Takayoshi Inoue

Dual Propulsive Mode Microthruster Using a Diode Laser

Introduction M ICROSPACECRAFT have increasingly attracted the interest of researchers in recent years. The research is motivated by the need to reduce in the cost of developing and launching spacecraft and to improve in the mission capability and redundancy using microspacecraft constellations. Although several laboratory and flight models of 1–10 kg class microspacecraft have been developed, most of them do not have propulsion systems.1−3 To enable future microspacecraft missions, such as formation flying, a small propulsion system suitable for microspacecraft, namely, a microthruster, is needed.4 One of the most important requirements in the microthruster is the capability to generate both lower range thrust and higher range thrust. For instance, microspacecraft require lower thrust for attitude controls and higher thrust for slew maneuvers. In the case of formation flying,4 microspacecraft need lower thrust for the constellation controls and higher thrust for the rearrangement of their formation patterns. In particular, formation flying inevitably requires propulsive capability, although attitude control is accomplished by passive systems such as momentum wheels and magnetic torqueres. To limit the weight and size of microspacecraft, it is essential to satisfy the requirement of lower and higher range thrusts with the same propulsion system. To our knowledge, there is as yet no single propulsion system that can supply such a wide range of thrust for the 1–10 kg class microspacecraft. A diode laser ablation microthruster and digital microthruster array seem to be promising candidates for the 1–10 kg class microspacecraft. The diode laser ablation microthruster5 uses laser beams to irradiate the surface of a polymer propellant, and the heated

Formation of water clusters in a free molecular jet of binary mixtures

The formation process of water clusters is investigated experimentally with a supersonic free molecular jet of water vapor mixtures of Ar, Xe, N2, CO2 and CO, especially noticing the effect of the solute molecules on the cluster formation. The terminal concentrations of clusters formed through a supersonic molecular expansion are measured with a mass spectrometer by changing the mole fraction of water vapor at the source. It is observed that, in the range of relatively small H2 O mole fraction of binary mixtures at the source, the formation process of water clusters is controlled mainly by the thermodynamical effects of the expansion. On the other hand, at larger H2 O mole fractions, the molecular dynamical behavior of mixture molecules must be taken into account for understanding the formation process of water clusters. In both cases, the binary species play an important role in the formation process of water clusters.

An Experimental Study on Energy Conversion Process of an in‐Space CW Laser Thruster

CW laser propulsion has been investigated to develop a prospective propulsion system that may be used in space. OTV (Orbit Transfer Vehicle) is placed as one of the most effective applications of the propulsion system. In this study, the energy partitioning of incident laser energy was investigated over the wide range of velocity of the flow field in low pressure. Flow velocity is thought to have significant effects on energy conversion process because the distribution of temperature and the position of a laser sustained plasma in the focusing laser beam should be determined so that flow velocity and propagation velocity of optical discharge balance out. It was found that the higher energy conversion efficiency can be achieved by lowering the pressure and increasing the velocity of the flow field.

Effects of Swirl Flow on an Atmospheric Inductively Coupled Plasma

An atmospheric inductively coupled plasma is expected to be used in the development of the thermal protection system for Venus missions. In this study effects of the swirl flow injection on the characteristics of an atmospheric ICP generator were investigated. The total enthalpy was measured by two ways; the sonic flow method and calorimetric method. A diode laser absorption spectroscopy was also applied to the measurement of the temperature and velocity of an extracted plume. The stagnation pressure was about 60 kPa and the work gas was argon. The experimental found that the specific enthalpy increased with decreasing the swirl flow fraction. This seems to arise from the change in the shape and the flow pattern inside the plasmas.

Inductively Coupled Plasmas Supported by Laser Plasmas for High Enthalpy Flows

In this study a fundamental study on stability of an atmospheric inductively coupled plasma generator (ICPG) for high-enthalpy and high-stagnation pressure flow were conducted. Whereas ICPG is expected to be used as a simulator of the planetary entry flowfield, the existing ICPGs have been operated with the pressure of less than 1 atm. We demonstrated the generation of ICPs with the pressure of more than 1 atm and it was found that the operational conditions strongly depend on the design of the tangential flow injection ring and the pressure. It was also successfully demonstrated that Laser Sustained Plasma (LSP) could be applied to the ICP stabilization. Especially a double tube configuration will provide a wide range of the capability to stabilize the ICPs.

Experimental Investigation of a Chemically-Augmented, Diode Laser Thruster for Microspacecrafts

Recently microspacecraft have attracted a lot of attention because they might reduce launch cost and offer various mission capabilities. However, no suitable propulsion system exists for microspacecraft, and the development of new miniaturized propulsion components is strongly required. A diode laser ablation microthruster has been recently proposed as one of the promising microthrusters. It can be miniaturized and operate in a wide range of low momentum impulses. However, the momentum impulse generated by ablation is too small for orbit insertions and momentum unloading of the microsatellites. In this study, a new concept of the impulse augmentation of a diode laser thruster using chemical reactions is proposed, where the diode laser ignites high-energy chemical propellants and produces high momentum impulse. A prototype thruster was designed and fabricated, and its thrust performance was measured. The momentum coupling coefficient was dramatically increased compared with that of using non-chemical propellants.