Chemically Augmented Laser-thermal Thrusters
Mitsutoshi TSUCHIYA1), Yuka ARAI1), Kai WADA1), Miya ISODA1),Shoko SHIBAGAKI1),
Tomoyuki IKEDA2), Hideyuki HORISAWA3)
1) Graduate student of Mechanical Engineering, Tokai University, Japan
2) Department of Aerospace and Astronautics Engineering, Associate Professor Tokai University, Japan
3) Department of Aerospace and Astronautics Engineering, Professor, Tokai University, Japan

Abstract
In this study, evaluations of chemical exothermic energies of propellants, which were chosen from chemicallystable liquids in room temperature except fuels, were conducted using chemical equilibrium calculation code,
which were water, acetic acid, HFE (Hydrofluoroether), and hydrogen peroxide. Among them, HFE, HFEsolution, and hydrogen peroxide showed high temperature characteristics. In a wide range of specific powers (1~ 40 kJ/g), reaction temperatures increased with HFE concentration in water solution. In a range of 0 ~ 20% ofHFE concentration, specific impulses rapidly increased. Especially, at 40 kJ/g, specific impulse showed thehighest value (710 s at 20%).

Keywords: Liquid propulsion, Chemical Equilibrium Calculation, LaserPropulsion

1. Introduction
The current trend towards miniaturized satellites,
which is not only mass limited but also power limited,
has produced a strong interest in development of
micropropulsion devices.1-4) Although in the past, allof those miniaturized satellites have lacked propulsion
systems altogether, future micro-spacecraft will
require significant propulsion capability to provide ahigh degree of maneuverability and capability. The
benefit of using electric propulsion for the reductionof spacecraft mass will likely be even more significant
for mass limited micro-spacecraft missions.
Various potential micropropulsion systems for
micro-spacecraft applications, such as ion thrusters,
field emission thrusters, pulsed plasma thrusters(PPTs), resistojets, arcjets, etc., have been proposed
and are under significant development for primary andattitude control applications. In particular, small-sizedonboard laser plasma thrusters are also undersignificant development with rapid evolution of novelcompact high-power laser systems. The advantages ofthe laser thrusters are system simplicity andcompactness with significant controllability of thethrust.
The thrust performance of laser ablation thrusters
mainly depends on lasers (i.e. average or peak power,
fluence or intensity, wavelength, pulse duration, etc.)5). It was shown in a recent work that the thrust
performance was also dominated by chemical
properties of the propellant such as reactivity,exothermic energy, etc. The use of energetic materials

enabled high thrust-to-power ratios and high thrust
efficiency, which could even be over 100% withadditional energy release through exothermic
chemical reactions.
Lippert et. al. achieved thrust efficiencies of over100% with the use of energetic materials, such as GAP,PVN, etc., which could produce chemical exothermic
energy in addition to the laser energy augmenting
thrust performance5).
However, most of those energetic materials are
regarded as hazardous materials and thus hard tohandle especially for small satellites. Regarding theconvenience and simplicity of the miniaturizedsatellites, the use of those hazardous materials should
be avoided. Therefore, in this study, an investigationand development of non-hazardous, low-cost, andstable materials under room temperature wasconducted for the laser ablation thruster either in solidFig. 1 Flowchart of chemical equilibrium calculation.

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geometry of the laser-ablation crater.

