, and as a future operational system.

European Space Agency (ESA) has addressed the key points like higher power demand and system efficiency, system reusability, adaptability and flexibility, decrease in system mass, size and cost, increase in modularity and standardization for the next generation (NG) power systems on future missions at 8 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">th</sup> Space Power Conference. Since the purpose of a power distribution module is to ensure reliable delivery of electrical power and prevent failure propagation, under all foreseeable conditions, during all mission phases, reliability and redundancy become critical issues in design. This paper describes UYGAR, which is the power distribution module designed in TUBITAK UZAY for Low Earth Orbit (LEO), Geostationary Earth Orbit (GEO) and Science Missions with its single point failure free, 100 kRad radiation tolerant and internally redundant electronic design while considering the key points addressed by ESA and the experiences gained in TUBITAK UZAY's previous satellite missions RASAT and GÖKTÜRK-2. This paper describes the high reliable, radiation tolerant, flexible, and unique design details compatible with ECSS-E-ST-20C and AIAA-S-122-2007 of NG power distribution module, UYGAR, which is considered as a part of higher power demanded and more complex power system architecture for next generation missions of various orbits. Moreover, the qualifications test results and details are presented.

Hall Effect thrusters (HET) have demonstrated its applicability on satellites for the Low earth orbit (LEO), Geo-stationary earth orbit (GEO) and long duration missions. High thrust density and long lifetimes are attractive parameters of the HET. In order to improve the thruster performance and lifetimes, decades of efforts are made to understand the plasma physics. Several intrusive and non-intrusive diagnostics techniques are employed for HET investigation. Simple and precise diagnostics technique is attractive to delineate the characteristics of the thruster. Optical emission spectroscopy provides several advantages over the other methods which are used for the HET diagnostics. Using this diagnostics tool in correlation with the collisional radiative model, the information of electron kinetics is extracted instantaneously. Collisional radiative model is developed by using the xenon near-infrared emission lines. This kinetic model can be used to determine the local electron temperature with error less than 15 % for investigating the HET physics.

ESA's current approaches to end-of-life strategies for HEO missions

Abstract. We present an Observing System Simulation Experiment (OSSE) dedicated to the evaluation of the added value of the Sentinel-4 and Sentinel-5P missions for tropospheric nitrogen dioxide (NO2). Sentinel-4 is a geostationary (GEO) mission covering the European continent, providing observations with high temporal resolution (hourly). Sentinel-5P is a low Earth orbit (LEO) mission providing daily observations with a global coverage. The OSSE experiment has been carefully designed, with separate models for the simulation of observations and for the assimilation experiments and with conservative estimates of the total observation uncertainties. In the experiment we simulate Sentinel-4 and Sentinel-5P tropospheric NO2 columns and surface ozone concentrations at 7 by 7 km resolution over Europe for two 3-month summer and winter periods. The synthetic observations are based on a nature run (NR) from a chemistry transport model (MOCAGE) and error estimates using instrument characteristics. We assimilate the simulated observations into a chemistry transport model (LOTOS-EUROS) independent of the NR to evaluate their impact on modelled NO2 tropospheric columns and surface concentrations. The results are compared to an operational system where only ground-based ozone observations are ingested. Both instruments have an added value to analysed NO2 columns and surface values, reflected in decreased biases and improved correlations. The Sentinel-4 NO2 observations with hourly temporal resolution benefit modelled NO2 analyses throughout the entire day where the daily Sentinel-5P NO2 observations have a slightly lower impact that lasts up to 3–6 h after overpass. The evaluated benefits may be even higher in reality as the applied error estimates were shown to be higher than actual errors in the now operational Sentinel-5P NO2 products. We show that an accurate representation of the NO2 profile is crucial for the benefit of the column observations on surface values. The results support the need for having a combination of GEO and LEO missions for NO2 analyses in view of the complementary benefits of hourly temporal resolution (GEO, Sentinel-4) and global coverage (LEO, Sentinel-5P).

