Aircraft Engineering and Aerospace Technology, 2005
ABSTRACT Purpose – To compare the conventional reaction wheel and battery systems with the combin... more ABSTRACT Purpose – To compare the conventional reaction wheel and battery systems with the combined energy and attitude control system. The system mass, volume and power requirements are revealed corresponding to the small satellite missions. Design/methodology/approach – All the relevant system parametric equations are established. The system mass, volume and power are estimated accordingly for the conventional and the combined systems. Then, both systems are compared with respect to the typical small satellite missions. Findings – The combined system outperforms the conventional system in most small satellite missions. However, there are some small satellite missions where the conventional systems are better in terms of the mass and volume budgets. Research limitations/implications – This research work is exclusively for small satellites in the LEO orbits. Practical implications – A reasonable information for sizing the combined energy and attitude control system is established. The system mass, volume and power budgets can be extracted from this research work. Originality/value – The results provide an instant answer regarding the feasibility of the combined energy and attitude control system for small satellites.
Mitigation of Hazardous Comets and Asteroids, 2004
... Therefore, it is categorized as a" moderate" level risk which requires certain prec... more ... Therefore, it is categorized as a" moderate" level risk which requires certain precautionary actions (Gritzner and Fasoulas 2002 ... An example of such a mitigation maneuver is discussed in Section 5. 3.3 Attached thrusters When applying thrusters to a NEO the heliocentric velocity ...
The collision of a near-Earth asteroid or comet (NEO) with the Earth is a rare but disastrous cat... more The collision of a near-Earth asteroid or comet (NEO) with the Earth is a rare but disastrous catastrophe. To mitigate the impact risk numerous technologies have been proposed for either the deflection of NEOs by changing their orbital velocity or for the destruction of NEOs by means of high energetic collisions or explosions. From our perspective, the second option is not recommended because of the unknown interior of any particular hazardous NEO. We have improved the model by Carusi et al. (2002, Icarus 159, 417-422) who presented the first real n-body analysis but with the restriction of velocity change Delta v along the track of orbital motion only (parallel attack). In our approach we optimize both Delta v and the attack angle. In this paper we describe our model and apply it to fictitious asteroids with typical NEO orbital parameters. We compare our results with those of the parallel attack. Finally, we analyse the optimal Delta v required to deflect the possible impactor 2004...
Die folgenden Beschreibungen, Analysen und Ergebnisse wurden im Rahmen der AMSAT/DLR Mond-Mission... more Die folgenden Beschreibungen, Analysen und Ergebnisse wurden im Rahmen der AMSAT/DLR Mond-Missionsstudie in der Phase 0 durch das DLR RB-RT angefertigt. Die Arbeit umfasst eine analytische Beschreibung der Bahnelemente für stabile niedrige und nahezu kreisförmige Mondbahnen und deren Untersuchung bezüglich einer polarnahen 100 km hohen Mondbahn. In der anschließenden numerischen Untersuchung werden die Anfangselemente über einen 1,5 jährigen Zeitraum propagiert, um Aussagen zur Langzeitstabilität zu treffen. Demnach lässt die Wahl eines um 85° inklinierten Mondorbits in 100 km Höhe einen unkontrollierten Betrieb über 1 Jahr mit Höhenvariationen <50 km zu (teilweise auch <40 km für bestimmte Anfangsbedingungen). Schließlich wird exemplarisch die Stationssichtbarkeit für die DLR-Station in Weilheim sowie das AMSAT-Stationsnetzwerk diskutiert.
TanDEM-X will be the first space mission flying two satellites in close HELIX formation with typi... more TanDEM-X will be the first space mission flying two satellites in close HELIX formation with typical dis-tances between 200 and 500 m. Illumination by SAR transmissions of one by the other satellite is an important issue that requires additional functionalities and operational measures in the TanDEM-X system.
Tandem-L is a proposal for a highly innovative satellite mission for the global observation of dy... more Tandem-L is a proposal for a highly innovative satellite mission for the global observation of dynamic processes on the earth’s surface with hitherto unknown quality and resolution. Thanks to the novel imaging techniques and the vast recording capacity, Tandem-L will provide urgently needed information for solving pressing scientific questions in the areas of the biosphere, geosphere, cryosphere, and hydrosphere. Tandem-L will make a vital contribution towards a better understanding of the earth system and its dynamics. Important mission goals are the global measurement of forest biomass for a better understanding of the carbon cycle, the systematic recording of deformations of the earth’s surface with millimetre accuracy for earthquake research and risk analysis, the quantification of glacier movements and melting processes in the polar regions, the large scale observation of ocean currents and the high resolution measurement of variations in soil moisture close to the surface. Hen...
