Aiming at increasing the satellite link performance, advanced modulation techniques have been thoroughly studied. On the other hand, reliable transmission techniques with a low computational overhead are pursued for many applications in critical scenarios such as: control operation of a satellite while it is placed into its orbit, the disposal of a satellite at the end of its life or the deep-space missions. In these specific mission critical scenarios, fast and correct data reception is even more important than high channel capacity. An unknown and fast variable channel state condition, with large Doppler shifts and low available power require incoherent and light computationally modulation techniques. This paper introduces a whole digital implementation of a receiver, based on the Double Differential PSK (DD-PSK) modulation, that is perfectly compliant with these requirements.

Following a business as usual scenario, some Low Earth Orbit (LEO) regions could be unusable for many decades because of the space debris growth. In order to reduce that trend, the current probability of success of the chosen End of Mission (EOM) disposal method shall ensure a target value of 90% [1]. Understanding reliability of satellites and their subsystems for different spacecraft classes allows determining which disposal solution could better fit with a particular space mission. However, spacecraft are quite often different from each other, so a statistical approach is required. An in depth study has been performed on 1086 spacecraft launched between January 2000 and December 2014 using data from the SpaceTrak™ database. Spacecrafts have been separated by mass and by the presence/absence of the propulsion subsystem. The non-parametric Kaplan-Meier survival analysis has been used because the dataset presented censored events, namely the observed variable value is partially known. Empirical reliabilities obtained have been fitted using the Weibull distribution. Because each disposal method needs a combination of subsystems in order to operate, the reliabilities of the different subsystems have been combined by means of the System Reliability Theory. General spacecraft reliability was found to be about 92% after 4 years. The presence of the propulsion subsystem results in a better reliability trend. Furthermore, the propulsion presence/absence classification being equal, the heavier the mass the worse the reliability. Disposal solutions that use communication and power subsystems can count on reliabilities above 90% up to 7 years, whereas those ones that need also the attitude control can rely on only an 85% reliability after 4 years. A trade-off was performed and it showed that the film aerobrake and the propulsive D-Orbit decommissioning device can be key resources as disposal methods for future missions. The results presented could be useful to the space industry, to better address its efforts in improving spacecraft reliability and to design more reliable EOM disposal methods in order to reduce space debris growth

Reliability and effectiveness are essential features of satellite transceivers for telemetry and telecommand applications. Modem performance has a strong impact on the success of a satellite mission, in particular, during critical scenarios as the early operation phase, the disposal of a satellite at the end of its life, or the deep-space missions. In these specific mission critical scenarios, fast and correct data reception is even more important than high channel capacity. An unknown and fast variable channel condition, which can be caused by uncertain spacecraft attitude and large Doppler shift with respect to the data rate, requires efficient and innovative receiver architecture. This paper introduces a complete digital implementation of a transceiver for TM/TC application in low Earth orbit mission that is perfectly compliant with aforementioned requirements. Particular attention is dedicated to the definition and selection of the most appropriate frequency recovery technique; 2 open-loop techniques that are derived from ML optimal estimator are presented and compared. Additionally, the performance of the proposed receiver is extensively studied and compared with an incoherent technique that is based on the double differential PSK modulation and is known to be suitable for sat-com in critical scenarios. KEYWORDScritical scenarios, frequency recovery, satellite modems, telemetry and telecommand applications INTRODUCTIONThe success of a space mission strongly depends on the quality and performance of satellite subsystems. The Telemetry and Telecommand (TM/TC) is an essential module for a spacecraft along with the electrical power system, on-board data handling and attitude and determination control system.The availability of the communication link with the satellite from the early mission phase allows the ground operator to monitor satellite status and to perform recovery actions if something goes wrong; an on-board computer failure may be recovered by rebooting the associated power line through a direct telecommand to the electrical power system.The early operations after separation from upper launcher stages, as well as the end of life disposal manoeuvres, are critical satellite mission phases that require a robust and reliable communication system. 1,2 In these scenarios, the spacecraft may have reduced functionalities and uncontrolled attitude, and consequently, the communication link could be weak and unstable, eg, signal's amplitude may be subjected to deep fading according to satellite tumbling rate. 3 In this context, the communication becomes bursty and the link reliability harms the bit-rate performance.Moreover, new challenges are receiving the interest of the space communication community. Nowadays, an innovative and popular way to access space is by means of new low-cost satellite solutions such as micro or nano-satellites. 4,5 These systems have typically less stringent performance requirements when compared with traditional space systems but, on the other hand, limited energetic and computationa...

Effective answers to the major problems in society can be achieved by resorting to the integration of telecommunication platforms, heterogeneous systems of localization, and sensing capabilities and intelligent objects [1]. Particularly, the pursuit of long term technological solutions has to be made with the support of a revolutionary multidisciplinary approach, especially in the areas of transport, smart environments, quality of life, security, etc.As a result, new and more intelligent services will become available, allowing the realization of smart contexts for what concerns home, building, cities, work-places, and implementing new concepts as ambient intelligence, ambient assistant living, ubiquitous computing, context awareness, and many more. This pervasive communication ecosystem will solve many, if not most, problems in our life, by increasing security and safety perception and improving interaction and conditions of activities; information and communications technologies will be a pillar of this society evolution by providing a complex net of information exchanges and exploiting the big data that are involved in the procedures [2].Moreover, the satellite segment will contribute significantly to the evolution of the services by means of the synergistic use of communication, positioning, and monitoring techniques: this objective will be realized by means of meshed heterogeneous architectures [2] that can afford remarkable systems and networks performance. At the same time, some of the envisaged future services such as the global tracking, monitoring, and maintaining of some specific assets or contexts don't mandatorily request the implementation of classic wireless or satellite communication systems which are subject to coverage and cost limitations; conversely, the uprising Machine-to-Machine (M2M) and Internet of Things paradigms seem to be more appropriate in such scenarios where a global packet connectivity has to be afforded in order to permit the exchange of information between the network and the ultimate users but the requirements in terms of data-rate and latency are not stringent [3], [4].On the other hand, this strategy can be successful if some operating conditions and key factors can be granted; particularly, the following conditions are compelling:C this strategy has to be general, i.e., a very large set of future services has to rely on it, even if their requirements are rather diversified and even divergent;C the communications, both within the system and between the system and the external world, will have to be highly efficient and to deliver all the necessary information in due time, where needed, with required quality of service (QoS) and energy consumption.Among the systems which allow the achievement of both of these goals, the new class of "SmallSats" also affords the reduction of the implementation costs and the increase of system availability because of their recent exponential growth [5], [6], [7]. As a result, the exploitation of SmallSats solutions, such as the CubeSat, as a b...

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