Alberto Graziani

A Low-Cost Microsatellite Platform for Multispectral Earth Observation

In the Microsatellite Laboratory of the University of Bologna a project was started in 2003, aimed at the development of a multipurpose microsatellite platform named ALMASat. The launch into orbit of the first prototype ALMASat-1 is currently foreseen by the end of 2008. One of the natural applications of the modular ALMASat platform is in the field of space-based Earth observation. At this aim, a spin-off company named ALMASpace was established in 2006, with the goal of designing and demonstrating the feasibility of a low-cost Earth observation mission based on the technological achievements obtained by the ALMASat project. This paper summarizes the main characteristics of the ALMASat-1 spacecraft and describes the current status of the design and development of the ALMASat-EO (Earth Observation) spacecraft bus and optical payload whose launch into orbit is currently scheduled at the end of 2010.

On the Use of Microwave Radiometers for Deep Space Mission Applications by Means of a Radiometric-Based Scalar Indicator

The estimation of the path delay due to water vapor is a crucial aspect for the calibration of the Doppler observables of a deep space probe. The advanced water vapor radiometer (AWVR) developed by the Jet Propulsion Laboratory (JPL, NASA) already proved its capability to accurately estimate the path delay during the entire Cassini mission. Here, from the AWVR measurements, a scalar sky status indicator (SSI) was developed as a criterion for selecting the radiometric path delay estimations in the orbit determination process. Results indicate that the use of such index allows a reduction of the range rate residual root mean square (rms).

AWARDS: Advanced microwave radiometers for deep space stations

The objective of this study, named AWARDS Advanced microWAve Radiometers in Deep space Stations, is the preliminary design of a transmission Media Calibration System MCS to be located at an ESA Deep Space Antenna DSA site. The crucial aspect is the capability to accurately retrieve the tropospheric path delay along the line-of-sight of the deep space probe in order to allow precise tropospheric calibration of deep space observables range and range-rate with particular reference to the BepiColombo spacecraft and its primary DSA at Cebreros ES. The study focuses on two main aspects which lead to the preliminary design of the Mercury Orbiter Radioscience Experiment MORE MCS: the characterization of current microwave radiometers MWRs available at ESA/ESTEC and the atmospheric fluctuation effects on the MCS error budget, in terms of the Allan standard deviation ASD. In the course of the study, further critical aspects have been identified effects of Sun contamination, effects of ground noise emission, and mitigation strategies have been proposed. The final outcome is a preliminary design of the MWR and the entire MCS to be deployed at the ESA/ESTRACK ESA Tracking station network sites and being compliant with MORE requirements.

Assessment of Ground-Based Microwave Radiometry for Calibration of Atmospheric Variability in Spacecraft Tracking

In a suggested radio propagation experiment using a deep space antenna, accurate calibration of the propagation delay through the Earths atmosphere is essential. One or two microwave radiometers can be used for this purpose. Differences in precise locations of the radiometer(s) and antenna to be calibrated leave a residual wet path delay value. We computed the Allan Standard Deviation (ASD) of this residual, as well as the one resulting from different pointing positions in the plane of the sky, by simulations. Pointing offsets, e.g., to avoid solar radiation into the radiometer beam, lead in general to an increased ASD. However, for many observation geometries a deliberate pointing offset can compensate for the location differences. In the case studied we found a reduction of the ASD with up to 45% compared to the ASD obtained for a zero pointing offset. The size of the calculated ASD depends strongly on the model parameters used, e.g., the turbulence strength parameter Cn2, which has a significant natural variation over a year.

Results from the scenario simulation of the radio occultation experiment onboard ALMASat-EO mission

Radio occultation technique performed with GNSS observables acquired by low Earth orbit satellites offer a great amount of data to carry out experiments and measurements in the framework of Earth survey. A dedicated GNSS-based radio occultation experiment has been designed to be installed onboard the microsatellite ALMASat-EO mission, developed at the Microsatellite Laboratory of the II Faculty of Engineering of the University of Bologna. The experiment, named ALASE (ALMASat Atmosphere Sounding Experiment) will offer a large amount of occultation events in order to perform scientific measurements of the atmosphere profile and climatology studies. In order to evaluate the feasibility of the experiment, it has been simulated with a dedicated ALMA GNSS Scenario Simulator Software (ALMAG3S) specifically developed for this purpose. The scenario software includes all GNSS satellites position in a precise post processing and pseudo real time environment. The modeled GNSS observables are perturbed considering the main error sources: satellite clock, receiver clock, instrumental errors, relativistic errors and propagation models. ALMAG3S models the errors and the GNSS satellites position by using the IGS products.

Low-Cost Assembly Technologies for Microsatellite Solar Panels

At the University of Bologna in Forli, a program has been established for the low-cost design, manufacturing and operation in orbit of microsatellites. This is intended mainly as an educational program, being students directly involved in all mission phases, but also as a technological test bench, where novel technologies and original design and assembly procedures could be tested in orbit with short development times. The on-board power generation system follows the same design guidelines as the materials and manufacturing process are partly borrowed from terrestrial solar power generation technologies. We show here how the adaptation of this technologies, made in order to let the spacecraft solar arrays to withstand the harsh space environment, lead to a reliable product, as demonstrated by the successful environmental (thermal and mechanical) tests performed on solar panel samples produced in the University laboratories.