**2.1 Overview**

The concept presented is of gradual migration to equivalent RHP, or "green propulsion" systems. The proposed gradual conversion of monopropellant systems to RHP is by dual capability of entire conventional hydrazine systems to operate with ADN-based RHP, if so decided even just before the propellant loading. Namely, the suggested concept is of a propulsion system that may accept last moment decision on fueling with either hydrazine or with an RHP. This flexibility will enable the project to progress until a very late stage without necessary commitment to either one of the propellants, thus allowing a smooth transfer to RHP [23].

The hereby presented concept proposes to go a significant step further than the European "green" Myriade program, which has already sought components compatible both with hydrazine and ADN-based "green" monopropellant, with

**5**

*Green Comparable Alternatives of Hydrazines-Based Monopropellant and Bipropellant Rocket…*

the notable exception of the thruster assemblies, which will in their case have to be the special ECAPS thrusters [25]. In the "green" Myriade bus, the existing 230 mm propellant tank could be replaced with the one that has a silica-free diaphragm and flown successfully for over 5 years aboard the Swedish Prisma satellite with an ADN-based "green" propellant. For increased propellant capacity, existing larger tanks, using the same materials, can be used. These tanks are also compatible with hydrazine, as has been proven for the diaphragm material for long-term service aboard constellations such as Galileo-IOV and Globalstar-2 that are propelled by

The ECAPS dual-mode thrusters and system employ their special thrusters as described in their patent of a thruster and a propulsion system that can be operated either in monopropellant mode or in bipropellant mode [28], as well as their new LMP-103S #1127-3 propellant variant [29]. It combusts at lower temperature giving a specific impulse (*Isp*), thus comparable with hydrazine, and it is stated that the lower combustion temperature may enable the usage of less expensive materials for the thrust chamber assembly (TCA). This last point is further elaborated in the paragraph below, detailing the risk reduction program of the dual capability monopropellant system, with a concept that has rather drawn some inspiration from the multifuel engine of the Reo trucks, which have had quite a widespread military use [30].

The initial risk reduction program that has been carried out is described here. It includes proof of concept of dual capability of all propulsion system parts and components, such as thrusters, valves, diaphragm tanks, pressure transducers, filters, and pipework. Materials' compatibility and operational use have been taken into consideration for both hydrazine and RHP, in view of a proposed system endto-end proof by firing testing in space environment. The program was carried out

In the subparagraphs to follow, a number of areas are described, for which steps have been taken to reduce development risks. For most components, the materials compatibility is the main issue. This means that the effect of the propellant on the components must not be harmful, and on the other hand, the effect of the compo-

Thereafter, functional issues are treated. The chemical reaction that converts the liquid propellant to the necessary high-energy gases takes place in the thrust chamber assembly (TCA) of the thruster. The catalytic effect on the ADN-based propel-

The temperature of the high-energy gases, using the basic ADN-based propellant, is higher than is normally tolerated by the materials of construction of the hydrazine thruster's TCA. This issue is dealt with in a dedicated paragraph below. The temperature necessary for inducing the nominal decomposition and oxidation reactions for ADN-based propellant is considerably higher than the 120–180°C necessary for hydrazine nominal decomposition. The tests that have shown the capability to achieve the necessary higher preheating of ADN-based propellant are

nents' materials of construction shall not degrade the propellant itself.

lant has been proven with the same catalyst as in the hydrazine thruster.

**2.3 Compatibility with ADN-based liquid propellants of COTS hydrazine** 

The possibility to use commercial off-the-shelf (COTS) construction materials, which are used in typical hydrazine propulsion system components (tubing, valves,

*DOI: http://dx.doi.org/10.5772/intechopen.82676*

hydrazine [26, 27].

**2.2 Risk reduction program**

by analysis of data as well as dedicated tests.

described in the last subparagraph below.

