Development of a High-Performance HAN/HN-Based Low-Toxicity Monopropellant

Trans. JSASS Aerospace Tech. Japan Vol. 14, No. ists30, pp. Pa_101-Pa_105, 2016

1) 1) 2) 2) By Shinji IGARASHI, Apollo B. FUKUCHI, Nobuyuki AZUMA, Keigo HATAI, 2) 2) Hideshi KAGAWA and Hirohide IKEDA

1)IHI Aerospace Co., Ltd., Japan 2)Japan Aerospace Exploration Agency, Japan

(Received July 31st, 2015)

We have developed a hydroxylammonium nitrate (HAN)/hydrazinium nitrate (HN)-based low-toxicity monopropellant [high-performance, no-detonation propellant (HNP)] that has safety characteristics such as no autocatalytic reaction (no autocatalytic reaction: Combustion cannot continue without a source of heat) and no detonation. However, its specific impulse (Isp), a rocket engine performance indicator, was lower than that of hydrazine. Therefore, we investigated many types of compositions and found methanol to be suitable as a fuel ingredient for increasing the Isp of the developed propellant and reducing its viscosity. We produced the developed monopropellant consisting of HAN/HN/methanol/water and having a low viscosity and an Isp of 260 s at the laboratory scale.

Key Words: HAN, HN, Methanol, Green Propellant

Nomenclature calculated using NASA’s CEA computer program for chemical propellant performance prediction, and the HAN : Hydroxylammonium nitrate calculation conditions were as follows: vacuum, HN : Hydrazinium nitrate combustion pressure Pc = 1 MPaA, and nozzle expansion TEAN : Tri-ethanol-ammonium nitrate ratio  100. HNP : High-performance, no-detonation propellant We developed a hydroxylammonium Isp : Specific impulse nitrate/hydrazinium nitrate (HAN/HN)-based low-toxicity

Tad : Adiabatic flame temperature monopropellant characterized by safety features such as

tr : Reaction time of propellant with no autocatalytic reaction and no detonation but with a catalyst lower Isp value than that of hydrazine. 1,2) P : Combustion pressure c  : Nozzle expansion ratio 2. Previous Work on HAN/HN-based Monopropellant  : Density  Isp : Density-specific impulse We developed an HAN/HN-based low-toxicity JISHA : Japan Industrial Safety & Health monopropellant that has safety characteristics such as no Association autocatalytic reaction and no detonation. In addition, we

selected a low-viscosity composition to be able to employ 1. Introduction a conventional thruster. The details of the previous

composition (hereinafter called HNP115) are listed in Several countries are working on the development of a Table 1. HNP115 has safety characteristics such as no low-toxicity monopropellant. Regulations pertaining to autocatalytic reaction and no detonation, but its Isp of 203 chemical substances, such as REACH in Europe, are s is lower than that of hydrazine (237 s). However, other becoming stringent in line with the trend of environmental works have achieved Isp values higher than that of protection, and hydrazine is affected by such regulations. hydrazine. Accordingly, there would be demand for a low-toxicity

monopropellant in the future. In the USA, Green Table 1. Components and characteristics of HNP115. 3) Propellant Infusion Mission (GPIM) is planning to Composition HAN/HN/TEAN/Water = 46/23/6/25 (wt%) ※1 demonstrate a green propellant thruster system in-orbit in Theoretical specific impulse (s) 203 4) Theoretical adiabatic flame 1325 the near future. In Europe, the satellite PRISMA carried temperature※1 (K) Characteristics out an orbital flight in 2010. 5) The theoretical specific Density (g/cm3) 1.4 10 impulse (Isp) value achieved in these works is 260–270 s, Viscosity (mPa·s) Autocatalytic reaction No

which is higher than that of hydrazine. The Isp value was ※1 Calculation conditions are Pc = 1.0 MPaA,  = 100.

