A novel emergency system for low earth orbit satellites using Galileo GNSS

Low Earth Orbit (LEO) satellites have a limited direct contact time with the stations of their ground segment. This fundamentally constraints a timeliness reaction of the mission control center in case of emergency situations onboard the LEO spacecraft. To enable such a rapid reaction to emergency situations onboard LEO satellites, it is proposed to use a Search and Rescue (SAR) beacon onboard that spacecraft to transmit an alert message via Galileo satellites which support SAR through the Cospas-Sarsat (C/S) system to the satellite mission control center. While SAR up to now is limited to terrestrial, maritime, and aviation user scenarios, this space user concept presents a novel emergency system which helps facilitating the valuable space assets which LEO satellites in many cases represent. However, such a space user system faces various technical, system, and business challenges as well as legal and regulatory issues. The frequency band assigned for the SAR system is limited to low power satellite emergency position-indicating radio beacons and is foreseen for earth-space transmissions only. The International Telecommunication Union (ITU) should agree on opening this band for space-space communication for space user distress beacons. The Distress Alerting Satellite System (DASS) and the SAR/Glonass system will also operate in this band and an agreement will be required for these as well. A visibility analysis is presented for LEO to Galileo satellites. Depending on the placement of the antenna of the distress beacon on the LEO spacecraft, between 6 and 21 Galileo satellites are visible. The space user beacon may cause interference to the current SAR system when it’s signals collide with those of Earth-bound users in time or overlap in frequency at the Galileo transponder. When they collide in time one of the signals might still be processed if one of the signal levels is significantly higher than the other. Upon sharing the same frequency, both signals could be lost in a worst case scenario. This overlap in frequency can be caused by Doppler shifts. Therefore, a Doppler analysis was performed and Doppler shifts of about ?11 kHz were identified. Next to frequency overlaps the traffic load in the adjacent channels can increase. Different methods to prevent these Doppler shifts were analyzed. To reduce system complexity and benefit from existing technology, the space user beacon could be similar to that of an Earth beacon. However, the repetition time could be increased and the frequency channel selected for the Doppler analysis is chosen such that the interference is minimal. A high level design of the SAR payload onboard the LEO satellite was performed and different protocol options were valuated.Space EngineeringAerospace Engineerin

Magnetic Detumbling of Fast-tumbling Picosatellites

The problem of pure magnetic detumbling of a fast-tumbling picosatellite is considered. A new weighted B-dot control algorithm is proposed. The algorithm enables power reduction while not sacrificing detumbling performance. Analytical expressions relating the maximal expected rotational rate to the minimum sampling time required are presented. Simulation results demonstrate the practical benefits of the proposed approach for picosatellites.Space Systems EgineeringSpace Engineerin

Relative state estimation and observability for formation flying satellites in the presence of sensor noise

This paper presents an investigation into the relative state estimation and observability for two formation flying satellites using two different relative navigation sensor sets. The first set consists out of a transmitter antenna on one satellite and a single receiver antenna on the other satellite to measure the inter-satellite range using a radiofrequency ranging signal. The second set uses three receiver antennas to measure multiple ranges, effectively providing angular information. It is derived in the paper that for the more complete sensor set, the error in the estimation of the relative state is a function of the pseudorange error, the inter-satellite distance, and the receiver antenna baselines. By varying these variables, conditions are found for which the observations obtained using the first sensor set result in relative state estimation and observability comparable to those obtained with the more complete sensor set. This offers potential reductions in cost and complexity for certain mission scenarios.Space EngineeringAerospace Engineerin

Preliminary Analysis of a Novel SAR Based Emergency System for Earth Orbit Satellites using Galileo

This paper presents a preliminary analysis of a novel Search and Rescue (SAR) based emergency system for Low Earth Orbit (LEO) satellites using the Galileo Global Navigation Satellite System (GNSS). It starts with a description of the space user SAR system including a concept description, mission architecture and legal and regulatory aspects. This is followed by a visibility and interference analysis and a high level payload design will be presented.Space EngineeringAerospace Engineerin

Snapshot GNSS receivers for low-effort, high-gain space situational awareness

This paper proposes a novel concept of using highly efficient Snapshot Global Navigation Satellite Systems (GNSS) receivers to provide precise position fixes of single or multiple satellites in Low-Earth Orbit (LEO) to improve upper atmospheric modeling and thus contribute to superior space situational awareness (SSA). While tracking of LEO satellites and the use of onboard GNSS receivers for drag measurements and upper atmosphere modeling are well-established techniques, the expected advent of snapshot GNSS receivers for spaceborne scientific applications will allow massive improvements on the GNSS sensor's Size, Weight, Power and Cost (SWaP-C). With chip-size dimensions of 4x4 mm2, a mass of less than 5 gr, an average power level below 0.1 mW, snapshot receiver technology is expected to provide position fixes in space with an accuracy of ∼19 m (3D r.m.s.), which will surpass the accuracy of Two-Line Elements (TLE) provided by the US Joint Space Operations Center (JSpOC) by at least two orders of magnitude. Equally important to their SWaP-C benefits, Snapshot GNSS receivers will allow mission and spacecraft designers to trade onboard-processing requirements versus payload downlink requirements, leading to either minimum onboard processing or a minimum amount of downlinked data. In this research, we establish the concept and architectural overview of using snapshot GNSS receivers for SSA, including the role of using them in a Distributed Space System (DSS), and detail their characterization and performance in terms of the required GNSS hardware and the impact of these payload on the power budget, the link budget and the OnBoard Data Handling (OBDH) budget of a satellite. It will be shown that these receivers lend themselves especially to their use on femto-, pico- and nano-satellites, although integrated snapshot modules may be flown as auxiliary payloads on micro- or mini-satellites as well. While this work focuses on the implications of the use of snapshot GNSS receivers on spacecraft design for the use of upper atmosphere modeling and SSA, their use may open up other science applications which avoid the need for expensive high-grade GNSS receivers.Space Systems Egineerin