or liquid state, including their mixtures. Thesematerials should be energetic producing chemicalexothermic energy when given an input energy
density above certain thresholds, or namely only withlaser irradiation. Since the objective of this study is aninvestigation of exothermic characteristics fromthe non-exothermic, stable, non-hazardous materials,
these novel propellants must be “exotic propellants”
with abnormally exothermic characteristics.
2. Method of Calculation
2.1 Chemical Equilibrium Calculation
In this study, for chemical equilibrium
calculation of chemical reactions, a widely-usedsimulation code, NASA Chemical Equilibrium withApplications (NASA-CEA) developed by S. Gordonand B. J. McBride at NASA Glenn Research Center
was utilized6).
The process of determination of the adiabatic
flame temperature and chemical equilibriumcomposition is shown in Fig.1. In this process using
energy balance method assuming isenthalpic
conditions, first of all, an enthalpy before chemical
reaction is determined by assuming chemicalcomposition and temperature at plenum chamber.
Secondly, assuming a temperature of reactant, anenthalpy, or a temperature, is calculated fromchemical composition and then compared with that ofbefore reaction. The iterative calculation continues
until the value has reached a convergent value, inwhich the enthalpy, or temperature, has become
consistent with that of former iteration.
The chemical composition in the reaction iscalculated using equilibrium constants from JANAF
thermochemical data. In addition, based on quasi-one
dimensional nozzle flow theory, thrust performance(i.e., specific impulse, etc.) can be calculated from theadiabatic flame temperature and a given expansion
ratio of a nozzle (=10).
In this study, to evaluate chemical exothermic
energies of the propellant, prediction of thetemperature after the reaction and specific impulse
was conducted. A laser energy is assumed as an initialheat to the target which is added to an enthalpy offormation of reactants, or propellant components.
Although, absorption coefficients of materials varywith combination of the laser and material, it isassumed that all the laser energy is absorbed to thetarget for simplicity. Moreover, in this study, since athrust, or an impulse, generated through the laser
ablation of the solid material is considered, anexpansion ratio of 10 for a nozzle, which is namely alaser-ablation crater, was assumed, considering the2.2 Chemical Equilibrium Calculation
To verify our simulation procedure and results,
some previous experimental results, employing PTFE(Polytetrafluoroethylene, or Teflon®) and POM(Polyoxymethylene, or polyacetal)7) for thepropellants, were compared with our numericalprediction.
Variations of specific impulse with specific input energyfor PTFE and POM propellants are plotted in Fig. 2 and3, respectively. Although relatively large scatters ofexperimental data for PTFE in Fig. 2, results from thenumerical prediction are within those scatters and thenconsistent with experimental results.

Fig. 2 Verification of calculation for PTFE.

On the other hand, for POM in Fig. 3, results fromsimulation are significantly large and overestimating
the experimental results, i.e., 3 ~ 6 times larger thanthose obtained in the experiment. Since an energy
absorption rate of an incident laser beam by thematerial surface in the simulation is assumed 100%for simplicity, some overestimated predictions must beinevitable.

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Fig. 3 Verification of calculation for POM.

Fig. 4 Variation of reaction temperatures vs specific powers
for liquids.

3. Results and Discussion
To discover and investigate exothermal propertiesof liquid propellants from chemically stable liquids instandard condition, some liquids and theircombinations were examined. Moreover, calculationof hydrazine was conducted as a widely used, standard
liquid propellant for comparison.
Variations of reaction temperatures with specificpower (or specific energy) for water, acetic acid,acetic acid solution, HFE, HFE solution, hydrogenperoxide, acetic acid and ethanol solution andhydrazine are plotted in Fig.4. In all propellants,
reaction temperatures increase monotonically withspecific power. Especially, HFE and HFE solution
show high temperature characteristics among them(i.e., HFE: 1,000 ~ 3,900 K, HFE solution: 1500 ~3500 K) for a wide range of specific powers (1 ~ 40kJ/g). Subsequently, hydrogen peroxide follows (1100~ 3100 K).
Variations of specific impulses with specificpower (or specific energy) for water, acetic acid,acetic acid solution, HFE, HFE solution, hydrogenperoxide, acetic acid and ethanol solution andhydrazine are plotted in Fig.5. Similar to reaction
temperature, specific impulses increase monotonicallywith specific power in all propellant cases. In a wide
range of specific powers (5 ~ 40 kJ/g) except 1 kJ/g,hydrazine shows the highest values (330 ~ 610 s),
followed by HFE solution (320 ~ 560 s). However, at
1kJ/g, HFE solution shows higher value (280 s) thanhydrazine (230 s).

Fig. 5 Variation of specifc impulses vs specific powers for liquids.

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Fig ・ .6 Variation of reaction temperatures vs HFEconcentrations.