The precise TSX/TDX formation control is realized by means of TDX cold-gas propellant, which is l... more The precise TSX/TDX formation control is realized by means of TDX cold-gas propellant, which is likely to deplete by May 2015. This document discusses the TSX/TDX formation flying capabilities without cold-gas propulsion, which can be applied to prolong the cold-gas depletion to the end of 2015 and further allows the continuation of formation flying until year 2023.
TerraSAR-X is an advanced synthetic aperture radar satellite system operated in a 505 km altitude... more TerraSAR-X is an advanced synthetic aperture radar satellite system operated in a 505 km altitude sun-synchronous repeat orbit. A tight orbit control requirement, driven by interferometric applications, is formulated as a 250 m radius “tube” defined about an Earth-fixed reference orbit. In this paper we review the orbit control requirements and constraints and discuss the implemented guidance and control concept. Since the launch in 2007 more than six years of in-flight experience have been gained, including almost 500 orbit control maneuvers. The presented flight results proof that both the implemented reference orbit and the orbit control concept work remarkably well, and that the tight control requirement is fully met.
The TanDEM-X mission comprises two nearly identical satellites – TSX and TDX – that fly at an alt... more The TanDEM-X mission comprises two nearly identical satellites – TSX and TDX – that fly at an altitude of ~515 km in a close formation at distances down to 120 m. The standard orbit corrections are made with hydrazine propulsion on both spacecraft, but the relative geometry is maintained by a dedicated cold gas system on TDX only, which initially comprised 36 kg of nitrogen. The routine formation-keeping requires at least one pair of cold gas maneuvers daily. Formation flight started in late 2010 and continued ever since in several configurations. This means that by now of the order of 2500 cold gas maneuvers have been performed and the remaining amount of fuel will allow for another 1500 to be made. Maneuvers were done mainly with the four 40 milli-Newton thrusters of branch-A, but about 25 % of the time branch-B was used. The construction of a digital elevation model of the Earth requires very precise orbit information, which is delivered by the flight dynamics department at GSOC....
Within this document we develop a maneuver sequence to conduct the TanDEM-X / TerraSAR-X formatio... more Within this document we develop a maneuver sequence to conduct the TanDEM-X / TerraSAR-X formation swap with minimal fuel and minimal risk of collision. A formation breakup procedure for the back-drift phase is provided. The extended ground-station network and the sequence of events are provided. This work is applicable to the mission operations segment during the TDX-TSX formation swap on August 6-9, 2013.
ABSTRACT Recently, a method for the n-body analysis of the velocity change required to deflect a ... more ABSTRACT Recently, a method for the n-body analysis of the velocity change required to deflect a hazardous near-Earth object (NEO) was presented by Carusi et al. [Carusi, A., Valsecchi, G.B., D&#39;Abramo, G., Boattini A., 2002. Icarus 159, 417–422]. We extent this method in order to optimize the velocity change vector instead of its along-track magnitude. From an application of both methods to a fictitious NEO we find Carusi&#39;s parallel approach to be reasonable for phases of unperturbed two-body motion. But, for orbit phases inhering third-body perturbations, i.e., for planetary close approaches or prior to a collision, the results obtained from the new method show the radial component of deflection impulse to play a major role. We show that a fivefold greater efficiency can be achieved by a deflection impulse being non-parallel to orbital velocity. The new method is applied to two possible 99942 Apophis impact trajectories in order to provide constraints for future Apophis deflection mission analysis.
This paper describes selected areas in which the TerraSAR-X ground segment had to be extended in ... more This paper describes selected areas in which the TerraSAR-X ground segment had to be extended in order to incorporate the TanDEM-X mission, namely flight dynamics, instrument operations and receiving stations and addresses their testing.
