Precision spacecraft navigation using a low-cost GPS receiver

Within the PROBA-2 microsatellite mission, a miniaturized single-frequency GPS receiver based on commercial-off-the-shelf (COTS) technology is employed for onboard navigation and timing. A rapid electronic fuse protects against destructive single-event latch-ups (SEL) and enables a quasi-continuous receiver operation despite the inherent sensitivity to space radiation. While limited to single-frequency C/A-code tracking with a narrow-band frontend, the receiver is able to provide precision navigation services through processing of raw GPS measurements on ground as well as a built-in real-time navigation system. In both cases, ionospheric path delays are eliminated through a combination of L1 pseudorange and carrier phase measurements, which also offers a factor-of-two noise reduction relative to code-only processing. By comparison with satellite laser ranging (SLR) measurements, a 0.3-m (3D rms) accuracy is demonstrated for the PROBA-2 reduced dynamic orbit determinations using post-processed GPS orbit and clock products. Furthermore, the experimental onboard navigation system is shown to provide real-time position information with a 3D rms accuracy of about 1 m, which notably outperforms the specification of the Standard Positioning Service (SPS). In view of their lower hardware complexity, mass budget and power requirements as well as the reduced interference susceptibility, legacy C/A-code receivers can thus provide an attractive alternative to dual-frequency receivers even for demanding navigation applications in low Earth orbit

PROBA-V: AN OPERATIONAL AND TECHNOLOGY DEMONSTRATION MISSION – RESULTS AFTER COMMISSIONING AND ONE YEAR OF IN-ORBIT EXPLOITATION

Proba-V, the third mission of ESA’s Programme for In-orbit Technology Demonstration (IOD), conceived and developed following the footsteps of its predecessors, Proba-1 and Proba-2, is an operational mission based on a small, high performance satellite platform and a compact payload, whose main aim is the continuation of the SPOT/Vegetation programme, now planned for decommissioning. Successfully launched by the ESA VEGA launcher in May 2013, it has completed its commissioning and the full calibration of platform, main instrument and additional payloads and is, since last October, fully operational. The development of the Vegetation Instrument, the main satellite’s instrument, required the use of a number of innovative technologies, in order for it to be compatible with a small platform’s resources, while at the same time being able to enhance Vegetation images’ resolution performances from 1km to 100m at Nadir. Besides its main instrument, Proba-V embarks a number of advanced technologies, some of which represent first-ever in-space applications, integrated into its baseline platform’s design, for the enhancement of the its capabilities, flexibility and robustness, in order to meet the mission’s stringent objectives. Additionally, Proba-V embarks five technological payloads providing early flight opportunities for novel instruments and space technologies: • ADS-B: first-ever in-space demonstration of this air traffic surveillance system, • An X-Band transmitter based on Gallium Nitride RF power amplifier, • EPT: a new technology application for advanced radiation monitoring, • HERMOD: a high density fibre optics connector’s demonstration device, • SATRAM: a miniaturised radiation monitoring sensor. This paper will present the ESA approach to the In-Orbit Demonstration programme, and will highlight the Proba-V mission, focusing on the new technologies flying on-board, their in-orbit initial results and achieved performances

PROBA-V: The example of onboard and onground autonomy

The PROBA-V satellite, built by QinetiQ Space (Belgium), was launched on May 7th 2013. It is a small ESA satellite tasked with a full-scale mission: to map land cover and vegetation growth across the entire planet on an daily basis (+90% per day). It is the third satellite in the PROBA series, after PROBA-1 (launched on 22/10/2001) and PROBA-2 (launched on 2/11/2009), which are both still in nominal operations. The PROBA satellites are part of ESA’s In-orbit Technology Demonstration Programme, which handles missions dedicated to the demonstration of innovative technologies. PROBA stands for PRoject for OnBoard Autonomy. From the very first design phases, upto the in-orbit operations, everything is oriented to achieve a maximum autonomy for the mission. This includes fully autonomous platform and payload operations, requiring only limited inputs from ground. Apart from onboard autonomy, this also includes a fully automated flight operations segment, where satellite contacts are usually executed unattended and scientific requests are passing through transparently without the need for operator presence. With three satellites in orbit, the realisation of onboard and onground autonomy has lead QinetiQ Space (as prime of an industrial consortia) to be recognized as key reference in satellite autonomy. For its next generation, the PROBANEXT platform will keep focusing on maximum autonomy as a tool to ensure an optimised design, a cost-efficient design and development process and extremely low cost operations

GPS Based Precise Orbit Determination and Real-Time Navigation of the PROBA-2 Spacecraft

The PROBA-2 (Project for Onboard Autonomy) spacecraft is a micro-satellite serving as joint platform for technology demonstration and astronomical observations of the Sun. The satellite is equipped with two kinds of GPS receivers: a miniaturized single-frequency receiver (Phoenix-XNS) supporting the attitude and orbit control system and the first European space receiver for tracking the civil GPS signals on both the L1 and L2 frequency. Both receivers provide raw measurements for precise orbit determination on ground and are also equipped with a real-time navigation system enabling accurate onboard positioning. The paper discusses the flight performance of both receivers based on data collected during the first year of operation

State of the Art of Steel Reinforced Grout Applications to Strengthen Masonry Structures

Load-bearing unreinforced masonry structures represent a significant proportion of the building stock in several countries worldwide, and include historical constructions that belong to cultural heritage. Because of the limited tensile strength of unreinforced masonry, fiber-reinforced composites are an effective strengthening technique, which has already been widely used, especially in seismic prone areas, to delay the onset of collapse mechanisms of the entire structure or portions of it. Steel reinforced grout (SRG), which consists of steel textiles embedded in a cement or lime based mortar, is a particularly appealing alternative to fiber-reinforced polymer (FRP) composites, as well as to other mortar based composites (i.e., fabric reinforced cementitious matrix, FRCM), especially when applied to masonry structures. This paper sheds light into the retrofitting of masonry structures with SRG, providing an overview of the experimental investigations carried out in the laboratory and in the field on full-scale structural members. SRG proved effective for improving the out-of-plane flexural strength and deflection capacity of masonry walls (for which three or four-point bending tests and shake table tests were performed), the load-bearing and deflection capacity of vaults (tested both in the laboratory and in the field under quasi-static vertical loads), and the compressive strength of columns (subjected in the laboratory to centred axial load). Further research needs are identified, which are considered useful for the development of design guidelines

State of the Art of Steel Reinforced Grout Applications to Strengthen Masonry Structures

Load-bearing unreinforced masonry structures represent a significant proportion of the building stock in several countries worldwide, and include historical constructions that belong to cultural heritage. Because of the limited tensile strength of unreinforced masonry, fiber-reinforced composites are an effective strengthening technique, which has already been widely used, especially in seismic prone areas, to delay the onset of collapse mechanisms of the entire structure or portions of it. Steel reinforced grout (SRG), which consists of steel textiles embedded in a cement or lime based mortar, is a particularly appealing alternative to fiber-reinforced polymer (FRP) composites, as well as to other mortar based composites (i.e., fabric reinforced cementitious matrix, FRCM), especially when applied to masonry structures. This paper sheds light into the retrofitting of masonry structures with SRG, providing an overview of the experimental investigations carried out in the laboratory and in the field on full-scale structural members. SRG proved effective for improving the out-of-plane flexural strength and deflection capacity of masonry walls (for which three or four-point bending tests and shake table tests were performed), the load-bearing and deflection capacity of vaults (tested both in the laboratory and in the field under quasi-static vertical loads), and the compressive strength of columns (subjected in the laboratory to centred axial load). Further research needs are identified, which are considered useful for the development of design guidelines