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

Space missions in Low Earth Orbit (LEO) are severely affected by the build-up of orbital debris. A key practice, to be compliant with IADC (Inter-Agency Space Debris Coordination Committee) mitigation guidelines, is the removal of space systems that interfere with the LEO region not later than 25 years after the End of Mission. It is important to note that the current guidelines are not generally legally binding, even if different Space Agencies are now looking at the compliance for their missions. If the guidelines will change in law, it will be mandatory to have a post mission disposal strategy for all satellites, including micro and smaller classes. A potential increased number of these satellites is confirmed by different projections, in particular in the commercial sector. Micro and smaller spacecraft are, in general, not provided with propulsion capabilities to achieve a controlled re-entry, so they need different de-orbit disposal methods. When considering the utility of different debris mitigation methods, it is useful to understand which spacecraft subsystems are most likely to fail and how this may affect the operation of a de-orbit system. This also helps the consideration of which components are the most relevant or should be redundant depending on the satellite mass class. This work is based on a sample of LEO and MEO satellites launched between January 2000 and December 2014 with mass lower than 1000 kg. Failure analysis of satellite subsystems is performed by means of the Kaplan-Meier survival analysis; the parametric fits are conducted with Weibull distributions. The study is carried out by using the satellite database SpaceTrak™ which provides anomalies, failures, and trends information for spacecraft subsystems and launch vehicles. The database identifies five states for each satellite subsystem: three degraded states, one fully operational state, and one failed state (complete failure). The results obtained can guide the identification of the activation procedure for a de-orbit strategy and the level of integration it should have with the host satellite in order to be activated before a total failure. At Cranfield Space Research Centre two different solutions have already been developed as de-orbit sail payloads for micro satellites (Icarus-1 on TechDemoSat-1 and Icarus-3 on Carbonite-1 currently on-orbit, DOM for future ESA ESEO mission). This study will provide a useful input to improve and refine the current de-orbit concepts for future satellite missions.

The continuous growth of space debris motivates the development and the improvement of tools that support the monitoring of a more and more congested space environment. Satellite breakup models play a key role to predict and analyze orbital debris evolution, and the NASA Standard Breakup Model represents a widely used reference, with current activities relevant to its evolution and improvements especially towards fragmentation of small mass spacecraft. From an operational perspective, an important point for fragmentation modelling concerns the tuning of the breakup model to achieve consistency with orbital data of observed fragments. In this framework, this paper proposes an iterative approach to estimate the model inputs, and in particular, the parents’ masses involved in a collision event. The iterative logic exploits the knowledge of Two Line Elements (TLE) of the fragments at some time after the event to adjust the input parameters of the breakup model with the objective of obtaining the same number of real fragments within a certain tolerance. Atmospheric re-entry is accounted for. As a result, the breakup model outputs a set of fragments whose statistical distribution, in terms of number and size, is consistent with the catalogued ones. The iterative approach is demonstrated for two different scenarios (i.e., catastrophic collision and non-catastrophic collision) using numerical simulations. Then, it is also applied to a real collision event.

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