Important increases in maneuver duration and propellant consumption, even mission loss, are observed. The thrusters’ impact on the design of the ADCS is quantified through the development of an AOCS simulation environment. They also omit the effects of the power and thermal requirements in terms of added mass, which sometimes result in unrealistic solutions at the CubeSat scale. Classical performance indexes for propulsion systems are proved to be deficient, for instance focusing on the propellant mass at the expense of the dry mass of the system. It results that the conventional approach tends to neglect the attitude control required to ensure the expected pointing during the maneuver, usually considered to be within the limits of the nondedicated ADCS. Thanks to a functional analysis, the fundamental links between the required subsystems for a successful orbital maneuver are emphasized. This work proposes a high-level approach based on identified representative cases, such as deorbiting from LEO, escaping Earth orbit or proximity operations. For our concern, the distinction between the attitude control and the orbit control (ADCS/GNC) hides inherent mutual impacts. Current "commercial off-the-shelf" (COTS) approach tends to consider each subsystem individually, making it difficult to ensure performances at system level. This thesis aims to highlight the remaining discrepancies between the CubeSat philosophy and the complexity of the Attitude and Orbit Control System (AOCS), and tackle some of them. It is expected to allow more flexibility to LEO missions and pave the way to interplanetary trajectories. Among the limitations that this class of satellites still faces is the orbit control. However, because of the drastic constraints imposed by the standard in terms of mass, volume and power, most CubeSats to date were launched in Low Earth Orbit (LEO). This standard has paved the way to the democratization of subsystems available as "commercial off-the-shelf" (COTS). The exponential growth of CubeSat launches during the past 20 years, combined with the growing interest of private companies and space agencies has confirmed the sustainability of a new approach to space missions: standardization, short release cycle and shared launches. The domain of nano/microsatellites has been irreversibly modified by the apparition of the CubeSat standard. Using the GP-B spacecraft as an example we conclude that it is feasible to build a liquid helium based propulsion system with a very stable supply temperature and pressure. The manifold pressure upstream of the thrusters is shown to remain remarkably stable even with fairly large flow rate variations. We show how the net mass flow rate can be controlled independently from the desired output thrust. Based on this model a controller is developed which regulates the liquid helium supply temperature and pressure by varying the net helium mass flow rate through the thrusters. A thermodynamic model relating the temperature, pressure, and flow rate of the propulsion system is derived. This article is concerned with implementing these thrusters into an effective overall propulsion system. Due to extensive development and testing work, the ultra low flow rate helium thrusters for such a propulsion system are now considered proven technology. Effective propulsion systems can be implemented for these spacecraft by directing the helium gas which boils off from the cryogenic systems in specific directions through a set of thrusters. Two spacecraft, gravity probe B (GP-B) and the satellite test of the equivalence principle (STEP), incorporating onboard liquid helium cryogenic systems are scheduled to fly around the turn of the century.
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