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Isp = 280 s 0 Isp = 270 s 3. Design of HNP Compositions 100 260 s 20 We tried to increase the Isp of HNP115. Furthermore, Detonation area 80 250 s HNP115 Increasing Isp we attempted to maintain the advantages of HNP115 240 s N 40 W H 60 a t such as no autocatalytic reaction and no detonation. + e N r A 200 s Figure 1 shows the components of the previous H 60 40 compositions in a ternary plot. The figure also shows the Detonation No Detonation 80 20 plots of Isp and the detonation area. Target area The TEAN component in the fuel was increased to （no detonation、, high Isp） 100 increase Isp in order to avoid the detonation area shown 0 100 80 60 40 20 0 in Fig. 2. As the amount of TEAN increases, the TEAN ※ Original data of this ternary map is taken from 8). viscosity of the composition increases because TEAN is Fig. 1. Contour map of Isp and detonation area of a solid ingredient soluble in water. The high-Isp area HAN/HN/TEAN/Water. that avoids the detonation area is indicated by a broken Table 2. Results of composition design. line in Fig. 1. This area represents high-viscosity HAN Propellant compositions that influence a thruster design. Therefore, Hydrazine9,10) we investigated measures to achieve high Isp and low (Conventional Improved Propellant) HNP115 (HNP202, HNP206 viscosity by replacing TEAN with a liquid ingredient. HNP207) We compared the toxicity, physical properties, Isp, and HAN/HN/ HAN/HN/ Composition N H 2 4 TEAN/Water Methanol/Water adiabatic flame temperature (Tad) of many fuel *1 *3 ingredients. Based on the results of this comparison, we Isp (s) 239 203 250–270 *1 *3 adopted methanol as the liquid fuel ingredient. Methanol Tad (K) 1170 1325 1508–2055 ρIsp is readily available, and it has some actual use as a 239*3 290 309–369 (g/cm3·s) low-toxicity monopropellant. 6,7) Viscosity 7 We designed a few low-viscosity compositions with 0.9 <15*2 (Target) (mPa·s) at 15°C an Isp higher than that of hydrazine using methanol as a ※1 Theoretical Specific Impulse. Calculation conditions are Pc = fuel ingredient. Table 2 summarizes the results of our 1.0 MPaA,  = 100. ※2 Viscosity of improved composition is an estimate. composition design exercise. ※3 Calculated based on 60% ammonia dissociation. We estimated the viscosity of the fuel compositions using methanol as a component, as shown in Fig. 2. The 0 100 Isp = 270 s figure shows that we can obtain a high Isp and low Isp = 280 s 260 s Isp = 270 s viscosity (10–15 mPa·s), similar to HNP115. In addition, 20 250 s viscosity = 10–15 mPa·s 80 for an Isp of 240 s (the same as hydrazine), the viscosity 240 s of the composition is less than 10 mPa·s, and we can N 40 W H 60 a Estimated Viscosity + te N r  obtain compositions with much lower viscosity. A (mPa s) H 1 60 Figure 3 shows the Tad versus Isp of a few 40 5 monopropellants, namely the HAN/HN low-toxicity 10 15 80 monopropellant designed by us, conventional hydrazine 20 Isp = 240 s 20 viscosity = 5–10 mPas 25 monopropellant, and other low-toxicity propellants (Tad 100 30 0 and Isp are estimated). As can be seen from the figure, 100 80 60 40 20 0 there seems to be a similarity in the trends of our Methanol low-toxicity monopropellants and other low-toxicity Fig. 2. Isp and estimated viscosity of HAN/HN/methanol/water. monopropellants, i.e., Isp increases as the adiabatic flame temperature increases.

