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Construction and realization of a Low-cost Satellite Attitude Simulator concept
... Another focus of the investigations at the IA are the verification of the antenna pointing mechanism and the antenna pointing algorithms used for actuating the mechanism. Therefore, the antenna turn table was converted into a satellite attitude simulator [7] to simulate the movement of a satellite orbiting in LEO using real satellite attitude data [9], Fig. 4. The IA ground station also has to support LEO satellite missions on S-band. One of the restrictions for such missions is to utilize a right-hand circular polarized signal (RHCP) for communication. ...
The research activities of the Institute of Astronautics (IA) are focused on the analysis of the communication scenario of robotic space missions in detail. That includes also verification of a newly developed Light-weight Inter Satellite Link Antenna (LISA) for small satellites, corresponding steering mechanism and pointing algorithm. The investigation of inter-satellite links is mainly focused on transparent relay satellites which allow data relay between low earth orbit (LEO) and geostationary orbit (GEO) satellites. Therefore the ESA satellite ARTEMIS stands in the main focus of the research work of the Institute. The most important requirement for robotic space missions is given by the time delay between the operator on earth and the manipulator in space. Data processing and data handling strategies are playing also a important role in robotic space mission and are under investigation. The Institute of Astronautics realized a special test environment to investigate these points in detail.
A satellite attitude simulator, a modified S-Band ground station and special operations software build the main elements of this test environment and is described in detail in this paper. The outcomes of the test environment are time delay measurement values for different communication configurations. These measurements are basic results for further robotic space missions.
... Therefore, it features a pointing mechanism with 2 rotational degrees of freedom. For verifying the operational reliability and the pointing algorithms , LISA was connected to a satellite attitude simulator (Stoll et al., 2006), and capable of changing its attitude in three degrees of freedom. AsFig. ...
Orbital robotics focuses on a variety of applications, as e.g. inspection and repair activities, spacecraft construction or orbit correc-tions. On-Orbit Servicing (OOS) activities have to be closely monitored by operators on ground. A direct contact to the spacecraft in Low Earth Orbit (LEO) is limiting the operational time of the robotic application. Therefore, geostationary satellites are desirable to relay the OOS signals and extend the servicing time window. A geostationary satellite in the communication chain not only introduces additional boundary conditions to the mission but also increases the time delay in the system. The latter is not very critical if the servicer satellite is operating autonomously. However, if the servicer is operating in a supervised control regime with a human in the loop, the increased time delay will have an impact on the operator's task performance. This paper describes the challenges, which have to be met when utilizing a relay satellite for orbital telerobotics. It shows a series of ground experiments that were undertaken with a relay satellite in the communication chain to simulate the end-to-end system. This case study proves that complex robotic applications in Low Earth Orbit (LEO) are controllable by human operators on ground.
... 4.Fig. 4: Conversion between ground station and 3-axis test bed [4] The simulator is based on an existing S-band antenna (dish diameter 2.0 m) pedestal. This pedestal allowed the removal of the antenna reflector. ...
The Institute of Astronautics (IA, Lehrstuhl Raumfahrttechnik / LRT) at Technische Universität München has a strong background in inter-satellite communication. The efforts were driven by the need of developing key methods and hardware for controlling robotic space applications by a user on ground. In this framework, research was conducted to control robotic applications on Earth via a geostationary relay satellite. Extensive tests showed that high bandwidth is necessary to fulfill the high performance requirements on a communication link for robotic systems featuring haptic and visual feedback. Thus, a Ka-band ground station and a Ka-band satellite mock-up system was set up at the LRT. The antenna system was developed with a special measurement configuration to meet the requirement of a high flexibility degree for measurements. To guarantee high precision measurements, the ground station is equipped with an inject-pilot system in the reception. The high precision coupler and power meter in the transmission path allow a well adjustable uplink power to the satellite. The performance of the ground station was verified with an extended ESVA (Earth Station Verification & Acceptance) test together with EUTELSAT and ESA (European Space Agency). The whole antenna system was calibrated with a high precision Standard-Gain-Horn to increase the measurement performance. This paper describes ongoing activities at the LRT, focusing the Ka-band ground station and the Ka-band satellite mock-up system. It further outlines the possibilities that arise from using a Ka-band environment (ground station and mock-up) that can be easily accessed and used by research partners, since the ground station and the mock-up are not dedicated to one satellite operator only. I. INRODUCTION In the field of satellite communications the frequency band of 20/30 GHz (Ka-band) has been increasingly utilized in the last five years. Higher data rates are the prerequisite for the upcoming services such as broad band internet access via satellite and High-Definition Television (HDTV). Commercial satellite providers like EUTELSAT, ASTRA or Avanti are already operating Ka-band transponders following the market demand [6].Besides the commercial satellite communication market, other fields such as remote sensing , using Unmanned Aerial Vehicles (UAV) or Earth observation satellite, and the On-Orbit servicing (OOS) are in need of higher data rates. In this connection, high resolution and multispectral sensors generate an enormous number of data volume per second. The data transmission link from a UAV, an Earth observation satellite or a robotic servicing satellite become more and more the bottle neck of the data stream of the whole mission. The Institute of Astronautics (IA) of the Technical University Munich (TUM) identified the field ofOn-Orbit Servicing as the major research topic [9]. It is subsequently operating a fully functional Ka-band ground station in an academic research environment, which is unparalleled in Europe. Since communication is an inherent and important part for OOS, the investigation of satellite communication links on higher frequencies with higher data rates is one of the main activities at IA. The following sections will give a detailed insight in the currently available and planned infrastructure, which was developed to investigate open and upcoming questions like the rain-fade problem, thermal stability of the antenna reflector and antenna pedestal, Quality of Service of a Ka-band communication link for OOS.
The rapid increase of available Ka-band and Ku-band transponders in orbit proves that these frequency bands will be in common use in the near future. However, compared to the Ku-band and lower frequencies, Ka-band transmission is much more sensitive to atmospheric moisture. To determine its impact, we have measured the beacon (27.5 GHz) signal of the communication satellite KA-SAT with high precision on the ground. In this paper we describe and discuss the concept and the results of our measurements.
Low Earth orbit satellites such as Earth observation satellites usually use the store and forward approach to dump their data to the user during overflight over a ground station. This method relies on a large number of ground stations or on the patience of the user. If the data is needed on time or if long-lasting real time access to the satellite itself is essential, the implementation of a relay satellite is reasonable. This paper introduces BayernSat, a micro-satellite which demonstrates the technology necessary for telepresence in space. BayernSat will use a commercial geostationary relay satellite to send live video footage to the user on ground. Furthermore, the satellite can be con-trolled in real-time from ground using the return link also via the relay satellite. Besides the demonstration of the telepresence technology, BayernSat will demonstrate a newly developed high performance onboard computer system, a color video camera for space application and a steerable low profile high gain S-band antenna. BayernSat also acts as a tool to inspire the public for space. The live video footage will be presented on the Internet and selected users will be able to steer the satellite via Internet.