Performance analysis of crosslink radiometric measurement based autonomous orbit determination for cislunar small satellite formations

Recent advances in space technology provide an opportunity for small satellites to be launched in cislunar space. However, tracking these small satellites still depends on ground-based operations. Autonomous navigation could be a possible solution considering the challenges presented by costly ground operations and limited onboard power available for small satellites. There have been various studies on autonomous navigation methods for cislunar missions. One of them, LiAISON, provides an autonomous orbit determination solution solely using inter-satellite measurements. This study aims at providing a detailed performance analysis of crosslink radiometric measurements based on autonomous orbit determination for cislunar small satellite formations considering the effects of measurement type, measurement accuracy, bias, formation geometry, and network topology. This study shows that range observations provide better state estimation performance than range-rate observations for the autonomous navigation system in cislunar space. Line-of-sight angle measurements derived from radiometric measurements do not improve the overall system performance. In addition, less precise crosslink measurement methods could be an option for formations in highly observable orbital configurations. It was found that measurement biases and measurements with high intervals reduce the overall system performance. In case there are more than two spacecraft in the formation, the navigation system in the mesh topology provides a better overall state estimation than the centralized topology.Space Systems Egineerin

Advancing nano-satellite platforms: The Delfi Program

The Delfi Program aims to launch a nano-satellite every 2.5 years with the objectives to give the best education for space engineering, to test and qualify novel space technology and to enhance the nanosatellite platform to open doors for new applications. With Delfi-C3 in orbit, Delfi-n3Xt in development for a launch in 2010 and preliminary plans for the future, TU Delft wants to put itself at the top level of small satellites engineering. Although the size of nano-satellites puts some constraints on the potential performance and applications, the theoretical limits are still far ahead and nano-satellites might have more potential than typically assumed. This potential can only be made possible if the development goal for each satellite matches the availability of resources and a realistic planning in time.Space EngineeringAerospace Engineerin

Performance Analysis of Radiometric Autonomous Navigation for Lunar Satellite Network Topologies

This study provides a performance analysis of radiometric autonomous navigation for the lunar satellite network topologies formed by three spacecraft at various orbits. This work is built on the Linked Autonomous Interplanetary Satellite Orbit Navigation (LiAISON) method and uses mesh (distributed) and centralized (star) network topologies. The optimal interlink network topologies and Distributed Satellite Systems (DSS) geometry have been investigated based on the Circular-Restricted Three-Body problem (CRTBP) and the Extended Kalman Filter (EKF) for state estimation. The network topologies consisted of all the possible combinations of 16 spacecraft at various L1/L2 Halo, Lyapunov, and Lunar orbits. It has been shown that the autonomous navigation system provided better state estimation results for the mesh topology than for the centralized topology. Overall, the lunar satellite network topologies consisting of orbits with large inter-satellite link distances and short orbital periods would bene_t most from the radiometric autonomous navigation.Space Systems Egineerin

Generation of Secondary Space Debris Risks from Net Capturing in Active Space Debris Removal Missions

Mitigation strategies to eliminate existing space debris, such as with Active Space Debris Removal (ASDR) missions, have become increasingly important. Among the considered ASDR approaches, one involves using a net as a capturing mechanism. A fundamental requirement for any ASDR mission is that the capture process itself should not give rise to new space debris. However, in simulations of net capturing, the potential for structural breaking is often overlooked. A discrete Multi-Spring-Damper net model was employed to simulate the impact of a 30 m × 30 m net travelling at 20 m/s onto an ESA Envisat mock-up. The Envisat was modelled as a two-rigid-body system comprised of the main body and a large solar array with a hinge connection. The analysis revealed that more than two significant substructures had a notable likelihood of breaking, prompting the recommendation of limiting the impacting velocity. The generation of secondary space debris indicates that net capturing is riskier than previously assumed in the literature.Astrodynamics & Space MissionsSpace Systems Egineerin

Integrating systems and business engineering in an international context: The SpaceTech Postgraduate Program

Successful education of engineers needs continuous adaptation to track the changing needs of industry. The adaptation is not limited to technological advance or to the changing mentality of new students but also to end-to-end engineering approaches using Systems Engineering. However, industries today require more and more engineers with profound knowledge of business engineering to arrive at successful products – a fact which universities typically have not sufficiently taken into account yet. The SpaceTech program of the Delft University of Technology is an international postgraduate program for experienced high potentials seeking expertise in space systems and business engineering. The program centres around a Central Case Project where a group of international participants exercise space systems engineering fundamentals together with marketing and business engineering tools to create a financially viable virtual business. Based on more than 10 years of experience from the SpaceTech program, the learning objectives of Systems Engineering and business engineering and their interrelations are analyzed. Topics of past Central Case Projects are summarized and trends are extracted. The potentials of integrating Systems and Business Engineering are identified and their limitations in an educational environment are addressed.Space EngineeringAerospace Engineerin