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This paper presents a modern digital sun sensor for attitude determination that is under development at the Department of Space Science and Engineering of the University of Naples. The sensor, which adopts a CMOS Photodetector and microtechnology solutions, has been selected as one of the technology demonstration payloads in the first mission of the Italian Space Agency microsatellite bus standard, scheduled for flight by the end of 2008. In this work, sensor concept, development and laboratory test are presented. Sensor average accuracy better than 0.01° is demonstrated by laboratory tests. It is also proved that sensor average precision is improved of about one order of magnitude using an innovative multi-aperture configuration.

This work presents an analysis of the attainable performance of a bistatic SAR for oceanographic applications, such as the determination of sea state parameters and the reconstruction of the sea wave spectrum. The analysis has been developed with regard to the spaceborne bistatic SAR of the BISSAT mission. It is based on a receiving-only antenna, flying on board a small satellite, that gathers echoes from the area illuminated by an active SAR operating on an independent large platform. It is shown that in the case of bistatic acquisitions the region of the sea wave spectrum that can be retrieved through linear inversion is wider than the one relevant to a monostatic survey. Specifically, the improvement consists of higher sea states (up to 15-20%) and a wider range of azimuth angles of propagation of the sea waves, increasing for larger antenna baselines. Also, the image degradation due to acceleration smearing is reduced. Improvements can achieve 20% for larger azimuth angles of propagation and baselines.

This paper analyses some aspects dealing with indoor testing of modern star trackers for attitude determination. An end-to-end approach has been considered, which requires that realistic star field scenes are simulated and supplied to the sensor under test. First of all, the features of the scene that is observed during a space mission are presented. Characterising astronomic parameters are converted into radiometric quantities to be directly exploited for simulation. Then, the need of collimating optics to reproduce the huge distance of the true scene is demonstrated by quantitative analysis of typical sensor performance. Relevant design is also presented. Finally, the relationship between the accuracy of sensor installation in the test facility and the consequent attitude measurement uncertainty is evaluated.

This paper deals with the activities carried out at the Department of Aerospace Engineering of the University of Naples “Federico II” for the design, development, and test operation of a star sensor prototype with real-time, fully-autonomous capability. A laboratory facility for indoor tests, based on the simulation of star field scenes, and the relevant software have been realized as well. The system is based on Commercial-Off-The-Shelf (COTS) components, thus allowing low-cost and short time development. The paper presents a description of the sensor laboratory prototype and the test facility. Performance of the latter are analyzed for both static and dynamic simulations.

This paper describes the digital sun sensor under development at the University of Naples. The sensor optical head exploits a CMOS photodetector and a mask with multiple holes. This original design allows forming multiple simultaneous images of the sun on the focal plane, which, once processed, produce multiple measurements of the sun line orientation. These are then averaged to improve sensor precision. To achieve high accuracy in sun line determination a calibration function based on neural networks is developed. The sensor can be operated either with a fixed number or with a variable number of sun spots, depending on the required field of view and sun-line measurement precision. This improves sensor flexibility and operation range but, at the same time, increases the computational load when multiple spots are used. Specific techniques are developed to minimize the computational load needed to process multiple acquisitions and to extract the sun line orientation with high accuracy and precision, and adequate updating frequency. These techniques have been tested by extensive test campaigns, carried out by using a laboratory test facility reproducing sun spectrum, apparent size and distance, and variable illumination directions. Specifically, tests reproducing the in-orbit planned experiment profile in terms of a sequence of sun line orientations are performed. Test results validate the sensor concept, confirming the precision improvement achievable with multiple apertures, and the sensor capability of operating with a variable number of sun spots.

Main focus of this paper is on the integrated, multi-band, hyper-spectral, electro-optical sensor that has been studied for applications of forest fire risk management. It is based on the mini-UAV platform named “1st”. The integrated sensor consists of a thermal imager and a hyperspectral sensor in VIS-NIR band. It is completed by a compact onboard computer for operation control, and a transceiver for real-time data download and command upload. Additional onboard equipment, such as GNC sub-system, is relevant to the UAV platform. Hardware characterization and laboratory tests are discussed and, finally, the results of a flight test session with both remote sensing and GNC sub-systems are presented.

This papers deals with the large-FOV, micro-sun-sensor under development at the University of Naples. The sensor exploits a multi-hole mask to measure the sun line with high precision. Nevertheless, multi-spot operation exhibits failures near FOV borders, due to the uncertainty in the number of spots that can be reli-ably acquired. After a short description of the sensor concept, hardware model, and laboratory test equipment, this paper focuses on the latest upgrades of the sensor operation mode, aimed at getting reliable operation ability and improved precision over a wider FOV (at least 90x80 deg). Specifically, an original tech-nique is implemented in which the sensor shutter-time is automatically adapted based on detected image intensity to improve precision near FOV borders. Re-sults of the validation and performance assessment campaign of the upgraded operation mode executed with the ground facility are presented. In these tests sensor precision is characterized as a function of the separation of the illumina-tion direction from FOV centre, showing that the upgraded operation mode al-lows getting high precision (about 0.001°) also near FOV borders.

This paper aims at characterizing the attitude determination performance of a non-conventional star tracker based on a hyper-hemispheric panoramic camera designed as a multi-functional sensor for applications onboard small/micro-satellites. The peculiar features of the optical system allow imaging a field of view of 360° in azimuth and up to 135° in elevation (zenith), thus being able to observe an extremely wide portion of the celestial sphere, though at the expense of limited capabilities in terms of detector resolution and sensitivity. For this reason, each mode of the multi-functional sensor requires ad-hoc, original algorithmic solutions. In this respect, the star tracker mode relies on an innovative approach for star identification, based on template matching and image registration concepts inherited from the computer vision and robotic research community, combined with a standard solution to the Wahba's problem to determine the spacecraft attitude parameters during the lost-in-space condition. A numerical simulation environment is developed to realistically reproduce the star pattern imaged by the sensor including all the major sources of noise (e.g., outliers, hot pixels). Hence, the performance of the proposed approach is evaluated in terms of attitude determination accuracy and reliability over a wide set of attitude states characterized by a uniform distribution of the camera pointing in the celestial sphere. Also, this is done considering highly-variable settings in terms of sensor's specifications and algorithm's operational parameters.