**3. Comparable bipropellant rocket propulsion system**

## **3.1 Overview**

*Aerospace Engineering*

vacuum chamber (**Figure 7**). This is consistent with the end-to-end testing of the

Here, the handling procedures can be simplified, thanks to the reduced hazards involved with the handling of RHP. The Prisma satellite fueling campaign serves as an example for that, as illustrated in **Figure 8**. During the launch campaign of the Prisma satellite, the first in-space demonstration of an ADN-based propulsion system, ECAPS loaded the hydrazine and RHP propellants at the Yasny launch base. The handling of ADN-based RHP was evaluated and declared as a "nonhazardous operation" by the Range Safety, so SCAPE suits were not required during the Prisma

The firing program, like any new type of testing, needs to go through the common procedural requirements. These include safety reviews and safety approvals, test procedure preparation and approval, allocation of thruster and propellant, and allocation of the test facility. The procedural requirements have been fulfilled, with

entire system, as was done with the hydrazine system EM firing tests.

ADN-based propellant loading operation [20, 48].

the exception of the facility allocation.

**10**

**Figure 8.**

**Figure 7.**

*Propellant loading of satellite Prisma [20].*

*Entire system EM testing vacuum chamber [1].*

This section describes a hypergolic system based on kerosene and hydrogen peroxide, similar in performance to MMH/N2O4 that has been developed by NewRocket© [24]. The NewRocket Green Propellant (NRGP) hypergolic bipropellant is based on concentrated hydrogen peroxide (HTP—high test peroxide) as oxidizer and on a kerosene-based fuel. NRGP is used in a family of bipropellant rocket and gas-generator applications. Neat HTP and kerosene are not hypergolic, while NRGP has been made such by addition of a minute amount of a solid energetic activator to the fuel. The activator is maintained homogeneously distributed in the fuel by its suitable gelation to a shear-thinning yield-stress fluid. Shear-thinning fluids exhibit decreased viscosity with increasing applied shear stresses, such as by pressure gradients (ΔP). The shear-thinning feature of the fuel enables its full functionality in propulsion systems, including pressurized or pumped feed flow and injection to the reaction chamber, just like any liquid propellant.

Usually, decomposition of hydrogen peroxide is achieved using catalyst beds based on silver, platinum, and other materials. Catalyst beds produce hightemperature-decomposed hydrogen peroxide that can burn with a hydrocarbon fuel; however, the system complexity and weight are both increased.

Another method is based on the idea of using catalytic or reactive material (such as metal oxides—MnO2, PbO2, F2O3, etc.) that is dissolved in a liquid fuel. The reactive material decomposes hydrogen peroxide and ignites the fuel, so hypergolic ignition is achieved without the use of a catalyst bed. However, this method requires fuels such as ethanol or methanol that serve as solvents for the reactive material. All these solvents used either alone or with kerosene-based fuels and have relatively low heat of combustion; therefore, the energetic performance of the system is low.

#### *Aerospace Engineering*

By nature, hydrogen peroxide and kerosene do not ignite upon contact. However, in a gelled fuel, the existence of yield stress assures that particles (reactive or catalytic) can be added without the effect of sedimentation or buoyancy. Gels enable the suspension of reactive or catalyst particles, uniformly distributed in the fuel, without compromising the energetic performance of the system. The use of suspended particles enables a quite large variety of combinations of fuels and oxidizers that can become hypergolic by gelling one of the liquids and adding the proper material.

Natan et al. [49] came up with the idea of embedding reactive particles with hydrogen peroxide in gelled kerosene. Drop-on-drop tests exhibited that this kind of gelled kerosene is hypergolic with hydrogen peroxide as shown in a sequence of photographs in **Figure 9**. Total ignition delay time was 8 ms. Connell et al. [50–52] also investigated the issue and showed that it is feasible.

The idea was adopted by a start-up company, NewRocket that proceeded with the development of a prototype motor using gelled kerosene with reactive particles and hydrogen peroxide [24]. **Table 3** shows the characteristics of their NRGP propellant in comparison to other candidate propellants.

Here again the specific impulse relation to temperature, *Isp*~√ \_\_\_\_\_\_ *Tc*/*M*, is applicable to comparing MMH/N2O4 and the kerosene and hydrogen peroxide-based green bipropellant NRGP. The specific impulse *Isp* of NRGP, as shown in **Table 4**, is some 4% lower than that of MMH/N2O4, in accordance with its considerably lower chamber temperature; but it is noteworthy that its *ρIsp* is higher by 4% thanks to its 8% higher average density.

Experiments have been conducted in a lab-scale motor to verify the feasibility of the idea. The main problems were the atomizers because the particles initially caused plugging of the exit. The problem was solved by changing the type of reactive particles and by increasing the atomizer diameter. The system (**Figure 10**) was found to operate properly, and by using adequate valves, operation in pulses was achieved as shown in **Figure 11**.

In the next sections, the stability of the fuel for no phase separation or sedimentation throughout its life cycle is demonstrated by theoretical and experimental considerations.
