1,721,040 research outputs found
Sapienza S5Lab student driven small-scale space missions and experiments
No full textThe rising number of concepts for small size space payloads, e.g. space station experiments, nano- or pico-satellites and stratospheric experiments, is widening the users number for such payloads to virtually all the people in the world, as per the so-called “New Space Economy”. In this framework, the involvement of students at the early stages of their academic careers into development of space payloads is beneficial on multiple points of view. As an example, students have the chance to face and solve “reallife” problems and to gain their soft skills (e.g. team working skills or basic manufacturing and coding capabilities). Moreover, students learn how to face success and failure of their small missions and how to improve processes for their future. At Sapienza Space Systems and Space Surveillance Laboratory (S5Lab), a group of around 50 students is developing small-scale missions since 2014. Four CubeSats have been launched with the support of ASI and other institutions, while a fifth CubeSat will be launched in mid-2022 on the maiden Vega-C launch. Three stratospheric payloads manufactured by S5Lab have been successfully launched from the Esrange Space Center in Sweden, through the REXUS/BEXUS and HEMERA international programmes. The new perspectives of payload development, besides continuing to manufacture CubeSats (through the selection of a new 2-Unit mission to be launched in 2023) and stratospheric experiments (through a new participation in REXUS/BEXUS) include the possibility of developing a student-led analog mission simulating lunar lava tube operations, and the chance to study and develop prototypes for innovative launcher navigation systems and suborbital experiments. The main lessons learned obtained by the years of development with students deals with reaching a certain continuity of payload manufacturing, from a “one-shot” concept in the early years to a better knowledge management for launch opportunities potentially obtainable every year. Other lessons learned are dealing with the correct time and year of involvement of the students, and with manpower management when the involved students are volunteering for joining the teams. This paper will deal with the experience in payload and missions development at Sapienza S5Lab. After an introduction over the present, past and future space missions, the main lessons learned from how to turn these projects into success stories of students involvement will be presented. The future perspectives for reaching a more stable continuity of launch opportunities and payloads development with a wider knowledge management among students will be discussed
Lightcurve inversion for attitude determination
No full textThe interest in determining the attitude of an orbiting object has grown significantly in recent years. Besides being one of the key parameters needed to obtain a precise orbital determination, the attitude is also crucial in the perspective of planning a space debris removing mission. In this paper, we present a method to retrieve the attitude of an orbiting object, based on a virtual reality simulation together with a global optimization. The attitude will be determined using the object's lightcurve derived information, i.e. the total reflected light variation in time. This technique, derived from the asteroids attitude and trajectory reconstruction techniques, has recently been introduced in the uncooperative satellite optical attitude determination. The idea behind the proposed method is to generate, for a selected target, different synthetic lightcurves to be compared with the observed one; the synthetic lightcurve most similar to the experimental one will be chosen as the presumable object attitude. In such a context, the crucial procedure tool is the synthetic lightcurve generator, that needs to be as realistic as possible in terms of optical and physical properties. To satisfy these requirements, the orbital position of the object will be recovered by propagating its orbit from the known TLE (Two-Line Element) through an SGP-4 (Simplified General Perturbations) routine. At the same time, the real positions of the observer and the Sun will be used to derive a precise value of the phase angle Sun-object-observer, aimed at obtaining an estimate of the light reflected by each object part. A realistic image of the object will be then produced at each instant of time using an advanced rendering algorithm, that takes into account parameters such as the atmospheric extinction, the object shape and materials, and the direction of the sunlight. A particular effort is made to accurately reproduce the shadow areas cast by the different object's components. Finally, to find the best attitude parameters, an evolutive algorithm that minimizes the residual between the real and the simulated lightcurves is employed. The results obtained on very heterogeneous datasets show a very promising potential in terms of applicability of the developed method. In this paper, this method developed for the attitude reconstruction is discussed: first, the used lightcurve analysis tools are described, and then the simulation environment able to generate artificial lightcurves is presented. The achieved results (on synthetic and on real data, acquired during in January and February 2018), and future perspectives will be found in the conclusions
Evaluation of time difference of arrival (Tdoa) networks performance for launcher vehicles and spacecraft tracking