This paper describes the current operational TerraSAR- X (TSX) flight dynamics system (FDS) and d... more This paper describes the current operational TerraSAR- X (TSX) flight dynamics system (FDS) and depicts its extensions needed to fulfil the requirements for TanDEM-X, which shall form a close formation with TSX. Operational constraints imposed by the instrument operation and the ground station network are explained and the impact on the FD operations concept is discussed. The paper specifically elaborates
Near-Earth asteroid 99942 Apophis provides a typical example for the evolution of asteroid orbits... more Near-Earth asteroid 99942 Apophis provides a typical example for the evolution of asteroid orbits that lead to Earth-impacts after a close Earth-encounter that results in a resonant return. Apophis will have a close Earth-encounter in 2029 with potential very close subsequent Earth-encounters (or even an impact) in 2036 or later, depending on whether it passes through one of several so-called
Aircraft Engineering and Aerospace Technology, 2005
ABSTRACT Purpose – To compare the conventional reaction wheel and battery systems with the combin... more ABSTRACT Purpose – To compare the conventional reaction wheel and battery systems with the combined energy and attitude control system. The system mass, volume and power requirements are revealed corresponding to the small satellite missions. Design/methodology/approach – All the relevant system parametric equations are established. The system mass, volume and power are estimated accordingly for the conventional and the combined systems. Then, both systems are compared with respect to the typical small satellite missions. Findings – The combined system outperforms the conventional system in most small satellite missions. However, there are some small satellite missions where the conventional systems are better in terms of the mass and volume budgets. Research limitations/implications – This research work is exclusively for small satellites in the LEO orbits. Practical implications – A reasonable information for sizing the combined energy and attitude control system is established. The system mass, volume and power budgets can be extracted from this research work. Originality/value – The results provide an instant answer regarding the feasibility of the combined energy and attitude control system for small satellites.
Mitigation of Hazardous Comets and Asteroids, 2004
... Therefore, it is categorized as a" moderate" level risk which requires certain prec... more ... Therefore, it is categorized as a" moderate" level risk which requires certain precautionary actions (Gritzner and Fasoulas 2002 ... An example of such a mitigation maneuver is discussed in Section 5. 3.3 Attached thrusters When applying thrusters to a NEO the heliocentric velocity ...
The collision of a near-Earth asteroid or comet (NEO) with the Earth is a rare but disastrous cat... more The collision of a near-Earth asteroid or comet (NEO) with the Earth is a rare but disastrous catastrophe. To mitigate the impact risk numerous technologies have been proposed for either the deflection of NEOs by changing their orbital velocity or for the destruction of NEOs by means of high energetic collisions or explosions. From our perspective, the second option is not recommended because of the unknown interior of any particular hazardous NEO. We have improved the model by Carusi et al. (2002, Icarus 159, 417-422) who presented the first real n-body analysis but with the restriction of velocity change Delta v along the track of orbital motion only (parallel attack). In our approach we optimize both Delta v and the attack angle. In this paper we describe our model and apply it to fictitious asteroids with typical NEO orbital parameters. We compare our results with those of the parallel attack. Finally, we analyse the optimal Delta v required to deflect the possible impactor 2004...
Die folgenden Beschreibungen, Analysen und Ergebnisse wurden im Rahmen der AMSAT/DLR Mond-Mission... more Die folgenden Beschreibungen, Analysen und Ergebnisse wurden im Rahmen der AMSAT/DLR Mond-Missionsstudie in der Phase 0 durch das DLR RB-RT angefertigt. Die Arbeit umfasst eine analytische Beschreibung der Bahnelemente für stabile niedrige und nahezu kreisförmige Mondbahnen und deren Untersuchung bezüglich einer polarnahen 100 km hohen Mondbahn. In der anschließenden numerischen Untersuchung werden die Anfangselemente über einen 1,5 jährigen Zeitraum propagiert, um Aussagen zur Langzeitstabilität zu treffen. Demnach lässt die Wahl eines um 85° inklinierten Mondorbits in 100 km Höhe einen unkontrollierten Betrieb über 1 Jahr mit Höhenvariationen <50 km zu (teilweise auch <40 km für bestimmte Anfangsbedingungen). Schließlich wird exemplarisch die Stationssichtbarkeit für die DLR-Station in Weilheim sowie das AMSAT-Stationsnetzwerk diskutiert.
TanDEM-X will be the first space mission flying two satellites in close HELIX formation with typi... more TanDEM-X will be the first space mission flying two satellites in close HELIX formation with typical dis-tances between 200 and 500 m. Illumination by SAR transmissions of one by the other satellite is an important issue that requires additional functionalities and operational measures in the TanDEM-X system.
Tandem-L is a proposal for a highly innovative satellite mission for the global observation of dy... more Tandem-L is a proposal for a highly innovative satellite mission for the global observation of dynamic processes on the earth’s surface with hitherto unknown quality and resolution. Thanks to the novel imaging techniques and the vast recording capacity, Tandem-L will provide urgently needed information for solving pressing scientific questions in the areas of the biosphere, geosphere, cryosphere, and hydrosphere. Tandem-L will make a vital contribution towards a better understanding of the earth system and its dynamics. Important mission goals are the global measurement of forest biomass for a better understanding of the carbon cycle, the systematic recording of deformations of the earth’s surface with millimetre accuracy for earthquake research and risk analysis, the quantification of glacier movements and melting processes in the polar regions, the large scale observation of ocean currents and the high resolution measurement of variations in soil moisture close to the surface. Hen...