Pa_102 S. IGARASHI et al.: Development of a High-Performance HAN/HN-Based Low-Toxicity Monopropellant

300 absence of a source of heat (heated wire in this case). 290 HNP203 280 Therefore, methanol is a candidate material for a 270 HNP202 composition that has a high Isp and the desired safety 260 characteristics. 250

Isp [s] Isp 240 IA's high Isp compositions 230 LMP-103S(estimated) ※ 220 AF-315E(estimated) Table 3. Results of lab-scale production and evaluation of SHP163(estimated) improved compositions. 210 Hydrazine(60% Ammonia Dissosiation) 200 HAN Propellant 1000 1200 1400 1600 1800 2000 2200 2400 2600 Hydrazine6) Properties HNP202, Tad [K] (Conventional) HNP115 HNP206, ※ Isp and Tad of these compositions were calculated by IA HNP207 from the following sources: 11, 12, 7). Fig. 3. Relationship between Isp and Tad of low-toxicity 7 7–13 Viscosity (mPa·s) 0.9 monopropellants. at 15°C at 15°C

Density (g/cm3) 1.0 1.4 1.2–1.4 4. Results of Lab-scale Production and Evaluation of Improved Compositions pH (-) 10.1–10.7 1.3 1.3–1.4 Onset temperature 100–120 >170 140–170 4.1. Results of lab-scale production and data (°C) @ 1 atm collection No Autocatalytic reaction No No We produced a few compositions (including HNP202, (over 5 MPa) HNP206, and HNP207) in quantities of up to 1 kg for Detonable No No No analysis on the basis of composition design.3) We (Φ10-mm steel pipe) (Isp  260 s) obtained various characteristics of the compositions, 0 such as their physical properties (viscosity, density, and 100 Isp = 270s Isp = 280 s 260s pH) and safety properties (exothermic onset temperature, 20 250s 80 burning rate, and detonation). If the propellant has the 240s Calculated by CEA, and the calculation conditions autocatalytic reaction characteristic, it can decompose are Pc = 1 MPaA,  40 Wa N 60 H te when passing through a feed tube to a fuel tank, which + r N A ▲ could cause the tank to burst. Table 3 summarizes the H 60 Partial Reaction 40 gathered data. The viscosities employed herein were Water 6 % × No Detonation Water 12 % useful for achieving the target value below the 80 20 composition design point. The densities and pH 100 employed herein were useful for achieving the same 0 values as those of HNP115. The exothermic onset 100 80 60 40 20 0 temperature was 140°C–170°C, as measured by Methanol * Partial Reaction: The steel pipe was partly broken. differential scanning calorimetry (DSC). These obtained Fig. 4. Results of the detonation test along with an Isp map of HN/HN/methanol/water. properties seem to present no concern from the practical usage viewpoint. The burning rate was zero up to a maximum pressure of 7 MPa, as determined using the burning rate measurement apparatus. The results of a Heated wire detonation test, conducted using a φ10-mm steel pipe, indicate that the propellant compositions with Isp values Filled of up to 260 s do not detonate, as shown in Fig. 4. propellant Figure 5 shows the burning rate measurement apparatus. In this test, we ignited the propellants using a N2 gas flow heated wire in a glass tube with N2 gas flow. The Glass tube burning rate was measured by moving images captured Fig. 5. Burning rate measurement apparatus. with a camera through the window. The results of the burning rate measurement test are shown in Fig. 6. As can be seen from the figure, the burning rate was zero because the combustion could not continue in the

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HNP202 (Isp = 250 s) 7 MPaG HNP202 and HNP206 are similar to HNP115 in terms of Interrupting Before ignition Ignition combustion response time. The response time of HNP202 and HNP206 are slightly shorter than that of HNP115 at the same catalyst temperature. We consider that the decrease in response time has little influence of thruster operation performance and stability.

HNP206 (Isp = 260 s) 7 MPaG Video Camera Pipette Interrupting Before ignition Ignition combustion Propellant droplet Thermocouple Laboratory dish Hot Plate Catalyst

HNP207 (Isp = 270 s) 7 MPaG Interrupting Before ignition Ignition combustion Fig. 7. Equipment for “open cup test.”

