Hiroto HABU

An overview of research on high-energetic ionic-liquid propellants (EILPs) in Japan to realize a green space propulsion system is reported in this paper. First, two kinds of propellant compositions consisting of ammonium dinitramide/monomethylamine nitrate/urea were selected as candidates as the compositions with sufficiently low melting temperature and higher propulsion performance than conventional hydrazine. For innovative combustion control methods to solve the problems of catalyst ignition, thermal and catalytic reaction characteristics were investigated, and laser heating ignition and electrolytic ignition were experimentally studied. The results show the feasibility of both laser heating ignition and electrolytic ignition and provide knowledge of the influences of several design parameters on the ignition characteristics.

To create a new flyable detonation propulsion system, a detonation engine system (DES) that can be stowed in sounding rocket S-520-31 has been developed. This paper focused on the first flight demonstration in the space environment of a DES-integrated rotating detonation engine (RDE) using S-520-31. The flight result was compared with ground-test data to validate its performance. In the flight experiment, the stable combustion of the annulus RDE with a plug-shaped inner nozzle was observed by onboard digital and analog cameras. With a time-averaged mass flow of [Formula: see text] and an equivalence ratio of [Formula: see text], the RDE generated a time-averaged thrust of 518 N and a specific impulse of [Formula: see text], which is almost identical to the ideal value of constant pressure combustion. Due to the RDE combustion, the angular velocity increased by [Formula: see text] in total, and the time-averaged torque from the rotational component of the exhaust during 6 s of operation was [Formula: see text]. The high-frequency sampling data identified the detonation frequency during the recorded time as 20 kHz in the flight, which was confirmed by the DES ground test through high-frequency sampling data analysis and high-speed video imaging.

In this study, the viscosity characteristics of bimodal Al/hydroxyl-terminated polybutadiene (Al/HTPB) suspensions were experimentally investigated to improve the propulsion performance and manufacturability of low-cost solid propellants with ease of application. Several Al particles with different mean volume diameters were used to prepare the bimodal Al. The Al/HTPB suspensions behaved like a continuum in solid propellant slurries. The reason is that Al particles were sufficiently small for ammonium perchlorate particles. The suspension viscosities were measured using a rotational viscometer at 1.92 s ^-1. The optimum coarse fraction of Al particles in the bimodal Al/HTPB suspensions was 0.75. The viscosity of bimodal Al/HTPB suspensions was suppressed with an increase in the diameter ratio. These results were attributed to the improvement of Al packing in the suspensions. The experimental results show that the viscosity reduction by applying bimodal Al particles was more effective when the minimum void fraction was reduced. Furthermore, the performance enhancement of solid propellants was confirmed by adding the bimodal Al/HTPB. The calculation results showed that the bimodal Al/HTPB enhanced the propulsion performance of the propellant without the viscosity variation to a higher side. Moreover, the suppression of viscosity of up to 23 % could be achieved using the bimodal Al/HTPB similar to the conventional composition of solid propellants. Therefore, replacing monomodal Al particles with bimodal ones in solid propellants effectively improved the performance of the propellants.

<p>In recent years, because development of space technology has been increasing for the purpose of improving social infrastructure, the expansion of space transportation system based on low-cost and high-frequency rockets is important. Due to the compactness, inexpensiveness, and easy-handling properties of solid propellants used in solid-fuel rockets, numerous studies on solid propellants have been conducted. However, solid propellants are highly viscous slurries and highly explosive. As there is no device capable of continuously and safely transporting the solid propellant, the process of manufacturing the solid propellant is a batch process. We focused on the movement of human intestines that knead and transport with a small force, as part of the development process. In this paper, we developed a peristaltic pump, Mk. III, for kneading a solid propellant. The pump was comprised of a heating system, an input device for the powder and fluid, and a rapid exhaust valve. An investigation into the amount of input of the raw materials was undertaken, and the tendency of kneading at the point of introduction of the powder and highly viscous fluid was determined.</p>

&lt;p&gt;Gel propellants have been recognized as future propulsion systems. Gel propellants are liquid fuels such as hydrazine, of which the rheological properties have been altered by the addition of gelation agents. Ammonium dinitramide (ADN) based energetic ionic-liquid propellants (EILPs) are expected to be used as replacements for hydrazine, which has high toxicity, and also for ionic liquid gel propellants (ILGPs). However, there have been few studies conducted on ADN based ILGPs. Here, ADN based ILGPs were prepared to obtain a better understanding of their thermal properties. The thermal behavior of the ADN based ILGP samples were measured using differential scanning calorimetry and the evolved gases were analyzed using thermogravimetry–differential thermal analysis with mass spectrometry. An ADN based ionic liquids (ILs) formed a gel using gelation agents of agarose and hydroxypropyl cellulose. The gas evolved from ADN based ILGPs was determined to be different from that from ADN based ILs due to reaction between the IL and the gelation agents.&lt;/p&gt;