Satellite mission life, especially for commercial Geostationary Earth Orbit (GEO) missions, has recently been aimed at extending its nominal 15 years life of services to an additional 5 to 8 years via the in-orbit refueling concept. This goal, driven by customers’ demand and competitive market, has challenged Attitude Control Subsystem (ACS) engineers to develop adequate ACS algorithms to accommodate this extended life of services in the presence of limited and aging hardware components, i.e., ACS sensors (e.g., star Trackers and IRUs) and actuators (i.e., Reaction Wheel Assembly) since thrusters alone will not provide adequate pointing accuracy due to its intended design for station keeping and orbit maintenance only. This paper investigates an attractive ACS scheme, which is designed using the nonlinear state dependent factorization modeling approach coupled with the  D  controller as an efficient on-line solver (which offers many advantages over the traditional Riccati solver), to maintain the satellite pointing accuracy subject to loss of one or two reaction wheels out of its four wheels assembly mounted in a pyramid configuration. The high fidelity reaction wheel model and 3 degrees of freedom attitude dynamics are used in the simulation to demonstrate the robust performance characteristics of the  D  based adaptive controller where the baseline PID controller fails to provide sufficient robustness.

Satellite mission life, especially for commercial Geostationary Earth Orbit (GEO) missions, has recently been aimed at reaching its 18 years life of services. This goal, driven by customers’ demand and competitive market, has challenged Attitude Control Subsystem (ACS) engineers to develop adequate ACS algorithms to accommodate this extended life of services in the presence of limited and aging hardware components (i.e., ACS sensors and actuators). This paper evaluates the robustness of an attractive ACS scheme, which has recently been proposed using the  D  control design technique to maintain the satellite pointing accuracy subject to loss of one or two reaction wheels out of its four wheels assembly mounted in a pyramid configuration. The robust performances of the  D  controller are evaluated using the following two conditions: (1) Loss of Various Wheel Locations and Pair Combinations and (2) Initial Condition Uncertainties (i.e., “tolerant range” per axis that the proposed controller can still handle).

This paper verifies the applicability of multiple Global Navigation Satellite Systems (GNSSs) and side lobe signal utilization in Space Service Volume (SSV), especially for Geostationary Earth Orbit (GEO) missions over the Korean region. Unlike the ground or terrestrial systems, various constraints of space exploration in SSV cause a problem when estimating position using GNSS. This is mainly due to the limit of GNSS signal availability where its dominant variables include altitude, side lobe issues, as well as longitude because of different constellations of several GNSS. The numerical simulation shows the effectiveness of additional side lobe signals from multi-GNSS. In addition, the effect of non-MEO satellites’ signals in SSV for different longitudes is presented.

Statistical relationships between satellite anomalies at geostationary orbit and high-energy particles

Satellite system architectures based on geostationary or Low Earth Orbit (LEO)/Medium Earth Orbit (MEO) constellation suffer from their intrinsic limitations in terms of coverage or flexibility. Traffic requirements concerning broadband services are expected to be very uneven both in time and space. To match this requirement and to improve coverage an innovative satellite system architecture, composed of a LEO/MEO segment to complement a Geostationary Earth Orbit (GEO) segment, has been proposed. In this scenario, to achieve interworking and to make it possible to hold the call while switching between the two segments, efficient intersegment handover (ISHO) procedures must be identified.The paper, after introducing the classical ISHO schemes, aims at defining and analysing an ISHO procedure developed to perform handover in case of hybrid constellations based on the use of both GEO and LEO/MEO orbits. Performance evaluation will be carried out for different system configurations utilizing a dynamic satellite constellation simulator in the time domain. The execution delay and its complementary cumulative distribution have been evaluated for different constellation geometry at different distances from the gateway. Copyright © 2002 John Wiley &amp; Sons, Ltd.