The precise TSX/TDX formation control is realized by means of TDX cold-gas propellant, which is l... more The precise TSX/TDX formation control is realized by means of TDX cold-gas propellant, which is likely to deplete by May 2015. This document discusses the TSX/TDX formation flying capabilities without cold-gas propulsion, which can be applied to prolong the cold-gas depletion to the end of 2015 and further allows the continuation of formation flying until year 2023.
TerraSAR-X is an advanced synthetic aperture radar satellite system operated in a 505 km altitude... more TerraSAR-X is an advanced synthetic aperture radar satellite system operated in a 505 km altitude sun-synchronous repeat orbit. A tight orbit control requirement, driven by interferometric applications, is formulated as a 250 m radius “tube” defined about an Earth-fixed reference orbit. In this paper we review the orbit control requirements and constraints and discuss the implemented guidance and control concept. Since the launch in 2007 more than six years of in-flight experience have been gained, including almost 500 orbit control maneuvers. The presented flight results proof that both the implemented reference orbit and the orbit control concept work remarkably well, and that the tight control requirement is fully met.
The TanDEM-X mission comprises two nearly identical satellites – TSX and TDX – that fly at an alt... more The TanDEM-X mission comprises two nearly identical satellites – TSX and TDX – that fly at an altitude of ~515 km in a close formation at distances down to 120 m. The standard orbit corrections are made with hydrazine propulsion on both spacecraft, but the relative geometry is maintained by a dedicated cold gas system on TDX only, which initially comprised 36 kg of nitrogen. The routine formation-keeping requires at least one pair of cold gas maneuvers daily. Formation flight started in late 2010 and continued ever since in several configurations. This means that by now of the order of 2500 cold gas maneuvers have been performed and the remaining amount of fuel will allow for another 1500 to be made. Maneuvers were done mainly with the four 40 milli-Newton thrusters of branch-A, but about 25 % of the time branch-B was used. The construction of a digital elevation model of the Earth requires very precise orbit information, which is delivered by the flight dynamics department at GSOC....
Within this document we develop a maneuver sequence to conduct the TanDEM-X / TerraSAR-X formatio... more Within this document we develop a maneuver sequence to conduct the TanDEM-X / TerraSAR-X formation swap with minimal fuel and minimal risk of collision. A formation breakup procedure for the back-drift phase is provided. The extended ground-station network and the sequence of events are provided. This work is applicable to the mission operations segment during the TDX-TSX formation swap on August 6-9, 2013.
ABSTRACT Recently, a method for the n-body analysis of the velocity change required to deflect a ... more ABSTRACT Recently, a method for the n-body analysis of the velocity change required to deflect a hazardous near-Earth object (NEO) was presented by Carusi et al. [Carusi, A., Valsecchi, G.B., D&#39;Abramo, G., Boattini A., 2002. Icarus 159, 417–422]. We extent this method in order to optimize the velocity change vector instead of its along-track magnitude. From an application of both methods to a fictitious NEO we find Carusi&#39;s parallel approach to be reasonable for phases of unperturbed two-body motion. But, for orbit phases inhering third-body perturbations, i.e., for planetary close approaches or prior to a collision, the results obtained from the new method show the radial component of deflection impulse to play a major role. We show that a fivefold greater efficiency can be achieved by a deflection impulse being non-parallel to orbital velocity. The new method is applied to two possible 99942 Apophis impact trajectories in order to provide constraints for future Apophis deflection mission analysis.
This paper describes selected areas in which the TerraSAR-X ground segment had to be extended in ... more This paper describes selected areas in which the TerraSAR-X ground segment had to be extended in order to incorporate the TanDEM-X mission, namely flight dynamics, instrument operations and receiving stations and addresses their testing.
This paper describes the current operational TerraSAR- X (TSX) flight dynamics system (FDS) and d... more This paper describes the current operational TerraSAR- X (TSX) flight dynamics system (FDS) and depicts its extensions needed to fulfil the requirements for TanDEM-X, which shall form a close formation with TSX. Operational constraints imposed by the instrument operation and the ground station network are explained and the impact on the FD operations concept is discussed. The paper specifically elaborates
Near-Earth asteroid 99942 Apophis provides a typical example for the evolution of asteroid orbits... more Near-Earth asteroid 99942 Apophis provides a typical example for the evolution of asteroid orbits that lead to Earth-impacts after a close Earth-encounter that results in a resonant return. Apophis will have a close Earth-encounter in 2029 with potential very close subsequent Earth-encounters (or even an impact) in 2036 or later, depending on whether it passes through one of several so-called
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Papers by Ralph Kahle