<p>In recent years, the demand for rocket launching has increased due to the development of space technology. However, using inexpensive rockets is not always possible. Although the cost of solid-propellant rockets is relatively reasonable, safely manufacturing a large amount of solid propellant is difficult, and the manufacturing process is disjointed. Therefore, safe and continues manufacturing of solid propellant is necessary. On the basis of the movements of the intestinal tract, we proposed that the movements required for transport and mixing of solid propellants are possible to achieve without the application of a large shear force. The peristaltic motion enables not only the mixing but also conveying even high viscosity slurry. By mimicking these intestinal movements, we have considered and developed the peristaltic pumping by driven artificial muscle as one of the candidates for the continuous and safety mixer. In this research, the mixing completeness of the composite solid propellant slurry by the peristaltic pumping mixer was estimated. The result showed that the mixer we proposed could mix the propellant slurry. In the propellant samples, these variances were sufficiently small. An appropriate combustion state as a solid propellant was confirmed.</p>

<p>As a replacement for hydrazine, ammonium-dinitramide-based ionic liquid propellant (ADN-based ILP) has been developed by JAXA and Carlit Holdings Co., Ltd. This propellant is made by mixing three solid powers: ADN, monomethylamine nitrate, and urea. The propellant's theoretical specific impulse is 1.2 times higher than that of hydrazine, and its density is 1.5 times higher at a certain composition. Although ionic liquids were believed to be non-flammable for a long time owing to their low-volatility, recently combustible ILs have been reported. The combustion mechanism of ILs is not yet understood. The objective of this paper is to understand the combustion wave structure of ADN-based ILP. The temperature distribution of the combustion wave in a strand burner test shows a region of constant temperature. This region would indicate boiling in a gas-liquid phase. Thus, the combustion wave structure consists of liquid, gas-liquid, and gas phases. The dependence of boiling point on pressure would identify chemical substances in the gas-liquid phase. The dependence of combustion and ignition characteristics on ADN content is also discussed. </p>

&lt;p&gt;The condensed phase decomposition reactions of ADN were investigated both experimentally and theoretically. Thermogravimetric-differential thermal analysis coupled with mass spectrometry (TG-DTA-MS) was employed to generate Friedman plots for the thermal decomposition of ADN with the evolution of N&lt;sub&gt;2&lt;/sub&gt;O and N&lt;sub&gt;2&lt;/sub&gt;. The activation energy associated with the evolution of N&lt;sub&gt;2&lt;/sub&gt;O during initial decomposition was found to be 150 kJ/mol. Chemical equilibrium calculations based on the reaction N(NO&lt;sub&gt;2&lt;/sub&gt;)&lt;sub&gt;2&lt;/sub&gt;&lt;sup&gt;-&lt;/sup&gt; + NH&lt;sub&gt;4&lt;/sub&gt;&lt;sup&gt;+&lt;/sup&gt; &lt;tt&gt;&amp;#8652&lt;/tt&gt; HN(NO&lt;sub&gt;2&lt;/sub&gt;)&lt;sub&gt;2&lt;/sub&gt; + NH&lt;sub&gt;3&lt;/sub&gt; demonstrated that the concentration of HN(NO&lt;sub&gt;2&lt;/sub&gt;)&lt;sub&gt;2&lt;/sub&gt; gradually increased with temperature, although the HN(NO&lt;sub&gt;2&lt;/sub&gt;)&lt;sub&gt;2&lt;/sub&gt; to N(NO&lt;sub&gt;2&lt;/sub&gt;)&lt;sub&gt;2&lt;/sub&gt;&lt;sup&gt;-&lt;/sup&gt; ratio was still only approximately 3.1 &amp;times; 10&lt;sup&gt;-6&lt;/sup&gt;, even at the decomposition temperature of 130&amp;deg;C. Thus, molten ADN was found to contain primarily N(NO&lt;sub&gt;2&lt;/sub&gt;)&lt;sub&gt;2&lt;/sub&gt; and NH&lt;sub&gt;4&lt;/sub&gt;&lt;sup&gt;+&lt;/sup&gt; with only minor amounts of liquid HN(NO&lt;sub&gt;2&lt;/sub&gt;)&lt;sub&gt;2&lt;/sub&gt; and NH&lt;sub&gt;3&lt;/sub&gt;. The reaction ADN &amp;rarr; N&lt;sub&gt;2&lt;/sub&gt;O + NH&lt;sub&gt;4&lt;/sub&gt;NO&lt;sub&gt;3&lt;/sub&gt; was also investigated using &lt;i&gt;ab-initio&lt;/i&gt; calculations at the CBS-QB3//&amp;omega;B97XD/6-311++G(d,p) level. It was determined that four reaction pathways are possible via different transition states. The energy barrier of 161 kJ/mol obtained from these calculations agreed with the experimental value.&lt;/p&gt;