Get PDFTime Difference of Arrival (TDOA) networks could support spacecraft orbit determination or near-space (launcher and suborbital) vehicle tracking for an increased number of satellite launches and space missions in the near future. The evaluation of the geometry of TDOA networks could involve the dilution of precision (DOP), but this parameter is related to a single position of the target, while the positioning accuracy of the network with targets in the whole celestial vault should be evaluated. The paper presents the derivation of the MDOP (minimum dilution of precision), a parameter that can be used for evaluating the performance of TDOA networks for spacecraft tracking and orbit determination. The MDOP trend with respect to distance, number of stations and target altitude is reported in the paper, as well as examples of applications for network performance evaluation or time precision requirement definitions. The results show how an increase in the baseline enables the inclusion of more impactive improvements on the MDOP and the mean error than an increase in the number of stations. The target altitude is demonstrated as noninfluential for the MDOP trend, making the networks uniformly applicable to lower altitude (launchers and suborbital vehicles) and higher altitude (Low and Medium Earth Orbits satellites) spacecraft
Ground simulation of the effects of the space environment on ceramic nano-coated panels for space environment protection
No full textA critical aspect to be addressed through materials engineered for aerospace missions is to provide the protection of space subsystems from the aggressive operative environment, in order to extend the life of such subsystem. Taking this fact into account, carbon-based ceramic composites are ideal candidates for the next development of industrial research in the aerospace field, thanks to the wide range of multi-functional elements obtainable using these materials. For example, ceramic-based hybrid structures can be designed to perform the environmental shielding function as well as to ensure the reusability of the structure itself. In particular, covering the surface of a C/C structure with a protective coating based on nano-particles and metal oxides it would be possible to preserve the functionality of the bulk (i.e. resistance to the critical conditions of the atmospheric re-entry phase) from the dangerous effects due to the LEO space environment where most of the missions takes place (mainly due to outgassing and oxygen erosion/corrosion atomic). In this paper the effects of the Space Environment on self-produced Carbon/Carbon nano coated panels have been evaluated in order to study a possible dual use
Feasibility study of mini rf-helicon-double-layer plasma thruster for microsatellite attitude control
No full textVhf omnidirectional range (Vor) experimental positioning for stratospheric vehicles
Get PDFThe usage of aeronautical radio-frequency navigational aids can support the future stratospheric aviation as back-up positioning systems. Although GNSS has been extensively redundant in the last years of space operations, radio NavAids can still be supportive of navigation and tracking for novel mission profiles. As an example, in 2016, VHF Omnidirectional Range (VOR) has been proven to work well above its standard service volume limit on a stratospheric balloon flight with the STRATONAV experiment. While VOR provides the “radial” measurement, i.e., the angle between the Magnetic North and the line between the receiver and the transmitting ground station, the intersection of two or more radials at a time allows to perform ground track reconstruction for the vehicle to be tracked. This paper reports the results from the data re-processing from STRATONAV: the acquired radials have been intersected in order to achieve positioning. The radials interfacing method, the position calculation methodology, and the data acquisition strategies from STRATONAV are reported together with the data analysis results
Experimental reflection evaluation for attitude monitoring of space orbiting systems with nrl arch method
Get PDFThe increasing number of satellites orbiting around Earth has led to an uncontrolled increase in objects within the orbital environment. Since the beginning of the space age on 4 October 1957 (launch of Sputnik I), there have been more than 4900 space launches, leading to over 18,000 satellites and ground‐trackable objects currently orbiting the Earth. For each satellite launched, several other objects are also sent into orbit, including rocket upper stages, instrument covers, and so on. Having a reliable system for tracking objects and satellites and monitoring their attitude is at present a mandatory challenge in order to prevent dangerous collisions and an increase in space debris. In this paper, the evaluation of the reflection coefficient of different shaped objects has been carried out by means of the bi‐static reflection method, also known as NRL arch measurement, in order to evaluate their visibility and attitude in a wide range of frequencies (12–18 GHz). The test campaign aims to correlate the experimental measures with the hypothetical reflection properties of orbiting systems
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Space environment exposure effects on ceramic coating for thermal protection systems
No full textCarbon/carbon (C/C) structures are widely considered for space thermal protection systems (TPSs), being able to withstand critical reentry conditions thanks to an excellent thermal stability. In low-Earth-orbit long-time missions, however, the TPS effectiveness is significantly lowered due to the surfaces' prolonged staying within the harsh space environment. In particular, the detrimental oxidation due to thermal cycles and atomic oxygen (AtOx) exposure greatly affects the TPS integrity, thus leaving the spacecraft's outer surface less protected during reentry. A great effort is thus made for testing solutions based on advanced coatings aimed at preserving TPS materials from oxidation. In the present work, ceramic coatings are evaluated by measurements of the thermal expansion coefficient and AtOx erosion rate. The specimens tested are C/C substrates on which commercial refractory varnishes are applied. Silicon carbide and aluminum and zirconium oxides are the basic ceramic constituents, and the effect of silica nanoparticles' inclusion on the coating performances is also evaluated. A phenomenological modeling is then introduced to approach the relationship between erosion mechanism due to AtOx impact and surface energy variation induced by thermal cycles; such analysis highlights the importance of considering the combined action of different aging factors, in order to achieve a reliable interpretation of the space environment's effect on spacecraft structures and subsystems
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