Fig. 7 Variation of specific impulses vs HFE concentrations.

Relations of reaction temperatures versus moleconcentrations of HFE solutions are plotted in Fig.6.
In a wide range of specific powers (1 ~ 40 kJ/g),
reaction t empera tu res increase with HFEconcentration. In particular, at higher specific powerover 30 kJ/g, reaction temperatures increase
monotonically with HFE concentration.
Relations of specific impulses and moleconcentrations of HFE solutions are plotted in Fig.7.
In a range of 0 ~ 20% of HFE concentration, specificimpulses rapidly increase. Especially, at 40 kJ/g,
specific impulse shows the highest value (710 s at20%). This value is higher than that of pure hydrazine,
which is 610 s at 40 kJ/g.

Fig. 8 The reaction temperature for the ratio of HFE in ethanol andHFE solution.

Fig. 9 The specific impulse for the ratio of HFE in ethanol and HFEsolution

At 1 kJ/g, it shows the maximum value (about190 s) at the ethanol concentration of 60%.
On the other hand, at 5 kJ/g, the maximum value(about 223 s) can be obtained at 80%.
Moreover, reaction temperatures and specificimpulses for various mixtures HFE to ethanol are
shown in Fig.8 and 9. In all range of specific powers(1 ~ 40 kJ/g), pure HFE showed high reaction
temperatures. Following that, a high reaction
temperature of about 3500 K can be obtained at 20%
concentration at 40 kJ/g. Also, as shown in Fig. 9, atover 10 kJ/g (to 40 kJ/g), higher specific impulses(360 to 550 s) can be obtained for HFE concentratinof 80%.On the other hand, the maximum values for 5kJ/g and 1 kJ/g are 350 s (at 60%) and 240 s (at 40%),respectively.

Fe-Base Metallic Glass Coating Produced by Gas Tunnel Type Plasma Spraying
Small Spacecraft (Prog. Astronautics and Aeronautics 187)”,
American Institute of Aeronautics and Astronautics, 2000.

4. Conclusions
To discover exothermal properties of liquid
propellants including their combinations withsignificant characteristics from chemically stableliquids in standard conditions (excluding liquid fuels),some liquids and their combinations were examined,
which were pure water, pure acetic acid, water
solution of acetic acid, HFE (Hydrofluoroether), water
solution of HFE, acetic acid and ethanol solution,
ethanol and HFE solution, pure hydrogen peroxideand hydeazine. Primary results are as follows;

1.

2.

3.

4.

5.

In all propellants, reaction temperatures increased
monotonically with specific power. HFE andHFE solution showed high temperature
characteristics (i.e., HFE: 1,000 ~ 3,900 K,
HFE solution: 1500 ~ 3500 K) for a wide rangeof specific powers (1 ~ 40 kJ/g). Then,hydrogen peroxide followed (1100 ~ 3100 K).
Specific impulses increased monotonically withspecific power in all propellants. In a wide
range of specific powers (5 ~ 40 kJ/g) except 1kJ/g, hydrazine showed the highest values (330~ 610 s), followed by HFE solution (320 ~ 560s). However, at 1kJ/g, HFE solution showed
higher value (280 s) than hydrazine (230 s).
In a wide range of specific powers (1 ~ 40 kJ/g),
reaction temperatures increased with HFEconcentration in water solution. In particular, at
higher specific power over 30 kJ/g, reaction
temperatures increased monotonically with
HFE concentration.
In a range of 0 ~ 20% of HFE concentration,
specific impulses rapidly increased. Especially,
at 40 kJ/g, specific impulse showed the highestvalue (710 s at 20%).
For HFE and ethanol mixtures, higher specificimpulses (360 to 550 s) can be obtained for
HFE concentration of 80% at over 10 kJ/g (to40 kJ/g). On the other hand, the maximum
values for 5 kJ/g and 1 kJ/g are 350 s (at 60%)
and 240 s (at 40%), respectively.
References

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Generation in Laser Propulsion”, Ph.D. Dissertation, Univ. ofAlabama in Huntsville, Huntsville, (2008)