Temperature just before dropping HNP：T0 Dropping of Producing smoke 200 HNP Maximum Fig. 6. Results of the burning rate measurement test. 180 temperature after ｔ： r dropping HNP Tmax

) 160

4.2. Decomposition of HNP on a pre-heated catalyst ℃ 140 We conducted an “open cup test” to confirm that the 120 decomposition of HNP on a pre-heated catalyst 100 Catalyst temperature (hereinafter called catalyst A) occurs in a conventional Temperature ( 80 hydrazine thruster. The “open cup test” apparatus is 60 ： shown in Fig. 7. The catalyst was placed on a hot plate, Minimum temperature after dropping HNP Tmin 40 and the catalyst temperature was measured using a 10 20 30 40 50 60 Time (s) thermocouple (diameter: 1.0 mm, time constant: 0.7s in the boiling water, the temperature increasing from RT to Fig. 8. Example of open cup test results.

100 °C). The catalyst was heated to temperatures of 80°C–250°C, and HNP was dropped onto the pre-heated 100 catalyst using a pipette. A few bubbles were generated (s)

as soon as the HNP was dropped onto the catalyst. r Thereafter, the reaction proceeded to completion along 10 HNP115 with the generation of smoke. The time (tr) between HNP202 dropping of the HNP and achievement of the maximum HNP206 1 temperature changes with the pre-heated catalyst

temperature. An example of the measured temperature TimeReaction t data is shown in Fig. 8. Figure 9 shows a plot of tr versus 0.1 the pre-heated catalyst temperature just before dropping 50 150 250 the HNP. For either composition, HNP could be Catalyst Temperature before drop T0 (℃) decomposed using catalyst A. t decreased as the catalyst r temperature increased for both methanol and TEAN as Fig. 9. tr versus pre-heated catalyst temperature just before fuel components. Previously, HNP115 was fired using dropping. 4-N and 20-N thrusters. The test results showed good reaction characteristics when using catalyst A. 2)