**systems' parts, components, and materials**

*Green Comparable Alternatives of Hydrazines-Based Monopropellant and Bipropellant Rocket… DOI: http://dx.doi.org/10.5772/intechopen.82676*

the notable exception of the thruster assemblies, which will in their case have to be the special ECAPS thrusters [25]. In the "green" Myriade bus, the existing 230 mm propellant tank could be replaced with the one that has a silica-free diaphragm and flown successfully for over 5 years aboard the Swedish Prisma satellite with an ADN-based "green" propellant. For increased propellant capacity, existing larger tanks, using the same materials, can be used. These tanks are also compatible with hydrazine, as has been proven for the diaphragm material for long-term service aboard constellations such as Galileo-IOV and Globalstar-2 that are propelled by hydrazine [26, 27].

The ECAPS dual-mode thrusters and system employ their special thrusters as described in their patent of a thruster and a propulsion system that can be operated either in monopropellant mode or in bipropellant mode [28], as well as their new LMP-103S #1127-3 propellant variant [29]. It combusts at lower temperature giving a specific impulse (*Isp*), thus comparable with hydrazine, and it is stated that the lower combustion temperature may enable the usage of less expensive materials for the thrust chamber assembly (TCA). This last point is further elaborated in the paragraph below, detailing the risk reduction program of the dual capability monopropellant system, with a concept that has rather drawn some inspiration from the multifuel engine of the Reo trucks, which have had quite a widespread military use [30].

#### **2.2 Risk reduction program**

*Aerospace Engineering*

In Section 3, a similar comparable attitude is proposed for the hypergolic system based on kerosene and hydrogen peroxide, similar in performance to MMH/N2O4. Results are presented of the firing tests of the proof-of-concept and development model systems and of the NRGP fuel rheological characterization. The results of various engine types demonstrate the capability to operate this technology in both pulse and steady modes and in various thrust levels. This bipropellant technology offers a promising alternative to the presently employed hydrazine-based systems, through the fact that the fuel and oxidizer show very robust hypergolicity and short ignition delays, as well as characteristic velocity

The concept presented is of gradual migration to equivalent RHP, or "green propulsion" systems. The proposed gradual conversion of monopropellant systems to RHP is by dual capability of entire conventional hydrazine systems to operate with ADN-based RHP, if so decided even just before the propellant loading. Namely, the suggested concept is of a propulsion system that may accept last moment decision on fueling with either hydrazine or with an RHP. This flexibility will enable the project to progress until a very late stage without necessary commitment to either

The hereby presented concept proposes to go a significant step further than the European "green" Myriade program, which has already sought components compatible both with hydrazine and ADN-based "green" monopropellant, with

**4**

efficiency (*ηC*\*) exceeding 98%.

**2.1 Overview**

**Figure 3.**

**2. Dual capability monopropellant propulsion system**

*The bipropellant module schematic (left) and test firing setup (right).*

one of the propellants, thus allowing a smooth transfer to RHP [23].

The initial risk reduction program that has been carried out is described here. It includes proof of concept of dual capability of all propulsion system parts and components, such as thrusters, valves, diaphragm tanks, pressure transducers, filters, and pipework. Materials' compatibility and operational use have been taken into consideration for both hydrazine and RHP, in view of a proposed system endto-end proof by firing testing in space environment. The program was carried out by analysis of data as well as dedicated tests.

In the subparagraphs to follow, a number of areas are described, for which steps have been taken to reduce development risks. For most components, the materials compatibility is the main issue. This means that the effect of the propellant on the components must not be harmful, and on the other hand, the effect of the components' materials of construction shall not degrade the propellant itself.

Thereafter, functional issues are treated. The chemical reaction that converts the liquid propellant to the necessary high-energy gases takes place in the thrust chamber assembly (TCA) of the thruster. The catalytic effect on the ADN-based propellant has been proven with the same catalyst as in the hydrazine thruster.

The temperature of the high-energy gases, using the basic ADN-based propellant, is higher than is normally tolerated by the materials of construction of the hydrazine thruster's TCA. This issue is dealt with in a dedicated paragraph below.

The temperature necessary for inducing the nominal decomposition and oxidation reactions for ADN-based propellant is considerably higher than the 120–180°C necessary for hydrazine nominal decomposition. The tests that have shown the capability to achieve the necessary higher preheating of ADN-based propellant are described in the last subparagraph below.
