Solid vs Liquid Propellant

[nightcrawler]

Liquid propellant,which was easier to operate, since it makes it possible to stop and re-start the engine. This is an advantage, according to experts, for the higher stages of launchers or missiles. Solid propulsion is more advantageous in lower stages, which require a stronger thrust. Slower combustion and more effective protection of engines internal walls. The situation shifted toward better control of solid propellant combustion, using combustion-inhibiting coating, preventing it from propagating on certain charge surfaces. Similarly, the development of new production techniques associated with adapted charge profiles made it possible to develop important dimension blocks, capable of burning for a long time as well as optimising the thrust.
Hence,in a liquid propelled engine,two propellants are stored separately and injected in the combustion chamber. For a solid propellant, the components are, on the contrary, directly stored in the combustion chamber, already mixed, called the charge. Overall, the advantage of one propellant over the other is not clear-cut. However, the advantage of solid propellant lies in its security, thus it is much better adapted for missiles operated aboard submarines.
From an economical point of view, due to the complexity of their design and production, liquid systems are generally considered expensive, especially when it comes to having a long-range, for which some components are difficult to produce (turbo-pump, injector, combustion chamber&#8230.
Three Technical Points

• Air-independent propulsion Since it requires no atmospheric oxygen to work, this type of propulsion is the preferred method for platforms whose trajectory extends beyond the earth!s atmosphere (space launchers, ballistic missiles)
• Solid propellant In an air-independent engine, the thrust is obtained thanks to a propellant stored inside the engine. This propellant is composed of two basic elements (combustible, often ammonium perchlorate), which, when put together, burn and provide the thrust.
• Know-how Aside from chemistry, at the heart of the design and production of solid propellants is a combination of know-how, from mechanics to multiphase “aerothermochemistry,” which makes their realisation possible. The development and production of a propellant charge are crucial steps as they require many tests.
  
  
  

FOUR STEPS IN THE PRODUCTION OF PROPELLANT

• Structure coating The first step is to apply a coat of resin on the thermal protection inside the propellant chamber. Resin is the binder that ensures contact between the structure and the solid propellant charge
• Propellant kneading The various elements (oxidising, reducing agent, binder and additive) are mixed to form a paste. The preparation differs according to the size of the charge. The goal is to allow homogenisation and polymerisation of the element.
• Flow and reticulation Propellant, once at the paste state, is poured into the propellant body. Once the polymerisation is obtained, the core, which will provide the shape of the propellant!s internal canal, is withdrawn. This is a particularly delicate process.
• Assembly and engine formation The thrust nozzle that ensures the flow, expansion and ejection of the gas produced by combustion is assembled including the igniting device, with the charge produced for the shape of the propellant engine.
  
  
  
  

STATES OF INTEREST

• USA From the creation of the first composites to the use of NitralaneTM for Trident-II D5 systems, American laboratories have pursued the development of new components. This is especially true in the field of binding agents, with the use of energetic polymers (glycidyle polyazoture or PAG), and in the field of oxidising charges, with the use of high energy materials (hexa-nitro-hexa- aza-isowurtzitane or CL20). The United States is seeking to improve its strategic vehicles while positioning itself on the space launcher market. Hence, the three stages of the Trident II-D5 use solid propellant mainly based on octogen (HMX).
• Russia The first missile powered by solid propellant, the SS-13, entered operational service at the end of the 1960s. The SS-13 is the result of work by the Moscow Thermal Engineering Institute on a composite propellant based on ammonium perchlorate.Russian researchers are pursuing their efforts, with in the ground sector the development of two missiles (RS-24 and Topol-M) and in the naval segment the SS-NX-30 Bulava, announced with a 8,000 km range.
• Israel, which has acquired considerable autonomy
  regarding the solid composite charges, with the Shavit and Jericho systems. Recent tests of the Jericho 3 suggest ongoing
  Israeli research, with enhancements to the systems range, thanks to an additional propulsion floor. Moreover, work
  carried out on the development of the Arrow-2 interceptor may
  favour technology transfers between the U.S. and Israel.
• Others India has also been at the forefront of research in this field over the past 30 years. Its expertise is reported to equal that of the Chinese with the AGNI-III. In Pakistan, solid technology also exists in the Shaheen range of products, but under a strong dependence on the Chinese. Finally, Iran appears to have sufficient knowledge to produce short-range missiles that use solid propellants.