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5. Toxicity Risk Assessment catalyst for HNP, and we will demonstrate the firing of HNP and the new catalyst in the near future. A qualitative risk assessment was performed on HAN/HN/methanol/water [HAN: 36–50, HN: 18–25, References methanol: 0–40 by weight percent (including HNP202, HNP206, and HNP207)] and high-purity hydrazine 1) S. Nagase, S. Miyazaki, M. Ayabe, M. Kohno, “A Preliminary Work on HAN/HN-Based Monopropellant”, 24th International using a control banding method modified by JISHA. Symposium on Space Technology and Science, 30 May-6 June This assessment was conducted to compare the risk 6, 2004, Miyazaki, Japan. 2) A. B. Fukuchi, T. Inamoto, S. Miyazaki, H. Maruizumi, M. levels of propellant loading and high-purity hydrazine Kohno, “HAN/HN-based Monopropellant Thrusters”, The 26th loading operations. The JISHA method is essentially the International Symposium on Space Technology and Science. 13) 3) S. Igarashi, A. B. Fukuchi, K. Yamamoto, K. Miyagawa, same as COSHH essentials, except for the “Study of the HAN/HN base Low Toxic Mono Propellant introduction of stricter and more quantitative criteria for Developing to Obtain High performance”, Space Transportation Symposium FY2013, 16-17 January 2014, control banding in the former. The COSHH essentials Institute of Space and Astronautical Science, Japan Aerospace provide guidelines for controlling the use of chemicals Exploration Agency (JAXA)(ISAS), Sagamiahra, Kanagawa in a range of common tasks. 14) Japan. 4) R. A. Spores, R. Masse, S. Kimbrel, C. McLean, “GPIM From the qualitative evaluation, it was clear that the AF-M315E Propulsion System Development”, 50th AIAA/ASME/SAE/ASEE Joint Propulsion Conference & risk level of HAN/HN/methanol/water was “Acceptable Exhibit, 28-30 July 2013, Cleveland, Ohio, AIAA 2014-3482. Risk,” or risk lower than that of high-purity hydrazine, 5) N. Pokrupa, K. Anflo, O. Svensson, “Spacecraft System Level which is categorized as “Large Risk” in situations where Design with Regards to Incorporation of a New Green Propulsion System”, 47th AIAA/ASME/SAE/ASEE Joint the concentration of the leaked gas or liquid in the Propulsion Conference & Exhibit, 31 July-03 August 2011, San atmosphere is controlled by the local exhaust ventilation Diego, California, AIAA 2011-6129. 15) 6) T. Katsumi, H. Kodama, T. Matsuo, H. Ogawa, N. Tsuboi, K. system. Therefore, for green propellant candidates, we Hori, “Combustion Characteristics of a Hydroxylammonium can expect propellant loading operations to be performed Nitrate Based Liquid Propellant Combustion Mechanism and Application to Thrusters”, Combustion, Explosion, and Shock without operation personnel requiring to wear a SCAPE Waves, Vol. 45, No. 4, pp. 442–453, 2009. suit, provided there is a local exhaust ventilation system. 7) M. Lange, M. Holzwarth, G. Schulte, M. Peukert, O. Feindt, However, the necessity of protective suits or other “Feasibility Study and Performance Assessment of a Myriade Propulsion Module with an ADN Based Green protective gear depends on the regulations defined by Monopropellant”, Astrium GmbH - Space Transportation, each operator. 74215 Möckmühl, Germany, 46th AIAA/ASME/SAE/ASEE Joint Propulsion Conference & Exhibit, 25-28 July 2010, Nashville, TN. 6. Conclusion 8) S. Nagase, S. Miyazaki, S. Iihara, M. Ayabe, H. Shibamoto, M. Kohno, “A Work on HAN/HN-Based Monopropellant for Practical Use”, Space Transportation Symposium FY2004. An HAN/HN-based monopropellant was modified to 9) Special Project Fire, Explosion, Compatibility, and Safety have a high Isp and low viscosity using methanol as a Hazards of Hypergols – Hydrazine, AIAA SP-084-1999. fuel. The propellant was produced at the laboratory scale, 10) E. W. Schmidt, Hydrazine and Its Derivatives Preparation, Properties, Applications, Second Edition, pp. 1331-1332. and we confirmed via a detonation test that the 11) R. Delanoë, “Injector Design and Test for a High Power propellant does not undergo autocatalytic reaction and it Electrodeless Plasma Thruster”, Master of Science Thesis, Stockholm, Sweden 2011, pp. 7-8. does not detonate for Isp values of up to 260 s. A few 12) Fortini, A. J. et al., “Self-Adjusting Catalyst for Propellant reactions between HNP and a conventional catalyst for Decomposition”, United States Patent Application Publication, US 2008/0064913 A1, March 13, 2008. decomposing hydrazine were tested, and HNP could be 13) A. N. I. Garrod, P. G. Evans, C. W. Davy, “Risk Management reacted by the catalyst. The reaction exhibited the same Measures for Chemicals: The “COSHH Essentials” Approach”, tendency as the previous composition, which has been Journal of Exposure Science and Environmental Epidemiology, Vol. 17, pp. S48-S54, 2007. fired on a thruster. 14) COSHH Essentials, 2014, from We performed qualitative risk assessments of the http://www.hse.gov.uk/coshh/essentials/index.htm. 15) Azuma, N. et al.,” Basic Properties of Hydroxyl Ammonium green propellant candidates. The results of these Nitrate (HAN) Based Monopropellant for Thrusters”, Tenth assessments elucidated that the risk levels of the green International Symposium on Special Topics in Chemical Propulsion (10-ISICP), 2-6 June 2014, Poitiers, France, Paper propellant candidates are lower than that of hydrazine. #85. Therefore, we can expect no-SCAPE suit operation when handling the green propellant candidates In addition, we are developing a high-heat-resistant

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